Rhodamine-labeled 2β-carbomethoxy-3β-(3,4-dichlorophenyl)- tropane analogues as high-affinity fluorescent probes for the dopamine transporter

Novel fluorescent ligands were synthesized to identify a high-affinity probe that would enable visualization of the dopamine transporter (DAT) in living cells. Fluorescent tags were extended from the N- or 2-position of 2 beta-carbomethoxy-3 beta-(3,4-dichlorophenyl)tropane, using an ethylamino linker. The resulting 2-substituted (5) and N-substituted (9) rhodamine-labeled ligands provided the highest DAT binding affinities expressed in COS-7 cells (K-i = 27 and 18 nM, respectively) in the series. Visualization of the DAT with 5 and 9 was demonstrated by confocal fluorescence laser scanning microscopy in stably transfected HEK293 cells.