Stereochemistry of cleistanthane diterpenoid glucosides from Phyllanthus emblica
Stereochemistry of cleistanthane diterpenoid glucosides from Phyllanthus emblica
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DOI：
10.1039/c4ra16624h
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发表时间：
2015-03
期刊：
影响因子：
3.9
通讯作者：
Jun-Jiang Lv;Shan Yu;Ying Xin;Hong-Tao Zhu;Dong Wang;Rong-Rong Cheng-Rong;Chong-ren Yang;Min Xu;Ying-Jun Zhang
中科院分区：
文献类型：
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作者：
Jun-Jiang Lv;Shan Yu;Ying Xin;Hong-Tao Zhu;Dong Wang;Rong-Rong Cheng-Rong;Chong-ren Yang;Min Xu;Ying-Jun Zhang
应用含时密度泛函理论（TDDFT）计算的电子圆二色性（ECD）和Mosher方法，研究了从余甘子根中分离得到的6个新的含氧二萜苷类化合物phyllanembloidsA-F（1-6）的绝对构型。化合物1-5的特征在于在C-13处的羧基与在C-12处的羟基相邻，并且是具有水杨酸片段的二萜类化合物的第一个实例。C-13位的羧基能显著地影响二萜类化合物的CD光谱，使苯乙烯的激发在240和280 nm处主导Cotton效应，而不是13-甲基类似物中苯环的激发在220和240 nm处主导Cotton效应。根据实验和计算的ECD曲线，总结了二萜类化合物的特征Cotton效应，为确定该类化合物的绝对构型提供了一种通用方法。
Time-dependent density functional theory (TDDFT) calculated electronic circular dichroism (ECD) and Mosher’s method were applied to establish the absolute configurations of six new highly oxygenated cleistanthane diterpenoid glucosides, phyllanembloids A–F (1–6), isolated from the roots of Phyllanthus emblica. Compounds 1–5 featured a carboxyl group at C-13 adjacent to the hydroxyl group at C-12, and are the first examples of cleistanthane diterpenoids with a salicylic acid fragment. The carboxyl group at C-13 can significantly affect the CD spectrum of cleistanthane diterpenoids, and make the excitations of phenylethylene dominate the Cotton effects (240 and 280 nm), rather than the benzene ring excitations dominating the Cotton effects at 220 and 240 nm as in the 13-methyl analogues. The characteristic Cotton effects of cleistanthane diterpenoids were summarized according to the experimental and calculated ECD curves, which can be applied as a common method to determine the absolute configurations of this type of diterpenoid.