Quercetin and kaempferol 3-O-[α-L-rhamnopyranosyl-(→2)-α- L-arabinopyranoside]-7-O-α-L-rhamnopyranosides from Anthyllis hermanniae: Structure determination and conformational studies

The study reports the isolation and structural identification of two new flavonol triglycosides from the methanolic extract of Anthyllis hermanniae, exhibiting the same glycosylation pattern: quercetin 3-O-[α-L- rhamnopyranosyl-(→2)-α-l-arabinopyranoside]-7-O-α-L- rhamnopyranoside (1) and kaempferol 3-O-[α-L-rhamnopyranosyl-(→2)- α-l-arabinopyranoside]-7-O-α-L-rhamnopyranoside (2). A conformational study related to the central arabinoside moiety was carried out including the analysis of the contribution of NOE effects and acetylation to the elucidation of the 2-O-linked arabinoside configuration of the anomeric carbon. We also report the total synthesis of a model compound, quercetin 3-O-α-L-rhamnopyranosyl-(→2)-α-l-arabinopyranoside (3), which verifies the structures of the isolated compounds. © 2011 The American Chemical Society and American Society of Pharmacognosy.