Process for preparing lankacidine carbamate derivatives

Abstract: A process for preparing a lankacidine carbamate derivative of the formula or a salt thereof, by the reaction of a lankacidine 8-substituted carbonate with an amine, wherein R₁ is a hydroxy group or an alkanoyloxy group; and R₂ and R₃ are each a hydrogen atom, an optionally substituted lower alkyl group, a cycloalkyl group or a phenyl group; or R₂ and R₃ together with an adjacent nitrogen atom to which they bond form an optionally substituted heterocyclic group.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for preparing lankacidine carbamate derivatives having antimicrobial activities. 2. Prior Art Lankacidines are antibiotics which are produced and accumulated by cultivating a Streptomyces strain and have the structure represented by the formula: In the above formula, where Ra is COCH₃, the compound is lankacidine A, and where Ra is H, it is lankacidine C. Known derivatives of the lankacidines are, for example, those having an ester group at the 8 and/or 14 positions of lankacidine C [see Kagaku & Seibutsu (Chemistry and Organism, Vol. 15, pp. 337 - 342 (1977)): Journal of the Takeda Research Laboratories, Vol. 41, pp. 81 - 113 (1982)], those having an acyloxy group or the like at 8 and/or 14 positions thereof [see The Journal of Antibiotics, Vol. 26, pp 647 (1973)], and those having 8-substituted alkyl ester, 8-carbonate ester and 8-substituted carbamate (Japanese Published Unexamined Patent Application No. 240687/1987). Japanese Published Unexamined Patent Application No. 240687/1987 and EP-A-0 226 896 also disclose processes for preparing lankacidine A carbamate in which lankacidine A is reacted with isocyanates, and pentachlorophenoxy- or 2,4,5-trichlorophenoxycarbonate of lankacidine A are reacted with amines. These known processes are, however, required to use high toxic isocyanates or expensive polyhalogenophenoxycarbonylchloride, while their yields are not satisfactory. SUMMARY OF THE INVENTION The present invention is to provide an industrially advantageous process for preparing 8-lankacidine carbamate derivatives having excellent antimicrobial activities. Thus, the present invention provides a process for preparing a compound represented by the formula [III]: wherein R₁ is a hydroxy group or an alkanoyloxy group; and R₂ and R₃ are each a hydrogen atom, a lower alkyl group which may be substituted by hydroxy, amino, mono - lower alkyl amino, lower alkoxy, halogen or pyridyl, a cycloalkyl group or a phenyl group; or R₂ and R₃ together with the adjacent nitrogen atom to which they bond form a heterocyclic group being a 4-7 membered ring having at least one nitrogen atom which may have an oxygen atom and/or a sulfur atom and which may be substituted by lower alkyl (unsubstituted or substituted with hydroxy), chlorophenyl or pyridyl, or a salt thereof, comprising reacting a compound represented by the formula [I]: wherein R₁ has the same meaning as above; X is a halogen atom; and Y is a hydrogen atom, a lower alkyl group or a trihalogenoalkyl group, with a compound represented by the formula [II]: wherein R₂ and R₃ have the same meaning as above. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The term "lower alkyl group" used in the above formula is meant by a straight or branched chain alkyl group having 1-6 carbon atoms. Examples thereof are methyl, ethyl, n-propyl, i-propyl, n-butyl, tert-butyl, n-pentyl and n-hexyl. The term "cycloalkyl group" used here is meant by a cycloalkyl group having 3-6 carbon atoms. Examples thereof are cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. The term "alkanoyloxy group" is meant by an alkanoyloxy having 2-6 carbon atoms. Examples thereof are acetyloxy, propionyloxy, butyryloxy, valeryloxy and hexanoyloxy. The substituents for the optionally substituted lower alkyl group represented by R₂ or R₃ are a hydroxy, an amino, a mono-lower alkylamino (e.g., methylamino or ethylamino), a lower alkoxy (e.g., methoxy or ethoxy), a halogen (e.g., chlorine or bromine) and pyridyl. In the case that R₂ and R₃ together with the adjacent nitrogen atom to which they bond form a heterocyclic group, the heterocyclic group is meant by a 4 - 7 membered ring having at least one nitrogen atom, and optionally an oxygen atom and/or an sulfur atom. Usually preferred is a 5 or 6 membered ring. Examples of the 5 or 6 membered rings are pyrrolidino, piperidino, morpholino and piperazino. Each of these 5 or 6 membered rings may be substituted by an optionally with