Structural analogues of some highly active non-competitive AMPA antagonists

Some 5-methyl analogues (14a-e) of the non-competitive AMPA antagonists 3-acylated 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-4,5-dihydro-3H-2,3-benzodi azepines (2,3) have been synthesized. Generally they show diminished or low biological activity but two derivatives (14a,b) reveal effects comparable to those of GYKI 52466 (1), the prototype non competitive AMPA antagonist.     

Effect of ionotropic glutamate receptors antagonists on the modifications in extracellular glutamate and aspartate levels during picrotoxin seizures: a microdialysis study in freely moving rats

Our previous studies have shown a local decrease in glutamate and aspartate levels during seizures, induced by picrotoxin microdialysis in the hippocampus of chronic freely moving rats. In this paper, we study the effect of continuous hippocampal microperfusion of the NMDA, AMPA and kainate glutamate receptor inhibitors 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine (MK-801); 6,7-dinitroquinoxaline-2,3-dione (DNQX), and 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride (GYKI 52466). We also examine the action of L(-)-threo-3-hydroxyaspartic acid (THA), a glutamate and aspartate reuptake blocker, on the modification of extracellular glutamate and aspartate levels induced by picrotoxin, using the microdialysis method in freely moving rats. We found that changes in extracellular hippocampal concentrations in both amino acids are prevented by NMDA, AMPA and kainate receptor inhibitors. Seizures elicited under DNQX also induce a transient increase in aspartate extracellular levels coincident with seizure time. L(-)-threo-3-hydroxyaspartic acid increased the basal extracellular concentrations of both amino acids, but did not prevent the seizure-related decrease. Our results suggest that glutamate, the major neurotransmitter at the synaptic level, may also play an important role in non-synaptic transmission during seizures.     

Characterization of the Glutamate Receptors Mediating Release of Somatostatin from Cultured Hippocampal Neurons

Abstract: l -Glutamate, NMDA, dl -α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), and kainate (KA) increased the release of somatostatin-like immunoreactivity (SRIF-LI) from primary cultures of rat hippocampal neurons. In Mg²⁺-containing medium, the maximal effects (reached at ∼100 µ M ) amounted to 737% (KA), 722% (glutamate), 488% (NMDA), and 374% (AMPA); the apparent affinities were 22 µ M (AMPA), 39 µ M (glutamate), 41 µ M (KA), and 70 µ M (NMDA). The metabotropic receptor agonist trans -1-aminocyclopentane-1,3-dicarboxylate did not affect SRIF-LI release. The release evoked by glutamate (100 µ M ) was abolished by 10 µ M dizocilpine (MK-801) plus 30 µ M 1-aminophenyl-4-methyl-7,8-methylenedioxy-5 H -2,3-benzodiazepine (GYKI 52466). Moreover, the maximal effect of glutamate was mimicked by a mixture of NMDA + AMPA. The release elicited by NMDA was sensitive to MK-801 but insensitive to GYKI 52466. The AMPA- and KA-evoked releases were blocked by 6,7-dinitroquinoxaline-2,3-dione (DNQX) or by GYKI 52466 but were insensitive to MK-801. The release of SRIF-LI elicited by all four agonists was Ca²⁺ dependent, whereas only the NMDA-evoked release was prevented by tetrodotoxin. Removal of Mg²⁺ caused increase of basal SRIF-LI release, an effect abolished by MK-801. Thus, glutamate can stimulate somatostatin release through ionotropic NMDA and AMPA/KA receptors. Receptors of the KA type (AMPA insensitive) or metabotropic receptors appear not to be involved.     

A novel specific binding site for anxiolytic homophthalazines in the rat brain.

Radioligand binding studies were performed in order to elucidate the mechanism of action of anxiolytic-neuroleptic homophthalazines. Rat striatal membrane preparations were found to bind 3H-EGIS 6775 [3H-GYKI-52 322, 3H-(1-(4-aminophenyl)-4-methyl-7,8-dimethoxy-5H-homophthalazine)] in a specific and displaceable manner. Several other brain regions tested were devoid of similar binding activity. Saturation analysis revealed that binding affinity was in the 10(-8)-10(-7) M range. Binding was enhanced by Mg2+ ions and, to a smaller extent by Ca2+ ions. The binding principle was sensitive to heat or trypsin treatment. This specific binding site appears, according to competition studies, different from the receptors whose presence in the rat striatum has been reported earlier.     

