Dermorphin tetra‐ and heptapeptide analogues containing a [3,4] amide bond replacement by a carbon‐carbon double and single bond

Seven dermorphin hepta- and tetrapeptide analogues containing [3,4] amide bond replacement by a carbon-carbon double and single bond were prepared. 1H NMR studies of the pseudoheptapeptide in DMSO indicate the presence of extended conformations with stacking of the side chains in the N-terminal part and an inverse γ-turn around Ser7 in the conformational equilibrium. The binding data show that the affinity of the analogues for the μ-receptor is only slightly diminished in the d-Ala2 series and is more affected in the d-Arg2 series. Since the Gly4NH is not present in these compounds we conclude that this NH is not required to stabilize the bioactive conformation nor is it directly involved in binding to the receptor.