Abstract:
The present invention relates to a process for producing an optically active 2-substituted propanal derivative, and more particularly, a process for producing an optically active 2-substituted propanal derivative which comprises stereoselectively reducing a carbon-carbon double bond of a 2-substituted acrolein derivative by using an enzyme source capable of stereoselectively reducing said carbon-carbon double bond. According to the present invention, it becomes possible to produce an optically active 2-substituted propanal derivative, in particular an optically active 2-alkylpropanal derivative, which is useful as an intermediate of pharmaceutical products, sweetening agents, etc., in a convenient manner from inexpensive and easily available materials.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a process for producing an optically active 2-substituted propanal derivative, in particular an optically active 2-alkylpropanal derivative, which is useful as an intermediate of pharmaceutical products, sweetening agents, etc. More particularly, the present invention relates to a process for producing an optically active 2-substituted propanal derivative, in particular an optically active 2-alkylpropanal derivative, which comprises stereoselectively reducing a 2-substituted acrolein derivative, which is available at low cost, by using an enzyme source capable of stereoselectively reducing a carbon-carbon double bond of the derivative. 
       REFERENCE OF RELATED APPLICATIONS 
       [0002]    The whole disclosure including the description, the claims, the drawings and the abstract in Japanese Patent 2005-158393 (filed on 2005, May 31) is herein incorporated in the present application by reference. 
       BACKGROUND ART 
       [0003]    At present, methods mentioned below are known as processes for producing an optically active 2-substituted propanal derivative. 
         [0000]    1) A method for synthesizing (R)-2-methylpentanal with the optical purity of 94% ee by asymmetric alkylation of propanal using a proline derivative as an asymmetric auxiliary group (Non-Patent Document 1).
 
2) A method for synthesizing optically active 2-methylpentanal which comprises reducing 2-methyl-2-pentenal by a microorganism using  Beauveria Sulfurescens  to obtain optically active 2-methyl-1-pentanol and oxidizing the same. (Non-Patent Document 2).
 
