Substituted analogues of GV150526 as potent glycine binding site antagonists in animal models of cerebral ischemia

Redox-Neutral Ru(0)-Catalyzed Alkenylation of 2-Carboxaldimine-heterocyclopentadienes

A new Ru₃(CO)₁₂-catalyzed directed alkenylation of 2-carboxaldimine-heterocyclopentadienes has been accomplished. This process allows coupling of furan, pyrrole, indole, and thiophene 2-carboxaldimines with electron-poor alkenes such as acrylates, vinylsulfones, and styrenes. This regio- and chemoselective oxidative C-H coupling does not require the presence of an additional sacrificial oxidant. Density functional theory calculations allowed us to propose a mechanism and unveiled the nature of the H₂ acceptor.

Therapeutic time windows of compounds against NMDA receptors signaling pathways for ischemic stroke

Much evidence has proved that excitotoxicity induced by excessive release of glutamate contributes largely to damage caused by ischemia. In view of the key role played by NMDA receptors in mediating excitotoxicity, compounds against NMDA receptors signaling pathways have become the most promising type of anti-stroke candidate compounds. However, the limited therapeutic time window for neuroprotection is a key factor preventing NMDA receptor-related compounds from showing efficacy in all clinical trials for ischemic stroke. In this perspective, the determination of therapeutic time windows of these kinds of compounds is useful in ensuring a therapeutic effect and accelerating clinical application. This mini-review discussed the therapeutic time windows of compounds against NMDA receptors signaling pathways, described related influence factors and the status of clinical studies. The purpose of this review is to look for compounds with wide therapeutic time windows and better clinical application prospect.

Regioselective C-H Alkenylation and Unsymmetrical Bis-olefination of Heteroarene Carboxylic Acids with Ruthenium Catalysis in Water

An efficient weak carboxylate-assisted oxidative cross-dehydrogenative C-H/C-H coupling (CDC) of heteroarenes with readily available olefins has been devised employing water as green solvent under ruthenium(II) catalysis. The reaction is operationally simple, accommodates a large variety of heteroaromatic carboxylic acids as well as olefins, and facilitates a diverse array of high-value olefin-tethered heteroarenes in high yields (up to 87%). The potential of this ortho-C-H bond activation strategy has also been exploited toward tunable synthesis of densely functionalized heteroarenes through challenging unsymmetrical bis-olefination process in a one-pot sequential fashion. Mechanistic investigation demonstrates a reversible ruthenation process and C-H metalation step might not be involved in the rate-determining step.

Selective inhibition of butyrylcholinesterase by singlet oxygen-generated melatonin derivatives

The inhibition of cholinesterases plays a crucial role in a therapy of neurodegenerative diseases, including Alzheimer's disease. Especially, butyrylcholinesterase (BChE) has recently gained special interest. On the other hand, compounds having antioxidative properties may have a beneficial role in slowing down neurodegeneration processes. To combine these two effects, we synthesized a series of new derivatives of melatonin, which is a strong antioxidant, possessing structural elements essential for the inhibitory activity against cholinesterase. The structure of the new compounds was confirmed by NMR spectroscopy and mass spectrometry, and their activity against cholinesterases was measured in vitro using modified Ellman's method. The compounds obtained showed a high inhibitory activity, together with a strong selectivity against BChE. These results may point at new area of interest in a research on cholinesterase inhibitors.

Design, synthesis and biological evaluation of new ionone derivatives as potential neuroprotective agents in cerebral ischemia

A new series of ionone derived allylic alcohols have been evaluated for anti-ischemic activity. Out of them, 12f and 13b decreased infarct volume to 23.98+/-4.7 mm3 and 93.98+/-24.8 mm3 as compared to ischemic group.

Neuroprotective effect of STAZN, a novel azulenyl nitrone antioxidant, in focal cerebral ischemia in rats: dose-response and therapeutic window

Stilbazulenyl nitrone (STAZN) is a potent antioxidant that, in a rat model of transient focal cerebral ischemia, confers significant enduring functional and morphological neuroprotection. This study investigated the influence of dose and time of administration on the neuroprotective effects of STAZN in the intraluminal suture model of middle cerebral artery occlusion (MCAo). Dose response: At 2 and 4 h after the onset of MCAo, animals received intravenously either STAZN (low dose=0.07 mg/kg, n=8; medium dose=0.7 mg/kg, n=9; high dose=3.5 mg/kg, n=9), an equivalent volume of vehicle (30% Solutol HS15 and 70% isotonic saline, 0.37 ml/kg, n=5) or saline (0.37 ml/kg, n=5). Only the medium dose improved scores (p<0.05) on a standardized neurobehavioral test at 1, 2 and 3 days after MCAo. Only the medium dose reduced the total infarction (51%, p=0.014) compared to controls. These results indicate that STAZN exhibits maximal neuroprotection at the 0.7 mg/kg dose. Therapeutic window: STAZN (0.6 mg/kg) dissolved in dimethylsulfoxide was given intra-peritoneally at 2 and 4 h (n=11), 3 and 5 h (n=10), 4 and 6 h (n=10) or 5 and 7 h (n=7) after the onset of MCAo. Additional doses were given at 24 and 48 h. Vehicle (dimethylsulfoxide, 2.0 ml/kg, n=6) was administered at 3, 5, 24 and 48 h. STAZN treatment initiated at 2 or 3 h after the onset of MCAo improved neurological scores (p<0.001) and reduced total infarction (42.2%, p<0.05) compared to controls.

