Structure–Activity Relationship Study of Cyclic Pentapeptide Ligands for Atypical Chemokine Receptor 3 (ACKR3)

The atypical chemokine receptor 3 (ACKR3)/CXC chemokine receptor 7 (CXCR7) recognizes stromal cell-derived factor 1 (SDF-1)/CXCL12 and is involved in a number of physiological and pathological processes. Here, we investigated the SAR of the component amino acids in an ACKR3-selective ligand, FC313 [<i>cyclo</i>(-d-Tyr-l-Arg-l-MeArg-l-Nal­(2)-l-Pro-)], for the development of highly active ACKR3 ligands. Notably, modification at the l-Pro position with a bulky hydrophobic side chain led to improved bioactivity toward ACKR3