NAB-14 is a negative allosteric modulator (NAM) selective for GluN2C/2D-containing NMDA glutamate receptors. NAB-14 was >800-fold selective for recombinant GluN2C/GluN2D over GluN2A/GluN2B in Xenopus oocytes and exhibited an IC50 value of 580 nM at recombinant GluN1/GluN2D receptors.