         [0004]    Non-Patent Document 1: New Journal of Chemistry, 24(12), 973-975 (2000) 
         [0005]    Non-Patent Document 2: Tetrahedron, 37(22), 3825-3829 (1981) 
       SUMMARY OF THE INVENTION 
       [0006]    The above method 1) requires use of an expensive asymmetric auxiliary group for the asymmetric alkylation reaction. And by the above method 2), a large amount of 2-methyl-2-pentene-1-ol is produced as a byproduct. 
         [0007]    In view of the above-mentioned state of the art, the present invention has for its object to provide a process for producing an optically active 2-substituted propanal derivative, in particular an optically active 2-alkylpropanal derivative, which is useful as an intermediate of pharmaceutical products, sweetening agents, etc., in a convenient manner from inexpensive and easily available materials. 
         [0008]    The present inventors had made intensive investigations for solving the above-mentioned subjects, and as a result, found a process for producing, in a convenient manner, an optically active 2-substituted propanal derivative which comprises stereoselectively reducing a 2-substituted acrolein derivative, which is available at low cost, by using an enzyme source capable of stereoselectively reducing a carbon-carbon double bond of the derivative. 
         [0009]    That is, one of the features of the present invention is to provide 
         [0010]    a process for producing an optically active 2-substituted propanal derivative represented by the general formula (2): 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    (in the formula, R is a methyl group having a substituent, an alkyl group containing 2 to 10 carbon atoms which may optionally be substituted, or an aralkyl group containing 5 to 15 carbon atoms which may optionally be substituted, and * is an asymmetric carbon) 
         [0011]    which comprises reacting a 2-substituted acrolein derivative represented by the general formula (1): 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    (in the formula, R is as mentioned above) with an enzyme source capable of stereoselectively reducing the carbon-carbon double bond of said 2-substituted acrolein derivative (1). 
       EFFECT OF THE INVENTION 
       [0012]    Other features of the present invention and those effects are shown in the following embodiment and FIGURE. 
         [0013]    By the above-mentioned process of the present invention, an optically active 2-substituted propanal derivative which is useful as an intermediate of pharmaceutical products, sweetening agents, etc. can be produced in a convenient manner from inexpensive materials. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0014]      FIG. 1  is a schematic view of the process for producing a recombinant vector pTSYE2G1 and the constitution thereof. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     1. 2-Substituted Acrolein Derivative (Starting Material) 
       [0015]    First, compounds involved with the embodiment of the present invention are described. A starting material used in the process according to the embodiment of the invention is the 2-substituted acrolein compound represented by the above formula (1). As a substituent R in the formula (1), there may be mentioned a methyl group having a substituent, an alkyl group containing 2 to 10 carbon atoms which may optionally be substituted, or an aralkyl group containing 5 to 15 carbon atoms which may optionally be substituted. 
         [0016]    When substituted, the substituent is not particularly restricted as long as there is no adverse effect on the reaction caused by the enzyme source but, there may be mentioned, for example, a halogen atom, a hydroxyl group, an aldehyde group, a carboxyl group, a cyano group, an amino group, a nitro group, or the like substituent. 
         [0017]    As the methyl group having a substituent, there may be mentioned, for example, a chloromethyl group, a bromomethyl group, an iodomethyl group, a hydroxymethyl group, an aminomethyl group, a cyanomethyl group, or the like group. 
         [0018]    As the alkyl group containing 2 to 10 carbon atoms which may optionally be substituted, there may be mentioned a substituted or unsubstituted ethyl group, n-propyl group, iso-propyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, n-hexyl group, or the like group. When the alkyl group contains a substituent, the substituent is not particularly restricted as long as the reduction reaction of the invention is not adversely affected but, there may be mentioned a halogen atom, a hydroxyl group, an amino group, a cyano group, or the like group as the substituent. 
         [0019]    As the aralkyl group containing 5 to 15 carbon atoms which may optionally be substituted, there may be mentioned a benzyl group, an o-chlorobenzyl group, a m-bromobenzyl group, a p-fluorobenzyl group, a p-nitrobenzyl group, a p-cyanobenzyl group, a m-methoxybenzyl group, a phenethyl group, a naphthylmethyl group, a pyridylmethyl group, or the like group. 
         [0020]    Preferred as R among the above-mentioned groups, an alkyl group containing 2 to 10 carbon atoms which may optionally be substituted, more preferred is an alkyl group containing 2 to 4 carbon atoms which may optionally be substituted, still more preferred is an ethyl group, an n-propyl group or an n-butyl group, and most preferred is an n-butyl group. 
         [0021]    The compound represented by the above formula (1) is industrially available, or can be easily synthesized from materials which are industrially available. For example, 2-butylacrolein can be easily synthesized by stirring a mixture comprising n-hexanal, dimethylamine hydrochloride and a 37% formalin solution at 70° C. for 24 hours (refer to Journal of chemical research, Synopses 7, 262-3 (1978)). 
       2. Optically Active 2-Substituted Propanal Derivative (Product) 
       [0022]    The product obtained in the process according to the embodiment is the optically active 2-substituted propanal derivative represented by the above formula (2). In the above formula (2), R is the same as in the formula (1), and * is an asymmetric carbon. 
       3. Process for Producing an Optically Active 2-Substituted Propanal Derivative 
       [0023]    Next, the process for producing an optically active 2-substituted propanal derivative according to the embodiment of the invention is described. 
         [0024]    According to the embodiment, the optically active 2-substituted propanal derivative of the above formula (2) is produced by stereoselectively reducing a carbon-carbon double bond of the 2-substituted acrolein derivative of the above formula (1) in the presence of an enzyme source having an activity of stereoselectively reducing the carbon-carbon double bond of said 2-substituted acrolein derivative (1). 
       4. Enzyme Source 
       [0025]    Herein, “an enzyme source” includes an enzyme having the above-mentioned reduction activity, as well as a culture of microorganisms having the above-mentioned reduction activity and a processed product thereof. “A culture of microorganisms” refers to a culture medium containing cells or cultured cells, and also a processed product thereof is included therein. “A processed product thereof” refers to, for example, a crude extract, lyophilized cells, acetone-dried cells, and a product derived from those cells by grinding. Moreover, the enzyme source mentioned above can be immobilized by a method known in the art and used as an immobilized enzyme or an immobilized cell. The immobilization can be carried out by the method known to the person skilled in the art (for example, a crosslinking method, a physical adsorption method, an inclusion method, etc.). 
         [0026]    According to the embodiment, as the enzyme source having an activity of stereoselectively reducing the carbon-carbon double bond of the compound of the above formula (1), there may be mentioned those derived from a microorganism belonging to the genus  Candida , the genus  Kluyveromyces , the genus  Pichia , the genus  Rhodotorula , the genus  Saccharomyces , the genus  Sporidiobolus , the genus  Spolobolomyces , the genus  Trigonopsis , the genus  Zygosaccharomyces , the genus  Achromobacter , the genus  Acidiphilium , the genus  Alcaligenes , the genus  Arthrobacter , the genus  Bacillus , the genus  Corynebacterium , the genus  Escherichia , the genus  Micrococcus , the genus  Pseudomonas , the genus  Paenibacillus , or the genus  Xanthomonas.    
       4-1. Enzyme Source (Examples of an Enzyme Source Having an Activity of R-Selective Reduction) 
       [0027]    Among the above-mentioned enzyme sources, as the enzyme source having an activity of R-selectively reducing the carbon-carbon double bond of the compound of the above formula (1), preferred are those derived from microorganisms such as  Candida cantarellii, Candida etchellsii, Candida kefyr, Candida musae, Candida nitratophila, Candida sake, Candida stellata, Candida zeylanoides, Kluyveromyces lactis  var.  drosphilarum, Pichia membranaefaciens, Pichia heedii, Rhodotorula minuta, Saccharomyces unisporus, Saccharomyces bayanus, Saccharomyces cerevisiae, Saccharomyces castellii, Saccharomyces pastorianus, Sporidiobolus johnsonii, Sporidiobolus salmonicolor, Spolobolomyces salmonicolor, Trigonopsis variabilis, Zygosaccharomyces bailii, Arthrobacter nicotianae, Acidiphilium cryptum, Bacillus cereus, Bacillus coagulans, Bacillus lichenifonnis, Bacillus pumilus, Bacillus badius, Bacillus sphaericus, Micrococcus luteus, Pseudomonas stutzeri, Pseudomonas fragi, Pseudomonas putida, Paenibacillus alvei  and  Xanthomonas  sp. 
       4-2. Enzyme Source (Examples of an Enzyme Source Having an Activity of S-Selective Reduction) 
       [0028]    As the enzyme source having an activity of S-selectively reducing the carbon-carbon double bond of the compound of the above formula (1), preferred are those derived from microorganisms such as  Achromobacter xylosoxidans  subsp.  denitrificans, Alcaligenes faecalis, Alcaligenes  sp.,  Arthrobacter crystallopoietes, Arthrobacter protophormise, Corynebacterium ammoniagenes , and  Escherichia coli.    
       5. Microorganism 
       [0029]    In addition, the microorganism from which the above-mentioned reduction enzymes are derived may be a wild strain or a variant. A microorganism derived by a genetic engineering technique such as cell fusion or gene manipulation can be used as well. 
         [0030]    Furthermore, it is also possible to use a recombinant microorganism capable of producing a reductase derived from these microorganisms. The recombinant microorganism capable of producing such enzyme can be obtained, for example, by a method comprising a step of isolating and/or purifying such enzyme and then determining a part or whole of the amino acid sequence thereof, a step of obtaining a DNA sequence coding for the enzyme based on the amino acid sequence mentioned above, a step of obtaining a recombinant microorganism by introducing the DNA mentioned above into another microorganism, and a step of obtaining the enzyme by culturing the recombinant microorganism mentioned above (refer to the process disclosed in International Publication WO98/35025). 
