Synthesis of [18F]fluoroetanidazole: a potential new tracer for imaging hypoxia.

A method has been developed for the synthesis of [18F]fluoroetanidazole, a potential tracer for imaging hypoxia with positron emission tomography. The compound is prepared by an active ester coupling reaction between the 2,3,5,6-tetrafluorophenyl ester of 2-nitroimidazole acetic acid and [18F]fluoroethylamine. [18F]Fluoroethylamine is prepared from N-[2-(toluene-4-sulfonyloxy)-ethyl]-phthalimide and [18F]fluoride and purified by distillation. The overall reaction takes about 90 min and gives a yield, uncorrected, of about 25%. Purification on a reversed-phase column is straightforward.