Development of (S)-N6-(2-(4-(isoquinolin-1-yl)piperazin-1-yl)ethyl)-N6-propyl-4,5,6,7-tetrahydrobenzo[d]-thiazole-2,6-diamine and its analogue as a D3 receptor preferring agonist: potent in vivo activity in Parkinson's disease animal models.

Here we report structure-activity relationship study of a novel hybrid series of compounds where structural alteration of aromatic hydrophobic moieties connected to the piperazine ring and bioisosteric replacement of the aromatic tetralin moieties were carried out. Binding assays were carried out with HEK-293 cells expressing either D2 or D3 receptors with tritiated spiperone to evaluate inhibition constants (K(i)). Functional activity of selected compounds in stimulating GTPgammaS binding was assessed with CHO cells expressing human D2 receptors and AtT-20 cells expressing human D3 receptors. SAR results identified compound (-)-24c (D-301) as one of the lead molecules with preferential agonist activity for D3 receptor (EC(50) (GTP gamma S); D3 = 0.52 nM; D2/D3 (EC(50)): 223). Compounds (-)-24b and (-)-24c exhibited potent radical scavenging activity. The two lead compounds, (-)-24b and (-)-24c, exhibited high in vivo activity in two Parkinson's disease (PD) animal models, reserpinized rat model and 6-OHDA induced unilaterally lesioned rat model. Future studies will explore potential use of these compounds in the neuroprotective therapy for PD.