Discovery of 4,4-Disubstituted Quinazolin-2-ones as T-Type Calcium Channel Antagonists

Ensemble Docking Approach to Mitigate Pregnane X Receptor-Mediated CYP3A4 Induction Risk

Three structurally closely related dopamine D1 receptor positive allosteric modulators (D1 PAMs) based on a tetrahydroisoquinoline (THIQ) scaffold were profiled for their CYP3A4 induction potentials. It was found that the length of the linker at the C5 position greatly affected the potentials of these D1 PAMs as CYP3A4 inducers, and the level of induction correlated well with the activation of the pregnane X receptor (PXR). Based on the published PXR X-ray crystal structures, we built a binding model specifically for these THIQ-scaffold-based D1 PAMs in the PXR ligand-binding pocket via an ensemble docking approach and found the model could explain the observed CYP induction disparity. Combined with our previously reported D1 receptor homology model, which identified the C5 position as pointing toward the solvent-exposed space, our PXR-binding model coincidentally suggested that structural modifications at the C5 position could productively modulate the CYP induction potential while maintaining the D1 PAM potency of these THIQ-based PAMs.

Carbonyl-Assisted Iridium-Catalyzed C-H Amination Using 2,2,2-Trichloroethoxycarbonyl Azide

The carbonyl-directed, mono C-H amination of arenes has been achieved using [Cp*Ir(III)Cl₂]₂ as the catalyst and 2,2,2-trichloroethoxycarbonyl (Troc) azide as an aminating reagent. The amination proceeds smoothly with a variety of arylcarbonyl compounds, including alkyl and vinyl arylketones, secondary and tertiary aryl amides, and acetyl indoles. The resulting ortho-TrocNH arylcarbonyl compounds are easily transformed to the corresponding free arylamines, aryl carbamates, or aryl ureas. Taking advantage of the electrophilic nature of both Troc and carbonyl groups in ortho-TrocNH arylcarbonyl compounds, the subsequent cyclization with dinucleophilic reagents has also been demonstrated. This provides an efficient strategy for the construction of aryl-fused N-heterocycles.

C-H acylation of aniline derivatives with α-oxocarboxylic acids using ruthenium catalyst

An efficient and convenient synthetic strategy for ruthenium(II)-catalyzed ortho-acylation of N-(2-pyridyl)-anilines using α-oxycarboxylic acids as acyl sources is described. The procedure can smoothly proceed under mild conditions, showing good functional group tolerance. Valuable ortho-acylated aniline products have been obtained with moderate to good yields. Furthermore, the reaction could be easily scaled up to the gram scale.

A concise review on hPXR ligand-recognizing residues and structure-based strategies to alleviate hPXR transactivation risk

The human pregnane X receptor (hPXR) regulates the expression of major drug metabolizing enzymes. A wide range of drug candidates bind and activate hPXR, and hence are at risk of increasing drug-drug interactions and reducing clinical efficacy. hPXR structural features that function as hot spots for ligand binding are identified and highlighted in this concise review. Based on literature structure-activity relationship data as case studies, structure-based strategies to mitigate hPXR transactivation are summarized for medicinal chemists.

Scalable Asymmetric Synthesis of MK-8998, a T-Type Calcium Channel Antagonist

Two scalable and efficient synthetic routes for the synthesis of a T-type calcium channel antagonist MK-8998 were developed from a simple pyridine building block. The key step to set the stereochemistry relied on either chiral rhodium catalyst-mediated asymmetric hydrogenation of an enamide or transamination of an arylketone that provided the corresponding product in high enantioselectivity and high yield.

