There can be only one: Using a peptoid motif obtained by shifting the arginine side chain of a pentapeptide previously developed by Fujii et al. to the neighboring nitrogen atom restricts the conformational freedom and yields a conformationally homogeneous peptide (see picture) with a 100-fold higher binding affinity to the chemokine receptor CXCR4 in the picomolar range. Its efficiency to inhibit HIV-1 infections is also demonstrated.