CA1317287C - Cross-linked esters of hyaluronic acid - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Total or partial cross-linked esters of hyaluronic acid are provided which result from the esterification of aliphatic polyhydric alcohols with two or more carboxy groups of the hyaluronic acid polysaccharide, with the proviso that the cross-linked ester is not the cross-linked ester of hyaluronic and with a halomethyloxirane or a bisepoxy compound. Salts of partial such esters with inorganic or organic bases are also provided.
These cross-linked esters or their salts are useful in the field of biodegradable plastics for sanitary and surgical articles and in the pharmaceutical and cosmetic fields for the preparation of useful compositions and articles.

Description

~3~ 7~8~
The inventlon relates to total or partial esters of polyhydric alcohols of hyaluronic acid resulting f~om the esterification of such alcohols with two or more carboxy yroups of the hyaluronic acid polysaccharide.
These esters, due to the presence of bridge bonds between the above-defined carboxy functions of the same or different molecules of hyaluronic acid, may be described by the term "cross-linked". These cross-linked esters may be total or partial. In the case of the latter, further carboxy functions may be esterified with monohydric or polyhydric alcohols, without the formation of cross-links; (ester groups which shall also hereinafter be termed "simple"). In both types of cross-linked partial esters, non-esterified carboxy functions may be free or salified with metals or organic bases.
The invention also relates to the use of such cross-linked hyaluronic esters in the field of biodegradable plastic materials for the preparation of sanitary and surgical articles, in the pharmaceutical and cosmetic fields and, therefore, includes the various articles made with the same in such fields.
Application for European Patent No. 0 161887 of 3.5.85, published on 21.11.85, contained a description of some cross-linked derivatives of hyaluronic acid obtained by the reaction of epoxy compounds indicated as "polyfunctional". In the above patent publication, the term "polyfunctional epoxy compounds" had been defined as meaning hydrocarbons with at least one epoxy function and possibly also having convertible functions in epoxy r ,~, L~

:1 317287 func-tions, the cross-linking reaction o~curring through the epoxy groups. Of these functions, only the halogens are mentioned in the published p~tent application. of these polyfunctional epoxy compounds only a few examples were mentioned in the above published patent application, namely: epichlorohydrin, epibromohydrin, methylepichlorohydrin, methylepibromohydrin, 1,2-bis(2,3-epoxypropoxy)-ethane, 1,4-bis(2,3-epoxypropoxy)-butane, 1,6-bis (2,3-epoxypropoxy)-hexane and a glycidyl ether of bisphenol A and bisphenol F. The preparation process used in this published patent application, which was limited in the claims to the use of a halomethyloxyrane or a bisepoxy-compound, as well as being limited in its possible applications, gave cross-linked esters of hyaluronic acid with a low degree of esterification of hyaluronic acid with a low degree of esterification: in fact, as can be seen from the illustrative Examples of that published patent application, a maximum of 4%
esterification was reached in the case of reaction with epichlorohydrin (Example 4) to obtain a product with a low degree of solubility.
Application for UK Patent No. 2 151 244 A of 13.8.1984, published on 17.7.1985, and application for German Offenlegungsschrift 34 082 Al of 17.9.1984, published on 11.7.1985, contained descriptions of some cross-linked derivatives of hyaluronic aci~ obtainable by ~he action of the same on formaldehyde, dimethylolurea, dimethylol~thylenurea, a polyaziridine, a polyisocyanate and a divinylsulfone. Such FD

~3~7~7 derivatives were insoluble and were proposed, clue to their biocompatibility, for in vivo applications in the form of various prosthetic articles, e.g. cardiac valves, vascular clips, etc., or were proposed to be added to the various polymeric materials used to make such articles. The same published patent application provided for the use of ethyl oxide as an agent to achieve "cross-linking", but the procedure was not illustrated, and neither was the type of product obtained specified. The structure of other cross-linked derivatives was not specified and no mention was made of the type of bonds forming the cross-linking. In the case of formaldehyde and of the above-substituted ureas, this could mean derivatives involving the carboxy groups of hyaluronic acid with a semiacetalic structure, while in other cases it could mean alkylated products of hydroxyls.
It is possible, therefore, to de~ine an object of a main aspect of the present invention as being the provision of total and partial cross-linked esters of hyaluronic acid with polyhydric: alcohols of the aliphatic series. The partial cross-linked esters, carboxy groups may contain esterified withmonohydric or polyhydric alcohols of the aliphatic, alicyclic, araliphatic or heterocyclic series; the parkial esters may contain nonesterified, sali-Eied carboxy groups with inorganic or organic bases, with the exception of cross-linked esters obtained by the action of a halomethyloxyrane or of a bisepoxy-compound on hyaluronic acid.

Fl) ~ ~ ~L rJ ~ ~ 7 The present invention, in one of its broad aspects~ makes available a wide assortment of cross-lin~ed esters, including particular esters wherein the ester groups comprise radicals which are unsubstituted by a hydroxyl (as in the case of products resulting from the reaction of the epoxides on hyaluronic acid or its salts, as described in the above~identified published patent application). Importantly, the present invention, in another of its aspects, provides mixed esters comprising a mixture of ester groups which are cross-linked and some ester groups which are not cross-linked, wherein the percentage of cross-linking groups may exceed 10% o~ all of the disaccharide units of hyaluronic acid.
Thus, by another broad aspect of this invention, total or partial cross-linked esters of hyaluronic acid with an aliphatic polyhydric alcohol, or with an organic base, are provided, with the proviso that the cross-linked ester is not the cross-linked ester of hyaluronic acid with a halomethoxirane or with a bisepoxy compound.
In one variant thereof, the aliphatic polyhydric alcohol is a dihydric alcohol; preferably the dihydric alcohol is a member selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, and glycols derived from pentane, hexane, heptane and octane, and positional isomers thereof. The aliphatic polyhydric alcohol preferably has between 2 and 1~
carbon atoms. More especially, the aliphatic polyhydric alcohol is glycerine, erythritol or pentaerythritol.

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By another variant thereof, at least one non-cross-linked carboxy group in the hyaluronic acid is esterified with an aliphatic alcohol having a maximum of 34 carbon atoms. The aliphatic alcohol may be unsubstituted or may be substituted by one or two ~unctional groups selected from the group consisting of amino, hydroxy, mercapto, aldehyde, keto, carboxy, hydrocarbyl and dihydrocarbylamino groups, ether, ester, thioether, thioester, acetal, ketal, carbalkoxy, carbamidic and substituted carbamidic groups substituted by one or two alkyl groups, the hydrocarbyl radicals in the functionally-modified groups having a maximum of 6 carbon atoms. The aliphatic alcohols may be interrupted in the carbon atom chain by heteroatoms selected from the group consisting of oxygen, sulphur and nitrogen. Preferably the aliphatic alcohol is selected from the group consisting of ethyl, propyl, isopropyl, n-butyl, isobutyl, a tert-butyl alcohol, an amyl, a pentyl, a hexyl and an octyl alcohol.
By yet another variant, at least one non cross-linked carboxy group in the hyaluronic acid is esterified with an araliphatic alcohol having only cne benzene residue, in which the aliphatic chain in the araliphatic alcohol has a maximum of ~
carbon atoms, in which the aliphatic chain may be substituted with one or two functional groups selected from the group consisting of free- or mono- or diethyl amino groups, pyrrolidine and piperidine groups, and in which the benzene residue in the araliphatic alcohol may be substituted with between 1 and 3 methyl or hydroxy groups or with halogen atoms.

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By still another variant, at least one non-cross-linked carboxy group in the hyaluronic acid is esterified with a cycloaliphatic alcohol or with an aliphatic-cycloaliphatic alcohol or with a heterocyclic alcohol which is derived ~rom a mono- or polycyclic carbohydrate with a maximum of 34 carbon akoms and which is unsubstituted or which is substituted by one or more functional groups selected from the ~roup consisting o~
amino, hydroxy, mercapto, aldehyde, keto, carboxy, hydrocarbyl-and dihydrocarbylamino groups, ether, ester, thioether, thioe~ter, acetal, ketal, carbalkoxy, carbamidic and substituted carbamidic groups, by one or two alkyl groups, the hydrocarbyl radicals in these functionally modified groups having a maximum of 6 carbon atoms, and may be interrupted in the carbon atom chain by heteroatoms selected from the group consisting of oxygen, nitrogen and sulphur, and may have one or more aromatic bonds. Preferably at least one of the non-cross-linked carboxy groups is esterified with an alcohol selected from the group consisting of cortisone, hydrocortisone, prednisone, prednisolone, fluorocortisone, dexamethasone, betamethasone, corticosterone, deoxysicorticosterone, paramethasone, flumethasone, flucinolone and its acetonide, fluprednylidene, clobetasol and beclomethasone.
By another variant, the polyhydric alcohol is an aliphatic polyhydric alcohol, and the etheri~yin~ agent is an alkyl halogenide of an aliphatic polyhydric alcohol, e.g. where the aliphatic polyvalent alcohol is a bivalent alcohol. Preferably ~D

~1.3:~7~7 the aliphatic polyvalent alcohol is a member selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, glycols derived from pentane, hexane, heptane and octane, and positional isomers thereof, glycerine, erythritol and pentaerythritol.
By a still further variant, the salt is a salt of the cross-linked ~ster with an alkali metal, with an alkaline earth metal, with magnesium or with aluminum, e.g. a sodium or ammonium salt.
Preferably it is one deriving from ammonium, araliphatic, cycloaliphatic or heterocyclic groups.
By another broad aspect of this invention, a pharmaceutical composition is provided comprising a pharmaceutically-effective amount of a cross-linked ester or salt, as described in its various aspects and variants ahove, together with a pharmaceutically-acceptable carrier, excipient or diluent.
By yet another broad aspect of this invention, a pharmaceutical composition is provided comprising a pharmaceutically-effective amount of a cross-linked ester or salt, as described in its various aspects and variants above, as a vehicle, in admixture with a pharmaceutically-effective amount of a pharmacologically-active agent.
In the two above-described broad aspects of pharmaceutical compositions, the alcohol which is esterified with the non-cross-linked carboxy group is a pharmacologically-active alcohol.

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The specific use of the esters of aspects o~ this invention may be seen in relation to the degree of cross-lin~
esterification, that is, the number o~ cross-linked groups of carbo~y functions esterified with the above polyhydric alcohols, the number of simple esterified groups, and, lastly, also the number of salified groups, this degree of esterification or salification being itself related to the solubility of the product and to its viscous-elastic properties. Thus, for example, the total cross-linked esters are virtually insoluble in aqueous liquids and are very suitable, due to their molecular structure, for use in the making of plastic materials and resins and as additives for these materials. Esters with an average or low degree of esterification and their salts with inorganic or organic bases are more or less soluble in aqueous conditions and are suitable for the preparation of gels which may have many uses, both in cosmetics and pharmacology and in the medical-sanitary field in general.
Thus, by other aspects of the present in~ention, the following embodiments are provided using the cross-linked ester or salt as described in its various aspects and variants above:
a) a cosmetic article of a cross~linked ester or a salt thereof; b) a sanitary, medical or surgical article of a cross-linked ester or a salt thereof; c) a sanitary, medical or surgical article of threads o a cross-linked ester or a salt thereof; and d) a capsule or microcapsule for medicaments, of a cross-linked ester or a salt thereof.

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By still other aspects o~ the present invention, khe following embodiments are provided using the cross-linked ester or salt as described in its various aspects and variants above:
e) the use of the cross-linked ester or salt thereof for the manufacture of a film for use in dermatology as artificial skin, of a cross-linked ester or a salt thereof; and f) the use of the cross-linked ester or salt thereof for the manufacture of suture threads for use in surgical operations, of a cross-linked ester or a salt thereof.
By yet another aspect of this in~ention, a process is provided for the preparation of total or partial cr~ss-linked esters of hyaluronic acid comprising: reactin~ a potassium or sodium or quaternary ammonium salt of hyaluronic acid with an etherifying agent in an aprotic solvent.
In one variant of such process, the salt of hyaluronic acid is a potassium or sodium salt, and the reaction is conducted in the presence of a catalyzing quantity of a quakernary ammonium salt. ~ore especially, the quaternary ammonium salt is tetrabutyl ammonium iodide. Still more preferably, the aprotic solvent is a dialkylsulfoxide, a dialkylcarboxylamide, or a lower alkyl dialkylamide of a lower aliphatic acid.
By another variant of such process, the polyhydric hyaluronic acid or the non-cross-linked carboxy groups of the partial cross-linked ester of hyaluronic acid is esterlfied with an aliphatic, araliphatic or cycloaliphatic alcohol. The alcohol which is esterified with the non-cross-linked carboxy groups may ~D

