New production of (R)-(–)-5-bromomellein, a dihydroisocoumarin derivative from the marine-derived fungus Aspergillus ochraceus

Abstract

The addition of NaBr to the fermentation of a marine isolate of the fungus Aspergillus ochraceus resulted in induced production of a new brominated mellein analogue. A new radical-scavenging halogenated isocoumarin, (R)-(–)-5-bromomellein (1), and three known compounds, (R)-(–)-mellein (2), clavatol (3), and circumdatin A (4), were isolated from the culture. The structure of 1 was assigned through a combination of spectroscopic data analyses. Compounds 1–4 exhibited mild radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH). The IC50 values of each compounds (1–4) were 24, 25, 30, and 32 μM, respectively, which were less active than the positive control, L-ascorbic acid (IC50, 20.0 μM).