Structural revision of aspernigrin A, reisolated from Cladosporium herbarum IFB-E002

Aspernigrin A was reisolated as a secondary metabolite of the Cynodon dactylon-associated endophytic fungus Cladosporium herbarum IFB-E002 coproducing rubrofusarin B, fonsecinone A, 7-hydroxy-4-methoxy-5-methylcoumarin, orlandin, kotanin, and 3beta,5alpha,6beta-trihydroxyergosta-7,22-diene. The structure of aspernigrin A, previously elucidated to be 4-benzyl-6-oxo-1,6-dihydropyridine-3-carboxamide (1), was revised as 6-benzyl-4-oxo-1,4-dihydropyridine-3-carboxamide (2) on the basis of its additional NMR spectroscopic data and the X-ray crystallographic analysis.