How to increase the reactivity of [18F]fluoroethyl bromide:: [18F]fluoroethylation of amine, phenol and amide functional groups with [18F]FEtBr, [18F]FEtBr/NaI and [18F]FEtOTf

[F-18]Fluoroethyl bromide ([F-18]FEtBr) is a useful synthetic precursor to synthesize F-18-labeled compounds. However, the lower reactivity of [F-18]FEtBr with amine, phenol and amide functional groups than that of [C-11]CH3I partly limits its wide application in the synthesis of [F-18]fluoroethylated compounds. The aim of this study was to increase the reactivity of [F-18]FEtBr with various nucleophilic substrates for PET tracers containing amine, phenol and amide moieties. The present strategies included (1) adding NaI into the reaction mixture of [F-18]FEtBr and substrate, where [F-18]FEtI is reversibly formed and becomes more reactive; (2) converting [F-18]FEtBr into much more reactive [F-18]FEtOTf, similar to conversion of [C-11]CH3I into [C-11]CH3OTf. By these efforts, the [F-18]fluoroethylation efficiency of various substrates containing amine, phenol and amide groups with [F-18]FEtBr/NaI and [F-18]FEtOTf was significantly improved, compared with the corresponding reaction efficiency with [F-18]FEtBr. Copyright (C) 2003 John Wiley Sons, Ltd.