Highly glycosylated flavonols with an O-linked branched pentasaccharide from Iberis saxatilis (Brassicaceae)

Four flavonol glycosides isolated from non-flowering leafy shoots of Iberis saxatilis (Brassicaceae) were characterised by spectroscopic and chemical methods as saxatilisins A-D, the 3-O-β-D-glucopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)[β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→6)]-β-D-glucopyranoside, 3-O-β-D-glucopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)[α-L-rhamnopyranosyl-(1→6)]-β-D-glucopyranoside, 3-O-(6-O-E-sinapoyl)-β-D-glucopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)[β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→6)]-β-D-glucopyranoside, and 3-O-(6-O-E-feruloyl)-β-D-glucopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)[β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→6)]-β-D-glucopyranoside of isorhamnetin (3,5,7,4'-tetrahydroxy-3'-methoxyflavone), respectively. Analysis of (2)J(HC) correlations detected with the H2BC (heteronuclear two-bond correlation) pulse sequence aided the unambiguous assignment of glycosidic resonances in the (1)H and (13)C NMR spectra of these compounds. Saxatilisins A, C, and D, are the first flavonol glycosides to be described with a pentasaccharide chain at a single glycosylation site. Several pentaglycosides of kaempferol and quercetin, tentatively assigned as saxatilisin analogues from LC-MS/MS analyses, were present as minor constituents of the extracts.