New generation dopaminergic agents .1. Discovery of a novel scaffold which embraces the D2 agonist pharmacophore.: Structure-activity relationships of a series of 2-(aminomethyl)chromans

A series of 2-(aminomethyl)chromans (2-AMCs) was synthesized and evaluated for their affinity and selectivity for both the high-and low-affinity agonist states (D-2(High) and D-2(Low), respectively) of the dopamine (DA) D-2 receptor. The 7-hydroxy-2-(aminomethyl)chroman moiety was observed to be the primary D-2 agonist pharmacophore. The 2-methylchroman moiety was discovered to be an entirely novel scaffold which could be used to access the D-2 agonist pharmacophore. Attaching various simple alkyl and arylalkyl side chains to the 7-hydroxy 2-AMC nucleus had significant effects on selectivity for the D-2(High) receptor vs the 5HT(1A) and alpha(1) receptors. A novel DA partial agonist, (R)-(-)-2-(benzylamino)methyl)chroman-7-ol [R-(-)-35c], was identified as having the highest affinity and best selectivity for the D-2(High) receptor vs the alpha(1) and 5HT(1A) receptors. Several regions of the 2-AMC nucleus were modified and recognized as potential sites to modulate the level of intrinsic activity. The global minimum conformer of the 7-hydroxy-2-AMC moiety was identified as fulfilling the McDermed model D-2 agonist pharmacophoric criteria and was proposed as the D-2 receptor-bound conformation. Structure-activity relationships gained from these studies have aided in the synthesis of D-2 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 D-2 agonism or antagonism.