Liquid chromatographic and liquid-liquid chromatographic separation of structural isomeric oleanolic acid and ursolic acid using hydroxypropyl-β-cyclodextrin as additive

Two structural isomeric pentacyclic triterpenes, oleanolic acid and ursolic acid, were considered as the models for the quality control of many traditional Chinese herbal medicines and they have been proved to own important pharmacological activities. In the present work, liquid chromatographic and liquid-liquid chromatographic separation with high peak resolution of structural isomeric oleanolic acid and ursolic acid using hydroxypropyl-β-cyclodextrin as mobile phase additive was successfully achieved, respectively. A high peak resolution, R S =8.143, was achieved for the two structural isomeric compounds by conventional reverse phase high performance liquid chromatography, which was greatly improved compared with the published values. Meanwhile, a biphasic solvent system composed of n- hexane-ethyl acetate-0.1 mol/L hydroxypropyl-β-cyclodextrin (9:1:10, v/v) was selected for liquid-liquid chromatography, which provided a high peak resolution, R S  = 6.573, for analytical apparatus and R s  = 8.500 for semi-preparative apparatus after optimization by liquid-liquid extractions. Two elution modes including reverse phase mode and normal phase mode were investigated for preparative separation of two acids from crude exact of Eriobotrya japonica Thunb. Furthermore, the inclusion complex between each of the two structural isomers and hydroxypropyl-β-cyclodextrin were also investigated for high performance liquid chromatography and liquid-liquid chromatography, respectively, in which formation constants were determined for oleanolic acid and ursolic acid.