859504-83-9Relevant academic research and scientific papers
P450/NADPH/O2- and P450/PhlO-catalyzed N-dealkylations are mechanistically distinct
Bhakta, Mehul N.,Hollenberg, Paul F.,Wimalasena, Kandatege
, p. 1376 - 1377 (2005)
A high-valent iron-oxo species analogous to the compound I of peroxidases has been thought to be the activated oxygen species in P450-catalyzed reactions. Spectroscopic characterization of the catalytically competent iron-oxo species in iodosobenzene (PhIO)-supported model reactions and parallels between these model reactions and PhIO- and NADPH/O2-supported P450 reactions have been taken as strong evidence for this proposal. To support this proposal, subtle differences observed in regio- and chemoselectivities, isotope effects, and source of oxygen, etc., between NADPH/O2- and PhIO-supported P450 reactions have been generally attributed to reasons other than the mechanistic differences between the two systems. In the present study, we have used a series of sensitive mechanistic probes, 4-chloro-N-cyclopropyl-N-alkylanilines, to compare and contrast the chemistries of the NADPH/O2- and PhIO-supported purified CYP2B1 N-dealkylation reactions. Herein we present the first experimental evidence to demonstrate that the NADPH/O2- and PhIO-supported P450 N-dealkylations are mechanistically distinct and, thus, the P450/PhIO system may not be a good mechanistic model for P450/NADPH/O2-catalyzed N-dealkylations. Copyright
A mechanistic comparison between cytochrome P450- and chloroperoxidase-catalyzed N-dealkylation of N,N-dialkyl anilines
Bhakta, Mehul N.,Wimalasena, Kandatege
, p. 4801 - 4805 (2007/10/03)
Most peroxidases use histidine as an axial ligand for heme, while chloroperoxidase (CPO) uses a thiolate, which is similar to the ligand employed by cytochrome P450 (P450). Several studies have also shown that, unlike other peroxidases, CPO is capable of carrying out monooxygenation reactions in a similar manner to P450 in addition to typical peroxidase-like reactions. These observations have been attributed to the similarities of the active-site architecture of the two enzymes. Both enzymes have been shown to efficiently catalyze the oxidative N-dealkylation of amines. The similar magnitudes of the kinetic isotope effects determined for P 450- and CPO-catalyzed N-dealkylation of N,N-dimethylaniline have been used to propose that these reactions proceed through similar mechanisms. In this study, we have examined the mechanism of CPO-catalyzed N-dealkylation using a series of radical probes, 4-chloro-N-cyclopropyl-N-alkylanilines 1-3, which we have recently used in the mechanistic studies of P450, and compared the results with those of P450-catalyzed reactions. The results show that P450- and CPO-catalyzed reactions proceed through distinctly different mechanisms. As previously reported, while P 450-catalyzed reactions appear to proceed through a C α-hydrogen abstraction mechanism, CPO-catalyzed reactions proceed through a single electron/proton transfer (SET/H+) mechanism, similar to reactions catalyzed by Horseradish peroxidase (HRP). Thus, CPO may not be a good mechanistic model for P450-catalyzed N-dealkylations. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
