Antifungal metabolite with a new carbon skeleton from Keissleriella sp Y54108, a marine filamentous fungus

In addition to four known metabolites (4-acetyl-6,8-dihydroxy-5-methylisocoumarin, 6,8-dihydroxy-3-methylisocoumarin, 6,8-dihydroxy-3,5,7-trimethylisocoumarin and 3,3'-oxy-(5-methyl)phenol), bioassay-guided fractionation of the culture of Keissleriella sp., a marine filamentous fungus (strain number: YS 4108), afforded an antifungal metabolite with a new carbon skeleton whose structure was elucidated spectrometrically as 3,6,8-trihydroxy-3-[3,5-dimethyl-2-oxo-3(E)-heptenyl]-2,3-dihydronaphthalen-1(4H)-one. In vitro antifungal assays of all isolates revealed that the new metabolite and 3,3'-oxybis[5-methylphenol] were inhibitory to the growth of the human pathogenic fungi Candida albicans, Tricophyton rubrum and Aspergillus niger with MICs of the former being 40, 20 and 80 mug/ml, and those of the latter 10, 30 and 50 mug/ml, respectively.