Comparative evaluation of electrophilic aromatic iododemetallation techniques for labeling radiopharmaceuticals with iodine-122

A series of metallated arenes bearing σ-bonded tin, mercury, germanium, boron, or silicon were evaluated as labeling substrates for the generator-produced positron emitter ¹²²I (t _{1 2} = 3.6 min). Using dichloramine-T with ¹²²I, radiochemical yields exceeding 90% were achieved after 1 min at 25°C using stannylated or mercurated arenes in ethanol, or germylated arenes in acidic solvent. Stannylated or mercurated arenes resulted in high labeling yields even with deactivated aromatics in ethanol, but regiospecifically-iodinated products were obtained only from stannylated precursors due to differences in the syntheses of these organometallics. The implications of these results to the labeling of radiopharmaceuticals with ¹²²I are discussed.