         [0031]    As such recombinant microorganism mentioned above, there may be mentioned one obtained by transforming a host microorganism with a vector containing DNA coding for said reductase. As the host microorganism,  Escherichia coli  is preferred. More preferred is  Escherichia coli  HB101 (pTSYE2) transformed with a vector containing a gene of NADPH dehydrogenase derived from  Saccharomyces cerevisiae  (Old Yellow Enzyme 2) mentioned above (refer to The Journal of Biological chemistry, 268, 6097-6106 (1993)), and the like. The process for obtaining  Escherichia coli  HB101 (pTSYE2) is described in below-mentioned Example 7. 
         [0032]    Furthermore, as the above enzyme source, it is also possible to use an oxidoreductase classified into EC 1.6.99 according to the enzyme taxonomy of International Union of Biochemistry and Molecular Biology. As the oxidoreductases classified into EC 1.6.99, there may be mentioned an enzyme classified into EC 1.6.99.1: NADPH dehydrogenase, an enzyme classified into EC 1.6.99.2: NAD(P)H dehydrogenase (quinone), an enzyme classified into EC 1.6.99.3: NADH dehydrogenase, an enzyme classified into EC 1.6.99.5: NADH dehydrogenase (quinone), and an enzyme classified into EC 1.6.99.6: NADPH dehydrogenase (quinone). Among these, NADPH dehydrogenase classified into EC 1.6.99.1 (another name: Old Yellow Enzyme) is preferred. 
         [0033]    It has been reported that NADPH dehydrogenase is widely distributed among yeast belonging to the genus  Candida , the genus  Kluyveromyces , the genus  Saccharomyces , or the genus  Schizosaccharomyces . In particular, NADPH dehydrogenase derived from  Saccharomyces cerevisiae  (Old Yellow Enzyme 2) is preferred. 
         [0034]    The culture medium for the microorganism which is used as an enzyme source is not particularly restricted so long as the microorganism can grow thereon. For example, a normal liquid medium containing, as a carbon source, sugar such as glucose and sucrose, alcohols such as ethanol and glycerine, fatty acids such as oleic acid and stearic acid, and esters thereof, oils such as rapeseed oil and soybean oil; as a nitrogen source, ammonium sulfate, sodium nitrate, peptone, casamino acid, corn steep liquor, bran, yeast extract, etc.; as a inorganic salt, magnesium sulfate, sodium chloride, calcium carbonate, calcium monohydrogen phosphate, potassium dihydrogen phosphate, etc.; and, as an other nutrition source, malt extract, meat extract, etc. Culture is carried out aerobically, and usually, culture period is about 1 to 5 days, pH of the medium is 3 to 9, and culture temperature is 10 to 50° C. 
       6. Reduction Reaction 
       [0035]    In the embodiment, the reduction reaction of the carbon-carbon double bond in the compound represented by the above formula (1) can be carried out by adding the 2-substituted acrolein derivative of the formula (1) to serve as a substrate, the coenzyme NAD(P)H, and a cultured product derived from the above microorganism or a processed product thereof to an appropriate solvent, and stirring the mixture under pH adjustment. 
         [0036]    The conditions of the above reduction reaction are various depending on the enzyme and the microorganism or processed product thereof to be used, concentration of the substrate, and the like. Generally, concentration of the substrate may be approximately 0.1 to 100% by weight and preferably 1 to 60% by weight, concentration of the coenzyme NAD(P)H may be 0.0001 to 100 mole % and preferably 0.0001 to 0.1 mole % relative to the concentration of the substrate, the reaction temperature may be 10 to 60° C. and preferably 20 to 50° C., the pH during the reaction may be 4 to 9 and preferably 5 to 8, and the reaction period may be 1 to 120 hours and preferably 1 to 72 hours. In addition, an organic solvent can be used as a mixture with the other ingredients in the reaction. As an organic solvent, there may be mentioned, for example, toluene, ethyl acetate, n-butyl acetate, hexane, isopropanol, methanol, diisopropyl ether, acetone, dimethyl sulfoxide, and the like. 
         [0037]    The substrate can be added at once or continuously. The reaction can be carried out batchwise or continuously. 
       7. Reduction Reaction (Example Using a Coenzyme Regenerating System) 
       [0038]    In the reduction process of the embodiment, it is possible to use a coenzyme NAD(P)H regenerating system, which is generally used in combination. Thereby, the amount of use of an expensive coenzyme can be substantially decreased. As a representative NAD(P)H regenerating system, there may be mentioned, for example, a process using glucose dehydrogenase and glucose. 
         [0039]    When a transformed microorganism prepared by introducing a gene of a reductase and a gene of an enzyme (e.g., glucose dehydrogenase) capable of regenerating a coenzyme to be a part of the reductase into one and the same host microorganism, that is, a cultured product of a transformed microorganism prepared by introducing DNA coding for the reductase according to the embodiment and a gene of an enzyme (e.g., glucose dehydrogenase) capable of regenerating a coenzyme to be a part of the reductase into one and the same host microorganism, or a processed product thereof, etc. is used to carry out the same reaction as mentioned above, the optically active 2-substituted propanal derivative can be produced at lower cost since it is not necessary to prepare separately an enzyme source required for regenerating the coenzyme. 
         [0040]    As such transformed microorganism mentioned above, there may be mentioned one transformed with a plasmid containing both of the above-mentioned DNA coding for a reductase and DNA coding for an enzyme capable of regenerating a coenzyme to be a part of the reductase. Herein, as the enzyme capable of regenerating the coenzyme, glucose dehydrogenase is preferred, and glucose dehydrogenase derived from  Bacillus megaterium  is more preferred. And as the host microorganism,  Escherichia coli  is preferred. As such preferable transformed microorganism,  Escherichia coli  HB101 (pTSYE2G1) described in Examples below can be mentioned. 
         [0041]    The transformed microorganism can be cultured on a liquid nutrient medium containing ordinary carbon sources, nitrogen sources, inorganic salts, organic nutrients and so forth so long as the microorganism can grow thereon. 
         [0042]    In addition, the activity of the enzyme capable of regenerating a coenzyme in the transformed microorganism can be determined by conventional methods. For example, the activity of glucose dehydrogenase can be calculated by adding 100 mM of glucose, 2 mM of the coenzyme NADP or NAD, and the enzyme into 1M tris hydrochloride buffer (pH 8.0), subjecting the obtained mixture to reaction at 25° C. for 1 minute, and measuring the rate of increase in absorbance at a wavelength of 340 nm. 
         [0043]    When the reduction process of the invention is carried out in combination with a coenzyme regeneration system, or a cultured product of the above recombinant microorganism or the processed product thereof is used as the enzyme source, it is also possible to carry out the reaction by using, as a coenzyme, oxidized NAD(P) available at lower cost. 
       8. Purification of an Optically Active 2-Substituted Propanal Derivative 
       [0044]    A process for purifying the optically active 2-substituted propanal derivative produced by the reduction reaction is not particularly restricted. For example, the derivative can be purified by extracting the same with an organic solvent, for example, ethyl acetate, toluene, t-butylmethyl ether, hexane and methylene chloride, directly or after separating cells, etc. from a reaction mixture, and then subjecting the extract to dehydration, concentration, and processes such as distillation and chromatography. For the separation of cells from a reaction mixture, conventional methods such as centrifugation and filtration can be used. 
       9. Conversion into Other Derivatives 
       [0045]    After obtaining the optically active 2-substituted propanal derivative of the above formula (2) by the above-mentioned processes, oxidation of an aldehyde group of said compound can produce an optically active 2-substituted propionate derivative. Alternatively, reduction of an aldehyde group of the compound of the formula (2) can produce an optically active 2-substituted propanol derivative. 
         [0046]    As a process for oxidizing an aldehyde group, there may be mentioned a chemical technique using potassium permanganate (KMnO 4 ), chromic acid (CrO 3 ), nitric acid, and the like, or an enzymatic technique using an aldehyde dehydrogenase, and the like. Either technique can be used. 
         [0047]    Furthermore, as a process for reducing an aldehyde group, there may be mentioned a chemical technique using a metal hydride such as lithium aluminum hydride (LiAlH 4 ) and sodium borohydride (NaBH 4 ), or an enzymatic technique using an aldehyde reductase, and the like. Either technique can be used. 
       BEST MODE FOR CARRYING OUT THE INVENTION 
       [0048]    The following examples illustrate the present invention in further detail. These examples are, however, by no means limitative of the scope of the invention. 
       Example 1 
     Process for Producing Optically Active 2-Methyl-1-Hexanal 
       [0049]    A liquid medium (pH 6.5) comprising glucose (5%), peptone (1%) and yeast extract (1%) was prepared to be dispensed into 500 ml Sakaguchi flasks by 50 ml fractions, and each flask was subjected to steam sterilization at 120° C. for 20 minutes. A loopful of the microorganisms shown in Table 1 was respectively inoculated into each of these liquid media to be subjected to shaking culture at 30° C. for 2 to 3 days. Cells were separately collected from each of these culture media by centrifugation, washed with water, added with ice-cold acetone, and then subjected to vacuum drying to prepare acetone dried cells. Each 5-mg-portion of the obtained acetone dried cells was scaled into a test tube equipped with a plug, and then suspended into 500 μl of 100 mM phosphate buffer (pH 6.5). To each of these solutions, glucose 25 mg, NAD and NADP, 0.5 mg of each, and glucose dehydrogenase (product of Amano Enzyme Inc.) 5 U were added. After each 2-mg-portion of the substrate 2-butylacrolein was dissolved in a 500-μl-portion of ethyl acetate to be added into each of the test tubes each equipped with a plug, these tubes were stirred at 30° C. for 20 hours. After the reaction, each reaction mixture was centrifuged, and each of the substrate together with the product in an ethyl acetate layer was converted into trifluoroacetyl derivative thereof to be analyzed with gas chromatography (GC). Thus, the reaction conversion rates and optical purities of the products were determined. The results are shown in Table 1 (the reaction conversion is 10 to 100%). 
         [0050]    The analysis conditions and the method for calculating the reaction conversion rate and optical purity were as follows. 
       [GC Analysis Conditions] 
       [0051]    Capillary column: Cyclodex-β φ0.25 mm I.D.×60 m (product of J&amp;W Scientific Inc.) 
       Carrier gas: He 300 kPa 
     Detector: FID 
       [0052]    Column temperature: 45° C.
 
