Separation mechanism of oleanane and ursane pentacyclic triterpenoid isomers by coordination chromatography.

This paper focuses on the study of the separation mechanism of oleanane and ursane pentacyclic triterpenoid isomers by a coordination chromatographic method. Based on the calculation analysis, beta-cyclodextrin (beta-CD) and its derivatives were selected as the suitable agents. The experimental results showed that the resolution of madecassoside isomers with the addition of glucosyl-beta-cyclodextrin (Glu-beta-CD) to the mobile phase (11.95) was higher than that of the addition of beta-CD (9.61) or dimethyl-beta-cyclodextrin (DM-beta-CD) (9.89). The formation of 1:1 inclusion complexes was assumed. The apparent formation constants (K(F)) of pentacyclic triterpenes with beta-CD were determined by HPLC method. For asiaticoside-B, the K(F) value with the addition of Glu-beta-CD (2 534 L/mol) was larger than that with the addition of beta-CD (1 467 L/mol) or DM-beta-CD (1 373 L/mol). According to the infrared characteristic absorbing peaks and simulation, the methyl part of asiaticoside-B might enter into beta-CD cavity while the carbonyl group of asiaticoside-B might not enter into the cavity of beta-CD, and the large glycoside parts were kept outside, forming hydrogen-bond interaction with the exterior of beta-CD cavity. The results of the separation of oleanane and ursane pentacyclic triterpenoid isomers by coordination chromatography indicated that, the separation mechanism might be attributed to the steric differences (the place of methyl group in E cyclic), which lead to different chromatographic behaviors.