Next, we aimed to investigate the suitability of 14 as a molecular tool to study the binding of non-fluorescent ligands to the IABS of CCR2. Therefore, we set up displacement experiments with 14 and the known intracellular CCR2 antagonists SD-24 (1) and CCR2-RA (4). In agreement with previously reported nanomolar affinities, we obtained Ki values of 28.4 ± 3.8 nM for 1 and 17.2 ± 2.6 nM for 4 (Figure ).