Monoamine oxidase inhibitory components from Cayratia japonica.

Seven flavonoids were isolated from the whole plants and fruits of Cayratia japonica through the activity-guided isolation of a methanol extract using a monoamine oxidase (MAO) inhibition assay as a monitor. The chemical structures of the isolates were assigned as apigenin-7-O-beta-D-glucuronopyranoside (1), apigenin (2), luteolin (3), luteolin-7-O-beta-D-glucopyranoside (4), (+)-dihydroquercetin (taxifolin) (5), (+)-dihydrokaempferol (aromadendrin) (6) and quercetin (7). Among the isolated compounds, flavones such as apigenin (2) and luteolin (3), as well as the flavonol, quercetin (7) showed potent inhibitory effects against the MAO activity with IC50 values of 6.5, 22.6, and 31.6 microM, respectively. However, the flavone glycosides, apigenin-7-O-beta-D-glucuronopyranoside (1) and luteolin-7-O-beta-D-glucopyranoside (4), showed mild MAO inhibition (IC50 values: 81.7 and 118.6 microM, respectively). The flavanonol derivatives, taxifolin (5) and aromadendrin (6), also showed weak inhibition (IC50 values: 154.7 and 153.1 microM, respectively). Furthermore, quercetin (7) had a more potent inhibitory effect on MAO-A (IC50 value: 2.8 microM) than MAO-B (IC50 value: 90.0 microM). Apigenin (2) and luteolin (3) also preferentially inhibited MAO-A (IC50 values: 1.7 and 4.9 microM, respectively) compared with MAO-B (IC50 values: 12.8 and 59.7 microM, respectively).