Sulfoureido Lipopeptides from the Marine Sponge Discodermia kiiensis

New N-sulfoureidylated lipopeptides, sulfolipodiscamides A–C (1–3), were isolated by gel filtration chromatography of the n-butanol fraction of the marine sponge Discodermia kiiensis. By extensive NMR analyses and high-resolution mass spectrometry, the structures of 1–3 were elucidated as having an unprecedented N-sulfoureidyl group on the d-citrulline residue, a distinct feature that was not found in the structurally related lipodiscamides A–C (4–6), derived from the ether fraction of the same sponge. Furthermore, the absolute configurations of 1–3 were confirmed by comparisons of the HPLC retention times of the hydrolytic products and the corresponding authentic lipodiscamides. Interestingly, sulfolipodiscamide A displayed a 2.3-fold increase in cytotoxicity against murine leukemia (P388) cells, compared to the unconjugated parent compound.