Isolation and structure elucidation of isoaltenuene, a new metabolite of Alternaria alternata

Isoaltenuene, a previously unknown Alternaria metabolite has been isolated from a rice culture ofAlternaria alternata and purified by semipreparative HPLC. The assigned structure, elucidated by UV, IR, MS, and NMR spectroscopy, was 2?, 3?, 4?, 5?-tetrahydro-3, 4??, 5'?-trihydroxy-5-methoxy-2??-methyldibenzo (?)-pyrone and corresponded to a diasteroisomer of altenuene with inverted configuration at C-2?. Isoaltenuene showed a minor phytotoxic activity on tomato leaves at level of 20 ?g/spot and no antifungal activity onGeotrichum candidum (up to 20 ?g/disk).