| Summary: | A chemical investigation of a methanol extract of <i>Spongia</i> sp., a marine sponge collected from the Philippines, identified 12 unreported scalarane-type alkaloids—scalimides A–L (<b>1</b>–<b>12</b>)—together with two previously described scalarin derivatives. The elucidation of the structure of the scalaranes based on the interpretation of their NMR and HRMS data revealed that <b>1</b>–<b>12</b> featured a <i>β</i>-alanine-substituted E-ring but differed from each other through variations in their oxidation states and substitutions occurring at C16, C24, and C25. Evaluation of the antimicrobial activity of <b>1</b>–<b>12</b> against several Gram-positive and Gram-negative bacteria showed that <b>10</b> and <b>11</b> were active against <i>Micrococcus luteus</i> and <i>Bacillus subtilis,</i> respectively, with MIC values ranging from 4 to 16 μg/mL.
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