EN
Dansylated analogues of the potent and selective u opioid peptide agonist [Dmt1]DALDA (H-Dmt-D-Arg-Phe-Lys-NH2; Dmt = 2',6'-dimethyltyrosine) were prepared either by substitution of Nε-dansyl-a,β-diaminopropionic acid or Nε-dansyl- lysine for Lys4 , or by attachment of a dansyl group to the C-terminal carboxamide function via a linker. All three analogues displayed high u agonist potency in vitro and the C-terminally dansylated one retained significant u receptor selectivity. The three analogues showed interesting differences in their fluorescence emission maxima and quantum yields, indicating that the dansyl group in two of them was engaged in intramolecular hydrophobic interactions. These dansylated [Dmt1]DALDA analogues represent valuable tools for binding studies, cellular uptake and intracellular distribution studies, and tissue distribution studies.