Four new aaptamine alkaloids from marine sponge Aaptos aaptos

Four new aaptamine alkaloids, named as 9-methoxy-N-demethylaaptanone (1), 3,5-dicarbomethoxy-1,​6-​naphthyridine (2), aaptosvanphongs A and B (3 and 4), and three known aaptamine alkaloids as 2-methoxy-3-oxoaaptamine (5), 8,9,9-trimethoxy-9H-benzo[de][1,6]-naphthyridine (6), and demethyl(oxy)aaptamine (7) were isolated from the sponge Aaptos by various chromatographic methods. Their structures were established by extensive spectroscopic analyses (HR-ESI-MS, 1 D and 2 D NMR) and by comparison of the spectral data with those reported in the literature. Compounds 1-7 significantly showed cytotoxic effects against SK-LU-1, MCF-7, HepG2, and SK-Mel-2 cell lines with IC50 values in range from 7.7 ± 0.8 to 51.4 ± 1.8 µM. Among them, compound 7 exhibited the most cytotoxic activity with corresponding IC50 values of 9.2 ± 1.0, 7.8 ± 0.6, 8.4 ± 0.8, and 7.7 ± 0.8 µM.