Imidazo[1,2-a]pyridin-3-amines as potential HIV-1 non-nucleoside reverse transcriptase inhibitors

Iron-Catalyzed Sulfonylmethylation of Imidazo[1,2-α]pyridines with N,N-Dimethylacetamide and Sodium Sulfinates

Functionalized imidazo[1,2-α]pyridines are important scaffolds in pharmaceuticals. Herein, we present an efficient 3-sulfonylmethylation protocol for imidazo[1,2-α]pyridines by sodium sulfinates in DMA and H2O (2:1) via an FeCl3-catalyzed three-component coupling reaction. Various sulfonylmethyl imidazo[1,2-α]pyridines were thus afforded in high yields with excellent functional group tolerance. A plausible oxidation-addition mechanism was proposed.

Synthesis and site selective C-H functionalization of imidazo-[1,2-a]pyridines

Imidazo[1,2-a]pyridine has attracted much interest in drug development because of its potent medicinal properties, therefore the discovery of novel methods for its synthesis and functionalization continues to be an exciting area of research. Although transition metal catalysis has fuelled the most significant developments, extremely beneficial metal-free approaches have also been identified. Even though pertinent reviews focused on imidazo[1,2-a]pyridine synthesis, properties (physicochemical and medicinal), and functionalization at the C3 position have been published, none of these reviews has focused on the outcomes obtained in the field of global ring functionalization. We wish here to describe a brief synthesis and an overview of all the functionalization reactions at each carbon atom, viz, C2, C3, C5, C6, C7 and C8 of this scaffold, divided into sections based on site-selectivity and the type of functionalization methods used.

Copper-Catalyzed Oxidative [3 + 2] Cycloaddition of N-Alkyl Pyridinium Salts to Imidazo[1,2-a]pyridines

A copper-catalyzed reaction of pyridinium salts and trimethylsilyl cyanide (TMSCN) in the presence of diethyl phosphite is developed. This reaction, which allows the single-step construction of biologically important 2-cyanoimidazo[1,2-a]pyridine from readily available starting materials, is realized for the first time and is feasible at the gram scale. The scope of the protocol is demonstrated with 27 examples. A consecutive double cyanation and cyclization can be achieved in this one-pot process. TMSCN plays a dual role not only as the "CN" source but also as the coupling partner for the cyclization of imidazo[1,2-a]pyridines.

Synthesis of imidazo[1,2-a]pyridine-containing peptidomimetics by tandem of Groebke-Blackburn-Bienaymé and Ugi reactions

Peptidomimetics with a substituted imidazo[1,2-a]pyridine fragment were synthesized by a tandem of Groebke-Blackburn-Bienaymé and Ugi reactions. The target products contain substituted imidazo[1,2-a]pyridine and peptidomimetic moieties as pharmacophores with four diversity points introduced from readily available starting materials, including scaffold diversity. A small focused compound library of 20 Ugi products was prepared and screened for antibacterial activity.

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.

Imidazopyridine, a promising scaffold with potential medicinal applications and structural activity relationship (SAR): recent advances

Imidazopyridine scaffold has gained tremendous importance over the past few decades. Imidazopyridines have been expeditiously used for the rationale design and development of novel synthetic analogs for various therapeutic disorders. A wide variety of imidazopyridine derivatives have been developed as potential anti-cancer, anti-diabetic, anti-tubercular, anti-microbial, anti-viral, anti-inflammatory, central nervous system (CNS) agents besides other chemotherapeutic agents. Imidazopyridine heterocyclic system acts as a key pharmacophore motif for the identification and optimization of lead structures to increase medicinal chemistry toolbox. The present review highlights the medicinal significances of imidazopyridines for their rationale development as lead molecules with improved therapeutic efficacies. This review further emphasis on the structure-activity relationships (SARs) of the various designed imidazopyridines to establish a relationship between the key structural features versus the biological activities.Communicated by Ramaswamy H. Sarma.