New 7,8-ethylenedioxy-2,3-benzodiazepines as noncompetitive AMPA receptor antagonists

A series of 1-aryl-3,5-dihydro-7,8-ethylenedioxy-4H-2,3-benzodiazepin-4-ones 2a-f, were synthesized and screened as anticonvulsant agents in DBA/2 mice against sound-induced seizures. The new compounds display anticonvulsant properties although the ED(50) values are higher than those of prototypes 1-aryl-3,5-dihydro-7,8-methylenedioxy-4H-2,3-benzodiazepin-4-ones (1) and GYKI 52466, well-known noncompetitive AMPA receptor antagonists. Functional tests were performed to evaluate the antagonistic activity at the AMPA and kainate receptors.     

Determination of new 2,3-benzodiazepines in rat plasma using high-performance liquid chromatography with ultraviolet detection

A method for the analysis of [1-(4-aminophenyl)-3,5-dihydro-7,8-dimethoxy-4H-2,3-benzodiazepin-4-one] (CFM-2) and its analogues CFM-3, CFM-4 and CFM-5 in rat plasma was developed. The 2,3-benzodiazepines (2,3-BZs) were extracted by liquid–liquid extraction and analyzed using high-performance liquid chromatography (HPLC) with ultraviolet detection (UV) at 240 nm. The method exhibited a large linear range from 0.05 to 2 μg/ml with an intra-assay accuracy for all studied compounds ranging from 92 to 105.5%; whereas the intra-assay precision ranged from 0.59 to 8.16% in rat plasma. The inter-assay accuracy of CFM-2, CFM-4 and their 3-methyl derivatives, CFM-3 and CFM-5 ranged from 92.2 to 107% and the inter-assay precision ranged from 2.17 to 11.9% in rat plasma. The lower limit of detection was 5.5 ng/ml for CFM-2, 6.5 ng/ml for CFM-3, 7 ng/ml for CFM-4 and 8.5 ng/ml for CFM-5 in rat plasma. The pharmacokinetic study demonstrated that 2,3-BZs achieved a peak plasma concentration between 45 and 75 min after drug administration. Moreover, we observed that plasma chromatograms of rats treated with CFM-3, CFM-4 and CFM-5, respectively, showed a peak consistent with CFM-2. Our study suggests that CFM-4, CFM-5 and CFM-3 are prodrugs of CFM-2, in which they are biotransformed in vivo via different metabolic pathways. In particular, CFM-2 has been proven to possess anticonvulsant activity in various models of seizures, acting as α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptor antagonist.     

Effect of the Non-NMDA Receptor Antagonist GYKI 52466 on the Microdialysate and Tissue Concentrations of Amino Acids Following Transient Forebrain Ischaemia

Abstract: The effect of the non-N-methyl-D-aspartate (non-NMDA) receptor antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride (GYKI 52466) on ischaemia-induced changes in the microdialysate and tissue concentrations of glutamate, aspartate, and γ-aminobutyric acid (GABA) was studied in rats. Twenty minutes of four-vessel occlusion resulted in a transient increase in microdialysate levels of glutamate, aspartate, and GABA in striatum, cortex, and hippocampus. Administration of GYKI 52466 (10 mg/kg bolus + 10 mg/kg/60 min intravenously starting 20 min before onset of ischaemia) inhibited ischaemia-induced increases in microdialysate glutamate and GABA in striatum without affecting the increases in hippocampus or cortex. Twenty minutes of four-vessel occlusion resulted in immediate small decreases and larger delayed (72 h) decreases in tissue levels of glutamate and aspartate. Transient increases in tissue levels of GABA were shown in all three structures at the end of the ischaemic period. At 72 h, after the ischaemic period, significantly reduced GABA levels were observed in striatum and hippocampus. GYKI 52466, given under identical conditions as above, augmented the ischaemia-induced decrease in striatal tissue levels of glutamate and aspartate, without significantly affecting the decreases in hippocampus and cortex. Twenty minutes of ischaemia resulted in a large increase in microdialysate dopamine in striatum. GYKI 52466 failed to inhibit this increase. Kainic acid (500 μM infused through the probe for 20 min) caused increases in microdialysate glutamate and aspartate in the striatum. GYKI 52466 (10 mg/ kg bolus + 10 mg/kg/60 min) completely inhibited the kainic acid-induced glutamate release. In conclusion, the action of the non-NMDA antagonist, GYKI 52466, in the striatum is different from that in the cortex and hippocampus. The inhibition by GYKI 52466 of ischaemia-induced and kainate-induced increases in microdialysate glutamate concentration in the striatum may be related to the neuroprotection provided by GYKI 52466 in this region.     

