Sulfoamino derivatives of chondroitin sulfates, of dermaten sulfate and of hyaluronic acid and their pharmacological properties

Abstract: Novel derivatives are disclosed as obtained from chondroitin sulfate, dermatan sulfate and hyaluronic acid, having a molar ratio between sulfate groups and carboxylic groups like that of heparin and furthermore characterized by possessing, as the heparin, the sulfoamino group at the carbon atom at the 6 position hexosamine. The novel compounds show a very remarkable clearing activity in comparison with the starting mucopolysaccharides, this activity being similar and for some derivatives comparable with that of heparin. Moreover, differently from what normally happens upon sulfating the sulfomucopolysaccharides, the anticoagulating activity of the novel compounds is negligible or anyhow very reduced. the compound of the present invention find use in the therapy of arteriosclerosis.

Description: The present invention relates to derivatives of glycosaminoglycans and more particularly of chondroitin sulfates and of hyaluronic acid. More specifically, within the family of the chondroitin sulfates, are described compounds which are obtained from chondroitin sulfates A and C and related mixtures, as well as from dermatan sulfate. The glycosaminoglycans or sulfomucopolysaccharides or simply mucopoly-saccharides are polymers very widespread in animal organs and tissues. Among them the polymer which has undoubtedly achieved maximum use in the therapeutical field is heparin, a macromolecule characterized by a high content of sulfate groups and possessing anticoagulating, antithrombotic and clearing activity, the latter being due to lipoprotein lipase and to hepatic lipase. These peculiar pharmacological activities have stimulated in the past years, (although for a number of aspects these studies are still pending), a great number of investigations in order to clarify the possible relationship between the structure of the polymer and the above mentioned activities) for recent comprehensive papers see B. Casu, Advances Carbohydr. Chem. Biochem. 43 51 - 134 1985; L.A. Fransson in "The Polysaccharides", G.O. Aspinali Ed. Vol. 3, pp. 337 - 415 Academia Press, New York 1985). It has been thus assessed that to the said activities both the sulfoamino group (I. Danishefsky, Fed. Proc. Am. Soc. Exp. Biol. 36 pp. 33-35 1977) and the charge density of the polymer (R.E. Hurst et Alii, in "Chemistry and Biology of Heparin" Elsevier North Holland New York, pp. 29-40 1981; R.E. Hurst et Alii, J. Clin. Invest. 72 1042-1045 1983; U. Lindhal et Alii, in Annual Rev. Biochem. 47 pp. 401-406 1978) contribute in a relevant measure. With reference to the charge density, it has been found that in heparin it is on the average equal to 2 if it is given as the ratio between the moles of sulfate groups and the corresponding moles of carboxylic groups (B. Casu, see above). It is worth to note that in the past and in the recent times a number of attempts has been carried out to obtain from several glycosaminoglycans, through a reaction of direct sulfation, polymers having properties like those of heparin. For example it is known that the chondroitin sulfates directly sulfated (K.H. Meyer, Helv. Chim. Acta 75 574-588 1952), or initially N-deacetylated and then sulfated (M.L. Wolfrom, J.A.C.S. 75 1519 1953) acquire anticoagulating properties. Alternatively, through an initial depolymerisation followed by a sulfation at the hydroxyl groups, starting from the heparin itself as well as also from other glycosaminoglycans, it is possible to obtain polymers which are characterized by an antithrombotic activity which is comparable or even greater than that of heparin. However, it is worth to note that only the derivatives of the latter polysaccharide, among those which are described in the present invention, possess a very reduced anticoagulating activity (EP-A-2 14 879). It is moreover to be observed that in the literature several methods are reported for the sulfation of glycosaminoglycans, which generally afford only the sulfation of the hydroxyl groups. As a matter of fact by means of these methods it is not possible to obtain the selective sulfation of the nitrogen atom in the position 2 of hexosamine. By adopting particular conditions it is however possible to obtain, as it will be shown hereinafter, the selective sulfation of the hydroxyl groups occupying on the polymer chain the less sterically hindered position. However, these reactions normally lead to products with a high content of sulfur, wherein the distribution of the sulfate groups among the several positions takes place in a non specific manner. Said reactions often are carried out in an heterogenous phase, usually in anhydrous pyridine and using as the sulfating agent the pyridine-sulfuric anhydride adduct or chlorosulfonic acid. It is also possible to operate in a homogeneous phase, in apolar non aqueous solvents (for example dimethylformamide) using as the sulfating agent sulfure trioxyde or the trimethylamine-sulfur trioxide adduct (J.F. Kennedy, Advances Carbohyd. Chem. Biochem. 