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

A series of metallated arenes bearing sigma-bonded tin, mercury, germanium, boron, or silicon were evaluated as labeling substrates for the generator-produced positron emitter 122I(t1/2 = 3.6 min). Using dichloramine-T with 122I, radiochemical yields exceeding 90% were achieved after 1 min at 25 degrees 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.