In Search of NPY Y(4)R Antagonists: Incorporation of Carbamoylated Arginine, Aza-Amino Acids, or d-Amino Acids into Oligopeptides Derived from the C-Termini of the Endogenous Agonists

[Image: see text] The cross-linked pentapeptides (2R,7R)-diaminooctanedioyl-bis(Tyr-Arg-Leu-Arg-Tyr-amide) ((2R,7R)-BVD-74D, (2R,7R)-1) and octanedioyl-bis(Tyr-Arg-Leu-Arg-Tyr-amide) (2) as well as the pentapeptide Ac-Tyr-Arg-Leu-Arg-Tyr-amide (3) were previously described as neuropeptide Y Y(4) receptor (Y(4)R) partial agonists. Here, we report on a series of analogues of (2R,7R)-1 and 2 in which Arg(2), Leu(3), or Arg(4) were replaced by the respective aza-amino acids. The replacement of Arg(2) in 3 with a carbamoylated arginine building block and the extension of the N-terminus by an additional arginine led to the high-affinity hexapeptide Ac-Arg-Tyr-N(ω)-[(4-aminobutyl)aminocarbonyl]Arg-Leu-Arg-Tyr-amide (35), which was used as a precursor for a d-amino acid scan. The target compounds were investigated for Y(4)R functional activity in assays with complementary readouts: aequorin Ca(2+) and β-arrestin 1 or β-arrestin 2 assays. In contrast to the parent compounds, which are Y(4)R agonists, several ligands were able to suppress the effect elicited by the endogenous ligand pancreatic polypeptide and therefore represent a novel class of peptide Y(4)R antagonists.