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

[ 18 F]Fluoroethyl bromide ([ 18 F]FEtBr) is a useful synthetic precursor to synthesize 18 F‐labeled compounds. However, the lower reactivity of [ 18 F]FEtBr with amine, phenol and amide functional groups than that of [ 11 C]CH 3 I partly limits its wide application in the synthesis of [ 18 F]fluoroethylated compounds. The aim of this study was to increase the reactivity of [ 18 F]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 [ 18 F]FEtBr and substrate, where [ 18 F]FEtI is reversibly formed and becomes more reactive; (2) converting [ 18 F]FEtBr into much more reactive [ 18 F]FEtOTf, similar to conversion of [ 11 C]CH 3 I into [ 11 C]CH 3 OTf. By these efforts, the [ 18 F]fluoroethylation efficiency of various substrates containing amine, phenol and amide groups with [ 18 F]FEtBr/NaI and [ 18 F]FEtOTf was significantly improved, compared with the corresponding reaction efficiency with [ 18 F]FEtBr. Copyright © 2003 John Wiley & Sons, Ltd.