The new 2,3-benzodiazepine derivative EGIS-8332 inhibits AMPA/kainate ion channels and cell death

We observed in vitro neuroprotective and AMPA/kainate receptor antagonist effects of the new 2,3-benzodiazepine derivative EGIS-8332 (R,S-1-(4-aminophenyl)-7,8-methylenedioxy-4-cyano-4-methyl-3-N-acetyl-5H-3,4-dihydro-2,3-benzodiazepine) using the lactate dehydrogenase (LDH) release assay and patch clamp recordings on primary cultures of rat embryonic telencephalon neurons exposed to AMPA/kainate receptor agonists. EGIS-8332 potently decreased alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and quisqualate induced LDH release (IC(50)=5.2+/-0.4 and 7.4+/-1.3 microM, respectively) from the cells. Whole-cell patch clamp studies carried out on the ionotropic glutamate receptors N-methyl D-aspartate (NMDA), as well as AMPA (and kainate) in cultured telencephalon neurons verified that EGIS-8332 blocked steady state responses to AMPA and kainate (IC(50)=1.7+/-0.4 and 6.2+/-1.6 microM, respectively), but hardly influenced currents evoked by NMDA. EGIS-8332 also inhibited kainate-evoked response in CHO cells expressing the flop variant of GluR1 receptor and, in cerebellar Purkinje cells at similar efficiency. The stereoselectivity of the inhibitory site is established by the clearly dissimilar inhibitory potency of the enantiomer components of EGIS-8332 differing in the configuration of methyl and cyano substituents on carbon C(4): the R(-) enantiomer was found to be the efficient species. This finding suggests that the inhibitory interaction between the channel protein and drug is promoted by presence of the C(4) methyl group. The inhibition of the AMPA/kainate ion channels by EGIS-8332 is non-competitive, not use dependent, and depends neither on the closed/open state of the channel, nor the membrane potential. These findings suggest an allosteric mechanism for the inhibition. These in vitro observations suggest that the compound might be useful in the treatments of certain acute and chronic neurological syndromes initiated by derangements of ionotropic glutamate receptor function.     

Alkaloids from Toddalia aculeata

Two alkaloids N-methyl-4-hydroxy-7-methoxy-3-(2,3-epoxy-3-methylbutyl)-1H-quinolin-2-one (1) and 3-(2,3-dihydroxy-3-methylbutyl)-4,7-dimethoxy-1-methyl-1H-quinolin-2-one (2a) have been isolated from CH(2)Cl(2):methanol (1:1) and methanol extracts of leaves and stems of Toddalia aculeata. Their structures along with that of 15 other compounds, of which three are isolated for the first time from genus Toddalia, were established by their detailed spectral studies including 2D NMR viz. (1)H-(1)H COSY, (1)H-(13)C COSY, and HMBC.     

Synthesis and anticonvulsant activity of novel and potent 1-aryl-7,8-methylenedioxy-1,2,3,5-tetrahydro-4H-2,3-benzodiazepin-4-ones

The synthesis and anticonvulsant activity of 1-aryl-7,8-methylenedioxy-1,2,3,5-tetrahydro-4H-2,3-benzodiazepin-4-(thi)ones (4a-d) and their 3-N-alkylcarbamoyl derivatives (4e-h) are reported. The new compounds possess marked anticonvulsant properties, comparable to those of the dehydro analogues 3 and higher than that of GYKI 52466 (1). Noteworthy, compound 4c shows a longer-lasting anticonvulsant activity. Electrophysiological experiments show that derivative 4c is less effective than 1 and 3c to reduce the KA-evoked currents in cerebellar granule neurons.     

Naphthalenes and naphthoquinones from Ventilago species

Two new naphthalene derivatives and three naphthoquinones have been found in the root bark of Ventilago maderaspatana. Their structures are 2-acetyl-6,7-dimethoxy-3-methyl-1,8-methylenedioxynaphthalene (ventilaginone) and 1,3-dihydro-6,9-dihydroxy-7,8-dimethoxy-1-methylnaphtho[2,3-c]furan-3-one (ventilagol), 2(2′-acetoxypropyl)-3-hydroxy-5,7,8-trimethoxy-1,4-naphthoquinone (maderone), cordeauxione and isocordeauxione. The root bark of V. calyculata contains 2-methoxystypandrone and 1-hydroxy-6-methoxy-3-methylxanthone-8-carboxylic acid (calyxanthone).     

