Cytochrome P450-catalyzed oxidation of N-benzyl-N-cyclopropylamine generates both cyclopropanone hydrate and 3-hydroxypropionaldehyde via hydrogen abstraction, not single electron transfer.
The suicide substrate activity of N-benzyl-N-cyclopropylamine (1) and N-benzyl-N-(1'-methylcyclopropyl)amine (2) toward cytochrome P450 and other enzymes has been explained by a mechanism involving single electron transfer (SET) oxidation, followed by ring-opening of the aminium radical cation (protonated aminyl radical) and reaction with the P450 active site. Although the SET oxidation of N-cyclopropyl-N-methylaniline (3) by horseradish peroxidase leads exclusively to ring-opened (non-cyclopropyl) products, P450 oxidation of 3 leads to formation of cyclopropanone hydrate and no ring-opened products, and 3 does not inactivate P450. To help reconcile these discrepant behaviors we have determined the complete metabolic fate of 1 with P450 in vitro. 3-Hydroxypropionaldehyde (3HP), the presumptive "signature metabolite" for SET oxidation of a cyclopropylamine, was observed for the first time in 57% yield, along with cyclopropanone hydrate (34%), cyclopropylamine (9%), benzaldehyde (6%), benzyl alcohol (12%), and benzaldoxime (19%). Unexpectedly, N-benzyl-N-cyclopropyl-N-methylamine (4) was found not to inactivate P450 and not to give rise to 3HP as a metabolite without first undergoing oxidative N-demethylation to 1. These and other observations argue against a role for SET mechanisms in the P450 oxidation of cyclopropylamines. We suggest that a conventional hydrogen abstraction/hydroxyl recombination mechanism (or its equivalent as a one-step "insertion" mechanism) at C-H bonds in 1-4 leads to nonrearranged carbinolamine intermediates and thereby to "ordinary" N-dealkylation products including cyclopropanone hydrate. Alternatively, hydrogen abstraction at the N-H bond of secondary cyclopropylamines 1 gives a neutral aminyl radical which could undergo rapid ring-opening leading either to enzyme inactivation or 3HP formation.
Cerny
Matthew A
MA
Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66045, USA.
Hanzlik
Robert P
RP
D000447:Aldehydes / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D003521:Cyclopropanes / Q000737:chemistry* / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry* / Q000378:metabolism*; D005985:Glyceraldehyde / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism; D006859:Hydrogen / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D011407:Propane / Q000737:chemistry* / Q000378:metabolism
D000447:Aldehydes; D003521:Cyclopropanes; C047158:3-hydroxypropionaldehyde; C047294:1-benzylcyclopropylamine; D005985:Glyceraldehyde; D006859:Hydrogen; D003577:Cytochrome P-450 Enzyme System; D006735:Horseradish Peroxidase; D011407:Propane