Synthesis and biodistribution of 125I labeled bivalent analogs of practolol as potential myocardial imaging agents

Iodinated bivalent ligands 3 and 4 and a monovalent ligand 5 were prepared from the cardioselective β-antagonist, practolol. 125 I-labeled 3, 4 and 5 were prepared by solid phase isotopic exchange reaction with carrier-free Na 125 I and examined in rats as potential receptor-site-directed myocardial imaging agents. Biodistribution of these agents in rats indicated that 125 I-3 and 125 I-4 were localized in the heart similarly to 125 I-5 and the [ 125 I]iodobenzoyl practolol ( 6) that was previously reported. Localization of 125 I-3 and 125 I-4, was more persistent in the heart than that of 125 I-monovalent ligands 5 and 6. Heart-to-blood ratios of 125 I-3 and 125 I-4 were significantly lower than those of 125 I-5 and 125 I-6, due mainly to slow blood clearance rates of 125 I-3 and 125 I-4.