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 D2 template

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 pharmacopho...