Application of Spectroscopic Methods and Hyphenated Techniques to the Analysis of Complex Plant Extracts

Abstract

Through the selected examples of different classes of secondary metabolites two general approaches in the analysis of complex mixtures of natural products are presented. The first one involves isolation of the constituents using optimized semi-prep LC in combination with classical column chromatography (CC) and the second one represents direct (on-line) analysis of complex plant extracts prior to isolation of the constituents. Thus the isolation of mg-quantities of jatrophanes the bioactive constituents of Euphorbia dendroides, with their structure determination on the basis of spectroscopic data interpretation (IR, NMR, MS), is described. The direct analysis of the plant extracts is demonstrated by the characterization of antioxidative polyphenols, i.e. oligomeric proanthocynidins from the MeOH extracts of grape Vitis vinifera seeds by the application of hyphenated methods (LC/UV/MS) in combination with 13C NMR spectroscopy, as well as tandem mass spectrometry (MS/MS) and MSn in combination with and without LC for identification of oligomeric proanthocynidins from other sources. The potential of another hyphenated instrumentation, LC/UV/SPE-NMR is shown by on-line identification of the various constituents of the crude extract of Hypericum perforatum. The possibilities and limitations of the NMR technique named diffusion ordered spectroscopy (DOSY) for direct analysis of the complex mixture, such as e.g. methanolic extract of Gentiana lutea, is discussed.