| Summary: | Eleven new brominated depsidones, namely spiromastixones U-Z5 (<b>1</b>–<b>11</b>) along with five known analogues (<b>12</b>–<b>16</b>), were isolated from a deep-sea-derived fungus <i>Spiromastix</i> sp. through the addition of sodium bromide during fermentation. Their structures were elucidated by extensive analysis of the spectroscopic data including high-resolution MS and 1D and 2D NMR data. Compounds <b>6</b>–<b>10</b> and <b>16</b> exhibited significant inhibition against Gram-positive bacteria including methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) and vancomycin-resistant <i>Enterococcus faecium</i> (VRE) with MIC values ranging from 0.5 to 2.0 μM. Particularly, tribrominated <b>7</b> displayed the strongest activity against MRSA and VRE with a MIC of 0.5 and 1.0 μM, respectively, suggesting its potential for further development as a new antibacterial agent.
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