In Search of NPY Y4R Antagonists: Incorporation of Carbamoylated Arginine, Aza-Amino Acids, or d-Amino Acids into Oligopeptides Derived from the C-Termini of the Endogenous Agonists

The cross-linked pentapeptides (2 R ,7 R )-diaminooctanedioyl-bis(Tyr-Arg-Leu-Arg-Tyr-amide) ((2 R ,7 R )-BVD-74D, (2 R ,7 R )- 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 (2 R ,7 R )- 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.