PROCESS FOR PRODUCING OPTICALLY ACTIVE BENZYL ALCOHOL COMPOUNDS

Abstract: Process for preparing optically active α-cyanobenzyl alcohol compounds represented by formula (I), rich in an (S)-enantiomer useful as intermediates for synthesizing in­ secticidal pyrethroids, which comprises asymmetrically hydrolyzing (R,S)-α-cyanobenzyl alcohol esters of formula (II), using esterase of microorganism origin.

Description: The present invention relates to the production of an optically active benzyl alcohol compound. It is known, as a general proposition, that ester groups attached to asymmetric carbon atoms may be hydrolysed by esterases originating from micro-organisms. Agric.Biol.Chem., 45(6), 1389-1392, 1981, for example, describes experiments involving the stereoselective hydrolysis of methyl 2-phenylpropionate using strains of bacteria and of Aspergilli . The present invention now provides a process for producing an (S)-isomer-rich optically active α-cyano-benzyl alcohol compound represented by the formula (II): wherein X is a hydrogen atom, fluorine atom, chlorine atom or bromine atom, which comprises allowing an esterase originating from a microorganism belonging to a genus selected from Arthrobacter , Alcaligenes , Achromabacter , Pseudomonas , Chromobacterium , Bacillus , Nocardia , Rhodotorula , Candida , Rhizopus , Mucor , Aspergillus , Hansenula and Torulopsis to react at a pH of 7 or less with an ester of the (R,S)-isomer of an α-cyano-benzyl alcohol compound, the said ester being represented by the formula (I): wherein X has the same meaning as above; R means a hydrogen atom, a C₁-C₁₈ alkyl, C₂-C₁₈ alkenyl, C₂-C₁₈ alkynyl, C₁-C₄ halogen-substituted alkyl, C₂-C₄ halogen-substituted alkenyl, C₂-C₄ halogen-substituted alkynyl, C₁-C₈ alkoxyl, C₂-C₈ alkenyloxy or C₂-C₈ alkynyloxy group, in order to hydrolyze the ester asymmetrically until it is resolved into an (S)-isomer-rich α-cyano-benzyl alcohol compound represented by the formula (II) and an antipode ester thereof. The α-cyano-benzyl alcohol compound represented by the formula (II) mentioned above has been known as novel alcoholic moiety of a series of ester compounds of synthetic pyrethroids which have been excellent in insecticidal activity. Since the α-cyano-benzyl alcohol compound has an asymmetric carbon at the α-position there are two optical isomers. With respect to insecticidal activity as an ester, the (S)-isomer ester of α-cyano-benzyl alcohol compound is much superior to the antipode (R)-isomer ester. Accordingly, it has been desired to develop commercially advantageous technology to resolve optically the (R,S)-isomer of said α-cyano-benzyl alcohol compound into the (S)-isomer thereof. However, since said α-cyano-benzyl compound is unstable, the optical resolution thereof is not easy. The current situation is that the method now available for the optical resolution of said alcohol requires complicated processes and expensive optically active agents. The present inventors have been investigating to find out a commercially advantageous process for producing (S)-isomer of α-cyano-benzyl alcohol compound represented by the formula (II) mentioned above. At last, they have found that the biochemically asymmetric hydrolysis of a racemic isomer, namely, an (R,S)-isomer of the ester of the α-cyano-benzyl alcohol compound represented by the formula (I), which is the starting material, efficiently resolves the ester into (S)-isomer-rich optically active α-cyano-benzyl alcohol compound represented by the formula (II) and the antipode ester thereof. They have accomplished the present invention, adding various further investigations to the finding above. That is, the present invention a process for producing an (S)-isomer-rich optically active α-cyano-benzyl alcohol compound represented by the formula (II) mentioned above by allowing an esterase (in the present invention, esterase means esterase in a broad sense including lipase) originated from a microorganism selected from the genera listed above to react at not higher than pH 7 with an ester of the (R,S)-α-cyano-benzyl alcohol represented by the formula (I) mentioned above in order to asymmetrically hydrolyze the same until it is resolved into an (S)-isomer rich α-cyano-benzyl alcohol represented by the formula (II) and an antipode ester thereof. The more detailed description