Benzyne Formation in the Mechanism-Based Inactivation
of Cytochrome P450 by 1‑Aminobenzotriazole and N‑Benzyl-1-Aminobenzotriazole: Computational Insights
posted on 2015-05-01, 00:00authored byPratanphorn Chuanprasit, Shu Hui Goh, Hajime Hirao
Cytochrome P450 enzymes (P450s) are
ubiquitously distributed heme
enzymes that play catalytic roles in the essential oxidative biotransformation
of a wide range of exogenous and endogenous organic compounds. Strong
inhibition of P450s through mechanism-based inactivation (MBI) essentially
should not occur, because it would affect important metabolic processes
adversely. However, accumulated evidence shows that the MBI of a P450
is not a rare event. MBI can also be exploited for useful applications
such as reaction phenotyping. Thus, MBI is clearly one of the major
problems concerning P450s, but the reaction mechanisms underlying
MBI are not very clear in many cases. In this work, we used density
functional theory (DFT) calculations to understand how a metabolite
(benzyne) is formed from two mechanism-based inactivators of P450s:
1-aminobenzotriazole (ABT) and N-benzyl-1-aminobenzotriazole
(BBT). ABT has been widely used for reaction phenotyping. Our DFT
calculations show that the formation of benzyne from ABT occurs via
two sequential H-abstraction reactions from the exocyclic N–H
bonds, similar to the reaction of 1,1-dimethylhydrazine (Hirao, H.;
Chuanprasit, P.; Cheong, Y. Y.; Wang, X. Chem. Eur. J.2013, 19, 7361–7369). The transition
states for these H-abstractions are stabilized by a proton-coupled
electron transfer effect. The formation of benzyne from BBT is also
triggered by H-abstraction from the N–H bond. However, in this
case, the second step is H-abstraction from a benzylic C–H
bond. In addition, for the formation of benzyne from BBT, another
catalytic cycle should be necessary. Our computational study therefore
elucidates the difference in reaction mechanisms between ABT and BBT,
providing new insights into the processes involved in the MBI caused
by these compounds.