Detection time: 49.9 minutes for (R)-2-methyl-1-hexanal, 51.5 minutes for (S)-2-methyl-1-hexanal, and 44.6 minutes for 2-butylacrolein
 
Reaction conversion rate (%)=amount of product/(amount of substrate+amount of product)×100
 
Optical purity (% ee)=(A−B)/(A+B)×100
 
(both of A and B represent the amount of enantiomer, and the relation of A&gt;B is satisfied)
 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Reaction 
                   
                   
               
               
                   
                 conversion 
                 Optical purity 
               
               
                 Microorganism 
                 rate (%) 
                 (% ee) 
                 Configuration 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 
                   Candida cantarellii 
                 
                 NBRC 1261 
                 40.2 
                 96.7 
                 R 
               
               
                 
                   Candida etchellsii 
                 
                 NBRC 1229 
                 18.2 
                 95.9 
                 R 
               
               
                 
                   Candida kefyr 
                 
                 NBRC 0706 
                 27.9 
                 97.3 
                 R 
               
               
                 
                   Candida musae 
                 
                 NBRC 1582 
                 36.7 
                 73.4 
                 R 
               
               
                 
                   Candida nitratophila 
                 
                 NBRC 10004 
                 37.6 
                 90.2 
                 R 
               
               
                 
                   Candida sake 
                 
                 CBS 5093 
                 32.1 
                 92.2 
                 R 
               
               
                 
                   Candida stellata 
                 
                 NBRC 0701 
                 14.8 
                 89.9 
                 R 
               
               
                 
                   Candida zeylanoides 
                 
                 NBRC 0738 
                 27.2 
                 93.1 
                 R 
               
               
                   Kluyveromyces lactis  var.  drosophilarum   
                 NBRC 1012 
                 18.8 
                 97.0 
                 R 
               
               
                 
                   Pichia membranaefaciens 
                 
                 IAM 4258 
                 16.9 
                 91.8 
                 R 
               
               
                 
                   Pichia canadensis 
                 
                 NBRC 0976 
                 18.4 
                 95.0 
                 R 
               
               
                 
                   Pichia heedii 
                 
                 NBRC 10019 
                 48.8 
                 92.6 
                 R 
               
               
                 
                   Rhodotorula minuta 
                 
                 NBRC 0387 
                 46.7 
                 95.3 
                 R 
               
               
                 
                   Saccharomyces unisporus 
                 
                 NBRC 0215 
                 23.8 
                 95.8 
                 R 
               
               
                 
                   Saccharomyces bayanus 
                 
                 NBRC 0213 
                 20.1 
                 91.4 
                 R 
               
               
                 
                   Saccharomyces cerevisiae 
                 
                 ATCC26108 
                 48.2 
                 92.4 
                 R 
               
               
                 
                   Saccharomyces pastorianus 
                 
                 NBRC 1265 
                 35.9 
                 96.9 
                 R 
               
               
                 
                   Saccharomyces castellii 
                 
                 NBRC 0285 
                 27.3 
                 94.3 
                 R 
               
               
                 
                   Sporidiobolus johnsonii 
                 
                 NBRC 6903 
                 39.8 
                 69.1 
                 R 
               
               
                 
                   Sporidiobolus salmonicolor 
                 
                 NBRC 1035 
                 16.5 
                 74.8 
                 R 
               
               
                 
                   Sporobolomyces salmonicolor 
                 
                 IAM 12249 
                 20.2 
                 84.0 
                 R 
               
               
                 
                   Trigonopsis variabilis 
                 
                 NBRC 0671 
                 15.1 
                 81.9 
                 R 
               
               
                 
                   Zygosaccharomyces bailii 
                 
                 NBRC 0488 
                 23.8 
                 93.9 
                 R 
               
               
                   
               
             
          
         
       
     
       Example 2 
     Process for Producing Optically Active 2-Methyl-1-Hexanal 
       [0053]    A liquid medium (pH 6.5) comprising meat extract (1%), peptone (1%), yeast extract (0.5%) and sodium chloride (1%) was prepared to be dispensed into large test tubes by 5 ml fractions, and each tube was subjected to steam sterilization at 120° C. for 20 minutes. A loopful of the microorganisms shown in Table 2 was respectively inoculated into each of these liquid media to be subjected to shaking culture at 30° C. for 2 to 3 days. Cells were collected from each of these culture media by centrifugation. Each cell portion was washed with a 1-ml-portion of 100 mM phosphate buffer (pH 6.5), suspended into a 500-μl-portion of the same buffer, and then put into a test tube equipped with a plug. To each of these solutions, glucose 25 mg, NAD and NADP, 0.5 mg of each, and glucose dehydrogenase (product of Amano Enzyme Inc.) 5 U were added. After each 2-mg-portion of the substrate 2-butylacrolein was dissolved in a 500-μl-portion of ethyl acetate to be added into each of the test tubes each equipped with a plug, these tubes were stirred at 30° C. for 20 hours. After the reaction, each reaction mixture was centrifuged, and the amounts of substrate and product in an ethyl acetate layer were analyzed in the same manner as in Example 1 to determine the reaction conversion rate and optical purity of the product. The results are shown in Table 2 (the reaction conversion is 10 to 100%). 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Reaction 
                   
                   
               
               
                   
                 conversion 
                 Optical purity 
               
               
                 Microorganism 
                 rate (%) 
                 (% ee) 
                 Configuration 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 
                   Arthrobacter nicotianae 
                 
                 NBRC 14234 
                 45.2 
                 42.9 
                 R 
               
               
                 
                   Acidiphilium cryptum 
                 
                 NBRC 14242 
                 44.8 
                 45.7 
                 R 
               
               
                 
                   Bacillus cereus 
                 
                 NBRC 3466 
                 21.9 
                 84.3 
                 R 
               
               
                 
                   Bacillus coagulans 
                 
                 NBRC 3886 
                 19.0 
                 95.7 
                 R 
               
               
                 
                   Bacillus licheniformis 
                 
                 IAM 11054 
                 16.2 
                 83.1 
                 R 
               
               
                 
                   Bacillus pumilus 
                 
                 NBRC 12086 
                 18.3 
                 94.7 
                 R 
               
               
                 
                   Bacillus badius 
                 
                 ATCC 14574 
                 29.1 
                 88.7 
                 R 
               
               
                 
                   Bacillus sphaericus 
                 
                 NBRC 3525 
                 73.3 
                 90.7 
                 R 
               
               
                 
                   Micrococcus luteus 
                 
                 NBRC 13867 
                 47.8 
                 66.6 
                 R 
               
               
                 
