title: Elucidation of the mechanism of N-demethylation catalyzed by cytochrome P450 monooxygenase is facilitated by exploiting nitrogen-15 heavy isotope effects.
abstract: (15)N heavy isotope effects are especially useful when detail is sought pertaining to the reaction mechanism for the cleavage of a C-N bond. Their potential in assisting to describe the mechanism of N-demethylation of tertiary amines by the action of cytochrome P450 monooxygenase has been investigated. As a working model for the first step, oxidation of the N-methyl group to N-methoxyl, tropine and a cytochrome P450 monooxygenase reaction centre composed of a truncated heme with sulfhydryl as the axial ligand were used. It is apparent that this first step of the reaction proceeds via a hydrogen atom transfer mechanism. Transition states for this step are described for both the high spin ((4)TS(H)) and low spin ((2)TS(H)) pathways in both gas and solvation states. Hence, overall normal secondary (15)N KIE could be calculated for the reaction path modeled in the low spin state, and inverse for the reaction modeled in the high spin state. This partial reaction has been identified as the probable rate limiting step. The model for the second step, fission of the C-N bond, consisted of N-methoxylnortropine and two molecules of water. A transition state described for this step, TS(CN), gives a strongly inverse overall theoretical (15)N KIE.
authors.affiliation: Interdisciplinary Chemistry: Synthesis, Analysis and Modelling, UMR, University of Nantes-CNRS, France.
authors.forename: Renata A
authors.initials: RA
authors.lastname: Kwiecień
authors.forename: Roland
authors.initials: R
authors.lastname: Molinié
authors.forename: Piotr
authors.initials: P
authors.lastname: Paneth
authors.forename: Virginie
authors.initials: V
authors.lastname: Silvestre
authors.forename: Jacques
authors.initials: J
authors.lastname: Lebreton
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Robins
mesh_terms: D000588:Amines / Q000737:chemistry / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000378:metabolism*; D004583:Electrons; D006900:Hydroxylation; D008745:Methylation; D008958:Models, Molecular; D009587:Nitrogen Isotopes / Q000378:metabolism; D016958:Pseudomonas putida / Q000201:enzymology*; D011789:Quantum Theory; D014326:Tropanes / Q000737:chemistry / Q000378:metabolism
chemical_list: D000588:Amines; D009587:Nitrogen Isotopes; D014326:Tropanes; C005864:tropine; D003577:Cytochrome P-450 Enzyme System