Detailed NOESY/T-ROESY analysis as an effective method for eliminating spin diffusion from 2D NOE spectra of small flexible molecules

•Conformer populations calculated from NOESY spectra are distorted by spin diffusion.•Conformer fractions are obtained more accurately by combined NOESY/T-ROESY analysis.•Efficiency of NOESY/T-ROESY and QUIET-NOESY methods was tested on felodipine.•Correlation time and distribution of conformer groups of felodipine were found.

An intriguing property of the multistep magnetization transfer, so-called spin diffusion, is that it can affect the results of NMR-based analysis of conformer distribution of small molecules in solution. Therefore, the contribution of spin diffusion should be subtracted in order to obtain accurate data on molecular conformations and their distributions. Several methods have been developed for this purpose, but many of them have a lack of versatility. These methods were critically analysed, and two approaches to eliminate spin diffusion were tested during the study of felodipine as the drug molecule of small size. QUIET-NOESY was found to be a powerful technique to solve this problem. The second method, combined analysis of two sets of spectra, NOESY and T-ROESY, was tested and proved to be the most correct way of obtaining exact internuclear distances in a flexible molecule in solution.

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