Photoredox-mediated hydroalkylation and hydroarylation of functionalized olefins for DNA-encoded library synthesis

DNA-encoded library (DEL) technology features a time- and cost-effective interrogation format for the discovery of therapeutic candidates in the pharmaceutical industry. To develop DEL platforms, the implementation of water-compatible transformations that facilitate the incorporation of multifunctional building blocks (BBs) with high C(sp3) carbon counts is integral for success. In this report, a decarboxylative-based hydroalkylation of DNA-conjugated trifluoromethyl-substituted alkenes enabled by single-electron transfer (SET) and subsequent hydrogen atom termination through electron donor-acceptor (EDA) complex activation is detailed. In a further photoredox-catalyzed hydroarylation protocol, the coupling of functionalized, electronically unbiased olefins is achieved under air and within minutes of blue light irradiation through the intermediacy of reactive (hetero)aryl radical species with full retention of the DNA tag integrity. Notably, these processes operate under mild reaction conditions, furnishing complex structural scaffolds with a high density of pendant functional groups.

Designing Out PXR Activity on Drug Discovery Projects: A Review of Structure-Based Methods, Empirical and Computational Approaches

This perspective discusses the role of pregnane xenobiotic receptor (PXR) in drug discovery and the impact of its activation on CYP3A4 induction. The use of structural biology to reduce PXR activity on drug discovery projects has become more common in recent years. Analysis of this work highlights several important molecular interactions, and the resultant structural modifications to reduce PXR activity are summarized. The computational approaches undertaken to support the design of new drugs devoid of PXR activation potential are also discussed. Finally, the SAR of empirical design strategies to reduce PXR activity is reviewed, and the key SAR transformations are discussed and summarized. In conclusion, this perspective demonstrates that PXR activity can be greatly diminished or negated on active drug discovery projects with the knowledge now available. This perspective should be useful to anyone who seeks to reduce PXR activity on a drug discovery project.

Synthesis of substituted 3,4-dihydroquinazolinones via a metal free Leuckart-Wallach type reaction

The 3,4-dihydroquinazolinone (DHQ) moiety is a highly valued scaffold in medicinal chemistry due to the vast number of biologically-active compounds based on this core structure. Current synthetic methods to access these compounds are limited in terms of diversity and flexibility and often require the use of toxic reagents or expensive transition-metal catalysts. Herein, we describe the discovery and development of a novel cascade cyclization/Leuckart-Wallach type strategy to prepare substituted DHQs in a modular and efficient process using readily-available starting materials. Notably, the reaction requires only the addition of formic acid or acetic acid/formic acid and produces H₂O, CO₂ and methanol as the sole reaction byproducts. Overall, the reaction provides an attractive entry point into this important class of compounds and could even be extended to isotopic labelling via the site-selective incorporation of a deuterium atom.

Microwave Assisted Synthesis of 4-Phenylquinazolin-2(1H)-one Derivatives that Inhibit Vasopressor Tonus in Rat Thoracic Aorta

Quinazolinones have pharmacological effects on vascular reactivity through different mechanisms. We synthesized 4-phenylquinazolin-2(1H)-one derivatives under microwave irradiation and tested them on the rat thoracic aorta. The prepared compounds 2a–2f were obtained in about 1 h with suitable yields (31–92%). All derivatives produced vasorelaxant effects with IC₅₀ values ranging from 3.41 ± 0.65 µM to 39.72 ± 6.77 µM. Compounds 2c, 2e and 2f demonstrated the highest potency in endothelium-intact aorta rings (IC₅₀ 4.31 ± 0.90 µM, 4.94 ± 1.21 µM and 3.41 ± 0.65 µM respectively), and they achieved around 90% relaxation (30 μM). In aorta rings without an endothelium, the effect of compound 2f was abolished. Using the MTT assay to test for cell viability, only compound 2b induced cytotoxicity at the maximum concentration employed (30 µM). The results show that vasorelaxation by 4-phenylquinazolin-2(1H)-one derivatives might depend on the activation of a signalling pathway triggered by endothelium-derived factors.

