Acetylsalicylic acid (Aspirin) belongs to the group of non-steroid anti-inflammatory, drugs being at the same time effective in preventing myocardial ischemia and stroke. It also inhibits the aggregation of thrombocytes preventing the blood clotting. Although acetylsalicylic acid is a non-toxic drug, it irritates the mucous membrane of the stomach. Therefore the administration of acetylsalicylic acid is limited in the case of patients suffering from digestive tract illnesses.

Synthetic oligomers of 3-hydroxybutyric acid are analogues of natural poly ([R]-3- hydroxybutyric) acid (PHB), which can be found in living organisms, for example in some cell membranes. The studies of oligomers of [R]-3-hydroxybutyric acid described earlier (Z. Jedlinski, P. Kurcok, R. W. Lenz, Macromolecules 1998,31, 6718; Z. Jedliriski, M. Kowaiczuk, P. Kurcok, patent RP 172412,1993) as well as their applications in preparing synthetic cell membranes (S. Das, P. Kurcok, Z.

Jed) ihski, R. N Reusch, Macromolecules, 1999,32, 8781) showed that the oligomers of synthetic [R] -3-hydroxybutyric acid are hydrolyzed by enzymes in human body. They are completely biocompatible and their metabolites are non- toxic.

Esters of oligomers of synthetic 3-hydroxybutyric acid and acetylsalicylic acid have not been known so far.

Novel esters of acetylsalicylic acid with oligomers of 3-hydroxybutyric acid according to the invention are presented in formula 1, where n equals from 2 to 25.

The method of obtaining compounds with formula 1, where n equals from 2 to 25, according to the invention, consists in converting acetylsalicylic acid formula 2, preferably with the use of sodium or potassium hydride or hydroxide, into monosodium or monopotassium salt formula 3, where X denotes sodium or potassium, which in turn is reacted with ß-butyrolactone causing the opening of P-butyrolactone ring at the carbon-oxygen position, the formation of an ester bond with acetylsalicylic acid if the lactone is present in excess, polymerization of the lactone take place.

The new compound obtained in this way is acetylsalicylic acid connected by ester bond with biocompatible polymer carrier being oligomer of 3-hydroxybutyric acid with 2-25 mers.

The bond between acetylsalicylic acid and biocompatible polymer carrier is easily hydrolyzed in living tissue.

According to the invention the drug containing known, pharmaceutical permissible carriers and acetylsalicylic acid as an active substance features acetylsalicylic acid connected by ester bond with oligomer of [R]-3-hydroxybutyric acid having from 2 to 25 mers and being biocompatible polymer carrier.

Because of their lypophylicity and affinity to cell membranes, oligomers of 3- hydroxybutyric acid combined with acetylsalicylic acid via ester bonds result in new pharmaceutical properties, particularly the irritation of mucous membrane of the digestive tract by acetylsalicylic acid is eliminated. The polymer carrier hydrolyzing gradually in the digestive tract facilitates permeation of the drug through cell membranes because of its lypophylicity and gradually releases the active agent, acetylsalicylic acid. According to the invention, the new drug- conjugates limit the necessity of using gelatin capsules to coat drugs containing acetylsalicylic acid.

The advantage of such a solution, according to the invention, is limiting the irritation of stomach caused by acetylsalicylic acid and release of the drug proceeds only in small intestine, which broadens the range of drug application in the form of a conjugate to the group of patients, who do not tolerate drugs containing acetylsalicylic acid. It has been found that, the gradual hydrolysis of oligo (3-hydroxybutyrate) and acetylsalicylic acid-polymer ester bond cleavage releases 3-hydroxybutyric acid and its oligomers, which are non-toxic and belong to the group of ketone bodies. According to the present state of arts ketone bodies are particularly useful in the treatment of patients suffering also from Alzheimer's disease because 3-hydroxybutyrate prevents neurons.

The conjugates can be used also in the form of tablets obtained by pressing after granulating medical substance with auxiliary substances like starch, corn cellulose, etc.

The methods of producing esters of acetylsalicylic acid with oligomers of [R]-3- hydroxybutyric acid (polymer-drug conjugates) according to the invention are as follows : Example I Synthesis of sodium salt of acetylsalicylic acid In order to purify sodium hydride (NaH) used in the syntheses, it was washed with distilled tetrahydrofuran (THF) in atmosphere of neutral gas (argon) and then placed in a glass reactor in the quantity of 0.0392 g (0.0016 mole). Then 0.309 g (0.0017 mole) of acetylsalicylic acid was introduced into the reactor and then 5 mi of dimethyl sulfoxide (DMSO), previously dried over anhydrous calcium sulfate and stored over molecular sieves A4, were added. The content of the reactor was mixed with the use of magnetic stirrer for 2 hours in the atmosphere of nitrogen.

