Asymmetric Reduction Of Carbonyl Compounds By Microbial Cells In Nonaqueous Media

It is necessary to obtain enantiomeric purity compounds in many fields, especially in pharmaceutical industry. The optically active halo-β-hydroxyesters and 1-phenylethanol derivatives are very important building blocks for use in synthesis of many chiral drugs and other bioactive compounds. Combining the advantages of biocatalysis in nonaqueous media, asymmetric reduction of corresponding carbonyl compounds using microbial cells is an efficient method to produce these chiral alcohols.The analytic methods for determining enantiomeric purity of chiral alcolols were established. Acetylated ethyl 4-chloro-3-hydroxybutanoate was separated onβ-cyclodextrin (β-CD) chiral stationary phase in gas chromatography. Effects of different conditions on the resolution were investigated. Then various racemic alcohols were separated and their thermodynamic data were determined. The results showed that the factors such as velocity of carrier gas, column temperature, rate of programmed temperature, time of initially maintained temperature and injected sample amount were remarkably influenced the resolution. The aryl alcohols without derivatization have excellent resolution on theβ-CD chiral stationary phase, and the recognition ofβ-CD to the aryl alcohols was stronger than that to the aliphatic hydroxyesters. Analysis of thermodynamic data indicated that an enthalpy-entropy compensation effect exists within these alcohols. Accordingly, the mechanism of resolution the alcohols onβ-CD was identical.Toxicity of various organic solvents to microbial cells was investigated. The results indicated that there exists a correlation between toxicity to Aureobasidium pullulans GCMCC 1244 cells and logP of organic solvent and the transition between toxic and nontoxic solvents was observed in the logP range from 3 to 5. The toxicity of organic solvent decreased after the cells were immobilized in calcium alginate. Microbial cells in different growth phase have differently toxic response to organic solvent and the toxicity of organic solvent to the cells in rapid growth phase (incubated for 12 h) was more obvious than that to the cells in other growth phase. It was found that there was similar toxicity of an organic solvent to Baker's yeast and Aureobasidium pullulans, but less toxicity to Bacillas subtilis.A process of asymmetric reduction of ethyl 4-chloro-oxobutanoate (COBE) to ethyl (S)-4-chloro-3-hydroxybutanoate (CHBE) catalyzed by Aureobasidium pullulans GCMCC 1244 in an aqueous-organic solvent biphasic system was established. It was found that CHBE was steadier than COBE that was easy to degrade in water containing microbial cells. Both CHBE and COBE were toxic to the cells, and the later was more toxic than the former. By screening organic solvents, butylphthalate was found to be the most suitable solvent to use in...