Keramamide A, a Novel Peptide from the Okinawan Marine Sponge Theonella sp.

A novel peptide, keramamide A 1, has been isolated from the Okinawan marine sponge Theonella sp. and the structure established as a unique hexapeptide containing a hitherto unknown amino acid 6-chloro-5-hydroxy-N-methyltryptophan, and possessing an unusual ureido bond. The structural assignment was made on the basis of spectroscopic results (two-dimensional NMR: 1H–1H COSY, NOESY, ROESY, COLOC, HMQC, HMBC and HOHAHA; and FAB MS/MS).