齐墩果烷型和乌苏烷型五环三萜同分异构体配位色谱法分离机理（英文）

本文主要研究了配位色谱法分离齐墩果烷型和乌苏烷型五环三萜同分异构体的分离机理。基于计算模拟分析，β-环糊精（β-CD）和其衍生物为适宜的配位剂。采用HPLC法测定了包合物的表观形成常数，并制备了asiaticoside-B与β-CD包合物。实验结果显示:流动相中添加葡萄糖基-β-环糊精（Glu-β-CD）时，同分异构体的分离度为11.95，比添加β-CD或添加甲基-β-环糊精（DM-β-CD）时（分别为9.61和9.89）都略高些。假定五环三萜类化合物与β-CD形成1：1的包合物，对于asiaticoside-B，流动相中添加Glu-β-CD时，表观形成常数（K_F）为2534 L/mol，比添加β-CD或添加DM-β-CD时（分别为1467和1373 L/mol）都略大些。根据asiaticoside-B与β-CD包合物的红外光谱解析及计算模拟，推测asiaticoside-B的E环上甲基部分进入了β-CD的空腔内，而其羰基基团没有进入β-CD的空腔内，其糖苷部分与亲水性的β-CD空腔外部形成氢键作用力。因此，配位色谱法分离齐墩果烷型和乌苏烷型五环三萜同分异构体的分离机理可以推测如下：齐墩果烷型和乌苏烷型五环三萜同分异构体E环上甲基的不同空间位阻导致了同分异构体的不同色谱分离行为。

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,β-cyclodextrin (β-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-β-cyclodextrin (Glu-β-CD) to the mobile phase (11.95) was higher than that of the addition of β-CD (9.61) or dimethyl-β-cyclodextrin (DM-β-CD) (9.89). The formation of 1:1 inclusion complexes was assumed. The apparent formation constants (K_F) of pentacyclic triterpenes with β-CD were determined by HPLC method. For asiaticoside-B, the K_F value with the addition of Glu-β-CD (2534 L/mol) was larger than that with the addition of β-CD (1467 L/mol) or DM-β-CD (1373 L/mol). According to the infrared characteristic absorbing peaks and simulation, the methyl part of asiaticoside-B might enter into β-CD cavity while the carbonyl group of asiaticoside-B might not enter into the cavity of β-CD, and the large glycoside parts were kept outside, forming hydrogen-bond interaction with the exterior of β-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.