p-Methoxyamphetamine, a potent reversible inhibitor of type-A monoamine oxidase in vitro and in vivo.

p-Methoxyamphetamine is over 20 times as potent as (+)-amphetamine as an inhibitor of 5-HT oxidation by monoamine oxidase in mouse brain in vitro, with a Ki value of 0.22 microM. It is highly selective towards A-type monoamine oxidase and possesses only weak activity against the B-type enzyme (Ki value about 500 microM with benzylamine as substrate and solubilized rat liver mitochondria as enzyme source). It is 10 times more active than (+)-amphetamine in protecting mouse brain monoamine oxidase from inhibition by phenelzine in vivo. o-Methoxy- and m-methoxyamphetamines inhibit monoamine oxidase both in vitro and in vivo with potencies comparable with, or less than that of (+)-amphetamine.