(R)-CPP is a highly potent piperazine-based NMDA receptor antagonist. (R)-CPP is the more active isomer of racemic CPP preparations. (R)-CPP demonstrates selectivity for NMDAε1 receptors with an IC50 value of 41 nM. (R)-CPP is an inhibitor of NMDA ε 1, NMDA ε 2 and NMDA ε 3.