Quercetin and its glycosides in the flowers of Asclepias syriaca L.

The following flavonoid compounds have been isolated and identified from the flowers of Asclepiac syriaca L.: quercetin and its glycosides: 7-O-galactoside, 7-O-glucoside, 3-O-beta-D-xylopyranoside(1-->2) beta-D-galactoside and 3-O-beta-D-glucopyranoside(1-->2) beta-D-galactoside. Their structures were established by acid and enzymatic hydrolysis or H2O2 oxidation as well as spectral analysis (UV, 1H and 13C NMR).