Chemodivergent C(sp3)–H and C(sp2)–H cyanomethylation using engineered carbene transferases

The ubiquity of C–H bonds presents an opportunity to efficiently elaborate and build complexity in organic molecules. Methods for selective functionalization, however, must differentiate among multiple, chemically similar C–H bonds: enzymes are attractive because they can be finely tuned using directed evolution to achieve divergent reaction outcomes. Here we present engineered enzymes that effect a new-to-nature C–H alkylation (C–H carbene insertion) with distinct selectivities: cytochrome P450-based carbene transferases deliver an α-cyanocarbene either into the α-amino C(sp3)–H bonds or the ortho-arene C(sp2)–H bonds of N-substituted arenes. These two transformations proceed via different mechanisms, yet only minimal changes to the protein scaffold were needed to adjust the enzyme's chemoselectivity. Structural studies of the C(sp3)–H alkylase reveal an active-site helical disruption, which alters the structure and electrostatics of the substrate-binding pocket compared to the native enzyme. Overall, this work demonstrates advantages of using highly tuneable enzymes as C–H functionalization catalysts for divergent molecular derivatization. The design of complementary catalysts to target different C–H bonds in a specific molecule is challenging. Now, a pair of P450-based carbene transferase enzymes is engineered, which can selectively cyanomethylate either a C(sp3)–H or arene C(sp2)–H bond present in the same substrate.