Evaluating N-difluoromethyltriazolium triflate as a precursor for the synthesis of high molar activity [ F]fluoroform.

The trifluoromethyl group is a prominent motif in biologically active compounds and therefore of great interest for the labeling with the positron emitter fluorine-18 for positron emission tomography (PET) imaging. Multiple labeling strategies have been explored in the past; however, most of them suffer from low molar activity due to precursor degradation. In this study, the potential of 1-(difluoromethyl)-3-methyl-4-phenyl-1H-1,2,3-triazol-3-ium triflate as precursor for the synthesis of the [ F]trifluoromethylation building block [ F]fluoroform with high molar activity was investigated. The triazolium precursor was reacted under various conditions with [ F]fluoride, providing [ F]fluoroform with radiochemical yields (RCY) and molar activities (A ) comparable and even superior with already existing methods. Highest molar activities (A  = 153 ± 14 GBq/μmol, dc, EOS) were observed for the automated procedure on the Neptis® perform module. Due to its easy handling and good RCY and A in the [ F]fluoroform synthesis, the triazolium precursor is a valuable alternative to already known precursors.