Method for preparing optically active substances
BACKGROUND OF THE INVENTION 
     The present invention relates to a method for preparing optically active substances and, more particularly, to a method for preparing halohydrin-containing esters or arboxylic acids with high optical purity by efficient symmetric hydrolysis of halohydrin-containing esters with specific microbes. 
     Optically active halohydrins are useful as starting materials for ferroelectric liquid crystals, pharmaceuticals and pesticides, and techniques for preparing halohydrins having optically high purity with improved efficiency are in demand. However, never until now is there any report on methods for making optically active monocarboxylic acid containing halohydrins or their esters with microbes. Heretofore, it has been reported to produce L-threochloromalic acid from chlorofumaric acid with fumarase as one method for producing optically active dicarboxylic acids containing halohydrins or their esters. However, this method is disadvantageous in that the starting materials are not only expensive but also substantially difficult to obtain. Besides, some reports are found in Mem. Fac. Sci. Kyushu Univ., Ser. C., 11(2), 217-224 (1974); Tetrahedron 36(1), 87-90 (1980); and J. Am. Chem. Soc. 110, 7538-7539 (1988), but they all have a disadvantage of using expensive starting materials and other defects. 
     The present inventors have thus made intensive and extensive studies of the preparation of optically active substances containing halohydrins and, in consequence, have found that they can efficiently be prepared by the asymmetric hydrolysis of halohydrin-containing esters with a specific microbe. 
     SUMMARY OF THE INVENTION 
     More specifically, the present invention provides a method for preparing an optically active substance expressed by the following general formula: ##STR2## wherein R 1  stands for a hydrogen atom, an alkyl group or a substituted or unsubstituted phenyl group, R 2  denotes an alkyl group and X indicates a halogen atom, said method being characterized by the asymmetric hydrolysis of an ester expressed by the following formula: ##STR3## wherein R 1  R 2  and X have the same meaning as defined above, with a microorganism capable of asymmetrically hydrolyzing said ester and a method for preparing optically active substances expressed by the following general formulae: ##STR4## wherein R 3  and R 4 , which may be identical with or different from each other, each stand for an alkyl group and X denotes a halogen atom, said method being characterized by the asymmetric hydrolysis of an ester expressed by the following general formula: ##STR5## wherein R 3 , R 4  and X have the same meanings as defined above, with a microorganism capable of asymmetrically hydrolyzing said ester. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As the starting materials in the present invention, use may be made of a halohydrin-containing monocarboxylate expressed by the general formula I: ##STR6## wherein R 1  R 2  and X have the same meanings as defined above, or a halohydrin-containing dicarboxylate expressed by the general formula II: ##STR7## wherein R 3 , R 4  and X have the same meanings as defined above. The halohydrin-containing esters having the general formulae I and II may be of either erythro- or threo-forms. More illustratively, X in the general formulae I and II stands for Cl, Br and I. When R 1  stands for an alkyl group, it may be a lower alkyl group having 1 to 6 carbon atoms or a higher alkyl group having at least 7 carbon atoms. More illustratively, it denotes a methyl, ethyl, propyl, heptyl, octyl group, etc. The substituted phenyl group may be a phenyl group, one or more of hydrogen atoms of which are substituted by a halogen atom, a hydroxyl group, a methoxy group or an alkyl (e.g., methyl, ethyl or propyl) group. R 2  R 3  and R 4  may be identical with or different from each other, and each stand for a lower alkyl group having 1 to 6 carbon atoms or a higher alkyl group having at least 7 carbon atoms. More illustratively, they indicate methyl, ethyl, propyl, heptyl, and octyl groups. 
     In the present invention, any microorganisms suitable for the asymmetric hydrolysis of the above halohydrin-containing esters may be used, inclusive of those belonging to the following genera: Achromobacter, Acinetobacter, Arthrobacter, Ervinia, Enterobacter, Klebsiella, Chromobacterium, Corynebacterium, Pseudomonas, Bacteridium, Bacillus, Paracoccus, Flavobacterium, Brevibacterium, Proteus, Micrococcus, Rhodococcus, Candida, Nocardia, and Rhodotorula. Illustrative reference is made to Achromobacter lyticus IFO 12725, Achromobacter lyticus IFO 12726, Acinetobacter calcoaceticus IFO 12552, Arthrobacter sp. ATCC 27778, Erwinia herbicola ATCC 21434, Enterobacter sp. IAM 12247, Klebsiella pneumoniae IFO 3318, Chromobacterium chocolatum IFO 3758, Corynebacterium flavescens IAM 1642, Corynebacterium hydrocarbooxydans ATCC 21767, Pseudomonas aeruginosa ATCC 15522, Pseudomonas aeruqinosa ATCC 15523, Pseudomonas diminuta IFO 13181, Pseudomonas dimimuta IFO 13182, Pseudomonas pseudoalcaligenes ATCC 12815, Pseudomonas oleovorans ATCC 29347, Bacteridium sp. CBS 495-74,  Bacteridium sp. CBS 496-74, Bacillus cereus IFO 3131, Bacillus subtilis IFO 3108, Bacillus sp. CBS 494-74, Paracoccus denitrificans IFO 13301, Flavobacterium lutescens IFO 3084, Brevibacterium sp. CBS 717-73, Brevibacterium imperiale CBS 498-74, Brevibacterium paraffinoliticum ATCC 21195, Proteus mirabilis IFO 3849, Micrococcus sp. CBS 497-74, Micrococcus paraffinolyticus ATCC 15582, Rhodococcus erythropolis IFO 12320, Rhodococcus equi IFO 3730, Candida rugosa ATCC 14830 and Rhodotorula minuta var. texensis IFO 879, Norcardia sp. ATCC 21145. These microorganisms may be used alone or in combination of two or more. 
     The microorganisms may be applied in varied forms. For instance, proliferating, resting and immobilized microorganisms may be used. Further, use may be made of microbial extracts or culture solution. Microbial immobilization may be achieved by conventional immobilization techniques such as carrier bonding method, crosslinking method, inclusion method and the like. For extraction methods, microbial cells in a suspension are subjected to crushing by using ultrasonics waves, a French press, a high-pressure homogenizer, etc. and then by solid-liquid separation by, for example, centrifugation to give the soluble fraction. 
     No particular limitation is placed on culture media for culturing the above microorganisms. Use may thus be made of any medium suitable for the growth of the above microorganisms, e.g., a bouillon medium. 
     The starting halohydrin-containing esters expressed by the above general formulae I and II may be subjected to asymmetric hydrolysis at a concentration of 1 to 500 g/1, preferably 5 to 100 g/1 at a temperature of 0° to 60° C., preferably 10° to 40° C. and in a pH range of 4 to 11, preferably 6 to 8. The reaction may be carried out under aerobic or anaerobic conditions, which may be determined while taking the nature of the microorganisms used into consideration. It is understood that such reaction conditions may be selected depending upon the microorganisms used with a view to keeping them stable and obtaining the desired product with efficiency. 
     The starting halohydrin-containing esters expressed by the above general formula I or II may be added to a reaction system at a start of the reaction or added to the system from the outset with its additional feeding at any suitable time after the initiation of the reaction. The feed may be added to the reaction system in a batch or batches, or in continuous manners. 
     Thus, the halohydrin-containing monocarboxylates expressed by the above general formula I yield the halohydrin-containing, optically active esters and/or carboxylic acids expressed by the formulae: ##STR8## wherein R 1  R 2  and X have the same meanings as already indicated. The dicarboxylates expressed by the general formula II also yield the halohydrin-containing, optically active esters and/or monocarboxylic monoesters expressed by the formulae: ##STR9## wherein R 3 , R 4  and X have the same meanings as already indicated. No critical limitation is imposed upon the separation and purification of the resulting products. For instance, reliance may be placed upon conventional means in which distillation is directly applied or before distillation, absorption or desorption with activated charcoal, zeolite, etc. or extraction with organic solvents may be applied. 
     According to the present invention, the halohydrincontaining esters and carboxylic acids, both having high optical purity, can be produced at low costs and with improved efficiency. The obtained halohydrin-containing, optically active esters and carboxylic acids provide useful intermediates for chemicals, liquid crystals, pharmaceuticals and pesticides. 
     In the following, the method of the present invention is described in more detail by way of examples. 
    
