A mechanistic comparison between cytochrome P450- and chloroperoxidase-catalyzed N-dealkylation of N,N-dialkyl anilines

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 P-450 (P-450). Several studies have also shown that, unlike other peroxidases, CPO is capable of carrying out monooxygenation reactions in a similar manner to P-450 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 P-450, and compared the results with those Of P-450-catalyzed reactions. The results show that P-450- and CPO-catalyzed reactions proceed through distinctly different mechanisms. As previously reported, while P-450-catalyzed reactions appear to proceed through a C.-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. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)