Synthesis and characterization of iodobenzamide analogs: potential D-2 dopamine receptor imaging agents

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Abstract
(S)-N-[1-Ethyl-2pyrrolidinyl)methyl]-2-hydroxy-3-iodo-6-methoxybenzamide ([123I]IBZM) is a central nervous system (CNS) D-2 dopamine receptor imaging agent. In order to investigate the versatility of this parent structure in specific dopamine receptor localization and the potential for developing new dopamine receptor imaging agents, a series of new iodinated benzamides with fused ring systems, naphthalene (INAP) and benzofuran (IBF), was synthesized and radiolabeled, and the in vivo and in vitro biolgoical properties were characterized. The best analogue of IBZM is IBF (21). The specific binding of [125I]IBF (21) with rat striatal tissue preparation was found to be saturable and displayed a Kd of 0.106 .+-. 0.015 nM. Competition data of various receptor ligands for [125I]IBF (21) binding show the following rank order to potency: spiperone > IBF (21) > IBZM > (+)-butaclamol > (.+-.)-ADTN, 6,7 > ketanserin (G SCH-23390 .mchgt. propanolol. The in vivo biodistribution results confirm that [125I]IBF (21) concentrated in the striatal area after iv injection into rats. The study demonstrates that [123I]IBF (21) is a potential agent for imaging CNS D-2 dopamine receptors.