Nat. Chem. doi: 10.1038/nchem.2783 (2017)

Credit: NATURE CHEMISTRY

In nature, cytochrome P450 monooxygenases catalyze the insertion of oxygen into unactivated C–H bonds. Downstream reactions can then convert the hydroxyl group to an amine, but no known natural enzymes exist for the direct amination of C–H bonds. Using a heme-containing variant of a cytochrome P450, termed cytochrome P411, Prier et al. used directed evolution to generate an engineered enzyme for enantioselective C–H amination. The resulting aminase, P411CHA, uses tosyl azide (TsN3) as a nitrene source, reacting with the heme cofactor to generate an iron nitrenoid intermediate from which the nitrene moiety is inserted into an alkane C–H bond. P411CHA can catalyze up to 1,300 turnovers with >99% enantiomeric excess in water at room temperature, under either aerobic or anaerobic conditions, making it a more efficient and environmentally friendly catalyst than existing synthetic transition-metal complexes. Furthermore, P411CHA is also capable of aminating diverse arene-containing hydrocarbon substrates both as a purified enzyme and in whole Escherichia coli cells. Although P411CHA is not able to aminate allylic or aliphatic C–H bonds, and has limited capacity for large substrates, its development lays the foundation for future engineering of new enzymes for the selective and direct transformation of unactivated C–H bonds.