High‐Field FT NMR Application of Mosher′s Method. The Absolute Configurations of Marine Terpenoids.
High‐Field FT NMR Application of Mosher′s Method. The Absolute Configurations of Marine Terpenoids.
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DOI：
10.1002/chin.199134221
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发表时间：
1991-08
期刊：
影响因子：
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通讯作者：
I. Ohtani;T. Kusumi;Y. Kashman;H. Kakisawa
中科院分区：
文献类型：
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作者：
I. Ohtani;T. Kusumi;Y. Kashman;H. Kakisawa
Mosher（* H）方法阐明仲醇的绝对构型是重新检查通过使用高场FT NMR光谱，这使得大部分的质子的复杂分子的归属。对（/？）以及（-）-薄荷醇、（-）-胆固醇、麦角甾醇的（S）-MTPA酯，其绝对构型是已知的。通过对这些化合物的AS值的分析，得到了一个可以预测天然产物绝对构型的规则。将该规则应用于西松内酯和xenicane等海洋萜类化合物，对其绝对构型进行了归属，部分结果得到了X射线结构分析的证实。在具有空间位阻OH基团的sipholenol A的情况下，该规则不适用。但是，通过将OH基团反转到空间位阻较小的位置，可以克服这个问题;由此产生的差向异构体给出了系统排列的AS值，这使得能够阐明绝对构型。通过与Mosher的19 F方法的比较，发现Mosher的19 F核磁共振法缺乏恢复性
Mosher’s (* H) method to elucidate the absolute configuration of secondary alcohols was reexamined by use of high-field FT NMR spectroscopy, which enables assignment of most of the protons of complex molecules. There isa systematic arrangement of 5 (áj-SR) values obtainedfor the (/?)-and (S)-MTPA esters of (-)-menthol,(-)-borneol, cholesterol, and ergosterol, the absolute configurationsof which are known. Analysis of the AS values of these compounds led to a rule that could predict the absolute configurations of natural products. When this rule was applied to some marine terpenoids including cembranolides and xenicanes, their absolute configurations were assigned and a part of the results were confirmed by X-ray structural analyses. In the case of sipholenol A, which has a sterically hindered OH group, this rule is inapplicable. But the problem is overcome by inverting the OH groupto a less sterically hindered position; the resulting epimer gives systematically arranged AS values, which enabled the elucidation of the absolute configuration. Comparison of the present method with Mosher’s 19F method indicates that the latter one using 19F NMR lacks in rehab