C-glycosylflavone with rotational isomers from Vaccaria hispanica (Miller) Rauschert seeds

Abstract Five C-glycosylflavone were isolated from Vaccaria hispanica (Miller) Rauschert seeds. Their NMR spectra showed separate signals because of the existence of rotational isomers, which is an unusual phenomenon. The spectroscopic data revealed that compounds 1 – 5 were identified as apigenin 6- C -[ α - l -arabinopyranosyl-(1′′′→2′′)- β - d -glucopyranosyl]-7- O - β - d -glucopyranoside ( 1 ), apigenin 6- C -[ α - l -arabinopyranosyl-(1′′′→2′′)- β - d -glucopyranosyl]-7- O -(6′′′′- O -dihydroferuloyl)- β - d -glucopyranoside ( 2 ), apigenin 6- C - β - d -glucopyranosyl-7- O -(6′′′- O -dihydroferuloyl)- β - d -glucopyranoside ( 3 ) and isovitexin-2′′- O -arabinoside ( 4 ) and saponarin ( 5 ), respectively. The structure of ‘vaccarin’ was revised to apigenin 6- C -[ α - l -arabinopyranosyl-(1′′′→2′′)- β - d -glucopyranosyl]-7- O - β - d -glucopyranoside and consequently 1 should be named ‘vaccarin’. Among the isolated compounds, 2 and 3 are new and named vaccarin E and vaccarin F, respectively.