Peptide Synthesis in Aqueous Solution. II. Synthesis and Biological Activity of a Molluscan Neuropeptide, FMRFamide (Phe–Met–Arg–Phe–NH2) Analogs for N-Terminal Moiety

In order to elucidate the contribution of the N-terminal moiety (Phe1 or Met2) of FMRFamide to the activity, 16 kinds of FMRFamide analogs were synthesized and their structure-activity relations are discussed. From the results, it was found that hydrophobic or bulky group in N-terminal contributes to the contractile effect, while the precise length of the side chain of amino acid at 2-position is due to a relaxing effect.