Structure elucidation of cyanidin-3-sambubioside and assignments of the 1H and 13C NMR resonances through two-dimensional shift-correlated NMR techniques



The anthocyanin cyanidin-3-sambubioside was isolated from the acidified methanolic extract of the fruits of Sambucus nigra by successive application of an ion exchange resin, droplet countercurrent chromatography and gel filtration. By means of chemical degradation and spectroscopy (especially one- and two-dimensional NMR techniques) the structure has been determined to be cyanidin-3-O-β-D-xylopyranosyl-(1±2)-β-D-glucopyranoside with both the sugar rings assuming a 4C1 chair conformation.

The combination of several NMR techniques such as double-quantum filtered proton-proton shift correlation (DQF-COSY), homonuclear Overhauser enhancement (NOE) difference spectroscopy, heteronuclear coupling-modulated spin echo, proton-carbon shift correlation optimized for direct (HSC) and long-range coupling (COLOC) provided assignments of the 1H and 13C signals. The coupling constants of the sugar protons were obtained by iterative spin simulation. This is the first report of a heteronuclear shift correlation experiment applied on anthocyanins.