29 335-337 1974). E.E. Gilbert "Sulfonation and related reactions" Interscience publisher, New York 1965, pp 354-360; R.G. Schweiger "Polysaccharides sulfates. I Cellulose sulfate with a high degree of substitution" Carbohyd. Res. 21 219 1972: K. Nagasawa et Alii "Chemical sulfation of preparations of chondroitin 4 and 6 sulfate and dermatan sulfate. Preparations of chondroitin sulfate E-like materials from chondroitin sulfate" Carbohyd. Res. 158 1983 1986). The glycosaminoglycans to which the present invention relates are precisely chondroitinsulfate A and C and their mixtures, dermatan sulfate or chondroitin sulfate B and ialuronic acid, the structural formula of the related repeating disaccaride unit of which is hereinafter reported. A first object of the present invention thus consist in synthetic derivatives of some glycosaminoglycans and exactly of chondroitin sulfate A and C or their mixtures, chondroitin sulfate B and hyaluronic acid, obtained by selective N-deacetylation and substequent sulfation at the nitrogen atom (which in the case of the hyaluronic acid it is preceeded or followed, as it is disclosed in the examples 6 and 7, by sulfation at the hydroxyls in the position 6) so as to obtain polymers which have, besides the charge density which is characteristic of the heparin as above defined, also the nitrogen atom at the position 2 on the hexosamine ring substituted with a sulfate group. It has moreover been found and it is another object of the present invention that these macromolecules possesses a clearing activity. The polymers, with reference to the above indicated clearing actvity and to the said absence of a remarkable anticoagulating activity, are useful as drugs in the terapy of arteriosclerosis. Within the above indicated Pharmacological activity shown by the present compounds it is noticed a relevant increase of the activity due to the hepatic lipase which in the case of the derivatives of dermatan sulfate and of the chondroitins contributes by fifty percent and more to the clearing activity. As a matter of fact in Pharmacology it is attributed an important role to hepatic lipase as regards the metabolism of lipoproteins and their influence on the cholesterol catabolism (T. Kuusi et Alii, FEBS lett. 104 384 1979; H. Jansen et Alii, Biochim. Biophys. Res. Comm. 92 53 1980, A. Van Tol et Alii, Biochim. Biophys. Res. Comm 94 101, 1980; M. Bamberger et Alii, J. Lipid Res. 24 869 1983; H. Jansen et Alii, Trends Biochem. Sci. 5 265 1980). Moreover it has been recently assessed during clinical pharmacological experiments (Jacques D. Barth et Alii, Atherosclerosi 48 235 1983 and 68 51 1987) that in individuals suffering from heavy complications of arteriosclerosis the serum values of the hepatic lipase, differently than those of the lipoprotein lipase, are lower than those of normal patients. These information indicate per se the potential and remarkable importance in the terapy of these diseases of a drug which, could be able to stimulate an effective activity of the hepatic lipase in the blood stream without influencing the haemostasys. Coming back to the chemical structure of these compounds, it is worth to note that the reactions of N-deacetylation and subsequent selective N-sulfation, which are however carried out with per se known methods do not change the amount and distribution of the sulfate groups initially present in the polymer. It is furthermore to be mentioned, as it will be demonstrated hereinafter, that by using other methods already described in the literature for the sulfation of glycosaminoglycans, even in the presence of compounds which are partially or totally N-deacetylated, it is not possible to obtain polymers which, although having the same content of sulfur, have the same distribution of sulfate groups of those of the invention. The structures which are obtained by carrying out the above reactions on the above said macromolecules can be synthetically represented with the structural formulas which are hereinafter reported: The formula I relates