Regioselective Synthesis of 4,5-Diaryl-1-methyl-1H-imidazoles Including Highly Cytotoxic Derivatives by Pd-Catalyzed Direct C-5 Arylation of 1-Methyl-1H-imidazole with Aryl Bromides

Ligandless Palladium-Catalyzed Direct C-5 Arylation of Azoles Promoted by Benzoic Acid in Anisole

The palladium-catalyzed direct arylation of azoles with (hetero)aryl halides is nowadays one of the most versatile and efficient procedures for the selective synthesis of heterobiaryls. Although this procedure is, due to its characteristics, also of great interest in the industrial field, the wide use of a reaction medium such as DMF or DMA, two polar aprotic solvents coded as dangerous according to environmental, health, safety (EHS) parameters, strongly limits its actual use. In contrast, the use of aromatic solvents as the reaction medium for direct arylations, although some of them show good EHS values, is poorly reported, probably due to their low solvent power against reagents and their potential involvement in undesired side reactions. In this paper we report an unprecedented selective C-5 arylation procedure involving anisole as an EHS green reaction solvent. In addition, the beneficial role of benzoic acid as an additive was also highlighted, a role that had never been previously described.

Iridium-Catalyzed Direct Amidation of Imidazoles at the C-2 Position with Isocyanates in the Presence of Hydrosilanes Leading to Imidazole-2-Carboxamides

Regioselective coupling reaction of N-substituted imidazoles with isocyanates in the presence of a stoichiometric amount of hydrosilanes catalyzed by Ir4(CO)12 to give imidazole-2-carboxamides is reported. Imidazoles bearing an (O-silyl)carboximidate group at the 2-position appear to be initially formed in the reaction; these are then hydrolyzed to the final products in situ. The addition of the hydrosilane was essential for the catalytic reaction to proceed. Substituents on the imidazole ring had no effect on the reaction, except for certain bulky substituents such as t Bu and Ph groups at the 4-position. Triazoles such as 4-methyl-4H-1,2,4-triazole and 1-methyl-1H-1,2,4-triazole were also applicable to this C–H amidation, and the latter reaction proceeded regioselectively at the carbon atom between the sp3 and sp2 nitrogen atoms of the ring, and not between the two sp2 nitrogen atoms.

Palladium-Catalyzed Dehydrogenative C-2 Alkenylation of 5-Arylimidazoles and Related Azoles with Styrenes

The construction of carbon–carbon bonds by direct involvement of two unactivated carbon–hydrogen bonds, without any directing group, ensures a high atom economy of the entire process. Here, we describe a simple protocol for the Pd(II)/Cu(II)-promoted intermolecular cross-dehydrogenative coupling (CDC) of 5-arylimidazoles, benzimidazoles, benzoxazole and 4,5-diphenylimidazole at their C-2 position with functionalized styrenes. This specific CDC, known as the Fujiwara–Moritani reaction or oxidative Heck coupling, also allowed the C-4 alkenylation of the imidazole nucleus when both 2 and 5 positions were occupied.

Azole-Based Indoleamine 2,3-Dioxygenase 1 (IDO1) Inhibitors

The heme enzyme indoleamine 2,3-dioxygenase 1 (IDO1) plays an essential role in immunity, neuronal function, and aging through catalysis of the rate-limiting step in the kynurenine pathway of tryptophan metabolism. Many IDO1 inhibitors with different chemotypes have been developed, mainly targeted for use in anti-cancer immunotherapy. Lead optimization of direct heme iron-binding inhibitors has proven difficult due to the remarkable selectivity and sensitivity of the heme-ligand interactions. Here, we present experimental data for a set of closely related small azole compounds with more than 4 orders of magnitude differences in their inhibitory activities, ranging from millimolar to nanomolar levels. We investigate and rationalize their activities based on structural data, molecular dynamics simulations, and density functional theory calculations. Our results not only expand the presently known four confirmed chemotypes of sub-micromolar heme binding IDO1 inhibitors by two additional scaffolds but also provide a model to predict the activities of novel scaffolds.

