A series of a-amino-3-(phosphonoalkyl)-2-quinoxalinepropanoic acids was synthesized and evaluated for NMDA receptor affinity using a [3Hl CPP binding assay. Functional antagonism of the NMDA receptor complex was evaluated in vitro using a stimulated [3HlTCP binding assay and in vivo by employing an NMDA-induced seizure model. Some analogues also were evaluated in the I3H1-glycine binding assay. Several compounds of ...