to the derivatives which are obtained starting from chondroitin sulfate A and C respectively, or from their mixtures, and from dermatan sulfate or chondroitin sulfate B; more precisely: chondroitin 6-sulfate N-sulfate (dimeric unit: 2-sulfoamino, 2-deoxy 3-O-β-D-glucopyranurosyl, 6-sulfate, β-D-galactopyranose): R = OSO - / 3 R₁ = H, Y = H, X = COO⁻. chondroitin 4-sulfate N-sulfate (dimeric unit: 2-sulfoamino, 2-deoxy, 3-O-β-D-glucopyranurosyl, 4-sulfate, β-D-galactopyranose): R = OH, R₁ = SO - / 3, Y = H, X = COO⁻. dermatan sulfate N-sulfate (dimeric unit: 2-sulfoamino, 2-deoxy, 3-O-α-D-glucopyraniduronosyl, 4-sulfate, β-D-galactopyranose): R = OH, R₁ = SO - / 3, Y = COO⁻, X = H The formula II on the contrary relates to the compound obtained from hyaluronic acid (dimeric unit: 2-sulfoamino, 2-deoxy, 3-O-β-D-glucopyraniduronosyl, 6-sulfate, β-D-glucopyranose). The above dimeric units are repeated within the polymer for a number of times varying between 4 and 52, respectively equivalent, in the case of the corresponding sodium salt, to a molecolar weight of about 2,300 and 30,000. The reactions through which the synthesis of the above compounds has been carried out are per se known in the literature and consist, as regards the chondroitin sulfate, in an initial N-deacetylation carried out by heating in a carious pipe to the temperature of 105°C the substance with an excess of hydrazine sulfate and anhydrous hydrazine for a time of 6 hours or less (B.A. Dmitrev et Alii, "Selective cleavaye of glycosidic linkages" Carbohyd, Res. 29 451 1973; "Selective cleavage of glycosidic linkages, studies with the model compound benzyl-2-acetamido-deoxy-6-O -D-mannopyranosyl-D-glucopyranoside" Carbohyd. Res. 30 45 1973; "Selective cleavages of glycosidic linkages, studies with the O-specific polysaccharide from Shigella Disenteriae Type 3" Carbohyd. Res. 40 365 1975). The subsequent reaction of selective N-sulfation is carried out in aqueous phase at pH 9, using an excess of the sulfating agent trimethylamine-sulfuric anhydride (L. Levy et Alii, "Chemical and pharmacological studies on N-resulfated heparin" Proc. Soc. Exp. Biol. Med. 109 901 - 1982; Y. Ynoue et Alii, "Selective N-desulfation of heparin with dimethyl sulfoxide containing water and methanol" Carbohyd. Res. 46 87 1976). It is noticeable that the N-deacetylation reaction may be repeated a second time so as to lower the content of acetyl groups to the requested level when this was not possible in the first step. It is now to be pointed out that the ¹³ C NMR spectra herein enclosed and particularly those of the figures 1, 2, 3 and 6, clearly show that under the adopted conditions not only N-deacetylation but also the subsequent N-sulfation takes place in an almost complete manner as it is shown by the peak relating to the sulfoamino group (about 55 ppm) and from the small importance of the peak corresponding to the acetylamino group (25 ppm). It is furthermore to be observed that as regards the preparation of compounds having low molecolar weight the glycosaminoglycans may, if necessary, undergo a preliminary reaction of the depolimerization which can be carried out with per se known methods, either of chemical or of enzymatic nature (L.A. Fransson "Mammalian glycosaminoglycans" in G.O. Aspinall "The polysaccharides", Academic Press vol. 3 337 1985). Lastly, as regards the hyaluronic acid, the sulfation at the oxygen atom can be carried out before the depolimerisation or, as it is preferable, after this step. The sulfation reaction is carried out selectively at the hydroxyl of the carbon atom at 6, using methods known in the prior art, such as for example the reaction in dimethyl formamide using the trimethylamine-sulfurtrioxide adduct (example 4) of the sulfation with a mixture of sulfuric acid-chlorosulfonic acid (A. Naggi et Alii, "Supersulfated heparin fragments, a new type of low-molecular weight heparin". Biochem. Pharmacol. 