Structural determination of hypnosin, a spore germination inhibitor of phytopathogenic Streptomyces sp. causing root tumor in melon (Cucumis sp.).

The structure of a germination inhibitor, hypnosin, isolated from phytopathogenic Streptomyces sp. causing root tumor of melon was determined to be 3-acetylaminopyrazine-2-carboxylic acid (1) by mass spectrometry, computational chemical prediction of UV spectrum, and synthesis of candidates. The structure-activity relationship of hypnosin and anthranilic acid was examined, and it was concluded that pyrazinecarboxylic acid or pyridine-2-carboxylic acid was the fundamental structure with activity, that methylation of the carboxyl group or decarboxylation destroyed activity, and that the presence of an amino group was inhibitory to the activity, whereas acetylation or deletion of an amino group enhanced activity. Hypnosin inhibited spore germination of some Streptomyces spp. in addition to the species with which it was isolated.