PHYTOTOXIC METABOLITES ISOLATED FROM SCOLECOTRICHUM-GRAMINIS FUCKEL

Two new cercosporins, (+)-isocercosporin (1) and(+)-14-acetylisocercosporin (2), were isolated from culture filtrates of Scolecotrichum graminis Fuckel, which is the causal fungus of a leaf streak disease in orchardgrass. The structure of each was elucidated by spectroscopic analysis, and (+)-isocercosporin (1) is the first isolated enantiomer of known (-)isocercorporin (8b). Compounds 1 and 8b had higher phytotoxic activity than that of (+)-cercosporin (a), an atropisomer of 8b. The results of the bioassay suggest that the phytotoxic activity of cercosporins depends on the relative configuration, and not on the absolute configuration. In addition, three phenol compounds, 1-(2,4-dihydroxy-6-methylphenyl)ethanone (3), isosclerone (4), and trans-3,4-dihydro-3,4,8-trihydroxy-1(2H)-naphthalenone (5), were isolated as minor components and identified. Compound 3 was isolated for the first time as a natural products.