Diversity-oriented synthesis of fused-imidazole derivatives via Groebke–Blackburn–Bienayme reaction: a review

Imidazo[1,2-a]pyrimidine as a New Antileishmanial Pharmacophore against Leishmania amazonensis Promastigotes and Amastigotes

Leishmania poses a substantial threat to the human population all over the globe because of its visceral and cutaneous spread engendered by all 20 species. Unfortunately, the available drugs against leishmania are already hobbled with toxicity, prolonged treatment, and increasing instances of acquirement of resistance. Under these grave circumstances, the development of new drugs has become imperative to keep these harmful microbes at bay. To this end, a Groebke-Blackburn-Bienaymé multicomponent reaction-based library of different imidazo-fused heterocycles has been synthesized and screened against Leishmania amazonensis promastigotes and amastigotes. Among the library compounds, the imidazo-pyrimidine 24 has been found to be the most effective (inhibitory concentration of 50% (IC50) < 10 μM), with selective antileishmanial activity on amastigote forms, a stage of the parasite related to human disease. The compound 24 has exhibited an IC50 value of 6.63 μM, being ∼two times more active than miltefosine, a reference drug. Furthermore, this compound is >10 times more destructive to the intracellular parasites than host cells. The observed in vitro antileishmanial activity along with suitable in silico physicochemical and absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties of compound 24 reinforce the imidazo-pyrimidine scaffold as a new antileishmanial pharmacophore and encourage further murine experimental leishmaniasis studies.

Metal catalyst-free N-allylation/alkylation of imidazole and benzimidazole with Morita-Baylis-Hillman (MBH) alcohols and acetates

A highly α-regioselective N-nucleophilic allylic substitution of cyclic MBH alcohols and acetates with imidazole or benzimidazole, in toluene at reflux with an azeotropic distillation, was successfully carried out with no catalysts or additives, affording the corresponding N-substituted imidazole derivatives in good yields. On the other hand, in refluxing toluene or methanol, the aza-Michael addition of imidazole onto acyclic MBH alcohols was performed using DABCO as an additive, leading to the corresponding 1,4-adducts in 70-84% yields.

The Discovery of Novel Antimicrobial Agents through the Application of Isocyanide-Based Multicomponent Reactions

Multicomponent reactions (MCR) have been used to synthesize a wide range of analogs from several classes of heterocyclic compounds, with multifaceted medicinal uses. The synthesis of highly functionalized molecules in a single pot is a unique property of MCR, allowing researchers to quickly assemble libraries of compounds of biological interest and uncover novel leads as possible therapeutic agents. Isocyanide-based multicomponent reactions have proven to be extremely effective at swiftly specifying members of compound libraries, particularly in the discovery of drugs. The understanding of structure-activity correlations that drive the development of new goods and technology requires structural variety in these libraries. In today's world, antibiotic resistance is a major ongoing problem that poses risks to public health. The implementation of isocyanide-based multicomponent reactions upholds a significant potential in this regard. By utilizing such reactions, new antimicrobial compounds can be discovered and subsequently used to fight against such concerns. This study discusses the recent developments in antimicrobial medication discovery using isocyanide-based multicomponent reactions (IMCRs). Furthermore, the article emphasizes the potential of IMCRs (Isocyanide-based multicomponent based reactions) in the near future.

Isocyanide-Based Multicomponent Reactions Promoted by Visible Light Photoredox Catalysis

Isocyanide-based multicomponent reactions claim a one century-old history of flourishing developments. On the other hand, the enormous impact of recent progresses in visible light photocatalysis has boosted the identification of new straightforward and green approaches to both new and known chemical entities. In this context, the application of visible light photocatalytic conditions to multicomponent processes has been promoting key stimulating advancements. Spanning from radical-polar crossover pathways, to photoinduced and self-catalyzed transformations, to reactions involving the generation of imidoyl radical species, the present literature analysis would provide a general and critical overview about the potentialities and challenges of exploiting isocyanides in visible light photocatalytic multicomponent reactions.

