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Although the rhizomes of Rheum nobile Hook. f. et Thoms (Polygonaceae) are widely used in Tibetan medicine, no previous investigations regarding the biological activities and rarely chemical constituents of this plant have been reported. As part of an ongoing search for novel bioactive agents, a phytochemical investigation of R. nobile led to the isolation of two new compounds Rheumone B (1) and piceatannol-4'-O-β-D-(6″-O-acetyl)-glucoside (2), together with 15 known compounds by gel filtration over Sephadex LH-20 and preparative HPLC. Their structures were determined by combined spectroscopic methods. Compounds 1-10 were evaluated for their ability to scavenge 2,2-diphenyl-1-picrylhydzyl (DPPH) radical and compounds 7-10 showed relatively strong scavenging abilities with IC50 values from 2.76 μM to 11.80 μM. In conclusion, naphthalene glycosides, stilbene glycosides, flavanols, especially anthraquinones are main chemical constituents of this plant. The ability to scavenge DPPH radical of compound 8 was the highest among compounds 1-10.

Qumazi is a commonly used Tibetan medicine. With a long history, it can be found in the Four Medical Tantras written by gYu-thog rNying-ma Yon-tan mGon-po since the 8th century AD. Qumazi grows in mudflats and fields, including species growing in highlands, lowlands, mountains and farmlands. According to records in Crystal Beads Materia Medica, it features green sword-shaped leaves, thin stems with red veins, inserted panicles, white chicken-like flowers and copper needle row-like roots. However, there are many inconsistent morphological descriptions for Qumazi plants in many Chinese versions of Tibetan medicine books. In this article, after studying ancient and modern Tibetan medicine books, consulting experts and conducting surveys, the authors confirmed that Qumazi belongs to Rheum of Polygonaceae, including Rheum nobile Hook. f. et. Thoms, R. globulosum Gage, R. alexandrae Hook. f. et. Thoms, R. pumilum Maxim and R. delavayi Franch. In some regions, Qumazi is substituted by R. spiciforme Royle and R. przewalskyi Losinsk. After the Chinese version of Qinghai-Tibet Plateau Drug Illustrations was published in 1972, Qumazi has been miswritten as P. sibiricum Laxm in many Chinese versions of Tibetan medicine books, perhaps because P. sibiricum Laxm has many similar features with Qumazi as described in Crystal Beads Materia Medica and then is mistranslated from Tibetan to Chinese versions. According to records, Qumazi can reduce edema and is mainly applied to treat the minamata disease in clinic.