Directed Evolution toward an Iron-Heme Enzyme for Asymmetric C–H Amination
Enantioselective, Intermolecular Benzylic C–H Amination Catalysed by an Engineered Iron-Haem Enzyme.
Nat. Chem. 2017;
18. August 2017 (online)
Arnold and co-workers report the directed evolution from iron-heme P450BM3 to P411CHA for the highly enantioselective intermolecular amination of benzylic C–H bonds with up to 1300 catalytic turnovers. The authors suggest that the reaction proceeds through a commonly accepted iron nitrenoid intermediate, which undergoes nitrene insertion to afford valuable benzyl amines in up to 87% yield and >99.5:0.5 er.
The authors discovered that P-4, a P450BM3 variant with 17 mutations from the wild-type, catalyzes the benzylic C–H amination of 4-ethylanisole, albeit with low enantioselectivity. Through sequential rounds of site-selective mutagenesis, P-411CHA was found to dramatically improve the yield and enantioselectivity of the reaction for a wide range of electronically-differentiated substrates. X-ray crystallography showed that all of the beneficial mutations lie within the active site of the enzyme.