NEW APPROACHES TO THE SEARCH FOR NOVEL COMPOUNDS

Some selection of the plants to be investigated is necessary when searching for novel compounds because of the large numbers of plant species that exist. There has been a great interest in ethnopharmacological studies in recent years, which have led to the discovery of some very interesting compounds. The discovery of a molecule of interest in one species can lead to similar compounds being isolated because of chemotaxonomic relationships.

These more classical approaches have been augmented by selection linked to the hypotheses that exist for the reasons why plants produce complicated, stereospecific molecules with biological activity. Thus the ecological approach concentrates on species growing where competition may necessitate mobilisation of chemical defence systems. The existence of chemical races emphasises the need to explore the biodiversity even within one species. Chronological factors should also not be ignored as the identity and amounts of secondary metabolites vary throughout the life of the plant.

The approaches with the most potential lie in the areas of bioassay-guided fractionation and biotechnology. The rapid increase in small scale, high throughput methods for screening for activities linked with diseases is producing many new bioactive molecules. Biotechnology includes gene manipulation and plant tissue culture where the incorporation of enzymes or precursors different from those that occur naturally is likely to produce novel structures.

These topics are illustrated by examples from research at King's College London.