New 2'-substituted-4-deoxythiazolo[5,4-c]rifamycin SV derivatives

Abstract: The present invention concerns new 2′-substituted-4-deoxy-thiazolo[5,4-c]rifamycin SV derivatives of formula having antibacterial activity. These compounds are obtained by chemical modification of thiazolo[5,4-c]rifamycin SV.

Description: The present invention concerns new 2′-substituted-4-deoxy-thiazolo[5,4-c]rifamycin SV derivatives of formula I wherein R¹ represents hydrogen or acetyl, R² and R³ each independently represent (C₁-C₄) alkyl or R² and R³ taken together with the adjacent nitrogen atom represent a 4-7 membered saturated heterocyclic ring selected from azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, oxazolidinyl, pyrazolidinyl, thiazolidinyl, morpholinyl, imidazolidinyl, wherein a ring nitrogen atom may be substitued with a substituent R⁴ which is selected from (C₁-C₄) alkyl, hydroxy (C₂-C₄) alkyl, (C₂-C₄) alkanoyl, (C₁-C₄) alkoxycarbonyl, phenyl optionally substituted with 1 to 3 substituents selected from halogeno, hydroxy, (C₁-C₄) alkyl and (C₁-C₄) alkoxy ; phenyl-(C₁-C₄) alkyl wherein the phenyl ring may be optionally substituted with 1 to 3 substituents selected from halogeno, hydroxy, (C₁-C₄) alkyl, and (C₁-C₄) alkoxy; and phenyl-­ (C₁-C₄) alkoxycarbonyl wherein the phenyl ring may be substituted with from 1 to 3 substituents selected from halogeno, hydroxy, (C₁-C₄) alkyl and (C₁-C₄) alkoxy, and the pharmaceutically acceptable acid addition salts thereof. 4-deoxy-thiazolo[5,4-c]rifamycin SV (also called "rifamycin P") has been obtained both by fermentation of Nocardia strains and by chemical processes. The fermentation process has been disclosed in GB 1470426 while chemical processes are reported in US 4144234 and 4129562. 2′-Alkyl-4-deoxy-thiazolo[5,4-c]rifamycin SV derivatives are described in US 4169834; 2′-hydrazonomethyl 4-deoxythiazolo[5,4-c]rifamycin SV are described in EP-A-5140, while 4-deoxythiazolo[5,4-c]rifamycin SV having a mono-amino substituent or a hydrazino substituent in position 2′ are disclosed in DE-A-2741066 and are prepared by reacting 3-bromo rifamycin S with the proper thiourea derivative. In the present description and claims the term "(C₁-C₄) alkyl" either alone or in combination with other groups represents alkyl groups of 1 to 4 carbon atoms such as methyl, ethyl, propyl, 1-methylethyl, 2-methyl-1-propyl, 2-methyl-2-propyl and butyl. "(C₁-C₄) alkoxy" either alone or in combination with other groups represents alkoxy groups of 1 to 4 carbon atoms such as methoxy, ethoxy, propoxy, 1-methylethoxy, 2-methylpropoxy, 2-methyl-2-propoxy and butoxy. "Halogeno" represents an halogen atom selected from chloro, bromo, iodo, and fluoro. "4-7 membered saturated heterocyclic ring......" represents a 4, 5, 6 or 7 membered saturated heterocyclic ring selected from azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, oxazolidinyl, pyrazolidinyl, thiazolidinyl, morpholinyl, and imidazolidinyl. The further ring nitrogen, when present, may bear a substituent R⁴ which is defined as reported above. A preferred group of compounds of the invention is represented by those compounds of formula I wherein R¹ represents acetyl. Another group of preferred compounds is represented by those compounds of formula I wherein R² and R³ independently represents a (C₁-C₄) alkyl group or R² and R³ taken together with the adjacent nitrogen atom represent a 4-7 memberend heterocyclic ring selected from azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, oxazolidinyl, pyrazolidinyl, thiazolidinyl, morpholinyl, imidazolidinyl groups and the further ring nitrogen atom when present bears a substituent R⁴ which is as defined above. A further preferred group of compounds of the invention includes those compounds of formula I wherein R¹ represents acetyl and R² and R³ independently represent methyl or ethyl, or R² and R³ taken together with the adjacent nitrogen