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

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

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