    
     EXAMPLE 1 
     Corynebacterium flavescens IAM 1642 was inoculated on 150 ml of a bouillon medium (Nissui Seiyaku Co., Ltd.) and cultured at 30° C. overnight. After culturing, the microbial cells were collected and washed, and were then suspended at OD 660  = 5 in a 1/15M phosphate buffer of pH 7 containing 5 g/1 of ethyl erythro-2-chloro-3-hydroxybutyrate and a reaction was performed for 7 hours at 30° C. The residues of the substrate added was determined by gas chromatography with a condition of a carrier of PEG-20 M, a column length of 2 meters and a column temperature of 150° C. Consequently, the rate of hydrolysis after the completion of the reaction was found to be 56%. After hydrochloric acid had been added to the reaction solution to regulate its pH to 2, the microbial cells were removed by centrifugation, and the supernatant was then extracted with diethyl ether. After transferring 2-chloro-3-hydroxybutyric acid into the aqueous phase with saturated sodium bicarbonate, ethyl 2-chloro-3-hydroxybutyrate in the ether phase was obtained, followed by drying and evaporation of the solvent in vacuo. On the other hand, 2-chloro-3-hydroxybutyric acid being transferred into the aqueous phase was obtained by regulating its pH to 2 by the addition of hydrochloric acid, extracting with diethyl ether followed by a subsequent drying and evaporation of the solvent in vacuo. It is noted that ethyl 2-chloro-3-hydroxybutyrate and 2-chloro-3-hydroxybutyric acid were identified by gas chromatography. Subsequently, the products were measured in terms of their optical purity by high performance liquid chromatography (Chiralcel OB made by Daicel Chemical Industries, Ltd.) and their rotatory polarization by a polarimeter (SEPA-100 made by Horiba Co., Ltd.). In consequence, it was found that (+)ethyl-erythro-2-chloro-3-hydroxybutyrate with an optical purity of 99% ee and (-)-erythro-2-chloro-3-hydroxybutyric acid with an optical purity of 68% ee were obtained in yields of 0.92 g and 0.85 g, respectively. It is noted that the optical purity of 2-chloro-hydroxybutyric acid was determined after converted to the corresponding ethyl ester. 
     EXAMPLES 2 to 19 
     The procedure of Example 1 was substantially repeated except that the microorganisms set forth in Table 1 were used in place of Corynebacterium flavescens IAM 1642. The results are indicated in Table 1. 
     