atom represents a pyrrolidinyl, morpholinyl, piperidinyl or piperazinyl group optionnaly substituted as defined above with reference to the meanings of R⁴. Specific preferred embodiments of the invention are represented by the following compounds of formula I : 2′-(4″-morpholinyl) rifamycin P 2′-(1″-piperidinyl) rifamycin P 2′-(4″-methyl-1″-piperazinyl) rifamycin P 2′-(N,N-diethylamino) rifamycin P The compounds of the invention are prepared by reacting 4-deoxy-thiazolo[5,4-c]rifamycin SV (i.e. rifamycin P) or 25-desacetyl-4-deoxy-thiazolo[5,4-c]rifamycin SV, i.e. a compound of the following formula II wherein R¹ represents hydrogen or acetyl, with an amine of formula HNR²R³ in the presence of an inert organic solvent, with the proviso that when the HNR²R³ amine is piperazine R⁴ is different from hydrogen. To obtain the piperazine derivative wherein R⁴ is hydrogen, the corresponding phenyl (C₁-C₄) alkoxycarbonyl derivative is submitted to hydrogenolysis under conditions that prevent the hydrogenation of the ansa double bonds. The reaction temperature is generally between 5°C and 40°C and preferably between 15°C and 30°C, the preferred reaction temperature is room temperature. The inert organic solvent may be one of the organic solvents which do not unfavourably interfere with the reaction course which are capable of at least partially dissolve the starting material of formula II and the amine HNR²R³ while it is not necessary that either the starting materials or the final products be completely dissolved into the reaction so as to form a homogeneous phase. Representative examples of inert organic solvents are saturated "cyclic" ethers like tetrahydrofuran or dioxane, glycol ethers like dimethoxyethanel and (C₁-C₄) alkyl alkanoates such as ethyl acetate, propyl acetate or ethylpropionate, and mixtures thereof. The hydrogenolytic step which is required to obtain the piperazine derivative wherein R⁴ is hydrogen starting from the corresponding compound wherein R⁴ is as defined above but different from hydrogen must be carried out under conditions that do not lead to a substantial hydrogenation of the ansa double bonds. This hydrogenolysis is preferably conducted in a polar organic solvent such as a lower alkanol in the presence of a hydrogenation catalyst like palladium on carbon. Most preferred conditions are the presence of absolute ethanol as the solvent and 10% palladium on carbon as the catalyst. The reaction course is monitored as known in the art by HPLC or TLC techniques so that the skilled man is capable of adjusting the specific reaction conditions and deciding when the reaction is to be considered completed. Usual purification procedures such as extraction with solvents, precipitation by addition of non-solvents, or by changing the pH of the medium, and chromatographic procedures are suitable for the purification of the compounds of the invention. Chromatographic procedures includes preparative TLC, column chromatography and HPLC. The physico-chemical data, and purification methods, of some representative compounds of the invention are reported in the following Tables I and II. More particularly, the compounds listed below are compounds of formula I wherein R¹ represents acetyl, with the exception of compound 3b wherein R¹ represents hydrogen. Notes to Table I 1) When two quantities are reported the reagent was added in two portions at the times indicated. 2) a) Acid treatment as described for connpound la ; b) acid/base treatment as described for compound 3a; c) preparative TLC eluent mixture CH₂Cl₂/MeOH 95: 5, the compound is collected dissolved with a mixture of EtOAc and acid water, the organic layer is separated, and concentrated to a small volume; the product is precipitated with petroleum ether; d) preparative TLC, eluent mixture CH₂Cl₂/MeOH 95: 5, then worked up as described for compound 4 ; e) crystallized from EtOAc; f) precipitated from EtOAc with petroleum ether; g) precipitated from CH₂Cl₂ with petroleum ether; h) column chromatography, on Silica Gel 60 (0.06-0.2 mm; Merck Co.) eluent mixture CHH₂Cl₂/MeOH 95: 5. Notes to Table II On Silica Gel 60 F 254 plates (Merck); solvent-run 10.0 cm 1) The analytical results for C, H, N, S (and Cl) were within ± 0.4% of the theoretical values. 