A simple method for the preparation of 123I and 125I labeled iodobenzodiazepines

Abstract The tributyltin derivative of the benzodiazepine antagonist ethyl 7-iodo-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a] [1,4]benzodiazepine-3-carboxylate (Ro 16-0154) was synthesized by a one-step Pd catalyzed reaction between bistributyltin and Ro 16-0154. Electrophilic iodination of the tributylin compound with no-carrier-added 125 I and 123 I gave a 50–70% radiochemical yield of a greater than 98% radiochemically pure Ro 16-0154. The specific activity of [ 123 I]Ro 16-0154 and [ 125 I]Ro 16-0154 was 180,000 and 1700 Ci/mmol, respectively, but the effective specific activity was 6900 and 300 Ci/mool due to the presence of benzodiazepine impurities which have similar receptor binding properties.