Asymmetric Resolution Of Chiral Alcohol By Microbial Lipase

Fifteen stereoselective lipases from different microorganisms were applied to asymmetric resolve chiral alcohols such as glycidol,α-Phenylethanol and the mechanism of the reactions was investigated. The reactions in aqueous phase system, reverse micelle system and organic phase system was compared and the key factors that influence the chiral resolution was studied. In brief, an efficient lipase-catalyzed asymmetric resolution system was constructed which could be used for investigation of the properties of asymmetric resolution of chiral alcohol by lipases.(1) The enantioselectivity of the 15 different microbial lipases were tested by the asymmetric hydrolysis of racemic glycidyl butyrate in aqueous medium. Among which the lipase from Rhizopus chinensis (RCL) exhibited higher activity and enantioselectivity. Then, RCL was applied as model enzyme and glycidyl butyrate as model substrate to conduct asymmetric hydrolysis reaction. We investigated the influence of temperature, pH, enzyme dosage, substrate concentration and reaction time on the enzymatic resolution of glycidyl butyrate in aqueous media. The results indicated that the optimal reaction conditions were 20mg/g RCL at 40℃for 6h. Under the optimal conditions, the RCL showed the best performance to produce R-enantiomers with 57.3% ee and 50% conversion of substrate.(2) In order to obtain higher optically pure glycidyl butyrate, the hydrolysis of glycidyl butyrate was performed in reverse micelles system by RCL. Five different reverse micelles, based on cetyltrimethyl ammonium bromide (CTAB), Tetramethyl ammonium bromide (TBAB), sodium 2-ethylhexyl sulfosuccinate (AOT), sodium dodecylsulphonate (SDS) and Emulsifier OP-10(OP) were used as reaction media. The research discovered that CTAB had a great influence on the enantioselectivity of RCL. In the CTAB system the effect of pH, Wo, temperature, substrate concentration et al on the optical selectivity of RCL were investigated. The optimal resolution conditions were as follows: pH 7.5, Wo 40, 0.35 M substrate concentration, 40℃, 6 h under which RCL showed ee 81.7% of R-glycidol butyrate. Meanwhile, a clear trend was observed that the activity of RCL was greatly enhanced by the use of reverse micelles system in comparison with a classical aqueous media.(3) After screening of 15 different microbial lipases for asymmetric resolution ofα-phenylethanol, Lipase PS from Burkholderia cepacia was chosen to asymmetric transesterification resolutionα-phenylethanol in organic solvent. We investigated the influence factors which played a crucial role on the enantioselectivity of Lipase PS , such as reaction medium, enzyme dosage, substrate concentration, temperature, and water activity et al. The optimal reaction conditions were as follows: 0.3 mol/L (R,S)-α-phenylethanol, and 0.6 mol/L vinyl acetate, 5 mg/mL lipase PS, under 35°C and 200 r/min with the initial water activity of 0.75 for 14 h. lipase PS exhibited the best performance to produce 98.6% ee of (R)-phenylethyl acetate and the substrate conversion reached at 44.7%.