2) Eluent mixture CHCl₃/MeOH 9/1. Under these conditions the R f of rifamycin P is 0.42. 3) Determined in glass capillary tubes 4) Rifamycin P shows the following values of lambda max in methanol nm : 225, 260, 305, 352, 412. n.d. = not determined The compounds of the invention possess antimicrobial activity against gram positive and some gram negative bacteria and are also active against Mycobacteria strains, in particular against Mycobacterium tuberculosis . The minimum inhibitory concentration (MIC) of representative compounds of the invention was determined using two-fold dilution method in microtiter system. The media used were: Todd-Hewitt broth (Difco) for streptococci; Iso-Sensitest broth (Oxoid) for staphylococci and gram-negative bacteria. The final inoculum was about 10⁴ cfMy/ml. MIC was read as the lowest concentration which showed no visible growth after 18-24 hours incubation at 37°C. For M. tuberculosis H₃₇R V the inoculum consisted of 0.5-1% of a 7-9 day culture in Dubos medium. The tests were carried out in Kirschner medium supplemented with 10% horse serum. Observations were made after 7-days incubation at 37°C. The results obtained are summarized in the following Table III: The antimicrobial activity of the compounds of the invention is also confirmed in "in vivo" tests. The results of experimental septicemia in mice are reported in the following Table IV. The animals (groups of five mice) were infected by intraperitoneal injection of 16-hour broth culture of S. aureus tour L 165. Inocula were adjusted so that untreated animals died of septicemia within 48 hours. Animals were treated once daily for three days starting immediately after infection. On the 10th day the value for the ED₅₀ in mg/kg/day was calculated by the method of SPEARMAN-KÄRBER (Finney, D.J., Statistical method in biological assay, page 524. C. Griffin Ltd., London, 1952), on the basis of the percentage of surviving animals at each dose. The following examples further illustrate the invention. Example 1 : a) 2′-(1″-Pyrrolidinyl) rifamycin P Pyrrolidine (10 ml) is added to a solution of 1.0 g (1.35 mmole) of rifamycin P in 150 ml of THF at room temperature. The reaction mixture is stirred for 5 hours then it is poured into ice-water, acidified with diluted hydrochloric acid and extracted with ethyl acetate (EtOAc) (2×100 ml). The combined extracts are washed with water to neutrality, dried on anhydrous sodium sulphate and concentrated to a small volume at 45°C under vacuum. The addition of petroleum ether gives a precipitate that was collected and purified by preparative TLC as follows: the solid is dissolved in few milliliter of MeOH and the solution is applied to Silica Gel plates 60 PF₂₅₄ (Merck) that are developed with a mixture of CH₂Cl₂/MeOH 95: 5. The zone corresponding to the title product is scraped off and eluted with methanol (MeOH). The extract is evaporated to dryness, the residue is dissolved in ethyl acetate and washed with diluted hydrochloric acid, dried on sodium sulphate and concentrated to a small volume. By adding petroleum ether a precipitate forms which is filtered off and dried under vacuum. The yield and the physico-chemical data are reported in Tables I and II. By following the procedure of the above Example (1a) and using the appropriate amine reactant the following compounds are obtained whose reaction conditions, purification details, yields and physicochemical data are reported in Tables I and II : b) 2′-(4″-morpholinyl) rifamycin P HNR²R³ = morpholine c) 2′-(4″-phenyl-1″-piperazinyl) rifamycin