Induced production of 6,9-dibromoflavasperone, a new radical scavenging naphthopyranone in the marine-mudflat-derived fungus Aspergillus niger

The addition of metal bromides (NaBr and CaBr 2 ) during fermentation of the marine-mudflat-derived fungus Aspergillu s niger induced production of a new radical scavenging brominated naphthopyranone, 6,9-dibromoflavasperone ( 1 ); and three known naphtho-γ-pyranone monomers, flavasperone ( 2 ), TMC-256A1 ( 3 ), and fonsecin ( 4 ); and one naphtho-γ-pyranone dimer, aurasperone B ( 5 ). The structure of 6,9-dibromoflavasperone ( 1 ) was assigned through the combination of spectroscopic data analyses and comparison with the spectral data of flavasperone ( 2 ). Compounds 1 – 5 displayed potent radical scavenging activity against 2,2 - diphenyl - 1 - picrylhydrazyl, with IC 50 values of 21, 25, 0.3, 0.02, and 0.01 μM, respectively, and 3 – 5 were more potent than the positive control, ascorbic acid (IC 50 , 20.0 μM).