Construction of Covalent Organic Frameworks via Multicomponent Reactions

Multicomponent reactions (MCRs) combine at least three reactants to afford the desired product in a highly atom-economic way and are therefore viewed as efficient one-pot combinatorial synthesis tools allowing one to significantly boost molecular complexity and diversity. Nowadays, MCRs are no longer confined to organic synthesis and have found applications in materials chemistry. In particular, MCRs can be used to prepare covalent organic frameworks (COFs), which are crystalline porous materials assembled from organic monomers and exhibit a broad range of properties and applications. This synthetic approach retains the advantages of small-molecule MCRs, not only strengthening the skeletal robustness of COFs, but also providing additional driving forces for their crystallization, and has been used to prepare a series of robust COFs with diverse applications. The present perspective article provides the general background for MCRs, discusses the types of MCRs employed for COF synthesis to date, and addresses the related critical challenges and future perspectives to inspire the MCR-based design of new robust COFs and promote further progress in this emerging field.

Synthesis of Tunable Fluorescent Imidazole-Fused Heterocycle Dimers

A short, concise, and one-pot synthesis of imidazo-fused heterocycle dimers with tunable fluorescent properties has been developed. By the first time use of glyoxal dimethyl acetal in the Groebke–Blackburn–Bienaymé (GBB) three-component reaction (3CR), the innovation features a new series of fluorescence-tunable imidazo-fused heterocycle dimers exhibiting a broad substrate scope with good yields. Luminescence studies demonstrate that these GBB-dimers possess color-tunable properties, and their emission colors can be successively changed from blue to green and yellow by easy substituent control.

Fluorescent annulated imidazo[4,5-c]isoquinolines via a GBB-3CR/imidoylation sequence - DNA-interactions in pUC-19 gel electrophoresis mobility shift assay

Herein we report the development of a sequential synthesis route towards annulated imidazo[4,5-c]isoquinolines comprising a GBB-3CR, followed by an intramolecular imidoylative cyclisation. X-Ray crystallography revealed a flat 3D structure of the obtained polyheterocycles. Thus, we evaluated their interactions with double-stranded DNA by establishing a pUC-19 plasmid-based gel electrophoresis mobility shift assay, revealing a stabilising effect on ds-DNA against strand-break inducing conditions.

Selective C3-nitrosation of imidazopyridines using AgNO3 as the NO source

We developed a novel method for selective radical nitrosation of imidazo[1, 2-a]pyridine derivatives using AgNO3 as a NO source.

Diversity-Oriented Synthesis of [2.2]Paracyclophane-derived Fused Imidazo[1,2-a]heterocycles by Groebke-Blackburn-Bienaymé Reaction: Accessing Cyclophanyl Imidazole Ligands Library

This report describes the synthesis of a [2.2]paracyclophane‐derived annulated 3‐amino‐imidazole ligand library through a Groebke‐Blackburn‐Bienaymé three‐component reaction (GBB‐3CR) approach employing formyl‐cyclophanes in combination with diverse aliphatic and aromatic isocyanides and heteroaromatic amidines. The GBB‐3CR process gives access to skeletally‐diverse cyclophanyl imidazole ligands, namely 3‐amino‐imidazo[1,2‐a]pyridines and imidazo[1,2‐a]pyrazines. Additionally, a one‐pot protocol for the GBB‐3CR by an in situ generation of cyclophanyl isocyanide is demonstrated. The products were analyzed by detailed spectroscopic techniques, and the cyclophanyl imidazo[1,2‐a]pyridine was confirmed unambiguously by single‐crystal X‐Ray crystallography. The cyclophanyl imidazole ligands can be readily transformed to showcase their useful utility in preparing N,C‐palladacycles through regioselective ortho‐palladation.

Anti-tumor compounds identification from gossypol Groebke imidazopyridine product

Series of imidazo[1,2-a]pyridines designed from gossypol modification based on Groebke-Blackburn-Bienaymé reaction were discovered as potent Bcl-2 inhibitors. Compound 4 was found to display good anti-proliferative activities for 7 human cancer cell lines (0.33-1.7 µM) among them, which were better than separate gossypol and imidazopyridine moiety compounds. It was capable of suppressing antiapoptotic proteins Bcl-2 and Bcl-X_L demonstrated by mechanism studies, and possible binding model was also illustrated by molecular modelling.

