Resolving natural product epimer spectra by matrix-assisted DOSY

Abstract

High resolution diffusion-ordered NMR spectroscopy allows the separation of signals from different species based on their diffusion coefficients. In general this requires that the NMR spectra of the components do not have overlapping signals, and that the diffusion coefficients are significantly different. Modifying the solvent matrix in which a sample is dissolved can change the diffusion coefficients observed, allowing resolution ("matrix-assisted DOSY"). We show here that dissolving the two naturally-occurring epimers of naringin in an aqueous solution of β-cyclodextrin causes both shift and diffusion changes, allowing the signals of the epimers to be distinguished. Chiral matrix-assisted DOSY has the potential to allow simple resolution and assignment of the spectra of epimers and enantiomers, without the need for derivatisation or for titration with a shift reagent.

The application of high resolution diffusion NMR to the analysis of manuka honey

“…DOSY NMR has been used in the analysis of many other complex mixtures, simultaneously identifying and in part quantifying their components (Adams et al, 2011;Consonni & Cagliani, 2008;Donarski, Roberts, & Charlton, 2010;Lolli et al, 2008;McKenzie, Donarski, Wilson, & Charlton, 2011;Šmejkalová and Piccolo, 2010).…”

Natural product mixture analysis by matrix-assisted DOSY using Brij surfactants in mixed solvents

“…b-Cyclodextrin 13,14 has been used as a chiral matrix, allowing the resolution of a mixture of two native epimers of naringin. 13 Microemulsions have been used to separate the component signals in commercial drug formulations. 15 A simple change of solvent can also be effective.…”

Size‐exclusion chromatographic NMR of polymer mixtures

“…Diffusion ordered spectroscopy is often described as ‘NMR chromatography’ in that it enables the pseudo‐separation of mixtures based on the relative diffusion coefficients of the various constituent components . Over the past ten years or so, this concept has been extended and enhanced by the addition of chromatographic stationary phases or other sample modifiers . These additives modulate the observed diffusion coefficients as a result of some favourable interaction between the additive and the analyte of interest.…”

“…These additives modulate the observed diffusion coefficients as a result of some favourable interaction between the additive and the analyte of interest. In some cases, this can significantly improve the attainable resolution in the diffusion dimension . The exact nature of the interactions responsible for the diffusion modification is not fully understood.…”