Identification of chemical byproducts in the radiofluorination of structurally complex aryliodonium salts

The use of direct radiofluorination of aryliodonium salts represents a promising route to new PET tracers. This study tested the use of these precursors for obtaining candidate ligands of the cannabinoid type-2 receptor. F-18-labelling was performed using microfluidic technology, which allowed obtaining good incorporation yields. A closer inspection of the chemical composition of the reaction mixture evidenced the recurrent occurrence of chemical byproducts (H-adduct) due to a reductive side reaction of these substrates. The H-adduct formation seems to be unrelated to water presence, needed for obtaining a satisfactory incorporation, and may become an important feature for assessing the real-life accessibility of new radiotracers through the use of aryliodonium precursors.