Reaction of sodium acetylsalicylate obtained at the first stage with ß-butyrolactone [S]-p-butyrolactone was dried over calcium hydride (CaH2) and distilled over metallic sodium. Then 0. 41 g (0.048 mole) of purified [S]-ß-butyrolactone was introduced into the reactor containing sodium acetylsalicylate and the content was mixed by a magnetic stirrer in the atmosphere of argon until lactone reacted completely. Conversion was determined with the use of infrared spectroscopic analysis (IR). IR band at 1831 cm~1 characteristic for carbonyl carbon of P-butyrolactone ester group disappeared, the band at 1735 cm-1 characteristic for carbonyl carbon of ester groups in polyester was observed. After that 20 ml of acidified chloroform were introduced into the reactor and the obtained product was extracted by the mixture of chloroform-dimethyl sulfoxide-water. After the separation of diphase system, the product present in chloroform phase was precipitated in hexane and dried over low pressure.

Analysis of the product : Molecular weight (average) determined by GPC method (using polistyrene standards) Mn=451 [g/mole] Elementary analysis C= 57.33 % H= 5.81 % Analysis of the end product using mass spectrometry method ESI-MS and the analysis of positive ions showed the presence of following molecular ions: m/z = 461 adequate to [C9H804 (C4H602) 3HNa] + m/z = 571 adequate to [C9H804 (C4H602) 4HNa] + Example II The synthesis was carried out in the same way as in Example I. 1.241 g (0.0517 mole) Of sodium hydride (NaH) (or 0.0103 mole of potassium hydride), 9.349 g (0.0519 mole) of acetylsalicylic acid and 31.100 g (0.3616 mole) of P-butyrolactone were used in the reaction.

Analysis of the product Molecular weight (average) determined by GPC method (using polystyrene standards) Mn=742 [g/mole] Elementary analysis C = 56. 71 % H= 6.28% IR the band at 1735 cm-1 characteristic for carbonyl carbon ester groups in polyester was observed.

Analysis of the end groups using mass spectrometry method ESI-MS and the analysis of positive ions showed the presence of following molecular ions: m/z = 719 adequate to [csHso4 (c4H602) 6HNa] + m/z = 805 adequate to [CgHsO4 (C4H602) 7HNa] + m/z = 891 adequate to [CgH804 (C4H602) 8HNa] + Example Ill Synthesis of potassium acetvlsalicvlate 3.26 g (0.018 mole) of acetylsalicylic acid and 30 ml of dimethyl sulfoxide (DMSO) previously dried over anhydrous calcium sulfate and stored over molecular sieves were introduced into the reactor. Then 0.92 g (0.017 mole) of potassium hydroxide was added. The content of the reactor was mixed with the use of a magnetic stirrer in the atmosphere of argon under IR control.

Reaction of potassium acetvisalicylate obtained with fSI-P-butvroiactone 5.85 g (0.068 mole) of purified [S]-p-butyrolactone was introduced into the reactor containing potassium acetylsalicylate and the content was being mixed with a magnetic stirrer in the atmosphere of argon until lactone reacted completely.

Conversion was determined by infrared spectroscopic analysis (IR). IR the band at 1830 cm~1 characteristic for carbonyl carbon of ß-butyrolactone ester group and appearance of the band at 1735 cm~1 characteristic for carbonyl carbon ester groups in polyester were observed. After that 20 ml of acidified chloroform was introduced into the reactor and the obtained product was extracted by the mixture chloroform-dimethyl sulfoxide-water. After the separation of diphase system, the product present in chloroform phase was precipitated in hexane and dried over lowered pressure.

Analysis of the product: Molecular weight (average) determined by GPC method (using polystyrene standards) Mn=513 [g/mole] Elementary analysis C = 57.36 % H= 5.95% Analysis of the end groups using mass spectrometry method ESI-MS and the analysis of positive ions showed the presence of following molecular ions: m/z = 461 adequate to [CoH804 (C4H602) 3HNa] + m/z = 547 adequate to [C9H804 (C4H602) 4HNa] + The formed conjugates contain chains of oligomeric 3-hydroxybutyric acid of various lengths depending on stoichiometric ratios of p-butyro) actone and sodium or potassium acetylsalicylate used in the reactions.

Example Preparation of tablets containing a conjugate A conjugate was mixed with dried starch, granulated and then stearic acid was added.

Amounts of components : Conjugate 24. 00 g (contains 10 g of acetylsalicylic acid) Corn starch 1.00 g Stearic acid 1. 00 g Finally after mixing in the tablet machine tablets with the weight of 260 mg are formed (with the use of 9 mm stamps).