Radiosynthesis of the adenosine A3receptor ligand 5-(2-[18F]fluoroethyl) 2,4-diethyl-3-(ethylsulfanylcarbonyl)- 6-phenylpyridine-5-carboxylate ([18F]FE@SUPPY)

SummarySince to date very limited information on the distribution and function of the adenosine A3receptor is available, the development of a suitable radioligand is needed. Such a selective radioligand can then be used for quantitative autoradiography, preclinical studies in animals and subsequent human PET applications. Recently, a promising candidate compound, 5-(2-fluoroethyl) 2,4-diethyl-3-(ethylsulfanylcarbonyl)-6-phenylpyridine-5-carboxylate (FE@SUPPY), has been presented. The successful preparation of a suitable labelling precursor and the evaluation and optimization of the radiosynthesis of [18F] FE@SUPPY is presented herewith.For satisfactory yields, a reaction temperature of 75 °C has to be applied for at least 20 min using 8–10 mg of precursor. Until now, 15 complete high-scale radiosyntheses were performed. Starting from an average of 51±12 GBq (average ±SD; range: 30–67 GBq) [18F]fluoride, 9.4–3.6 GBq of formulated [18F]FE@SUPPY (32.3±12.4%, based on [18F]fluoride, corrected for decay) were prepared in <105 min.