Synthesis of a [F]-Ligand for Benzodiazepine Receptor Studies

5-[2-(2-Chlorophenoxy)phenyl]-1,3,4-oxadiazole-2-yl-4-fluorobenzoate , the non-classic benzodiazepine ligand, has been shown to elicit a significant anticonvulsant activity against pentylenetetrazole-induced convulsion. In order to perform biological studies, we decided to prepare the [F]-labeled compound. The latter compound was prepared in no-carrier-added (n.c.a) form from 5-[2-(2-chlorophenoxy)phenyl]-1,3,4-oxadiazole-2-yl-4-N,N,N-trimethylanilinium triflate in one step at 125°C in Kryptofix/[F] and DMSO as the solvent. Column chromatography afforded the pure compound in 20 min, overall radiochemical yield of 55-65% (EOS), with a specific activity about 2000 Ci/mmole and chemical-radiochemical purity more than 95%.