Novel and High Affinity Fluorescent Ligands for the Serotonin Transporter Based on (S)-Citalopram

Novel rhodamine-labeled ligands, based on (S)-citalopram, were synthesized and evaluated for uptake inhibition at the human serotonin, dopamine, and norepinephrine transporters (hSERT, hDAT, and hNET, respectively) and for binding at SERT, in transiently transfected COS7 cells. Compound 14 demonstrated high affinity binding and selectivity for SERT (Ki = 3 nM). Visualization of SERT, using confocal laser scanning microscopy, validated compound 14 as a novel tool for studying SERT expression and distribution in living cells.