A selective antagonist of NMDA receptors containing the NR2A subunit (pIC50s = 6.8 and <4.3 for human recombinant NR2A and NR2B, respectively); binds to a novel allosteric site located at the dimer interface between the GluN1 and GluN2 binding domains, thereby reducing glycine signal transduction and inhibiting NMDA receptor function