Biocatalytic, Enantioenriched Primary Amination of Tertiary C–H Bonds

Intermolecular functionalization of tertiary C–H bonds to construct fully substituted stereogenic carbon centers represents a formidable challenge: without the assistance of directing groups, the state-of-the-art catalysts struggle to introduce chirality to racemic tertiary sp3-carbon centers. Direct asymmetric functionalization of such centers is a worthy reactivity and selectivity goal for modern biocatalysis. Here we present an engineered nitrene transferase (P411-TEA-5274), derived from a bacterial cytochrome P450, that is capable of aminating tertiary C–H bonds to provide chiral α-tertiary primary amines with high efficiency (up to 2300 total turnovers) and selectivity (up to >99% enantiomeric excess (e.e.)). The construction of fully substituted stereocenters with methyl and ethyl groups underscores the enzyme’s remarkable selectivity. A comprehensive substrate scope study demonstrates the biocatalyst’s compatibility with diverse functional groups and tertiary C–H bonds. Mechanistic studies, incorporating both experimental and computational data, elucidate how active-site residues distinguish between the enantiomers and enable the enzyme to perform this transformation with excellent enantioselectivity.