STRUCTURE ELUCIDATION OF CYANIDIN-3-SAMBUBIOSIDE AND ASSIGNMENTS OF THE H-1 AND C-13 NMR RESONANCES THROUGH 2-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-beta-D-xylopyranosyl-(1 --> 2)-beta-D-glucopyranoside with both the sugar rings assuming a C-4(1) 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 H-1 and C-13 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.