Design, Synthesis of Novel, Potent, Selective, Orally Bioavailable Adenosine A2A Receptor Antagonists and Their Biological Evaluation

Our initial structure-activity relationship studies on 7-methoxy-4-morpholino-benzothiazole derivatives featured by aryloxy-2-methylpropanamide moieties at the 2-position led to identification of compound 25 as a potent and selective A_2A adenosine receptor (A_2AAdoR) antagonist with reasonable ADME and pharmacokinetic properties. However, poor intrinsic solubility and low to moderate oral bioavailability made this series unsuitable for further development. Further optimization using structure-based drug design approach resulted in discovery of potent and selective adenosine A_2A receptor antagonists bearing substituted 1-methylcyclohexyl-carboxamide groups at position 2 of the benzothiazole scaffold and endowed with better solubility and oral bioavailability. Compounds 41 and 49 demonstrated a number of positive attributes with respect to in vitro ADME properties. Both compounds displayed good pharmacokinetic properties with 63% and 61% oral bioavailability, respectively, in rat. Further, compound 49 displayed oral efficacy in 6-OHDA lesioned rat model of Parkinson diseases.