Efficient In Situ Regeneration of NADH Mimics by an Artificial Metalloenzyme

NADH mimics (mNADHs) have been shown to accelerate and orthogonally activate ene reductase-catalyzed reactions. However, existing regeneration methods of NAD(P)H fail for mNADHs. Catalysis with artificial metalloenzymes based on streptavidin (Say) variants and a biotinylated iridium cofactor enable mNADH regeneration with formate. This regeneration can be coupled with ene reductase-catalyzed asymmetric reduction of a,fi-unsaturated compounds, because of the protective compartmentalization of the organometallic cofactor. With 10 mol % mNAD+, a preparative scale reaction (>100 mg) gave full conversion with 98% ee, where TTNs reached 2000, with respect to the Ir cofactor under ambient atmosphere in aqueous medium.