High-field FT NMR application of Mosher's method. The absolute configurations of marine terpenoids

✍ Scribed by Ohtani, Ikuko; Kusumi, Takenori; Kashman, Yoel; Kakisawa, Hiroshi

• Book ID: 111686750
• Publisher: American Chemical Society
• Year: 1991
• Tongue: English
• Weight: 613 KB
• Volume: 113
• Category: Article
• ISSN: 0002-7863
• DOI: 10.1021/ja00011a006

✦ Synopsis

Mosher's (IH) 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 is a systematic arrangement of Ab (bs -8,) values obtained for the (R)-and (S)-MTPA esters of (-)-menthol, (-)-borneol, cholesterol, and ergosterol, the absolute configurations of which are known. Analysis of the Ab 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 group to a less sterically hindered position; the resulting epimer gives systematically arranged Ab values, which enabled the elucidation of the absolute configuration. Comparison of the present method with Mosher's I9F method indicates that the latter one using I9F NMR lacks in reliability.