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, RB; Ding, CZ; Borrillo, JL; Chang, JTJ Am. Chem. Soc. 1993, 115, 2982).[1, 1-2H2]-1 exhibits a deuterium isotope effect of 4.5 on inactivation, but in D2O the isotope effect is ...