Alternatamides A−D: New Bromotryptamine Peptide Antibiotics from the Atlantic Marine Bryozoan Amathia alternata

Four new bromotryptamine peptides, alternatamides A-D (1-4), have been isolated from the Atlantic bryozoan Amathia alternata. The structures of the alternatamides were assigned primarily on the basis of 2D NMR data. The absolute stereochemistry of the N-methylleucine amino acid was shown to be L (2'S) by hydrolysis and comparison with standards. The alternatamides show modest antibacterial activities against several Gram-positive bacteria.