A new quinoline alkaloid, aaptoline A (1), was isolated from the marine sponge Aaptos suberitoides, along with known alkaloids, aaptamine (2), isoaaptamine (3), and demethylaaptamine (4). Interestingly, 1-4 are presumably biosynthesized from common precursors, L-DOPA and β-alanine aldehyde. © 2014 The Japan Institute of Heterocyclic Chemistry.