Design of Potent, Orally Available Antagonists of the Transient Receptor Potential Vanilloid 1. Structure−Activity Relationships of 2-Piperazin-1-yl-1H-benzimidazoles

NaI-Mediated Electrochemical Cyclization-Desulfurization for the Synthesis of N-Substituted 2-Aminobenzimidazoles

An electrochemical method for the synthesis of N-substituted 2-aminobenzimidazoles through a NaI-mediated desulfurization-cyclization process is reported. This electrosynthesis method utilizes cost-effective NaI as both a mediator and an electrolyte in a catalytic amount (0.2 equiv), replacing traditional oxidizing reagents. N-Substituted o-phenylenediamines and isothiocyanates undergo a thiourea formation/cyclization/desulfurization process to provide N-substituted 2-aminobenzimidazoles (55 examples, up to 98% yield) in a single reaction vessel. Importantly, this electrochemical methodology is applicable to gram-scale synthesis, maintaining reaction efficiency.

In vitro and in silico antibacterial evaluation of coumarin derivatives against MDR strains of Staphylococcus aureus and Escherichia coli

The increase in antibiotic resistance rates has attracted the interest of researchers for antibacterial compounds capable of potentiating the activity of conventional antibiotics. Coumarin derivatives have been reported to develop effective antibacterials with possible new mechanisms of action for treating infectious diseases caused by bacteria with a profile of drug resistance. In this context, the aim of the present study we have now prepared one variety of new synthetic coumarins evaluating the pharmacokinetic and chemical similarity in silico, their antimicrobial activity against Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922), and potential for the modulation of antibiotic resistance against Staphylococcus aureus (SA10) and Escherichia coli (EC06) clinical isolate bacteria by in vitro assay. The antibacterial activity and antibiotic-enhancing properties were evaluated by the broth microdilution method and pharmacokinetically characterized according to the Lipinsk rule of 5 and had their similarity analyzed in databases such as ChemBL and CAS SciFinder. The results demonstrated that only compound C13 showed significant antibacterial activity (MIC ≤256 μg/mL), and all other coumarins did not display relevant antibacterial activity (MIC ≥1024 μg/mL). However, they did modulate the antibiotics activities to norfloxacin and gentamicin, except, compound C11 to norfloxacin against Staphylococcus aureus (SA10). The in silico properties prediction and drug-likeness results demonstrated that all coumarins presented a good drug-likeness score with no violations and promising in silico pharmacokinetic profiles showing that they have the potential to be developed into an oral drug. The results indicate that the coumarin derivatives showed good in vitro antibacterial activity. These new coumarin derivatives also demonstrated the capacity to modulate antibiotic resistance with potential synergy action for current antimicrobials assayed, as antibiotic adjuvants, to reduce the emergence of antimicrobial resistance.

Trifluoromethyl Vinamidinium Salt as a Promising Precursor for Fused β-Trifluoromethyl Pyridines

An efficient chlorotrimethylsilane-promoted synthetic protocol for the preparation of functionalized fused β-trifluoromethyl pyridines by cyclization of electron-rich aminoheterocycles or substituted anilines with a trifluoromethyl vinamidinium salt was developed. The efficient and scalable approach for producing represented trifluoromethyl vinamidinium salt demonstrated huge prospects for further use. The structure specificities of the trifluoromethyl vinamidinium salt and their impact on the reaction progress were determined. The procedure's scope and alternative ways of the reaction were investigated. The possibility of increasing the reaction scale up to 50 g and further modification of obtained products was shown. A minilibrary of potential fragments for ¹⁹F NMR-based fragment-based drug discovery (FBDD) was synthesized.

Novel piperazine urea derivatives as highly potent transient receptor potential vanilloid 1 (TRPV1) antagonists

Transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel with high permeability to Ca²⁺, which can be activated by low pH, noxious heat and vanilloid compounds such as capsaicin. TRPV1 has been proved to be very important in the process of pain production and is considered to be a highly effective analgesic target. In this work, three series of new piperazine urea TRPV1 antagonists were designed, synthesized and evaluated based on classical TRPV1 antagonists BCTC and GRT12360. Among them, N-(4,6-dimethylpyridin-2-yl)-4-(2-(pyrrolidin-1-yl)benzyl)piperazine-1-carboxamide (5ac) was finally identified, which had excellent TRPV1 antagonistic activity (IC₅₀ (CAP) = 9.80 nM), good bioavailability and did not cause side effects of hyperthermia. In the study of molecular docking, the compound 5ac fitted well with the amino acid residues on rTRPV1 through hydrophobic interaction. Collectively, compound 5ac is an efficient TRPV1 antagonist and can be used as a candidate for the development of analgesic drugs.