                   Pseudomonas stutzeri 
                 
                 NBRC 13596 
                 30.2 
                 55.4 
                 R 
               
               
                 
                   Pseudomonas fragi 
                 
                 NBRC 3458 
                 47.2 
                 65.0 
                 R 
               
               
                 
                   Pseudomonas putida 
                 
                 NBRC 14164 
                 24.7 
                 13.3 
                 R 
               
               
                 
                   Paenibacillus alvei 
                 
                 NBRC 3343 
                 35.7 
                 89.7 
                 R 
               
               
                   Xanthomonas  sp. 
                 NBRC 3084 
                 65.0 
                 86.1 
                 R 
               
               
                   Xanthomonas  sp. 
                 NBRC 3085 
                 52.2 
                 86.0 
                 R 
               
               
                 
                   Achromobacter xylosoxidans 
                 
                 NBRC 15125 
                 11.5 
                 33.5 
                 S 
               
               
                 subsp.  denitrificans   
               
               
                 
                   Alcaligenes faecalis 
                 
                 NBRC 13111 
                 15.7 
                 63.2 
                 S 
               
               
                   Alcaligenes  sp. 
                 NBRC 14130 
                 10.5 
                 29.9 
                 S 
               
               
                 
                   Arthrobacter crystallopoietes 
                 
                 NBRC 14235 
                 12.9 
                 54.0 
                 S 
               
               
                 
                   Arthrobacter protophormiae 
                 
                 NBRC 12128 
                 16.8 
                 25.2 
                 S 
               
               
                 
                   Corynebacterium ammoniagenes 
                 
                 NBRC 12072 
                 14.4 
                 65.0 
                 S 
               
               
                 
                   Escherichia coli 
                 
                 ATCC 11303 
                 55.1 
                 78.3 
                 S 
               
               
                   
               
             
          
         
       
     
       Example 3 
     Process for Producing Optically Active 2-Methyl-1-Alkylpropanal 
       [0054]    Each 5-mg-portion of the acetone dried cells prepared in Example 1 or the cells separated from the culture medium prepared in Example 2 was suspended into a 500-μl-portion of 100 mM phosphate buffer (pH 6.5) in a test tube equipped with a plug. To each of these solutions, glucose 25 mg, NAD and NADP, 0.5 mg of each, glucose dehydrogenase (product of Amano Enzyme Inc.) 5 U were added. After each 2-mg-portion of the substrates shown in Table 3 was dissolved in a 500-μl-portion of ethyl acetate to be added into a test tube equipped with a plug, these tubes were stirred at 30° C. for 20 hours. After the reaction, each reaction mixture was centrifuged, and the amounts of substrate and product in an ethyl acetate layer were analyzed with gas chromatography (GC) to determine the reaction conversion rate and optical purity of the product. The results are shown in Table 3. 
         [0055]    The analysis conditions were as follows. 
       [GC Analysis Conditions (2-Methylbutanal: Trifluoroacetyl Derivatization of the Substrates and Products)] 
       [0056]    Capillary column: Cyclodex-β φ0.25 mm I.D.×60 m (product of J&amp;W Scientific Inc.) 
       Carrier gas: He 300 kPa 
     Detector: FID 
       [0057]    Column temperature: 40° C.
 
Detection time: 16.7 minutes for (R)-2-methyl-1-butanal, 17.0 minutes for (S)-2-methyl-1-butanal, 15.0 minutes for 2-ethylacrolein
 
       [GC Analysis Conditions (2-Methyloctanal)] 
       [0058]    Capillary column: TC-WAX φ0.25 mm I.D.×15 m (product of GL Sciences Inc.) 
       Carrier gas: He 80 kPa 
     Detector: FID 
       [0059]    Column temperature: 80° C.
 
Detection time: 2.8 minutes for 2-methyl-1-octanal, 3.6 minutes for 2-hexylacrolein
 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 2-ethylacrolein 
                 2-hexylacrolein 
               
             
          
           
               
                   
                 Reaction 
                   
                   
                 Reaction 
                   
                   
               
               
                   
                 conversion 
                 Optical purity 
                   
                 conversion 
                 Optical 
               
               
                 Microorganism 
                 rate (%) 
                 (% ee) 
                 Configuration 
                 rate (%) 
                 purity (% ee) 
                 Configuration 
               
               
                   
               
             
          
           
               
                 
                   Candida cantarellii 
                 
                 NBRC 1261 
                 40.8 
                 93.5 
                 R 
                 83.7 
                 — 
                 — 
               
               
                 
                   Candida etchellsii 
                 
                 NBRC 1229 
                 13.3 
                 89.7 
                 R 
                 26.2 
                 — 
                 — 
               
               
                 
                   Candida kefyr 
                 
                 NBRC 0706 
                 25.2 
                 93.2 
                 R 
                 39.5 
                 — 
                 — 
               
               
                   Kluyveromyces lactis  var. 
                 NBRC 1012 
                 17.6 
                 93.0 
                 R 
                 25.6 
                 — 
                 — 
               
               
                 
                   drosophilarum 
                 
               
               
                 
                   Pichia canadensis 
                 
                 NBRC 0976 
                 15.4 
                 91.4 
                 R 
                 15.7 
                 — 
                 — 
               
               
                 
                   Rhodotorula minuta 
                 
                 NBRC 0387 
                 32.7 
                 92.7 
                 R 
                 56.0 
                 — 
                 — 
               
               
                 
                   Saccharomyces unisporus 
                 
                 NBRC 0215 
                 19.2 
                 90.7 
                 R 
                 31.7 
                 — 
                 — 
               
               
                 
                   Saccharomyces cerevisiae 
                 
                 ATCC 26108 
                 48.2 
                 92.4 
                 R 
                 52.8 
                 — 
                 — 
               
               
                 
                   Saccharomyces pastorianus 
                 
                 NBRC 1265 
                 28.7 
                 94.1 
                 R 
                 44.4 
                 — 
                 — 
               
               
                 
                   Bacillus coagulans 
                 
                 NBRC 3886 
                 12.3 
                 65.9 
                 R 
                 6.7 
                 — 
                 — 
               
               
                 
                   Bacillus pumilus 
                 
                 NBRC 12086 
                 49.8 
                 97.8 
                 R 
                 11.9 
                 — 
                 — 
               
               
                 
                   Bacillus badius 
                 
                 ATCC 14574 
                 13.2 
                 85.6 
                 R 
                 5.8 
                 — 
                 — 
               
               
                 
                   Bacillus sphaericus 
                 
                 NBRC 3525 
                 51.2 
                 79.5 
                 R 
                 19.0 
                 — 
                 — 
               
               
                 
                   Paenibacillus alvei 
                 
                 NBRC 3343 
                 10.0 
                 80.4 
                 R 
                 91.6 
               
               
                   Xanthomonas  sp. 
                 NBRC 3084 
                 16.4 
                 89.0 
                 R 
                 22.1 
                 — 
                 — 
               
               
                   Xanthomonas  sp. 
                 NBRC 3085 
                 14.3 
                 90.0 
                 R 
                 18.0 
                 — 
                 — 
               
               
                 
                   Alcaligenes faecalis 
                 
                 NBRC 13111 
                 0.7 
                 40.5 
                 S 
                 0.5 
                 — 
                 — 
               
