Celenamide E, a novel tripeptide alkaloid and a possible biosynthetic precursor of the previously reported celenamides A-C, was isolated from the Patagonian sponge Cliona chilensis collected at Rada Tilly, Chubut, Argentina. The structure of celenamide E was elucidated by spectroscopic techniques-UV, IR, 1D and 2D NMR (COSY, NOESY, HETCOR, COLOC) experiments - HIRFABMS, and preparation of an hexaacetate derivative. An unusual feature of celenamide E is the presence of a N-terminal dehydroamino acid. Celenamide E shows antibiotic activity against Gram-positive bacteria at 50 μg/disk.