                                           TABLE 1                                 
__________________________________________________________________________
                         Rate of Optical Rotatory                         
Example                                                                   
     Microorganisms used hydrolysis (%)                                   
                                 purity* (% ee)                           
                                         polarization                     
__________________________________________________________________________
 2   Achromobacter lyticus IFO12726                                       
                         63      31      +                                
 3   Acinetobacter calcoaceticus IFO12552                                 
                         53      69      -                                
 4   Arthrobacter sp. ATCC27778                                           
                         86      99      -                                
 5   Ervinia herbicola ATCC21434                                          
                         76      89      -                                
 6   Enterobacter sp. IAM12247                                            
                         51      17      -                                
 7   Klebsiella pneumoniae IFO3318                                        
                         83      57      +                                
 8   Chromobacterium chocolatum IFO3758                                   
                         61      100     +                                
 9   Pseudomonas oleovorans ATCC29347                                     
                         22      43      -                                
10   Bacteridium sp. CBS495-74                                            
                         72      71      -                                
11   Bacillus cereus IFO3131                                              
                         80      28      +                                
12   Paracoccus denitrificans IFO13301                                    
                         68      41      +                                
13   Flavobacterium lutescens IFO3084                                     
                         52      59      +                                
14   Brevibacterium sp. CBS717-73                                         
                         62      52      -                                
15   Proteus mirabilis IFO3849                                            
                         42      18      -                                
16   Micrococcus sp. CBS497-74                                            
                         66      67      -                                
17   Rhodococcus erythropolis IFO12320                                    
                         66      56      +                                
18   Candida rugosa ATCC14830                                             
                         56      20      -                                
19    Rhodotorula minuta var. texensis IFO879                             
                         39      32      -                                
__________________________________________________________________________
 *Optical purity of unreacted starting material after the completion of   
 reaction.                                                                
 