Benzoazepine derivative as potent antagonists of the glycine binding site associated to the NMDA receptor

A series of benzoazepine derivatives, bearing suitable substituents at the C-3 position, was designed and evaluated by superimposition with the pharmacophore model of the glycine binding site. To fully explore the SAR of this class of compounds and to allow the preparation of new different compounds at the C-3 position, appropriate synthetic routes were set up. The benzoazepines were evaluated in terms of in vitro affinity using [3H]glycine binding assay and in vivo potency by inhibition of convulsions induced by N-methyl-D-aspartate (NMDA) in mice. This further analysis confirmed the preliminary results previously reported and that compound 27 is the most promising compound (Ki=32 nM, ED(50)=0.09 mg/kg, i.v.) in this series. Significant neuroprotective effect was observed after both pre- and post-ischaemia administration in the MCAo model. In particular, after post-ischaemia administration, it was found to be still effective when the administration was delayed up to 6 h after occlusion of the middle cerebral artery.

Enantiomerically pure tetrahydroquinoline derivatives as in vivo potent antagonists of the glycine binding site associated to the NMDA receptor

To identify neuroprotective agents after stroke, new substituted tetrahydroquinoline derivatives were designed as antagonists of the glycine binding site associated to the NMDA receptor, satisfying the key pharmacophoric requirements. In particular, the racemate 3c exhibited outstanding in vivo activity in the MCAo model in rats, when given iv both pre- and post-ischemia. Pure enantiomers 3c-(+) and 3c-(-) have been prepared following an original synthetic route. Despite the significant difference of activity observed in vitro, they shown similar neuroprotective profile in the MCAo model in rats.

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.

Glycine and neuroprotective effect of hypothermia in hypoxic-ischemic brain damage

The beneficial effects of hypothermia have long been known in non-traditional medicine but it is only in the past few decades that studies on the neuroprotective effects of hypothermia in hypoxic-ischemic brain injury have begun. Different mechanisms have been put forward to explain hypothermic neuroprotection including reduction of the excessive release of the excitatory amino acid neurotransmitter, glutamate. Recent experiments have questioned the key role of this neurotoxin in hypoxic-ischemic neuropathogenesis. In contrast, a mediatory role for another neurotransmitter, glycine in the neuroprotective effects of hypothermia has become more attractive, along with an indication of its role in the pathogenesis of ischemic neuronal damage. Thus, on the basis of reviewing relevant literature the hypothesis of a glycine-related mechanism of hypothermic neuroprotection in ischemia-induced neuronal injury has been put forward.

The selective glycine antagonist gavestinel lacks phencyclidine-like behavioral effects

Gavestinel [GV150526A; ( E)-3[(phenylcarbamoil)ethenyl]-4,6-dichloroindole-2-carboxylic acid sodium salt] is a selective antagonist at the strychnine-insensitive glycine site of the -methyl-D-aspartate (NMDA) receptor. It was tested for its ability to substitute for phencyclidine (PCP) in rats and rhesus monkeys trained to discriminate PCP from saline, under a two-lever fixed-ratio (FR) food reinforcement schedule, and for its ability to maintain responding in rhesus monkeys trained to self-administer PCP under a FR reinforcement schedule. No PCP-lever responding was observed after gavestinel (1-56 mg/kg i.p.) administration to rats discriminating PCP (2.0 mg/kg i.p.) from saline. The highest dose of gavestinel (100 mg/kg i.p.) tested eliminated responding. Likewise, no PCP-lever responding was observed after gavestinel (1-30 mg/kg s.c.) administration to rhesus monkeys discriminating PCP (0.08 or 0.1 mg/kg i.m.) from saline; the highest dose of gavestinel (30 mg/kg s.c.) tested reduced response rates to approximately 50% of those observed after its vehicle ( -cyclodextrin in 0.9% saline). Gavestinel (0.1-1 mg/kg per i.v. infusion) was not self-administered by rhesus monkeys that reliably self-administered PCP (0.0056 or 0.01 mg/kg per i.v. infusion). Infusion rates at the highest dose were typically lower than those for vehicle or saline, suggesting behavioral activity. Together, these results suggest that at behaviorally active doses gavestinel is not PCP-like and is likely to have low abuse liability.

