Synthesis and biodistribution of an 123I labelled flunitrazepam derivative: a potential in vivo tracer for benzodiazepine receptors

A method for the synthesis of no-carrier-added of 7-[123I]iodo-1,3-dihydro-5-(2-fluorophenyl)-1-methyl-2H-1,4-benzodiazepine-2-one with a radiochemical yield of 25-30% has been developed. This benzodiazepine was prepared by reaction of [123I]iodide with the corresponding piperidyltriazene in acid medium and the reaction has been optimized for solvent, time and temperature. The triazene was synthesized by reduction of flunitrazepam to the amine, diazotisation and coupling with piperidine. Biodistribution studies of this radioligand in rats showed a maximum brain uptake of 0.35% of the injected dose at 15 min, which declines to 0.02% at 120 min. (author)