Relay Oxidation with Engineered P450 BM3 and Aldo-Keto Reductase: Chemoenzymatic Synthesis of Erythrina Alkaloids

Direct selective C–H oxidation poses a significant challenge in natural product synthesis. Enzymes serve as enabling catalysts to precisely control the transformation with high chemo-, regio-, and stereoselectivity. In this study, we report the screening and engineering of a P450 BM3 variant capable of selective hydroxylation in the tricyclic core of erythrina alkaloids with high diastereoselectivity. To further address the enantioselectivity to construct the chiral α-tertiary amine, an enzymatic kinetic resolution by relay oxidation with engineered P450 BM3 and aldo-keto reductase was successfully implemented, utilizing a highly enantioselective aldo-keto reductase, resulting in the chiral intermediate, which has been successfully applied to the synthesis of 3-demethoxyerythratidinone. The selectivity modulation not only deepens our understanding of enzyme-catalyzed non-natural chemical transformations but also inaugurates an alternative synthetic route for bioactive molecules.