Structure-Activity Relationship Analysis of Benzimidazoles as Emerging Anti-Inflammatory Agents: An Overview

A significant number of the anti-inflammatory drugs currently in use are becoming obsolete. These are exceptionally hazardous for long-term use because of their possible unfavourable impacts. Subsequently, in the ebb-and-flow decade, analysts and researchers are engaged in developing new anti-inflammatory drugs, and many such agents are in the later phases of clinical trials. Molecules with heterocyclic nuclei are similar to various natural antecedents, thus acquiring immense consideration from scientific experts and researchers. The arguably most adaptable heterocyclic cores are benzimidazoles containing nitrogen in a bicyclic scaffold. Numerous benzimidazole drugs are broadly used in the treatment of numerous diseases, showing promising therapeutic potential. Benzimidazole derivatives exert anti-inflammatory effects mainly by interacting with transient receptor potential vanilloid-1, cannabinoid receptors, bradykinin receptors, specific cytokines, 5-lipoxygenase activating protein and cyclooxygenase. Literature on structure–activity relationship (SAR) and investigations of benzimidazoles highlight that the substituent’s tendency and position on the benzimidazole ring significantly contribute to the anti-inflammatory activity. Reported SAR analyses indicate that substitution at the N1, C2, C5 and C6 positions of the benzimidazole scaffold greatly influence the anti-inflammatory activity. For example, benzimidazole substituted with anacardic acid on C2 inhibits COX-2, and 5-carboxamide or sulfamoyl or sulfonyl benzimidazole antagonises the cannabinoid receptor, whereas the C2 diarylamine and C3 carboxamide substitution of the benzimidazole scaffold result in antagonism of the bradykinin receptor. In this review, we examine the insights regarding the SARs of anti-inflammatory benzimidazole compounds, which will be helpful for researchers in designing and developing potential anti-inflammatory drugs to target inflammation-promoting enzymes.

Methods to Access 2-aminobenzimidazoles of Medicinal Importance

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Benzimidazole (BI) and derivatives are interesting because several of these compounds have been found to have a diversity of biological activities with clinical applications. In view of their importance, the synthesis of BI and its derivatives is still considered as a challenge for synthetic chemists. Examples of compounds used in medicinal chemistry containing BI, as important nucleus, are Astemizole (antihistaminic), Omeprazole (antiulcerative) and Rabendazole (fungicide), some of these compounds have the 2- aminobenzimidazole (2ABI) as base nucleus. The structure of 2ABI derivatives contains a cyclic guanidine moiety, which is interesting because of its free lone pairs, labile hydrogen atoms and planar delocalized structure. The delocalized 10-π electron system and the extension of the electron conjugation with the exocyclic amino group, in 2ABI, making these heterocycles to have amphoteric character. The 2ABI has been used as building blocks for the synthesis of several BI derivatives as medicinally important molecules. On these bases, herein, we present a bibliographic review concerning the recent methodologies used in the synthesis of 2ABIs, including the substituted ones.

Copper-catalysed C-H functionalisation gives access to 2-aminobenzimidazoles

This paper describes the development, optimisation and exemplification of a copper-catalysed C-H functionalisation to form pharmaceutically relevant 2-aminobenzimidazoles from aryl-guanidines. High throughput screening was used as a tool to identify a catalytically active copper source, DoE was used for reaction optimisation and a range of aryl-guanidines were prepared and exposed to the optimum conditions to afford a range of 2-aminobenzimidazoles in moderate to good yields. The methodology has been applied to the synthesis of Emedastine, a marketed anti-histamine pharmaceutical compound, with the key cyclisation step performed on a gram-scale.