    
     EXAMPLES 20 &amp; 21 
     The procedure of Example 1 was substantially repeated, provided however that the starting materials and microorganisms set forth in Table 2 were used. The results are summarized in Table 2. It is noted that the identification of the products and the measurement of their optical purity and rotatory polarization were carried out in similar manners as applied in Example 1. 
     
                                           TABLE 2                                 
__________________________________________________________________________
                                                Rate of                   
                                                     Optical              
                                                          Rotatory        
     Microorganisms                             hydroly-                  
                                                     purity*.sup.1        
                                                          polari-         
Example                                                                   
     used      Starting material                                          
                                Products        sis (%)                   
                                                     (%                   
                                                          zation          
__________________________________________________________________________
20   Corynebacterium flavescens IAM 1642                                  
                ##STR10##                                                 
                                 ##STR11##      59   100  nd*.sup.2       
21   Pseudomonas aeruginosa ATCC 15522                                    
                ##STR12##                                                 
                                 ##STR13##      49     37*.sup.3          
                                                          +               
__________________________________________________________________________
 *.sup.1 Optical purity of unreacted starting material after the completio
 of reaction                                                              
 *.sup.2 Undetermined                                                     
 *.sup.3 For optical splitting, Eu(tfmc).sup.3 was added as a shift reagen
 (LSR) and determination was carried out by .sup.1 HNMR.                  
 
    
     EXAMPLES 22 to 35 
     The procedure of Example 1 was substantially repeated, except that the microorganisms set forth in Table 3 were used in place of Corynebacterium flavescens IAM 1642. The results are shown in Table 3. 
     
                                           TABLE 3                                 
__________________________________________________________________________
                      Rate of Optical Rotatory                            
Example                                                                   
     Microorganisms used                                                  
                      hydrolysis (%)                                      
                              purity* (% ee)                              
                                      polarization                        
__________________________________________________________________________
22   Achromobacter lyticus                                                
                      64      29      +                                   
     IFO12725                                                             
23   Corynebacterium hydrocarbooxydans                                    
                      77      35      -                                   
     ATCC21767                                                            
24   Pseudomonas aeruginosa                                               
                      38      18      -                                   
     ATCC15522                                                            
25   Pseudomonas aeruginosa                                               
                      34      19      -                                   
     ATCC15523                                                            
26   Pseudomonas diminuta                                                 
                      87      36      +                                   
     IFO13181                                                             
27   Pseudomonas diminuta                                                 
                      81      30      +                                   
     IFO13182                                                             
28   Pseudomonas pseudoalcaligenes                                        
                      46      19      -                                   
     ATCC12815                                                            
29   Bacteridium sp.  57      32      -                                   
     CBS946-74                                                            
30   Bacillus subtilis                                                    
                      59      52      +                                   
     IFO3108                                                              
31   Bacillus sp.     49      46      -                                   
     CBS494-74                                                            
32   Brevibacterium imperiale                                             
                      82      90      -                                   
     CBS498-74                                                            
33   Brevibacterium paraffinoliticum                                      
                      34      21      -                                   
     ATCC21195                                                            
34   Micrococcus paraffinolyticus                                         
                      64      44      -                                   
     ATCC15582                                                            
35   Rhodococcus equi 34      20      -                                   
     IFO3730                                                              
__________________________________________________________________________
 *Optical purity of unreacted starting material after the completion of   
 reaction.                                                                
 
