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. Copyright © 2011 John Wiley & Sons, Ltd.