α-Aminoazoles/azines: key reaction partners for multicomponent reactions

Aromatic α-aminoazaheterocycles are the focus of significant investigations and exploration by researchers owing to their key role in diverse biological and physiological processes. The existence of their derivatives in numerous drugs and alkaloids is due to their heterocyclic nitrogenous nature. Therefore, the synthesis of a structurally diverse range of their derivatives through simple and convenient methods represents a vital field of synthetic organic chemistry. Multicomponent reactions (MCRs) provide a platform to introduce desirable structure diversity and complexity into a molecule in a single operation with a significant reduction in the use of harmful organic waste, and hence have attracted particular attention as an excellent tool to access these derivatives. This review covers the advances made from 2010 to the beginning of 2020 in terms of the utilization of α-aminoazaheterocycles as synthetic precursors in MCRs.

The Ugi three-component reaction and its variants

A broad variety of α-aminoamide-based compounds have been synthesized via the three-component version of the Ugi reaction (U-3CR) or by any of its variants (Ugi-Zhu-3CR, Orru-3CR, Ugi-4C-3CR, Ugi-Joullié-3CR, GBB-3CR, Ugi-Reissert-3CR, and so on).

The status of isocyanide-based multi-component reactions in Iran (2010-2018)

Isocyanides as key intermediates and magic reactants have been widely applied in organic reactions for direct access to a broad spectrum of remarkable organic compounds. Although the history of these magical compounds dates back more than 100 years, it still has been drawing widespread attention of chemists who confirmed their versatility and effectiveness. Because of their wide spectrum of pharmacological, industrial and synthetic applications, many reactions with the utilization of isocyanides are reported in the literature. In this context, Iranian scientist played a significant role in the growth of isocyanides chemistry. The present review article covers literature from the period starting from 2010 onward and encompasses new synthetic routes and organic transformation involving isocyanides by Iranian researchers. During this period, a diverse range of isocyanide-based multi-component reactions (I-MCRs) has been reported such as a new modification of Ugi, post-Ugi, Passerini and Groebke-Blackburn-Bienayme condensation reactions, isocyanide-based [1 + 4] cycloaddition reactions, isocyanide-acetylene-based MCRs, isocyanide and Meldrum's acid-based MCRs, several unexpected reactions besides green mediums and novel catalytic systems for the synthesis of diverse kinds of pharmaceutically and industrially remarkable heterocyclic and linear organic compounds. This review also emphasizes the neoteric applications of I-MCR for the synthesis of valuable peptide and pseudopeptide scaffolds, enzyme immobilization and functionalization of materials with tailorable properties that can play important roles in the plethora of applications.

First imidazole-fused carbaporphyrinoid and its conversion to a N-heterocyclic carbene precursor

A series of novel imidazole-fused carbaporphyrinoids were obtained by a surprisingly simple approach by exploiting the reaction of tosylmethylisocyanide (TOSMIC) with readily obtainable 2-aza-21-carbaporphyrins. A facile methylation of silver(iii) complexes of these fused systems leads to cationic N-heterocyclic carbene precursors.

La(OTf)3-catalysed one-pot synthesis of pyrazole tethered imidazo[1,2-a]azine derivatives and evaluation of their light emitting properties

La(OTf)₃catalysed one-pot facile protocol has been unfolded towards diversity-oriented synthesis of highly fluorescent pyrazole C-3(5) tethered imidazo[1,2-a]azines.

The Groebke-Blackburn-Bienaymé Reaction

Imidazo[1,2-a]pyridine is a well-known scaffold in many marketed drugs, such as Zolpidem, Minodronic acid, Miroprofen and DS-1 and it also serves as a broadly applied pharmacophore in drug discovery. The scaffold revoked a wave of interest when Groebke, Blackburn and Bienaymé reported independently a new three component reaction resulting in compounds with the imidazo[1,2-a]-heterocycles as a core structure. During the course of two decades the Groebke Blackburn Bienaymé (GBB-3CR) reaction has emerged as a very important multicomponent reaction (MCR), resulting in over a hundred patents and a great number of publications in various fields of interest. Now two compounds derived from GBB-3CR chemistry received FDA approval. To celebrate the first 20 years of GBB-chemistry, we present an overview of the chemistry of the GBB-3CR, including an analysis of each of the three starting material classes, solvents and catalysts. Additionally, a list of patents and their applications and a more in-depth summary of the biological targets that were addressed, including structural biology analysis, is given.