of the process of the present invention will be given hereinafter. The microorganisms which produce the esterase used in the present invention are selected from the genera Arthrobacter , Alcaligenes , Achromobacter , Pseudomonas , Chromobacterium , Bacillus , Nocardia , Rhodotorula , Candida , Rhizopus , Mucor , Aspergillus , Hansenula and Torulopsis . Amongst these, from the viewpoints of hydrolysis capability and optical purity of the optically active α-cyano-benzyl alcohol compound represented by the formula (II), the esterase produced by microorganisms belonging to genuses Arthrobacter , Alcaligenes , Achromobacter , Pseudomonas and Chromobacterium is preferable. As the typical examples of microorganisms belonging to those genera mentioned above, there can be illustrated following strains: All these strains have been deposited at Institute of Fermentation, Osaka (IFO) or American Type Culture Collection (ATCC), and are available from these depositories. Some of the esterase originated from microorganisms have been commercially available in the market. Also these enzymes commercially availble in the market can be used for the present invention. The enzymes commercially available in the market which can be used for the present invention are illustrated below. In carrying out the present invention, the asymmetric hydrolysis of the (R,S)-isomer of the ester represented by the formula (I) mentioned above is conducted by mixing cultured liquor of such microorganisms, filtrate of the cultured liquor, suspension of microorganism cells or aqueous solution containing treated product thereof such as crude esterase or purified esterase and said (R,S)-isomer of the ester, and stirring or shaking the mixture. If necessary, a nonester type surfactant may be added. Also it is possible for the enzyme to be in the immobilized form. The suitable reaction temperature in this reaction is 10 to 65°C, preferably 20 to 50°C. The reaction time usually ranges from 3 to 48 hours. However, the reaction time can be shortened by elevating the reaction temperature or using enzymes having higher activities. It is important to keep the pH in the reaction at not higher than pH 7, preferably in a range of pH 3.5 to pH 6.0. Furthermore, it is preferable to keep the pH constant by utilization of a buffer solution, in order to prevent pH from lowering due to an organic acid such as acetic acid by-produced from the hydrolysis. As the buffer solution, either one containing inorganic acid salt or organic acid salt may be used. The substrate,the (R,S)-isomer of the ester represented by the formula (I) may be used in a concentration of 1 to 80 w/w %, preferably 5 to 40 w/w % on the basis of the reaction liquid. After carrying out the asymmetric hydrolysis reaction as mentioned above, the optically active α-cyano-benzyl alcohol compound represented by the formula (II) in the free form is separated from the unreacted ester of the antipode alcohol compound and they are recovered by an operation such as liquid phase separation by standing, extraction with a solvent or column chromatography. Such a separation and recovery operation is conducted, for example, in such a manner that the reaction mixture is extracted with an organic solvent such as ether, benzene or toluene, and the extract is subjected to column chromatography using silica gel, etc. and a cyclohexaneether (95:5) solution as an eluent to isolate the free optically active α-cyano-benzyl alcohol compound represented by the formula (II) and the unreacted antipode ester, respectively. In addition, the unreacted organic carboxylic acid ester which has been separated and recovered as mentioned above is subjected to racemization by bringing it in contact with a base compound such as ammonia, pyridine or triethylamine, and can be used again as the starting material for the process of the present invention. The (R,S)-isomer of the ester represented by the formula (I) which is used as the starting material in the present invention can be easily obtained by an ordinary process for producing ester, for instance, by a process wherein a halide of an organic carboxylic acid represented by the formula (III): wherein R₁ is a hydrogen atom, a C₁-C₁₈ alkyl, C₂-C₁₈ alkenyl, C₂-C₁₈ alkynyl, C₁-C₄ halogen-substituted alkyl, C₂-C₄ halogen-substituted alkenyl or C₂-C₄ halogen-substituted alkynyl group, for example, acid chloride or acid bromide, or an acid anhydride thereof is allowed to react with an (R,S)-isomer of α-cyano-benzyl alcohol compound represented by the formula (II), or by a process wherein a halide of the organic carboxylic acid represented by the formula (III) mentioned above, for example, acid chloride or acid bromide, an aldehyde compound represented by the formula (IV): wherein X has the same meaning as above, and sodium cyanide are allowed to react, or by a process wherein one of chloroformic acid esters represented by the formula (V): wherein R₂ is a C₁-C₈ alkyl, C₂-C₈ alkenyl or C₂-C₈ alkynyl group, is allowed to react with an (R,S)-isomer of α-cyano-benzyl alcohol compound represented by the formula (II). As the organic carboxylic acid represented by the formula (III) mentioned above, there are illustrated, for example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, isovaleric acid, caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, or halogen-substituted compounds thereof and the like. On account of the easiness in handling and the optical purity of the reaction product obtained by the asymmetric hydrolysis, a C₂-C₁₂ fatty acid or a C₁-C₄ halogen-substituted fatty acid having one chlorine or bromine atom at the α-position thereof is preferable; further, from the viewpoints of easiness in availability and economy, acetic acid, propionic acid, monochloroacetic acid or monobromoacetic acid is more preferable. Also as chloroformic acid ester represented by the formula (V), methyl chlorocarbonate, ethyl chlorocarbonate, propyl chlorocarbonate and the like are preferable from the viewpoints of easiness in availability and economy. Furthermore, the process of the present invention can be applied to the case wherein the substrate is a half-ester of an organic carboxylic acid of α-cyano-benzyl alcohol compound represented by the formula (II) in place of the ester represented by the formula (I). The following Examples further illustrate the invention: Examples 1-8 To 15 mℓ each of an acetate buffer solution having a concentration of 0.2 M (pH 4.0) were added 1.0 g each of acetic acid ester of (R,S)-α-cyano-3-phenoxy-4-fluorobenzyl alcohol and 40 mg each of esterases described in Table 1. The mixtures were allowed to react at 40°C with stirring. After the reaction was conducted for 24 hours, the reaction mixture each was extracted with toluene. The extract was analyzed with a high-performance liquid chromatography (HPLC) [Lichrosorb RP-18, methanol-water (6:4), 254nm, UV detection], and conversion rate was calculated from the peak area ratio of α-cyano-3-phenoxy-4-fluorobenzyl alcohol with acetic acid ester of α-cyano-3-phenoxy-4-fluorobenzyl alcohol. After concentrating the extract each, the concentrate was subjected to a silica gel column chromatography. The elution was conducted with a solution of cyclohexaneethyl ether (95:5) to separate and remove unaltered acetic acid ester of α-cyano-3-phenoxy-4-fluorobenzyl alcohol. Then, the elution was additionally conducted with methanol containing a small amount (10⁻⁵%) of p-toluenesulfonic acid until the free α-cyano-3-phenoxy-4-fluorobenzyl alcohol was obtained. In 1 mℓ each of toluene was dissolved 10 mg each of the free α-cyano-3-phenoxy-4-fluorobenzyl alcohol thus obtained. To this solution each was added equimolar chloride of (S)-(+)-2-(4-chlorophenyl)-isovaleric acid together with pyridine. The mixtures were allowed to react to produce (S)-(+)-2-(4-chlorophenyl)-isovaleric diastereomer of α-cyano-3-phenoxy-4-fluorobenzyl alcohol, respectively. The analysis of the optical isomers was conducted with gas chromatography (column: DCQF-1, 2.5 m, column temperature: 250°C). The results are shown in Table 1. Examples 9-13 To 15 mℓ each of 0.2M concentration of an acetate buffer solution (pH 4.0) were added 2.0 g each of various esters of (R,S)-isomer of α-cyano-benzyl alcohol mentioned in Table 2, the substrate and 40 mg each of esterases listed in Table 2. The mixtures were allowed to react at 40°C with stirring. Thereafter the same operation as in Examples 1-8 was conducted. The results are shown in Table 2. Examples 17-23 In flasks with shoulder (500 mℓ each) were charged 100 mℓ each of a liquid medium, respectively. The medium was sugared bouillon medium for bacteria in