Biocatalytic Carbene Transfer Using Diazirines.

Biocatalytic carbene transfer from diazo compounds is a versatile strategy in asymmetric synthesis. However, the limited pool of stable diazo compounds constrains the variety of accessible products. To overcome this restriction, we have engineered variants of protoglobin (Pgb) that use diazirines as carbene precursors. While the enhanced stability of diazirines relative to their diazo isomers enables access to a diverse array of carbenes, they have previously resisted catalytic activation. Our engineered Pgb variants represent the first example of catalysts for selective carbene transfer from these species at room temperature. The structure of an Pgb variant, determined by microcrystal electron diffraction (MicroED), reveals that evolution has enhanced access to the heme active site to facilitate this new-to-nature catalysis. Using readily prepared aryl diazirines as model substrates, we demonstrate the application of these highly stable carbene precursors in biocatalytic cyclopropanation, N-H insertion, and Si-H insertion reactions.