Phenolic Derivatives and Free-Radical-Scavenging Activity from Ixeridium gracile (DC.) SHIH

Phytochemical investigation of the Tibetan medicinal plant Ixeridium gracile resulted in the isolation and identification of twelve flavonoids and two coumarins, compounds 1–14, the dimeric 92a,3a-epoxy- 5,7,3’,4’-tetrahydroxyflavan-(4b!8)-epicatechin; (1) being a new constituent. The free-radical-scavenging potentials of different extract fractions as well as of the pure compounds towards the DPPH (1,1- diphenyl-2-picrylhydrazyl) radical were evaluated, and are discussed in terms of structure–activity relationship (SAR). The flavonoids were found to be the major constituents contributing to the freeradical- scavenging activity of I. gracile, but the high concentration of coumarins additionally contributed to the observed activity.