SYNTHESIS OF -METHYL-6-NITROPYRIDO[3,4-F]-QUINOXALINE-2,3-DIONE AND RELATED QUINOXALINEDIONES - CHARACTERIZATION OF LPHA-AMINO-3-HYDROXY-5-METHYL-4-ISOXAZOLEPROPIONIC ACID (AND N-METHYL-D-ASPARTATE) RECEPTOR AND ANTICONVULSANT ACTIVITY

Four related series of substituted quinoxalinediones containing angula r fused-piperidine rings have been synthesized as lpha-amino-3-hydroxy -5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists with p otential as neuroprotective agents, primarily for acute therapy immedi ately following a stroke.(2) The compounds were tested for their affin ity to the AMPA, kainate, and strychnine-insensitive glycine receptor sites. In AMPA binding, the most potent compound was 27a (PNQX, IC50 = 63 nM), with affinity comparable to the literature standard 1 (NBQX, IC50 = 52 nM). Other 6-nitro analogs from the 9-aza series had compara ble affinity at the AMPA receptor, as did 6-nitro-8-aza derivatives su ch as 13a (iPNQX, IC50 = 290 nM). The receptor binding profile of 27a differed from that of 1 in that 27a possessed significant affinity at the glycine site of the N-methyl-D-aspartate (NMDA) receptor, whereas 1 was essentially inactive. Three compounds, 26c, 26d, and 26e, demons trated moderate selectivity for kainate relative to AMPA receptors. Se lected analogs reported herein as well as in the literature were super imposed to generate an AMPA pharmacophore model, and 6-substituted com pounds from the PNQX and iPNQX series were combined and analyzed via q uantitative structure-activity relationship techniques. Compounds with high affinity at non-NMDA receptors were further characterized in fun ctional assays in neuronal cell culture and in a cortical wedge prepar ation. Both 1 and 27a showed comparable effectiveness in an AMPA- and kainate-induced excitoxicity assay. Both inhibited AMPA-induced depola rizations in the cortical wedge. However, 27a also inhibited spontaneo us epileptiform discharges in the cortical wedge (reversed by glycine) , while 1 was ineffective. The combination of AMPA and NMDA antagonist activity may contribute to the 30-fold difference in potency between 27a and 1 in the maximal electroshock convulsant assay in mice. The si gnificant in vivo potency of 27a suggests that it has potential clinic al utility.(2)