lo 13~7~7 be a pharmacologically-active alcoholO Preferably, the partial cross-linked ester having a~ least one free carboxy group is salified with an alkali metal or with alkaline earth metal, or with magnesium or with ammonium.
5By yet another variant of such process, the hyaluronic acid is a hyaluronic acid fraction having an average molecular weight of between 50,000 to 730,000 and is substantially-free of hyaluronic acid having an average molecular weight of less than 30,000. More especially, the hyaluronic acid fraction may be one 10which has an average molecular weight of 50,000 to 100,000, or which has an average molecular weight of 250,000 to 350,000 or one which has an average molecular weight of 500,000 to 730,000.
The term ~Ihyaluronic acid" (abbreviated "HY") is used in literature to mean acidic polysaccharides with different 15molecular weights constituted by residues of D-glucuronic and N-acetyl-D-glucosamine acids, which occur naturally in cell surfaces, in the basic extracellular substances of the connective tissue of vertebrates, in the synovial fluid of the joints, in the endobulbar fluid of the eye, in human umbilical cord tissue 20and in cocks' combs. Hyaluronic acid plays an important role in the biological organism, as a mechanical support for the cells of many tissues, e.g. the skin, tendons, muscles and cartilage and, therefore, it is a main component of the intercellular matrix. It also plays other important roles in the biological 25processes, e.g. the moistening of tissues, lubrication, cell migration, cell functions and differentiation. (See for example 1~ lL 3 ~
A. Balazs et al. in "Cosmetics & Toiletries", Italian edition No.
5/84, pages 8-17).
Hyaluronic acid may be extracted from the above natural tissues, for example ~rom cocks' combc or also f~om some bacteria. It is also possible today to prepare hyaluronic acid by microbiological methods. The molecular weight of integral hyaluronic acid obtained by extraction is 8-13 million. However, the molecular chain of this polysaccharide is quite easily degraded by means of various physical and chemical factors, ~or example by mechanical means or under the influence of radiation or hydrolysing, oxidizing or enzymatic agents. For this reason, even by using the usual purification procedures of original extracts, the degraded fractions obtained have a lower molecular weight (see Balazs et al. cited above).
Hyaluronic acid, its molecular fractions and the respective salts have been used as medicaments and they have been proposed for use in cosmetics (see for example the above articles by Balazs et al. and French Pa-tent No. 2~78468). As a therapeutic agent, hyaluronic acid and its salts have been used especially in therapy for arthropathies, for example in the veterinary fielcl for the treatment of arthritis in horse [Acta Vet. Scand. 167, 379 (1976)]. As an auxiliary and substitute therapeutic agent for natural organs and tissues, hyaluronic acid and its molecular fractions and their salts have been used in ophthalmic surgery (see for example Balazs et al~ in "Modern Problems in Ophthalmology", Vol. 10, 1~70, p.3 - E.B. Strieff, S. Karger ~I) L3.~7~8~

eds., Basel, or "Viscosurgery and the Use of Sodium Hyaluronate During Intraocular Lens Implantation", Paper presented at the International Congress and First Film Festival on Intraocular Implantation, Cannes, 1979, and U.S. Patent No. 4,328,803 with a summary of the literature on uses of HY in ophthalmology, and also U.S. Patent No. 4,141,973). In EP publication No. 0138572A3 of 24 April 1985 there is a description of a molecular fraction of hyaluronic acid which may be used, for example as a sodium salt, for intraocular and intraarticular injections respectively, suitable as a substitute for the endobulhar fluids in the eye and suitable in therapy for arthropathies.
Hyaluronic acid may be used also as an additive for various polymeric materials used for sanitary and surgical articles, e.g.
polyurethanes, polyesters, polyolefins, polyamides, polysiloxanes, vinyl and acrylic polymers, and carbon fibres with the effect of rend~ring these materials biocompatible. In this case, the addition of HY or its salts is effected, for example, by coating the surface of such materials, or by dispersion in the same or by both these procedures. Such materials may be used to make various sanitary and medical articles, e.g. cardiac valves, intraocular lenses, vascular clips, pace-makers and similar articles (see U.S. Patent No. 4,500,676).
The term "hyaluronic acid" is, in fact, usually used incorrectly, meaning, as has been seen, a whole series of polysaccharides with alternating residues of D-glucuronic and N-acetyl-D-glucosamine acids with varying molecular weights or even ~'~
L~

~31~ 7 ~ 3 the degraded fractions of the same. It would therefore seem more correct to use the plural term of "hyaluronic acids" The sinyular term will, however, be used all the same in this description, and likewise in the case of the molecular fractions.
In addition, the above-defined abbreviation "HY" will frequently be used in place of this collective term.
It has also been found that the esters of hyaluronic acid with aliphatic, araliphatic, cycloaliphatic or heterocyclic alcohols possess similar and even superior properties to those of the acidic polysaccharide itself and they are even more suitable for the above uses. These esters and a process for their preparation are described in co-pending Canadian Application Serial No. 513,350. The esters with a high degree of esterification and especially the total esters have, unlike hyaluronic acid, good solubility in organic solvents, for example, in dimethylsulfoxide. Thus, for example, at room temperature, the benzyl ester of HY dissolves in DMSO in the measure of 200 mg/ml. This solubility in certain organic solvents, together with particular and marked viscous-elastic properties, makes it possible to obtain sanitary, medical and surgical articles which are insoluble in saline and which have the particular desired form, by the following procedural steps:
first a solution of the HY ester is prepared in an organic solvent; then, the very viscous solution is shaped into the form desired for the finished article; and lastly the organic solvent is extracted with another solvent which mixes with the first but 14 1 3~7~
in which the HY ester is insoluble. These advantages are also to be found, possibly to an even greater degree, in the cross-linked compounds of aspects o~ the present invention.
The cross-linked esters of aspects of the present invention may derive from any polyhydric alcohol of an aliphatic nature.
These derive, however, preferably from polyhydric alcohols with a maximum of 8 alcohol functions and especially 4 such functions and a maximum of 16 carbon atoms. The term "polyhydric", strictly speaking, generally refers to alcohols having three or more hydroxy groups, while the terms "dihydric" or "glycol"
generally refer to alcohols having two hydroxy groups. However, as used herein the term "polyhydric" is meant to encompass alcohols having two or more hydroxy groups. Thus, the "polyhydric" alcohols may be dihydric alcohols, trihydric, tetrahydric, penta and hexahydric alcohols. Of thesel special mention should be given to glycerin, the three erythritol isomers, pentaerythritol, the four xylitol isomers and the 10 dulcitol isomers.
In the ester of aspects of the present invention, the "cross-links" may derive from various of the above polyhydric alcohols; however it is preferable to prepare esters in which all the "cross-links" derive from the same polyhydric alcohol.
The most important class of the esters of aspects of the present invention, is the one deriving from dihydric alcohols, that is, from glycols. Such glycols preferably have the maximum of 16 carbon atoms, but preferably a maximum of 8 carbon atoms ~ 3 ~
and are especially ethyleneglycol, propyleneglycol, butyleneglycol, the glycols deriving from pentane, hexane, heptane, octane and their position isomers. Such glycols may however also have double bonds, for example between one and three double bonds.
The simple ester groups, which may be present in addition to the cross-linked groups, may derive from alcohols of the aliphatic, araliphatic, alicyclic or heterocyclic ser:ies and may be substituted or unsubstituted, saturated or unsaturated.
Alcohols of the aliphatic series arej for example, those with a maximum of 34 carbon atoms, which may be saturated or unsaturated and which may possibly also be substituted by o-ther free functional or functionally modified groups, e.g. amino, hydroxy, aldehyde, keto, mercapto, carboxy groups or by groups deriving from these, e.g. hydrocarbyl or dihydrocarbylamino groups (here and hereafter the term "hydrocarbyl" should be taken to mean not only monovalent radicals of hydrocarbons e.g. of the -CnH2n+l type, but also bivalent or trivalent radicals, e.g. "alkylenes" -CnH2n-or "alkylidenes"> CnHn), ether or ester groups, acetal or ketal groups, thioether or thioester groups and esterified carboxy groups or carbamidic groups and esterified carboxy groups or carbamidic groups and substituted carbamidic groups by one or two hydrocarbyl groups, by nitrile groups or by halogens. Of the substituted alcohols it is pre~erable to choose those with one 2S or two of the above functions.

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of the aforementioned groups containing hydrocarbyls, these are preferably lower aliphatic radicals, for example, alkyls with a maximum of 6 carbon atoms. Such alcohols may then also be interrupted in the carbon atom chain by heteroatoms, e.g. oxygen atoms, nitrogen, or s~lphur. Alcohols of the above group to be used preferentially within the limits of aspects of the present invention' are those with a maximum of 12 and especially a maximum of 6 carbon atoms. Those, of the substituted ones, in which the hydrocarbyl radicals in the above amino, ether, ester, thioether, thioester, acetal, and ketal groups represent alkyl groups with a maximum of 4 carbon atoms. In the esterified carboxy groups too, or in the substituted carbamidic groups, the hydrocarbyl groups are alkyls with the same number of carbon atoms. The amino or carbamidic groups may be alkyleneamine or alkylene-carbamidic groups with a maximum of 8 carbon atoms. Of these alcohols, first and foremost should be mentioned those which are saturated and unsubstituted, for example, methyl, ethyl, propyl, isopropyl alcohols, n-butyl, isobutyl, tert-butyl alcohol, amyl alcohols, pentyl, hexyl, octyl, nonyl and dodecyl alcohols and especially those ~ith a linear chain, e.g. n-octyl and n-dodecyl alcohols.
Of the substituted alcohols, preferred are the already mentioned glycols, otherwise used for the formation of "cross links", but also polyhydric alcohols, e.g. glycerine, the

2~ aldehyde alcohols, e.g. tartronic alcohol, carboxy alcohols, e.g.
lactic a cids, for example, a~oxypropionic acid, glycolic acid, ~D

malic acid, tartaric acids, citric acid, aminoalcohols, e.g.
aminoethanol, aminopropanol, n-aminobutanol and their dimethyl and diethyl derivatives in the amino function, choline, pyrrolidinylethanol, piperidinylethanol, piperazinyl-ethanol and the corresponding derivatives of n-propyl alcohol or n-butyl alcohol, monothioethylenglycol or its alkyl derivatives, for example, the ethyl derivative in the mercapto function. Of the saturated higher aliphatic alcohols, preferred are; ~or example, cetyl alcohol and myricyl alcohol but of special importance for the aims of aspects of the present invention are the higher unsaturated alcohols with one or two double bonds, e.g.
especially those contained in many essential oils and having an affinity with terpenes, for example, citrinellol, geraniol, nerol, nerolidol, linalool, farnesol and phytol. Of the unsaturated lower alcohols, allyl alcohol and propargyl alcohol are useful.
Of the araliphatic alcohols, those to be mentioned above all are all those with only one benzene residue and in which the aliphatic chain has a maximum of 4 carbon atoms and in which the benzene residue may be substituted by between 1 and 3 methyl or hydroxy groups or by halogen atoms, especially by chlorine, bromine or iodine, and in which the aliphatic chain may be substituted by one or more functions chosen from the yroup constituted by free amino or mono or dimethyl groups or by pyrrolidinyl or piperidinic yroups. Of these alcohols, most preferred are benzyl alcohol and phenethyl alcohol.

1~ ~3~7.~
'rhe alcohols of the cycloaliphatic series (including also cycloaliphatic-aliphatic alcohols) may derive ~rom mono- or polycyclic hydrocarbons and may preferably have a maximum of 34 carbon atoms. In the case of substituted alcohols, the substituents may be those already mentioned for the alcohols o~
the aliphatic series.
Of the alcohols derived from monoannular cyclic hydrocarbons, special mention should be given to those with a maximum of 12 carbon atoms, the rings preferably having between 5 and 7 carbon atoms, which may be substituted, for example, by between one and three lower alkyl groups, e.g. methyl, ethyl, - propyl or isopropyl groups. As specific alcohols of this group preferred are cyclohexanol, cyclohexanediol, 1,2,3-cyclohexanetriolandl,3,5-cyclohexanetriol (phloroglucitol),and inositol. The heterocyclic alcohols may be considered as deriving from the above cycloaliphatic or aliphatic-cycloaliphatic alcohols if, in these, the linear or cyclic chains are interrupted by one or more heteroatoms, for example between 1 and 3 heteroatoms selected from the group formed by - O -, - S -, - N = and - NH -. In them, there may be one or more double bonds, in particular between 1 and 3, thus also including heterocyclic compounds with aromatic structures. They may be simple alcohols, e.g. furfuryl alcohol or alcohols with a more complicated structure, e.g. as are present in many alkaloid derivatives and in many medicaments.

1~

19 ~ 3 ~
~ s already stated, the cross-linked derivatives of aspects of the present invention may be used for all the main applications suitable for hyaluronic acid or its salts or the above esters described in the above-described co-pending Canadian patent application. As already said, the derivatives of aspects of the present invention are therefore particularly suitable for the preparation of: 1) medicaments; 2) pharmaceutical vehicles for medicaments; 3) cosmetics and vehicles for cosmetics; and ~) plastic articles for sanitary, medical and surgical uses. The present invention includes, in particular, all these uses;
The type of cross-linked ester is obviously chosen according to the use to which it is to be put. Usually, a high degree of esterification to the point of total esterification of the hyaluronic acid increases its lipophilic character and therefore diminishes its solubility in water. For therapeutic or cosmetic uses it is especially important to regulate the degree of esterification in such a way as to ensure sufficient solubility in water, although it does have good lipophilic qualities compared to hyaluronic acid or its salts. Naturally, the molecular size of the esterifying component itself should be borne in mind, as this usually influences hydrosolubility in an inversely proportional manner. As far as the use of medicaments is concerned, the greater or lesser degree of hydrophilic or lipophilic qualities should be considered in relation to the type of tissue to be treated, for example, the skin in the case of dermal medicaments.