An Updated Review on the Synthesis and Antibacterial Activity of Molecular Hybrids and Conjugates Bearing Imidazole Moiety

The rapid growth of serious infections caused by antibiotic resistant bacteria, especially the nosocomial ESKAPE pathogens, has been acknowledged by Governments and scientists and is one of the world's major health problems. Various strategies have been and are currently investigated and developed to reduce and/or delay the bacterial resistance. One of these strategies regards the design and development of antimicrobial hybrids and conjugates. This unprecedented critical review, in which our continuing interest in the synthesis and evaluation of the bioactivity of imidazole derivatives is testified, aims to summarise and comment on the results obtained from the end of the 1900s until February 2020 in studies conducted by numerous international research groups on the synthesis and evaluation of the antibacterial properties of imidazole-based molecular hybrids and conjugates in which the pharmacophoric constituents of these compounds are directly covalently linked or connected through a linker or spacer. In this review, significant attention was paid to summarise the strategies used to overcome the antibiotic resistance of pathogens whose infections are difficult to treat with conventional antibiotics. However, it does not include literature data on the synthesis and evaluation of the bioactivity of hybrids and conjugates in which an imidazole moiety is fused with a carbo- or heterocyclic subunit.

Synthesis of Benzo[d]imidazo[2,1-b]thiazole-Propenone Conjugates as Cytotoxic and Apoptotic Inducing Agents

BACKGROUND

Cancer can be considered as a disease in which normal cells start behaving badly, multiplying uncontrollably, ignoring signals to stop and accumulating to form a mass that is generally termed as a tumor. Apoptosis or programmed cell death is a physiological process that enables organisms to control their cell numbers in many developmental and physiological settings and to eliminate unwanted cells and it plays essential role in chemotherapy-induced tumor-cell killing. The correct balance between apoptosis and inhibition of apoptosis is important in animal development as well as in tissue homeostasis. The aim of this paper is to introduce the readers about the design strategy and synthesis of effective cytotoxic and apoptotic inducing agents based on benzo[d]imidazo[2,1-b]thiazole scaffold.

METHODS

Benzo[d]imidazo[2,1-b]thiazole-propenone conjugates were synthesized by the condensation of 7- methoxy-2-(aryl)benzo[d]imidazo[2,1-b]thiazol-3-yl)prop-2-yn-1-ones with aryl/hetero aryl amines in ethanol at room temperature. These in turn were obtained from 7-methoxy-2-(aryl)benzo[d]imidazo[2,1-b]thiazole-3- carbaldehydes on treatment with ethynylmagnesium bromide followed by oxidation.

RESULTS

3-Arylaminopropenone linked 2-arylbenzo[d]imidazo[2,1-b]thiazole conjugates prepared in this investigation exhibited significant cytotoxic activity and arrested HeLa cancer cells in G1 phase. The treatment of the conjugate led to 40% of loss of mitochondrial membrane potential (DΨm) in HeLa cells and 4 fold increase in the levels of reactive oxygen species (ROS). In addition, it induces apoptosis in HeLa cells, this was examined by the wound healing assay, Actin filaments and Hoechst staining assay.

CONCLUSION

The encouraging biological profile exhibited by these 3-arylaminopropenone 2-aryl linked benzo[d]imidazo[2,1-b]thiazole conjugates demonstrate that they have the potential to be developed as a lead by further structural modifications to obtain potential chemotherapeutic agents that are likely to target the HeLa cancer cells.

Current Advances in the Synthesis and Biological Evaluation of Pharmacologically Relevant 1,2,4,5-Tetrasubstituted-1H-Imidazole Derivatives

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In recent years, the synthesis and evaluation of the biological properties of 1,2,4,5-tetrasubstituted-1H-imidazole derivatives have been the subject of a large number of studies by academia and industry. In these studies it has been shown that this large and highly differentiated class of heteroarene derivatives includes high valuable compounds having important biological and pharmacological properties such as antibacterial, antifungal, anthelmintic, anti-inflammatory, anticancer, antiviral, antihypertensive, cholesterol-lowering, antifibrotic, antiuricemic, antidiabetic, antileishmanial and antiulcer activities.

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The present review with 411 references, in which we focused on the literature data published mainly from 2011 to 2017, aims to update the readers on the recent developments on the synthesis and biological evaluation of pharmacologically relevant 1,2,4,5-tetrasubstituted-1H-imidazole derivatives with an emphasis on their different molecular targets and their potential use as drugs to treat various types of diseases. Reference was also made to substantial literature data acquired before 2011 in this burgeoning research area.

