Development of biocompatible DES/NADES as co-solvents for efficient biosynthesis of chiral alcohols.

The novel deep eutectic solvents (DESs) and natural deep eutectic solvents (NADESs) were designed and synthesized by cell protective components, in which the compounds were derived from natural alternative sources. The performances of designed DESs/NADESs as co-solvent were investigated in asymmetric reduction catalyzed by microbial cells. The DESs/NADESs synthesized by three different types of hydrogen bond receptor (betaine, L-proline and L-carnitine) conferred an advantage over conventional choline chloride-based DESs/NADESs and aqueous buffer system, with regard to efficient bioproduction of (R)-1-[4-(trifluoromethyl)phenyl]ethanol by recombinant Escherichia coli cells. TEM images exhibited that the cell membrane integrity during exposure to the developed NADESs was better than that after treatment with choline chloride-based NADES, which accounted for enhanced catalytic efficiency. This bioprocess was also feasible at 500 mL preparation scale with 92.4% yield under 400 mM substrate loading. To broaden the applicability of three types of DES/NADESs that increased catalytic efficiency in the process of E. coli-mediated reduction, the production of various chiral alcohols in developed reaction media were further examined, with some positive results. It was also found that lysine-based NADES could even reverse the enantioselectivity of biocatalyst at high water content in the reaction medium. These findings may aid in the development of novel DESs/NADESs for biocatalysis.

High-Efficient Production of (S)-1-[3,5-Bis(trifluoromethyl)phenyl]ethanol via Whole-Cell Catalyst in Deep-Eutectic Solvent-Containing Micro-Aerobic Medium System.

The ratio of substrate to catalyst (S/C) is a prime target for the application of asymmetric production of enantiomerically enriched intermediates by whole-cell biocatalyst. In the present study, an attractive increase in S/C was achieved in a natural deep-eutectic solvent (NADES) containing reaction system under microaerobic condition for high production of (S)-1-[3,5-bis(trifluoromethyl)phenyl]ethanol ((S)-3,5-BTPE) with Candida tropicalis 104. In PBS buffer (0.2 M, pH 8.0) at 200 rpm and 30 °C, 79.5 g (Dry Cell Weight, DCW)/L C. tropicalis 104 maintained the same yield of 73.7% for the bioreduction of 3,5-bis(trifluoromethyl)acetophenone (BTAP) under an oxygen-deficient environment compared with oxygen-sufficient conditions, while substrate load increased 4.0-fold (from 50 mM to 200 mM). Furthermore, when choline chloride:trehalose (ChCl:T, 1:1 molar ratio) was introduced into the reaction system for its versatility of increasing cell membrane permeability and declining BTAP cytotoxicity to biocatalyst, the yields were further increased to 86.2% under 200 mM BTAP, or 72.9% at 300 mM BTAP. After the optimization of various reaction parameters involved in the bioreduction, and the amount of biocatalyst and maltose co-substrate remained 79.5 g (DCW)/L and 50 g/L, the S/C for the reduction elevated 6.3 times (3.8 mM/g versus 0.6 mM/g). By altering the respiratory pattern of the whole-cell biocatalyst and exploiting the ChCl:T-containing reaction system, the developed strategy exhibits an attractive potential for enhancing catalytic efficiency of whole-cell-mediated reduction, and provides valuable insight for the development of whole-cell catalysis.