Design and Synthesis of Poly(ADP-ribose) Polymerase Inhibitors: Impact of Adenosine Pocket-Binding Motif Appendage to the 3-Oxo-2,3-dihydrobenzofuran-7-carboxamide on Potency and Selectivity

Poly(adenosine 5'-diphosphate-ribose) polymerase (PARP) inhibitors are a class of anticancer drugs that block the catalytic activity of PARP proteins. Optimization of our lead compound 1 (( Z)-2-benzylidene-3-oxo-2,3-dihydrobenzofuran-7-carboxamide; PARP-1 IC50 = 434 nM) led to a tetrazolyl analogue (51, IC50 = 35 nM) with improved inhibition. Isosteric replacement of the tetrazole ring with a carboxyl group (60, IC50 = 68 nM) gave a promising new lead, which was subsequently optimized to obtain analogues with potent PARP-1 IC50 values (4-197 nM). PARP enzyme profiling revealed that the majority of compounds are selective toward PARP-2 with IC50 values comparable to clinical inhibitors. X-ray crystal structures of the key inhibitors bound to PARP-1 illustrated the mode of interaction with analogue appendages extending toward the PARP-1 adenosine-binding pocket. Compound 81, an isoform-selective PARP-1/-2 (IC50 = 30 nM/2 nM) inhibitor, demonstrated selective cytotoxic effect toward breast cancer gene 1 ( BRCA1)-deficient cells compared to isogenic BRCA1-proficient cells.

Copper-catalyzed synthesis of 2-aminophenyl benzothiazoles: a novel approach

Substituted 2-aminophenyl benzothiazoles have been constructed from thiourea via copper-catalyzed desulfurization/nucleophilic substitution followed by domino intra- and intermolecular C–N cross-coupling reactions under moderate reaction conditions.

General Procedures for the Lithiation/Trapping of N-Boc Piperazines

To provide α-substituted piperazines for early stage medicinal chemistry studies, a simple, general synthetic approach is required. Here, we report the development of two general and simple procedures for the racemic lithiation/trapping of N-Boc piperazines. Optimum lithiation times were determined using in situ IR spectroscopy, and the previous complicated and diverse literature procedures were simplified. Subsequent trapping with electrophiles delivered a wide range of α-functionalized N-Boc piperazines. The scope and limitations of the distal N-group were investigated. The selective α- and β- arylation of N-Boc piperazines via lithiation/Negishi coupling is reported.

TRPV1 antagonism by piperazinyl-aryl compounds: A Topomer-CoMFA study and its use in virtual screening for identification of novel antagonists

Transient Receptor Potential Vanilloid, member 1 (TRPV1), is a non-selective cation channel belonging to the transient receptor potential (TRP) family of ion channels. It occurs in the peripheral and central nervous system, activated by a variety of exogenous and endogenous stimuli, thus playing a key role in transmission of pain. This has been a target for chronic pain since more than a decade and a number of antagonists that progressed into clinical trials have failed due to the unexpected side effect of core body temperature rise, thus halting progress in this field. Of late, there has been an upsurge in research on this target, with the rat TRPV1 structure being determined, many new antagonists discovered that are temperature-neutral and many new therapeutic avenues being discovered for TRPV1, including diseases of respiratory and digestive systems, skin and bladder. Towards identifying diverse compounds to decipher the role of this target in various indications, here we report a 3D-QSAR model built using the new topomer-CoMFA methodology on a series of piperazinyl-aryl TRPV1 antagonists and the use of this model, along with a pharmacophore model and the shape of one of the potent compounds of this series, to virtually screen a subset of the ZINC database to find novel and diverse hits. These can serve as starting points to develop modality-selective antagonists for chronic pain and to elucidate the critical role of TRPV1 in the various new therapeutic areas.

Probing the molecular and structural elements of ligands binding to the active site versus an allosteric pocket of the human farnesyl pyrophosphate synthase

In order to explore the interactions of bisphosphonate ligands with the active site and an allosteric pocket of the human farnesyl pyrophosphate synthase (hFPPS), substituted indole and azabenzimidazole bisphosphonates were designed as chameleon ligands. NMR and crystallographic studies revealed that these compounds can occupy both sub-pockets of the active site cavity, as well as the allosteric pocket of hFPPS in the presence of the enzyme's Mg(2+) ion cofactor. These results are consistent with the previously proposed hypothesis that the allosteric pocket of hFPPS, located near the active site, plays a feed-back regulatory role for this enzyme.

TRPV1: A Potential Drug Target for Treating Various Diseases

Transient receptor potential vanilloid 1 (TRPV1) is an ion channel present on sensory neurons which is activated by heat, protons, capsaicin and a variety of endogenous lipids termed endovanilloids. As such, TRPV1 serves as a multimodal sensor of noxious stimuli which could trigger counteractive measures to avoid pain and injury. Activation of TRPV1 has been linked to chronic inflammatory pain conditions and peripheral neuropathy, as observed in diabetes. Expression of TRPV1 is also observed in non-neuronal sites such as the epithelium of bladder and lungs and in hair cells of the cochlea. At these sites, activation of TRPV1 has been implicated in the pathophysiology of diseases such as cystitis, asthma and hearing loss. Therefore, drugs which could modulate TRPV1 channel activity could be useful for the treatment of conditions ranging from chronic pain to hearing loss. This review describes the roles of TRPV1 in the normal physiology and pathophysiology of selected organs of the body and highlights how drugs targeting this channel could be important clinically.