hydroxy substituted lower alkyl (e.g., methyl, ethyl or hydroxy ethyl), chlorophenyl or pyridyl. As Y in the formula [I], desirable is methyl, ethyl, propyl, butyl, trichloromethyl or tribromomethyl group, and particularly preferable is methyl or trichloromethyl group. As the halogen atom, desirable is chlorine, bromine or iodine. According to the present invention, the compound of the formula [III] can be prepared by reacting a compound of the formula [I] with an amine of the formula [II]. The reaction is suitably conducted in an organic solvent optionally coexisted with water. Examples of the organic solvents are dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran, 1,4-dioxane, acetonitrile, ethyl acetate and methyl acetate. The amount of the amine [II] used in this reaction is suitably approximately 1 - 10 mol equivalents, to the compound [I]. The reaction time and reaction temperature vary within approximately 0 - 100°C and approximately 30 minutes to 24 hours, respectively, depending on the sort of the amine used. The objective compounds [III] thus obtained can be isolated and purified by a well known technique such as concentration, solvent extraction, chromatography, crystallization or recrystallization. In case where the compound has a basic group such as an amino group or a substituted amino group as R₂ and R₃, the basic group may form an acid-addition salt. Examples of such acid-addition salts are the hydrochloride, hydrobromide, hydroiodide, nitrate, sulfate, phosphate, acetate, benzoate, maleate, fumarate, succinate, tartrate, citrate, methanesulfonate and, benzenesulfonate. In a preferred embodiment of the process the prepared compound of formula III are compounds, wherein a) R₁ is a hydroxy or acetoxy group, and either one of R₂ and R₃ is a hydrogen atom and the remaining one is a lower alkyl group which may be substituted by pyridyl, which lower alkyl group preferably is methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, tert-butyl, n-pentyl or n-hexyl; b) R₁ is a hydroxy or acetoxy group, and either one of R₂ and R₃ is a hydrogen atom and the remaining one is a phenyl group; and c) R₁ is a hydroxy or acetoxy group, and R₂ and R₃ together with the adjacent nitrogen atom to which they bond are a 5 or 6 membered heterocyclic group which may be substituted by hydroxyethyl or pyridyl, which 5 or 6 membered heterocyclic group preferably is pyrrolidino, piperidino, morpholino or piperazino. Elution in column chromatography in the Reference Example and Examples was conducted while monitoring with TLC (Thin Layer Chromatography). In the TLC monitoring, the TLC plate used was 60F₂₅₄ manufactured by Merck Co., the developing solvent was the same one as used for eluting in the column chromatography, and the detection was conducted with a UV detector. The silica gel for the column was Kieselgel 60 (230 - 400 mesh) manufactured by Merck Co. NMR spectra were measured using tetramethylsilane as an internal or external standard in a spectrometer of XL-100A (100MHz), EM360 (60MHz), EM390 (90MHz) or T₆₀ (60MHz) type, and all s values are expressed in ppm. The value shown in ( ) for a mixed solvent is a mixing ratio in volume of constituent solvents. The symbols in the Reference Example and Examples mean as follows: s : singlet d : doublet t : triplet q : quartet ABq : AB type quartet dd : double doublet m : multiplet br. : broad J : coupling constant Reference Example 1 Lankacidine A 8-(1-chloroethyl)carbonate Lankacidine A (50 g) was dissolved in 950 ml of dichloromethane, to which a solution of 19 g of 1-chloroethyl chloroformate [see Synthesis, 627 (1986)] in 40 ml of dichloromethane was added under ice cooling. To the mixture was dropwise added 10.3 g of pyridine. Then, the mixture was stirred at room temperature for an hour, mixed with 2 ml of 1- chloroethyl chloroformate and 1.5 ml of pyridine sequentially and stirred for an hour. The reaction mixture was washed with 1N-HCl, water and then dilute sodium bicarbonate solution, and dried over MgSO₄. The mixture was evaporated under reduced pressure to remove its solvent, and the resulting residue was crystallized from 500 ml of a mixture of ether-hexane (1 : 1) to obtain 53.7 g of the title compound. NMR (90 MHz, CDCl₃)δ : 1.32 (d, 3H, J=7Hz), 1.40 (s, 3H), 1.57 (s, 3H), 1.82 (d, 3H, J=6Hz), 1.93 (s, 3H), 2.05 (s, 3H), 2.2-2.7 (m, 5H), 2.47 (s, 3H), 4.42 (dt, 1H, J= 3 & 12Hz), 4.47 (d, 1H, J = 11Hz), 4.8-5.2 (m, 1H), 5.3-6.1 (m, 6H), 6.30 (d, 1H, J = 15Hz), 6.40 (q, 1H, J = 6Hz), 8.10 (d, 1H, J = 