3-Aryl-5-phenoxymethyl-1,3-oxazolidin-2-ones as positive allosteric modulators of mGluR2 for the treatment of schizophrenia: Hit-to-lead efforts

Recent advances in the exploration of oxazolidinone scaffolds from compound development to antibacterial agents and other bioactivities

Bacterial infections cause a variety of life-threatening diseases, and the continuous evolution of drug-resistant bacteria poses an increasing threat to current antimicrobial regimens. Gram-positive bacteria (GPB) have a wide range of genetic capabilities that allow them to adapt to and develop resistance to practically all existing antibiotics. Oxazolidinones, a class of potent bacterial protein synthesis inhibitors with a unique mechanism of action involving inhibition of bacterial ribosomal translation, has emerged as the antibiotics of choice for the treatment of drug-resistant GPB infections. In this review, we discussed the oxazolidinone antibiotics that are currently on the market and in clinical development, as well as an updated synopsis of current advances on their analogues, with an emphasis on innovative strategies for structural optimization of linezolid, structure-activity relationship (SAR), and safety properties. We also discussed recent efforts aimed at extending the activity of oxazolidinones to gram-negative bacteria (GNB), antitumor, and coagulation factor Xa. Oxazolidinone antibiotics can accumulate in GNB by a conjugation to siderophore-mediated β-lactamase-triggered release, making them effective against GNB.

Efficient methods for the synthesis of chiral 2-oxazolidinones as pharmaceutical building blocks

Although the wide variety of heterocyclic compounds is common knowledge, chiral 2-oxazolidinones are recognized as some of the most important heterocycles in medicinal chemistry. Many important pharmaceutical molecules have been constructed based on the chiral 2-oxazolidinone backbone. Therefore, the development of even more efficient catalytic methods for the synthesis of chiral 2-oxazolidinones remains a very important pursuit in the field of synthetic organic chemistry. This review summarizes the coupling reactions of epoxides and isocyanates for the preparation of 2-oxazolidinones. Both metal catalysts and organocatalysts promote these reactions. Optically pure 2-oxazolidinones are prepared from optically pure epoxide substrates via these catalytic methods. A synthetic example of a commercially available pharmaceutical compound utilizing this method is also introduced.

Synthesis of Chiral N-Nitro-oxazolidin-2-ones and O-(β-Nitraminoalkyl) Carbamates in Liquefied 1,1,1,2-Tetrafluoroethane Medium

A convenient synthesis of chiral N-nitro-oxazolidin-2-ones by nitration of α-amino acid derived 1,3-oxazolidin-2-ones containing one or two stereogenic centers with dinitrogen pentoxide in liquefied 1,1,1,2-tetrafluoroethane medium has been developed. The obtained N-nitroheterocycles were converted into enantiomerically pure O-(β-nitraminoalkyl) carbamates by treatment with ammonia or amines in the same solvent. The synthesized N-nitro compounds are slightly toxic in vitro to Human Embryonic Kidney 293 (HEK293) cells.

5-(Carbamoylmethylene)-oxazolidin-2-ones as a Promising Class of Heterocycles Inducing Apoptosis Triggered by Increased ROS Levels and Mitochondrial Dysfunction in Breast and Cervical Cancer

Oxazolidinones are antibiotics that inhibit protein synthesis by binding the 50S ribosomal subunit. Recently, numerous worldwide researches focused on their properties and possible involvement in cancer therapy have been conducted. Here, we evaluated in vitro the antiproliferative activity of some 5-(carbamoylmethylene)-oxazolidin-2-ones on MCF-7 and HeLa cells. The tested compounds displayed a wide range of cytotoxicity on these cancer cell lines, measured by MTT assay, exhibiting no cytotoxicity on non-tumorigenic MCF-10A cells. Among the nine tested derivatives, four displayed a good anticancer potential. Remarkably, OI compound showed IC₅₀ values of 17.66 and 31.10 µM for MCF-7 and HeLa cancer cells, respectively. Furthermore, we assessed OI effect on the cell cycle by FACS analysis, highlighting a G1 phase arrest after 72 h, supported by a low expression level of Cyclin D1 protein. Moreover, mitochondrial membrane potential was reduced after OI treatment driven by high levels of ROS. These findings demonstrate that OI treatment can inhibit MCF-7 and HeLa cell proliferation and induce apoptosis by caspase-9 activation and cytochrome c release in the cytosol. Hence, 5-(carbamoylmethylene)-oxazolidin-2-ones have a promising anticancer activity, in particular, OI derivative could represent a good candidate for in vivo further studies and potential clinical use.

