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A novel dimer of piceatannol glycoside, named rheumaustralin (1) was isolated from the underground parts of the ethnomedicinal plant Rheum austral (Polygonaceae) collected from Tibet together with 17 known compounds, including rheumin (2),2,5-dimethyl-7-hydroxychromone (3), 2,5-dimethylchromone-7-O-β-D-glucopyranoside (4),7-hydroxy-2-(2′-hydroxypropyl)-5-methylchromone (5), torachrysone (6) torachrysone-8-O-β-D-glucopyranoside (7), 4-(4′-hydroxyphenyl)-2-butanone-4′-O-β-D-glucopyranoside (8), amabiloside (9), N-trans-feruloyl tyramine (10), chrysophanol (11), aloe-emodin (12), emodin (13), physcion (14), physcion-1-O-β-D-glucopyranoside (15), emodin-8-O-β-Dglucopyranoside (16), D-catechin (17) and gallic acid (18). Their structures were determined by combined spectroscopic methods and by comparison of their spectral data with those reported in literature. Compounds 1–10 were tested for their ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. [ABSTRACT FROM AUTHOR]

This paper reports the isolation and characterization of seven piceatannol derivatives (1-7), including two new compounds (4 and 6), along with resveratrol (8) and polydatin (9), from the underground parts of Rheum austral D. Don collected from Tibet. The structures of the isolates were identified based on analysis of their spectroscopic data and comparison with literature. Compounds 3-7, piceatannol-4'-O-glucopyranoside and its 6"-O-acylated derivatives reported in this study may be useful chemotaxonomic markers for R. austral collected from Tibet. [ABSTRACT FROM AUTHOR]