Four new minor brominated indole related alkaloids with antibacterial activities from Laurencia similis

• Four new brominated indole related alkaloids were isolated from Laurencia similis.
• 1 was the first naturally occurring 3-benzyl-indole derivative.
• 2 was the first natural 1,3-dihydro-indole-2-one with 2-isopropylidene group.
• 3 and 4 were the first carbazole and 2-carbonylamino-benzoate from the genus Laurencia.
• 1 showed the most potent antibacterial activity against seven bacterial strains.

Four new minor brominated indole related alkaloids (one indoles, 1, one 1,3-dihydro-indole-2-one, 2, one carbazole, 3, and one 2-carbonylamino-benzoate, 4) were isolated and identified from Laurencia similis by extensive chromatographic and spectrometric methods. Among them, 1 and 2 were the first example of naturally occurring indole with 3-benzyl group and 1,3-dihydro-indole-2-one with 2-isopropylidene group, respectively, whereas 3 and 4 were the first carbazole alkaloids and 2-carbonylamino-benzoate, respectively, isolated from the genus Laurencia. Moreover, 1 showed the most potent antibacterial activity against seven bacterial strains with MIC values ranging from 2 to 8 μg/mL.

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