Quercetin and kaempferol 3-O-[α-L-rhamnopyranosyl-(1→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-(1→2)-α-L-arabinopyranoside]-7-O-α-L-rhamnopyranoside (1) and kaempferol 3-O-[α-L-rhamnopyranosyl-(1→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-(1→2)-α-L-arabinopyranoside (3), which verifies the structures of the isolated compounds.