Biocatalytic Asymmetric Reduction of Ethyl Acetoacetate with Immobilized Acetobacter sp. CCTCC M209061 Cells in a Micro-water-containing Organic Solvent

In present study, the highly anti-Prelog stereoselective reduction of ethyl acetoacetate(EAA) to(R)-ethyl-3-hydroxybutyrate(EHB) with immobilized Acetobacter sp. CCTCC M209061 cells was successfully conducted in a micro-water-containing organic solvent. Use of organic solvent-containing system as the reaction medium, in place of aqueous monophasic system, could not only effectively eliminate the inhibition of the substrate and product, but also improve the concentration of the substrate and the product yield of the tested organic solvents, n-hexane was selected as the most suitable organic phase for the reaction, due to its good ability to dissolve the substrate and biocompatibility with Acetobacter sp. CCTCC M209061 cells. Therefore, the bioreduction reaction with n-hexane became faster and the achieved product yield was relatively higher. Isopropanol was found to be the best co-substrate for the bioreduction and its optimal concentration was 60 mmol/L. For the bioreduction of EAA with immobilized Acetobacter sp. CCTCC M209061 cells, the optimum percentage of n-hexane, reaction temperature, substrate concentration were 100.00%(containing around 0.01 wt% water), 35 ℃, 40 mmol/L, respectively. Under the optimized reaction conditions, the obtained initial reaction rate, yield and product e.e. was 0.72 μmol/min, 85.24% and 99.00% above, which was better than the results observed with aqueous monophasic system as the reaction medium.