Turning the band alignment of carbon dots for visible-light-driven enzymatic asymmetric reduction of aromatic ketone.

Keto reductases are crucial NAD(P)H-dependent enzymes used for the enantioselective synthesis of alcohols from prochiral ketones. Typically, the NADPH cofactor is regenerated through a second enzyme and/or substrate. However, photocatalytic cofactor regeneration using water as a sacrificial electron and hydrogen donor presents a promising alternative, albeit a challenging one. Herein we fabricated several nitrogen-doped carbon dots (CDs) with visible light absorption properties, good water solubility and biocompatibility for photocatalytic regeneration of NADPH. The CD with a smaller size and suitable redox potential gave the highest NADPH yield (55.7 %). Based on this, NADPH-dependent aldo-keto reductase crosslinked aggregates (AKR-CLEs) were initially applied as a stable biocatalyst to reduce the prochiral ketone. (S)-1-(2-Chlorophenyl) ethanol, an intermediate for LPA1R antagonists, was obtained in 65.3 % yield and 99.99 % enantiomeric excess (ee) under visible light irradiation. The isotope tracer experiment confirmed that water is the hydrogen donor in this light-driven, photo-enzymatic asymmetric hydrogenation system. This method is useful for the sustainable synthesis of chiral alcohols. Moreover, the general principle of utilizing water as the sacrificial hydrogen and electron donor holds potential for application in other redox cofactor regeneration systems.