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Solid‐state NMR studies and DFT calculations of flavonoids: baicalein, baicalin and wogonoside
Author(s) -
Wolniak Michał,
Oszmiański Jan,
Wawer Iwona
Publication year - 2008
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.2165
Subject(s) - chemistry , baicalin , magic angle spinning , solid state nuclear magnetic resonance , baicalein , intramolecular force , scutellaria baicalensis , nuclear magnetic resonance spectroscopy , analytical chemistry (journal) , carbon 13 nmr , density functional theory , chemical shift , conformational isomerism , computational chemistry , stereochemistry , nuclear magnetic resonance , organic chemistry , molecule , high performance liquid chromatography , medicine , physics , alternative medicine , traditional chinese medicine , pathology , biology , genetics
Three flavonoids of pharmaceutical importance—baicalein, baicalin, and wogonoside—were isolated from a Chinese medicinal plant Scutellaria baicalensis Georgi and studied by 13 C NMR in solution and solid state. Two‐dimensional (2D) NMR spectroscopy in the liquid phase and dipolar dephasing (DD) experiments in magic‐angle spinning (MAS) spectra enabled the assignment of 13 C resonances. The cross‐polarization (CP) time constants T CH and relaxation times T H 1ρ were obtained from the variable‐contact time experiments. The principal elements of the 13 C chemical shift tensor were determined in the spectra recorded under slow sample spinning (2 kHz) using phase‐adjusted spinning sideband (PASS)‐2D NMR technique, and were verified by density functional theory gauge‐independent atomic orbital (DFT GIAO) calculations of shielding constants. Analysis of the 13 C δ ii and comparison with shielding parameters calculated for different conformers of compounds 1–3 enabled the selection of the most reliable geometry in the solid phase. In all three compounds, an intramolecular hydrogen bond C5OH···C4 is formed; the existence of baicalein and baicalin with ‘anticlockwise’ orientation of OH groups is more probable. Copyright © 2007 John Wiley & Sons, Ltd.