Discovery of nonxanthine adenosine A<inf>2A</inf>receptor antagonists for the treatment of Parkinson's disease

During a program to investigate the biochemical basis of side effects associated with the antimalarial drug mefloquine, the authors made the unexpected discovery that the (-)-(R,S)-enantiomer of the drug is a potent adenosine A2Areceptor antagonist. Although the compound was ineffective in in vivo animal models of central adenosine receptor function, it provided a unique nonxanthine adenosine A2Areceptor antagonist lead structure and encouraged the initiation of a medicinal chemistry program to develop novel adenosine A2Aantagonists for the management of Parkinson's disease (PD). The authors have synthesized and screened more than 2,000 chemically diverse and novel adenosine A2Aantagonists. Early examples from two distinct chemical series are the thieno[3,2-dy]pyrimidine VER-6623 and the purine compounds VER-6947 and VER-7835, which have high affinity at adenosine A2Areceptors (Kivalues 1.4, 1.1, and 1.7 nmol/L, respectively) and act as competitive antagonists. In particular, VER-6947 and VER-7835 demonstrate potent in vivo activity reversing the locomotor deficit caused by the D2receptor antagonist haloperidol, with minimum effective doses comparable with that of KW6002 (0.3 to 1 mg/kg). In conclusion, the authors have discovered potent, selective, and in vivo active nonxanthine adenosine A2Aantagonists that have considerable promise as a new therapy for PD.