36 17 1985 1987). The chemical parameters which characterise the polymers obtained through the above reactions are the following (the data have been calculated on dry basis and relate to the corresponding sodium salt of these substances): - Sulfonic sulfur: 8.0-12% preferably 9.5-11.4% - Sulfates/carboxyls: 1.5-2.3 preferably 1.8-2.1 - Residual N-acetyl groups: <3% preferably <1% - Molecular weight: 2,3-30 X 10³ preferably 3-15 X 10³ In order to demonstrate that by performing hydroxyl sulfation on the above sulfomucopolysaccharides it is not possible to obtain compounds having the chemical properties described in the present invention, on a preparation of dermatan sulfate which previously had been selectively N-deacetylated sulfation was carried out by reaction with trimethylamin-sulfur trioxyde adduct in dimethylformamide, according to the disclosure of the EP-A-2 14 879. The polymer, as it is required by the process described in the above patent application, was previously converted into the corresponding salt with a quaternary ammonium cation (triethylammonium). The experiment and the results obtained are described under example 4. It has been assessed that within the range (1.5-2.3) of the ratio between the sulfate groups/carboxylic groups of interest for the present invention under the above conditions sulfation reaction takes place almost exclusively at the oxygen atom of the alcoholic group which in the polymer chain has the less sterically hindered position, namely that of the carbon atom positioned at position 6 of the galactosamine ring. It has been moreover assessed (example 5) that even adopting the sulfation conditions reported by M.L. Wolfrom in J.A.C.S. 75 1519 1953 (pyridine + chlorosulfonic acid) starting from a preparation of dermatan sulfate previously N-deacetylated it is not possible to have the reaction occurring at the ammonium group of the galactosamine. As a matter of fact, also in this case it has been demonstrated that the reaction takes place at the hydroxyl groups; more precisely sulfation takes places at the hydroxyl at position 6 of galactosamine and that at the position 2 of iduronic acid (figure 5). From the preceeding information it is evident that the sulfated product of the present invention can be obtained only under particular sulfation conditions. As regards to the methods which have been used to evaluate the pharmacological properties of the novel derivatives of the invention, the anticoagulating activity has been assessed in vitro according to the method USP XX, using as the reference standard the third international standard of heparin. The clearing activity induced both by lipoprotein lipase and by hepatic lipase has been assessed according to the method described in the paper by R. Pescador et Alii, Biochem. Pharmacol. 36 4 253 1987. For the reasons which are hereinafter stated on commenting table I, in said table have been reported the results obtained for the activity of lipoprotein lipase and of hepatic lipase (expressed in micromoles of free fatty acids) relating to the lowest and to the highest among the administered doses. The data which have been obtained in the previous experiments, are reported in table I in which a comparison is made with the corresponding of the starting glycosaminoglycans. For these substances however no statistically significant relationship between the administered dose and the corresponding activity has been assessed. For these reasons the results reported in table I correspond to the lowest dose and to the highest dose among those administered, in order to render anyhow possible a comparison. From table I it is evident the relevant increase of the clearing activity of the novel compounds in comparison with that of the starting sulfomucopolysaccarides. Moreover, it is observed that in the case of the derivatives of chondroitins and of the dermatan sulphate the hepatic lipase contributes to the total clearing activity by fifty percent and more. It is worth to note with reference to the data reported in the same table, that at the dose of 1.25 mg/kg, the activity of the hepatic lipase is similar and in the case of the compounds obtained from dermatan sulfate and from hyaluronic acid comparable with the corresponding one of heparin at the dose of 1.4 mg/kg. In the case of the derivative of hyaluronic acid the activity of lipoprotein lipase is comparable with that of heparin. In table II it is demonstrated that by introducing in a N-deacetylated, N-sulfated derivative of chondroitin sulfate (in the subject case chondroitin sulfate A + C) a sulfate group on a hydroxyl for the repeating unit, see the previous structural formula) a relevant increase of anticoagulating activity is obtained which is three times that of the starting polymer. In table III are illustrated data relating to the anticoagulating activity of a sample of dermatan sulfate having some hydroxyl functions substituted with sulfate groups (GAG 938) and furthermore characterized in having a ratio between sulfate groups and carboxylic groups of 2, as such formally falling within the range foreseen by the present invention. The above said table demonstrates that the sulfation at the oxygen atom does not produce the