Synthesis, Fluorine-18 Radiolabeling, and Biological Evaluation of N-((E)-4-Fluorobut-2-en-1-yl)-2β-carbomethoxy-3β-(4′-halophenyl)nortropanes: Candidate Radioligands for In Vivo Imaging of the Brain Dopamine Transporter with Positron Emission Tomography

The N-(E)-fluorobutenyl-3β-(para-halo-phenyl)nortropanes 9−12 were synthesized as ligands of the dopamine transporter (DAT) for use as 18F-labeled positron emission tomography (PET) imaging agents. In vitro competition binding assays demonstrated that compounds 9−12 have a high affinity for the DAT and are selective for the DAT compared to the serotonin and norepinephrine transporters. MicroPET imaging with [18F]9−[18F]11 in anesthetized cynomolgus monkeys showed high uptake in the putamen with lesser uptake in the caudate, but significant washout of the radiotracer was only observed for [18F]9. PET imaging with [18F]9 in an awake rhesus monkey showed high and nearly equal uptake in both the putamen and caudate with peak uptake achieved after 20 min followed by a leveling-off for about 10 min and then a steady washout and attainment of a quasi-equilibrium. During the time period 40−80 min postinjection of [18F]9, the ratio of uptake in the putamen and caudate vs cerebellum uptake was ≥4.