Structure–activity relationship studies on 3-(5-pyridin-2-yl-2H-tetrazol-2-yl) benzonitrile 2 led to the discovery of 2-{2-[3-(pyridin-3-yloxy) phenyl]-2H-tetrazol-5-yl} pyridine (10)—a highly potent and selective mGlu5 receptor antagonist with good brain penetration and in vivo receptor occupancy in rat and cross-species oral bioavailability.