Antagonism of the adenosine A2a receptor offers great promise in the treatment of Parkinson's disease. In the course of exploring pyrazolo [4, 3-e]-1, 2, 4-triazolo [1, 5-c] pyrimidine A2A antagonists, which led to clinical candidate SCH 420814, we prepared 1, 2, 4-triazolo [1, 5-c] pyrimidines with potent and selective (vs A1) A2a antagonist activity, including oral activity in the rat haloperidol-induced catalepsy model. Structure–activity ...