One-step, no-carrier-added, synthesis of a (18)F-labelled benzodiazepine receptor ligand
5-(2-Phenoxy)phenyl-1,3,4-oxadiazole-2-yl-4-fluorobenzoate, a non-classical benzodiazepine receptor ligand, has shown anticonvulsant activity against pentylenetetrazole-induced convulsion. In order to perform biological studies, we decided to label the compound with positron-emitting fluorine-ls (t(1/2)=109.7 min). The latter compound was prepared in no-carrier-added form from [(18)F]fluoride and 5-(2-phenoxy)phenyl-1,3,4-oxadiazole-2-yl-4-N,N,N-trimethylanilinium triflate in one step. The best results were obtained using Kryptofix2.2.2/[(18)F]fluoride with dimethylsulfoxide as the solvent at 90 degrees C. Column chromatography afforded the desired compound in 15 min in an overall radiochemical yield of 70-75% corrected to the end of radionuclide production with a specific radioactivity of about 3000 Ci/mmol and a radiochemical purity of more than 95% and high chemical purity.