~.3~7~87 The cross-linked derivatives of aspects of the present invention may be used as therapeutic agents due to the intrinisic property of the hyaluronic component itself. For example, they may be used as drugs for the treatment of arthritis, both in human and veterinary medicine. In this case, they derive from polyhydric aliphatic alcohols with no pharmacological properties or with n~gligible activity, especially from dihydric alcohols with between 2 and 8 carbon atoms. The other simple ester groups present possibly also derive from alcohols with no pharmacological action, for example from monohydric aliphatic alcohols with a maximum number of eight carbon atoms.
Administration is effected by parenteral route and more precisely by intraarticular route.
Other cross-linked derivatives according to other aspects of the invention may also derive from alcohols with a pharmacological effect and this is especially true of alcohols from which simple ester groups are derived. They possess properties which are qualitatively similar to those of the selected alcohol, but with a more differentiated range of action, ensuring a more balanced, constant and regular pharmacological action and usually having a marked "retard" effect. Other cross-linked derivatives again may contain simple ester groups of two or more different types of alcohols with or without their own pharmacological action. By suitably dosing the ratio of the different types of alcohols as esterifying components, it is possible to obtain esters without the specific activity of ~D

~1 ~3:L7~
hyaluronic acid, and having those qualities described above of greater stability and bioavailability with respect to the desired activity and the characteristics of the pharmacologically-active alcohols.
In the derivatives described above, deriviny from pharmacologically-active alcohols, the cross-linked hyaluronic molecule acts basically as a vehicle for the pharmacologically-active component. They may therefor also be included in uses 2) or 3) described above. Since the cross-linked derivatives of aspects of the present invention act as actual vehicles according to the above-described uses 2) and 3), they are preferabl~ also derived from the above therapeutically-inactive polyhydric alcohols. Ester groups deriving from monohydric alcohols are also preferably without any pharmacological action. The active substance is physically mixed with the derivatives of aspects of the present invention. The resulting medicaments may also contain other ingredients and excipients commonly used in conventional pharmaceutical preparations. In place of an active substance it is possible to have an association oE active substances. Particularly interesting are medicaments of this kind in which the hyaluronic derivatives of aspects of the present invention act as vehicle and contain topically-active substances.
The pharmacologically-active alcohols to be used for the esterification of carboxy groups not yet cross-linked in the new derivative, may be, apart from those already listed, aliphatic~
cycloaliphatic polycyclic alcohols, for example, steroids, e.g.

22 ~ 3 ~ 7 2 ~ ~
sexual hormones and their synthe~ic analogues. Particularly, they may be corticosteroids and their derivatives, ~or example, estradiol and its methyl derivatives, and its ethinyl or propinyl derivatives in position 17, testosterone and its derivatives, e.g. 17-~-methyl-testosterone,17-~-ethinyl-testosterone, 1, 1,2-dehydro-testosterone, nor~gestrel, 19 nor-testosterone, and 19-nor-17-~-methyl-testosterone; and anti-hormones, e.g.
cyproterone, cortisone, hydrocortisone, dexamethasone, betamethasone, paramethasone, flumethasone, fluocinolone, clobetasol, beclomethasone, alfaxo]one, and bolasterone. Other therapeutically-active alcohols are, for example, vitamins, e.g.
axerophthol, vitamins D2 and D3, aneurine, lacto~lavine, ascor~ic acid, riboflavine, thiamine and pantothenic acid. Of the heterocyclic alcohols also can be mentioned atropine, scopolamine, cinchonine, cinchonodine, quinine, morphine, codeine, nalorphine, N-butylscopolammonium bromide, and ajmaline;
phenylethylamines, e.g. ephedrine, isoproterenol, and epinephrine, phenothiazine drugs, e.g. perphenazine, pipotiazine, carphenazine, homofenazine, acetophenazine, fluphenazine, and N-hydroxyethylpromethazine chloride; thioxanthene drugs, e.g.
flupentioxol and clopenthixol; anticonvulsivants, e.g.
meprophendiol; antipsychotics, e.g. opipramol; anti-emetics, e.g.
oxypendyl; analgesics, e.g. carbetidine, phenoperidine and methadol; hypnotics, e.g. etodroxizine; anorexics, e.g.
benzhydrol and diphemethoxidine; minor tranquilizers, e.g.
hydroxizine; muscle relaxants, e.g. cinnamedrine, diphylline, ~D

23 ~7~
mephenesin, methocarbamol, chlorphenesin, 2,2-diethyl-~,3-propandiol, guaiphenesin, and hydrocilamide; coronary vasodilators, e.g. dipyrldamole and oxyfe~rine; adrenergic blockers, e.g. propanolol, timolol, pindolol, bupranolol, atenolol, metoprolol, and practolol; anti~neoplastics, e.g. 6-azuridine, cytarablne, and floxuridine; antibiotics, e.g.
chloramphenicol, thiamphenicol, erythromycin, oleandomycin, and lincomycin; antivirals, e.g. idoxuridine; peripheral vasodilators, e.g. isonicotinyl alcohol; carbonic anhydrase inhibitors, e.g. sulocarbilate; anti-asthmatics and anti-inflammatories, e.g. tiaramide; and sulphamidics, e.g. 2-- p-sulphanylanilinoethanol.
The cross-linked derivatives of aspects of the present invention described here may of course be used in the same cases as the free alcohols.
One particularly interesting aspect of the present invention is the possibllity of preparing more stable drugs than those available up till now. It is possible, there~ore, on the one hand to prepare cross-linked derivatives for use in the indications which are typical of hyaluronic acid itself, for example, for intra-articular injections where the cross-linked derivative acts as lubricant. Due to the better stability of the - derivatives when the hyaluronidase is compared to the free acid, it is possible to obtain a quite notably prolonged action. On the other hand, it is possible to obtain drugs with a '7retard"
ackion for the above derivatives also containing ester groups 1~ E) 24 ~ 7 deriving from therapeutically-active alcohols. In these, the pharmacologically-active alcohol is very slowly released into the organism by means of esterases~ For use according to the above-described use 4), the new cross-linked derivatives of aspects of the present invention may be prepared above all with pharmacologically-inert alcohols, for example bivalent saturated aliphatic alcohols, especially those with between 2 and 8 carbon atoms, glycerin and from monovalent alcohols, above all aliphatic alcohols, but also some others of the above series for partial esterification in the carboxy groups which are not cross-linked.
Of this la~st group, particularly interesting are the unsaturated alcohols, for example those with one or more double bonds, e.g.
vinyl or allyl alcohols and their condensed derivatives, e.g.
polyvinyl alcohol and glycerin. In this case, too, it is possible to use mixed esters, according to the particular intended use. Alicyclic alcohols are also useful. For example, such alcohols derived from cyclopentane and cyclohexane and from their derivatives substituted by inferior alkyl groups, for example, alkyls with between 1 and 4 carbon atoms, especially by methyl groups are useful.
For cosmetic use it is preferable to use cross-linked derivatives with esterified groups substantially identical to those listed above for the use of sanitary, medical and surgical articles. Also to be considered are terpene alcohols, e.g. those mentioned above, especially odoriferous alcohols for the preparation of perfumes and scented creams.

'D

25 ~ 7 In all the cross-linked derivatives according to aspects o~
the present invention, the carboxy groups not "cross-linked" or not esterified may be free or salified. The salts may have inorganic bases, for example, alkaline metals, e.g. potassium and particularly sodium and ammonium, and alkaline earth metals, e.g.
calcium, or magnesium and aluminium salts. They may have organic bases, especially azotized bases and therefore aliphatic, araliphatic, cycloaliphatic or heterocyclic amines. These salts may derive from therapeutically-acceptable but inactive amines, or from amines with a therapeutic action.
Of the former, consideration is to be given above all to the aliphatic amines, for example mono-, di- and tri-alkylamines with alkyl groups with a maximum of 18 carbon atoms or arylalkylamines with the same number of carbon atoms in the alipha-tic part.
"Aryl" means a benzene group, possibly substituted by between 1 and 3 methyl groups or halogen atoms or hydroxy groups. The biologically-inactive bases for the formation of the salts may also be cyclic, e.g. monocyclic alkylenamines with cycles of between 4 and 6 carbon atoms, possibly interrupted in the cycle by heteroatoms selected from the group consisting of nitrogen, oxygen and sulphur, e.g. piperidine, piperazine or morpholine, or may be substituted, for example, by amino or hydroxy functions, e.g. aminoethanol, ethylendiamine, ephedrine, or choline.
It is also possible to form the quaternary ammonium salts of partial esters, for example, tetraalkylammonium salts with the ~3~7~'~3 l above number of carbon atoms and preferably salts of the same type in which the fourth alkyl group has between 1 and 4 car~on atoms, for example, a methyl group.
Those biologically-active amines whose therapeutic action may be put to use, include azotated and basic drugs, e.g. those included in the following groups: alkaloids, peptides, phenothiazine, benzodiazepine, thioxantene, hormones, vitamins, anticonvulsivants, antipsychotics, antiemetics, anaesthetics, hypnotics, anorexics, tranquilizers, muscle-relaxants, coronary vasodilators, antineoplastics, antibiotics, antibacterials, antivirals, antimalarials, carbonic anhydrase inhibitors, nonsteroid anti-inflammatories, vasoconstrictors, cholinergic agonists, cholinergic antagonists, adrenergic agonists, adrenergic blockers, and narcotic antagonists.
All those drugs with the basic azotated groups listed above can be mentioned as examples regarding the use of the esters.
Salification of the nonesterified carboxy groups with therapeutically-active bases may substitute or integrate the vehicling function of the new cross-linked derivatives obtained ZO by esterification with therapeutically active alcohols and therefore represents another particular case of the use of the new compounds as therapeutic vehicles according to the above-described use 2): the active bases are vehicled both by the neutral salts obtainable by addition of the basic stoichiometric quantity, both from the basic salts obtainable by addition of an II) ~.3~72~l excess of base or of those acids obtainable by addition o~ a basic defect.
The hyaluronic derivatives according to aspects of the present invention are particularly useful since they are medicaments for local or topical use, especially in ophthalmology, where they show particular compatibility with the corneal epithelium and are therefore very well tolerated, with no sensitization effects. Furthermore, when the medicaments are administered in th~ form of concentrated solutions with elastic-1~ viscous characteristics or in solid form, it is possible, on thecorneal epithelium, to obtain homogenous, stable and transparent films which are also adhesive, guaranteeing prolonged bioavailability of the drug and which therefore constitute excellent preparations with a retard effect.
These ophthalmic medicaments are of exceptional value especially in the veterinary field, considering that there are at present no veterinary specialities containing chemical agents.
Indeed, products intended for human use are used on animals, and these cannot always guarantee a specific range of action and are sometimes unsuitable for application in the conditions under which they are to be administered. For example, this is the case of therapy for infective keratoconjunctivitis, pink eye or IBK, an infection which usually affects cattle, sheep and goats.
Presumably, specific etiological factors exist for these three species. More particularly, in cattle, the main micro-organism involved seems to be Moraxella bovis (even though other agents t T-~
L~

28 ~L3~7~8~
of viral origin are not to be excluded, e.g. the Rhinotracheitis virus, in sheep ~ycoplasma, Rickettsia and Chlamydia, in goats Rickettsia). The disease presents itself in acute ~orm and tends to spread rapidly. In the initial stages, the symptomatology is characterised by blepharospasm and excessive lacrimation, followed by purulent discharge, conjunctivitis and keratitis, often associated with fever, a reduction in appetite and milk productions. Particularly serious are the corneal lesions which, in the final stages, may even cause perforation of the cornea itself. The clinical course varies from a few days to several weeks.
A vast range of therapies involving chemical agents are used, administered both by a topical route (often associated ~ith steroid anti-inflammatory agents), and by a systemic route, for example, tetracyclines, e.g. oxytetracycline; penicillins, e.g.
cloxacillin and benzyl penicillin; sulphamidics; polymyxin B
(associated with miconazole and prednisolone); chloramphenicol;
tylosin; and chloromycetin. Topical treatment of the disease, despite its apparent simplicity, is still an open problem, since, with the ocular preparations used until now, it has not been possible for one reason or another to obtain concentrations of therapeutically-effective antibiotics or sulphamidics in the lachrymal secretion. This fact is fairly understandable in the case of solutions, considering the predominantly inclined position of the head in the animals mentioned above, but it is also true of semlsolid medicaments, since the excipients commonly ~L~

29 ~ 2~
used in the same do not have the necessary qualities to adhere to the surface of the cornea. This is because they do not usually have a sufficiently high concentrakion of active substance and cannot obtain distribution o* the same (presence of a distribution gradient). These drawbacks to conventional collyriums for ophthalmics have, for example, been described by Slatter et al in "Austr. vet.J.," 1982, 59 (3), pp. 69-72. With the esters of aspects of the present invention, these difficulties can be overcome. Indeed, the presence of the hyaluronic ester as a vehicle in ophthalmic drugs allows for the formulation o~ excellent preparations with no concentration - gradient of active substance. They are there~ore homogenous, transparent and adhesive to the corneal epithelium, with no sensitization effects and with the active substance acting as an excellent vehicle, possibly also with a retard effect.
Medicaments containing the derivatives of aspects of this invention which may be used in ophthalmic treatments mainly concern miotic, wound healing, anti-inflammatory and anti-microbial/antibiotic effects. Some examples of antibiotic substances are: basic and non-basic antibiotics, for example, aminoglucosidics, macrolidics, tetracyclines and peptides, for example gentamycin, neomycin, streptomycin, dihydrostreptomycin, kanamycin, amikacin, tobramycin, spectinomycin, erythromycin, oleandomycin, carbomycin, spiramycin, oxytetracycline, rolitetracycline, bacitracin, polymyxin B, gramicidin, colistin, chloramphenicol, lincomycin, vancomycin, novobiocin, ristocetin~

D

30 1~7f~37 clindamycin, amphotericin B, griseofulvin, nystatin and possibly their salts, e.g. sulphates or nitrates, or associations o~ the same either among themselves or with other active principles, for example, those mentioned below.
Other ophthalmic drugs to be used to advantage according to the present invention are: other anti-infectives, e.g.
diethylcarbamazine, and mebendazole; sulphamidics, e.g.
sulfacetamide, sulfadiazine, and sulfisoxazole; antivirals and antitumorals, e.g. iododeoxyuridine, adenine arabinoside, trifluorothymidine, acyclovir, ethyldeoxyuridine, bromovinyldeoxyuridine, and 5-iodo-5'-amino-2',5'-dideoxyuridine;
steroid anti~in~lammatories, e.g. dexamethasone, hydrocortisone, prednisolone, fluorometholone, medrysone and possibly their esters, for example, phosphoric acid esters; non-steroid anti-in~lammatories, e.g. indomethacin, oxyphenbutazone, and flurbiprofen; wound healers, e.g. epidermal growth factor EGF;
local anaesthetics, e.g. benoxinate, proparacaine and possibly their salts; cholinergic agonis~ drugs, e.g. pilocarpine, methacholine, carbamylcholine, aceclidine, physostigmine, neostigmine, demecarium and possibly their salts; cholinergic blocker drugs, e.g. atropine and its salts; adrenergic ayonist drugs, e.g. noradrenaline, adrenalin, naphazoline, methoxamine and possibly their salts; adrenergic blocker drugs, e.g.
propanolol, timolol, pindolol, bupranolol, antenolol, metoprolol, oxprenolol, practolol, butoxamine, sotalol, butadrin, labetalol and possibly their salts.

