Phenolic composition of rhubarb

Extracts of different parts (leaves, petioles and rhizomes) of domestic garden rhubarb (hybrids of Rheum rhabarbarum L. and Rheum rhaponticum L.) were investigated for their content of phenolic ingredients. Two stilbenes (trans-rhapontigenin, trans-desoxyrhapontigenin), five stilbene glycosides (trans-rhaponticin, cis- and trans-desoxyrhaponticin, trans-resveratrol-4'-O-beta-D-glucopyranoside, trans-piceatannol-3'-O-beta-D-glucopyranoside) and seven flavonoids [rutin, quercetin-3-O-glucuronide, isovitexin, 6,8-di-C-beta-D-glucosylapigenin, 6-C-beta-D-glucosyl-8-C-beta-D-arabinosylapigenin (schaftoside), 6-C-beta-D-arabinosyl-8-C-beta-D-glycosylapigenin (isoschaftoside), (+)-catechin] were unequivocally established. Separation was done in two steps. Multilayer countercurrent chromatography was applied to separate different extracts of plant material. Preparative HPLC was then used to obtain pure substances. The purity and identity of isolated compounds was confirmed by different NMR experiments, HR-MS and HPLC-DAD analysis.