               
                 
                   Escherichia coli 
                 
                 ATCC 11303 
                 18.8 
                 57.0 
                 S 
                 18.0 
                 — 
                 — 
               
               
                   
               
             
          
         
       
     
       Example 4 
     Process for Producing Optically Active 2-Methyl-3-Phenylpropanal 
       [0060]    Each 5-mg-portion of acetone dried cells prepared in Example 1 or the cells separated from the culture medium prepared in Example 2 was suspended into a 500-μl-portion of 100 mM phosphate buffer (pH 6.5) in a test tube equipped with a plug. To each of these solutions, glucose 25 mg, NAD and NADP, 0.5 mg of each, and glucose dehydrogenase (product of Amano Enzyme Inc.) 5 U were added. After each 2-mg-portion of the substrate 2-benzylacrolein was dissolved in a 500-μl-portion of ethyl acetate to be added into each of the test tubes each equipped with a plug, these tubes were stirred at 30° C. for 20 hours. After the reaction, each reaction mixture was centrifuged, and each of the substrate together with the product in an ethyl acetate layer was converted into trifluoroacetyl derivative thereof to be analyzed with gas chromatography (GC). Thus, the reaction conversion rates and optical purities of the products were determined. The results are shown in Table 4. 
         [0061]    The analysis conditions were as follows. 
       [GC Analysis Conditions] 
       [0062]    Capillary column: Cyclodex-β φ0.25 mm I.D.×60 m (product of J&amp;W Scientific Inc.) 
       Carrier gas: He 300 kPa 
     Detector: FID 
       [0063]    Column temperature: 80° C. 
         [0064]    Detection time: 113.9 minutes for (R)-2-methyl-3-phenylpropanal, 116.9 minutes for (S)-2-methyl-3-phenylpropanal, 96.2 minutes for 2-benzylacrolein 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Reaction 
                   
                   
               
               
                   
                 conversion 
                 Optical purity 
               
               
                 Microorganism 
                 rate (%) 
                 (% ee) 
                 Configuration 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 
                   Candida cantarellii 
                 
                 NBRC 1261 
                 63.4 
                 86.4 
                 R 
               
               
                 
                   Candida etchellsii 
                 
                 NBRC 1229 
                 22.2 
                 43.0 
                 R 
               
               
                 
                   Candida kefyr 
                 
                 NBRC 0706 
                 33.7 
                 85.6 
                 R 
               
               
                   Kluyveromyces lactis  var.  drosophilarum   
                 NBRC 1012 
                 25.1 
                 42.0 
                 R 
               
               
                 
                   Pichia canadensis 
                 
                 NBRC 0976 
                 18.0 
                 68.0 
                 R 
               
               
                 
                   Rhodotorula minuta 
                 
                 NBRC 0387 
                 61.1 
                 83.2 
                 R 
               
               
                 
                   Saccharomyces unisporus 
                 
                 NBRC 0215 
                 32.9 
                 33.8 
                 R 
               
               
                 
                   Saccharomyces cerevisiae 
                 
                 ATCC 26108 
                 61.6 
                 94.2 
                 R 
               
               
                 
                   Saccharomyces pastorianus 
                 
                 NBRC 1265 
                 44.5 
                 78.0 
                 R 
               
               
                 
                   Bacillus coagulans 
                 
                 NBRC 3886 
                 12.3 
                 22.0 
                 R 
               
               
                 
                   Bacillus pumilus 
                 
                 NBRC 12086 
                 32.8 
                 14.8 
                 R 
               
               
                 
                   Bacillus badius 
                 
                 ATCC 14574 
                 10.3 
                 55.0 
                 R 
               
               
                 
                   Bacillus sphaericus 
                 
                 NBRC 3525 
                 39.1 
                 67.0 
                 R 
               
               
                 
                   Paenibacillus alvei 
                 
                 NBRC 3343 
                 9.1 
                 55.2 
                 R 
               
               
                   Xanthomonas  sp. 
                 NBRC 3084 
                 7.4 
                 65.3 
                 R 
               
               
                   Xanthomonas  sp. 
                 NBRC 3085 
                 7.4 
                 55.9 
                 R 
               
               
                 
                   Alcaligenes faecalis 
                 
                 NBRC 13111 
                 2.7 
                 81.2 
                 S 
               
               
                 
                   Escherichia coli 
                 
                 ATCC 11303 
                 57.4 
                 70.2 
                 S 
               
               
                   
               
             
          
         
       
     
