Preladenant

Preladenant is a drug that was developed by Schering-Plough which acts as a potent and selective antagonist of the adenosine A_2A receptor. It was being researched as a potential treatment for Parkinson's disease. Positive results were reported in Phase II clinical trials in humans, but it did not prove itself to be more effective than a placebo during Phase III trials, and so was discontinued in May 2013.
The drug has very high affinity for the A_2A receptor and shows more than 1,000-fold selectivity for the A_2A receptor over the other adenosine receptors.
Preladenant shows pro-motivational effects in animals and reverses tetrabenazine-induced motivational deficits. Other A_2A receptor antagonists, including istradefylline, Lu AA47070, MSX-3, and MSX-4, have also shown such effects. These agents may be useful in the treatment of motivational disorders in humans. Accordingly, istradefylline has been reported to reduce apathy, anhedonia, fatigue, and depression in people with Parkinson's disease.