Synthesis and dopaminergic properties of benzo-fused analogues of quinpirole and quinelorane

In an analogy to the potent catechol dopamine D-1 agonists dihydrexidine (1 ) and dinapsoline (2), benzo rings were fused onto the structures of the do pamine D-2-selective agonists quinelorane (3) and quinpirole (4). Each of t he phenyl ring-substituted derivatives had significant affinity for D-2 rec eptors, albeit somewhat lower than the two parent compounds, 3 and 4. Compo unds with N-propyl and N-allyl substituents (5b, 5c, 6c, and 6d) had higher affinity for the D-2 dopamine receptor than did their corresponding second ary amines (5a and 6a). Slightly different effects on affinity of an n-prop yl and an n-allyl group in the new analogues of 3 and 4 suggest that differ ent binding orientations may be invoked at the receptor.