Opioid peptides. VIII. Synthesis and preliminary biological activity of [D-Phe3]- or [alpha,beta-dehydro-Phe3]dermorphin tetrapeptides.
We describe the synthesis and preliminary in vitro pharmacological testing of two new tetrapeptide analogues of the opioid heptapeptide dermorphin H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2. The replacement of Phe3 by its D-enantiomer was hardly if at all tolerated. The unsaturated analogue carrying the phenyl ring of the delta Phe3 residue in the Z-configuration, was almost inactive.