NRC-8, EuCheMS International Conference on Nuclear and Radiochemistry

Electrosynthesis of electrophilic n.c.a. 18F-fluorinating reagents

17 Sept 2012, 17:30

1h 30m

Como, Italy

Poster Radiopharmaceutical chemistry, radiodiagnostics, radiotherapy, theragnostics Poster Session

Speaker

Mr Christian Drerup (Forschungszentrum Jülich GmbH, Germany)

Description

Because of its extraordinary suitable decay properties fluorine-18 is the most widely used radionuclide in positron emission tomography (PET) [1]. Presently the radioorganic syntheses of no-carrier-added (n.c.a.) 18F-labelled products are practically limited to nucleophilic procedures. This complicates or excludes n.c.a. syntheses of many putative tracer compounds and intensifies a special demand for electrophilic 18F-labelling. There is the unanswered question whether an electrochemical oxidation of nucleophilic [18F]fluoride can lead to an electrophilic [18F]fluorine analogue. Since in organic fluorochemistry N-F compounds are known as highly effective and selective electrophilic fluorinating agents [2], they were chosen to be synthesized with n.c.a. [18F]fluoride. Based on cyclic voltammetric measurements an electrochemical synthesis of [18F]N-fluorobis(phenylsulfonyl)amine was attempted. Bis(trifluoromethylsulfonyl)imide with 1-butyl-1-methylpyrrolidinium as counter anion was chosen as a putative suitable precursor. Due to its excellent physical and electrochemical properties this ionic liquid serves as conducting salt, solvent and starting material at once and offers a simplified performance by avoiding major side reactions. Cyclic voltammetry of bis(trifluoromethylsulfonyl)imide showed two succeeding oxidation steps. The first step may lead to a resonance-stabilized radical before further oxidation causes the generation of an unstable cation and finally the decomposition of the compound. Further electrosynthetic experiments were carried out in an established electrochemical cell [3]. After intercalating [18F]fluoride from aqueous solution into glassy carbon (Sigradur®G) the ionic liquid was added. At a tension of 6-8 V intercalated fluoride and bis(trifluoromethylsulfonyl)imide were expected to co-oxidize and recombine at the surface of the electrode. Products were separated from their ionic contents and analyzed by radio-HPLC. An unambiguous identification could not be achieved due to the lack of a reference compound. A resulting n.c.a. organic product, however, showed a similar HPLC-retention with co-injected bis(phenylsulfonyl)imide as “pseudostandard”. Thus, in principle a production of an n.c.a. electrophilic 18F-fluorinating reagent starting from [18F]fluoride appears probable. References: [1] H. H. Coenen, Fluorine-18 Labeling Methods in PET Chemistry, The Driving Force in Molecular Imaging, P. A. Schubiger, L. Lehmann, M. Friebe (eds.), Springer Verlag 2007, 16-50. [2] G. G. Furin, A. A. Fainzilberg, Russ. Chem. Rev., 68, (1999), 653-684. [3] K. Hamacher, T. Hirschfelder, H. H. Coenen, Appl. Radiat. Isot., 56, (2002), 519-523.