Separation of catalpol from Rehmannia glutinosa Libosch. by high-speed countercurrent chromatography

The bioactive iridoid component catalpol was successfully separated by high-speed countercurrent chromatography with high purity from the partially purified crude extract of Rehmannia glutinosa. A polar two-phase solvent system composed of ethyl acetate-n-butanol-water (2:1:3, v/v/v) was selected by thin-layer chromatography and run on a preparative scale where the lower aqueous phase was used as the mobile phase with a head-to-tail elution mode. A 105 mg quantity of the partially purified sample containing 39.2% catalpol was loaded on a 270-mL capacity high-speed countercurrent separation column, yielding 35 mg of catalpol at 95.6% purity. The chemical structure of catalpol was determined by comparison with the high-performance liquid chromatography retention time of standard substance as well as the (1)H NMR spectrum.