Stereodynamics of some pyridoxine derivatives

• Published in: Magnetic resonance in chemistry 2017-04, Vol.55 (4), p.304-311
• Main Authors: Rakhmatullin, I. Z., Galiullina, L. F., Balandina, A. A., Garipov, M. R., Strelnik, A. D., Galiullina, A. S., Shtyrlin, Y. G., Klochkov, V. V.
• Format: Article
• Language: English
• Subjects: 2D NOESY NMR; Barriers; Chemical bonds; conformational exchange; Derivatives; dynamic 1H NMR; Dynamic tests; Dynamics; energy barrier; Exchange; Nuclear magnetic resonance; Pyridoxine
• ISSN: 0749-1581; 1097-458X
• DOI: 10.1002/mrc.4528

The conformational properties of three pyridoxine derivatives were studied by 1H dynamic NMR spectroscopy. Conformational exchange caused by a rotation of 2‐nytrophenyl group around one single C–C bond, of 2,4‐dinitrophenyl substituent around two single C–O bonds, and twist‐twist transformations of the seven‐membered ketal cycle was observed by NMR experiments at low temperatures. Meanwhile, the conformational exchange of the acetal ring remains fast in the NMR timescale even at 198 K. The energy barriers for all observed conformational exchange processes were determined by the lineshape analysis of dynamic NMR spectra. The activation barriers of the 2‐nitrophenyl group rotation were almost the same for all studied compounds, about 40–41 kJ/mol. The energy barriers of the conformational exchange processes of the 2,4‐nitrophenyl group and the ketal cycle increased significantly up to 10 kJ/mol in comparison with previously studied compounds with similar structure. Copyright © 2016 John Wiley & Sons, Ltd. Conformational features and dynamics for three new pyridoxine derivatives were studied by 1H dynamic NMR and 2D NOESY experiments. The energy barriers for all observed conformational exchange processes were determined by the lineshape analysis of dynamic NMR spectra, and PM3 calculations of rotational barriers were carried out.