Regioselective piperidine-catalyzed tandem imination-isocyanate annulation to fused tricyclic triazines

A novel tandem imination-isocyanate-mediated annulation was explored. Ionic liquid-immobilized 2-aminobenzimidazoles react sequentially with aldehydes and isocyanates to give highly functionalized benzimidazole-embedded triazines. The second-stage transformation revealed that the formation of triazinone functionality is entirely regioselective to allow rapid assembly of biologically interesting tricyclic skeletons. In conjunction with the application of microwave irradiation and IL support, this method provides an efficient route to access substituted benzoimidazotriazines.

Benzimidazole: an emerging scaffold for analgesic and anti-inflammatory agents

Within the vast range of heterocycles, benzimidazole and its derivatives are found to be trendy structures employed for discovery of drugs in the field of pharmaceutical and medicinal chemistry. The unique structural features of benzimidazole and a wide range of biological activities of its derivatives made it privileged structure in drug discovery. Recently, benzimidazole scaffold has emerged as a pharmacophore of choice for designing analgesic and anti-inflammatory agents active on different clinically approved targets. To pave the way for future research, there is a need to collect the latest information in this promising area. In the present review we have collated published reports on this versatile core to provide an insight so that its full therapeutic potential can be utilized for the treatment of pain and inflammation.

2-Phenylamino-6-cyano-1H-benzimidazole-based isoform selective casein kinase 1 gamma (CK1γ) inhibitors

Screening of the Amgen compound library led to the identification of 2-phenylamino-6-cyano-1H-benzimidazole 1a as a potent CK1 gamma inhibitor with excellent kinase selectivity and unprecedented CK1 isoform selectivity. Further structure-based optimization of this series resulted in the discovery of 1h which possessed good enzymatic and cellular potency, excellent CK1 isoform and kinase selectivity, and acceptable pharmacokinetic properties.

Activators of P-glycoprotein: Structure-activity relationships and investigation of their mode of action

P-glycoprotein (P-gp), a 170 kDa plasma membrane protein, is one of the most relevant ABC transporters involved in the development of multidrug resistance (MDR). Understanding its mechanism of transport as well as its interactions with various substrates are basic requirements for the development of adequate therapeutic approaches to overcome this kind of resistance against a broad spectrum of structurally unrelated cytostatic drugs. P-gp modulators (activators) that exert various effects on the intracellular accumulation of distinct P-gp substrates are useful tools for investigating the interactions between multiple drug binding sites of this transport protein. In this study, a series of 27 different imidazobenzothiazoles and imidazobenzimidazoles structurally related to the known P-gp activators QB102 and QB11 was designed, and their modulating properties were investigated. Most of them were able to stimulate P-gp-mediated efflux of daunorubicin and rhodamine 123 in a concentration-dependent manner, but some compounds also displayed weak inhibitory effects. Additionally, P-gp-mediated efflux of vinblastine and colchicine was inhibited by several compounds. Therefore, we concluded that the novel compounds bind to the H site of P-gp and activate the efflux of specific substrates of the R site in a positive cooperative manner, whereas binding of H-type substrates is inhibited competitively. This hypothesis is confirmed by the observation that the modulators do not influence hydrolysis of ATP or its affinity toward P-gp.

CuI-catalyzed amination of arylhalides with guanidines or amidines: a facile synthesis of 1-H-2-substituted benzimidazoles

CuI/L5 (N,N'-dimethylethylenediamine) proves to be an efficient catalyst system for the amination of arylhalides with guanidines. The same catalyst system is then successfully applied to the one-step synthesis of 1-H-2-amino-benzimidazoles through tandem aminations of 1,2-dihaloarenes in modest yields. This methodology is also applicable for the preparation of 1-H or 1-substutituted 2-aryl- or 2-alkyl-benzimidazoles.

Spiro-piperidine azetidinones as potent TRPV1 antagonists

A series of spiro-piperidine azetidinone were synthesized and evaluated as potential TRPV1 antagonists. An important issue of plasma stability was investigated and resolved. Further focused SAR study lead to the discovery of a potent antagonist with good oral pharmacokinetic profile in rat.