11Hz) Example 1 Lankacidine A 8-(4-methylpiperazino)carboxylate Lankacidine A 8-(1-chloroethyl)carbonate (6 g) was dissolved in 40 ml of dichloromethane, to which a solution of 6 g of N-methylpiperazine in 20 ml of dichloromethane was dropwise added under ice cooling. After stirring for 40 min., the reaction mixture was washed with 1N-HCl to remove excess amine, subsequently with a dilute sodium bicarbonate solution and water and dried over MgSO₄. The mixture was evaporated under reduced pressure to remove the solvent. The resulting residue was subjected to silica gel column chromatography (silica gel: 300 g) eluting with chloroformmethanol (30 : 1). The fractions including the objective compound were collected and concentrated. The resulting oily substance was then crystallized from a mixture of ether-hexane (1 : 1) to obtain 4.7 g of the title compound. Melting point: 203 - 207°C (decomp.) NMR (90 MHz, CDCl₃) δ : 1.32 (d, 3H, J=7Hz), 1.38 (s, 3H), 1.55 (s, 3H), 1.92 (s, 3H), 2.03 (s, 3H), 2.1-2.7 (m, 9H), 2.30 (s, 3H), 2.46 (s, 3H), 3.4-3.7 (m, 4H), 4.43 (d.d, 1H, J = 3 & 12Hz), 4.72 (d, 1H, J = 11Hz), 4.2-5.2 (m, 1H), 5.2-5.9 (m, 6H), 6.32 (d, 1H, J = 15Hz), 8.08 (d, 1H, J = 11Hz) Example 2 Lankacidine A 8-chloromethylcarbonate (300 mg, prepared by the process disclosed in Japanese Published Unexamined Patent Application No. 240687/1987) was dissolved in 10 ml of tetrahydrofuran, to which 100 mg of N-methylpiperazine was added at room temperature. After stirring for 3 hours, the reaction mixture was mixed with 50 ml of ethylacetate and washed with 60 ml of saturated aqueous sodium chloride solution. The resulting organic layer was dried over MgSO₄ and concentrated under reduced pressure. The residue was subjected to silica gel column chromatography (silica gel : 60 g) eluting with chloroform-methanol (30 : 1). The fractions including the objective compound were collected and concentrated. The residue was then crystallized from a mixture of ether-hexane (1 : 1) to obtain 180 mg of the compound identical to that prepared in Example 1. Example 3 Lankacidine A 8-iodomethylcarbonate (342 mg, prepared by the process disclosed in Japanese Published Unexamined Patent Application No. 240687/1987) was dissolved in 10 ml of tetrahydrofuran, to which 120 mg of N-methylpiperazine was added at room temperature. After stirring for 30 min. at room temperature, the reaction mixture was mixed with 50 ml of ethylacetate and washed with 60 ml of saturated aqueous sodium chloride solution. The resulting organic layer was dried over MgSO₄ and evaporated to remove the solvent. The residue was subjected to silica gel column chromatography (silica gel: 60 g) eluting with chloroform-methanol (30 : 1). The fractions including the objective compound were collected and concentrated. The residue was then crystallized from a mixture of ether-hexane (1 : 1) to obtain 193 mg of the compound identical to that prepared in Example 1. Examples 4 - 13 Lankacidine A 8-(1-chloroethyl)carbonate was reacted with various amines by the method as described in Example 1 to obtain the compounds shown in Table 1. Example 14 Lankacidine C 8-(4-methylpiperazino)carboxylate Lankacidine C 8-iodomethylcarbonate (300 mg, prepared by the process disclosed in Japanese Published Unexamined Patent Application No. 240687/1987) was dissolved in 10 ml of tetrahydrofuran, to which 110 mg of N-methylpiperazine was added at room temperature. After stirring for 30 min. at room temperature, the reaction mixture was mixed with 50 ml of ethylacetate and washed with 60 ml of saturated aqueous sodium chloride solution. The resulting organic layer was dried over MgSO₄ and evaporated under reduced pressure to remove the solvent. The residue was subjected to silica gel column chromatography (silica gel: 60 g) eluting with chloroform-methanol (30 : 1). The fractions including the objective compound were collected and concentrated under reduced pressure to obtain 230 mg of the title compound. Melting point: 201 - 203°C Elemental analysis for C₃₁H₄₃N₃O₈.3/2H₂O: Calcd.: C, 60.77; H, 7.57; N, 6.86 Found: C, 60.82; H, 7.30; N, 6.67 NMR (90 MHz, CDCl₃) δ : 1.25 (d, 3H, J=6Hz), 1.38 (s, 3H), 1.54 (s, 3H), 1.92 (s, 3H), 2.1-2.7 (m, 9H), 2.46 (s, 3H), 3.4-3.7 (m, 4H), 4.2-4.6 (m, 2H), 4.70 (d, 1H, J = 11Hz), 4.8-6.0 (m, 6H), 6.17 (d, 1H, J=15Hz), 8.07 (d, 1H, J = 11Hz) According to the present invention, 8-lankacidine carbamate derivatives having excellent antimicrobial activities can be efficiently prepared using stable reactants of low prices.