same effect, as regards the anticoagulating activity, as the same reaction at the nitrogen atom of galactosamine. As a matter of fact in the case of GAG 938 derivative the activity is at least twice that of the starting polymer and anyhow greater than that of the corresponding derivative wherein the sulfation has instead occurred at the nitrogen atom of the galactosamine (GAG 944 IV, table I). These examples confirm that for the therapeutical use as drugs endowed of clearing activity and having no side effects on haemostasis of the sulfate derivatives of chondroitin sulfates, dermatan sulfate and hyaluronic acid, two structural requirements are essential, namely the selective sulfation at the nitrogen atom in the position 2 of the pyranose ring of hexosamine and that the ratio between the moles of sulfate groups and of carboxylic groups must be within the range foreseen by the present invention. As a confirmation of the above structural requirements, which as stated are critical in order to obtain compounds having an evident clearing activity without undesired effects on the coagulation, it is worth to note that by performing on a polymer which does not contain sulfate groups at the hydroxyls as for example hyaluronic acid, a N-sulfation reaction at the nitrogen atom in the position 2 of hexosamine according to the process described in the example 6, was obtained a substance (GAG 1045) having a very reduced clearing activity with respect to the corresponding derivatives in which also the hydroxyl in the position 6 is substituted for a group -OSO₃. The substances according to the presente invention can be administered in form of their pharmacologically acceptable salts, such as, as a non limiting example, the corresponding salts with alkali and earth-alcali metals, for example sodium and calcium salts. The foreseen pharmaceutical forms are the standard ones: sterile and apyrogenic solutions in vials and lyophilized preparations packaged in sterile bottles to be dissolved extemporarily in the solvent for the administration by parenteral and subcutaneous route; tablets, gelatin or gastroresistant capsules, granulates for the oral administration. The solutions for parenteral administration may contain 1 to 250 mg/ml of active principle, preferably 1 to 150 mg/ml, whereas the compositions for oral use have a content of active principle as a unitary dose Of 1-500 mg. The daily posology may vary from 1 to 2,000 mg, preferably from 1 to 500 mg. Example 1 1 g of chondroitin 4-sulfate (ratio sulfate groups/ carboxylic groups = 1.07; code n. GAG 920; m.w. 12,000) is N-deacetylated for a time of 5 hours using anhydrous hydrazine and hydrazine sulfate as disclosed in the papers of Dmitrev et alii formerly hereabove referred to. In this experiment the quantity of anydrous hydrazine was of 0,325 g. At the end the liquid phase is evaporated under reduced pressure making use of subsequent addition of toluene to promote the removal of hydrazine. The residue is taken with water and the alcalinity is neutralized by adding 1 M HCl end by cooling in water and ice bath. The solution is then dialized with distilled water throught dialysis membranes of 3500 D (Thomas dialyzer tubing 3787-H47). The solution is then evaporated under reduced pressure thus recovering 700 mg of chondroitin 4-sulfate N-deacetylated (identification No. GAG 957). 1 g of the product is dissolved in 20 ml of distilled water, the pH of the resulting solution being adjusted to 9 by means of few drops of 2N NaOH. The solution is heated to 55°C and under stirring 1 g of the trimethylamine-sulfur trioxide complex is added together with about 900 mg of sodium bicarbonate, in order to restore the alcaline pH. Subsequently, at 4-hour intervals (at the fourth and eight hour) the addition of 1 g of reactant and of 900 mg of the salt is repeated. After 16 hours the reaction is stopped by cooling the reaction mixture to room temperature. The solution is then dialized, by using the same above indicated membrane but substituting the distilled water with a 0.5M solution of sodium chloride. By evaporation under reduced pressure are obtained 1.1 g of chondroitin sulfate N-sulfate with a ratio sulfate/carboxylic groups = 2.2; m.w. 8000; code number: GAG 973). The ¹³C NMR spectrum (figure 1) shows an attenuated signal at 25 ppm (group-CH3, letter A), a signal at about 55 ppm (letter E) corresponding to the carbon atom at position 2 of the galactosamine bearing the group NH-SO₃. There are furthermore seen, as in the starting polymer, a signal at about 60 ppm (letter C) corresponding to