Examples 17-19, which is prepared by dissolving 10.0 g of glucose, 5.0 g of peptone and 5.0 g of meat extract in 1 ℓ of water and adjusting the pH to 7.2, or a malt extract-yeast extract medium for fungi and yeast in Examples 20-23, which is prepared by dissolving 5.0 g of peptone, 10.0 g of glucose, 3.0 g of malt extract and 3.0 g of yeast extract in 1 ℓ of water and adjusting the pH to pH 6.5. After sterilization, the medium each was inoculated with 2 platinum loops of slant cultured microorganisms as described in Table 3 and cultured on a reciprocating shaker at 30°C for 72 hours. Then, pH value of the cultured medium each was adjusted to pH 4.5 by using a 2M aqueous solution of hydrochloric acid. To the cultured medium each was added 3.0 g each of acetic acid ester of (R,S)-α-cyano-3-phenoxy-4-fluorobenzyl alcohol. The mixtures were allowed to react at 30°C for 30 hours with stirring, respectively. Thereafter, the separation of the reaction product was conducted in the same manner as in Example 1 and the ratio of optical isomers and the conversion rate of α-cyano-3-phenoxy-4-fluorobenzyl alcohol obtained were measured. The results are shown in Table 3. Examples 24-29 Each of microorganisms described in Table 4 was cultured in the same process as in Examples 17-23. Then, the pH of each culture medium was adjusted to pH 4.5 by using a 2M aqueous HCℓ solution. To this medium each was added 3.0 g of acetic acid ester of (R,S)-α-cyano-3-(4-chlorophenoxy)-4-fluorobenzyl alcohol, and the mixture was allowed to react at 30°C for 30 hours with stirring. Thereafter, the separation of the reaction product was conducted in the same manner as in Example 1, and the ratio of optical isomers and the conversion rate of α-cyano-3-(4-chlorophenoxy)-4-fluorobenzyl alcohol obtained were measured. The results are shown in Table 4.

Claims: A process for producing an (S)-isomer-rich optically active α-cyano-benzyl alcohol compound represented by the formula (II): wherein X is a hydrogen atom, fluorine atom, chlorine atom or bromine atom, which comprises allowing an esterase originating from a micro-organism belonging to a genus selected from Arthrobacter , Alcaligenes , Achromobacter , Pseudomonas , Chromobacterium , Bacillus , Nocardia , Rhodotorula , Candida , Rhizopus , Mucor , Aspergillus , Hansenula and Torulopsis to react at a pH of 7 or less with an ester of the (R,S)-isomer of the α-cyano-benzyl alcohol compound, the said ester being represented by the formula: wherein X has the same meaning as above; R means a hydrogen atom, a C₁-C₁₈ alkyl, C₂-C₁₈ alkenyl, C₂-C₁₈ alkynyl, C₁-C₄ halogen-substituted alkyl, C₂-C₄ halogen-substituted alkenyl, C₂-C₄ halogen-substituted alkynyl, C₁-C₈ alkoxyl, C₂-C₈ alkenyloxy or C₂-C₈ alkynyloxy group, in order to hydrolyze the ester asymmetrically until it is resolved into an (S)-isomer rich α-cyano-benzyl alcohol compound represented by the formula (II) and an antipode ester thereof. A process according to Claim 1 wherein the esterase originates from a microorganism belonging to genus Arthrobacter , genus Alcaligenes , genus Achromobacter , genus Pseudomonas or genus Chromobacterium . A process according to Claim 1 or 2 wherein the substituent group R in the ester of formula (I) is a C₁-C₁₁ alkyl group, C₂-C₁₁ alkenyl group, C₂-C₁₁ alkynyl group, C₁-C₄ alkyl group having a chlorine atom or bromine atom at the α-position thereof, C₂-C₄ alkenyl group having a chlorine atom or bromine atom at the α-position thereof, C₂-C₄ alkynyl group having a chlorine atom or bromine atom at the α-position thereof, or C₁-C₃ alkoxyl group. A process according to Claim 1, 2 or 3 wherein the substituent group R in the ester of formula (I) is a methyl group, ethyl group, monochloromethyl group, monobromomethyl group, methoxy group, ethoxy group or propoxy group. A process according to any one of claims 1 to 4 wherein the asymmetric hydrolysis reaction is conducted at a pH of from 3.5 to 6.0. A process according to any one of claims 1 to 5 wherein the asymmetric hydrolysis reaction is conducted at 20-50°C.

Inventors: HIROHARA, HIDEO 31-18, TAKAKURADAI 4-CHO, MATSUO, NORITADA 29-2, MINAMINO-AZA-YAMAMICHI, MITSUDA, SATOSHI 10-439, SONEHIGASHIMACHI 2-CHOME
Applicants: SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1984
Main classification: C12P13
IPC codes: C12P7, C12P41, C12P13