3-Chlorostyrylcaffeine (CSC), or 8-(3-chlorostyryl)caffeine (8-CSC), is a potent and selective adenosine A<sub>2A</sub> receptor antagonist which is used in scientific research.
It has 520-fold selectivity for the adenosine A<sub>2A</sub> receptor over the adenosine A<sub>1</sub> receptor (K<sub>i</sub> = 54nM and 28,000nM for the rat receptors, respectively). Its affinities for the adenosine A<sub>2B</sub> and A<sub>3</sub> receptors are similarly low (K<sub>i</sub> = 8,200nM and >10,000nM, respectively).
CSC has been found to reverse the catalepsy induced by the dopamine D<sub>1</sub> receptor antagonist SCH-23390 and the dopamine D<sub>2</sub> receptor antagonists raclopride and sulpiride in animals.
The drug was one of the first selective adenosine A<sub>2A</sub> 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 (K<sub>i</sub> = 80.6nM for baboon MAO-B). CSC was first described in the scientific literature by 1993.