SODIUM SALT OF ETODOLIC ACID AND PROCESS FOR ITS PREPARATION

Abstract: The sodium salt of etodolic acid (1,8-diethyl-1,3,4,9-­ tetrahydropyran-[3,4-b]indol-1-acetic acid) and a process for its preparation are described. The obtained sodium salt has an appreciable solubility in water and is, therefore, suitable for preparing pharmaceu­ tical formulations particularly fit for parenteral as well as topic and rectal administration.

Description: "SODIUM SALT OF ETODOLIC ACID AND PROCESS FOR ITS PREPARATION" The present invention concerns the preparation of salts of 1,8-diettiyl-1,3,,9-tetrahydropyran-[3,-bJ indol-1-acetic acid, hereinafter briefly called etodolic acid, and particularly the preparation of the water-soluble sodium salt. In U.S. Patent No.3,843,681 the preparation of indolic derivatives is described, which are characterized by the presence of a 1,3,4,9-tetrahydropyran (or thiopyran) [3,4-b]-indole group substituted in position 1, and possibly also in other positions. Such derivatives are described as anti-inflammatory, analgesic, antibacterial and antifungal agents. Such indolic derivatives, among which also etodolic acid is included, show, however, the disadvantage of generally being as such water-insoluble, and this restricts their possible ways of administration only to the oral route, with a consequent possibility of gastro-enteric intolerance, as it is generally reported with regard to most of the anti-inflammatory agents administered by mouth. In order to obtain derivatives of said compounds, which could possibly the water-soluble, a research has been carried out, the results of which form the object of this invention. Etodolic acid was taken into consideration as a typical representative, particularly appreciated from the pharmacological point of view, of said derivatives and some typical salts thereof were prepared. While also most of the so obtained salts were practically fully water-insoluble, at least from the practical point of view, it was found that sodium salt, particularly if prepared under suitable conditions, is, on the contrary, easily water-soluble with the formation of solutions sufficiently stable during time also at temperatures higher than normal room-temperatures. In order to avail oneself of a derivative usable in therapy, it is necessary, in fact, to obtain a highly soluble substance, also considering the doses of etodolic acid which have to be administered for getting an effieient therapeutic action (at least 200 mg twice a day in the adult man). By employing as bases for salification some amino acids such as arginine and lysine or potassium, which are often utilized in substances having anti-inflammatory and analgesic action for injectable preparations, the respective salts of etodolic acid were prepared, which, however, turned out to be almost completely water-insoluble in the case of amino acids and where characterized by a very poor solubility (2%) in the case of potassium salt. In this latter case the obtained solutions are deeply coloured and not much stable, when submitted to quickened ageing tests. The sodium salt of etodolic acid, which appears in the form of white crystal powder, turned out on the contrary highly water-soluble ( > 20% by weight) thus producing solutions, which are only fleebly yellowcoloured and, above all, are very stable during time. The salification of etodolic acid can be easily carried out, for instance, by dissolving the acid into ethanol and slowly adding an aqueous solution of sodium hydroxide or carbonate. The resulting white crystalline product provides, however, deeply brown-coloured aqueous solutions, probably owing to the presence of by-products or impurities. By working, on the contrary, in an anhydrous medium, as described hereinafter, a white, very water-soluble powder is obtained, which provides weakly yellowcoloured stable solutions. The present invention will now be more particularly described on the basis of an embodiment which in no case must be regarded as limiting the invention. EXAMPLE 1 - -Sodium salt of etodolic acid 28.73 g of etodolic acid are dissolved into 100 ml of anhydrous ethanol and to the obtained solution, kept under stirring, a solution consisting of 2.3 g metallic sodium dissolved into 100 ml of anhydrous ethanol is slowly added by instalments. At the end of the addition, the stirring is continued for 15 min. and then the solution is concentrated to dryness under vacuum in a rotating eveporator. The obtained residue, after addition of 200 ml petroleum ether, is separated by filtration and washed firstly with petroleum ether, then with diethyl ether. After a new desiccation, the product is finely powdered and suspended into 200 ml petroleum ether, by stirring for 15 min., then filtered and washed with diethyl ether. After a final desiccation, 30 g of sodium salt are obtained in the form of white micro-crystalline