Isolation of Monoamine Oxidase Inhibitors from Glycyrrhiza uralensis Roots and the Structure-Activity Relationship

Abstract

Two active compounds that inhibit the mitochondrial monoamine oxidase (MAO) of rat liver were isolated from Glycyrrhiza uralensis roots and identified as liquiritigenin and isoliquiritigenin. The latter compound was more active than the former, showing a substrate-competitive inhibition of MAO (K_i = 2.11 µM). Studies on the structure-activity relationship suggested that the inhibitory activity of the chalcone derivatives can be attributed to either 4- or 4′-hydroxy group and the possible coplanarity between the phenyl ring and the adjacent conjugated ketone.