Imidazo[4,5-b]pyridine derived tubulin polymerization inhibitors: Design, synthesis, biological activity in vitro and computational analysis

Imidazo[4,5-b]pyridine derived acrylonitriles were synthesized and explored for their in vitro antiproliferative effect on a diverse human cancer cell line panel. Three compounds, 20, 21 and 33, showed strong activity in the submicromolar range (IC₅₀ 0.2-0.6 μM), and were chosen for further biological experiments. Immunofluorescence staining and tubulin polymerization assays confirmed tubulin as the main target, but excluded its colchicine-binding site as a potential interacting unit. This was supported by the computational analysis, which revealed that the most potent ligands act on the extended colchicine site on the surface between interacting tubulin subunits, where they interfere with their polymerization and reveal pronounced antitumor properties. In addition, lead molecule 21 potently inhibited cancer cell migration, while it did not affect the viability of normal cells even at the highest concentration tested (100 µM).

Synthesis of Imidazo[1,2-a]pyridines via Near UV Light-Induced Cyclization of Azirinylpyridinium Salts

An efficient one-pot synthesis of imidazo[1,2-a]pyridines from 2-bromoazirines and pyridines has been developed. The construction of the bicyclic framework of imidazo[1,2-a]pyridines occurs in two steps through the formation of (2H-azirin-2-yl)pyridinium bromides followed by dehydrobrominative UV light-induced cyclization. The method can also be applied for the synthesis of imidazo[2,1-a]isoquinolines. Unstable in solution, (2H-azirin-2-yl)pyridinium/isoquinolinium bromides were quantitatively converted to stable tetrafluoroborates, which can be cyclized to imidazo[1,2-a]pyridines under UV irradiation in the presence of bromide ions.

Crystal structure and Hirshfeld surface analysis of 2-oxo-2-phenylethyl 3-nitroso-2-phenylimidazo[1,2-a]pyridine-8-carboxylate

In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds, generating (5) and (28) ring motifs. In addition, weak C—H⋯π and π-stacking inter­actions are observed.

The title compound, C₂₂H₁₅N₃O₄, is built up from a central imidazo[1,2-a]pyridine ring system connected to a nitroso group, a phenyl ring and a 2-oxo-2-phenyl­ethyl acetate group. The imidazo[1,2-a] pyridine ring system is almost planar (r.m.s. deviation = 0.017 Å) and forms dihedral angles of 22.74 (5) and 45.37 (5)°, respectively, with the phenyl ring and the 2-oxo-2-phenyl­ethyl acetate group. In the crystal, the mol­ecules are linked into chains parallel to the b axis by C—H⋯O hydrogen bonds, generating R₂¹ (5) and R₄⁴ (28) graph-set motifs. The chains are further linked into a three-dimensional network by C—H⋯π and π-stacking inter­actions. The inter­molecular inter­actions were investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing that the most important contributions for the crystal packing are from H⋯H (36.2%), H⋯C/C⋯H (20.5%), H⋯O/O⋯H (20.0%), C⋯O/O⋯C (6.5%), C⋯N/N⋯C (6.2%), H⋯N/N⋯H (4.5%) and C⋯C (4.3%) inter­actions.

Synthesized NaA nanozeolite as a catalyst for the preparation of 3-amino imidazo[1,2-a]pyridines under solvent-free conditions

Abstract:

The present study explores a new method for the fabrication of NaA nanozeolite as a simple and efficient catalyst for the production of 3-aminoimidazo [1,2-a] pyridines through the 3-component reaction of aldehydes, 2-aminoperidines and isocyanides under solvent-free conditions. The production of organic template free (OTF) NaA nanozeolite was performed at room temperature. The prepared nanozeolite was identified by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electronic microscopy (FESEM), N2 sorption isotherm and particle size analysis (PSA). The particle sizes of synthesized spherical NaA nanozeolite were under 100 nm via the FESEM method. The BET surface area, total pore volume and mean pore diameter of the created sample were attained to be 362 m2g-1, 0.44 cm3 g-1 and 5.9 nm, respectively. The developed method has some advantages such as OTF production of NaA nanozeolite, simple synthesis method with short reaction time and easy separation using filtration and the ability to recycle and reuse of catalyst several times without reducing its efficiency.