The phenomenon of one-trial tolerance to the anxiolytic effect of chlordiazepoxide in the elevated plus-maze test is abolished by previous administration of chlordiazepoxide or buspirone

It has been repeatedly reported that the anxiolytic action of benzodiazepines in the elevated plus-maze test is abolished in rats that have received a single prior experience of the test apparatus (one-trial tolerance effect). To analyze whether the one-trial tolerance effect of chlordiazepoxide can be influenced by administration of chlordiazepoxide or buspirone on trial 1, male Wistar rats received an IP injection of vehicle, chlordiazepoxide (8 mg/kg) or buspirone (2.5 mg/kg) 30 min. before testing for 5 min. in the plus-maze (trial 1). Seventy-two hours later, the rats received vehicle or chlordiazepoxide 30 min. before the re-exposure to the plus-maze for 5 min. (trial 2). Groups injected with chlordiazepoxide or buspirone on trial 1 and with chlordiazepoxide on trial 2 showed an anxiolytic effect of chlordiazepoxide on trial 2, as opposed to rats injected with vehicle on trial 1 and with chlordiazepoxide on trial 2. As opposed to previous studies, the present results suggest that the influence of prior experience with the plus-maze on the anxiolytic action of chlordiazepoxide during re-exposure seems to depend critically on the drug state in which trial 1 is experienced. These results are discussed with respect to the hypothesis proposed to explain the phenomenon of one-trial tolerance.     

The non-competitive AMPA receptor antagonist (GYKI 52466) blocks quisqualate-induced acetylcholine release from the rat hippocampus and striatum: an in vivo microdialysis study

The effects of the non-N-methyl-D-aspartate (NMDA) agonist quisqualate (QUIS) and selective AMPA/kainate receptor antagonist 1-(aminophenyl)-methyl-7, 8-methyilendioxy-5H-2,3-benzodiazepine (GYKI 52466) on the release of acetylcholine (ACh) from the hippocampus and striatum of freely moving rats were studied by transversal microdialysis. Acetylcholine level in the dialisate was measured by the high performance liquid chromatography (HPLC) method with an electrochemical detector. The QUIS (100 microM) perfused through the striatum induced an increase of extracellular ACh level (250%) which lasted for over 1h and gradually returned to basal values. Local perfusion of GYKI 52466 (10-100 microM) to the striatum did not change the basal release of ACh. GYKI 52466 (10 microM) administered together with QUIS (100 microM) in he striatum antagonized the stimulant effect of QUIS on the ACh release.Local administration of the QUIS (100 microM) through the microdialysis fiber implanted in the hippocampus, caused a long lasting increase of extracellular hippocampal ACh level (360%) which was reversed when the drug was withdrawn from the perfusion solution. The stimulant effect of QUIS was antagonized by concomitant perfusion of GYKI (10 microM). No effect was seen on the basal ACh release when GYKI (10-100 microM) was perfused through the hippocampus.Local perfusion with tetrodotoxin (1 microM) decrease the basal release of ACh and prevented the QUIS-induced increase of ACh both in the hippocampus and striatum.Our in vivo neurochemical results indicate that hippocampal and striatal cholinergic systems are regulated by non-NMDA (probably AMPA) glutamatergic receptors located in the hippocampus and striatum.     

Mechanism of inhibition of the GluA2 AMPA receptor channel opening: consequences of adding an N-3 methylcarbamoyl group to the diazepine ring of 2,3-benzodiazepine derivatives

