Structure-activity relationships of dermorphin tetrapeptides carrying a ketomethylene linkage.

The synthesis and in vitro pharmacological tests of 5 ketomethylene tetrapeptide analogues of the opioid heptapeptide dermorphin H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2 are described in this study. The substitution of the original Phe-Gly peptide bond (-CO-NH-) by the ketomethylene linkage (-CO-CH2-) provided analogues with reduced opioid activity.