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The Use of Coupled HSQC Spectra to Aid in Stereochemical Assignments of Molecules with Severe Proton Spectral Overlap
Author(s) -
PowderGeorge Yomica,
Frank Julia,
Ramsewak Russel S.,
Reynolds Willam F.
Publication year - 2011
Publication title -
phytochemical analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 72
eISSN - 1099-1565
pISSN - 0958-0344
DOI - 10.1002/pca.1354
Subject(s) - chemistry , heteronuclear single quantum coherence spectroscopy , pyranose , spectral line , heteronuclear molecule , analytical chemistry (journal) , proton , spectral resolution , resolution (logic) , nuclear magnetic resonance , two dimensional nuclear magnetic resonance spectroscopy , nuclear magnetic resonance spectroscopy , stereochemistry , chromatography , physics , quantum mechanics , astronomy , artificial intelligence , computer science
A simple glycoside with only 13 carbons exhibited extensive overlapping of four of the glycosidic protons, causing extreme difficulty in the determination of the stereochemistry of the pyranose unit. However, acquisition of a high‐resolution coupled heteronuclear single‐quantum coherence (HSQC) spectrum overcame this problem. This spectrum provides a useful method for determining vicinal proton coupling constants between strongly coupled protons. Objective To show the potential of high‐resolution coupled HSQC spectra in overcoming spectral overlap. Methodology The sample was obtained by methanol extraction, followed by fractionation and column chromatography of the dried leaves of Montrichardia arborescens (Araceae). NMR spectra were obtained on 1.5 mg of sample dissolved in 120 μL of CD 3 OD containing 0.1% trimethylsilyl (TMS) as internal standard. A gradient‐selected HSQC spectrum was obtained using standard Varian library pulse sequences in phase sensitive mode. The high‐resolution coupled HSQC spectrum focused on the saccharide region with a 1025 Hz 1 H spectral window, a 6300 Hz 13 C spectral window, 1024 data points, a 0.3 Hz relaxation delay, 384 time increments (linear predicted to 4096), and 80 scans per time increment. Results The use of a high‐resolution coupled HSQC spectrum allowed determination of the coupling patterns of the various pyranose protons with sufficient accuracy. This enabled completion of the assignments and identification of the pyranose unit as glucose. Conclusion The study has shown the effectiveness of the use of a high‐resolution coupled HSQC spectrum in the assignment of molecules with severe spectral overlap. Copyright © 2011 John Wiley & Sons, Ltd.