McLean, Stewart; Reynolds, W.; Yang, Ji-Ping; Jacobs, Helen M.; Jean-Pierre, L.L.
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
Total assignment of the 1H and 13C chemical shifts for a mixture of cis- and trans-p-Hyroxycinnamoyl Ester of taraxerol with the aid of high-resolution, 13C-detected, 13C-1H shift correlation spectra
Magnetic Resonance in Chemistry
Date of Publication
A mixture of two slowly interconverting isomeric compounds was isolated from Bernardia laurentii and identified as the trans-and cis-p-hydroxycinnamoyl ester of the triterpene taraxerol. Their 13C and 1H 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 13C resolution and severe spectral crowding. However, the assignments could be made unabiguously by HECTOR and FLOCK experiments, relying on the superior 13C resolution of the 13C-detected experiments. Comparison of 13C spectral assignments for a series of eight pentacy-clic 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....