GB2200353A - Rifamycin derivative salts - Google Patents

Abstract

Rifamycin derivative salts of the following formula (I): <IMAGE> wherein OB represents (i) O<->X<+> wherein X<+> represents an equivalent of a non-toxic, pharmacologically acceptable, inorganic cation or (ii) OH.Y wherein Y represents a non-toxic, pharmacologically acceptable organic base, are useful for treating bacterial, especially mycobacterial, and viral infections.

Description

RYFAMYCIN DERIVATIVE SALTS It is known that rifamycins represent an important class of antibiotics, rifampicin being particularly the choice drug in the infections due to mycobacteria (such as M. tuberculosis) owing to its powerful anti-bacterial activity as well as high bio-availability after oral administration.

In our Italian Patent Application No. 20278/83 and in other patents, such as U.S. Pat. 4,562,203, we described and claimed, inter alia, a novel rifamycin derivative corresponding to 3-[(1-diethylamino ethylidene) azinomethyl] rifamycin SV, having more exactly the formula (I) wherein B is hydrogen:

This derivative nosseses a powerful activity against a number of stocks of r.ycobac-eria as well as against other gram-positive and, i part, gram-negative oactera, on the average appearing as active as rifampicin itself, or even more than that.

As to the pharmacokinetics, the compound of formula (I), B = H, exhibits distinct advantages over rifampicin, because clearly higher blood half-life values have resulted for a number of animal species, which implies a much longer circulatory persistence and, therefore, a greater in vivo effectiveness.

The subsequent phar-..acokinetic parameter of evaluation, i.e. the maximum haematic concentration after oral administration, appeared on the average similar to rifampicin, which proves analogous bio-availability in the various tested animal species.

We have now found that the bio-availability of the orally administered compound of formula (I), B = H, can be sharply improved by its previous salification in order to obtain compounds of formula (I), wherein B represents a non toxic, pharmacologically acceptable, inorganic or orsanic,base.

These salts, object of the present invention, are novel compounds not hitherto known in the clinical literature.

Preferred salification products are those obtained with alkali metal bases, e.g. the sodium salt, or with aminoacids, e.g. the lysin salt, or even with simple organic amines, such as triethylamine.

All these salif cat-on processes have proved suitable to convert t product in acid form tI, B = H), substantially water-insoluble (and consequently liable to pass, at least in part inaltered and limitedly absorbed, through the gastro-intestine tract) into very water-soluble salts, whereby essential conditions for its better in vio bio-availability are established. It is also to be taken into account that such solubility properties of saline substances, however necessary, nevertheless are not generally enough by themselves to assure a high absorption degree after oral administration, because the gastric acid can decompose the salt itself and precipitate again the acl as insoluble crystalline substance.The improved bio-availabilìty of these salts, therefore, can be more closely explained in that said acid substance precipitates in the -stomach, in this case, as amorphous and finely divided material and consequently in a more soluble and/or more easily dissoluble form in the following basic intestinal environment.

Apart from the innermost physico-chemical and bio-chemical mechanisms producing the hightly increased bio-availability of said salts. a number of experiments carried out on several animal species and finally on the man (see, for exemplificative purposes, table 1) constantly show that the rifamycin derivative in form of a salt can provide sharply higher haematic levels that the same dose of products in form of an acid.

TABLE 1 Haematic levels (serum) in man after oral administration of 300 mg of the salt of formula (I, B = Na) and of the corresponding free acid (I, B = H) Conc. (mcg/ml) Hours Compound I, B=Na Compound I, B = H Subject 1 Subject 2 Subject 3 2 8.0 9.6 2.0 4 8.4 8.5 3.1 6 7.9 8.2 2.9 10 6.6 7.2 2.5 26 2.9 2.1 2.5 34 1.9 1.0 1.1 50 0.7 0.2 0.3 Needless to point out that the use of the novel water-soluble salts of the rifamycin derivative of formula (I) allows said derivative to be formulated as injectable composition, which was impossible with the non-salified, therefore non-soluble, product.

The salts according to formula (I) are easily prepared by directly reacting nearly equimolar amounts of the compound in acid form (I, B = H) and of the appropriate base, either in water or in the presence of organic solvents, e.g. ethanol.

Optionally, the preparation is carried out in the presence of small amounts of ascorbic acid or its salts to prevent, by means of their known r'educing power, the possible conversion of the rifamycin derivative into the quinone form. The desired salt is then easily isolated either by evaporating to dryness the resulting solution or by freeze-dryingr when the preparation, is carried out in an aqueous medium, or even by precipitating the salt from the solution by means of other suitable organic solvents.

If necessary, the isolated product can be further purified by crystallization or other usual means.

