Inhibition of Monoamine Oxidase by Stilbenes from Rheum palmatum.

Seven stilbenes and one catechin were bioactivity-guidedly isolated from the rhizomes of . Their structures were identified as piceatannol (1), resveratrol (2), piceid (3), rhapontigenin (4), piceatannol-3-O-β-D-glucopyranoside (5), rhaponticin (6), catechin (7) and desoxyrhapontigenin (8). Anti-monoamine oxidase (MAO) activities of compounds 1-8 were tested. Compounds 1 and 8 showed significant MAO inhibitory activities with IC values 16.4 ± 1.5 μM and 11.5 ± 1.1, respectively, when the IC value of iproniazid as a standard was 6.5 ± 0.5 μM. The selectivity of compounds 1-8 against MAO-A and MAO-B were also evaluated. The results showed that compounds 4˴6˴8 preferred to inhibit MAO-A rather than MAO-B with selectivity values ([IC of MAO-B]/ [IC of MAO-A]) of 4.74, 10.01 and 9.42, respectively. The preliminary structure-activity relationships (SARs) of these compounds were discussed and the molecular modeling was also performed to explore the binding mode of inhibitors at the active site of MAO-A and MAO-B.