Chemical Studies on Growth Self-inhibitors Produced by Phytopathogenic Fungi.

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1. Chloromonilicin, a growth self-inhibitor produced by cherry brown fungus Momilinia fructicola.(1) A new growth self-inhibitor, chloromonilicin (I), was isolated from M. fructicola, and its structure having a novel seven-membered lactone ring was determined on the basis of chemical and spectroscopic evidence. 4-Chloropinselin (II), a probable precursor of I, was also isolated and identified. I showed strong antifungal activity against phytopathogenic fungi.(2) The bromine congener, bromomonilicin, was prepared by fermentation. In addition, moniliphenone (III), a new benzophenone metabolite, was isolated from the bromomonilicinfe- fermentation broth. The biosynthetic pathway, III-> II-> I, was revealed by feeding experiments using deuterated III.(3) Novel lactone-reduced catabolites of I, which were named chloromonilinic acids A and B, were isolated from the chloromonilicin-fermrntation broth. They hardly showed antimicrobial activity. Bromomonilicin was transformed into bromomonilinic acid B, and then the latter into bromomonilinic acid A by M. fructicola.2. Growth self-inhibiting substances produced by other phytopathogenic fungi.(1) Two structurally related growth self-inhibitors were isolated form circular leaf spot fungus Mycosphaerella nawae. One of them was identified as (-)-usnic acid isomethoxide.(2) A growth self-inhibiting substance was obtained from cherry anthracnose fungus Glomerella cingulata. The active substance was unstable, and gave an inactive compound by methanolysis.