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Total assignment of the 1H and 13C chemical shifts for a mixture of cis- and trans-p-hydroxycinnamoyl esters of taraxerol with the aid of high-resolution, 13C-detected, 13C1H shift correlation spectra

✍ Scribed by Stewart McLean; William F. Reynolds; Ji-Ping Yang; Helen Jacobs; Laurent L. Jean-Pierre

Publisher
John Wiley and Sons
Year
1994
Tongue
English
Weight
631 KB
Volume
32
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

A mixture of two slowly interconverting isomeric compounds was isolated from Bernardia laurentii and identified as the trans‐ and cis‐p‐hydroxycinnamoyl esters of the triterpene taraxerol. Their ^13^C and ^1^H NMR spectra were totally assigned with the aid of concerted two‐dimensional NMR experiments. Not all assignments could be made using HMQC and HMBC owing to the limited ^13^C resolution and severe spectral crowding. However, the assignments could be made unambiguously by HETCOR and FLOCK experiments, relying on the superior ^13^C resolution of the ^13^C‐detected experiments. Comparison of ^13^C spectral assignments for a series of eight pentacyclic triterpenes with identical A and B ring structures but differences in C, D and/or E rings illustrates the risks and limitations of the use of model compounds for spectral assignments.

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