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.