Preparative Separation of Aurantio-obtusin and Rhein from Semen cassiae by High Speed Counter-current Chromatography Using pH-gradient Elution

OBJECTIVE To establish an efficient method for preparative separation of the characteristic constituent aurantio-obtusin from the crude extract of Semen cassiae.METHODS High speed counter-current chromatography was employed and the optimum two-phase solvent system methyl tert.-butyl ether-water was selected for the target compounds with a pH-gradient elution.RESULTS 28 mg aurantio-obtusin at over 98.7% purity and 30 mg of rhein at over 95.5% purity by high-performance liquid chromatography (HPLC) analysis were isolated by preparative high speed counter-current chromatograpy from 150 mg of the crude extract and their structures were identified by 1H-NMR.CONCLUSION A simple and quick preparative separation method was presented for purification of hydroxyanthraquinones from the traditional Chinese herb.