International Union of Pure and Applied Chemistry

Strategy for the biological and chemical evaluation of plant extracts*

K. Hostettmann

Institut de Pharmacognosie et Phytochimie, Université de Lausanne, BEP, CH- I 0 1 5 Lausanne-Dorigny, Switzerland
E-mail: [email protected]

Abstract: Only a small percentage of the 400'000 to 500'000 species in the plant kingdom has been investigated phytochemically. Even fewer species have been studied simultaneously for their biological and pharmacological properties. For these reasons, it is essential to have efficient systems available for the rapid chemical and biological screening of plant extracts.

Different techniques can be used for the chemical evaluation of plants. Thin-layer chromatography (TLC) is the simplest and cheapest method but new hyphenated HPLC systems are now available which provide improved on-line information about the composition of extracts, with good selectivity and sensitivity : LC/UV, LC/MS and LC/NMR (1). By these means, it is possible to avoid known or trivial compounds during searches for new lead compounds.

The biological testing requires simple, fast and reproducible methods in order to allow the screening of a large number of extracts. The test targets are of various nature. Thin-layer chromatography is also ideal for biological screening. The technique of bioautography combines TLC with a bioassay in situ and allows localization of active constituents in a complex matrix (2). Antifungal, antibacterial, pesticide and antioxidant activities can all be investigated by TLC bioautography. These and other benchtop bioassays are rapid and simple to perform. They provide efficient methods for activity-guided isolation of natural products.

Examples will be given of the strategies employed to obtain new bioactive compounds from plant sources, including initial screening and subsequent preparative chromatography of extracts selected for study.