2,3-Benzodiazepine derivatives are AMPA receptor inhibitors, and they are potential drugs for treating some neurological diseases caused by excessive activity of AMPA receptors. Using a laser-pulse photolysis and rapid solution flow techniques, we characterized the mechanism of action of a 2,3-benzodiazepine derivative, termed BDZ-f, by measuring its inhibitory effect on the channel-opening and channel-closing rate constants as well as the whole-cell current amplitude of the homomeric GluA2Q AMPA receptor channels. We also investigated whether BDZ-f competes with GYKI 52466 for binding to the same site on GluA2Q(flip). GYKI 52466 is the prototypic 2,3-benzodiazepine compound, and BDZ-f is the N-3 methylcarbamoyl derivative. We found that BDZ-f is a noncompetitive inhibitor with a slight preference for the closed-channel state of both the flip and the flop variants of GluA2Q. Similar to other 2,3-benzodiazepine compounds that we have previously characterized, BDZ-f inhibits GluA2Q(flip) by forming an initial, loose intermediate that is partially conducting; however, this intermediate rapidly isomerizes into a tighter, fully inhibitory receptor-inhibitor complex. BDZ-f binds to the same noncompetitive site as GYKI 52466 does. Together, our results show that the addition of an N-3 methylcarbamoyl group to the diazepine ring with the azomethine feature (i.e., GYKI 52466) is what makes BDZ-f more potent and more selective toward the closed-channel conformation than the original GYKI 52466. Our results have useful implications for the structure-activity relationship of the 2,3-benzodiazepine series.     

Mechanism of inhibition of GluA2 AMPA receptor channel opening by 2,3-benzodiazepine derivatives: functional consequences of replacing a 7,8-methylenedioxy with a 7,8-ethylenedioxy moiety

2,3-Benzodiazepine (2,3-BDZ) compounds are a group of AMPA receptor inhibitors and are drug candidates for treating neurological diseases involving excessive AMPA receptor activity. We investigated the mechanism by which GluA2Q(flip) receptor channel opening is inhibited by two 2,3-BDZ derivatives, i.e., 1-(4-aminophenyl)-3,5-dihydro-7,8-ethylenedioxy-4H-2,3-benzodiazepin-4-one (2,3-BDZ-11-2) and its 1-(4-amino-3-chlorophenyl) analogue (2,3-BDZ-11-4). Both compounds have a 7,8-ethylenedioxy moiety instead of the 7,8-methylenedioxy feature present in the structure of GYKI 52466, the prototypic 2,3-BDZ compound. Using a laser-pulse photolysis approach with a time resolution of ~60 μs and a rapid solution flow technique, we characterized the effect of the two compounds on the channel opening process of the homomeric GluA2Q(flip) receptor. We found that both 2,3-BDZ-11-2 and 2,3-BDZ-11-4 are noncompetitive inhibitors with specificity for the closed-channel conformation of the GluA2Q(flip) receptor. However, 2,3-BDZ-11-4 is ~10-fold stronger, defined by its inhibition constant for the closed-channel conformation (i.e., K(I) = 2 μM), than 2,3-BDZ-11-2. From double-inhibitor experiments, we determined that both compounds bind to the same site, but this site is different from two other known, noncompetitive binding sites on the GluA2Q(flip) receptor previously reported. Our results provide both mechanistic clues to improve our understanding of AMPA receptor regulation and a structure-activity relationship for designing more potent 2,3-BDZ compounds with predictable properties for this new noncompetitive site.     

Three isoflavanones with cannabinoid-like moieties from Desmodium canum

Three further derivatives of 5,7,2',4'-tetrahydroxy-6-methyl isoflavanone have been isolated from the root extract of Desmodium canum and assigned the structures 2,3-dihydro-5,7-dihydroxy-6-methyl-3-(1a,2,3,3a,8b,8c-hexahydro-6-hydroxy-1,1,3a-trimethyl-1H-4-oxabenzo[f]cyclobut[c,d]inden-7-yl)-4H-1-benzopyran-4-one (1) 2,3-dihydro-5,7-dihydroxy-6-methyl-3-(6a,7,8,10a-tetrahydro-3-hydroxy-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-2-yl)-4H-1-benzopyran-4-one (2) 2,3-dihydro-5,7-dihydroxy-6-methyl-3-(3-hydroxy-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-2-yl) 4H-1-benzopyran-4-one (3). The three compounds and the previously isolated chromene 4 all derive from the geranylated precursor 5 by a series of cannabinoid-like oxidative rearrangements.     

Flavonoids from Lonchocarpus latifolius roots

From the petrol extract of Lonchocarpus latifolius roots, 10 flavonoids were isolated. These included: 3,5-dimethoxy-2',2'-dimethylpyrano-(5',6':8,7)-flavone, 3-methoxy-(2',3':7,8)-furanoflavanone, 3',4'-methylenedioxy-(2',3':7,8)-furanoflavanone, and (2,3-trans-3,4-trans)-3,4-dimethoxy-(2',3':7,8)-furanoflavan, as well as the previously known karanjachromene, karanjin, lanceolatin B, pongachromene, pongaglabrone and ponganpin. Only nine flavonoids could be quantified through HPLC analysis.     