powder, easily soluble in water. The 20% solution has a pH of 8.7, while a 7.3% solution has a pH of 7.8. Elemental analysis for C17H20NO3Na (M.W. 309.34): Calculated: C 66.9%; H 6.51%; N 4.53% Found : C 66.33%; H 6.58%; N 4.37 /O A thin layer chromatography through HPTLLC process of 10 mg of the so obtained sodium salt on silica gel (60 F Silicagel), using toluene-ethanol (70:30) as the development solvent, shows at the ultra-violet light of 254 nm, only one spot with Rf = 0.60. The infra-red absorption spectrum shows typical maxima at the following wavelengths: between 3,500 and 3,300 cm 1 for the secundary amino group, between 1,080 -1 and 1,040 cm for the cyclic ether, at 1,590 cm for the salified carboxyl and at 740 cm for the three adjacent hydrogens at positions 5,6 and 7. The obtained spectrum is reproduced in the enclosed figure. For the identification reaction, 0.1 g of sodium salt are dissolved into 5 ml water and the solution is acidified by means of diluted hydrochloric acid, thus obtaining a precipitate which is filtered and thoroughly washed with water. After desiccation, the precipitate shows a melting point of 147-1480C, characteristic of the free etodolic acid. The following tables No.1, 2 and 3 respectively show the stability data of sodium etodolate in aqueous solutions at 10% and 20% at various temperatures and again at 10% after sterilization in autoclave in a closed container. TABLE 1 Stability of sodium salt of etodolic acid in a 10 % aqueous solution. At starting 45 C 25 C 5 C point 1 month 2 month 3 month 1 month 2 month 3 month 1 month 2 month 3 month Titre % 100 100 99 100 100 100 99 99 100 100 (HPLC) pH 7.8 7.8 7.8 7.7 7.8 7.85 7.8 7.8 7.8 7.75 Colour pale yellow unchanged unchanged unchanged unchanged unchanged unchanged unchanged unchanged unchanged TABLE 2 Stability of sodium salt of etodolic acid in a 20 % aqueous solution. At starting 45 C 25 C 5 C point 1 month 2 month 3 month 1 month 2 month 3 month 1 month 2 month 3 month Titre % 100 99 98 99 100 99 100 99 100 97 (HPLC) pH 8.7 8.6 8.7 8.7 8.7 8.6 8.7 8.7 8.7 8.6 Colour pale yellow unchanged deep deep unchanged unchanged unchanged unchanged unchanged unchanged yellow yellow TABLE 3 Stability of sodium salt of etodolic acid after sterilization at 1200C in autoclave for 20 min. At starting-point After sterilization Titre (%) 100 100 (HPLC) pH 7.8 7.8 Appearance of the solution limpid limpid Colour of the solution pale yellow pale yellow As it may be noticed from the reported data, the sodium etodolate appears quite stable under the most different storage and treatment conditions. The so obtained sodium etodolate, thanks to this solubility, which can even exceed 20% by weight at normal temperature, is suitable for the preparation of various pharmaceutical formulations both for oral and particularly parenteral and rectal use. Tablets, pills, granules, syrups and solutions for oral administration can thus be prepared, as well as sterile aqueous solutions for injections or for hypodermoclysis and also ovules or suppositories. The following non-limiting example explains the preparation of suppositories based on sodium etodolate. EXAMPLE 2 69.3 g of an excipient for suppositories, known by the name of Suppocire AM, are heated to a temperature between 450 and 500C into a container provided with stirrer. After complete melting 12 g of sodium etodolate are slowly added, always under stirring. At the end of the addition the mass is maintained under stirring and, when the temperature has dropped to 40 C, it is poured into the suppository mould, thus obtaining suppositories each weighing 2.71 g on average and containing 0.40 g of sodium etodolate and 2.31 g of excipient. Having thus described a preferred embodiment of the present invention, changes and/or alterations can obviously be made without departing for this reason from the scope of the invention.

Claims: CLAIMS 1. A process for preparing sodium salt of 1,8-die thyl-1,3,4,9-tetrahydropyran- 3,4-b]indol-1-acetic acid (etodolic acid), characterized in that said acid is reacted under stirring in an anhydrous solvent with sodium alcoholate and, after evaporation, the residue is purified twice with petroleum ether and desiccated. 2. The process according to claim 1, characterized in that said anhydrous solvent is anhydrous ethanol and said sodium alcoholate Is sodium ethoxide. 3. The sodium salt of etodolic acid prepared according to claim 1 or 2, characterized in that said salt provides aqueous solutions feebly yellow-coloured till to concentrations of at least 20% by weight. 4. Pharmaceutical preparations having anti-inflammatory, analgesic and antipyretic action, characterized in that they contain an effective quantity of sodium etodolate.

Inventors: CASERO, RICCARDO
Applicants: FARMAKA S.R.L.
Application year: 1986
Main classification: C07D491
IPC codes: C07D491, A61P25, A61K31, A61P29