Abstract
The first high-performance liquid chromatography–nuclear magnetic resonance (HPLC–NMR) investigation of exchangeable protons of low-molecular-mass natural products is reported. Model alkaloids or crude plant extracts were dissolved in 2H 2O– 1H 2O–MeCN (deuterium oxide–water–acetonitrile) or 2H 2O–MeCN and, after direct injection or chromatographic separation, examined in a 60-μl NMR flow probe. Exchangeable amino protons initially detected by HPLC–electrospray ionization mass spectrometry were subsequently identified and investigated by stop-flow 1H-NMR, two-dimensional (2D) total correlation spectroscopy (TOCSY), and 2D nuclear Overhauser effect spectroscopy (NOESY). These experiments extend the applicability of HPLC–NMR for the investigation and structure elucidation of natural products.
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