~.D

31 ~3~P~
Examples of active substances to be used on their own or in association among themselves with other active principles in dermatology are: therapeutic agents, e.g. anti-infective agents, antibiotics, antimicrobials, anti inflammatories, cytostatics, cytotoxics, antivirals, anaesthetics, and preventive agents, e.g.
sun shields, deodorants, antiseptics and disinfectants.
From the examples quoted for ophthalmology and dermatology, it is reasonable to assume by analogy which are the medicaments according to aspects of the present invention which woul~ be suitable for use in the various fields of medicine, ~or example, otolaryngology, gynaecology, angiology, neurology or any other type of pathology of the internal organs which may be treated by local topical applications, for example by rectal action. It is of course possible to prepare associations of therapeutically-active substances with the derivatives according to aspects ofthe present invention, suitable for parenteral administration.
In the latter case, to obtain aqueous solutions for injection, hyaluronic derivatives with a low level of cross-linkiny and/or esterification should be chosen. Derivatives which are only slightly, or not at all soluble in water, can be used to make associations containing the active substances for administration in solutions of organic substances, for example oil solutions.
The medicaments of the type described here for topical use may be in solid form, e.g. freeze-dried powders containing only the two components as a mixture or separately. Such solid form medicaments, on contact with the epithelium to be treated, form 32 ~ 3 ~ 7 ~w 8 ~
more or less concentrated solutions according to the nature of the particular epithelium having the same characteristics as the solutions previously prepared ln vitro and which represent another particularly interestin~ aspect of the present invention.
Such solutions are preferably in distilled water or sterile saline and preferably contain no other pharmaceutical vehicle besldes the hyaluronic ester or one of its salts. The concentrations of such solutions may also vary within wide limits, for example between 0.01 and 75% both for each of the two components taken separately, and for their mixtures or salks.
Particular preference is given to solutions with pronounced elastic viscous properties, for example, with a content of between 10% and 90% of the medicament or of each of its components. Particularly important are medicaments of this type, both in an anhydrous form (freeze-dried powder) or as concentrated solutions or diluted in water or saline, possibly with the addition of additive or auxiliary substances, e.g. in particular disinfectant substances or mineral salts actin~ as vehicle or others, for ophthalmic use.
Of the medicaments of aspects of the present invention, it is preferably to choose, as the case may be, those with a degree of acidity suitable for the en-~ironment to which they are to be applied, that its, with a physiologically-tolerable pH. The p~, for example in the above salts of the hyaluronic acid esters with a basic active substance, may be adjusted by suitably regulating the quantity of polysaccharide, of its salts and of the basic 33 ~ 3 ~ J ~
substanc~ itself. I'hus, ~or example, if the acidiky of a salt of a hyaluronic ester with a basic substance is too high, the excess of free acid groups may be neutralized with the above inorganic bases, for example, with sodium or potassium or ammonium hydrate.
The cross-linked derivatives of aspects of the present invention may be prepared by processes per se known for the esterification of carboxy acids. For example, the process may be for treatment of free hyaluronic acid with the above polyhydric alcohols in the presence of catalysts, e.g. strong inorganic acids or acid-type ionic exchangers, or with an etherifying agent able to introduce the desired alcohol residue in the presence of inorganic or organic bases. As etherifying agents it is possible to use those named in literature, e.g.
~5 especially the esters of various inorganic acids or organic sulphonic acids, e.g. hydrogen acids, that is, the alkyl halogenide, e.g. methyl iodide or other alkyl groups which are at the base of the above bivalenk alcohols.
The reaction may be effected in a suitable solvent, for example, an alcohol, preferably the one corresponding to the alkyl group to be introduced into the carboxy group. It may also be effected in non-polar solvents, e.g. ketones, ethers, e.g.
dioxane or aprotic solvents, e.g. dimethylsulfoxide. As a base, it is possible to use, for example, a hydrate of an alkali metal, of an alkaline earth metal or of magnesium or an oxide of silver or a basic salt of one of these metals, e.g. carbonate. Of the organic bases, it is possible to use a tertlary ~z~ ~zed base, e.g. pyridine or collidine. Instead of the base, a basic~type ion exchanger may be used.
Another esterification process involves metal salts or salts with organic a~otized bases, for example, ammonium or ammonium substitute salts. Preferably, the salts of alkali metals or alkaline earth metals should be used, but ~ny other metal salt may also be used. The esterifying agents are also in this case those mentioned above and the same is true of the solvents.
Preferably, aprotic solvents, for example, dimethylsulfoxide and dimethylformamide should be used. These esterification processes may of course also be used to prepare the simple esters described above.
According to the procedure described in U.S. Patent No.
4,851,521 and regarding the simple esters of hyaluronic acid, these may be prepared to advantage, starting with the quaternary ammonium salts of hyaluronic acid wi~h an etherifying agent in an aprotic solvent, e.g. dialkylsulfoxides, dialkylcarboxylamides, e.g. in particular lower alkyl dialkylsulfoxides, above all dimethylsulfoxide, and lower alkyl dialylamides of inferior aliphatic acids, e.g. dimethyl or diethyl formamide or dimethyl or diethylacetamide. The reaction is effected preferably at a temperature range of between 0~ and 100, and especially between 25 and 750, for example, at 30.
Esterification is preferably effected by gradually adding the 13~72~7 esterifying agent to the above ammonium salt dissolved in one of the solvents mentioned, for example, in dimethylsulfoxide.
The same process can be used to prepare the typical cross-linked esters of aspects of the present invention. The bridge bonds between two carboxy groups are easily formed by etherif~ing substances deriving from the above polyhydric alcohols on the quaternary ammonium salts of hyaluronic acid. As starting quaternary ammonium salts, it is preferable to use an inferior ammonium tetraalkylate, the alkyl groups preferably having between 1 and 6 carbon atoms. As a first choice, tetrabutylammonium hyaluronate should be used. These ~uaternary ammonium salts can be prepared by reacting a metal salt of hyaluronic acid, preferably one of those mentioned above, especially a sodium or potassium salt, in aqueous solution with a sulphonic resin salified with the quaternary ammonium base.
Tetraalkylammonium hyaluronate can be obtained by freeze-drying the eluate.
The tetraalkylammonium hyaluronates deriving from lower alkyls, especially alkyls with between 1 and 6 carbon atoms, are new and provide another aspect of the present invention.
Unexpectedly, such salts have proved to be soluble in the above aprotic solvents, and esterification of hyaluronic acid according to the above procedure is therefore particularly easy and gives abundant yields. It is, therefore, only by such a procedure that 2S it is possible exactly to dose the number of hyaluronic acid carboxy groups to be esterified.

~ ~D

36 ~ 3 ~ 7 One variation of the previously~specified process consists in reacting the potassium or sodium salt of hyaluronic acid, suspended in a suitable solvent, e.g. dimethylsulfoxide, with a suitable etherifying agent in the presence of a catalyzing quantity of quatern~ry ammonium salt, e.g. tetrabutylammonium iodide. For the preparation of the esters according to aspects of the present invention, hyaluronic acids of any origin, for example, the acids extracted from the above natural starting materials, for example from cock's combs, may be used. The preparation of such acids is described in literature: preferably, purified hyaluronic acids should be used. According to aspects of the present invention, it is preferable to use hyaluronic acids comprising the molecular fractions of the integral acids obtained directly by extraction of the organic materials with molecular weights which may vary greatly, for example, between 90~ - 80%~and 0.2% of the molecular weight of the integral acid, preferably between 5% and 0.2%. These fractions may be obtained by various procedures described in literature. That is, they may be obtained by hydrolysing or oxidiziny or enzymatic agents or physical procedures, for example, mechanical procedures or by irradiation, and often therefore, primordial extracts are formed during these same purification procedures (see for example the above-mentioned article by Balazs et al in 'ICosmetics &
Toiletries"). The separation and purification of the molecular fractions obtained is effected for example by known techni~ues, for example by molecular filtration.

lD

37 1~7~g~
One purified HY fraction suitable to use according to an aspect of the present invention is, for example, the one name "non-inflammatory sodium hyaluronate-NIF-NaHA described by Balazs in the leaflet "Healon" - A Guide To Its Use In Ophthalmic Surgery - D. Miller & R. Stegmann, eds. John Wiley & Sons N.Y
81983: p.5. Particularly important as starting materials for the esters of aspects of the present invention are two purified fractions obtainable from hyaluronic acid, *or example, the type extracted from cocks' combs, and known by the trade-marks of "HYALASTINE" and "HYALECTIN". The fraction HYALASTINE has an average molecular weight of between 50,000 and 100,000 while the fraction HYALECTIN has an average molecular weight of between 500,000 and 730,000. One fraction combined with these two fractions also has been isolated and is characterized as having an average molecular weight of between 250,000 and 350,000. ~his combined fraction may be obtained giving a yield of total hyaluronic acid equal to 80% of the amount available in the particular starting material, while the fraction HYAI.E~TIN can he obtained with a yield of 30% and the fraction HYALASTINE with a yield of 50% of the starting HY.
In the cross-linked derivatives of hyaluronic acid of aspects of the present invention, the nonesterified carboxy groups may be free or salified or partially salified and various different types of cross-linked products are therefore obtained.
That is, those products obtained include those in which the remaining carboxy groups are free or salified, those in which the ' L~

3~ 7 remaining carboxy groups are totally or partially esteri~ied, an~
in the latter, the remaining groups may in turn be free or salified. Thus, a whole range of products is availa~le, varyiny in their physical properties and especially regarding their degree of acidity and visco-elastic properties and their ability to form gels. The number of acid groups to be kept free may be important for the preparation of medicaments with ~ particular pH.
Preparation of the salts of the derivatives of aspects of the present invention can be carried out in the known manner, for example, by reacting on the hyaluronic derivative the calculated basic quantity of alkaline hydrates, for example, or basic salts of alkaline metals, e.g. carbonates or bicarbonates. It is possible, for example, first to prepare aqueous solutions of the hyaluronic derivative and of the base, freeing such substances from the aqueous solutions of their salts with suitable ionic exchangers, and pooling the two solutions at a low temperature, for example, between 0 and 20. If the salt thus obtained is easily so~uble in water, it is freeze-dried, while the less soluble salts may be separated by centrifugation or filtration or decanting and possibly then dried. In the case of organic bases, to be vehicled with the new cross-linked derivatives, the medicaments obtained as salts of such bases with the new derivatives may be neutral, acid or basic according to whether stoichiometric quantities are added, or whether there is a basic defect or excess.

38a ~3 ~ 72~ l According to a particular aspect of the i~vention, it is possible to prepare medicaments of the above type startiny with the previously isolated salts and possibly puri~ied, in an anhydrous state, e.g. amorphous powders, which on contact with the tissue to be treated constitute a concentrated aqueous solution of a gelatinous character, viscous consistency and with elastic properties. These qualities are maintained also at stronger dilutions and may ~e used in place of the above anhydrous salts, more or less concentrated solutions in water or saline, possibly with the addition of other excipients or additives, e.g. other mineral salts to regulate the pH and osmotic pressure. It is of course also possible to use the salts to make gels, inserts, creams or ointments, including other excipients or ingredients used in traditional formulations of these pharmaceutical preparations.
Of the products of aspects of the present invention, the esters described above and their salts and those featuring in the following illustrative Examples are of particular relevance.
The present invention also includes modifications of processes for the preparation of the esters and of their salts.
Aspects of the present invention include processes in which a procedure i~ interrupted at any stage or in which the procedure starts with an intermediate compound and the remaining stages are then effected, or in which the starting products are formed in situ.
The invention is illustrated by the following Examples, in which DMS0 means dimethylsulfoxide. The products described in ~.D

38b i 3 ~. 7 2 8 ~

the Examples comprise cross-linked esters according to aspects of the present invention, having a percentage of the hyaluronic acid carboxyls esterified with a polyhydric alcohol, and having the remaining carboxyls salified and/or esterified with a monohydric alcohol. Table 1 hereinafter lists the various products according to Examples 1 - 37 describing the number of carboxyls esterified with the specified polyhydric alcohol, and the number of carboxyls salified with sodium and/or esterified with the specified monohydric alcohol.

