Xanthone glycosides from herbs of Polygala hongkongensis Hemsl and their antioxidant activities.

Two new xanthone O-glycosides, polyhongkongenosides A (1) and B (2), together with four known xanthone glycosides, were isolated from the herbs of Polygala hongkongensis Hemsl. Their structures were elucidated on the basis of UV, IR, NMR, and MS spectral data. The antioxidant in vitro activities of 1-6 were determined by the scavenging activities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and hydroxyl radicals and their reductive activities to Fe3+. Mangiferin, one of the four known xanthone glycosides, showed potential scavenging effect on DPPH and hydroxy radicals and reductive activity to Fe3+ with IC50 values of 4.7, 13.9, 23.7 microM, respectively.