Ten peptides related to the μ-receptor agonist, dermorphin (Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) having structural modifications at positions 2,3,4 and 7 were synthesised by the solid phase method by using 9-fluorenylmethyloxycarbonyl (Fmoc)-amino acid trichlorophenyl (Tcp) ester as coupling agents and Merrifield resin as the solid support and their biological activities namely the effect on guinea pig ileum, the analgesic and the antidiarrhoeal activity were studied. The synthetic peptides were found to possess more antidiarrhoeal activity than any other activity and this is most pronounced in the analogues, (D-Met(O)2, MePhe3, Sar4, Tyr7) dermorphin and (D-Met(O)2, MePhe3, Sar4, Thr7) dermorphin.
