Regiospecific Aromatic Radioiodination via No-Carrier-Added Copper(I) Chloride-Assisted Iododebromination

Copper(I) chloride-assisted aromatic iododebromination was investigated as a no-carrier-added radioiodination technique. Using CuCl, and simple brominated aromatic substrates in DMSO, radiohalogenation conditions were optimized in terms of reaction time, temperature, and cuprous Chloride concentration. Radioiodination was rapid, regiospecific, and high labeling yields were achieved (50 - 80% after 30 min at 140°C) regardless of the degree of electronic activation/ deactivation of the substrate. Radiohalogenation yields were only slightly affected by up to 25 volume percent water in the reaction solvent. A two-step reaction mechanism is proposed in which radioiodinated copper species coordinate to the aromatic bromine atom prior to ipso substitution. The Utility of this technique for the high specific-activity radioiodination of biomolecules is discussed.