Preparative isolation and purification of trans-3,5,4′-trihydroxystilbene-4′-O-β-d-glucopyranoside and (+)catechin from Rheum tanguticum Maxim. ex Balf. using high-speed counter-current chromatography by stepwise elution and stepwise increasing the flow-r

Preparative high-speed counter-current chromatography (HSCCC) was successfully used for isolation and purification of trans-3,5,4′-trihydroxystilbene-4′-O-β-d-glucopyranoside (compound 1) and (+)catechin (compound 2) from Rheum tanguticum Maxim. ex Balf. by stepwise elution with a pair of two-phase solvent system composed of ethyl acetate–ethanol–water (25:1:25, v/v) and (5:1:5, v/v), and stepwise increasing the flow-rate of the mobile phase from 0.8 to 2.0 ml min−1 after 5 h. The preparative HSCCC separation was performed on 250 mg of crude extract yielding pure compound 1 (10.2 mg) and compound 2 (26.7 mg) all at purities of over 96% in a single run. The structures of the two compounds have been elucidated by means of spectroscopic methods including MS and 1H, 13C nuclear magnetic resonance spectroscopy.