Two-Step Concerted Mechanism for the Hydrocarbon Hydroxylation by Cytochrome P450

Abstract

Abstract A possible two-step mechanism for the hydrocarbon hydroxylation by the oxoferryl active species of cytochrome P450 is discussed. We propose that the catalytic reaction is initiated by the formation of a reactant complex involving a five-coordinate carbon species or a σ-complex, followed by concerted hydrogen and alkyl migrations which lead to the formation of a product complex involving alcohol as a ligand. The porphyrin ring is predicted from molecular mechanics and extended Hückel calculations to be significantly bent in the reactant complex and in the hydroxy intermediate to form an energetically preferred octahedral environment at the iron active center. Such bent structures for the porphyrin ring are consistent with observed cis-coordination geometries for the M(porphyrin)L2 complexes, in which M is a large transition-metal ion and L is a ligand. We suggest that possible inversion at the five-coordinate carbon species in the reactant complex can occur to lead to partial inversion of stereochemistry at a labeled carbon.