Design, synthesis, SAR, and biological evaluation of highly potent benzimidazole-spaced phosphono-alpha-amino acid competitive NMDA antagonists of the AP-6 type.

A series of 2-amino-(phosphonoalkyl)-1H-benzimidazole-2-alkanoic acids was synthesized and evaluated for NMDA receptor affinity using a [3H]CPP binding assay. Functional antagonism of the NMDA receptor complex was evaluated in vitro using a stimulated [3H]TCP binding assay and in vivo by employing an NMDA-induced seizure model. Several compounds of the AP-6 type demonstrated potent and selective NMDA antagonistic activity both in vitro and in vivo. In particular, [R(-)]-2-amino-3-(5-chloro-1-phosphonomethyl-1H-benzoimidazol-2-yl)-propionic acid (1) displayed an IC(50) value of 7.1 nM in the [3H]CPP binding assay and an ED(50) value of 0.13 mg/kg (ip) in the NMDA lethality model. Compound 1, when administered intravenously as a single bolus dose of 3 mg/kg following permanent occlusion of the middle cerebral artery in the rat, reduced the volume of infarcted brain tissue by 45%. These results support a promising therapeutic potential for compound 1 as a neuroprotective agent.

Design and synthesis of [2-(8,9-dioxo-2,6-diazabicyclo[5.2.0]non-1(7)-en-2-yl)-ethyl]phosphonic acid (EAA-090), a potent N-methyl-D-aspartate antagonist, via the use of 3-cyclobutene-1,2-dione as an achiral alpha-amino acid bioisostere.

The diazabicyclic amino acid phosphonate 15, [2-(8,9-dioxo-2,6-diazabicyclo[5.2.0]non-1(7)-en-2-yl)ethyl]phosphonic acid, was identified as a potent NMDA antagonist. It contains the alpha-amino acid bioisostere 3,4-diamino-3-cyclobutene-1,2-dione and an additional ring for conformational rigidity. Compound 15 was as potent as CGS-19755 (5) in the [3H]CPP binding assay, the stimulated [3H]TCP binding assay, and the NMDA-induced lethality model in mice. A single bolus dose of compound 15, administered intravenously following permanent occlusion of middle cerebral artery (MCA) in the rat, reduced the size of infarcted tissue by 57%. Structure-activity relationship (SAR) studies have indicated that the six- and eight-membered ring derivatives had diminished activity and that the two-carbon side chain length was optimum for NMDA receptor affinity. Substitution on the ring was found to be counterproductive in the case of sterically demanding dimethyl groups and of no consequence in the case of an H-bonding hydroxyl group. Replacement of the phosphonic acid group by either a carboxylic acid or a tetrazole group was unproductive. The potent bicyclic NMDA antagonists were synthesized efficiently by virture of their achiral nature and the ease of vinylgous amide formation from squaric acid esters. Compound 15, being a unique NMDA antagonist structural type with a favorable preclinical profile, may offer advantages over existing NMDA antagonists for the treatment of neurological disorders such as stroke and head trauma. Compound 15 is currently under clinical evaluation as a neuroprotective agent for stroke.

Potent quinoxaline-spaced phosphono alpha-amino acids of the AP-6 type as competitive NMDA antagonists: synthesis and biological evaluation.

A series of alpha-amino-3-(phosphonoalkyl)-2-quinoxalinepropanoic acids was synthesized and evaluated for NMDA receptor affinity using a [3H] CPP binding assay. Functional antagonism of the NMDA receptor complex was evaluated in vitro using a stimulated [3H]TCP binding assay and in vivo by employing an NMDA-induced seizure model. Some analogues also were evaluated in the [3H]-glycine binding assay. Several compounds of the AP-6 type show potent and selective NMDA antagonistic activity both in vitro and in vivo. In particular alpha-amino-7-chloro-3-(phosphonomethyl)-2-quinoxalinepropanoic acid (1) displayed an ED50 of 1.1 mg/kg ip in the NMDA lethality model. Noteworthy is alpha-amino-6,7-dichloro-3-(phosphonomethyl)-2-quinoxalinepropanoic++ + acid (3) with a unique dual activity, displaying in the NMDA receptor binding assay an IC50 of 3.4 nM and in the glycine binding assay an IC50 of 0.61 microM.