3-Chlorostyrylcaffeine (CSC), or 8-(3-chlorostyryl)caffeine (8-CSC), is a potent and selective adenosine A2A receptor antagonist which is used in scientific research.
It has 520-fold selectivity for the adenosine A2A receptor over the adenosine A1 receptor (Ki = 54nM and 28,000nM for the rat receptors, respectively). Its affinities for the adenosine A2B and A3 receptors are similarly low (Ki = 8,200nM and >10,000nM, respectively).
CSC has been found to reverse the catalepsy induced by the dopamine D1 receptor antagonist SCH-23390 and the dopamine D2 receptor antagonists raclopride and sulpiride in animals.
The drug was one of the first selective adenosine A2A receptor antagonists to be developed. However, in addition to its adenosine receptor antagonism, CSC was subsequently found to be a potent monoamine oxidase B (MAO-B) inhibitor (Ki = 80.6nM for baboon MAO-B). CSC was first described in the scientific literature by 1993.