A new class of powerful inhibitors of monoamine oxidase A

It is well established that 1-methyl-4-phenylpyridinium (MPP), the neurotoxic bioactivation product of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and most of its analogs are good competitive inhibitors of monoamine oxidase A, with K _i values in the micromolar range, but they inhibit monoamine oxidase B only at much higher concentrations. We report here the finding that alkyl derivatives of MPP ⁺ substituted at the 4′ position of the aromatic ring are considerably more effective reversible inhibitors of the A type enzyme, with K _i values in the nanomolar range (0.075 -1.6 μM). They inhibit the B type enzyme only at 2 to 3 orders of magnitude higher concentrations (32-374 μM).