Performance of Recombinant-Whole-Cell-Catalyzed Reductions in Deep-Eutectic-Solvent-Aqueous-Media Mixtures

Deep-eutectic solvents (DES) are cost-effective, nonhazardous solvents that may be used in biocatalysis as nonconventional media that enable biotransformations with industrially sound high substrate loadings. Based on promising prognoses, this paper explores successfully the use of whole cells overexpressing oxidoreductases as biocatalysts for the stereoselective reduction of ketones in different DES-aqueous-media solutions. Enzymes like Ralstonia sp. alcohol dehydrogenase (ADH) and horse liver ADH, overexpressed in Escherichia coli, remain active at different DES proportions (for example, DES: buffer, 80:20 v/v) to enable nonconventional biotransformations. Furthermore, the enantiomeric excesses obtained for a broad range of aromatic substrates increase significantly if DES is added, which provides a useful tool for combining high substrate loadings and improved enzymatic selectivities while working with nonhazardous solvents. Different DES are successfully employed, which gives hints of the potential that these emerging solvents may have.