Enhancing Asymmetric Reduction of 3-Chloropropiophenone with Immobilized Acetobacter sp. CCTCC M209061 Cells by Using Deep Eutectic Solvents as Cosolvents

Use of deep eutectic solvents (DESs) to improve biocatalytic asymmetric reduction of 3-chloropropiophenone to ( S )-3-chloro-1-phenylpropanol catalyzed by whole-cell of Acetobacter sp. CCTCC M209061 was successfully performed. The cells immobilized on PVA-sodium sulfate exhibited markedly enhanced stability. Diverse DESs, as cosolvents, manifested significantly different influences on the reaction. Among them, the DES choline chloride/urea ([ChCl][U]) showed the best biocompatibility and moderately increased the cell member permeability, as demonstrated by MAR and flow cytometry assays, and consequently gave the best results. For the bioreduction conducted in the [ChCl][U]-containing system, the optimum [ChCl][U] content, substrate concentration, glucose concentration, pH and temperature were 5% (v/v), 10.0 mmol/L, 60 mmol/L, 5.5 and 30 °C, respectively. Under the optimized conditions, the obtained yield and product e.e. were 82.3% and above 99.0% at a reaction time of 6 h, respectively, and the productivity was 1.37 mmol/L/h. The efficient whole-cell biocatalytic process proved to be feasible on a 500 mL preparative scale. Moreover, the combination of water-immiscible ionic liquid C 4 MIM·PF 6 with [ChCl][U] in a biphasic system further enhanced substrate concentration (16.0 mmol/L), product yield (93.3%) and productivity (1.87 mmol/L/h) significantly, showing to be very promising for biocatalytic synthesis of ( S )-3-chloro-1-phenylpropanol with immobilized Acetobacter sp. CCTCC M209061 cells.