isolated from the sea hare Aplysia kurodai together with the congeners aplyronines B (3) and C (4). The absolute stereostructure of aplyronine A (2) was determined by the instrumental analysis (mainly NMR and MS) and the enantioselectivesynthesis of the fragments obtained from chemical degradation of aplyronine A (2). The structures of aplyronines B (3) and C (4) were also elucidated. Cytotoxicity and