P HNR²R³ = 1-phenylpiperazine d) 2′-(4″-phenylmethyl-1″-piperazinyl) rifamycin P HNR²R³ = 1-benzylpiperazine e) 2′-(4″-ethoxycarbonyl-1″-piperazinyl) rifamycin P HNR²R³ = 1-ethoxycarbonylpiperazine f) 2′-(4″-phenylmethoxycarbonyl-1″-piperazinyl) rifamycin P HNR²R³ = 1-phenylmethoxycarbonylpiperazine Example 2: 2′-(1″-Piperidinyl) rifamycin P Rifamycin P (1.0 g, 1.35 mmole) is dissolved in 15 ml of piperidine and the resulting solution is stirred for 30 hours at room temperature. The reaction mixture is poured in ice-water and worked up as described in the foregoing Example (1a). Purification details, yield and physico-chemical data are reported in Tables I and II. Example 3: a) 2′-(4″-Methyl-1″-piperazinyl) rifamycin P 1-Methylpiperazine (10 ml) is added to a solution of rifamycin P (2.0 g, 2.7 mmole) in 300 ml of EtOAc and the reaction mixture is stirred for 90 min at room temperature, then an additional 10 ml of 1-methylpiperazine is added. Stirring is continued for 3.5 hours, then the reaction mixture is poured into ice-water and made acidic with diluted hydrochloric acid, maintaining the pH between 4 and 5. The organic layer is discarded and the aqueous phase is brought to about pH 7 with NaHCO₃ and extracted with EtOAc. The organic extract is dried over sodium sulfate and concentrated to a small volume. By cooling the compound of the title is obtained as crystalline powder which precipitates. Purification details, yield and physico-chemical data are reported in Tables I and II. By following the procedure of the above Example (3a) and using the appropriate amine reactant the following compounds are obtained whose purification details, yield and physico-chemical data are reported in Tables I and II. b) 25-Desacetyl-2′-(4″-methyl-1-piperazinyl) rifamycin P (starting from 25-desacetyl rifamycin P) HNR²R³ = 1-methylpiperazine c) 2′-[4″(2‴-hydroxyethyl)-1″-piperazinyl]-­ rifamycin P HNR²R³ = 1-(2-hydroxyethyl) piperazine d) 2′-[4″(4‴-chlorophenyl)-1-piperazinyl]ifamycin P HNR²R³ = 1-(4-chlorophenyl) piperazine e) 2′-[4″(4‴-methoxyphenyl)-1-piperazinyl]­ rifamycin P, HNR²R³ = 1-(4-methoxyphenyl)-piperazine. Example 4: 2′-(1″-Piperazinyl) rifamycin P A solution of 0.22 g (0.23 mmole) of 2′-[4″-phenylmethoxycarbonyl-1″-piperazinyl]­ rifamycin P in 40 ml of absolute ethanol is left under hydrogen stream with stirring at room temperature and atmospheric pressure in the presence of 50 mg of 10% palladium on carbon for 1 hour. The reaction is monitored by TLC (Rf 0.4, relative to the starting compound). Once the reaction is complete the reaction mixture is filtered and the solvent evaporated. The residue is dissolved with MeOH and purified by preparative TLC on Silica Gel 60 PF₂₅₄ plates (eluent mixture CHCl₃/MeOH 9: 1). The zones which contain the product of the title are eluted with MeOH. The methanolic extracts are evaporated to dryness, the residue is dissolved with ethyl acetate and the solution is washed with an aqueous NaHCO₃ solution at pH 8.5, dried over sodium sulfate and concentrated to a small volume. Upon adding petroleum ether the compound of the title precipitates which is filtered off and dried under vacuum. Example 5: 2′-(N,N-diethylamino) rifamycin P N,N-Diethylamine (5 ml) is added to a solution of rifamycin P (0.5 g, 0.67 mmole) in 25 ml of EtOAc and the reaction mixture is allowed to stand at room temperature for five days, then it is poured into ice-water and made acid with diluted hydrochloric acid. The organic layer is separated, washed with water to neutrality, dried on sodium sulphate and evaporated to dryness. The residue is dissolved with 2 ml of CH₂Cl₂ and subjected to flash chromatography by applying it to a column of 35 g of Silica Gel 60 (0.04-0.06 mm) Merck which is developed with: a) CH₂Cl₂ (250 ml), b) CH₂Cl₂ containing 0.5% (v/v) of methanol (500 ml), c) CH₂Cl₂ containing 1% (v/v) of methanol (500 ml), d) CH₂Cl₂ containing 1.8% (v/v) of methanol (1 liter). This last mixture elutes the product of the title and is collected in fractions of 100 ml each (12 fractions). Those fractions which contain the product of the title are combined and evaporated to dryness obtaining 33 mg of pure compound. Preparation of the starting materials: rifamycin P: (4-deoxy-thiazolo[5,4-c]rifamycin) SV rifamycin P is prepared as described in GB patent 1470426, US patent 4144234 or US patent 4129562. 