Biological activity of a heptaketide metabolite from Pleiochaeta setosa

An uncommon heptaketide metabolite, setosol (2,8-dimethyl-4 methoxy-6,10,11-trihydroxy-benzo-oxaonin), was isolated from a liquid culture filtrate of the fungus Pleiochaeta setosa. The biological activity of the molecule was studied by using 12 microbial strains consisting of three bacteria, three yeasts and six fungi. The level of activity was compared with those of known antibiotics and antifungal agents. The metabolite exhibited antifungal and antibiotic activity against Drechslera oryzae, Gerlachia oryzae, Pyricularia oryzae, Cryptococcus neoformans, and Staphylococcus aureus. The acetylated derivative of setosol did not inhibit the growth of any of the target pathogens. Phytotoxicity studies on whole lupine leaves show that setosol is implicated in the pathogenesis of the brown spot disease of lupines since artificial inoculation of the leaves with the metabolite provoked lesions similar to the characteristic brown spots and lesions on lupine leaves infected by the fungus.