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

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