       Example 5 
     Cloning of NADPH Dehydrogenase Gene Derived from  Saccharomyces cerevisiae  S288C (ATCC26108) Strain (Old Yellow Enzyme 2 Gene) 
       [0065]    An expression vector was prepared by the method mentioned below for expressing an NADPH dehydrogenase derived from  Saccharomyces cerevisiae  S288C (ATCC26108) strain (Old Yellow Enzyme 2, hereinafter, referred to as “OYE2”) in  Escherichia coli  (refer to Appl. Environ. Microbiol., 69, 933, (2003)). 
         [0066]    First, a DNA fragment containing OYE2 gene was amplified by a first-step PCR using a chromosomal DNA of  Saccharomyces cerevisiae  S288C (ATCC26108) strain as a template. Then, by a second-step PCR using the DNA fragment obtained by the first-step PCR as a template, a double-stranded DNA was obtained in which a SacI site is added to the initiation codon site of OYE2 gene and a new termination codon and a SalI site are added to just after the termination codon. Details are shown below. 
         [0067]    A primer 1: 5′-cggtccagatatagaataaatcatcatattaag-3′ (SEQ ID NO:1 in the sequence listing) and a primer 2: 5′-gaaatggtgctacaaagtacggttaacac-3′ (SEQ ID NO:2 in the sequence listing) were synthesized. 50 μl of an ExTaq buffer containing each 50 pmol of these two species of primers (primers 1 and 2), 200 ng of a chromosomal DNA of  Saccharomyces cerevisiae  S288C (ATCC26108) strain, each 10 nmol of dNTP, and 2.5 U of ExTaq (product of Takara Shuzo Co., Ltd.) was prepared. A PCR reaction was carried out under the conditions of thermal denaturation (97° C., 0.5 minute), annealing (55° C., 1 minute), and elongation (72° C., 1 minute). After cooling the buffer to 4° C., amplification of the DNA fragment was confirmed by agarose gel electrophoresis, and the amplified fragment was collected from gel. The chromosomal DNA was prepared by usual DNA isolation method, e.g., a potassium acetate method, etc. Then, a primer 3: 5′-atcgagctctaaggaggttaacaatgccatttgttaaggac-3′ (SEQ ID NO:3 in the sequence listing) resulting from addition of the  Escherichia coli -derived Shine-Dalgarno sequence (SD sequence, 9 nucleotides) at upstream of the initiation codon of OYE2 gene and a SacI recognition site just before thereof, and a primer 4: 5′-acgcgtcgacttattaatttttgtcccaaccg-3′ (SEQ ID NO:4 in the sequence listing) resulting from addition of a new termination codon and a SalI recognition site just after the termination codon were synthesized. 50 μl of an ExTaq buffer containing each 50 pmol of these two species of primers (primers 3 and 4), 200 ng of the DNA fragment amplified by the PCR reaction mentioned above, each 10 nmol of dNTP, and 2.5 U of ExTaq (product of Takara Shuzo Co., Ltd.) was prepared to carry out a PCR reaction under the same conditions as mentioned above. As a result, a double-stranded DNA was obtained in which the  Escherichia coli -derived Shaine-Dalgarno sequence (SD sequence) is added at a site 5 bases upstream of the initiation codon of OYE2 gene and a SacI recognition site is added just before that sequence and, further, a new termination codon and a SalI recognition site are added just after the termination codon. This double-stranded DNA was digested with SacI and SalI, and the digest was inserted into the SacI and SalI sites at downstream of lac promoter of a plasmid pUCT resulting from conversion, in an NdeI site of a plasmid pUCNT (obtainable by the person skilled in the art by the method described in International Publication WO94/03613), of G into T in order to construct a recombinant vector pTSYE2. 
       Example 6 
     Construction of an Expression Vector Further Comprising a Glucose Dehydrogenase Gene 
       [0068]    Using a primer 5: 5′-acgcgtcgactaaggaggttaacaatgtataa agatttagaagg-3′ (SEQ ID NO:5 in the sequence listing) and a primer 6: 5′-gcgctgcagttatccgcgtcctgcttgga-3′ (SEQ ID NO:6 in the sequence listing), and using a plasmid pGDK1(refer to Eur. J. Biochem., 186, 389 (1989)) as a template, PCR was carried out to obtain a double-stranded DNA in which the  Escherichia coli -derived Shaine-Dalgarno sequence (SD sequence) is added at a site 5 bases upstream of the initiation codon of a glucose dehydrogenase (hereinafter referred to as “GDH”) gene derived from the  Bacillus megaterium  IAM 1030 strain, a SalI recognition site is added just before that sequence and, further, a new termination codon and a PstI recognition site is added just after the termination codon. This double-stranded DNA obtained was digested with SalI and PstI. The digest was inserted between a SalI recognition site and PstI recognition site of the above recombinant vector pTSYE2 to construct a recombinant vector pTSYE2G1. The process for producing pTSYE2G1 and the construction thereof are shown in  FIG. 1 . 
       Example 7 
     Production of a Transformant 
       [0069]    Using the recombinant vector pTSYE2 constructed in Example 5,  Escherichia coli  HB101 (product of Takara Shuzo Co., Ltd.) was transformed to obtain a strain transformant  Escherichia coli  HB101 (pTSYE2). In the same manner, using the recombinant vector pTSYE2G1 constructed in Example 6,  Escherichia coli  HB101 (product of Takara Shuzo Co., Ltd.) was transformed to obtain a transformant  Escherichia coli  HB101 (pTSYE2G1). 
       Example 8 
     Gene Expression in a Transformant 
       [0070]    Two species of transformants obtained in Example 7 and a transformant  Escherichia coli  HB101 (pUCT) introduced with a vector plasmid pUCT (refer to Example 5) alone were respectively inoculated into a 2×YT liquid medium (bactotriptone 1.6%, bactoyeast extract 1.0%, sodium chloride 0.5%, pH 7.0) containing 100 μg/ml of ampicillin, and subjected to shaking culture at 37° C. for 24 hours. From the culture media, cells were collected by centrifugation, suspended into 100 mM phosphate buffer (pH 6.5), and subjected to ultrasonic disruption using an UH-50 type ultrasonic homogenizer (product of SMT Co., Ltd). Then, cell residues were removed by centrifugation to obtain a cell-free extraction. The OYE2 activity and GDH activity of this cell-free extraction were determined and shown in Table 5. 
         [0071]    In both two species of transformants obtained in Example 7, expression of OYE2 activity was observed. Moreover, in a GDH gene-containing transformant  Escherichia coli  HB101 (pTSYE2G1), expression of GDH activity was also observed. 
         [0072]    Additionally, the OYE2 activity was calculated by adding 1 mM of the substrate 2-cyclohexenone, 0.2 mM of coenzyme NADPH and a crude enzyme solution to 100 mM phosphate buffer (pH 6.5), subjecting the mixture to reaction at 30° C. for 1 minute, and measuring the rate of decrease in absorbance at a wavelength of 340 nm. The enzyme activity for oxidizing 1 μmol of NADPH to NADP +  per minute under these reaction conditions was defined as 1 unit. 
         [0073]    The GDH activity was calculated by adding 0.1 M of glucose, 2 mM of coenzyme NADP, and a crude enzyme solution to 1 M tris hydrochloride buffer (pH 8.0), subjecting the mixture to reaction at 25° C. for 1 minute, and measuring the rate of increase in absorbance at a wavelength of 340 nm. The enzyme activity for reducing 1 μmol of NADP to NADPH per minute under these reaction conditions was defined as 1 unit. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                   
                 OYE2 
                 GDH 
               
               
                   
                 Strain 
                 activity (U/ml) 
                 activity (U/ml) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   E. coli  HB101(pUCT) 
                 0.00 
                 0.0 
               
               
                   
                   E. coli  HB101(pTSYE2) 
                 0.30 
                 0.0 
               
               
                   
                   E. coli  HB101(pTSYE2G1) 
                 1.20 
                 82.0 
               
               
                   
                   
               
             
          
         
       
     
       Example 9 
     Process for Producing (R)-2-Methyl-1-Alkylpropanal Using a Transformant 
       [0074]    The transformant  Escherichia coli  HB101 (pTSYE2) obtained in Example 7 was inoculated to 50 ml of a 2×YT medium (bactotriptone 1.6%, bactoyeast extract 1.0%, sodium chloride 0.5%, pH 7.0) sterilized in a 500 ml Sakaguchi flask, and subjected to shaking culture at 30° C. for 2 days. The culture medium obtained was concentrated and subjected to ultrasonic disruption using an UH-50 type ultrasonic homogenizer (product of SMT Co., Ltd). Then, cell residues were removed by centrifugation to obtain a cell-free extraction. In 450 μl of 100 mM phosphate buffer (pH 6.5), this cell-free extraction 50 μl, glucose 25 mg, NAD and NADP, 0.5 mg of each, and glucose dehydrogenase (product of Amano Enzyme Inc.) 5 U were dissolved, and the solution was put into a test tube equipped with a plug. After each 2-mg-portion of the substrates shown in Table 6 was dissolved in a 500-μl-portion of ethyl acetate to be added into each of the test tubes each equipped with a plug, these tubes were stirred at 30° C. for 2 hours. After the reaction, each reaction mixture was centrifuged and the amounts of substrate and product in an ethyl acetate layer were analyzed in the same manner as in Examples 1 and 3 to determine the reaction conversion rate and optical purity of the product. The results are shown in Table 6. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                   
                 Reaction 
                   
               
               
                   
                   
                 conversion rate 
                 Optical 
               
               
                   
                 Substrate 
                 (%) 
                 purity (% ee) 
               
               
                   
                   
               
             
             
               
                   
                 2-ethylacrolein 
                 96.7 
                 96.0 
               
               
                   
                 2-butylacrolein 
                 99.7 
                 94.5 
               
               
                   
                 2-hexylacrolein 
                 98.6 
                 — 
               
               
                   
                   
               
             
          
         
       
