Asymmetric Reduction Of Aromatic Ketones Catalyzed By Yeast Cells In The Presence Of Cyclodextrins

The asymmetric reduction of aromatic ketones catalyzed by yeast cell in the presence of cyclodextrin is systematicly studied in this paper, employingβ-cyclodextrin and self-made hydroxypropyl-β-cyclodextrin as chiral additives. The impact of the structure and addition amount of cyclodextrin, the structure and nature of aromatic ketone on the reaction results(conversion and ee) is detailed researched. Main conclusions are as follows:1 The optimized condition for synthesis of hydroxypropyl-β-cyclodextrin was: the reaction time was 24 h, the reaction temperature was 5℃, the molar ratio of epoxypropane toβ-cyclodextrin was 1:6, and the concentration of NaOH was 3%. The yield of hydroxypropyl-β-cyclodextrin reached 22.5% under the condition.2 Range an alysis showed the molar rate of aromatic ketones toβ-cyclodextrin was the most important factor affecting the inclusion rate of aromatic ketones-β- cyclodextrin, followed by the inclusion temperature and then the inclusion time. Acetophenone-β- cyclodextrin and propiophenone-β-cyclodextrin can form steady inclusion complex and the inclusion rate respectively was 80.6% and 59.1% under this conditions: inclusion temperature was 50℃, the molar ratio was 1:7 and the inclusion time was 2h. While for 4'-methyl- acetophenone-β-cyclodextrin and 4'-chlorophenyl-acetophenone-β-cyclodextrin, the inclusion rate reached 74.8% and 65% when inclusion temperature was 50℃, the molar ratio was 1:7 and the inclusion time was 1 h.3 The asymmetric reduction of aromatic ketones catalyzed by yeast cell in the presence of chiral additiveβ-cyclodextrin and hydroxypropyl-β-cyclodextrin were detailed investigated by studying the influences of additiveβ-cyclodextrin and hydroxypropyl-β-cyclodextrin. The results showed that the substrate conversion rate and the product enantiomeric excess value were markedly affected by both steric effect and electronic effect of substituted group. The acetophenone conversion rate increased by 18.5 % and ee value of S-(4'-chlorobenzene) ethanol improved by 22.9%. Cyclodextrions affected the reaction results by enhancing the catalytic efficiency of yeast fermentation broth and inclusion of the substrate, among which the key factor is p-substituted group of the substrate aromatic cycle. According to the above experiments, the results of asymmetric reduction of aromatic ketones catalyzed by yeast cells were determined by both the space and electronic effects which join the carbonyl. In the whole biocatalysis process, oxidoreductase in yeast cells and chiral additives affect the reaction results together, however, the essence of reaction were determined by yeast cells and substrate characteristics, which determined the effect of additives on the extent and nature of the reaction.