Characterisation of the binding of [3H]MDL 105,519, a radiolabelled antagonist for the N-methyl-D-aspartate-associated glycine site, to pig cortical brain membranes

Dynorphin displaces binding at the glycine site of the NMDA receptor in the rat striatum

Binding of dynorphin A (1-17 and 2-17) to NMDA receptors in the rat striatum was studied by displacing radioactive ligands for the receptor's polyamine ([3H]-Ifenprodil), glutamate ([3H]-CGP-39653), dizocilpine ([3H]-MK-801) and glycine ([3H]-MDL105,519) sites with the neuropeptide. Dynorphin A selectively displaced [3H]-MDL105,519 and none of the other ligands. Opioid antagonists did not affect displacement. Thus, in the striatum dynorphin may regulate NMDA receptor function via the glycineB site through non-opioid mechanisms. This may contribute to the long-term changes in behavioral responsiveness seen after dopamine depletion and treatment with dopaminomimetics which are associated with substantial changes in striatal dynorphin metabolism.

Novel pyrrolinones as N-methyl-D-aspartate receptor antagonists

A series of oximes, deriving from 2-arylidene-pyrroline-3,4-diones (7, 8, 22, 23) has been prepared. The presence of tautomers in their solutions has been established by spectroscopic means. The compounds reacted with diazomethane chiefly by N-methylation forming nitrones (10, 11). The analogously prepared 2-arylidene-4-nitropyrrolin-3-ones (12, 13, 24, 25), formally derived from nitrotetramic acids, yielded nitronic acid esters (14, 15, 26) upon reaction with diazomethane. The structures were elucidated by spectral evidence and-in the case of compounds 10 and 20b-by X-ray diffraction analysis. The binding affinity of some of the new compounds toward the N-methyl-d-aspartate (NMDA) (glycine site) receptor has been measured thus providing the basis for further structure-activity relationship studies. Oxime 8b showed the highest binding potency (Ki= 9.2 microM).

Rigid nonproteinogenic cyclic amino acids as ligands for glutamate receptors:trans-Tris(homoglutamic) acids

The second-generation asymmetric synthesis of the trans-tris(homoglutamic) acids reported herein proceeds via Strecker reaction of chiral ketimines, obtained from condensation of racemic 2-ethoxycarbonylmethylcyclopentanone and commercially available (S)- and (R)-1-phenylethylamine, respectively. In the key stereodifferentiating step, the cyanide addition leads to mixtures of diastereomeric alpha-amino nitrile-esters, the composition of which is independent of the reaction temperature and the type of the solvent, respectively. Hydrolysis of the alpha-amino nitrile-esters with concentrated H(2)SO(4) yielded diastereomeric mixtures of secondary alpha-amino amido-esters, which after separation were hydrogenolyzed and hydrolyzed each to the enantiomeric trans-1-amino-2-carboxymethylcyclopentanecarboxylic acids. Their configuration was completely established by NMR methods, CD spectra, and X-ray analysis of the trans-1S,2R-configured secondary alpha-amino amido-ester. In receptor binding assays and functional tests, trans-1S,2R-1-amino-2-carboxymethylcyclopentanecarboxylic acid hydrochloride was found to behave as a selective mGluR(2)-antagonist without relevant binding properties at iGluRs.

Hydantoin-substituted 4,6-dichloroindole-2-carboxylic acids as ligands with high affinity for the glycine binding site of the NMDA receptor

