Abstract
1) Ophiobolosins A and B were isolated as new metabolites of Cochliobolus miyabeanus, the pathogenic fungus of the helminthosporium leaf spot disease of rice plants; the former from the mycelium cultured on the malt medium containing glucose and polypeptone, the latter also from the mycelium on Asada's medium which contained sucrose, potassium nitrate and biotin.
2) OA was identified as zizanin, an anti-biotic from Helminthosporium zizaniae, by optical rotation, IR, Mass and NMR spectra and mixed melting point. The new molecular formula, C25, H38O4, is presented for this com-pound.
3) OB is a colorless prism from benzene and melts at 193_??_194°C with decomposition. The molecular formula, C27, H42_??_6OO7, is presented for the compound.
4) Both ophiobolosins show the inhibiting effect on the growth of rice seeds at the concentration of 500 p.p.m. for coleoptiles and at 10 p.p.m. for roots. But OA has a promoting effect on the growth of coleoptiles at 10 p.p.m. OBA has no toxicity on them. Ophiobolosins has also an antifungal activity against Trichophyton spp. at the concentration of 10_??_20 p.p.m. and OB showed a strong effect to Trichomonas vaginalis (minimum 5p.p.m.).