Oxazolidinone derivatives: cytoxazone-linezolid hybrids induces apoptosis and senescence in DU145 prostate cancer cells

In this study, we report the synthesis of novel oxazolidinone derivatives derived from linezolid 3 having p-methoxyphenyl group at C-4 position. In vitro evaluation for their anticancer activity toward cultured A549, DU145, HELA, and MCF7 were carried out. The series of compounds prepared displayed wide range of cytotoxicity in MTT assays (10-70 μM) across the cell lines tested. Of the all tested compounds 16 and 17 displayed good anticancer potential against A549 (lung) and DU145 (prostate) cancer cells. Further, to determine their anticancer potential, in the present study we have assessed effect of 17 on DU145 cells growth in in vitro assays. The results clearly demonstrated that the exposure of DU145 cells to 17 inhibits cell proliferation and induces apoptosis by activation of caspase-3 and -9. Long term exposure of DU145 cells to 17 induced cellular senescence confirmed by senescence marker β-galactosidase staining of cells on post exposure to 17. The results from this current report support that the oxazolidinone derivatives with ethyl and acryl substitutions showed promising anticancer activity which will be helpful to develop further novel anticancer agents with better therapeutic potential.

mGluR2 positive allosteric modulators: a patent review (2009 - present)

INTRODUCTION

The mGlu2 receptor, which belongs to the group II subfamily of metabotropic glutamate receptors (mGlu) along with the mGlu3 receptor, has proven to be of particular importance in neuropharmacology. Preferentially expressed on presynaptic nerve terminals, the mGlu2 receptor negatively modulates glutamate and GABA release and is widely distributed in the brain. High levels of mGlu2 receptors are seen in brain areas such as prefrontal cortex, hippocampus and amygdala where glutamate hyperfunction may be implicated in disorders and diseases such as anxiety and schizophrenia. Given the promise offered by mGlu2/3 receptor activation, there is increased interest in identifying small molecules which activate the receptor. A preferred approach is via positive allosteric modulators (PAMs) which bind at an alternative site to agonists.

AREAS COVERED

This review covers the patent applications which were published between April 2009 and December 2012 on PAMs of the mGlu2, and it is a continuation of an earlier review published in this journal.

EXPERT OPINION

Advances in medicinal chemistry and pharmacology have set the stage in the field of mGlu2 receptor PAMs. Compounds currently advancing in clinical trials will soon establish the therapeutic potential of this allosteric approach.

An Efficient Approach to the Synthesis of Novel Oxazolidinones as Potential Antimicrobial Agents

Oxazolidinone, either mononuclear or condensed with other heterocyclics, has established its importance in medicinal chemistry. A variety of biological activities have been reported by oxazolidinone derivatives. The present work describes the synthesis of several oxazolidinone derivatives, 3-(2-(7-chloroquinoline-4-ylamino)ethyl)-2-imino-5-(4-chloro/nitro/methoxy benzylidene)oxazolidin-4-one 4(a–c) and 4-(2-(7-chloroquinolin-4-ylamino)ethyl)-2(4-chloro/nitro/methoxy-benzylidene)-1,6-diox-4,9-di-azaspiro[4,4]nonane-3,8-dione 5(a–c). Synthesized compounds (1, 3, 4a, 5a, and 5c) were screened against bacterial strains such asS. aureus(MTCC 96) andE. coli(MTCC119) and fungal strainsA. niger(MTCC 1344) andC. albicans(MTCC 871) compared with penicillin for bacteria and fluconazole for fungi as reference drugs by disk diffusion method. All synthesized compounds were identified by the means of IR, NMR, and MS.

