Abstract
In a relatively short period of time, transition metal-mediated radiofluorination reactions have changed the PET radiochemistry landscape. These reactions have enabled the radiofluorination of a wide range of substrates, facilitating access to radiopharmaceuticals that were challenging to synthesize using traditional fluorine-18 radiochemistry. However, the process of adapting these new reactions for automated radiopharmaceutical production has revealed limitations in fitting them into the confines of traditional radiochemistry systems. In particular, the presence of bases (e.g. K2CO3) and/or phase transfer catalysts (PTC) (e.g. kryptofix 2.2.2) associated with fluorine-18 preparation has been found to be detrimental to reaction yields. We hypothesized that these limitations could be addressed through the development of alternate techniques for preparing [18F]fluoride. This approach also opens the possibility that an eluent can be individually tailored to meet the specific needs of a metal-catalyzed reaction of interest. In this communication, we demonstrate that various solutions of copper salts, bases, and ancillary ligands can be utilized to elute [18F]fluoride from ion exchange cartridges. The new procedures are effective for fluorine-18 radiochemistry and, as proof of concept, have been used to optimize an otherwise base-sensitive copper-mediated radiofluorination reaction.
Highlights
In a relatively short period of time, transition metal-mediated radiofluorination reactions have changed the Positron emission tomography (PET) radiochemistry landscape
The presence of K2CO3 and/or K2.2.2 can be detrimental to subsequent reactions and/or protecting group manipulations, as we have discovered in recent PET
This paper introduces the concept of tailoring [18F]fluoride processing conditions to enhance late-stage radiofluorination reactions
Summary
In a relatively short period of time, transition metal-mediated radiofluorination reactions have changed the PET radiochemistry landscape. The presence of bases (e.g. K2CO3) and/or phase transfer catalysts (PTC) (e.g. kryptofix 2.2.2) associated with fluorine-18 preparation has been found to be detrimental to reaction yields We hypothesized that these limitations could be addressed through the development of alternate techniques for preparing [18F]fluoride. This approach opens the possibility that an eluent can be individually tailored to meet the specific needs of a metal-catalyzed reaction of interest. In this communication, we demonstrate that various solutions of copper salts, bases, and ancillary ligands can be utilized to elute [18F]fluoride from ion exchange cartridges. This classical approach has worked satisfactorily for numerous nucleophilic radiofluorination reactions[9] since its introduction in 198610–13
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