Design, Synthesis, and Pharmacological Characterization of Carbazole Based Dopamine Agonists as Potential Symptomatic and Neuroprotective Therapeutic Agents for Parkinson’s Disease

We have developed a series of carbazole-derived compounds based on our hybrid D2/D3 agonist template to design multifunctional compounds for the symptomatic and disease-modifying treatment of Parkinson's disease (PD). The lead molecules (−)-11b (D-636), (−)-15a (D-653), and (−)-15c (D-656) exhibited high affinity for both D2 and D3 receptors and in GTPγS functional assay, the compounds showed potent agonist activity at both D2 and D3 receptors (EC50 (GTPγS); D2 = 48.7 nM, D3 = 0.96 nM for 11b, D2 = 0.87 nM, D3 = 0.23 nM for 15a and D2 = 2.29 nM, D3 = 0.22 nM for 15c). In an animal model of PD, the test compounds exhibited potent in vivo activity in reversing hypolocomotion in reserpinized rats with a long duration of action compared to the reference drug ropinirole. In a cellular antioxidant assay, compounds (−)-11b, (−)-15a, and (−)-15c exhibited potent activity in reducing oxidative stress induced by neurotoxin 6-hydroxydopamine (6-OHDA). Also, in a cell-based PD neuroprotection model, these lead compounds significantly increased cell survival from toxicity of 6-OHDA, thereby producing a neuroprotective effect. Additionally, compounds (−)-11b and (−)-15a inhibited aggregation and reduced toxicity of recombinant alpha synuclein protein in a cell based in vitro assay. These observations suggest that the lead carbazole-based dopamine agonists may be promising multifunctional molecules for a viable symptomatic and disease-modifying therapy of PD and should be further investigated.