Opioid peptides. Structure-activity relationships of dermorphin endothiotetrapeptides. VII

We describe the synthesis and preliminary in vitro and in vivo pharmacological tests of five endothiotetrapeptide analogues of the opioid heptapeptide dermorphin H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser.-NH2. The modification obtained by substituting Phet for Phe3 or Glyt for Gly4 provided further analogues with significant opioid activity.