Four chlorinated depsidones from a seaweed-derived strain of Aspergillus unguis and their new biological activities.

Four chlorinated depsidones (two reported for the second time (1 and 2) and two known (3 and 4)) were isolated from a seaweed-derived Aspergillus unguis strain. Their structures were spectroscopically elucidated. Compounds 1, 3 and 4 strongly inhibited methicillin-resistant Staphylococcus aureus (MRSA) with minimum inhibitory concentrations (MICs) of 2, 2 and 4 μg/mL and killed Artemia larva with LC50 of 4.1, 1.7 and 2.8 μg/mL, respectively. Besides, in DNA-damaging test, they also selectively inhibited a DNA repair capacity-defective Escherichia coli strain AB3027(-) (MICs: 2, 32 and 4 μg/mL, respectively) compared with the wild-type strain AB1157(+) (MICs: over 512, over 512 and 256 μg/mL, respectively). Furthermore, compound 1 also strongly inhibited cancer cell line A-549 (IC50: 0.5 μg/mL). The above-mentioned bioactivities were newly reported for compound 1. In contrast, compound 2 did not exhibit significant activity. The structure-activity relationship indicated that a complete lactone ring may be important.