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 alpha-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.