Observation of exchangeable protons by high-performance liquid chromatography-nuclear magnetic resonance spectroscopy and high-performance liquid chromatography-electrospray ionization mass spectrometry: a useful tool for the hyphenated analysis of natural products

The first high-performance liquid chromatography-nuclear magnetic resonance (HPLC-NMR) investigation of exchangeable protons of low-molecular-mass nat ural products is reported. Model alkaloids or crude plant extracts were dis solved in (H2O)-H-2-(H2O)-H-1-MeCN (deuterium oxide-water-acetonitrile) or (H2O)-H-2-MeCN and, after direct injection or chromatographic separation, e xamined in a 60-mul NMR how probe. Exchangeable amino protons initially det ected by HPLC-electrospray ionization mass spectrometry were subsequently i dentified and investigated by stop-flow H-1-NMR, two-dimensional (2D) total correlation spectroscopy (TOCSY), and 2D nuclear Overhauser effect spectro scopy (NOESY). These experiments extend the applicability of HPLC-NMR for t he investigation and structure elucidation of natural products. (C) 2000 El sevier Science B.V. All rights reserved.