2′-Methoxycarbonyl rifamycin P: 2′-Methoxycarbonyl rifamycin P is prepared as described by Cricchio et al., in Tetrahedron, 36 , 1415-1421 (1981) and US patent 4129562. 25-Desacetyl rifamycin P: A solution of 4.5 g (5.5 mmole) of 2′-methoxycarbonyl rifamycin P in 200 ml of acetone and 100 ml of 50% aqueous NaOH is allowed to stand at room temperature with stirring. The reaction is monitored by TLC (CHCl₃/MeOH, 95: 5) until the starting compound disappears (about 30 min). The reaction mixture is poured into ice-water and extracted with EtOAc. The extracts are dried on sodium sulfate and then evaporated to dryness under vacuum during 30 min. The residue is dissolved into 300 ml of the same acetone/aqueous NaOH mixture and the solution is evaporated again. The residue is dissolved with CHCl₃ and purified by silica gel (220 g) column chromatography eluting with CHCl₃ containing increasing amounts of MeOH (from 1.5 to 2% in volume). Fractions containing the desired product are pooled, and the solvents are evaporated to dryness. By crystallization from EtOAc, 3.5 g (90%) of the desired compound is obtained; mp 172-174°C; UV (MeOH) lambda max nm (log epsilon) 224 (4.26), 260 (4.21) 298 (4.17), 405 (4.14). Anal. Calcd for C₃₆H₄₄N₂O₁₀S : C 62.05. H 6.36; N 4.02; S 4.60. Found : C 61.76; H 6.30; N 3.95; S 4.47.

Claims: Claims for the contracting states : BE DE CH GB FR IT NL LU SE 1. 2′-substituted-4-deoxy-thiazolo[5,4-c]­ rifamycin SV derivatives of formula I wherein R¹ represents hydrogen or acetyl, R² and R³ each independently represent (C₁-C₄) alkyl or R² and R³ taken together with the adjacent nitrogen atom represent a 4-7 membered saturated heterocyclic ring selected from azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, oxazolidinyl, pyrazolidinyl, thiazolidinyl, morpholinyl, imidazolidinyl, wherein a ring nitrogen atom may be substituted with a substituent R⁴ which is selected from (C₁-C₄) alkyl, hydroxy (C₂-C₄) alkyl, (C₂-C₄) alkanoyl, (C₁-C₄) alkoxycarbonyl, phenyl optionally substituted with 1 to 3 substituents selected from halogeno, hydroxy, (C₁-C₄) alkyl and (C₁-C₄) alkoxy ; phenyl (C₁-C₄) alkyl wherein the phenyl ring may be optionally substituted with 1 to 3 substituents selected from halogeno, hydroxy, (C₁-C₄) alkyl, and (C₁-C₄) alkoxy ; and phenyl-­ (C₁-C₄) alkoxycarbonyl wherein the phenyl ring may be substituted with from 1 to 3 substituents selected from halogeno, hydroxy, (C1-C4) alkyl and (C1-C4) alkoxy, and the pharmaceutically acceptable acid addition salts thereof. 2. A compound of claim 1 wherein R¹ represents acetyl. 3 . A compound of claim 1 wherein R¹ represents acetyl, R² and R³ independently represent methyl or ethyl, or R² and R³ taken together with the adjacent nitrogen atom represent a pyrrolidinyl, morpholinyl, piperidinyl or piperazinyl group optionally substituted as defined in claim 1 with reference to the meanings of R⁴. 4. A compound according to claim 1 wherein R¹ represents acetyl and NR²R³ represents 4-morpholinyl, 1-piperidinyl, 4-methyl-1-piperazinyl, or diethylamino. 5. A process for preparing a compound of claim 1 which comprises reacting a compound of formula II wherein R¹ represents hydrogen or acetyl, a) with an amine of formula HNR²R³ in the presence of an inert organic solvent, to obtain a compound of formula I wherein the NR²R³ group is as defined in claim 1 with the exclusion of the compound wherein NR²R³ represents an unsubstituted piperazine ; b) when a compound of formula I is desired wherein the NR²R³ group is an unsubstituted piperazine, subjecting to controlled hydrogenolysis the corresponding compound of formula I wherein R⁴ represent phenyl-(C₁-C₄)alkoxycarbonyl. 