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

Leafy shoot extracts of Iberis saxatilis (Brassicaceae) afforded four isorhamnetin glycosides including three characterised by the branched pentasaccharide, β-d-Glcp-(1→3)-α-l-Rhap-(1→2)[β-d-Glcp-(1→2)-α-l-Rhap-(1→6)]-β-d-Glcp. [Display omitted] ► Four isorhamnetin glycoside structures determined using cryoprobe NMR and MS. ► First flavonol glycosides to be described with an O-linked pentasaccharide chain. ► Kaempferol and quercetin pentaglycosides detected as minor components by LC–MS/MS. ► Sinapoylation of glucosyl residues typical of Brassicaceae chemistry. 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 2JHC correlations detected with the H2BC (heteronuclear two-bond correlation) pulse sequence aided the unambiguous assignment of glycosidic resonances in the 1H and 13C 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.