Two novel linear peptide alkaloids have been isolated as their hexaacetyl derivatives from acetylated methanol extracts of the sponge Cliona celata. The structures of hexaacetylcelenamide A (3) and B (4) were established by spectroscopic analysis and chemical degradation by ozonolysis and acid-catalyzed hydrolysis. The unique amino acid a,β-didehydro-3,4,5-trihydroxyphenylalanine was shown to be a subunit of both 3 and 4. A small-scale isolation employing acetic-d6 anhydride as the acetylating agent indicated that celenamides A (1) and B (2) were the naturally occurring sponge metabolites. © 1980, American Chemical Society. All rights reserved.