In order to better illustrate the present invention some preparatie examples, however not limitat've, are reported.

EXAMPLE 1 5.0 g of 3--(1-diethylaminoethylidene)azinomethy, rifamycin SV (I, B = H) are suspended ln 20 ml of ethanol and then 60 mg of sodium ascorbate dissolved in 1 ml water for preventing the formation of small amounts of oxidation product (rifamycin in quinone form) are added. To the resulting suspension an equimolar amount of sodium methoxide, 323 mg, is added with stirring, whereby the free acid is ir.stantly solubilized, by conversion ir.to the corresponding sodium salt.The small amounts of undissolved material. essentially sodium ascorbate, are filtered off and the solution is evaporated to dryness, under vacuum and at reduced temperature, whereby a crystalline residue is obtained, with nearly quantitative yield, which is the sodium salt of 3-[(1-diethylaminoethylidene)azinomethyl] rifamycin SV (I, B = Na) in substantially pure form. If so desired, the product can be further purified by crystallization from isopropanol (50 ml), with a crystallization yield in excess of 90,0. The compound is a red-orange crystalline solid, hightly soluble in water, soluble in methanol, ethanol, acetone, ethyl acetate, chloroform, not very soluble in isopropanol, insoluble in ethyl ether and petroleum ether.By heating, the carbonization starts taking place around 2100C, without melting at even higher temperatures, and the spectrophotometric analysis (0.1 methanol solution with following dilution to 0.02 mg/ml in phosphate buffer at pH6) shows absorption peaks at 231, 261, 338 and 485 nm.

Analysis: C44H59N4Ga (M.W. 858.95) C, H, N within experimental error (0.5%) Na (titration with 0.2N HCl) = 99.6 EXAMPLE 2 5.0 g of 3-[(1-diethylaminoethylidene)azinoethyl] rifamycin SV (I, B = H) are suspended in 100 ml water (suspension pH = 5.2) and reacted, under stirring and cooling to 5-100C, with 5.:7 ml of lN sodium hydroxide, carefully added dropwise over a period of about 3 hours. The product gradually, slowly dissolves and the final solution (pH 9.9) is clarified by filtration and evaporated by freeze-drying so affording quantitative yields of the desired sodium salt (I, B = Na) as amorphous red-orange powder, similar to the products obtained according to the procedure of Example 1.

EXAMPLE 3 1.0 g of 3-(1-diethylaminoethylidene)azinomethyl] rifamycin SV (I, B = H) is suspended in 10 ml water and to the suspension an equimolar amount of D,L-lysin (i.e. 0.32 ml of its 50% aqueous solution) is added. A ready complete solubilization results and, therefore, the solution is clarified by filtration and evaporated to dryness at reduced temperature and pressure. The desired lysin salt (I, B=D,L-lysin.H) is thereby obtained, with nearly quantitative yield, as red crystalline solid.

If so desired, the product can be further purified from appropriate isopropanol/isopropylether mixture.

Analysis: C50H7gHe 01$M.W. 983.17) C, H, N within experimental error ((0.5) base assay = 99.4%

Claims (10)

1. A rifamycin derivative salt having the following general formula (I):

wherein OB represents (i) O X wherein X represents an equivalent of a non-toxic, pharmacologically acceptable, inorganic cation or (ii) OH.Y wherein Y represents a non-toxic, pharmacologically acceptable organic base.

2. A salt according to claim 1, which is the sodium salt of 3-[ (l-diethylaminoethylidene)azinomethyl] rifamycin SV.

3. A salt according to claim 1, which is the D,L-lysine salt of 3-! (diethylaminoethylidene)azinomethyl) rifamycin SV.

4. A process for preparing a salt as defined in claim 1, which process comprises reacting 3-[(l-diethylamino ethylidene)azinomethyl] rifamycin SV directly with an about equimolar amount of the appropriate inorganic or organic base in an aqueous or organic solvent and optionally in the presence of ascorbic acid or a salt thereof and isolating the salt thus obtained.

5. A process according to claim 4, wherein the salt is isolated by evaporation to dryness.

6. A process according to claim 4, wherein the salt is isolated by adding an agent to cause precipitation of the salt.

7. A process for preparing a salt as defined in claim 1, said process being substantially as hereinbefore described in any one of Examples 1 to 3.

8. A pharmaceutical formulation comprising a pharmaceutically acceptable carrier or diluent and as active ingredient a salt as defined in any one of claims 1 to 3.

9. A salt as defined in claim 1 for use in the treatment of a bacterial or viral infection.

10. A salt according to claim 9 for use in the treatment of an infection caused by mycobacteria.