A novel series of C-3 substituted 4,6-dichloroindole-2-carboxylic acids was synthesized to investigate the influence of different hydrogen-bond donor and acceptor groups at this specific position on the affinity to the glycine site of the NMDA receptor. These novel 3-indolylmethyl derivatives with ring-open (amines, sulfonamides, amides, ureas) and cyclic substituents (imidazolidin-2-ones, (thio)hydantoins) led to the discovery that compounds bearing a hydantoin substituent at the C-3 position of the indole nucleus are the most promising ones. In this series the hydantoins, ureas, and imidazolidin-2-ones were identified as very potent inhibitors of the binding of the glycine site specific ligand [(3)H]MDL 105,519 to pig cortical brain membranes. Since the hydantoins can be produced via a versatile synthetic approach, further amendments of the hydantoin-substituted compounds were conducted to elucidate the influence of aromatic and aliphatic moieties at position 3 of the hydantoin as well as of sterically hindered compounds (5-substituted hydantoins). On the basis of the pharmacological data obtained in displacement experiments with [(3)H]MDL 105,519 and the emerging structure-activity relationships, we confirm the existing pharmacophore model that suggests a hydrogen-bond acceptor and an aromatic substituent at position 3 of the indole as the key features for high affinity. Log P values indicate brain permeability and selected compounds showed anticonvulsant activity in vivo. Binding studies for the sodium channel (site 2) were also performed on some selected compounds.

Azagrevellins, Part I. Grevellin analogs with affinity to the N-methyl-D-aspartate (glycine site) receptor, a novel lead structure

A series of piperidine-2,3,5-triones (azagrevellins) has been prepared. A new synthesis has been introduced using the rearrangement of spiroepoxides in the presence of triethyloxonium tetrafluoroborate. The binding affinity toward the N-methyl-D-aspartate (glycine site) receptor has been measured to provide a basis for more detailed structure-activity studies. Azagrevellin 18d showed the highest binding potency.

Brain concentrations of kynurenic acid after a systemic neuroprotective dose in the gerbil model of global ischemia

1. Kynurenic acid (KYNA) is a kynurenine metabolite and a broad spectrum excitatory amino acid antagonist that has been shown to be neuroprotective in models of cerebral ischemia, when administered exogenously. However, the actual concentration required in the CNS to evoke significant neuroprotection has never been assessed. 2. The purpose of this study was to address this question in the gerbil model of forebrain ischemia. KYNA (400-1600 mg/kg) or vehicle were administered i.p. 15 min before 5 min bilateral carotid occlusion. 3. Seven days after reperfusion, ischemia-induced hippocampal nerve cell loss (95% in vehicle-treated) was significantly lower in KYNA-treated gerbils (65% and 52% at 1000 and 1200 mg/Kg, respectively, P < 0.01). Treatment with 1000 mg/kg produced brain KYNA concentrations that were dramatically elevated (135.9 and 42.3 microM in CSF and whole brain, vs 0.032 and 0.16 microM in controls, at 15 min after ischemia), as measured in a separate group of transcardially-perfused gerbils. Cerebral KYNA concentrations tended to return to basal values 2 hours after reperfusion. 4. These results indicate that KYNA has a marked neuroprotective effect in a model of forebrain ischemia. This activity is associated with KYNA concentrations in the brain and CSF that are compatible with the in vitro affinity of the compound for ionotropic glutamate receptors.

Direct effects of metabotropic glutamate receptor compounds on native and recombinant N-methyl-D-aspartate receptors

The actions of glutamate in the central nervous system are mediated through interaction with fast activating ionotropic receptors and G protein-coupled metabotropic glutamate receptors (mGluRs). Studies of these receptors have relied on the availability of agonists and antagonists selective for each receptor class. Compounds that were thought to be selective for mGluRs have been extensively used to study the role of these receptors in the brain. Their use has implicated mGluRs in a wide range of physiological and pathological processes including the modulation of N-methyl-D-aspartate (NMDA) receptors and NMDA receptor-dependent processes. We report that some of the most commonly used mGluR compounds act as antagonists on NMDA receptors at concentrations commonly used to activate or block mGluRs. In addition, several of the drugs also act as agonists at higher concentrations due at least in part to high levels of contaminant amino acids. Our results indicate that caution should be used when using these drugs to study the roles of mGluRs in various NMDA-dependent processes. The antagonist effects were dependent on the concentration of the NMDA receptor coagonists, preventing reappraisal of previously published work.