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Total assignment of the 1 H and 13 C chemical shifts for a mixture of cis ‐ and trans‐p ‐hydroxycinnamoyl esters of taraxerol with the aid of high‐resolution, 13 C‐detected, 13 C 1 H shift correlation spectra
Author(s) -
McLean Stewart,
Reynolds William F.,
Yang JiPing,
Jacobs Helen,
JeanPierre Laurent L.
Publication year - 1994
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260320708
Subject(s) - chemistry , triterpene , stereochemistry , chemical shift , resolution (logic) , nmr spectra database , ring (chemistry) , carbon 13 nmr , spectral line , organic chemistry , medicine , physics , alternative medicine , pathology , astronomy , artificial intelligence , computer science
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.