SYNTHESIS OF THE I-123 LABELED AND I-125 LABELED CHOLINERGIC NERVE MARKER (-)-5-IODOBENZOVESAMICOL

The highly toxic curaremimetic and cholinergic neuron marker (-)-5-iod obenzovesamicol (IBVM) has been labeled with iodine-125 and iodine-123 . [I-125]IBVM, suitable for animal distribution and ex vivo autoradiog raphic studies, was synthesized by solid-state exchange; isolated yiel ds were 65-89% with specific activities in the range of 130-200 Ci/mmo l. The synthesis of no-carrier-added (-)-5-[I-125]IBVM from the corres ponding chiral (-)-5-(tri-n-butyltin) derivative using (NaI)-I-125 was evaluated using the oxidants H2O2, peracetic acid and chloramine-T. B oth peracetic acid and chloramine-T gave good yields (70-95%). However , when (NaI)-I-123 Was utilized, acceptable yields of [I-123]IBVM were obtained only with chloramine-T. Use of the latter oxidant did produc e 5-chlorobenzovesamicol which was eliminated during HPLC purification . After optimization of the reaction parameters, [I-123]IBVM in batch sizes of 10-27 mCi, is routinely obtained with a specific activity of 30-70,000 Ci/mmol, radiochemical purity (> 97%) and chiral purity (> 9 8 %). Isolated radiochemical yields have averaged 71 % (N = 40). Distr ibution analyses of [I-125]IBVM and [I-123]IBVM in mice 4 h following intravenous administration show essentially equivalent concentrations of the two tracers in the four brain regions sampled. The exceptionall y high specific activity of [I-123]IBVM has made possible the evaluati on of this radiotracer in humans.