Abstract
The genus Chaetomium was targeted as a potentially rich source of antiinsectan natural products because different Chaetomium species have been shown to be avoided by or harmful to fungus-feeding insects. Bioassay guided studies using both antiinsectan assays (Helicoverpa zea) and antifungal assays (Aspergillus flavus) led us to a variety of known Chaetomium metabolites (i.e. antibiotic 1233A; chaetochromins ; chaetoglobosins A, B, D, and F ; 19-O-acetylchaetoglobosins A and D; chaetoviridins A, B, and X; chetocin; chetomin ; dethiotetra (methylthio) chetomin; cochliodinol, cyclosporins A and C; eugenitin; sterigmatocystin; O-methylsterigmatocystin). Two novel compounds, closely related to cytochalasins, but with previously undescribed ring systems, were discovered to have antiin-sectan activity. Among the compounds isolated in this work, only cyclosporin A and sterigmatocystin had been previously reported to have toxicity to insects. Most of these compounds were originally isolated as mycotoxins. The study confirmed our hypothesis that Chaetomium spp. produce potent insecticides as chemical defenses.
