Fumiquinazoline S (1), a new quinazoline-containing alkaloid, and the known fumiquinazolines F (6) and L (7) of the same structural class were isolated from the solid-substrate culture of an Aspergillus sp. fungus collected from marine-submerged wood. In addition, isochaetominines A-C (2-4) and 14-epi-isochaetominine C (5), new alkaloids possessing an unusual amino acid-based tetracyclic core framework related to the fumiquinazolines, were isolated from the same fungal strain. The structures of these compounds were determined by combined spectroscopic methods, and the absolute configurations were assigned by NOESY, ROESY, and advanced Marfey's analyses along with biogenetic considerations. The new compounds exhibited weak inhibition against Na(+)/K(+)-ATPase.