6. A process as claimed in claim 5 wherein the reaction temperature of step a) is between 5 and 40°C. 7. A process as claimed in claim 5 wherein the reaction temperature of step a) is room temperature. 8. A process as claimed in claim 5 wherein the hydrogenolysis of step b) is carried out in a polar organic solvent in the presence of a hydrogenation catalyst. 9. A compound of claim 1 for use as a medicine. 10. Use of a compound of claim 1 for preparing a medicament for antibacterial use. 11. A pharmaceutical composition which comprises a compound of claim 1 in admixture with a pharmaceutically acceptable carrier. Claims for the following Contracting States: AT, ES, GR. 1. A process for preparing a 2′-substituted-4-deoxy-thiazolo[5,4-c]rifamycin SV derivatives of formula I wherein R¹ represents hydrogen or acetyl, R² and R³ each independently represent (C₁-C₄) alkyl or R² and R³ taken together with the adjacent nitrogen atom represent a 4-7 membered saturated heterocyclic ring selected from azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, oxazolidinyl, pyrazolidinyl, thiazolidinyl, morpholinyl, imidazolidinyl, wheirein a ring nitrogen atom may be substituted with a substituent R⁴ wich is selected from (C₁-C₄) alkyl, hydroxy (C₂-C₄) alkyl, (C₂-C₄) alkanoyl, (C₁-C₄) alkoxycarbonyl, phenyl optionally substituted with 1 to 3 substituents selected from halogeno, hydroxy, (C₁-C₄) alkyl and (C₁-C₄) alkoxy ; phenyl-(C₁-C₄) alkyl wherein the phenyl ring may be optionally substituted with 1 to 3 substituents selected from halogeno, hydroxy, (C₁-C₄) alkyl, and (C₁-C₄) alkoxy ; and phenyl (C₁-C₄) alkoxycarbonyl wherein the phenyl ring may be substituted with from 1 to 3 substituents selected from halogeno, hydroxy, (C₁-C₄) alkyl and (C₁-C₄) alkoxy, and the pharmaceutically acceptable acid addition salts thereof. Which comprises reacting a compound of formula II wherein R¹ represents hydrogen or acetyl, a) with an amine of formula HNR²R³ in the presence of an inert organic solvent, to obtain a compound of formula I wherein the NR²R³ group is as defined in claim 1 with the exclusion of the compound wherein NR²R³ represents an unsubstituted piperazine ; and b) when a compound of formula I is desired wherein the NR²R³ group is an unsubstituted piperazine, subjecting to controlled hydrogenolysis the corresponding compound of formula I wherein R⁴ represent phenyl-(C₁-C₄) alkoxycarbonyl. 2. A process as in claim 1 for preparing a compound of formula I wherein R¹ represents acetyl. 3 . A process as in claim 1 for preparing a compound of formula I wherein R¹ represents acetyl, R² and R³ independently represent methyl or ethyl, or R² and R³ taken together with the adjacent nitrogen atom represent a pyrrolidinyl, morpholiriyl, piperidinyl or piperazinyl group optionally substituted as defined in claim 1 with reference to the meanings of R⁴. 4. A process for preparing a compound according to claim 1 wherein R¹ represents acetyl and NR²R³ represents 4-morpholinyl, 1-piperidinyl, 4-methyl-1-piperazinyl, or diethylamino. 5. A process as claimed in claim 1 wherein the reaction temperature of step a) is between 5 and 40°C. 6 . A process as claimed in claim 1 wherein the reaction temperature of step a) is room temperature. 7. A process as claimed in claim 1 wherein the hydrogenolysis of step b) is carried out in a polar organic solvent in the presence of a hydrogenation catalyst. 8. Use of a compound of claim 1 for preparing a medicament for antibacterial use.

Inventors: CAVALLERI, BRUNO, TAMBORINI, GIOVANNI, TURCONI, MARCO
Applicants: GRUPPO LEPETIT S.P.A.
Application year: 1986
Main classification: C07D513
IPC codes: A61K31, A61P31, C07D513