The impact of β-azido(or 1-piperidinyl)methylamino acids in position 2 or 3 on biological activity and conformation of dermorphin analogues.

The synthesis of new dermorphin analogues is described. The (R)-alanine or phenylalanine residues of natural dermorphin were substituted by the corresponding α-methyl-β-azidoalanine or α-benzyl-β-azido(1-piperidinyl)alanine residues. The potency and selectivity of the new analogues were evaluated by a competitive receptor binding assay in rat brain using [(3) H]DAMGO (a μ ligand) and [(3) H]DELT (a δ ligand). The most active analogue in this series, Tyr-(R)-Ala-(R)-α-benzyl-β-azidoAla-Gly-Tyr-Pro-Ser-NH2 and its epimer were analysed by (1) H and (13) C NMR spectroscopy and restrained molecular dynamics simulations. The dominant conformation of the investigated peptides depended on the absolute configuration around C(α) in the α-benzyl-β-azidoAla residue in position 3. The (R) configuration led to the formation of a type I β-turn, whilst switching to the (S) configuration gave rise to an inverse β-turn of type I', followed by the formation of a very short β-sheet. The selectivity of Tyr-(R)-Ala-(R) and (S)-α-benzyl-β-azidoAla-Gly-Tyr-Pro-Ser-NH2 was shown to be very similar; nevertheless, the two analogues exhibited different conformational preferences. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.