Microwave-Assisted aza-Friedel-Crafts Arylation of N-Acyliminium Ions: Expedient Access to 4-Aryl 3,4-Dihydroquinazolinones

A one-pot microwave-assisted aza-Friedel-Crafts arylation of N-acyliminium ions, generated in situ from o-formyl carbamates and different amines, is reported. This metal-free protocol provides rapid access to diverse 4-aryl 3,4-dihydroquinazolinones in excellent yield without any aqueous workup. A solvent-directed process for the selective aza-Friedel-Crafts arylation of electron-rich aryl/heteroaryl/butenyl-tethered N-acyliminium ions is also described.

T-type Calcium Channels in Health and Disease

Low Voltage-Activated (LVA) T-type calcium channels are characterized by transient current and Low Threshold Spikes (LTS) that trigger neuronal firing and oscillatory behavior. Combined with their preferential localization in dendrites and their specific "window current", T-type calcium channels are considered to be key players in signal amplification and synaptic integration. Assisted by the emerging pharmacological tools, the structural determinants of channel gating and kinetics, as well as novel physiological and pathological functions of T-type calcium channels, are being uncovered. In this review, we provide an overview of structural determinants in T-type calcium channels, their involvement in disorders and diseases, the development of novel channel modulators, as well as Structure-Activity Relationship (SAR) studies that lead to rational drug design.

Catalytic asymmetric de novo construction of dihydroquinazolinone scaffolds via enantioselective decarboxylative [4+2] cycloadditions

The first de novo construction of enantioenriched dihydroquinazolinones via an intermolecular strategy has been established. This approach also represents the first catalytic asymmetric [4+2] cycloaddition of vinyl benzoxazinanones with sulfonyl isocyanates.

Hydrophobically directed, catalyst-free, multi-component synthesis of functionalized 3,4-dihydroquinazolin-2(1H)-ones

A one-pot three-component reaction of o-formyl carbamate, a primary amine, a nucleophile (1H-indole or 2-napthol) in water generated a variety of functionalised 3,4-dihydroquinazolin-2(1H)-one derivatives.

A microwave-assisted multicomponent synthesis of substituted 3,4-dihydroquinazolinones

A series of structurally diverse 3,4-dihydroquinazolinones was synthesized via a novel cascade imine/cyclization/aza-Henry reaction in moderate to excellent yields.

Palladium-catalyzed direct addition of arylboronic acids to 2-aminobenzonitrile derivatives: synthesis, biological evaluation and in silico analysis of 2-aminobenzophenones, 7-benzoyl-2-oxoindolines, and 7-benzoylindoles

A palladium-catalyzed direct addition of arylboronic acids to unprotected 2-aminobenzonitriles has been developed, leading to a wide range of 2-aminobenzophenones with moderate to excellent yields. The transformation has broad scope and high functional group tolerance. Moreover, 2-oxoindoline-7-carbonitrile and indole-7-carbonitrile were applicable to this process for the construction of 7-benzoyl-2-oxoindolines and 7-benzoylindoles, respectively. Among the compounds examined, compound 4e possessed the most potent anticancer activity against H446 and HGC-27 in vitro, with IC50 values of 0.02 μmol L(-1) and 0.09 μmol L(-1), respectively, while compound 4a showed the best potent anticancer activity against SGC-7901 with an IC50 value of 0.01 μmol L(-1). Furthermore, we also performed in silico molecular docking calculations to investigate the interaction mode and binding affinity between the examined compounds and their tubulin target.

Modification of triclosan scaffold in search of improved inhibitors for enoyl-acyl carrier protein (ACP) reductase in Toxoplasma gondii

Through our focused effort to discover new and effective agents against toxoplasmosis, a structure-based drug design approach was used to develop a series of potent inhibitors of the enoyl-acyl carrier protein (ACP) reductase (ENR) enzyme in Toxoplasma gondii (TgENR). Modifications to positions 5 and 4' of the well-known ENR inhibitor triclosan afforded a series of 29 new analogues. Among the resulting compounds, many showed high potency and improved physicochemical properties in comparison with the lead. The most potent compounds 16 a and 16 c have IC50 values of 250 nM against Toxoplasma gondii tachyzoites without apparent toxicity to the host cells. Their IC50 values against recombinant TgENR were found to be 43 and 26 nM, respectively. Additionally, 11 other analogues in this series had IC50 values ranging from 17 to 130 nM in the enzyme-based assay. With respect to their excellent in vitro activity as well as improved drug-like properties, the lead compounds 16 a and 16 c are deemed to be excellent starting points for the development of new medicines to effectively treat Toxoplasma gondii infections.

