Natural Products bioassay screening

In our continuing interests in natural product discovery,40,41 ellagic acid and an extract of fruit from Melia volkensii (MP-extract) were screened for inhibition of Agrobacterium tume-faciens-md uced tumors using the potato disk assay.42 bioassay s usefu] for the examination of plant extracts and purified compounds which inhibit crown gall tumors (a plant neoplastic disease) that may have potential human anticancer activity.43,44... 

Some plant pathogenic bacteria and their phytotoxins have been screened in bioassays that monitor the effects of their toxins (antibiotic and phytotoxic) on other sensitive bacteria. For example, several fluorescent Pseudomonas syringae pvs. produce extracellular phytotoxins.76,106,116 Tabtoxin is produced by P. syringae pv. tabaci and pv. coronafacines, and this natural product inhibits glutamine synthetase.34,46,116 Phaseolotoxin, produced by P. syringae pv. phaseolicola... 

If the bioactive molecule is a synthetic product, its structure may be rapidly deduced by a simple comparison of NMR parameters (often combined with MS) of the product relative to those of the known precursor, to see whether the desired chemical transformation has taken place. If the bioactive compound is an unknown molecule discovered in an active fraction in bioassay-guided screening, then the first step is to elucidate its structure. Typical molecules that form the basis of such natural products-based drug discovery studies include "organic" natural products as well as small peptides and proteins. The approaches to structure elucidation for natural products and peptides/proteins are a little different from each other and are described in turn. 

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