Synthesis and evaluation of 18F-trifluoroborate derivatives of triphenylphosphonium for myocardial perfusion imaging

Four trifluoroborate derivatives of phosphonium cations 2a-d were radiolabeled with fluorine-18 (F-18) and evaluated for imaging myocardial perfusion with positron emission tomography (PET). Tracers were radiolabeled simply via F-18-F-19 isotope exchange reaction in acidic (pH 2) aqueous solution. On average, [F-18]2a-d were obtained in 10-17% non-decay-corrected radiochemical yield with 25.9-48.1 GBq/mu mol specific activity, and >96% radiochemical purity. In vitro stability study showed no decomposition of [F-18]2a-d after being incubated in mouse plasma for up to 2 h. Myocardial uptake in mice was visualized in PET images by using [F-18]2b-d but not [F-18]2a. [F-18]2a-d were stable against in vivo defluorination as no significant bone uptake was observed. Despite sub-optimal heart uptake of [F-18]2b-d, we successfully demonstrated that F-18-F-19 isotope exchange reaction on trifluoroborates could be a promising strategy for the design of potential F-18-labeled tracers even for intracellular targets. (C) 2016 Elsevier Ltd. All rights reserved.