Affinity of 2-(tetrahydroisoquinolin-2-ylmethyl)- and 2-(isoindolin-2-ylmethyl)imidazolines for .alpha.-adrenoceptors. Differential affinity of imidazolines for the [3H]idazoxan-labeled .alpha.2-adrenoceptor vs the [3H]yohimbine-labeled site

Abstract
A series of 2-(tetrahyroisoquinolin-2-ylmethyl)- and 2-(isoindolin-2-ylmethyl)imidazolines were prepared and tested for .alpha.1- and .alpha.2-adrenoceptor affinity with radioligand binding. Several compounds, 5-fluoro- (5h), 5-chloro- (5j), 5,8-dimethoxy- (5r), and 5,8-dimethoxy-1-methyl-(5s) 2-(tetrahydroisoquinolin-2-methylimidazoline, were found to be selective .alpha.2-adrenoceptor ligands on the basis of displacement of [3H]yohimbine from rat cerebral cortical membranes. One compound, 2-[(8-chloro tetrahydroisoquinolin-2-yl)methyl]imidazoline (5m), showed a 36-fold difference in affinity for the [3H]idazoxan-labeled .alpha.2-adrenoceptor relative to the [3H]yohimbine-labeled site, which may be evidence for .alpha.2adrenoceptor subtypes.

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