Development of Novel and Efficient Processes for the Synthesis of 5-Amino and 5-Iminoimidazo[1,2-a]imidazoles via Three-Component Reaction Catalyzed by Zirconium(IV) Chloride

General and efficient approaches for the synthesis of new 5-amino and 5-iminoimidazo[1,2-a]imidazoles were developed through a three-component reaction of 1-unsubstituted 2-aminoimidazoles with various aldehydes and isocyanides mediated by zirconium(IV) chloride. The protocols were established considering the reactivity of the starting substrate, which varies depending on the presence of a substituent on the 2-aminoimidazole moiety. A library of new N-fused ring systems with wide structural diversification, novel synthetic, and potential pharmacological interest was obtained in moderate to good yields.

Consecutive multicomponent reactions for the synthesis of complex molecules

Multicomponent reactions (MCRs) involving a minimum of three reactants or reaction centers are conducted in one pot and with a single operational step. This synthetic method has a good pot, atom and step economy in the preparation of diverse and complex molecular scaffolds. Consecutive MCRs, also known as sequential or multiple MCRs, by combining two or more MCRs, exhibit even higher synthetic efficiency, product structural diversity, and molecular complexity. This review article highlights the Ugi, Groebke-Blackburn-Bienaymé, Biginelli, Huisgen, Petasis, Gewald, and Asinger reaction-initiated consecutive MCRs.

Multicomponent Reactions Upon the Known Drug Trimethoprim as a Source of Novel Antimicrobial Agents

Novel antibiotic compounds have been prepared through a selective multicomponent reaction upon the known drug Trimethoprim. The Groebke-Blackburn-Bienaymé reaction involving this α-aminoazine, with a range of aldehydes and isocyanides afforded the desired adducts in one-step. The analogs display meaningful structural features of the initial drug together with relevant modifications at several points, keeping antibiotic potency and showing satisfactory antimicrobial profile (good activity levels and reduced growth rates), especially against methicillin-resistant Staphylococcus aureus. The new products may open new possibilities to fight bacterial infections.

Micellar Brønsted Acid Mediated Synthesis of DNA-Tagged Heterocycles

The translation of well-established molecular biology methods such as genetic coding, selection, and DNA sequencing to combinatorial organic chemistry and compound identification has made extremely large compound collections, termed DNA-encoded libraries, accessible for drug screening. However, the reactivity of the DNA imposes limitations on the choice of chemical methods for encoded library synthesis. For example, strongly acidic reaction conditions must be avoided because they damage the DNA by depurination, i.e. the cleavage of purine bases from the oligomer. Application of micellar catalysis holds much promise for encoded chemistry. Aqueous micellar dispersions enabled compound synthesis under often appealingly mild conditions. Amphiphilic block copolymers covalently functionalized with sulfonic acid moieties in the lipophilic portion assemble in water and locate the Brønsted catalyst in micelles. These acid nanoreactors enabled the reaction of DNA-conjugated aldehydes to diverse substituted tetrahydroquinolines and aminoimidazopyridines by Povarov and Groebke-Blackburn-Bienaymé reactions, respectively, and the cleavage of tBoc protective groups from amines. The polymer micelle design was successfully translated to the Cu/Bipyridine/TEMPO system mediating the oxidation of DNA-coupled alcohols to the corresponding aldehydes. These results suggest a potentially broad applicability of polymer micelles for encoded chemistry.