~3~7~

Example 1 - Preparation of hyaluronic acid SHY) partially esterified with ethanol and partially cross-linked with 1-3 propandiol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C under rigorously damp-free conditions~ in nitrogen atmosphere and away from light. 0.078 g of ethyl iodide are added (0.5 mM) and the solution is agitated for 15 hr at 3QC. 0.074 g of 1-3 diiodopropane are added (0.25 mM, corresponding to 0.5 mEq) and after homogeni~ation the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution is added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while cooling it fxom th~ out-side with a hath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, then vacuum-dried.

4.01 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et alO (Anal. Biochem. 33, 1028, 1961) and shows a content of 0.56~ w/w as ethanol (theoretical: 0.574). Analysis of the total ~o ~ ~72~7 ester groups is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as indicator. In this way it is possible to determine a total ester group content equal to 0.24 mEq/g (theoretical: 0.25).

E~ample 2 - Preparation of hyaluronic acid (HY~
partially esterified with ethanol and partially cross-linked with 1-3 propandiol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml di DMSO a 25C in rigourously damp-free conditions, in nitrogen atmosphere and away from light. 0.078 g of ethyl iodide are added (0,5 mM) and the solution is agitated for 15 hr at 30C. 0.148 g of 1-3 diiodopropane are added (0.5 mM, corresponding to 1 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution is added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while cooling it from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml f~ ~
oip~ :
, ~

- 41 - 1 317 ~7 of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, then vacuum-dried.
3.99 g of the compound featured in the titl~ are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 0.56% w~w as ethanol (theoretical: 0.574). Analysis of the total ester groups is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as indicator. In this way it is possible to determine a total ester group content equal to 0.36 mEq/g (theoretical 0.374).

Example 3 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-3 propandiol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml di DMSO at 25C in rigourously damp-free conditions, in nitrogen atmosphere and away from light. 0.078 g of ethyl iodide are added (0.5 mM) and the solution is agitated for 15 hr at 30C. 0.296 g of 1-3 diiodopropane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C per 24 hr.

, . b . ~

7~

- ~2 -For conversion of the residue tetrabutylammonium carbo~y groups into sodium salt, to the resulting solution is added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while cooling it from the outside with a bath of H2O/ice.
500 ml of acetone arP added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, then vacuum-dried.
3.98 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 0.56% w/w as ethanol (theoretical: 0.574). Analysis of the total ester groups is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The e~cess is determined by titration with HCl 0.lN using pheonlphthalein as indicator. In this way it is possible to determine a total ester group content equal to 0.61 mEq~g (theoretical 0.623).
xample 4 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross linked with 1-3 propandiol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C under ~7~

- ~3 -rigourously damp-free conditions, in nitrogen atmosphere and away from light. 0.156 g of ethyl iodide are added ~1 mM) and the solution is agitated for 15 hr at 30C. 0.296 g of 1-3 diiodopropane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.00 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 1.08% w/w as ethanol (theoretical: 1.15). Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The e~cess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of ~.735 mEq~g (theoretical 0~747 ~ 3~7~

- 4~ -xample 5 - Preparation of hyaluronic acid (HY) partially eskerified with ethanol and partially cross-linked with 1-3 propandiol 6.21 g o tetrabutylammonium salt of HY (10 mEq3 are solubilized in 248 ml of DMSO at 25C in absolut~ly dry conditions, in nitrogen atmosphere and away from light. 0.312 9 of ethyl iodide are added (2 mM) and the solution is agitated for 15 hr at 30C. 0.296 g of 1-3 diiodopropane are added (1 t~M, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylar~nonium carboxy groups into sodiusn salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H20, while it is cooled from the outside with a bath of H20/ice.
500 ml o acetone are added, the precipita~A~ is separated by filtration, washed 3 times with 100 ml of acetone/H20 5:1 and 3 times with 100 ml of pure acetone, and then vacuum drisd.
4.01 g of the cotnpound featured in the title are obtained.
Etho~yl determination is carried out according to the method of Cundiff et al. and sho~Js a content of 2.18% w/w as ethanol (theoretical: 2.29~. Total ester group analysis is carried out by saponification reaction with an excess quantity-of NaOH O.lN a "' ~ ; d' ~ r f i ~ s ;!

~ :L 7 i v ~ ~

50C for 30 min. The excess is determined by titration with HCl O.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.98 mEq/g ~theoretical 0.995).

Example 6 - Preparation of hyaluronic acid (HY3 partially esterified with ethanol and partially cross-linked with 1-3 propandiol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 298 ml of DMSO at 25C in rigourously damp-free conditions, in nitrogen atmosphere and away from light. 0.624 g of ethyl iodide are added (4 mM) and the solution is agitated for 15 hr at 30C. 0.296 g of 1-3 diiodopropane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutyla~nonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O~ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with lOQ ml of acetone~H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.00 9 of the compound featured in the title are obtained.

- ~6 -Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 4.5% wJw as ethanol (theoretical: 4.57). Total ester group analysis is carried out by saponification reaction with an e~cess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 1.43 mEq/g (theoreticalo 1.49).
~ample 7 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-3 propandiol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.934 g of ethyl iodide are added (6 mM) and the solution is agitated for 15 hr at 30C. 0.296 g of 1-3 diiodopropane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylam~onium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2Q, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml J
- ~7 -of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.03 g of the compound featured în the title are obtained.
Ethoxyl determination is carried out according -to the method of Cundiff et al. and shows a content of 6.74% w/w as ethanol (theoretical: 6.8~. Total ester group analysis is carried out by saponification reaction with an excess quantity o NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 1O96 mEq/g (theoretical: 1.98).
xample 8 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-3 propandiol 6.21 g of tetrabutylammonium salt of HY (10 mEq~
are solubilized in 248 ml of DMSO a 25C in absolutely dry conditions, in nitrogen atmosphers and away from light. 1.170 g of ethyl iodide are added (7.5 mM) and the solution is agitated for 15 hr at 30C. 0.296 g of 1-3 diiodopropane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr, For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting ~3~7~J~7 solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H20, while it is cooled from the outside with a bath of H20/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H20 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
9.02 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 8.46% w/w as ethanol (theoretical: 8.52). Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH O.lN at 50C for 30 min. The excess is determined by titration with HCl O.lN using phenolphthalein as an indicator. It is thus possible to determine ~ total ester group content of 2.28 mEq/g (theoretical: 2034).
xample 9 - Preparation of hyaluronic acid ~HY?
partially esterified with ethanol and partially cross-linked with 1-3 propaniol 6.21 g of tetrabutylammonium salt of HY (10 mEq~
are solubilized in 248 ml o DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.624 g of ethyl iodide are added t4 mM) and the solution is agitated for 15 hr at ~3:L728~

30C. 0.592 g of 1-3 diiodopropane are added (2 mM, corresponding to 4 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while cooling it from the outside with a bath of H~O/ice.
500 ml of acetone are added, the precipitate is separated by ~iltration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
3.99 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method o~ Cundif et al. and shows a content of 4.42% w/w a~ ethanol (theoretical: 4.57). Total ester group analysis is carried out by saponification reaction with an e~cess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.lM using phenolphthalein as an indicator. It is thus possible to determine a total ester yroup content of 1.96 mEq~g (theoretical: l.g9).
xample 10 - Preparation of hyaluronic acid ~HY) partially esterified with ethanol and partially cro~s-linked with 1-4 butanediol 6O21 g of tetrabutylammonium salt of HY (lD mEq) are solubilized in 248 ml of DMSO at 25C in ~ ~7~$~

absolutely dry conditions, in nitrogen atmosphere and away from light. 0.312 g of ethyl iodide are added ~2 mM) and the solution is agitated for 15 hr at 30C. 0.310 g of 1-3 diiodobutane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 9 of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O~ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.02 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 2.3% w~w as ethanol (theoretical: 2.28). Total e~ter group analysis is carried out by saponification reaction with an sxcess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.1N using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.97 mEq/g (theoretical: 0.g9).

~ 3 ~

Example ll - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-4 butanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq~
are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.6~4 g of ethyl iodide are added ~4 mM) and the solution is agitated for 15 hr at 30C. 0.310 g of 1-4 diiodobutane are added (l mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resultlng solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone~H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
3.95 g of the compound eatured in the title are obtained.
Ethoxyl determination is carrisd out according to the method of Cundiff et al. and shows a content o 2.25~ w/w as ethanol (theoretical: 2.28). Total ester group analysis is carried out ~y saponification reaction with an excess quantity of NaOH 0.lN at ~ 3 ~

50C for 30 min. The excess is determined hy titration with HCl O.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 1.41 mEq/g ~theoretical: 1.48).
xample 12 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-4 butanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away rom light. 0.936 g of ethyl iodide are added (6 mM~ and the solution is agitated for 15 hr at 30C. 0.310 g of 1-4 diiodobutane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carbo~y groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with lOQ ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
3.9B g of the compound featured in the titl~ are obtained.

~3~72~7 Etho~yl determination is carried out according to the method of Cundiff et al. and shows a content of 6.69% w/w as ethanol (theoretical: 6.81). Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The e~cess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 1.91 mEq/g (theoretical: 1.97).
xample 13 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-6 heY~anediol ~ .21 g of tetrabutylammonium salt of HY (10 mEq~
are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.312 9 of ethyl iodide are added (2 mM) and the solution is agitated for 15 hr at 30C. 0.244 g of 1-6 dibromohexane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution ;s kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml ~ 3 ~

of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.05 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 2.18% w/w as ethanol (theoretical: 2.27). Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to deterrnine a total ester group content of 0.96 mEq/g ~theoretical 0.985).
xample 14 - Preparation of hyaluronic acid tHY) partially esterified with ethanol and partially cross-linked with 1-6 hexanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, ln nitrogen atmosphere and away from light. 0.624 g of ethyl iodide are added (4 mM) and the solution is agitated for 15 hr at 30C. 0.244 g of 1-6 dibromohexane are added (1 mM, corresponding to 2 mE~) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resultin~

~3~7~ 1 solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H20, while it is cooled from the outside with a bath of H20/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H20 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.02 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 4.46% w/w as ethanol (theoretical: 4.52). Total ester group analysis is carried out by saponification reaction with an excess quantity of NaQH O.lN at 50C for 30 min. The e~cess is determ ned by titration with HCl O.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 1.43 mEq/g (theoretical: 1.47).
~ample 15 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-6 hexanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMS0 at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.934 g of ethyl iodide are added (6 mM) and the solution is agitated for 15 hr at ~3~7~87 - ~6 -30C. 0.244 g of 1-6 dibromohexane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.00 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 6.68% w/w as ethanol (theoretical: 6.76). Total ester group analysis is carried out by saponification reaction with an e~cess quantity of ~aOH 0.lN at 50C for ~0 min. The e~cess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 1.91 mEq/g (theoretical: 1.96).
~ample 16 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-8 octanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are ~31l7~J

solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.078 g of ethyl iodide are added (0.5 mM) and the solution is agitated for 15 hr at 30C.
0.068 g of 1-8 dibromooctane are added (0.25 mM, corresponding to 0.5 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carbo~y groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetoneJH2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
3.99 g of the compound featured in the title are obtained.
Etho~yl determination is carried out according to the method of Cundiff et al. and shows a content of 0,54% w~w as ethanol ~theoretical: 0.571~. Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.23 mEq/g (theoretical: 0.25).

~3~

xample 17 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-8 octanediol 6.21 g of tetrabutylammonium salt o HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.078 g of ethyl iodide are added (O.5 mM) and the solution is agitated for 15 hr at 30C. 0.136 g of 1-8 dibromooctane are added (0.5 mM, corresponding to 1 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium sait, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O~ice.
500 ml of acetone are added, khe precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
3.97 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 0.55% wJw as ethanol (theoretical: 0~569. Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0OlN at p~

50C for 30 min. The excess is dete mined by titration with HCl O.lN using phenolphthalein as an indicator. It is thus possible to determine a total aster group content of 0.35 mEq/g ~theoretical~ 0.373.
~ample 18 - Preparation of hyaluronic acid ~HY) partially esterified with ethanol and partially cross-linked with 1-~octanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq~
are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.078 9 of ethyl iodide are added (O.5 mM) and the solution is agitated for 15 hr at 30C. 0.272 g of 1-8 dibromooctane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.05 g of the compound featured in the title are obtained.

~ 3~7~Y7 Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 0.55~ w/w as ethanol (theoretical: 0.564. Total ester group analysis is carried out by saponification reaction with an e~cess quantity of NaOH 0OlN at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator, It is thus possible to determine a total ester group content of n . 60 mEq/g (theoretical: Q.61).
~ample 19 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-8 octanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.156 g o ethyl iodide are added (1 mM) and the solution is agitated for 15 hr at ~0C. 0.272 g of 1-8 dibromooctane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrahutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml ~ 61 - ~3~7~87 of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.01 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 1.09% w~w as ethanol (theoretical: 1.13. Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.1N at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.70 mEq/g (theoretical: 0.73).
~ample 20 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-8 octanediol 6.21 g of tetrabutylammonium salt of HY ~10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.312 9 of ethyl iodide are added (2 ~M) and the solution is agitated for 15 hr at 30C. 0.272 g of 1-8 dihromooctane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting ~ 3 ~

solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2Oiice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.05 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 2.05% w/w as ethanol (theoretical: 2.25). Total ester group analysis is carried out by saponification reaction of an e~cess quantity of NaOH 0.lN at 50C
for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator.
It is thus possible to determine a total ester group content of 0.96 mEq~g (theoretical: 0.98~.
xample 21 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-8 octanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen a$mosphere and away from light. 0.624 g of ethyl iodide are added (4 ~M) and the solution is agitated for 15 hr at - 6~ _ ~3~7~

30C. 0.272 g of 1-8 dibromooctane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 9 of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
3.99 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 4.33% w/w as ethanol (theoretical: 4.4g). Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The e~cess is determined by titration with HCl 0.lN using phanolphthalein as an indicator. It is thus possible to determine a total ester group content of 1.43 mEq/g (theoretical: 1.46).
xample 22 - Preparation of hyaluronic acid ~HY) partially esterified with ethanol and partially cross-linked with 1-8 octanediol 6.21 g of tetrabutylammonium salt of ~IY (10 mEq) are solubilized in 248 ml of DMSO at 25 C in ~ 3~ 7~
- 6~ -absolutely dry conditions, in nitrogen atmosphere and away from light. 0.934 g of ethyl iodide are added ~6 mM) and the solution is agitated for 15 hr at 30C. 0.272 g of 1-8 dibromooctane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O~ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.10 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 6.66% w/w as ethanol ~theoretical: 6.72). Total ester group analysis is carried out by saponification reaction with an excess quantity of of NaOH 0.lN at 50C for 30 min. The excess is determine~ by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to ~etermine a total ester group content of 1.89 mEq/g (theoretical: 1.94S.