    
     EXAMPLE 36 
     Corynebackerium flavescens IAM 1642 was inoculated on 25 l of a bouillon medium (Nissui Seiyaku Co., Ltd.) and cultured at 30° C. for 45 hrs. After culturing, the microbial cells were collected and washed, and were then suspended at OD 660  = 5 in a 1/15M 2-(N-Morpholine) ethanesulfornic acid buffer of pH 6, which is called MES buffer purchased from DOJINDO Laboratories, containing 25 g/1 of ethyl erythro-2-chloro-3-hydroxybutyrate and a reaction was performed for 118 hrs. 
     It is noted that the identification of the products and the measurement of their optical purity and rotatory polarization were carried out in similar manners as applied in Example 1. In consequence, the rate of hydrolysis was found to be 75%, and it was found that (+)-ethyl erythro-2-chloro-3-hydroxy butyrate with an optical purity of 98% ee and (-)-erythro-2-chloro-3-hydroxybutyric acid with an optical purity of 46% ee were obtained in yields of 32.47 g and 87.20 g, respectively. 
     EXAMPLES 37 to 50 
     The procedure of Example 1 was substantially repeated, provided however that ethyl 2-chloro-3-hydroxypropionate was used for the starting material and microorganisms set forth in Table 4 were used and that the reaction was formed at OD 660  = 10. The results are shown in Table 4. 
     
                                           TABLE 4                                 
__________________________________________________________________________
                      Rate of Optical Rotatory                            
Example                                                                   
     Microorganisms used                                                  
                      hydrolysis (%)                                      
                              purity* (% ee)                              
                                      polarization                        
__________________________________________________________________________
37   Chromobacterium chocolatum                                           
                      64      98      +                                   
     IFO3758                                                              
38   Corynebacterium flavescens                                           
                      59      100     +                                   
     IAM1642                                                              
39   Corynebacterium hydrocarbooxydans                                    
                      73      21      +                                   
     ATCC21767                                                            
40   Pseudomonas aeruginosa                                               
                      34      17      -                                   
     ATCC15522                                                            
41   Pseudomonas diminuta                                                 
                      69      31      -                                   
     IFO13181                                                             
41   Pseudomonas diminuta                                                 
                      74      36      -                                   
     IFO13182                                                             
43   Bacteridium sp.  71      16      +                                   
     CBS495-74                                                            
44   Bacteridium sp.  82      32      +                                   
     CBS496-74                                                            
45   Flavobacterium lutescens                                             
                      50      25      +                                   
     IFO3084                                                              
46   Micrococcus paraffinolyticus                                         
                      75      27      +                                   
     ATCC15582                                                            
47   Micrococcus sp.  77      28      +                                   
     CBS497-74                                                            
48   Nocardia sp.     57      24      -                                   
     ATCC21145                                                            
49   Rhodococcus erythropolis                                             
                      74      13      -                                   
     IFO12320                                                             
50   Rhodococcus equi 74      21      +                                   
     IFO3730                                                              
__________________________________________________________________________
 *Optical purity of unreacted starting material after the completion of   
 reaction.                                                                
 
    
     EXAMPLE 51 
     Chromobacterium chocolatum IFO 3758 was inoculated on medium which contains 20 g of soluble starch (Extra pure reagent, Wako Pure Chemical Industries, Ltd., Osaka), 10 g of Bact Yeast extract (Difco Laboratories, Detroit, Mich., USA), 10 g of Polypepton (Nippon Seiyaku Co., Ltd.) and 2 liters of distilled water, and cultured for 48 hours. After culturing, the microbial cells were collected and washed, and were then suspended at OD 660  = 30 in a 1/15M MES buffer (DOJINDO Laboratories) of pH 6 containing 50 g/l of ethyl 2-chloro-3-hydroxypropionate and a reaction was performed at 30° C. for 8 hours. In consequence, the rate of hydrolysis was found to be 77%, and it was found that (+) ethyl 2-chloro-3-hydroxypropionate with an optical purity of 98% ee and (-) 2-chloro-3-hydroxypropionic acid were obtained in yields of 1.9 g and 4.1 g, respectively.