Claims: A process for preparing a compound represented by the formula [III]: wherein R₁ is a hydroxy group or an alkanoyloxy group; and R₂ and R₃ are each a hydrogen atom, a lower alkyl group which may be substituted by hydroxy, amino, mono - lower alkyl amino, lower alkoxy, halogen or pyridyl, a cycloalkyl group or a phenyl group; or R₂ and R₃ together with the adjacent nitrogen atom to which they bond form a heterocyclic group being a 4-7 membered ring having at least one nitrogen atom which may have an oxygen atom and/or a sulfur atom and which may be substituted by lower alkyl (unsubstituted or substituted with hydroxy), chlorophenyl or pyridyl, or a salt thereof, comprising reacting a compound represented by the formula [I]: wherein R₁ has the same meaning as above; X is a halogen atom; and Y is a hydrogen atom, a lower alkyl group or a trihalogenoalkyl group, with a compound represented by the formula [II]: wherein R₂ and R₃ have the same meaning as above. The process of claim 1 in which the reaction is conducted in an organic solvent selected from the class consisting of dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran, 1,4-dioxane, acetonitrile, ethyl acetate and methyl acetate. The process of claim 1 which is adopted to prepare a compound of the formula [III] wherein R₁ is a hydroxy or acetoxy group, and either one of R₂ and R₃ is a hydrogen atom and the remaining one is a lower alkyl group which may be substituted by pyridyl. The process of claim 3 in which the lower alkyl group in the lower alkyl group which may be substituted by pyridyl is methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, tert-butyl, n-pentyl or n-hexyl. The process of claim 1 which is adopted to prepare a compound of the formula [III] wherein R₁ is a hydroxy or acetoxy group, and either one of R₂ and R₃ is a hydrogen atom and the remaining one is a phenyl group. The process of claim 1 which is adopted to prepare a compound of the formula [III] wherein R₁ is a hydroxy or acetoxy group, and R₂ and R₃ together with the adjacent nitrogen atom to which they bond are a 5 or 6 membered heterocyclic group which may be substituted by hydroxyethyl or pyridyl. The process of claim 6 in which the 5 or 6 membered heterocyclic group in the 5 or 6 membered heterocyclic group which may be substituted by hydroxyethyl or pyridyl is pyrrolidino, piperidino, morpholino or piperazino. The process of claim 1 wherein the prepared compound is selected from Lankacidine A 8-(4-methylpiperazino)carboxylate, Lankacidine A 8-morpholinocarboxylate, Lancacidine A 8-(4-pyridin-4-yl piperazino)carboxylate. The process of claim 1 in which the heterocyclic group is selected from a class consisting of pyrrolidino, piperidino, morpholino and piperazino which may be substituted by lower alkyl, chlorophenyl or pyridyl.

Inventors: KAWAI TATSUHIKO, MIYAKE AKIO, KAWAI, TATSUHIKO, MIYAKE, AKIO
Applicants: TAKEDA CHEMICAL INDUSTRIES LTD, TAKEDA CHEMICAL INDUSTRIES, LTD.
Application year: 1990
Main classification: C07D493
IPC codes: C07D493, A61K31, A61P31