Recent research efforts have suggested that overstimulation of the N-methyl-D-aspartate (NMDA) receptor plays a critical role in the neuropathology of disease states including epilepsy, Huntington's chorea, and anoxic conditions, such as stroke. A large body of work has shown that the NMDA receptor complex is composed of several distinct binding domains including the glutamate agonist site, the strychnine-insensitive glycine site, the receptor gated ion channel, a zinc ion site, and a recently described polyamine site. The glycine site, which recognizes glycine and certain analogs as agonists, was originally thought to be a modulatory site; however, recent work has proven that glycine is obligatory for L-glutamic acid to activate this receptor complex. These findings suggest that potent, selective glycine site antagonists of the NMDA receptor complex would find utility in therapeutic areas, such as epilepsy and stroke. The earliest reported glycine site antagonist, kynurenic acid (1), an endogenous product of the tryptophan metabolism pathway, has micromolar binding affinity for both the glycine site and the L-glutamate site (IC50 = 16 μM versus [3H]glycine, IC50 = 71 μM versus [3H]CPP, respectively). Subsequently, the chloro derivatives 7-chlorokynurenic acid (2) (IC50 = 0.4 μM versus [3H]glycine; IC50 = 162 μM versus [3H]CPP) and 5,7-dichlorokynurenic acid (3) (IC50 = 0.08 μM versus [3H]glycine; IC50 = 37 μM versus [3H]CPP) were found to be more potent and selective than kynurenic acid. In this communication we describe the synthesis and evaluation of two new potent, selective glycine site antagonists: 4-[(carboxymethyl)oxy]-5,7-dichloroquinoline-2-carboxylic acid (4) and 4-[(carboxymethyl)amino]-5,7-dichloroquinoline-2-carboxylic acid (5).