Michael M. Gilbert's research while affiliated with University of Michigan and other places

The diversification of late stage synthetic intermediates provides significant advantages in efficiency in comparison to conventional linear approaches. Despite these advantages, accessing varying ring scaffolds and functional group patterns from a common intermediate poses considerable challenges using existing methods. The combination of regiodivergent nickel-catalyzed C–C couplings and site-selective biocatalytic C–H oxidations using the cytochrome P450 enzyme PikC addresses this problem by enabling a single late-stage linear intermediate to be converted to macrolactones of differing ring size and with diverse patterns of oxidation. The approach is made possible by a novel strategy for site-selective biocatalytic oxidation using a single biocatalyst, with site selectivity being governed by a temporarily installed directing group. Site selectivities of C–H oxidation by this directed approach can overcome positional bias due to C–H bond strength, acidity, inductive influences, steric accessibility, or immediate proximity to the directing group, thus providing complementarity to existing approaches.

The hallmark of enzymes from secondary metabolic pathways is the pairing of powerful reactivity with exquisite site selectivity. The application of these biocatalytic tools in organic synthesis, however, remains under-utilized due to limitations in substrate scope and scalability. Here, we report how the reactivity of a monooxygenase (PikC) from the pikromycin pathway is modified through computationally guided protein and substrate engineering, and applied to the oxidation of unactivated methylene C-H bonds. Molecular dynamics and quantum mechanical calculations were used to develop a predictive model for substrate scope, site selectivity and stereoselectivity of PikC-mediated C-H oxidation. A suite of menthol derivatives was screened computationally and evaluated through in vitro reactions, where each substrate adhered to the predicted models for selectivity and conversion to product. This platform was also expanded beyond menthol-based substrates to the selective hydroxylation of a variety of substrate cores ranging from cyclic to fused bicyclic and bridged bicyclic compounds.