Abstract
Positron emission tomography (PET) is an important imaging modality for biomedical research and drug development. PET requires biochemically selective radiotracers to realize full potential. Fluorine-18 (t1/2 = 109.8 min) is a major radionuclide for labeling such radiotracers but is only readily available in high activities from cyclotrons as [18F]fluoride ion. [18F]fluoroform has emerged for labeling tracers in trifluoromethyl groups. Prior methods of [18F]fluoroform synthesis used difluoro precursors in solution and led to high dilution with carrier and low molar activity (Am). We explored a new approach for the synthesis of [18F]fluoroform based on the radiosynthesis of [18F]fluoromethane from [18F]fluoride ion and then cobaltIII fluoride mediated gas phase fluorination. We estimate that carrier dilution in this process is limited to about 3-fold and find that moderate to high Am values can be achieved. We show that [18F]fluoroform so produced is highly versatile for rapidly and efficiently labeling various chemotypes that carry trifluoromethyl groups, thereby expanding prospects for developing new PET radiotracers.
Highlights
Positron emission tomography (PET) is an increasingly important molecular imaging modality for drug development[1,2], biomedical research[3], and medical diagnosis[4,5,6]
Because of the role of PET in drug development and a frequent requirement to label drugs and new radiotracers with a positron-emitter, academic groups have pursued the development of methods for labeling CF3 groups with fluorine-1823,24, with the most recent methods being based on generation of [18F]CuCF3 from [18F]fluoride ion either directly or via synthesis of [18F]fluoroform (Fig. 2)[25,26,27,28,29]
We explored the radiosynthesis of [18F]fluoroform according to a different strategy involving initial installation of the fluorine-18 followed by subsequent gas phase difluorination
Summary
Positron emission tomography (PET) is an increasingly important molecular imaging modality for drug development[1,2], biomedical research[3], and medical diagnosis[4,5,6]. Because of the role of PET in drug development and a frequent requirement to label drugs and new radiotracers with a positron-emitter, academic groups have pursued the development of methods for labeling CF3 groups with fluorine-1823,24, with the most recent methods being based on generation of [18F]CuCF3 from [18F]fluoride ion either directly or via synthesis of [18F]fluoroform (Fig. 2)[25,26,27,28,29]. Pilot experiments confirmed the production of [18F]fluoroform from this process with the CoF3 column operating between 230 and 350 °C
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