István Ling

New Non Competitive AMPA Antagonists

New halogen atom substituted 2,3-benzodiazepine derivatives condensed with an azole ring on the seven membered part of the ring system of type 3 and 4 as well as 5 and 6 were synthesized. It was found that chloro-, dichloro- and bromo-substitutions in the benzene ring and additionally imidazole ring condensation on the diazepine ring can successfully substitute the methylenedioxy group in the well known molecules GYKI 52466 (1) and GYKI 53773 (2) and the 3-acetyl-4-methyl structural feature in 2, respectively, preserving the highly active AMPA antagonist characteristic of the original molecules. From the most active compounds (3b,i) 3b (GYKI 47261) was chosen for detailed investigations. 3b revealed an excellent, broad spectrum anticonvulsant activity against seizures evoked by electroshock and different chemoconvulsive agents indicating a possible antiepileptic efficacy. 3b was found to be highly active in a transient model of focal ischemia predictive of a therapeutic value in human stroke. 3b also reversed the dopamine depleting effect of MPTP and antagonized the oxotremorine induced tremor in mice indicating a potential antiparkinson activity.

2,3-Benzodiazepine-type AMPA receptor antagonists and their neuroprotective effects

AMPA receptors are fast ligand-gated members of glutamate receptors in neuronal and many types of non-neuronal cells. The heterotetramer complexes are assembled from four subunits (GluR1-4) in region-, development- and function-selective patterns. Each subunit contains three extracellular domains (a large amino terminal domain, an agonist-binding domain and a transducer domain), and three transmembrane segments with a loop (pore forming domain), as well as the intracellular carboxy terminal tail (traffic and conductance regulatory domain). The binding of the agonist (excitatory amino acids and their derivatives) initiates conformational realignments, which transmit to the transducer domain and membrane spanning segments to gate the channel permeable to Na+, K+ and more or less to Ca2+. Several 2,3-benzodiazepines act as non-competitive antagonists of the AMPA receptor (termed also negative allosteric modulators), which are thought to bind to the transducer domains and inhibit channel gating. Analysing their effects in vitro, it has been possible to recognize a structure-activity relationship, and to describe the critical parts of the molecules involved in their action at AMPA receptors. Blockade of AMPA receptors can protect the brain from apoptotic and necrotic cell death by preventing neuronal excitotoxicity during pathophysiological activation of glutamatergic neurons. Animal experiments provided evidence for the potential usefulness of non-competitive AMPA antagonists in the treatment of human ischemic and neurodegenerative disorders including stroke, multiple sclerosis, Parkinsons disease, periventricular leukomalacia and motoneuron disease. 2,3-benzodiazepine AMPA antagonists can protect against seizures, decrease levodopa-induced dyskinesia in animal models of Parkinsons disease demonstrating their utility for the treatment of a variety of CNS disorders.

Asymmetric reduction of a carbon–nitrogen double bond: enantioselective synthesis of 4,5-dihydro-3H-2,3-benzodiazepines

A highly specific enantioselective reduction, elaborated for the reduction of the 3,4-carbon–nitrogen double bond of 4-methyl-7,8-methylenedioxy-1-(4-nitrophenyl)-4,5-dihydro-3H-2,3-benzodiazepine 4 made possible the synthesis of the enantiomers of the potent non-competitive AMPA/kamate antagonists 2a, b. NMR Investigations of the reducing complex show that there is no formation of an 1,3,2-oxazaborolidine ring as may have been presumed on the basis of literature data.

A novel GABAA alpha 5 receptor inhibitor with therapeutic potential

Novel 2,3-benzodiazepine and related isoquinoline derivatives, substituted at position 1 with a 2-benzothiophenyl moiety, were synthesized to produce compounds that potently inhibited the action of GABA on heterologously expressed GABAA receptors containing the alpha 5 subunit (GABAA α5), with no apparent affinity for the benzodiazepine site. Substitutions of the benzothiophene moiety at position 4 led to compounds with drug-like properties that were putative inhibitors of extra-synaptic GABAA α5 receptors and had substantial blood-brain barrier permeability. Initial characterization in vivo showed that 8-methyl-5-[4-(trifluoromethyl)-1-benzothiophen-2-yl]-1,9-dihydro-2H-[1,3]oxazolo[4,5-h][2,3]benzodiazepin-2-one was devoid of sedative, pro-convulsive or motor side-effects, and enhanced the performance of rats in the object recognition test. In summary, we have discovered a first-in-class GABA-site inhibitor of extra-synaptic GABAA α5 receptors that has promising drug-like properties and warrants further development.

Neurotransmitter Release in Experimental Stroke Models: The Role of Glutamate-Gaba Interaction

Stroke or cerebrovascular accident reduces blood flow and decreases oxygen supply (ischemia) in brain tissue. This may be resulted from vascular obstruction when a blood vessel is blocked or by hemorrhage when bleeding occurs into the brain tissue. Decrease in oxygen supply shifts pH to acidosis and increases extracellular K+ concentration, which depolarizes neural cell membrane. Anoxic depolarization leads to excessive release of glutamate, which then activates various glutamate receptors in the synapse or the extrasynaptic space. Opening of ionotropic glutamate receptors (NMDA, AMPA and kainate receptors) causes influx of Na+ through the activated glutamate-gated ion channels. In response to anoxia, Ca2+ also enters the cells in excessive amounts via activated NMDA receptors and Ca2+-permeable AMPA receptors. This will lead to activation of several Ca2+-dependent intracellular signal transduction pathways (proteases, kinases, endonucleases, lipoxygeneses and nitric oxide synthase), which ultimately leads to neural death (Vizi et al., 1996; Parsons et al., 1998).

Loop-F of the α-subunit determines the pharmacologic profile of novel competitive inhibitors of GABAA receptors

ABSTRACT The neurotransmitter &ggr;‐amino butyric acid (GABA) has a fundamental role in CNS function and ionotropic (GABAA) receptors that mediate many of the actions of GABA are important therapeutic targets. This study reports the mechanism of action of novel GABAA antagonists based on a tricyclic oxazolo‐2,3‐benzodiazepine scaffold. These compounds are orthosteric antagonists of GABA on heteropentameric GABAA receptors of &agr;x&bgr;2&ggr;2 configuration expressed in HEK293 cells. In silico modelling predicted that the test compounds docked in the GABA binding‐pocket and would interact with amino‐acid residues in the &agr;‐ and &bgr;‐subunit interface that are known to be important for the binding of GABA. Intriguingly, optimal docking also required an interaction with the non‐conserved amino‐terminal segment of Loop‐F of the &agr;–subunit. Testing of a compound with altered regiochemistry of the oxazolone moiety supported the model with respect to the conserved GABA‐interacting residues in vitro as well as in vivo. The prediction regarding loop‐F was examined by replacing the amino‐terminal variable segment of loop‐F of the &agr;5‐subunit with the corresponding residues in the &agr;1‐ and &agr;2‐subunits. When tested with the novel inhibitors, the receptors formed by the modified &agr;5‐subunits displayed the pharmacologic phenotype of the source of loop‐F. In summary, these data show that the variable amino‐terminal segment of loop‐F of the &agr;‐subunit determines the pharmacologic selectivity of the novel tricyclic inhibitors of GABAA receptors.