Photoenzymatic Cascade Catalysis with an Artificial CDCase for Stereoselective Cross-Dehydrogenative Coupling

The stereoselective cross-dehydrogenative coupling (CDC) reaction represents a highly promising approach for the direct synthesis of high-value non-natural amino acids. The photoenzyme cascade strategy synergistically integrates the reactivity of photocatalysts with the selectivity of enzymes, demonstrating attractive potential for eco-friendly asymmetric synthesis. In this study, we report a photoartificial CDCase cascade method for the asymmetric CDC reaction between N-aryl glycine esters and cycloketones. The optimal artificial CDCase was constructed by anchoring the biotinylated Cu-phenanthroline cofactor (5-NH2Phen-biotin*Cu(OAc)2) within the double mutant (S112H–K121M) of streptavidin obtained through genetic engineering optimization. In a mild aqueous medium, the resulting artificial CDCase cooperates with photocatalysis, efficiently catalyzing the asymmetric CDC reaction at a low enzyme loading (0.5 mol %), yielding a series of α-cycloketone-substituted N-aryl glycine esters with good yields and stereoselectivities. Comprehensive molecular docking and molecular dynamics (MD) simulations provided insights into the critical complex intermediates involved in the proposed reaction mechanism and clarified the interactions between the artificial CDCase and its substrates. Furthermore, through analysis of interatomic distances between pivotal reactive carbon centers and probable nucleophilic attack directions, we have deciphered the structural foundation underlying the formation of the predominant conformation, concurrently rationalizing the enhanced reactivity and stereoselectivity observed for the S112H–K121 M mutant.