the carbon atom at position 6 of the galactosamine bearing a hydroxyl group, and at about 70 ppm (letter D) relating to the carbon atom at position 4 of the galactosamine bearing a sulfate group. The signal indicated in figure 1 with the letter B corresponds to the carbon atom at position 2 of the galactosamine bearing as substituent the group -NH-CH₃. Example 2 1 g of chondroitin 6-sulfate ( ratio of sulfate/carboxylic group = 1, code No. GAG 921, m.w. 18.000) is admixed with the same amount of hydrazine indicated in the above example and the N-deacetylation reaction carried out as above described. Then the N-sulfation is carried out obtaining 1.2 g of final product (code N. GAG 974) having a ratio between sulfate groups and carboxylic groups of 2.1, m.w. 15.000. The spectrum reported in figure 2, apart from the signals common to that showed in figure 1 as regards to the almost total absence of N-acetyl groups and the appearance of the signal corresponding to the sulfoamino group, shows at about 70 ppm the signal (letter C) of the carbon atom at position 6 of the galactosamine bearing the sulfate group. Example 3 1 g of dermatan sulfate ( ratio between sulfate groups and carboxylic groups of 1.1; code n. GAG 968; m.w. 9000) is subjected to the N-deacetylation reaction and subsequent N-sulfation. There are obtained 695 mg of the corresponding derivative. The substance (code n. GAG 944 IV) has a sulfate groups/carboxylic groups ratio = 1.8 , m.w. 6000. The ¹³C NMR spectrum (figure 3) shows, as in the starting substance, one peak at 60 ppm (letter C) corresponding to the carbon atom at position 6 of the galactosamine bearing a hydroxyl group, one peak at 55 pm (letter E) relating to the carbon atom at position 2 of the galactosamine bearing a group NH-SO₃ and lastly, similarly to dermaten sulfate, one peak at 77 ppm (letter D) corresponding to the carbon atom at position 4 of the same ring bearing a sulfate group. Example 4 Comparative example of sulfation of N-deacetylated dermatan sulfate prepared according to EP-A-214 879. The N-deacetylated sample (1g) (see preceding example) is converted into the corresponding acidic form by dissolving the substance in 10 ml of distilled water and admixing with Amberlite IR 120 (form H⁺). The resin is removed by centrifugation and the pH of the solution is brougth to the value of 5 by means of a 10% w/v solution of triethylamine in ethanol. The solution is extracted with ether. The aqueous fase is lastly lyophilized. 1 g of the obtained salt (salt of N-deacetylated dermatan sulfate with triethylammonium) is dissolved in 140 ml of dimethylformamide. It is cooled to 0°C and 10 g of the trimethylamine - sulfur trioxide adduct, previously dissolved in 60 ml of dimethylformamide, are added. The reaction is carried out at the indicated temperature for one hour. Then water cooled at + 5°C is added, the pH is rapidly brought to 9 by adding 5N NaOH and the product is precipitated by adding 600 ml of ethanol saturated with sodium acetate. During this phase the temperature is constantly maintained at +5°C. It is filtered, dissolved again in water and dialysed against distilled water, using the above mentioned dialysis membrane. 900 mg of product code n. GAG 941) are obtained having a ratio sulfate groups/carboxylic group = 1.5. The NMR spectrum (figure 4) shows an intense signal at about 50ppm (letter D) corresponding to the carbon atom at position 2 of the galactosamine and bearing the primary amino group (-NH2), one signal between 60 and 65 ppm (letter C) corresponding to the carbon atom at position 6 of the galactosamine bearing a free hydroxyl and lastly a signal between 65 and 70 ppm (letter E) corresponding to the carbon atom at position 6 with a substituent-SO₃ . The peaks indicated by the letters A and B respectively maintain the meaning attributed thereto in the figure 1. Example 5 Comparative example of Sulfation of dermatan sulfate previously N-deacetylated according to the method described by M.L. Wolfrom, J.A.C.S. 75 1519 1953 (pyridine + chlorosulfonic acid). 