Marine natural products. XXVI. Biologically active tridecapeptide lactones from the Okinawan marine sponge Theonella swinhoei (Theonellidae). (2). Structures of theonellapeptolides Ia, Ib, Ic, and Ie.

Five tridecapeptide lactones, named theonellapeptolides Ia (1), Ib (2), Ic (3), Id (4), and Ie (5), were isolated from the Okinawan marine sponge Theonella swinhoei. Following the structure elucidation of theonellapeptolide Id (4), the structures of theonellapeptolides Ia (1), Ib (2), Ic (3), and Ie (5) were determined on the basis of chemical and physicochemical evidence including high performance liquid chromatography and circular dichroism combined analysis of the amino acid compositions. Theonellapeptolides Ib (2), Ic (3), Id (4), and Ie (5) exhibit moderate cytotoxic activity towards for L1210 in vitro (IC50 1.6, 1.3, 2.4, and 1.4 micrograms/ml, respectively), and theonellapeptolide Ie (5) exhibits ion-transport activities for Na+ and K+ ions.