Synthesis of polyheterocycles via multicomponent reactions

Polyheterocycles are one of the most desired synthetic targets due to their numerous and valuable applications in various fields. Multicomponent reactions (MCRs) are highly convergent one-pot processes, in which three or more reagents are combined sequentially to construct complex products, with almost all the atoms coming from the starting reagents. In this context, the syntheses of 'heterocycles' via MCR-based processes have been reviewed a number of times. However, there is not a single review (recent or otherwise) covering the synthesis of 'polyheterocycles' via a direct MCR or via a one-pot process involving MCRs coupled to further cyclizations (via ionic, metal-catalyzed, pericyclic, or free-radical-mediated cyclizations). This issue is consequently the main topic of the present review, which considers work from the last decade. The work is categorized according to the key processes involved in the syntheses of polyheterocycles, aiming to give readers an easy understanding of this MCR-based chemistry and to provide insights for further investigations. The reaction mechanisms providing novel elements to these MCR-based methods for the synthesis of polyheterocycles are also discussed.

Sulfated Ceria Catalyzed Synthesis of Imidazopyridines and Their Implementation as DNA Minor Groove Binders

The small molecules that bind to DNA minor groove are considered as potential therapeutic agents to fight against many human diseases. They induce cell death by interfering with transcription, replication and progression of cell cycle. Herein, we report the synthesis of imidazopyridine-3-amines using sulfated ceria catalyst by employing Groebkee-Blackburne-Bienayme reaction. We evaluated the possible antiproliferative and antimycobacterial activity against A549 cells and Mycobacterium tuberculosis, respectively. Among the tested compounds, N-tert-butyl-2-(2-butyl-4-chloro-1H-imidazol-5-yl)-5,7-dimethylimidazo[1,2-a]pyridin-3-amine (4g) was identified as cytotoxic heterocycle and antimycobacterial agent. Molecular docking studies of the imidazopyridine derivatives revealed the consistent positioning in the minor groove with a tight shape fit between receptor and ligands. Therefore, we speculate that new imidazopyridines induce their pharmacological effect by targeting the minor groove of DNA.

Aminoazole-Based Diversity-Oriented Synthesis of Heterocycles

The comprehensive review contains the analysis of literature data concerning reactions of heterocyclization of aminoazoles and demonstrates the application of these types of transformations in diversity-oriented synthesis. The review is oriented to wide range of chemists working in the field of organic synthesis and both experimental and theoretical studies of nitrogen-containing heterocycles.

Multiple Multicomponent Reactions: Unexplored Substrates, Selective Processes, and Versatile Chemotypes in Biomedicine

Multiple multicomponent reactions rapidly assemble complex structures. Despite being very productive, the lack of selectivity and the reduced number of viable transformations restrict their general application in synthesis. Hereby, we describe a rationale for a selective version of these processes based in the preferential generation of intermediates which are less reactive than the initial substrates. In this way, applying the Groebke-Blackburn-Bienaymé reaction on a range of α-polyamino-polyazines, we prepared a family compact heterocyclic scaffolds with relevant applications in medicinal and biological chemistry (live cell imaging probes, selective binders for DNA quadruplexes, and antiviral agents against human adenoviruses). The approach has general character and yields complex molecular targets in a selective, tunable and direct manner.

Solvent- and Catalyst-Free One-Pot Green Bound-Type Fused Bis-Heterocycles Synthesis via Groebke-Blackburn-Bienaymé Reaction/SNAr/Ring-Chain Azido-Tautomerization Strategy

A new, efficient, green, endogenous water-triggered, solvent- and catalyst-free ultrasound-assisted one-pot Groebke-Blackburn-Bienaymé reaction/S_NAr/ring-chain azido-tautomerization strategy to synthesize bound-type fused bis-heterocycles imidazo or benzo[d]imidazo[2,1-b]thiazoles and 1,5-disubstituted tetrazole (1,5-DsT) containing quinoline moiety is described, which allows synthesis of two types of fused heterocycles in one step under mild green conditions. Antibacterial and antiamebic activities of selected newly synthesized compounds were carried out against three bacterial species: Gram-positive bacterium Staphylococcus aureus ATCC 6538 and Gram-negative bacteria Pseudomonas aeruginosa ATCC 13384 and Escherichia coli O55 and against one amebic species: Entamoeba histolytica.