Use of ionic liquids to improve whole-cell biocatalytic asymmetric reduction of acetyltrimethylsilane for efficient synthesis of enantiopure(S)-1-trimethylsilylethanol

摘要

The two typical ionic liquids(ILs),one hydrophobic(BMIM-PF_6)and one hydrophilic(BMIM-BF_4),were tested as solvents for use in the asymmetric reduction of acetyltrimethylsilane(ATMS)to enantiopure(S)-1-trimethylsilylethanol {(S)-1-TMSE} catalyzed by immobilized Saccharomyces cerevisiae cells.The results demonstrate that BMIM-PF_6 and BMIM-BF_4 can markedly boost the activity and the stability of the immobilized cells.To better understand the reaction performed in these IL-containing systems,various variables that influenced the performance of the reaction were examined.The optimal buffer pH,reaction temperature and substrate concentration were 7.3,30 deg C and 84 mM,respectively,for the BMIM centre dot PF_6/buffer(1/6,v/v)biphasic system,and 7.5,30 deg C and 77 mM,respectively,for the 10%(v/v)BMIM-BF_4-buffer co-solvent system.Under the optimal conditions,the initial reaction rate,maximum yield and product e.e.were 63.4 mM h~(-1),99.9% and >99.9% with the former system,while those with the latter system were 74.5 mM h~(-1),99.2% and >99.9%,respectively,which were much higher than those achieved with either n-hexane/buffer(2/1,v/v)biphasic system or aqueous buffer.It was also found that the optimal pH and substrate concentration changed when n-hexane was replaced by BMIM centre dot PF_6 or BMIM centre dot BF_4.Although the optimal reaction temperature remained the same in the four kinds of reaction systems,the temperature profile of the reaction varied from case to case.Additionally,BMIM centre dot BF_4 and especially BMIM centre dot PF_6 exhibited greater biocompatibility with Saccharomyces cerevisiae than n-hexane,and could be used repeatedly for economically interesting whole-cell biocatalytic processes with in situ coenzyme regeneration.