Structure elucidation and antioxidant activity of the phenolic compounds from Rhynchosia suaveolens.

A new benzophenone, 2-hydroxy-3,4-dimethoxybenzophenone (1), together with a known C-glycosylxanthone, mangiferin (2) and two known C-glycosylflavones, isovitexin (3) and isoorientin (4), were isolated from the flowers of Rhynchosia suaveolens DC. (Fabaceae). The structure of the new compound (1) and the known compounds (2-4) were elucidated by extensive 1D and 2D NMR spectral studies. The plant extracts, as well as the isolated compounds, were evaluated for their total phenolic content (TPC), total flavonoid content (TFC) and DPPH radical scavenging activity. Among the isolated compounds, mangiferin (2) and isoorientin (4) showed significant radical scavenging activity comparable with that of ascorbic acid.