1 g of N-deacetylated dermatan sulfate is dissolved in 20 ml of distilled water and then precipitated by adding 60 ml of methanol. The precipitate is dried. In a flask maintained in a nitrogen atmosfere, equipped with condenser and and dropping funnel, there are initially charged 30 ml of anhydrous pyridine at 0°C. By maintaining said temperature there are slowly dropwise added 4 ml of chlorosulfonic acid. Upon the addition is completed, through the same inlet a suspension previously cooled at 0°C of N-deacetylated dermatan sulfate in anhydrous pyridine is quickly introduced. The mixture is moderately heated up to room temperature and then rapidly to 100°C, the reaction being prosecuted at that temperature for one hour. The mixture is cooled, the supernatant liquid is decanted and a portion of 20ml of distilled water is added. The solution is neutralized with 5 N NaOH. Then it is dialized against distilled water. Most of the liquid is then evaporated under a reduced pressure at 35°C by the aid of methyl alcohol and then lyophilized. There are obtained 750 mg of product (code n. GAG 986), having a ratio between sulfate groups and carboxylic group of 1.3. The NMR spectrum (figure 5) shows a signal at about 50 ppm (letter A) corresponding to the carbon atom at position 2 of the galactosamine bearing the group -NH₂, one signal at about 60 ppm (letter B) corresponding to the carbon atom at position 6 bearing a hydroxyl group and one peak at 74 ppm (letter C) corresponding to the carbon atom at position 2 of the ring of the iduronic acid bearing a sulfate group. Example 6 Synthesis of the hyaluronic acid N. 6-disulfate. 1 g of the compound previously depolymerized (GAG 1039) and having molecular weight of 15000, is subjected to the N-deacetylation reaction according to example 1. Then N-sulfation is carried out as described, leading to 800 mg of N-sulfate compound. The next reaction of O-sulfation at the carbon atom in the position 6 of the glucosamine is carried out according to the conditions already indicated in previous example 4 for the reaction on N-deacetylated dermatan sulfate leading to 650 mg of the compound (GAG 902); m.w. 7000, ratio between sulfate groups and carboxyl groups = 1.9. The ¹³C NMR spectrum shows a signal at about 55 ppm corresponding to the carbon atom at position 2 of the glucosamine bearing a group NH-SO₃ and a signal at about 70 ppm corresponding to the carbon atom at position 6 of the glucosamine bearing a sulfate group. Example 7 Synthesis of hyaluronic acid N, 6-disulfate. It is followed the same procedure of the previous example for that it concerns the N-deacetylation and subsequent N-sulfation reaction. The derivative which is obtained (GAG 1045, 0.96 g) has ratio sulfate/carboxyl groups of 0.9. The following reaction of sulfation at the oxygen atom at position 6 of the glucosamine is instead carried out by using a mixture of sulfuric acid and chlorosulfonic acid (A. Naggi et Alii, Biochem. Pharmacol. 36 12 1895 1987). 20 ml of 95% H₂SO₄ and 10ml of HClSO₃ are admixed in a flask at - 4°C. 1 g of N-deacetylated and N-sulfated hyaluronic acid, previously dried, is added to the stirred liquid phase at the same above mentioned temperature. The reaction is continued for one hour at -4°C and for further 60 minutes at 25°C. Sulfation is then terminated by pouring the solution in 500 ml of ethyl ether at -4°C. The precipitate is filtered, dissolved in 20 ml of distillated water and the obtained solution added of 0.5 N NaOH until the neutralization. It is dialyzed against distilled water and the product recovered by evaporation under reduced pressure followed by lyophilization. There are obtained 900 mg (GAG 1046) of a compound having a ratio between sulfate groups and carboxylic groups of 1.8, m.w. 8000. The ¹³C NMR spectrum is not different, as regard the distribution of the sulfate groups, from that reported for GAG 902. Example 8 Synthesis of GAG 952 (chondroitin sulfate A + C being N-deacetylated and subsequently sulfated both at the nitrogen atom and at the oxygen atom). 1.5 g of chondroitin sulfate A + C are treated as described in example 1, giving 1.3 g of product in wherein the nitrogen atom bound to the carbon atom at position 2 of the galactosamine is almost quantitatively substituted with a sulfate group. The next sulfation is carried out as described for sulfation at the oxygen atom in previous example 7. There are obtained 1.3 g of product having a ratio between sulfate and carboxyl groups of 2.7. Example 9 Synthesis of GAG 938 (dermatan sulfate sulfated at the hydroxyl groups). 1 g of dermatan sulfate, GAG 968 is sulfated under the conditions described in example 7, with reference to sulfation at the carbon atom at position 6 of the glucosamine. There are abtained 0.9 g of a product having a ratio sulfate groups/carboxylic groups = 2. The ¹³ C NMR spectrum shows at about 25 ppm an intense signal corresponding to the carbon atom at position 2 of galactosamine bearing a group NH-CH₃ and a weak signal at about 50 ppm corresponding to the same carbon atom bearing a primary amino function -NH₂.

