Highly potent NMDA antagonist; more active isomer. Shows some selectivity for NR2A-containing receptors (Ki values are 0.041, 0.27, 0.63 and 1.99 μM for inhibition of NR2A-, NR2B-, NR2C- and NR2D-containing recombinant NMDA receptors respectively). (RS)-CPP (Cat. No. 0173) also available.