A new flavone C-glycoside from Clematis rehderiana.

A new flavone C-glycoside, isovitexin 6''-O-E-p-coumarate (1) and two known flavonoid glycosides--quercetin 3-O-beta-D-glucuronopyranoside (2) and isoorientin (3)--were isolated from an ethanol extract of aerial parts of Clematis rehderiana. Their structures were determined by spectroscopic methods. The antioxidant effects of the two flavone C-glycosides were evaluated by both the MTT and DPPH assays. Compound 1 showed potent activities against H2O2-induced impairment in PC12 cells within the concentration range tested, whereas compound 3 scavenged DPPH radical strongly, with an IC50 value of 13.5 microM.