Biocatalytic, enantioenriched primary amination of tertiary C–H bonds

Intermolecular functionalization of tertiary C–H bonds to construct fully substituted stereogenic carbon centres represents a formidable challenge: without the assistance of directing groups, state-of-the-art catalysts struggle to introduce chirality to racemic tertiary sp3-carbon centres. Direct asymmetric functionalization of such centres 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 2,300 total turnovers) and selectivity (up to >99% enantiomeric excess). The construction of fully substituted stereocentres 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 explain how active-site residues distinguish between the enantiomers and enable the enzyme to perform this transformation with excellent enantioselectivity. Direct stereoselective amination of tertiary C–H bonds without the assistance of directing groups is a challenging task in synthetic organic chemistry. Now a nitrene transferase is engineered to aminate tertiary C–H bonds with high enantioselectivity, providing direct access to valuable chiral α-tertiary primary amines.