A series of 4-(phosphonoalkyl)-and 4-(phosphonoalkenyl)-2-piperidinecarboxylic acids were synthesized, and their biological activity was assessed as competitive ligands for the NMDA receptor, both in vitro by using a receptor binding assay ([3H] CGS 19755 binding) and in vivo by using an NMDA seizure model in mice. The analogues were also evaluated in [3H] AMPA and [3H] kainate binding to assess their affinity for non-NMDA excitatory amino ...