Discovery of 4-(4-(2-((5-Hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl)(propyl)amino)ethyl)piperazin-1-yl)quinolin-8-ol and its analogues as highly potent dopamine D2/D3 agonists and as iron chelator: in vivo activity indicates potential application in symptomatic and neuroprotective therapy for Parkinson's disease.

The role of iron in the pathogenesis of Parkinson's disease (PD) has been implicated strongly because of generation of oxidative stress leading to dopamine cell death. In our overall goal to develop bifunctional/multifunctional drugs, we designed dopamine D2/D3 agonist molecules with a capacity to bind to iron. Binding assays were carried out with HEK-293 cells expressing either D2 or D3 receptor with tritiated spiperone to evaluate inhibition constants (K(i)). Functional activity of selected compounds was carried out with GTPgammaS binding assay. SAR results identified compounds (+)-19a and (-)-19b as two potent agonists for both D2 and D3 receptors (EC(50) (GTPgammaS); D2 = 4.51 and 1.69 nM and D3 = 1.58 and 0.74 nM for (-)-19b and (+)-19a, respectively). In vitro complexation studies with 19b demonstrated efficient chelation with iron. Furthermore, the deoxyribose assay with 19b demonstrated potent antioxidant activity. In PD animal model study, (-)-19b exhibited potent in vivo activity in reversing locomotor activity in reserpinized rats and also in producing potent rotational activity in 6-OHDA lesioned rats. This reports initial development of unique lead molecules that might find potential use in symptomatic and neuroprotective treatment of PD.