Two runs of preparative HSCCC with a two-phase solvent system composed of n-hexane–ethyl acetate–methanol–water (1:7:1:7, v/v) were employed to separate the compounds from the flower of Polygonum cuspidatum. Three minor compounds, 8.6 mg of (+)-catechin (1), 12.3 mg of (−)-epicatechin (2) and 7.4 mg of 1-(S)-phenylethyl β-d-glucopyranoside (3) were obtained from 240 mg of the crude extract of the flower of P. cuspidatum with purities of 96.8%, 98.5% and 98.3%, respectively, as determined by HPLC. The structures of these compounds were identified by ESI-MS, 1H NMR and 13C NMR spectroscopy. Among them, compounds 2 and 3 were obtained from P. cuspidatum for the first time. In addition, antioxidant activities of (+)-catechin and (−)-epicatechin were evaluated and compared by the methods of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. Both (+)-catechin and (−)-epicatechin showed high radical scavenging activities with their EC50 values being 15.08 ± 0.46 and 9.44 ± 0.13 μg/ml in DPPH radical method.
Minor compounds; Preparative separation; Antioxidant activity; Flower of Polygonum cuspidatum; High-speed counter-current chromatography