Monoamine oxidase inhibitors from Cinchonae Cortex.

Three strong alkaloidal monoamine oxidase (MAO) inhibitors, quinine (1), cinchonicinol ([ 1S,3'R,4'R]-3-(3-ethenyl-4-piperidinyl)-1-(4-quinolinyl)-1-propanol) (2) and cinchonaminone ([ 3'R,4'S]-2-[2-(3-ethenyl-4-piperidinyl)-acetyl]-1H-indole-3-ethanol) (3), were isolated from Cinchonae Cortex (Cinchona succirubra Pav., Rubiaceae). The structures of 2 and 3 were elucidated on the bases of spectral data and chemical evidence, and 3 is a new alkaloid. The inhibitory effects on MAO of 1, 2, 3 and related alkaloids were assayed. The type of inhibition by 1 with respect to benzylamine as a substrate was competitive.