Inactivation of monoamine oxidase B by benzyl 1-(aminomethyl)cyclopropane-1-carboxylate

Article abstract of DOI:10.1016/S0968-0896(96)00235-0

Monoamine oxidase (MAO) is a flavoenzyme that catalyzes the oxidation of various biogenic and xenobiotic amines. Benzyl 1-(aminomethyl)cyclopropane-1-carboxylate (1) was designed as a diactivated cyclopropane mechanism-based inactivator of MAO (Silverman, R.B.; Ding, C.Z.; Borrillo, J.L.; Chang, J.T. J. Am. Chem. Sec. 1993, 115, 2982). [1,1-²H₂]-1 exhibits a deuterium isotope effect of 4.5 on inactivation, but in D₂O the isotope effect is only 2.3. [1-³H]-1 and [1-¹⁴C]-1 were synthesized; upon inactivation of MAO, 1.1 and 2.0 equiv of radioactivity, respectively, are incorporated into the enzyme. Tritium, as ³H₂O, is released during inactivation with [1-³H]-1. The flavin absorption spectrum changes from that of oxidized to that of reduced flavin after inactivation; denaturation of the inactivated enzyme shows a reduced flavin spectrum, suggesting the formation of a modified flavin. Tryptic digestion of the enzyme labeled with [1-³H]-1 or [1-¹⁴C]-1, followed by HPLC analysis, monitoring at 450 nm (flavin), shows that the radioactivity comigrates with the 450 nm absorptions. The metabolites that are generated during in activation are benzyl 1-formylcyclopropane-1-carboxylate, benzyl alcohol, and 1-formylcyclopropane-1-carboxylic acid; no ring-cleaved products were detected. The partition ratio, as determined from the ratio of nonamines to enzyme, is 110. These results are rationalized in terms of a single-electron transfer mechanism leading to the imine of benzyl 1-formylcyclopropane-1-carboxylate, which alkylates the flavin coenzyme.