Glutamatergic Approaches for the Treatment of Schizophrenia

Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system and plays a key role in most aspects of normal brain function including cognition, learning and memory. Dysfunction of glutamatergic neurotransmission has been implicated in a number of neurological and psychiatric disorders with a growing body of evidence suggesting that hypofunction of glutamatergic neurotransmission via the N-methyl-d-aspartate (NMDA) receptor plays an important role in the pathophysiology of schizophrenia. It thus follows that potentiation of NMDA receptor function via pharmacological manipulation may provide therapeutic utility for the treatment of schizophrenia and a number of different approaches are currently being pursued by the pharmaceutical industry with this aim in mind. These include strategies that target the glycine/d-serine site of the NMDA receptor (glycine transporter GlyT1, d-serine transporter ASC-1 and d-amino acid oxidase (DAAO) inhibitors) together with those aimed at enhancing glutamatergic neurotransmission via modulation of AMPA receptor and metabotropic glutamate receptor function. Such efforts are now beginning to bear fruit with compounds such as the GlyT1 inhibitor RG1678 and mGlu2 agonist LY2140023 proving to have clinical meaningful effects in phase II clinical trials. While more studies are required to confirm long-term efficacy, functional outcome and safety in schizophrenic agents, these agents hold real promise for addressing unmet medical needs, in particular refractory negative and cognitive symptoms, not currently addressed by existing antipsychotic agents.

Actions of Xanthurenic acid, a putative endogenous Group II metabotropic glutamate receptor agonist, on sensory transmission in the thalamus

Xanthurenic acid (XA), a molecule arising from tryptophan metabolism by transamination of 3-hydroxykynurenine, has recently been identified as an endogenous Group II (mGlu2 and mGlu3) metabotropic glutamate (mGlu) receptor ligand in vitro. Impairments in Group II mGlu receptor expression and function have been implicated in the pathophysiology of schizophrenia, as have multiple steps in the kynurenine metabolism pathway. Therefore, we examined XA in vivo to further investigate its potential as a Group II mGlu receptor ligand using a preparation that has been previously demonstrated to efficiently reveal the action of other Group II mGlu receptor ligands in vivo. Extracellular single-neurone recordings were made in the rat ventrobasal thalamus (VB) in conjunction with iontophoresis of agonists, an antagonist and a positive allosteric modulator and/or intravenous (i.v.) injection of XA. We found the XA effect on sensory inhibition, when applied iontophoretically and i.v., was similar to that of other Group II mGlu receptor agonists in reducing inhibition evoked in the VB from the thalamic reticular nucleus upon physiological sensory stimulation. Furthermore, we postulate that XA may be the first potential endogenous allosteric agonist (termed 'endocoid') for the mGlu receptors. As the Group II receptors and kynurenine metabolism pathway have both been heavily implicated in the pathophysiology of schizophrenia, XA could play a pivotal role in antipsychotic research as this potential endocoid represents both a convergence within these two biological parameters and a novel class of Group II mGlu receptor ligand. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Discovery of 1,4-disubstituted 3-cyano-2-pyridones: a new class of positive allosteric modulators of the metabotropic glutamate 2 receptor

The discovery and characterization of compound 48, a selective and in vivo active mGlu2 receptor positive allosteric modulator (PAM), are described. A key to the discovery was the rational exploration of the initial HTS hit 13 guided by an overlay model built with reported mGlu2 receptor PAM chemotypes. The initial weak in vitro activity of the hit 13 was quickly improved, although compounds still had suboptimal druglike properties. Subsequent modulation of the physicochemical properties resulted in compounds having a more balanced profile, combining good potency and in vivo pharmacokinetic properties. Final refinement by addressing cardiovascular safety liabilities led to the discovery of compound 48. Besides good potency, selectivity, and ADME properties, compound 48 displayed robust in vivo activity in a sleep-wake electroencephalogram (sw-EEG) assay consistent with mGlu2 receptor activation, in accordance with previous work from our laboratories.

Metabotropic glutamate receptors for new treatments in schizophrenia

Metabotropic glutamate receptors (mGluRs) represent exciting targets for the development of novel therapeutic agents for schizophrenia. Recent studies indicate that selective activation of specific mGluR subtypes may provide potential benefits for not only the positive symptoms, but also the negative symptoms and cognitive impairments observed in individuals with schizophrenia. Although optimization of traditional orthosteric agonists may still offer a feasible approach for the activation of mGluRs, important progress has been made in the discovery of novel subtype-selective allosteric ligands, including positive allosteric modulators (PAMs) of mGluR2 and mGluR5. These allosteric mGluR ligands have improved properties for clinical development and have served as key preclinical tools for a more in-depth understanding of the potential roles of these different mGluR subtypes for the treatment of schizophrenia.

