DEVELOPMENT OF BIOREACTOR FOR PRODUCTION OF CHIRAL ALCOHOLS WITH YEAST

Large-scale production of chiral alcohols with bakers' yeast was effec tively performed by examining the regeneration system of nicotineamide coenzymes in cells. First, a new procedure for the asymmetric reducti on of prochiral ketones was developed, based on the use of ethanol ins tead of carbohydrate as the energy source for NAD(P)H regeneration. In the asymmetric reduction of ethyl acetoacetate (EA), both the yield a nd the optical purity of the product, (S)-ethyl 3-hydroxybutanoate (E 3-HB), were considerably improved by applying fed-batch operation to t he new procedure. (S)-E 3-HB with >99% enantiomeric excess was effecti vely prepared on a large scale using a bubble-column reactor. Also, ac etol was reduced to (R)-propylene glycol (PG), a useful chiral buildin g block, in the same manner. A total scheme for NAD(P)H regeneration f rom NAD(P))(+) through the oxidative pathway of ethanol was proposed. The relationship between the condition of the oxygen supply and the ef ficiency (V-substrate/V-EtOH) was evaluated. Next, an enantioselective oxidation for preparing other chiral alcohols such as (S)-PG was deve loped. Treatment of a racemic 1,2-alkanediol with bakers' yeast follow ed by removal of the oxidation product, 1-hydroxy-2-alkanone, affords (S)-1,2-alkanediol. The outline of the oxidation, especially the relat ionship to oxygen transfer for regenerating NAD(+) from NADH, was esti mated. Finally, the microbial resolution of racemic 1,2-alkanediols wa s performed on a large scale by repeating the procedures with bakers' yeast, the oxidative resolution of racemic 1,2-alkanediols followed by the asymmetric reduction of the oxidation products.