The apparent formation constants of asiatic acid and its derivatives existing in Centella asiatica with cyclodextrins by HPLC

The retention of triterpenoids in the C18 column and apparent formation constants of triterpenoids with cyclodextrins (CDs) were studied using HPLC. As the effective mobile phase additives, CDs can improve the separation of triterpenoid glycosides (asiaticoside B, madecassoside and asiaticoside) and reduce the retention of triterpenoids, and it is attributed to that triterpenoids forms a 1:1 inclusion complexes with CDs. The apparent formation constants of these complexes depend on the structure of triterpenoids, as well as on the substituent group and the hydrophobic cavity size of CDs. Triterpenoid glycosides had less apparent formation constants with HP-β-CD and Glu-β-CD, which might be related that hydroxypropyl group and glucose group in the structure of HP-β-CD and Glu-β-CD were unfaver to formation of the inclusion complexes. Asiaticoside B had larger apparent formation constants with CDs than madecassoside and asiaticoside. Larger apparent association constants of triterpenoid acids (madecassic acid and asiatic acid) were obtained with γ-CD than β-CD and its derivatives, which are related that triterpenoid acids fit well into the γ-CD cavity, and form relatively stable inclusion complexes. The ∆G (25 °C), ∆H and ∆S reveal that the inclusion processes between triterpenoids and CDs were not spontaneous, exothermic, and enthalpically driven. In addition, the usefulness of CDs for simultaneous analysis of five triterpenoids in HPLC and drug delivery vehicles was described.