~3~7~

Example 23 - Preparation of hyaluronic acid (~) partially esterified with ethanol and partially cross-linked with 1-8 octanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25 C in absolutely dry conditions, in nitrogen atmosphere and away from light. 1.170 g of ethyl iodide are added (7.5 mM) and the solution is agitated for 15 hr at 30C. 0.272 9 of 1-8 dib.romooctane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For convarsion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H~O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.03 g of the compound eatured in the title are o~tained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 8.27% w/w as ethanol ~theoretical: 8.38). Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 13 ~ 7 ~ ~ ~

50C for 30 min. The excess is determined by titration with HCl O.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 2.05 mEq/g (theoretical: 2.3).
xample 24 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-8 octanediol 6.21 9 of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.624 g of ethyl iodide are added (4 mM) and the solution is agitated for 15 hr at 30C. 0.544 g of 1-8 dibromooctane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylar,rnoniuln carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a hath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.15 9 of the compound featured in the title are obtained.

~ thoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 4.36% w/w as ethanol ~theoretical: 4.42. Total ester group analys;s is carried out by saponification reaction with an excess quantity of of NaOH 0.lN at 50C for 30 minO The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to dete~mine a total ester group content of 1.90 mEq~g (theoretical: 1.92~.
xample 25 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-10 decanediol 6.21 g of tetrabutyla~nonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away frorn light. 0.312 g of ethyl iodide are added (2 mM~ and the solution is agitated for 15 hr at 30C. 0.300 g of 1-10 dibromodecane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylamrnonium carboxy groups into sodium salt, to the resulting solution are added 2.5 9 of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.

~3~ 7287 500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.12 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 2.12% w/w as ethanol (theoretical: 2.24). Total ester group analysis is carried out by saponi~ication reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.94 mEq/g ~theoretical: 0.97).
xample 26 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-10 decanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq~
are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosph~re and away from light. 0.624 g of ethyl iodide are added (4 mM) and the solution is agitated for 15 hr at 30C. 0.300 g of 1-10 dibromodecane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.

n ~3~7~

For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.10 9 of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 4.36% w/w as ethanol (theoretical: 4.46). Total ester group analysis is carried out by saponiication reaction with an excess quantity of of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total estex group content of 1.43 mEq/g (theoretical: 1.45).
xample 27 - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with 1-10 decanediol 6.21 g of tetrabutylammonium salt of HY ( 10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and ~3.~72~7 away from light. 0.934 g of ethyl iodide are added (6 mM) and the solution is agitated for 15 hr at 30C. 0.300 g of 1-10 dibromodecane (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For con~ersion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissol~ed in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.12 g of the compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a content of 6.5% w/w as ethanol (theoretical: 6.57~. Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.1~ at 50~C for 30 min. The e~cess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possihle to determine a total ester group content of 1.87 mEq/g (theoretical: 1.93).

~3~7~

Example 2~ - Preparation of hyaluronic acid (HY) partially esterified with ethanol and partially cross-linked with ~ , C~'-paraxylene diol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.624 g of ethyl iodide are added (4 mM) and the solution is agitated for 15 hr at 30C. 0.264 g of C~,~'-dibromo-p-~ylene are added ~1 mM, corresponding to 2 mEq) and after homogeni-æation the solution is kept at 30 for 24 hr.
For conversion of the residue tetrabutylammonium carbo~y groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2Ofice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.04 g o khe compound featured in the title are obtained.
Ethoxyl determination is carried out according to the method of Cundiff et al. and shows a contenk of 4.9% p/p as ethanol (theoretical: 4.5). Total ester group analysis is carried out by saponification reaction with an e~cess quantity of NaOH 0.lN at 13~ 7,~7 50C for 30 min. The e~cess is determined by titration with HCl O.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 1.36 mEq/g (theoretical~ 7).
~ample 29 - Preparation o-E hyaluronic acid (HY) partially esterified with benzyl alcohol and partially cross-linked with 1-8 octanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMS0 at 25C in absolutely dry conditions, in nitro~en atmosphere and away from light. 0.342 g of benzyl bromide are added (2 mM3 and the solution is agitated for 15 hr at 30C. 0.272 g of dibromooctane are added ~l mM, corresponding to 2 mEq) and after homogeni~ation the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution is added 2.5 9 of NaCl dissolved in lO0 ml of distilled H20, while it is coole,d from the outside with a bath of H20/ice.
500 ml of acetone are added, the precipitate is separated b~ filtration, washed 3 times with lO0 ml of acetone/H20 5:1 and 3 times with lO0 ml of pure acetone, and then vacuum dried.
4~15 g of the compound featured in the title are obtained.

_ 73 _ ~3~8~

Total ester group analysis is carried out by saponification reaction with an e~cess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.1~ using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.93 mEq/g (theoretical: 0.95).
xample 30 - Preparation of hyaluronic acid (HY~
partially esterified with benzyl alcohol and partially cross-linked with c~, CC'-paraxylenediol 6.21 g of tetrabutylammonium salt of HY ~10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphare and away from light. 0.342 g of benzyl bromide are added ~2 mM) and the solution is agitated for 15 hr at 30C. 0.264 g of ~ ,C~'-dibromo-p-~ylene (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylarnmonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.

~.3~7~7 4.11 g of the compound featur2d in tha title are obtained.
Total ester group analysis is carried out by saponification rPaction with an excess quantity of NaOH O.lN at 50C for 30 min. The excess is determined by titration with HCl 0.1~ using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.92 mEq/g ~theoretical: 0.95).
xample 31 - Preparation of hyaluronic acid (HY) partially cross-linked with 1-3 propanediol 6.21 g of tetrabutylammonium salt of HY t10 mEq) are solubilized in 248 ml of DMS0 at 25 C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.296 g of 1-3 diiodopropane are added (1 mM, corresponding to 2 mEg) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H20/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H20 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.

~3~728~

3.98 g of the compound featured in the title are obtainedO
Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH O.lN at 50C for 30 min. The excess is determined by titration with HCl O.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.47 mEq/~ ~thsoretical: 0.499).
xample 32 - Preparation of hyaluronic acid ~HY) partially cross-linked with 1-3 propanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.740 g of 1-3 diiodopropane are added (2.5 mM, corresponding to 5 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution is added of 2.5 g of NaCl dissolved in 100 ml of distilled H20, while it is cooled rom the outside with a bath of H20/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H20 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.

~ 3 3.89 g of the compound featured in the title are obtained.
Total ester group analysis is carried out by saponification reaction with an e~cess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with ~iCl 0.1~ usin~
phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 1.21 mEq/g (theoretical: 1.25).
xample 33 - Preparation of hyaluronic acid (~Y) partially cross-linked with 1--3 propanediol 6.21 g of tetrabutylarnmonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25C with in rigourously damp-free conditions, in nitrogen atmosphere and away from light. 1.184 g of 1-3 diiodopropane are added (4 mM, corresponding to 8 mEq) and after homogenization the solution is 3cept at 30C for 24 hr.
For conversion o~ the residue tetrabutylarnmonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 rnl of distilled H2O, while it is cooled from the outside with a ~ath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 kimes with 100 ml of pure ac~tone, and then vacuum dried.

~ 3 ~

3.87 g of the compound featured in the title are obtained.
Total ester group analysis is carried out by saponiication reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.1N using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 1.97 mEq/g (theoretical: 2.00).
xample 34 - Preparation of hyaluronic acid (HY) partially cross-linked with 1-~butanediol 6.21 g of tetrabutylammonium salt of HY (10 mEq) are solubilized in 24B ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.310 g of 1-4 diiodobutane are added (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C or 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed 3 tirnes with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.

:~ 3 ~

4.00 g of the compound featured in the title are obtained.
Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH O.lN at 50C for 30 min. The e~cess is determined by titration with HCl O.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.492 mEq/g (theoretical: 0.497).
xample 35 - Preparation of hyaluronic acid (HY) partially cross-linked with 1-6 hexanediol 6.21 g of tetrabutylammonium salt of HY ~10 mEq) are solubiliæed in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.370 g of tetrabutylammonium iodide are added (1 mM) and the solution is agitated for 1 hr at 20C. 0.244 g of 1-6 dibromohe~ane (1 mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tatrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H20, while cooling it from the outside with a bath of H20/ice.
500 ml of acetone are added, the precipitate is separated by filtration, washed ~ times with 100 ml ~3~7~

of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.01 g of the compound featured in the title are obtained.
Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The e~cess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total ester group conten-t of 0.486 mEg~g (theoretical: 0.494).
xample 36 - Preparation of hyaluronic acid (HY) partially cross-linked with 1-8 octanediol 6.21 g of tetra~utylammonium salt of HY (10 mEq) are solubilized in 248 ml of DMSO at 25 C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.370 g of tetrabutylammonium iodide (1 mM) and the solution is agitated for 1 hr at 20C. 0.272 g of 1-8 dibromooctane are added (1 mM, corresponding to 2 mEq~ and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium car~oxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.

- 80 - ~3~728~

500 ml of acetone are added, the precipitate is separated by filtration, washed 3 times with 100 ml of acetone~H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
4.02 g of the compound featured in the title are obtained.
Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min. The excess is determined by titration with HCl 0.1N using phenolphthalein as an indicator. It is thus possible to determine a total ester group content of 0.478 mEq/g (theoretical: 0.490).
xample 37 - Preparation of hyaluronic acid (HY) partially cross-linked with 1-10 decanediol 6.21 g of tetrabutylammonium salt o HY ~10 rnEq) are solubilized in 248 ml of DMSO at 25C in absolutely dry conditions, in nitrogen atmosphere and away from light. 0.369 g of iodide are added ~1 mM) and the solution is agitated for 1 hr at 20C.
0.300 g of 1-10 dibromodecane are added Sl mM, corresponding to 2 mEq) and after homogenization the solution is kept at 30C for 24 hr.
For conversion of the residue tetrabutylammonium carboxy groups into sodium salt, to the resulting solution are added 2.5 g of NaCl dissolved in 100 ml - 81 - ~3~7~8~

of distilled H2O, while it is cooled from the outside with a bath of H2O/ice.
500 ml of acetone are added, the precipitate is separated by ~iltration, washed 3 times with 100 ml of acetone/H2O 5:1 and 3 times with 100 ml of pure acetone, and then vacuum dried.
3.99 g of the compound featured in the title are obtained. .
Total ester group analysis is carried out by saponification reaction with an excess quantity of NaOH 0.lN at 50C for 30 min~ The excess is determined by titration with HCl 0.lN using phenolphthalein as an indicator. It is thus possible to determine a total e~ter group content of 0.476 mEq/g (theoretical: 0.487).

