Acetogenic isoquinoline alkaloids: CXXI. Use of on-line high-performance liquid chromatography–nuclear magnetic resonance spectrometry coupling in phytochemical screening studies: rapid identification of metabolites in Dioncophyllum thollonii

Abstract

Exemplarily for a root extract of the West African liana Dioncophyllum thollonii a strategy for the rapid identification of secondary metabolites in plant extracts is presented, based upon on-line coupling of high-performance liquid chromatography with nuclear magnetic resonance detection. For a first overview, an on-flow experiment was performed, which allowed the identification of the naphthylisoquinoline alkaloid dioncophylline A. A second alkaloid, 5′- O-demethyldioncophylline A, was identified by subsequent application of stop-flow two-dimensional HPLC–NMR ROESY experiments. In the case of coeluting compounds, the design of appropriate time-slice experiments allowed the characterization of the diastereomeric tetralones trans- and cis-isoshinanolone. Thus, through consequent use of all different experimental modes available in HPLC–NMR, a phytochemical screening of plant extracts can be realized in a fast and reliable way. The NMR detection allows the characterization of diastereomeric compounds even in the case of far-reaching chromatographic coelution.