Enhanced copper-mediated 18F-fluorination of aryl boronic esters provides eight radiotracers for PET applications

Positron emission tomography (PET) is a molecular imaging modality with wide-ranging applications in oncology, cardiology, neurology, as well as fundamental clinical research.1 Despite the great success of PET imaging, the development of new radiotracers remains a formidable challenge. Among all PET radioisotopes, 18F is a widely used clinically relevant radionuclide because of its advantageous properties;2 specifically, the half-life of fluorine-18 (109 min) is long enough to allow remote-site application of radiopharmaceuticals as demonstrated worldwide by distribution of 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG).3,4 A recent upsurge in fluorination chemistry has revealed a number of novel 18F-labeling methods,5 including the preparation of 18F-fluoroaromatics through aryl iodonium ylides,6 aryl sulfonium salts,7 preformed PdIV or NiII complexes,8 and aryl boronic precursors.9 These most recent advances could make an impact in the clinic if one progresses from proof of concept to the synthesis of radiotracers and radiopharmaceuticals, and ultimately apply these new methods for human use. Our group has demonstrated that arylboronates derived from pinacol are suitable substrates for Cu-mediated 18F-labeling with 18F-fluoride; one of the distinctive features of this reaction is its compatibility with arylboronates derived from electron rich, neutral and deficient arenes. In this report, we demonstrate that this transformation enables the preparation of eight radiotracers; [18F]FMTEB, [18F]FPEB, [18F]flumazenil, [18F]DAA1106, [18F]MFBG, [18F]FDOPA, [18F]FMT, and [18F]FDA (Scheme 1). To achieve this goal, our original reaction conditions were modified for radiotracers possessing an electron deficient fluoroarene. This study is significant as, for the first time, a range of radiotracers used in (pre)clinical studies, but difficult to prepare, is within reach applying a single reaction. Selected radiosyntheses were performed on automated platforms and in different laboratories, an advance indicating that the process is robust and amenable to broad use in PET radiochemistry facilities