.alpha.2-Adrenergic agonists/antagonists: the synthesis and structure-activity relationships of a series of indolin-2-yl and tetrahydroquinolin-2-yl imidazolines

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Abstract
The synthesis and .alpha.2-adrenergic activity of a series of indolin-2-yl and tetrahydroquinolin-2-yl imidazolines are described. The indolin-2-yl imidazoline 4b was found to possess potent .alpha.2-adrenergic agonist and antagonist activity in rats. The modification of the substituents on the indoline ring of 4b has led to the separation of these activities. Substitution on the aromatic ring of 4b with halogen or increasing the size of the N-alkyl substituent of 4b gave .alpha.2-adrenergic antagonists without agonist activity. The N-allylindoline 4d is more potent than idazoxan in vitro and is equipotent in vivo, but is less receptor selective (.alpha.2 vs. .alpha.1) than idazoxan. The cis-1,3-dimethylindolin-2-yl imidazoline 6a is an .alpha.2-adrenergic agonist equal in potency to clonidine in vitro, while the trans-1,3-dimethylindolin-2-yl imidazoline 6b is a moderately potent .alpha.2-adrenergic antagonist.