     
       Example 10 
     Process for Producing (R)-2-Methyl-3-Phenylpropanal Using a Transformant 
       [0075]    50 μl of a cell-free extraction of the transformant  Escherichia coli  HB101 (pTSYE2) prepared in the same manner as in Example 9, glucose 25 mg, NAD and NADP, 0.5 mg of each, and glucose dehydrogenase (product of Amano Enzyme Inc.) 5 U were dissolved in 450 μl of 100 mM phosphate buffer (pH 6.5), and put into a test tube equipped with a plug. Then, 2 mg of the substrate 2-benzylacrolein was dissolved in 500 μl of ethyl acetate and added into the test tube equipped with a plug, and then stirred at 30° C. for 2 hours. After the reaction, the reaction mixture was centrifuged and the amount of substrate and product in an ethyl acetate layer was analyzed in the same manner as in Example 4. As a result, (R)-2-methyl-3-phenylpropanal with the optical purity of 94.7% ee was obtained at the reaction conversion rate of 99.3%. 
       Example 11 
     Process for Producing (R)-2-Methyl-1-Hexanal Using a Transformant 
       [0076]    The transformant  Escherichia coli  HB101 (pTSYE2G1) obtained in Example 7 was inoculated to 50 ml of a 2×YT medium (bactotriptone 1.6%, bactoyeast extract 1.0%, sodium chloride 0.5%, pH 7.0) sterilized in a 500 ml Sakaguchi flask to be subjected to shaking culture at 30° C. for 2 days. The culture medium obtained was concentrated and subjected to ultrasonic disruption using an UH-50 type ultrasonic homogenizer (product of SMT Co., Ltd). Then, cell residues were removed by centrifugation to obtain a cell-free extraction. 30 ml of the above cell-free extraction, 195 ml of 100 mM phosphate buffer (pH 6.5), 25 ml of 55% glucose solution, and 25 mg of NADP were added to a 500 ml 4-necked flask. Then, 1 g of the substrate 2-butylacrolein was dissolved in 100 ml of hexane, and added dropwise into the reaction system for 25 minutes. Under pH adjustment, the obtained liquid was stirred at 30° C. for 1 hour, and the amount of substrate and product in a hexane layer was analyzed in the same manner as in Example 1. Then, the reaction mixture was separated and hexane was distilled off under reduced pressure to obtain (R)-2-methyl-1-hexanal with the optical purity of 96.3% ee in 80% yield. 
       Example 12 
     Process for Producing 5-Hydroxy-2-Methyl-1-Pentanal Using a Transformant 
       [0077]    500 μl of a culture medium of the transformant  Escherichia coli  HB101 (pTSYE2G1) prepared in the same manner as in Example 11, 30 μl of 55% glucose solution and 0.5 mg of NADP were mixed with 100 μl of 100 mM phosphate buffer (pH 6.5), and the mixture was put into a test tube equipped with a plug. Then, 10 mg of the substrate 2-(3-hydroxypropyl)acrolein was added thereto and the mixture was stirred for 2 hours. After the reaction, the reaction mixture was extracted with ethyl acetate, and the amount of substrate and product in an ethyl acetate layer was analyzed with GC under the below-mentioned analysis conditions. As a result, 5-hydroxy-2-methyl-1-pentanal was obtained at the reaction conversion rate of 96.9%. 
         [0078]    The analysis conditions were as follows. 
       [GC Analysis Conditions] 
       [0079]    Capillary column: β-DEX225 φ0.25 mm I.D.×30 m (product of SUPELCO Co., Ltd) 
       Carrier gas: He 100 kPa 
     Detector: FID 
       [0080]    Column temperature: 120° C.
 
Detection time: 7.1 minutes for 5-hydroxy-2-methyl-1-pentanal, 14.8 minutes for 2-(3-hydroxypropyl)acrolein
 
       Example 13 
     Process for Producing (R)-5-Benzyloxy-2-Methyl-1-Pentanal Using a Transformant 
       [0081]    500 μl of a culture medium of the transformant  Escherichia coli  HB101 (pTSYE2G1) prepared in the same manner as in Example 11, 30 μl of 55% glucose solution and 0.5 mg of NADP were mixed with 100 μl of 100 mM phosphate buffer (pH 6.5), and put into a test tube equipped with a plug. Then, 10 mg of the substrate 2-(3-benzyloxypropyl)acrolein was added thereto and the mixture was stirred for 2 hours. After the reaction, the reaction mixture was extracted with ethyl acetate, and the amounts of substrate and product in an ethyl acetate layer were analyzed with GC under the below-mentioned analysis conditions. As a result, 5-benzyloxy-2-methyl-1-pentanal was obtained at the reaction conversion rate of 99.1%. Furthermore, as a result of reducing 5-benzyloxy-2-methyl-1-pentanal with sodium borohydride (NaBH 4 ) and HPLC analysis under the below-mentioned analysis conditions, the optical purity was 90.0% ee(R). 
         [0082]    The analysis conditions were as follows. 
       [GC Analysis Conditions] 
       [0083]    Capillary column: TC-WAX φ0.25 mm I.D.×15 m (product of GL Sciences Inc.) 
       Carrier gas: He 80 kPa 
     Detector: FID 
       [0084]    Column temperature: 165° C.
 
Detection time: 11.1 minutes for 5-benzyloxy-2-methyl-1-pentanal, 13.2 minutes for 2-(3-benzyloxypropyl)acrolein
 
       [HPLC Analysis Conditions] 
       [0085]    Chiral column: OB-H φ4.6 mm I.D.×250 mm (product of Daicel Chemical Industries, Ltd.)
 
Eluant: hexane/2-propanol 95/5
 
       Detector: UV 254 nm 
       [0086]    Column temperature: 25° C.
 
Detection time: 12.2 minutes for (S)-5-benzyloxy-2-methyl-1-pentanol, 14.3 minutes for (R)-5-benzyloxy-2-methyl-1-pentanol
 
       Reference Example 1 
     Process for Producing (R)-2-Methyl-1-Hexanoic Acid 
       [0087]    5 U of aldehyde dehydrogenase (product of Sigma-Aldrich Corp.) and 13 mg of NAD were dissolved in 500 μl of 100 mM phosphate buffer (pH 8.0), and put into a test tube equipped with a plug. After 2 mg of (R)-2-methyl-1-hexanal obtained in Example 11 was added thereto, the mixture was stirred at 30° C. for 20 hours. After the reaction, 6 N hydrochloric acid solution was added for acidizing the reaction mixture, and 1 ml of ethyl acetate was added for extracting the substrate and product, which were analyzed with GC under the analysis conditions mentioned below. As a result, (R)-2-methyl-1-hexanoic acid with 96.5% ee was obtained at the reaction conversion rate of 99.1%. 
         [0088]    The analysis conditions were as follows. 
       [GC Analysis Conditions] 
       [0089]    Capillary column: G-PN φ00.25 mm I.D.×30 m (product of Tokyo Chemical Industry Co., Ltd.) 
       Carrier gas: He 150 kPa 
     Detector: FID 
       [0090]    Column temperature: 40° C.
 
Detection time: 22.0 minutes for (R)-2-methylhexanoic acid, 23.4 minutes for (S)-2-methylhexanoic acid, 15.1 minutes for 2-methyl-1-hexanal