Isolation and structure elucidation of isoaltenuene, a new metabolite ofAlternaria alternata.

Isoaltenuene, a previously unknownAlternaria 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'β, 5'α-trihydroxy-5-methoxy-2'α-methyldibenzo (α)-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 μg/spot and no antifungal activity onGeotrichum candidum (up to 20 μg/disk).