- B2 - ~, 3~ rl,~87 PEE~CE~TAGE COMPOSITION OF l~IE VA~IOUS CROSS-LINE~ED PRODUCTS
_ _ EXAMPLES ~O. NO. OF ES~EBI- ~O. OF CROSS- ~O. CARBOXYLS
FIED CAR~OXYLS LI~RED CARLOXYLS SALIFIED WITH
PER 100 WITH ......PER 100 WITH ...... SODIUM PER 100 1 5 / CH3_CH2_5 / _(CH2)3_ g 2 5 j CH3_CH2_10 / _[CH2)3_ 85 3 5 ~ CH3_CH2_20 / _(CH2)3_ 75 4 10 / CH3_CH2_20 / -(C~2)3- 70 20 ~ CH3-CH2-20 / _(CH2)3_ 60 ~ 40 / CH3-CH2_20 / _tCH2)3_ 40 7 60 / CH3_CH2_20 ~ _(CH2)3_ 20 8 -75 / CH3_C~2_20 / -(CH2)3- 5 9 4~ / C~3_CH2_40 ~ _(CH2)3_ 20 20 J CH3_C~2_20 / -(~2)4- 60 11 40 / CH3_CH2_20 J _(CH2)4_ 40 12 60 / CH3_CH2_20 / -(C~2)4- 20 13 20 / C~l3_CH2_20 / _(CH2)6_ 60 14 40 / CH3_C~2_20 / _(CH~)6_ 40 60 / CH3_CH2_20 / -(C~2)6- 20 16 S / CH3_C~2_5 / -(CX2)8- 90 17 5 / CH3_CH2_10 / -tCH2)8- 85 18 5 / CH3-CH2-20 / _(CH2)8_ 75 19 10 / CH3_CH2_20 / -~CH2)8- 70 20 / C~33-C~2-20 / _(CH2)8_ 60 21 40 / CH3 CH2_20 / -ICH2)8- 40 22 60 / C~I3_CH220 / -(C~2)8 20 23 75 / CH3-CH2-20 / -~CH2)8- 5 24 40 / CH~-CH2-40 / -~CH2)8- 20 20 / CH3_CH2_2U / -(CH2)10- 60 26 40 / C~3_CH2_20 / _~CH2)10_ 40 27 60 / C~3-CH2- 20 / -(CH2)10- 20 28 40 / CH3-CH2- 20 / -~CHz-O-CH2)- 40 29 20 / 0-CH2- 20 / (C~2)8- 60 20 / O_CH2_ 20 / tcH2-o-cH2)- 60 31 _20 / --(C~2)~3- 80 32 _50 / -tCH2)3- 50 33 _BO ,f _tCH2)3_ 20 34 -20 / _tCH2)4_ ao 20 / -(C~2)6- ao 36 _20 / (CH2) 8- ao 37 _20 / _(CH2)10_ .
~ ~7,~7 Ex~mple 37A - Prepara~ion of the ~partial and mixed~
octandiol antl cortisone ester o~
hyaluronic ac$d (HY) - 40~ o~ carboxylic groups esterified with octandiol 20 of carboxylic groups estarified with cortisone (C21) - 40~ o~ carboxylic groups salified (Na).
6,2 g of HY tetrabutylammonium salt with a moleculax weight of 125,000 corresponding to 10 m.Eg.
o~ a monomeric unit are solubilized in 310 ml o~
dimethyl~ul~oxide at 25~ 1,09 ~ t4 m.~q.~ o~
1,8-dib~omooctane are added and the solu~ion is kept for 24 hours at 30. 0.85 q (~ m.Eq.) of 21-bromo-4 pregnene-17a -1-3, 11, 20-trione are ad~ed and the solution i5 kept for 24 hour~ at 30.
A ~olution i5 then added containing 100 ml of water and 5 g of ~odium chloride and the xesulting mixture i~ slowly poured into 2,000 ml of ace~on~ under con3tant agitation. A precipitate i~ formed which i~
filtered and washed three times with 100 ml o~
acetone/water 5:1 and three times wi~h 100 ml ~
acetone and finally vacuum dried for eight hours at 30~C.
4.5 g o~ the compound featured in the title ar~
o~tained.
Quantitative determination o~ corti~one, a~ter mild alkalinQ hydroly3i~ with hydroalcoholia solution o~ Na2C03 and extraction with chloro~o~m, is carried ou~ according to ~ri~i~h Pharmacopea, 1980, p. 224.

!

~ 72~

Example 38 - Method by which a mixture of Hyalastine and Hyalectin ractions, with no inflammatory activity, may be obtained Fresh or frozen cocks' combs, (3000 g) are minced in a mincer and then carefully homogenized in a mechanical homogenizer. The paste thus obtained is placed in a AISI 316 stainless steel container or in glass and treated with 10 volumes of anhydrous acetone. The whole is agitated for 6 hours at a speed of 50 rpm. It is left to separate for 12 hrs and then the acetone is discarded by siphoning. A~etone extraction is repeated until the discarded acetone reaches the right degree of humidity (Karl-Fischer method). The whole is then centrifuged and vacuum dried at a suitable temperature for 5-8 hours.
Approximately 500-600 gr of dry powdered cocks' combs are thus obtained.
300 gr. of dry powder are exposed to enzymatic digestion with papain (0.2 93 in aqueous medium buffered with phosphate buffer in the presence of a suitable quantity of hydrochloride cysteine. It is agitated for 24 hrs at 60 rpm at a constant temperature of 60-65C. The whole is then cooled to 25C and CeliteR(60 gr) is added, maintaining agitation for another hour. The mi~ture obtained is filtered until a clear liquid is obtained. The clear liquid is exposed to molecular ultrafiltration on membranes with a molecular exclusion limit of 30,000 ~3~728~

to retain on the membrane those molecules with a molecular weight of over 30,000.

5 to S original volumes are ultrafiltered, continuously adding distilled water to the product being ultrafiltered. The addition of water is suspended and ultrafiltration is continued until the volume is reduced to 1/3 of the original.
The residue liquid is brought to O.lM with the addition o~ sodium chloride and the temperature is brought to 50C. Under agitation of 60 rpm, 45 9 of cetylpiridinium chloride are added. It is agitated for 60 minutes and then 50 g of CeliteR are added.
Under agitation, the temperature of the whole is brought to 25C and the precipitate formed by centrifugation is gathered. The precipitate obtained is suspended in a O.OlM solution in sodium chloride (5 litres) containing 0.5% cetylpyridinium chloride.
It is agitated for 60 minutes at 50C; the tempera-ture is then brought to 25C and the precipitate is centrifuged. Washing is repeated 3 times and finally the precipitate is gathered in a recipient containing 3 litres of a 0.05M solution of sodium chloride containing 0.5% cetylpyridinium chloride.
It is agitated at 60 rpm for 60 minutes and the temperature is kept constant at 25C for two hours~
The supernatant is eliminated by centrifugation. The procedure is repeated several times with solutions of O.lM sodium chloride containing Q.05% of - 85 - 13~72~

cetylpyridinium chloride. The mixture is centrifuged and the supernatant is discarded. The precipitate is dispersed in a solution of 0.30M sodium chloride containing 0.5% cetylpyridinium chloride (3 litres~.
The mixture is agitated and both the precipitate and the clear liquid are gathered. E~traction is repeated on the precipitate 3 more times, each time using 0.5 lt of the same aqueous solution.
Finally, the residue precipitate is eliminated and the clear liquids are gathered in a single container. The temperature of the liquid is brought to 50C while maintaining agitation. The liquid is then brought to 0.23M with sodium chloride. l gr of cetylpyridinium chloride is added, and agitation is maintained for 12 hrs.
The mixture is cooled to 25C and then filtered first on CeliteR and then through a filtre. It is then again exposed to molecular ultrafiltration on membrane with a molecular ~clusion limit of 30~000 ultrafiltering three initial volumes with the addition of a 0.33M sodium chloride solution. The addition of sodium chloride solution is suspended and the volume is reduced to l/4 o~ the initial volume.
The solution thus concentrated is precipitated under agitation ~50 rpm) at 25C with 3 volumes of ethanol (95%). The precipitate is gathered by centrifugation and the supernatant is discarded. The precipitate is dissolved in l lt of O.lM solution in - ~6 - ~3~7~

sodium chloride and precipitation is repeated with 3 volumes of 95~ ethanol. The precipitate is gathered and washed first with 75% ethanol 3 times, then with absolute ethanol (3 times), and lastly with absolute acetone (3 times).
The product thus obtained (HYALASTINE t HYALECTIN
fractions) has an average molecular weight of between 250,000 and 350,000.
The yield of HY is equal to 0.6~ of original fresh tissue.
xample 39 - Method for obtaining the fraction Hyalastine from the mixture obtained by the method described in E~ample 38.
The mixturè obtained by the method described in Example 38 is dissolved in apyrogenic distilled water in a measure of 10 mg of product per 1 ml of water.
The solution obtained is exposed to molecular filtration through filtre membranes with a molecular exclusion limit of 200,000, using a concentration technique without the addition of water on top of the membrane. During the ultrafiltration process through membranes with a molecular exclusion limit of 200,000, the molecules with a molecular weight of over 200,000 cannot pass, while the smaller molecules pass through the membrane together with the water.
During the filtration procedure no water is added on top of the membrane; so that the volume diminishes, ~3~72~

and consequently the concentration of molecules with a molecular weight of ovPr 200,000 increases.
Ultrafiltration is continued until the volume on top of the membrane is reduced to 10% of the initial volume. Two volumes of apyrogenic distilled water are added and it is again ultrafiltered until the volume is reduced to 1/3 of the original. The operation is repeated twice more. The solution passed through the membrane is brought to O.lM with sodium chloride and is then precipitated with 4 volumes of 95% ethanolO
The precipitate is washed 3 times with 75% ethanol and then vacuum dried.
The product thus obtained (HYA~ASTINE fraction) has an average molecular weight of between 50,000 and 100,000.
The yield of HY is equal to 0.4% of the original starting fresh tissue.
xample 40 - M,ethod for obtaining the Hyalectin fraction The concentrated solution gathered in the container on top of the ultrafiltration membrane with a molecular exclusion limit of 200,000 as in Example 39, is diluted with water until a solution containing 5 mg/ml of hyaluronic acid is obtained, as determined by quantitative analysis based on the dosage of glucuronic acid.

131 r~ 2 8 i7 ThP solution is broug~t to 0.1~ in sodium chloride and then precipitated with 4 volumes of 95%
ethanol. The precipitate is washed 3 times with 75%
ethanol and then vacuum dried.
The product thus obtained (HYALECTIN fraction) has a molecular weight of between 500,000 and 730,000. This corresponds to a specific hyaluronic acid fraction with a molcular chain measuxing hetween about 2,500 and 3,500 saccharide units and with a high degree of purity. The yield of HY is equal to 0.2% of original fresh starting tissue.
xample 41 - Preparation of films of cross-linked derivatives of hyaluronic acid (HY) and partially esterified with various alcohols The DMSO solutions, after addition of all the ingredients and after homogenization ob~ained as in Examples 6-15, 19-30 and 37, are layered in glass dishes to the desired thickness and in an atmosphere of nitrogen, in absolutely dry conditions and away from light for 24 hr.
The films of cross-linked and esterified hyaluronic derivatives thus obtained and in which are also present tetrabutylammonium carboxy groups are dialyzed first in NaCl 1% and then in distilled H2O
at 4C, the solutions being changed periodically.
The films containing sodium salts of the above - ~9 ~ 7 2 8 ~

cross-linked derivatives are then placed between two cellophane membranes and vacuum dried at 37 in a slab dryer. -~
., . _ . .

The pharmaceuticdl preparations containing thenew cross-linked derivatives of the present invention and their salts as active principle, both in the case of cross-linked derivatives possibly further esterified and~or salified with therapeutically active alcohols and intended for the same indications as HY itself, and in the case of esters with therapeutically active alcohols intended for use in indications corresponding to such alcohols, contain the common excipients and may be destined for oral, rectal, parenteral, subcutaneous, local, intradermal or topical use. They are therefore in solid or semisolid form, for example, pills, tablets, gelatinous capsules, capsules, suppositories, soft gelatin capsules. For parenteral and subcutaneous uses, it is possible to use forms intended for intramuscular or intradermal administration, or suitable for infusion or intravenous injections. It is, therefore, possible to present active compounds as solutions or as freeze-dried powders active compounds to be pooled with one or more excipients or diluents which are pharmaceutically acceptable, and convenient for the above uses and with a type of ~3~7~8~

osmolarity suitable for physiological liquids. For local use, preparations in spray form should b~
considered, for example nasal sprays, creams or ointments for topical use of plasters suitably prepared for intradermal administration.
The preparations of the invention may be destined for administration to man or animal. They contain preferably between 0.01~ and 10% of active component for solutions, sprays, ointments and creams and between 1% and 100% and preferably between 5% and 50%
of the active compound for preparations in solid form. The dosage to be administered depends on the indication, on the desired effect and on the chosen administration route. The daily dosage of such preparations may be deduced from that in use for the corresponding known preparations both of hyaluronic acid for the corresponding cures, for example for the cure of arthritis, for example in man or in horse, and of therapeutically active alcohol the action of which is to be exploited. Thus, for e~ample, the dosage of a hyaluronic ester with cortisone may be derived frorn its content in this ester and from its usual dosage in the known pharmaceutical preparations.
In cosmetic articles, the new cross-linked derivatives of the present invention and their salts are mixed with the excipients comrnonly used in this art and are for example those already listed above for pharmaceutical preparations. Above all, creams, - 91- 13~72~7 ointments, lotions for topical use are used in which the new cross-linked derivatives of the present invention may constitute the active cosmetic principle possibly with the addition of other cosmetically active principles, such as steroids, for example pregnenolone, or one of the principles reported ahove. In these preparations, the new cross-linkea derivatives of the present invention are prefarably esters with an alcohol without any cosmetic action, such as a lower aliphatic alcohol, for example one of those already mentioned. In these preparations the effect is due to the intrinsic cosmetic properties of the polysaccharide component, as in the case of free hyaluronic acid or its salts.
The cosmetic articles may, however, be based on substances with specific actions which differ from those of hyaluronic acid, for example disinfectants, sunshields, waterproofing or regenerating substances, or anti-wrinkle or odoriferous substances, especially perfumes. In this case the new cross-linked derivatives of the present invention may again be themselves the active ingredient and derive from alcohols with these properties, for example from higher aliphatic alcohols or terpene alcohols in the case of perfumes or may function above all as vehicles for substances with those properties with which they are associated. Particularly important, r therefore, are cosmetic compositions similar to th~
medicaments described above in which the pharmaceutically active component is substituted by a cosmetological factor and the respective salts.
The use of the above esters deriving from the alcohols used in the perfume industry represents an important step forward in technique, since it allows for a slow, constant and prolonged release of the odorous principles.
One important application of the present invention regards the sanitary and surgical articles already described above, the methods for their manufacture and use. The invention therefore includes all the articles similar to those already on the market containing hyaluronic acid but also containing the new cross-linked derivatives of the present invention in place of the free acid or one of its salts, for example inserts or ophthalmic lenses.
Completely new surgical and sanitary articles according to the present invention are represented hy the new cross-linked derivatives of the present invention regenerated as such by appropriate organic solutions capable of being made into sheet or thread form, thus obtaining films, sheets and threads for use in surgery, as auxiliaries and substitutes of the skin in cases of serious damage to this organ, for example following burns, or as suture threads in surgery. The invention includes in particular these 1~7~8r1 uses and one preparation procedure of these articles consists in (a) forming a solution of a hyaluronic ester or one of its salts in a suitable organic solvent, for e~ample a ketone, a~ ester or an aprotic solvent such as a carboxy acid amide, especially a dialkylamide of an aliphatic acid having between 1 and 5 carbon atoms and deriving from alkyl groups with between 1 and 6 carbon atoms, first and foremost from an organic sulfo~ide, that is, a dialkylsulfoxide with alkyl groups with a maximum of