Pharmacological tools based on imidazole scaffold proved the utility of PDE10A inhibitors for Parkinson's disease

AIM

Since neuroinflammation is partially mediated by cAMP levels and PDE10A enzyme is able to regulate these levels being highly expressed in striatum, its inhibitors emerged as useful drugs to mitigate this inflammatory process and hence the neuronal death associated with Parkinson's disease (PD). Methodology & results: To study the utility of PDE10A as a pharmacological target for PD, in this work we propose the search and development of new PDE10A inhibitors that could be useful as pharmacological tools in models of the disease and presumably as potential drug candidates. By using different medicinal chemistry approaches we have discovered imidazole-like PDE10A inhibitors and showed their neuroprotective actions.

CONCLUSION

Here, we demonstrate the neuroprotective effect of PDE10A inhibitors in cellular models of PD. [Formula: see text].

An atom-efficient and convergent approach to the preparation of NS5A inhibitors by C-H activation

A novel approach of the convergent functionalisation of aryl dibromides to form NS5A type inhibitors using C-H activation is reported. The focus of investigation was to reduce the formation of homodimeric side product, as well as to investigate the scope of different aryl dibromides that were tolerated under the reaction conditions. The C-H activation methodology was found to give a viable synthetic route to NS5A inhibitors, with late stage functionalisation of the core portion of the molecule, albeit with some chemical functionalities not tolerated.

Computational Methods to Predict the Regioselectivity of Electrophilic Aromatic Substitution Reactions of Heteroaromatic Systems

The validity of calculated NMR shifts to predict the outcome of electrophilic aromatic substitution reactions on different heterocyclic compounds has been examined. Based on an analysis of >130 literature examples, it was found that the lowest predicted (13)C and/or (1)H chemical shift of a heterocycle correlates qualitatively with the regiochemical outcome of halogenation reactions in >80% of the investigated cases. In the remaining cases, the site of electrophilic aromatic substitution can be explained by the calculated HOMO orbitals obtained using density functional theory. Using a combination of these two methods, the accuracy increases to >95%.

Regioselectivity in palladium-catalysed direct arylation of 5-membered ring heteroaromatics

In the past few years, several results using modified catalysts and new reaction conditions have been reported permitting better control of the regioselectivity of Pd-catalysed arylations.

Synthesis and Optical Properties of Imidazole- and Benzimidazole-Based Fused π-Conjugated Compounds: Influence of Substituent, Counteranion, and π-Conjugated System

Fused π-conjugated imidazolium chlorides having hydrogen (1-Cl), octyloxy (2-Cl), N,N-dibutylamino (3-Cl), trifluoromethyl (4-Cl), and cyano (5-Cl) groups substituted on the benzene ring at the 2-position of imidazole were prepared. Counteranion exchanges from chloride to bis(trifluoromethanesulfonyl)imidate (2-TFSI) and tetrafluoroborate (2-BF4) were performed. The optical properties of these compounds (absorption and emission wavelengths, fluorescence quantum yield, and solvatochromism) were influenced by both the substituent and anion character, which was investigated by theoretical calculations using the density functional theory (DFT) and symmetry-adapted cluster-configuration interaction (SAC-CI) methods. Fused π-conjugated benzimidazolium chlorides having N,N-dibutylamino (6-Cl) and cyano (7-Cl) groups were also prepared to observe the different solvatochromic shifts.

Development of a regioselective N-methylation of (benz)imidazoles providing the more sterically hindered isomer

An efficient and highly regioselective N-methylation of (NH)-(benz)imidazoles furnishing the sterically more hindered, less stable, and usually minor regioisomer has been developed. The methodology involves very mild reaction conditions and tolerates a wide range of functional groups.

Solvent-free palladium-catalyzed direct arylation of heteroaromatics with aryl bromides

Solvent is one of the major sources of waste in the course of catalyzed direct arylations. Some palladium-catalyzed direct arylations of heteroaromatics can be advantageously performed without any solvent. In the presence of palladium catalysts (1 mol %) and potassium acetate as the base, the direct 5-arylation of some thiazoles, thiophenes, furans, or pyrroles with aryl bromides as coupling partners proceeds highly regioselectively and in moderate to high yields. However, the use of these solvent-free conditions is limited to electron-deficient aryl bromides.