In vivo evaluation of [11C]-3-[2-[(3-methoxyphenylamino)carbonyl]ethenyl]-4,6-dichloroindole-2-carboxylic acid ([11C]3MPICA) as a PET radiotracer for the glycine site of the NMDA ion channel

Alterations in normal NMDA receptor composition, densities and function have been implicated in the pathophysiology of certain neurological and neuropsychiatric disorders such as Parkinson's Disease, Huntington's Chorea, schizophrenia, alcoholism and stroke. In our first effort to provide PET ligands for the NMDA/glycine site, we reported the synthesis of a novel high affinity glycine site ligand, 3-[2-[(3-methoxyphenylamino)carbonyl]ethenyl]-4,6-dichloroindole-2-carboxylic acid ((3MPICA), Ki = 4.8 +/- 0.9 nM) and the corresponding carbon-11 labeled PET ligand, [11C]3MPICA. We report here the in vivo evaluation of [11C]3MPICA in rats. Biodistribution analysis revealed that [11C]3MPICA exhibited low degree of brain penetration and high blood concentration. The average uptake at two minutes was highest in the cerebellum (0.19 +/- 0.04 %ID/g) and thalamus (0.18 +/- 0.05 %ID/g) and lower in the hippocampus (0.13 +/- 0.03) and frontal cortex (0.11 +/- 0.04 %ID/g). The radioactivity cleared quickly from all brain regions examined. Administration of unlabeled 3MPICA (1 mg/kg, i.v.) revealed at 60 minutes a small general reduction in regional brain radioactivity concentrations in treated animals versus controls, however, the blood radioactivity concentration was also lowered, confounding the assessment of the degree of saturable binding. Warfarin co-administration (100 mg/kg, i.v.) significantly lowered blood activity at 5 minutes post-injection (-27%, P < 0.01) but failed to significantly increase the brain uptake of the radiotracer. In view of these results, and especially considering the low brain penetration of this tracer, [11C]3MPICA does not appear to be a promising PET radiotracer for in vivo use.

Synthesis and pharmacological characterisation of a conformationally restrained series of indole-2-carboxylates as in vivo potent glycine antagonists

After the identification of GV150526, the indole-2-carboxylate template was further explored in order to identify novel potential anti-stroke agents. In particular, the SAR of the side chain present at the C-3 position of the indole nucleus was widely studied. In this paper, the synthesis and the pharmacological profile of a further class of conformationally restricted analogues of GV150526 as in vitro and in vivo potent glycine antagonists is reported. In particular, a pyrazolidinone derivative was identified as a potent neuroprotective agent in animal models of cerebral ischaemia.

Endogenous indoles as novel polyamine site ligands at the N-methyl-D-aspartate receptor complex

High-throughput ligand displacement screens of a series of endogenous indoles revealed that tryptamine, serotonin and 5-methoxytryptamine readily displace [3H]spermidine and [3H]MK-801 from their respective binding sites in rat brain homogenate. These data, coupled with their potent inhibition of spermidine-potentiated [3H]MK-801 binding, suggest that certain endogenous indoles may act as ligands to one or more polyamine binding sites in the brain, including those on the N-methyl-D-aspartate receptor complex.

Straightforward synthesis of new tetrahydroquinoline derivatives

To identify novel classes of glycine antagonists, compounds potentially useful as neuroprotective after stroke, novel substituted tetrahydroquinoline derivatives, satisfying the key pharmacophoric requirements for glycine antagonists, were designed. To explore the SAR of these compounds an efficient synthetic route was set up exploiting the outstanding reactivity of suitable N-aryl imine derivatives. In particular an allylmetalation reaction or the addition of bis(trimethyldisilyl)ketene acetals allowed the preparation of versatile intermediates which were smoothly transformed into the desired bicycle tetrahydroquinoline derivatives by a Heck-type cyclization reaction.Key words: glycine antagonists, neuroprotection, tetrahydroquinolines, synthesis, allylmetalation.

Synthesis and pharmacological properties of novel glycine antagonists

The NMDA receptor is an ionotropic receptor complex widely distributed in the central nervous system and its activation, particularly in hypoxic conditions such as stroke, traumatic head injury and hypoglycemia, results in a massive influx of calcium ions into the post-synaptic neurones, leading to cell death through the activation of several neurotoxic cascades. The NMDA receptor is a unique ionotropic receptor complex because its activation requires the simultaneous binding of glutamate and glycine and selective antagonists at the glycine binding site are endowed with a better side-effect profile than competitive NMDA antagonists. Then, considerable efforts have been devoted to find potent and selective ligands, resulting in the identification of several classes of glycine antagonists. The research at Glaxo Wellcome has been aimed at the identification of novel in vivo active glycine antagonists, and led to the synthesis and pharmacological characterization of a number of novel, potent and systemically active compounds belonging to different chemical classes.