The radioiodination procedure (scheme 17660801a) has been described earlier (1, 2) and was adapted for the synthesis of (II) as follows: Compound (I) (4.3 mg, 10 mcmol) was added to Na125I (1.5 mCi) contained in 0.1 N NaOH (100 mcl) in a round-bottom flask shielded from light. N-Chlorosuccinimide (0.4 mg, 3 mcmol) in THF (100 mcl) and sodium iodide (0.37 mg, 2.5 mcmol) in water (100 mcl) were then added, and the solution was stirred at room temperature in the dark for 40 min. Sodium thiosulfate (2.5 mg) in water (1 ml) was then added. Extraction with ethyl ether and purification by silica gel column chromatography yielded [125I]-IPM (II) in 25% radiochemical yield (375 mcCi) with a calculated specific activity of 1.5 Ci/mmol (Srivastava, P.C. et al. NucCompact 1989, 5: 145-9).