Neoflavonoids and the cinnamylphenol kuhlmannistyrene from Machaerium kuhlmannii and M. Nictitans

The trunkwood of Machaerium kuhlmannii contains methyl palmitate, 3-O-acetyloleanolic acid and sitosterol; the benzene derivatives 2,3-dimethoxyphenol, 2,6-dimethoxyphenol, 2-hydroxy-3-methoxyphenol, 2,3-dimethoxybenzaldehyde and methyl 3-(2-hydroxy-4-methoxyphenyl)-propionate; the isoflavonoids formononetin and (6aS,11aS)-medicarpin; the neoflavonoids (R)-3,4-dimethoxydalbergione, (R)-3,4-dimethoxydalbergiquinol, kuhlmanniquinol [(R)-3-(4-hydroxyphenyl)-3-(5-hydroxy-2,3,4-trimethoxyphenyl)-propene], dalbergin, kuhlmannin (6-hydroxy-7,8-dimethoxy-4-phenylcoumarin) and kuhlmannene (6-hydroxy-7,8-dimethoxy-4-phenylchrom-3-ene), as well as the cinnamylphenol kuhlmannistyrene [Z-1-(5-hydroxy-2,3,4-trimethoxybenzyl)-2-(2-hydroxyphenyl)-ethylene]. Five of these compounds, in addition to (R)-4′-hydroxy-3,4-dimethoxydalbergione, were also isolated from a trunkwood extract of M. nictitans. Structural assignments were confirmed by chemical interconversion and by the synthesis of (±)-kuhlmanniquinol.     

Tofizopam enhances the action of diazepam against tremor and convulsions

Tofizopam, an anxiolytic 3,4-benzodiazepine, increases the affinity of benzodiazepine receptors for 1,4-benzodiazepines. In this study we investigated whether this increased affinity of the receptors alters the sensitivity of mice to tremor and to convulsions. Convulsions induced by harmane were not affected by tofizopam (50-300 mg/kg), but diazepam (15 mg/kg) increased the ED50 of harmane from 9.9 to 25.1 mg/kg. Tofizopam did not alter the threshold for electroshock-induced convulsions, while a dose of 10 mg/kg diazepam protected mice from convulsions. Low doses of tofizopam (12.5-25 mg/kg) sensitized mice to the tremorogenic effect of harmaline. Diazepam inhibited tremor: the ED50 of harmaline increased by 153% after 50 mg/kg of diazepam. In contrast to 1,4-benzodiazepines, tofizopam has no anticonvulsive effect. It sensitises mice to the tremor induced by harmaline. In combination with diazepam, however, tofizopam enhanced the anticonvulsive and antitremorogenic actions of this 1,4-benzodiazepine by 12-65%. This effect probably results from a tofizopam-induced increase in the occupation of benzodiazepine receptors.     

Structure-activity study of 2,3-benzodiazepin-4-ones noncompetitive AMPAR antagonists: identification of the 1-(4-amino-3-methylphenyl)-3,5-dihydro-7,8-ethylenedioxy-4H-2,3-benzodiazepin-4-one as neuroprotective agent

In the search for AMPA receptor (AMPAR) antagonists, 2,3-benzodiazepines represent a family of specific noncompetitive antagonists with anticonvulsant and neuroprotective properties. We have previously shown that 2,3-benzodiazepin-4-ones possess marked anticonvulsant properties and high affinity for the noncompetitive binding site of the AMPAR complex. In this paper, we report the synthesis and pharmacological characterization of a full set of 2,3-benzodiazepin-4-ones in order to better define the structure-activity relationship (SAR) of this class of compounds. Binding assays and functional tests were performed to evaluate the antagonistic activity at the AMPARs. Through these results we have identified a potent AMPAR antagonist, 1-(4-amino-3-methylphenyl)-3,5-dihydro-7,8-ethylenedioxy-4H-2,3-benzodiazepin-4-one (5c). This compound noncompetitively inhibited AMPAR-mediated toxicity in primary mouse hippocampal cultures with an IC(50) of 1.6muM and blocked kainate-induced calcium influx in rat cerebellar granule cells with an IC(50) of 6.4muM. Thus, 5c has the in vitro potential as therapeutic drug in the treatment of various neurological disorders.