Gold-catalyzed oxidation of terminal alkynes to glyoxals and their reactions with 2-phenylimidazo[1,2-a]pyridines: one-pot synthesis of 1,2-diones

A novel one-pot protocol for the convenient and efficient synthesis of (2-phenylimidazo[1,2-a]pyridin-3-yl)alkane-1,2-diones (3) in good yields (32-88%) from 2-phenylimidazo[1,2-a]pyridines (1) and terminal alkynes (2) has been established with a wide range of substrate scope. A tandem reaction sequence containing gold-catalyzed double oxidations of terminal alkynes to generate glyoxals, nucleophilic addition of 2-phenylimidazo[1,2-a]pyridines to glyoxals to yield α-hydroxyl ketones, and oxygenation of the α-hydroxyl ketones to afford the final products 3 under air atmosphere is involved in this method. Simple operation, mild reaction conditions, and widely available substrates make this strategy more affordable.

Multicomponent reactions in the synthesis of antiviral compounds

BACKGROUND

Multicomponent reactions are one-pot processes for the synthesis of highly functionalized hetero-cyclic and hetero-acyclic compounds, often endowed with biological activity.

OBJECTIVE

Multicomponent reactions are considered green processes with high atom economy. In addition, they present advantages compared to the classic synthetic methods such as high efficiency and low wastes production.

METHOD

In these reactions two or more reagents are combined together in the same flask to yield a product containing almost all the atoms of the starting materials.

RESULTS

The scope of this review is to present an overview of the application of multicomponent reactions in the synthesis of compounds endowed with antiviral activity. The syntheses are classified depending on the viral target.

CONCLUSION

Multicomponent reactions can be applied to all the stages of the drug discovery and development process making them very useful in the search for new agents active against emerging (viral) pathogens.

Sulfonated β-cyclodextrins: efficient supramolecular organocatalysts for diverse organic transformations

The present review summarizes various organic transformations carried out by using sulfonated β-cyclodextrins such as β-cyclodextrin sulfonic acid, β-cyclodextrin propyl sulfonic acid, and β-cyclodextrin butyl sulfonic acid as an efficient, supramolecular reusable catalyst under diverse reaction conditions.

BF3-etherate promoted facile access to vinyloxyimidazopyridines: a metal-free sustainable approach

A convenient and metal-free synthesis of vinyloxyimidazopyridine derivatives has been attained via BF₃.OEt₂ promoted one-pot multicomponent approach. This procedure involves a facile coupling of 2-aminopyridine derivatives with arylglyoxal and alkyne derivatives. BF₃.OEt₂ complexation has successfully catalyzed the reaction at room temperature. Utilization of transition metal-free catalyst, mild reaction conditions, easy handling and operational simplicity are key features of developed process.

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

Microwave-assisted (MWA) multicomponent reactions (MCRs) have successfully emerged as one of the useful tools in the synthesis of biologically relevant heterocycles. These reactions are strategically employed for the generation of a variety of heterocycles along with multiple point diversifications. Over the last few decades classical MCRs such as Ugi, Biginelli, etc. have witnessed enhanced yield and efficiency with microwave assistance. The highlights of MWA-MCRs are high yields, reduced reaction time, selectivity, atom economy and simpler purification techniques, such an approach can accelerate the drug discovery process. The present review focuses on the recent advances in MWA-MCRs and their mechanistic insights over the past decade and shed light on its advantage over the conventional approach.

Synthesis and photophysical properties of 5-(3′′-alkyl/aryl-amino-1′′-azaindolizin-2′′-yl)-2′-deoxyuridines

The Groebke–Blackburn–Bienayame (GBB) reaction has been used for the efficient synthesis of novel fluorescent 5-azaindolizino-2′-deoxyuridines starting from commercially available thymidine following two strategies.

