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

Chiral aromatic alcohols, which chiral carbon connects with reactive hydroxyl functionalgroups, are the key chiral building blocks for the preparation of many chiral drugs. Prochiralketones can be asymmetric reduced to chiral aromatic alcohols in both chemical catalysis andbiocatalysis. Because biocatalysis has high efficiency and non-pollution, it has become aneffective way to the preparation of many chiral drugs. Baker’s yeast is one of the widely usedcheap microbes. Asymmetric reduction of aromatic ketones to corresponding chiral aromaticalcohols could be catalyzed by baker’s yeast with high stereoselectivity.In this paper, six aromatic ketones were reduced to corresponding racemic1-aryl ethanolby chemical catalysis using NaBH4as a catalyst. The six racemic products were analyzed byGC to obtain appropriate analysis conditions and the retention times of S-configurationproducts and R-configuration products, which can be used as the reference for the asymmetricreduction of aromatic ketones catalyzed by yeast cells.The asymmetric reduction of4’-chloroacetophenone to its corresponding chiral alcohol(S)-1-4’-chlorophenyl ethanol catalyzed by yeast cells was studied in aqueous buffer systemcontaining surfactants. The results indicated that the conversion of4’-chloroacetophenonewas distinctly improved and the enantiomeric excess of product (S)-1-4’-chlorophenyl ethanolwas barely changed when the appropriate concentration of surfactants were added to thesystems. NP-4was the most appropriate additive among being added surfactants. In addition,the influence of NP-4on the asymmetric reduction of aromatic ketones was studied. Theresults showed that the enantiomeric excesses of products (S)-1-aryl ethanol had little changeand the conversions of all aromatic ketones were significantly enhanced in the presence ofNP-4. The added values for the conversion of4’-methoxylacetophenone,4’-methylacetophen-one,4’-chloroacetophenone,3’-chloroacetophenone,2’-chloroacetophenone and4’-nitroacet-ophenone were30.3%,28.0%,23.7%,22.6%,22.0%and20.0%, respectively. The substrateconversion was relevant to the electronic effect and steric effect of the substituents on thearomatic ring. The stronger the electron-donating capacity of the substituents was, the biggerthe added value of substrate conversion became. The stronger the steric effect of thesubstituents was, the smaller the substrate conversion became.In this paper, high purity nano CuFe2O4of spinel structure was prepared by sol-gelmethod using citrate as a complexing agent. Then, the asymmetric reduction of aromaticketones catalyzed by yeast cells were investigated in aqueous buffer system containing metalions (Cu2+, Mg2+, Fe3+, Mn2+or Zn2+) or nano CuFe2O4. The results indicated that theconversions of all aromatic ketones were distinctly improved and the enantiomeric excessesof products (S)-1-aryl ethanol had little change when the appropriate concentration of Mg2+orMn2+or nano CuFe2O4were added to the system. However, the conversions of all aromaticketones and the enantiomeric excesses of products (S)-1-aryl ethanol would be reduced due tothe reaction inhibited when Zn2+, Cu2+or Fe3+were added to the system. The added value forthe conversion of all aromatic ketones reached about12%,9%and11%when theconcentrations of Mg2+, Mn2+and nano CuFe2O4were9mmol/L,9mmol/L and15mmol/L, respectively.