HPW-Catalyzed environmentally benign approach to imidazo[1,2-a]pyridines

The imidazo[1,2-a]pyridine moiety is present in drugs with several biological activities. The most direct way of obtaining this nucleus is the Groebke-Blackburn-Bienaymé three-component reaction (GBB-3CR) between aminopyridines, aldehydes, and isocyanides under both Lewis and Brønsted acid catalysis. However, several catalysts for this reaction have major drawbacks such as being expensive, extremely dangerous, strong oxidizing, and even explosive. In this scenario, heteropolyacids emerge as greener and safer alternatives due to their very strong Brønsted acidity. In particular, phosphotungstic acid (HPW) is an economical and green attractive catalyst for being cheap, non-toxic, and is known for its chemical and thermal stability. Herein, we report a straightforward approach to the GBB-3CR using HPW as catalyst in ethanol under microwave (μw) heating. This convenient environmentally benign methodology is broad in scope, provides the heterobicyclic products in high yields (up to 99%), with a low catalyst loading (2 mol %) in only 30 minutes, and allows the successful use of aliphatic aldehydes, substrates not so frequently explored with most usual catalysts for this reaction. Furthermore, the aforementioned advantages make this methodology very attractive and superior to the existing ones.

Design, synthesis and biological evaluation of indole-2-carboxylic acid derivatives as novel HIV-1 integrase strand transfer inhibitors

Integrase plays an important role in the life cycle of HIV-1, and integrase strand transfer inhibitors (INSTIs) can effectively impair the viral replication. However, drug resistance mutations have been confirmed to decrease the efficacy of INSTI during the antiviral therapy. Herein, indole-2-carboxylic acid (1) was found to inhibit the strand transfer of integrase, and the indole nucleus of compound 1 was observed to chelate with two Mg2+ ions within the active site of integrase. Through optimization of compound 1, a series of indole-2-carboxylic acid derivatives were designed and synthesized, and compound 17a was proved to markedly inhibit the effect of integrase, with IC50 value of 3.11 μM. Binding mode analysis of 17a demonstrated that the introduced C6 halogenated benzene ring could effectively bind with the viral DNA (dC20) through π-π stacking interaction. These results indicated that indole-2-carboxylic acid is a promising scaffold for the development of integrase inhibitors.

Gas-phase fragmentation of protonated 3-phenoxy imidazo[1,2-a] pyridines using tandem mass spectrometry and computational chemistry

Imidazo[1,2-a] pyridine is one of the pharmaceutically important scaffolds and has been widely studied due to its extensive biological activities. In this work, electrospray ionization tandem mass spectrometry (ESI-MS/MS) in positive mode was used to study the gas-phase fragmentation behavior of a series of 3-phenoxy imidazo[1,2-a] pyridines. Proposed fragmentation pathways were supported by ESI-MS/MS data and computational thermochemistry. Homolytic cleavage of the 3-phenoxy C-O bond was the characteristic fragmentation of 3-phenoxy imidazo [1,2-a] pyridines. The eliminations of the one substituted phenoxy radical and CO produced other diagnostic ions for 3-phenoxy imidazo [1,2-a] pyridines, which were useful to identify the 3-phenoxy group and imidazo [1,2-a] pyridine scaffold. The results contribute to the further understanding of the gas-phase fragmentation of 3-phenoxy imidazo [1,2-a] pyridines and the identification of other analogs using tandem mass spectrometry techniques.

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 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.

Enantioselective synthesis of novel pyrano[3,2-c]chromene derivatives as AChE inhibitors via an organocatalytic domino reaction

A series of optically active pyrano[3,2-c]chromenes have been synthesized through an asymmetric domino reaction of 4-hydroxy-2H-chromen-2-ones with malononitriles. The targeted molecules were obtained in excellent yields and enantioselectivities (up to 94% yield, 99% ee). The AChE inhibitory activity studies revealed that compounds 4n (IC₅₀ = 21.3 μM) and 4p (IC₅₀ = 19.2 μM) displayed potent acetylcholinesterase inhibition. In most cases, the S-enantiomers were superior to the corresponding R-enantiomers. Moreover, molecular modelling provides a practical method for understanding the enantioselective discrimination of AChE with these kinds of compounds.