Pyridyl amides as potent inhibitors of T-type calcium channels

A novel series of amide T-type calcium channel antagonists were prepared and evaluated using in vitro and in vivo assays. Optimization of the screening hit 3 led to identification of the potent and selective T-type antagonist 37 that displayed in vivo efficacy in rodent models of epilepsy and sleep.

Short-acting T-type calcium channel antagonists significantly modify sleep architecture in rodents

A novel phenyl acetamide series of short-acting T-type calcium channel antagonists has been identified and evaluated using in vitro and in vivo assays. Heterocycle substitutions of the 4-position of the phenyl acetamides afforded potent and selective antagonists that exhibited desired short plasma half-lives across preclinical species. Lead compound TTA-A8 emerged as a compound with excellent in vivo efficacy as indicated by its significant modulation of rat sleep architecture in an EEG telemetry model, favorable pharmacokinetic properties, and excellent preclinical safety. TTA-A8 recently progressed into human clinical trials, and in line with our predictions, preliminary studies (n = 12) with a 20 mg oral dose afforded a high C max of 1.82 ± 0.274 μM with an apparent terminal half-life of 3.0 ± 1.1 h.

T-type calcium channel antagonism produces antipsychotic-like effects and reduces stimulant-induced glutamate release in the nucleus accumbens of rats

T-type calcium channels are important in burst firing and expressed in brain regions implicated in schizophrenia. Therefore, we examined the effects of novel selective T-type calcium channel antagonists in preclinical assays predictive of antipsychotic-like activity. TTA-A2 blocked the psychostimulant effects of amphetamine and MK-801 and decreased conditioned avoidance responding. These effects appeared mechanism based, rather than compound specific, as two structurally dissimilar T-type antagonists also reduced amphetamine-induced psychomotor activity. Importantly, the ability to reduce amphetamine's effects was maintained following 20 days pre-treatment with TTA-A2. To explore the neural substrates mediating the observed behavioral effects, we examined the influence of TTA-A2 on amphetamine-induced c-fos expression as well as basal and stimulant-evoked dopamine and glutamate release in the nucleus accumbens. TTA-A2 decreased amphetamine-induced c-fos expression as well as MK-801-induced, but not basal, glutamate levels in the nucleus accumbens. Basal, amphetamine- and MK-801-induced dopamine efflux was altered. These findings suggest that T-type calcium channel antagonism could represent a novel mechanism for treating schizophrenia.

T-type calcium channels inhibitors: a patent review

IMPORTANCE OF THE FIELD

T-type calcium channels are transmembrane proteins that regulate calcium entry in the cell in a voltage-dependent manner. Intracellular calcium levels are the key to many physiological processes, ranging from neuron firing to cardiac pacemaking. Inhibition of T-type calcium channels is heralded as a potential treatment to peripheral and CNS disorders, including hypertension, heart failure, sleep, epilepsy, drug addiction and neuropathic pain.

AREAS COVERED IN THIS REVIEW

A comprehensive summary of patent literature disclosing T-type calcium channels inhibitors is provided.

WHAT THE READER WILL GAIN

In all, 46 patent applications including 15 chemical structure classes are reviewed. Available in vitro, in vivo and clinical results are also discussed.

TAKE HOME MESSAGE

Several selective T-type calcium channels inhibitors with demonstrated in vitro and in vivo effects, including one Phase I clinical candidate, are now available. While future clinical results will be paramount to assess target validity in patients, these novel inhibitors represent excellent tools to further investigate the role of T-type channels in pathophysiological conditions.