Recent progress in the synthesis and characterization of group II metabotropic glutamate receptor allosteric modulators

Group II metabotropic glutamate (mGlu) receptors consist of the metabotropic glutamate 2 (mGlu(2)) and metabotropic glutamate 3 (mGlu(3)) receptor subtypes which modulate glutamate transmission by second messenger activation to negatively regulate the activity of adenylyl cyclase. Excessive accumulation of glutamate in the perisynaptic extracellular region triggers mGlu(2) and mGlu(3) receptors to inhibit further release of glutamate. There is growing evidence that the modulation of glutamatergic neurotransmission by small molecule modulators of Group II mGlu receptors has significant potential for the treatment of several neuropsychiatric and neurodegenerative diseases. This review provides an overview of recent progress on the synthesis and pharmacological characterization of positive and negative allosteric modulators of the Group II mGlu receptors.

Allosteric modulation of family C G-protein-coupled receptors: from molecular insights to therapeutic perspectives

Allosteric receptor modulation is an attractive concept in drug targeting because it offers important potential advantages over conventional orthosteric agonism or antagonism. Allosteric ligands modulate receptor function by binding to a site distinct from the recognition site for the endogenous agonist. They often have no effect on their own and therefore act only in conjunction with physiological receptor activation. This article reviews the current status of allosteric modulation at family C G-protein coupled receptors in the light of their specific structural features on the one hand and current concepts in receptor theory on the other hand. Family C G-protein-coupled receptors are characterized by a large extracellular domain containing the orthosteric agonist binding site known as the "venus flytrap module" because of its bilobal structure and the dynamics of its activation mechanism. Mutational analysis and chimeric constructs have revealed that allosteric modulators of the calcium-sensing, metabotropic glutamate and GABA(B) receptors bind to the seven transmembrane domain, through which they modify signal transduction after receptor activation. This is in contrast to taste-enhancing molecules, which bind to different parts of sweet and umami receptors. The complexity of interactions between orthosteric and allosteric ligands is revealed by a number of adequate biochemical and electrophysiological assay systems. Many allosteric family C GPCR modulators show in vivo efficacy in behavioral models for a variety of clinical indications. The positive allosteric calcium sensing receptor modulator cinacalcet is the first drug of this type to enter the market and therefore provides proof of principle in humans.

New positive allosteric modulators of the metabotropic glutamate receptor 2 (mGluR2). Identification and synthesis of N-propyl-5-substituted isoquinolones

N-propyl-5-substituted isoquinolones were identified as mGluR2 PAMs via high-throughput screening (HTS). Initial SAR exploration led to the identification of compound 20.

Discovery of 1,5-disubstituted pyridones: a new class of positive allosteric modulators of the metabotropic glutamate 2 receptor

A series of 1,5-disubstituted pyridones was identified as positive allosteric modulators (PAMs) of the metabotropic glutamate receptor 2 (mGluR2) via high throughput screening (HTS). Subsequent SAR exploration led to the identification of several compounds with improved in vitro activity. Lead compound 8 was further profiled and found to attenuate the increase in PCP induced locomotor activity in mice.

Design and synthesis of an orally active metabotropic glutamate receptor subtype-2 (mGluR2) positive allosteric modulator (PAM) that decreases cocaine self-administration in rats

The modification of 3'-((2-cyclopentyl-6,7-dimethyl-1-oxo-2,3-dihydro-1H-inden-5-yloxy)methyl)biphenyl-4-carboxylic acid (BINA, 1) by incorporating heteroatoms into the structure and replacing the cyclopentyl moiety led to the development of new mGluR2 positive allosteric modulators (PAMs) with optimized potency and superior druglike properties. These analogues are more potent than 1 in vitro and are highly selective for mGluR2 vs other mGluR subtypes. They have significantly improved pharmacokinetic (PK) properties, with excellent oral bioavailability and brain penetration. The benzisothiazol-3-one derivative 14 decreased cocaine self-administration in rats, providing proof-of-concept for the use of mGluR2 PAMs for the treatment of cocaine dependence.

Discovery of Oxazolobenzimidazoles as Positive Allosteric Modulators for the mGluR2 Receptor

Novel oxazolobenzimidazoles are described as potent and selective positive allosteric modulators of the metabotropic glutamate receptor 2. The discovery of this class and optimization of its physical and pharmacokinetic properties led to the identification of potent and orally bioavailable compounds (20 and 21) as advanced leads. Compound 20 (TBPCOB) was shown to have robust activity in a PCP-induced hyperlocomotion model in rat, an assay responsive to clinical antipsychotic treatments for schizophrenia.