New Generation Dopaminergic Agents. 6. Structure−Activity Relationship Studies of a Series of 4-(Aminoethoxy)indole and 4-(Aminoethoxy)indolone Derivatives Based on the Newly Discovered 3-Hydroxyphenoxyethylamine D2Template

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Abstract
A series of 4-(aminoethoxy)indoles 7 and a related series of 4-(aminoethoxy)indolones 8 were synthesized and evaluated for their affinity for both the high- and low-affinity agonist states (D2High and D2Low, respectively) of the dopamine (DA) D2 receptor. The 4-aminoethoxy derivatives (i.e., 7 and 8) were designed as bioisosteric analogues based on the phenol prototype 4. The indolones 8 were observed to have high affinity for the D2High receptor. Comparison of their previously reported chroman analogues with the more flexible 4-(aminoethoxy)indoles revealed the chroman analogues to be more potent, whereas little loss in D2High affinity was observed when comparing the 4-(aminoethoxy)indolones with their respective chroman analogues. Several regions of the phenoxyethylamine framework were modified and recognized as potential sites to modulate the level of intrinsic activity. A conformational analysis was performed and a putative bioactive conformation was proposed which fulfilled the D2 agonist pharmacophore criteria based on the McDermed model. Structure−activity relationships gained from these studies have aided in the synthesis of D2 partial agonists of varying intrinsic activity levels. These agents should be of therapeutic value in treating disorders resulting from hypo- and hyperdopaminergic activity, without the side effects associated with complete D2 agonism or antagonism.