6 carbon atoms, such as especially dimethylsulfo~ide or diethylsulfoxide and again first and foremost by a fluorinated solvent with a low boiling point such as especially hexafluoroisopropanol, (b) making this solution into sheet or thread form and ~c~ removing the organic solvent by contact with another organic or aqueous solvent which can be mixed with the first solvent and in which the hyaluronic ester is not soluble, especially a lower aliphatic alcohol, for e~ample ethyl alcohol (Wet spinning), or if a solvent with a not too high boiling point has been used to prepare the solution of the hyaluronic derivative, in removing this solvent with a current of gas and especially suitably heated nitrogen (Dry spinning).
It is also possible to use to great advantage the system of Dry-wet spinning.
The threads obtained with the new cross-linked derivatives of the present invention may be used for

7,.~

the preparation of lints for use in the medication of wounds and in surgery. The use of such lints has the exceptional advantage of their biodegradation in the organism, effected by the enzymes it contains. These enzymes split the ester in hyaluronic acid and in the corresponding alcohol and in a compound already present in the organism, or rather, an innocuous compound such as an alcohol. Such lints and also the above threads may also therefore be left inside the organism after surgery, since these are subsequently slowly absorbed due to the above degradation process.
In the preparation of the sanitary and surgical articles mentioned above, it is convenient to add plasicizing materials to enhance their mechanical characteristics, such as in case of threads, to improve their resistance to tanqling. These plasticizers may be for example alkaline salts of fatty acids, for example sodium stearate or sodiurn palmitate, the esters of organic acids ~ith many carbon atoms, etc.
Another application of the new cross-linked derivatives of the present invention where their biodegradable qualities are utilized by the esterases prssent in the organism, is represented by the pre-paration of capsules for subcutaneous implatation of medicaments or of microcapsules for injection~ or example by subcutaneous and intramuscular route. For the application of subcutaneous medicaments for slow - 95 ~

release and consequently a "retard" action, capsules made of silicon material have been used until today, with the disadvantage that such capsules are liable to migrate within the organism and it is impossible to recover them. Obviously, with the new cross-linked derivatives of the present invention this danger no longer e~ists. Of great importance also is the preparation of microcapsules containing the new cross-linked derivatives of the present invention, avoiding the problems usually connected with their use, until now quite limited for the reasons mentioned above. This preparation opens up a whole new area of applications where a "retard" effect by injection is to be obtained.
A further application of the new cross-linked derivatives of the present invention in the Eield of medicine and surgery is represented by the preparation of various solid inserts such such as plates, discs, sheets, etc. substituting the metallic ones those containing synthetic plastic rnateri~l currently in use, in cases involving inserts intended for removal after a certain length of time.
Preparations containing animal collagen, being of a proteic nature, often provoke unpleasant reactions, such as inflammation or rejection. In the case of the new cross-linked derivatives of the present invention, even though they originate from animal and not human hyaluronic acid, this danger does not - 96 - ~3~

exist, since there is no incompatibility between the polysaccharides of various animal species.
Another use is for the correction of defects and the augmentation of soft tissues. A need has been felt for some time for safe and efficient biomaterials with which to substitute soft tissues which have been removed or damaged. Many alloplasty materials including paraffin, teflon paste, silicon and bovine collagene have heen used to substitute for lost soft tissue. However, these materials were associated with undesirable and permanent changes in the skin tissues, with migration in situ and with negative reactions. The need persists therefore for a versatile biomaterial for use in medicine. The new cross-linked derivatives of the present invention may be safely and effectively used to correct such defects of the soft tissues such as acne pimples, postsurgical atrophic irregularities, Mohs' chemosurgery, lacerated lip wounds and wrinkles caused by age.
Also included in the applications in the field of medicine and surgery of the new cross-linked derivatives of the present invention, are preparations made of expansive material, especially in the form of sponges, for the medication of wounds or lesions of various nature.

131~2~7 - 96a -I'he following are typical examples of formulations prepared - according to the inven~iDn.
Formulation 1 - Collirium containing cortisone of whieh 100 ml contain:
- Partial and mixed ester of hyaluronic acid with cortisone and octandiol ~Ex. 37A) gr. 0.300 - Ethyl p. hydroxybenzoate gr. 0.010 - Methyl p. hydroxybenzoate gr. 0.050 - Sodium chloride gr. 0.900 - Water for injectable preparation/q.b.a. ml. 100 Formulation 2 - Cream containing a partial ester of hyaluronic acid with 1,3-propandiol, of which 100 gr. contain:
- Partial ester of hyaluronic acid with 1,3-propandiol (Ex. 31) gr, 0.2 - PolyethylÆnglycol monostearate 400 gr. 10.000 - CETIOL V (Trade Mark~ gr. 5.000 - LA~ETTE SX (Trade Mark) gr. 2.000 - Paraoxybenzoate of methyl gr~ 0.075 - Paraoxybenzoate of propyl ~r. 0.050 - Sodium dihydroacetate gr. 0.100 - Glycerine F.U. gr. 1~500 - Sorbitol 70 gr. 1.500 - Test cream gr. 0.050 - Water for in~ectable preparation/q.b.a. gr. 100.00

Claims (36)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Total or partial cross-linked esters of hyaluronic acid with an aliphatic polyhydric alcohol, or salts of such partial esters with inorganic or organic bases, with the proviso that said cross-linked ester is not the cross-linked ester of hyaluronic acid with a halomethoxirane or a bisepoxy compound.

2. Cross-linked esters according to claim 1, wherein said aliphatic polyhydric alcohol is a dihydric alcohol.

3. Cross-linked esters according to claim 2, wherein said dihydric alcohol is a member selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, and glycols derived from pentane, hexane, heptane and octane, and positional isomers thereof.

4. Cross-linked esters according to claim 1, wherein said aliphatic polyhydric alcohol has between 2 and 16 carbon atoms.

5. Cross-linked esters according to claim 4, wherein said aliphatic polyhydric alcohol is a member selected from the group consisting of glycerine, erythritol and pentaerythritol.

6. Cross-linked esters according to claim 1, wherein at least one non-cross-linked carboxy group in said hyaluronic acid is esterified with an aliphatic alcohol having a maximum of 34 carbon atoms; wherein said aliphatic alcohol may be unsubstituted or substituted by one or two functional groups selected from the group consisting of amino, hydroxy, mercapto, aldehyde, keto, carboxy, hydrocarbyl and dihydrocarbylamino groups, ether, ester, thioether, thioester, acetal, ketal, carbalkoxy, carbamidic and substituted carbamidic groups substituted by one or two alkyl groups, the hydrocarbyl radicals in said functionally-modified groups having a maximum of 6 carbon atoms; and in which said aliphatic alcohols may be interrupted in the carbon atom chain by heteroatoms selected from the group consisting of oxygen, sulphur and nitrogen.

7. Cross-linked esters according to claim 6, wherein said aliphatic alcohol is selected from the group consisting of ethyl, propyl, isopropyl, n-butyl, isobutyl, a tert-butyl alcohol, an amyl, a pentyl, a hexyl and an octyl alcohol.

8. Cross-linked esters according to claim 1, wherein at least one non-cross-linked carboxy group in said hyaluronic acid is esterified with an araliphatic alcohol having only one benzene residue; in which the aliphatic chain in said araliphatic alcohol has a maximum of 4 carbon atoms; in which said aliphatic chain may be substituted with one or two functional groups selected from the group consisting of free- or mono- or diethyl amino groups, pyrrolidine and piperidine groups; and in which the benzene residue in said araliphatic alcohol may be substituted with between 1 and 3 methyl or hydroxy groups or with halogen atoms.

3. Cross-linked esters according to claim 1, wherein at least one non-cross-linked carboxy group in said hyaluronic acid is esterified with a cycloaliphatic alcohol, or with an aliphatic-cycloaliphatic alcohol, or with a heterocyclic alcohol which derives from a mono- or polycyclic carbohydrate with a maximum of 34 carbon atoms and which is unsubstituted or which is substituted by one or more functional groups selected from the group consisting of amino, hydroxy, mercapto, aldehyde, keto, carboxy, hydrocarbyl- and dihydrocarbylamino groups, ether, ester, thioether, thioester, acetal, ketal, carbalkoxy, carbamidic and substituted carbamidic groups, by one or two alkyl groups, the hydrocarbyl radicals in these functionally modified groups having a maximum of 6 carbon atoms, and may be interrupted in the carbon atom chain by heteroatoms selected from the group consisting of oxygen, nitrogen and sulphur, and may have one or more aromatic bonds.

10. Cross-linked esters according to claim 9, wherein at least one of said non-cross-linked carboxy groups is esterified with an alcohol selected from the group consisting of cortisone, hydrocortisone, prednisonel prednisolone, fluorocortisone, dexamethasone, betamethasone, corticosterone, deoxysicorticosterone, paramethasone, flumethasone, flucinolone and its acetonide, fluprednylidene, clobetasol and beclomethasone.

11. The total or partial-cross-linked esters according to claim 9, wherein said polyhydric alcohol is an aliphatic polyhydric alcohol.

12. The total or partial-cross-linked esters according to claim 11, wherein said aliphatic polyvalent alcohol is a bivalent alcohol.

13. The total or partial-cross-linked esters according to claim 11, wherein said aliphatic polyvalent alcohol is a member selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, glycols derived from pentane, hexane, heptane and octane, and positional isomers thereof, glycerine, erythritol and pentaerythritol.

14. Salts of partial esters according to claim 1, wherein said salt is a salt of said cross-linked ester with an alkali metal, with an alkaline earth metal, with magnesium or with aluminum.

15. Salts of a partial ester according to claim 14, comprising a sodium or ammonium salt.

16. Salts of partial esters according to claim 1 deriving from ammonium, araliphatic, cycloaliphatic or heterocyclic groups.

17. A pharmaceutical composition comprising a pharmaceutically-effective amount of a cross-linked ester according to claim 1, or its salts, together with a pharmaceutically-effective amount of a pharmaceutically-acceptable carrier, excipient or diluent.

18. A pharmaceutical composition comprising a cross-linked ester according to claim 1 as a vehicle, in admixture with a pharmaceutically-effective amount of a pharmacologically-active agent.

19. A pharmaceutical composition as claimed in claim 17 comprising a cross-linked ester, wherein an alcohol which is esterified with a non-cross-linked carboxy group is a pharmacologically-active alcohol.

20. A pharmaceutical composition as claimed in claim 18 comprising a cross-linked ester wherein an alcohol which is esterified with a non-cross-linked carboxy group is a pharmacologically-inactive alcohol.

21. The use, as an active ingredient in a cosmetic article, of a cross-linked ester or a salt thereof according to claim 1.

22. The use, as a cosmetic vehicle in a cosmetic article, of a cross-linked ester or a salt thereof according to claim 1.

23. The use, in a sanitary, medical or surgical article, of a cross-linked ester or a salt thereof according to claim 1.

24. The use, in a sanitary, medical or surgical article, of threads of a cross-linked ester or a salt thereof according to claim 1.

25. The use, as a capsule or microcapsule for medicaments, of a cross-linked ester or a salt thereof according to claim 1.

26. The use, for the manufacture of a film for use in dermatology as artificial skin, of a cross-linked ester or a salt thereof according to claim 1.

27. The use, for the manufacture of suture threads for use in surgical operations, of a cross-linked ester or a salt thereof according to claim 1 .

28. A process for the preparation of total or partial cross-linked esters of hyaluronic acid comprising: reacting a potassium or sodium or quaternary ammonium salt of hyaluronic acid with an etherifying agent in an aprotic solvent.

29. A process according to claim 28, wherein said salt of hyaluronic acid is a potassium or sodium salt, and wherein said reaction is conducted in the presence of a catalyzing quantity of a quaternary ammonium salt.

30. A process according to claim 29, wherein said quaternary ammonium salt is tetrabutyl ammonium iodide.

31. A process according to claims 28, 29 or 30 wherein said aprotic solvent is a dialkylsulfoxide, a dialkylcarboxylamide, or a lower alkyl dialkylamide of a lower aliphatic acid.

32. A process according to claim 28, wherein said hyaluronic acid or the non-cross-linked carboxy groups of said partial cross linked ester of hyaluronic acid is esterified with an aliphatic, araliphatic or cycloaliphatic alcohol.

33. A process according to claim 32, wherein said alcohol which is esterified with said non-cross-linked carboxy groups is a pharmacologically active alcohol.

34. A process according to claim 32, wherein said partial cross-linked ester having at least one free carboxy group is salified with an alkali metal or with alkaline earth metal, or with magnesium or with ammonium.

35. A process according to claim 28, wherein said hyaluronic acid is a hyaluronic acid fraction having an average molecular weight of between 50,000 to 730,000 and is substantially free of hyaluronic acid having an average molecular weight of less than 30,000.

36. A process according to claim 35, wherein said hyaluronic acid fraction has an average molecular weight of 50,000 to 100,000, or an average molecular weight of 250,000 to 350,000 or an average molecular weight of 500,000 to 730,000.