In vivo and in vitro characteristics of the N-Methyl derivative of [125I]3-Quinuclidinyl 4-Iodobenzilate

Radiolabeled analogues of 3-quinuclidinyl benzilate (QNB) localize in the myocardium by virtue of ligand-receptor interactions. The radioiodinated derivative exhibits less favorable non-receptor interactions than tritiated QNB in the myocardium, probably due to increased lipophilicity. In order to prevent intracellular localization and partitioning into lipid membranes, we prepared the N-methyl quaternary analogue of the iodinated derivative [ 125 I]3-quinuclidinyl 4-iodobenzilate. In vitro and in vivo results indicate that the quaternization reduces the affinity of the analogue to a value too low for advantageous receptor-mediated localization.