Pyrimidazole-Based Covalent Organic Frameworks: Integrating Functionality and Ultrastability via Isocyanide Chemistry

Development of new chemistry to simultaneously meet the demands for topology, connectivity, and functionality is highly desired in the research area of covalent organic frameworks (COFs). We explore herein the isocyanide chemistry so as to establish a facile paradigm to integrate functionality and ultrastability in COFs. Using the representative Groebke-Blackburn-Bienaymé (GBB) reaction based on isocyanide chemistry, we are able to construct a series of pyrimidazole-based COFs in one step from isocyanide, aminopyridine, and aldehyde monomers. Diversified functionalities have been bottom-up integrated by the simple replacement of readily available 2-aminopyridine monomers. Meanwhile, the ubiquitous formation of fused imidazole rings within the frameworks has guaranteed their ultrastability. In view of the rich synthetic possibilities provided by isocyanide chemistry, we expect that this contribution opens up a new avenue toward the divergent construction of robust COFs for practical applications.

Series of Functionalized 5-(2-Arylimidazo[1,2-a]pyridin-3-yl)pyrimidine-2,4(1H,3H)-diones: A Water-Mediated Three-Component Catalyst-Free Protocol Revisited

A water-mediated and catalyst-free practical method for the synthesis of a new series of pharmaceutically interesting functionalized 5-(2-arylimidazo[1,2-a]pyridin-3-yl)pyrimidine-2,4(1H,3H)-diones has been accomplished based on a one-pot multicomponent reaction between arylglyoxal monohydrates, 2-aminopyridines/2-aminopyrimidine, and barbituric/N,N-dimethylbarbituric acids under reflux conditions. The salient features of this protocol are avoidance of any additive/catalyst and toxic organic solvents, use of water as reaction medium, clean reaction profiles, operational simplicity, ease of product isolation/purification without the aid of tedious column chromatography, good to excellent yields, and high atom-economy and low E-factor.

Efficient one-pot synthesis of functionalised imidazo[1,2-a]pyridines and unexpected synthesis of novel tetracyclic derivatives by nucleophilic aromatic substitution

Novel tetracyclic imidazo[1,2-a]pyridine derivatives have been prepared by intramolecular nucleophilic aromatic substitution of 5-fluoroimidazo[1,2-a]pyridines under basic conditions. Use of the non-nucleophilic alcoholic solvent tert-butanol, rather than methanol, increased the yield of the tetracycles by reducing the competing intermolecular reaction observed for methanol. In addition, a modified protocol for the dehydration of formamides to isocyanides has been found to be tolerant of an unprotected hydroxyl functional group and one-pot conversion to imidazo[1,2-a]pyridyl-aminocyclohexanol analogues is reported.

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.

Crystal structure, DFT calculation, Hirshfeld surface analysis and energy framework study of 6-bromo-2-(4-bromo-phen-yl)imidazo[1,2-a]pyridine

The title imidazo[1,2-a] pyridine derivative, C13H8Br2N2, was synthesized via a single-step reaction method. The title mol-ecule is planar, showing a dihedral angle of 0.62 (17)° between the phenyl and the imidazo[1,2-a] pyridine rings. An intra-molecular C-H⋯N hydrogen bond with an S(5) ring motif is present. In the crystal, a short H⋯H contact links adjacent mol-ecules into inversion-related dimers. The dimers are linked in turn by weak C-H⋯π and slipped π-π stacking inter-actions, forming layers parallel to (110). The layers are connected into a three-dimensional network by short Br⋯H contacts. Two-dimensional fingerprint plots and three-dimensional Hirshfeld surface analysis of the inter-molecular contacts reveal that the most important contributions for the crystal packing are from H⋯Br/Br⋯H (26.1%), H⋯H (21.7%), H⋯C/C⋯H (21.3%) and C⋯C (6.5%) inter-actions. Energy framework calculations suggest that the contacts formed between mol-ecules are largely dispersive in nature. Analysis of HOMO-LUMO energies from a DFT calculation reveals the pure π character of the aromatic rings with the highest electron density on the phenyl ring, and σ character of the electron density on the Br atoms. The HOMO-LUMO gap was found to be 4.343 eV.

