Structure elucidation of a sodium salified anthraquinone from the seeds of Cassia obtusifolia by NMR technique assisted with acid-alkali titration

A new sodium salt of anthraquinone named sodium emodin-1-O-β-gentiobioside, together with nine known compounds, viz. rubrofusarin-6-O-β-D-gentiobioside, chrysophanol-1-O-β-D-glucopyranosyl-(1-3)-β-D-glucopyranosyl-(1-6)-β-D-glucopyranoside, obtusifolin-2-O-β-D-glucopyranoside, aurantio-obtusin-6-O-β-D-glucopyranoside, physcion-8-O-β-D-glucopyranoside, 1-hydroxyl-2-acetyl-3,8-dimethoxy-6-O-β-D-apiofuranosyl-(1-2)-β-D-glucosylnaphthalene, toralactone-9-O-β-D-gentiobioside, aurantio-obtusin, rubrofusarin-6-O-β-D-apiofuranosyl-(1-6)-O-β-D-glucopyranoside, was isolated from the seeds of Cassia obtusifolia and its structure was elucidated by (1)H and (13)C NMR technique assisted with acid-alkali titration. The change of chemical shifts of sodium emodin-1-O-β-gentiobioside before and after acid-alkali titration was also characterized.