Improved specific radioactivity of the PET radioligand [11C]FLB 457 by use of the GE medical systems PETtrace MeI microlab

Abstract

[11C]FLB 457 is a high affinity dopamine D2 receptor radioligand that is used for visualisation and quantitation of extrastriatal dopamine D2 receptors with positron emission tomography (PET). In this study, we report a comparison regarding the specific radioactivity of [11C]FLB 457 obtained by two different methods of synthesising [11C]methyl iodide. In addition, the synthesis of unlabelled FLB 457 and the corresponding desmethyl-precursor, starting from commercially available material, is reported. The first method used for [11C]methyl iodide synthesis was reduction of [11C]CO2 with lithium aluminium hydride in tetrahydrofuran to [11C]CH3OH, followed by conversion into [11C]CH3I= with hydrogen iodide. The second, recently developed method uses gas phase halogenation of [11C]CH4 with iodine. [11C]FLB 457 was labelled with [11C]methyl triflate produced on-line from [11C]methyl iodide. With the first method a specific radioactivity for [11C]FLB 457 of 2100 Ci/mmol (78 GBq/μmol) (n=13) at 40 min after end of bombardment (EOB) was achieved. Using the gas phase method a specific radioactivity of 3400 Ci/mmol (126 GBq/μmol) (n=7) at 40 min EOB could be obtained. The use of the gas phase method also resulted in shorter time for set-up compared to the regular method since no wet chemistry is involved in the preparation of [11C]methyl iodide. Copyright © 2000 John Wiley & Sons, Ltd.