N-.omega.-Fluoroalkyl Analogs of (1R)-2.beta.-Carbomethoxy-3.beta.-(4-iodophenyl)tropane (.beta.-CIT): Radiotracers for Positron Emission Tomography and Single Photon Emission Computed Tomography Imaging of Dopamine Transporters

Journal of Medicinal Chemistry
1994.0

Abstract

To extend the structure-activity relationships of tropanes as potential neuroradiological ligands and facilitate direct comparison of the same molecules in SPECT (123I-labeled) and PET (18F-labeled) applications, we synthesized and characterized a series of N-ω-fluoroalkyl analogs of β-CIT (4a and 5a), their isopropyl ester congeners IP-β-CIT (6a and 7a), and corresponding 4-trimethylstannyl derivatives (4b-7b) as radiolabeling precursors. Affinities for dopamine transporters (DAT) in rat brain striatum were determined via [3H]GBR-12935 displacement assays: para-iodinated analogs (4a, 5a, 6a, 7a) exhibited high DAT affinity (1-4 nM, similar to β-CIT), while trimethylstannyl derivatives had very low affinity. Preliminary behavioral testing in rats showed that the analogs induced sustained locomotor arousal, though less potent than cocaine and β-CIT. SPECT imaging in a baboon with [123I]-β-CIT-FP (4a) demonstrated significant striatal uptake (rich in DAT) with high target-to-background ratios and faster washout compared to [123I]-β-CIT. These fluoroalkyl phenyltropane derivatives show high affinity for DAT and are promising agents for PET or SPECT imaging; [123I]-β-CIT-FP, in particular, exhibits favorable imaging properties including high striatal uptake and relative specificity, making it a valuable tracer for in vivo studies of the dopamine system using tomographic imaging.

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