Antioxidant Flavone Glycosides from the Leaves of Sasa borealis

Sasa borealis (Poaceae) is a perennial medicinal plant which is a major source of bamboo leaves in Korea. The n-BuOH extract of S. borealis leaves exhibited significant antioxidant activity against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and a cytoprotective effect against oxidative damage in HepG2 cells. Bioactivity-guided fractionation by column chromatography led to the isolation of two antioxidative flavonoid C-glycoside derivatives, isoorientin (2) and isoorientin 2"-O-${\alpha}$-L-rhamnoside (4) along with tricin 7-O-${\beta}$-D-glucopyranoside (1) and apigenin 6-C-${\beta}$-D-xylopyranosyl-8-C-${\beta}$-D-glucopyranoside (3). Their structures were identified on the basis of chemical and spectroscopic methods. The radical scavenging activity and cytoprotective effect against oxidative damage of all the isolated compounds were also evaluated. Isoorientin (2) and isoorientin 2-O-${\alpha}$-L-rhamnoside (4) showed potent free radical scavenging activity with IC$_{50}$ values of 9.5 and 34.5 ${\mu}$M, respectively, and strong cytoprotective effects against t-BOOH-induced oxidative damage in HepG2 cells, at very low concentrations of 1.1 ${\mu}$M isoorientin and 0.8 ${\mu}$M isoorientin 2-O-${\alpha}$-L-rhamnoside. This is the first report of the isolation and antioxidant activity of compounds 2 and 4 from S. borealis.