Claims: Synthetic sulfoamino derivatives of glycosaminoglycans selected in the group comprising chondroitin sulfates A and C, their mixtures and dermatan sulfate, characterized by the following chemical parameters, calculated on dry basis and referred to the corresponding sodium salt : total sulfur 8,0-12% Sulfate/carboxyl groups 1,5-2,3 residual N-acetyl groups < 3% Molecular weight 2,3-30 x 10³ And by the following general formula of the dimeric unit: wherein n can vary between 4 and 52 and R, R₁, X and Y have the following meaning: for chondroitin 4-sulfate derivative : R = OH, R₁ = SO₃⁻, X = COO⁻ Y = H; for chondroitin 6-sulfate derivative : R = OSO₃⁻, R₁ = H, X = COO⁻, Y = H; for dermatan sulfate derivative R = OH, R₁ = SO₃⁻, X = H, Y = COO⁻. Synthetic sulfoamino derivatives of hyaluronic acid characterized by the following chemical parameters, calculated on dry basis and referred to the corresponding sodium salt: total sulfur 8,0-12% Sulfate/carboxyl groups 1,5-2,3 residual N-acetyl groups < 3% Molecular weight 2,3-30 x 10³ And by the following formula of the dimeric unit : wherein n can vary between 4 and 52. Synthetic derivatives according to claims 1 and 2 characterized in that the chemical parameters are included in the following ranges : total sulfur 9,5-11,4% sulfate/carboxyl groups 1,8-2,1 residual N-acetyl groups < 1% Molecular weight 3-15 x 10³ A process for the preparation of the derivatives of Claim 1, characterized in that a N-deacetylation step is carried out by heating the starting glycosaminoglycan to a temperature of 105°C with hydrazine sulfate and anhydrous hydrazine for a time of 5 hours and that a subsequent step of selective N-sulfation is carried out in aqueous medium at pH 9 with an excess of the sulfating agent trimethylamine-sulfuric anhydride. A process according to claim 4, characterized in that N-deacetylation reaction can be repeated a second time so as to lower the content of acetyl groups to the requested level when this has not been possible in the first step. A process according to claim 4, characterized in that for the preparation of compounds having low molecular weight the glycosaminoglycans may undergo a preliminary reaction of depolymerization which can be carried out with known methods, either of chemical or of enzymatic nature. A process for obtaining the derivatives of claims 2, characterized in that it comprises, in addition to the reactions of claim 4, a further selective sulfation at the hydroxyl of carbon atom in position 6 of glucosamine of hyaluronic acid. Process according to claim 7 characterized in that said selective sulfation is carried out by reacting the compound with trimethylamine-sulfur trioxide in dimethylformamide at 0°C for one hour or otherwise with sulfuric acid-chlorosulfonic acid at - 4°C for one hour and then at 25°C for further 60 minutes. Pharmaceutical composition characterized in that it contains, as the active ingredient, a glycosaminoglycan derivative according to claims 1 and 2. Pharmaceutical composition according to Claim 9 characterized in that said active ingredient is contained in a unitary dose of 1-500 mg for the oral dosage form and of 1-250 mg for that of parenteral use. Glycosaminoglycan derivatives of claims 1 - 2 for use as medicaments having clearing activity.

Inventors: CASU BENITU, MANTOVANI MARISA, NAGGI ANNAMARIA, PESCADOR RODOLFO, PORTA ROBERTO, PRINO GIUSEPPE, TORRI GIANGIACOMO, CASU, BENITU, MANTOVANI, MARISA, NAGGI, ANNAMARIA, PESCADOR, RODOLFO, PORTA, ROBERTO, PRINO, GIUSEPPE, TORRI, GIANGIACOMO
Applicants: CRINOS INDUSTRIA FARMACO, CRINOS INDUSTRIA FARMACOBIOLOGICA S.P.A.
Application year: 1989
Main classification: C08B37
IPC codes: A61K31, C08B37, A61P7