Bioreduction of 3,5-bis(trifluoromethyl)acetophenone using ionic liquid as a co-solvent catalyzed by recombinant Escherichia coli cells

• A novel quaternary ammonium-based ionic liquid was firstly evaluated in bioreduction.
• Reduction of BTAP to (R)-BTPE was conducted in a [N1,1,1,1][Cys]-containing system.
• Using [N1,1,1,1][Cys] as co-solvent can improve the whole cell-mediated reduction.
• The product titer, yield and productivity are 252.7 g/L, 98.7% and 21.058 g/(L h).
• The bioreduction process is feasible on a 5-L fermentor preparative scale.

We investigated the asymmetric bioreduction of 3,5-bis(trifluoromethyl) acetophenone (BTAP) to (R)-[3,5-bis(trifluoromethyl) phenyl] ethanol ((R)-BTPE) in a hydrophilic quaternary ammonium-based ionic liquid (IL)-containing system to improve the efficiency of bioreduction catalyzed by recombinant Escherichia coli cells overexpressing carbonyl reductase. Based on the low toxicity to microbial cells and moderately increased cell membrane permeability, tetramethylammonium cysteine ([N1,1,1,1][Cys]) was selected and employed as co-solvent. Some key reaction parameters involved in the bioreduction were also investigated in the [N1,1,1,1][Cys]-containing system. The optimum conditions for the process were found to be: 3.5% (w/v) [N1,1,1,1][Cys], 20% (v/v) isopropanol, 1 M BTAP, 12.7 g/L of recombinant E. coli cells, pH 6.8, reaction for 12 h at 30 °C. A 98.7% yield (with >99 % of enantiomeric excess (ee)) was obtained under the optimum conditions. The biocatalytic process was scaled up to a 5 L fermentor afforded high reaction yield in IL-containing system. The results demonstrated that the IL [N1,1,1,1][Cys] is a useful co-solvent to improve bioreduction process and may has potential applications in various biocatalytic reactions.