Synthesis of N-(3-[¹⁸F]fluoropropyl)-2β-carbomethoxy- 3β-(4-iodophenyl)nortropane ([¹⁸F]FP-β-CIT)

N-(3-[¹⁸F]fluoropropyl)-2β-carbomethoxy-3β-(4- iodophenyl)nortropane ([¹⁸F]FP-β-CIT) was synthesized in a two-step reaction sequence. In the first reaction, 1-bromo-3-(nitrobenzene-4- sulfonyloxy)-propane was fluorinated with no-carrier-added fluorine-18. The resulting product, 1-bromo-3-[¹⁸F]-fluoropropane, was distilled into a cooled reaction vessel containing 2β-carbomethoxy-3β-(4-iodophenyl)- nortropane, diisopropylethylamine and potassium iodide. After 30 min, the reaction mixture was subjected to a preparative HPLC purification. The product, [¹⁸F]FP-β-CIT, was isolated from the HPLC eluent with solid-phase extraction and formulated to yield an isotonic, pyrogen-free and sterile solution of [¹⁸F]FP-β-CIT. The overall decay-corrected radiochemical yield was 25 ± 5%. Radiochemical purity was >98% and the specific activity was 94 ± 50 GBq/μmol at the end of synthesis.