Diverse Oxidative C(sp2)-N Bond Cleavages of Aromatic Fused Imidazoles for Synthesis of α-Ketoamides and N-(pyridin-2-yl)arylamides

An efficient and chemoselective C(sp²)-N bond cleavage of aromatic imidazo[1,2- a]pyridine molecules is developed. A broad scope of amide compounds such as α-ketoamides and N-(pyridin-2-yl)arylamides are afforded as the final products in up to quantitative yields. Diverse C-N bond cleavages are controlled by the oxidative species used in this transformation, with various amide products afforded in a chemoselective fashion. A preliminary study indicated that some α-ketoamides exhibit anti-Tobacco Mosaic Virus activity for potential use in plant protection.

Intramolecular cyclization of imidazo[1,2-a]pyridines via a silver mediated/palladium catalyzed C–H activation strategy

Intramolecular cyclization of imidazo[1,2-a]pyridines has been developed via a C–H activation strategy to reach new chemical-space for drug discovery.

Synthesis, biological evaluation and molecular docking studies of 6-(4-nitrophenoxy)-1H-imidazo[4,5-b]pyridine derivatives as novel antitubercular agents: future DprE1 inhibitors

Tuberculosis is an air-borne disease, mostly affecting young adults in their productive years. Here, Ligand-based drug design approach yielded a series of 23 novel 6-(4-nitrophenoxy)-1H-imidazo[4,5-b]pyridine derivatives. The required building block of imidazopyridine was synthesized from commercially available 5,5-diaminopyridine-3-ol followed by four step sequence. Derivatives were prepared using various substituted aromatic aldehydes. All the synthesized analogues were characterized using NMR, Mass analysis and also screened for in vitro antitubercular activity against Mycobacterium tuberculosis (H₃₇Rv). Four compounds, 5c (MIC-0.6 μmol/L); 5g (MIC-0.5 μmol/L); 5i (MIC-0.8 μmol/L); and 5u (MIC-0.7 μmol/L) were identified as potent analogues. Drug receptor interactions were studied with the help of ligand docking using maestro molecular modeling interphase, Schrodinger. Here, computational studies showed promising interaction with other residues with good score, which is novel finding than previously reported. So, these compounds may exhibit in vivo DprE1 inhibitory activity.

Heterogeneous Gold(I)-Catalysed Annulation between 2-Aminopyridines and Propiolaldehydes Leading to 3-Acylimidazo[1,2-A]Pyridines

The heterogeneous annulation between 2-aminopyridines and propiolaldehydes was achieved in CH2Cl2 at 25 °C in the presence of 3 mol% of MCM-41-immobilised phosphine gold(I) complex (MCM-41-PPh3-AuCl) and AgSbF6 under air, yielding a variety of 3-acylimidazo[1,2-a] pyridines in good yields. This heterogeneous gold(I) catalyst can be easily prepared by a simple procedure, recovered by filtration of the reaction solution and recycled up to seven times without significant loss of activity.

Regioselective Opening of Nitroepoxides with Unsymmetrical Diamines

Nitroepoxides are easily transformed into benzodiazepines, tetrahydrobenzodiazepines, imidazopyridines, and N-alkyl tetrahydroquinoxalines by treatment with 2-aminobenzylamines, 2-aminopyridines, and N-alkyl 1,2-diaminobenzenes, respectively. Regioselectivity is controlled through attack of the most nucleophilic nitrogen of the unsymmetrical diamine to the β position of the epoxide. These reactions represent an efficient way to prepare privileged bioactive structures.

A practical and efficient approach to imidazo[1,2-a]pyridine-fused isoquinolines through the post-GBB transformation strategy

Diversity-oriented synthesis of the biologically intriguing imidazo[1,2-a]pyridine-fused isoquinoline systems from readily available starting materials was achieved through the Groebke–Blackburn–Bienaymé reaction followed by a gold-catalyzed cyclization strategy. The synthetic approach is characterized by mild reaction conditions and a broad substrate scope, allowing for the rapid construction of structurally complex and diverse heterocycles in moderate to good yields.

Visible-light-mediated C3-azolylation of imidazo[1,2-a]pyridines with 2-bromoazoles

3-Heterocycle-substituted imidazo[1,2-a]pyridines were produced by a visible-light-mediated coupling reaction of imidazo[1,2-a]pyridines with 2-bromoazoles.