Liquid chromatography coupled to mass spectrometry and nuclear magnetic resonance spectroscopy for the screening of plant constituents

Rapid detection of biologically active natural products plays a strategical role in the phytochemical investigation of crude plant extracts. In order to perform an efficient screening of the extracts, both biological assays and HPLC analysis with various detection methods are used. Hyphenated techniques such as HPLC coupled to UV photodiode array detection (LC–DAD-UV) and to mass spectrometry (LC–MS or LC–MS–MS) provide on-line numerous useful structural information on the metabolites prior to isolation. The recent introduction of HPLC coupled to nuclear magnetic resonance (LC–NMR) represents a powerful complement to the LC–UV–MS screening. Various plants belonging to the Gentianaceae and Leguminosae families have been analysed by LC–UV, LC–MS, LC–MS–MS and LC–NMR. The use of all these hyphenated techniques allows the rapid structural determination of known plant constituents with only a minute amount of plant material. With such an approach, the time-consuming isolation of common natural products is avoided and an efficient targeted isolation of compounds presenting interesting spectroscopical or biological features can be performed. In this paper several representative applications of this combined approach from our laboratory are discussed.