Photometallobiocatalytic Asymmetric Radical-Mediated Cross-Coupling of Organotrifluoroborate Salts and Pyridotriazoles.

The cooperative integration of photoredox catalysis and metalloenzyme catalysis has emerged as a powerful strategy for enabling stereoselective radical transformations beyond the capabilities of either catalytic mode alone. Herein, we report a photometallobiocatalytic enantioselective intermolecular C-C cross-coupling of pyridotriazoles and secondary alkyltrifluoroborate salts through cooperative catalysis between an organic photosensitizer and an engineered protoglobin. By combining visible-light-mediated radical generation with enzymatic activation of pyridotriazoles to form reactive Fe carbenoid intermediates, this transformation enabled highly enantioselective radical C-C bond formation through a proposed outer-sphere coupling mechanism. Through biocatalyst mining and directed evolution, engineered Aeropyrum pernix protoglobin catalysts were developed that catalyzed this radical C-C coupling with excellent efficiency and stereocontrol. The photobiocatalytic platform exhibited a broad substrate scope with respect to both secondary alkyltrifluoroborate salts and pyridotriazoles, affording a range of valuable N-heterocyclic products in excellent yields and enantioselectivities. Mechanistic studies supported the involvement of radical intermediates and revealed spontaneous binding between the photocatalyst eosin B and the engineered metalloenzyme. By leveraging cooperative photometallobiocatalysis, this work established an underexplored strategy for asymmetric intermolecular radical cross-coupling via an outer-sphere mechanism, further expanding the catalytic repertoire of transition-metal carbenoid chemistry.