New bioactive alkaloids from the marine sponge Stylissa sp.

Chemical investigation of the Indonesian marine sponge Stylissa species, which was collected at 2008 from Derawan Islands, Berau, NE Kalimantan, Indonesia offered four new brominated alkaloids, including 12-N-methyl stevensine (1), 12-N-methyl-2-debromostevensine (2), 3-debromolatonduine B methyl ester (3), 3-debromolatonduine A (4) together with eight known alkaloids identified as Z-hymenialdisine, Z-debromohymenialdisine, Stevensine, 2-debromostevensine, 3-bromoaldizine, 3,4-dibromopyrrole-2-carbamide, latonduine A, and latonduine B methyl ester (5-12), respectively. The structures of all isolated compounds were unambiguously elucidated based on extensive 1D and 2D NMR spectroscopy and HRMS analysis as well as comparison with those reported in literature. All isolated compounds were tested for their cytotoxicity against mouse lymphoma cell line L5187Y. The results showed that only 1, 5, 6, and 11 showed significant in vitro activity with EC50 values of 3.5, 1.8, 2.1, and 9.0 μg/mL, respectively.