Nuclear magnetic resonance fuels solvent system selection for counter-current separation of natural products

In countercurrent separation of natural products, suitable solvent system selection is both crucial and challenging. For conventional target molecules, general HPLC method is practical, however, it can be powerless for some isomers or compounds without UV absorption to some degree. In this study, NMR was employed as an alternative strategy to fuel the solvent system selection in counter-current separation, especially for isomers and compounds without UV absorption. Considering the complexity of NMR spectra of natural products, including baseline drifting and signals overlapping, quantum mechanical spin analysis was employed to extract individual component spectral information from the mixture, in terms of proton signal characterization and quantitation, for partition coefficient determination. The separation of three chlorogenic acid isomers and four triterpenoid saponins were selected as two typical examples to show its practicability. It demonstrated that NMR would be a powerful complementary alternative to routine HPLC method for solvent system selection to fuel counter-current separation of natural products.