Current Green Chemistry - Volume 10, Issue 1, 2023

Background: Heterocyclic chemistry is a highly significant and exciting segment of organic chemistry because of its high biological and pharmacological activities. An environmentally benign and synthetically proficient way of synthesis of fused heterocycles is the major goal of modern organic synthesis by developing greener synthetic strategies. Green synthetic approaches address our future challenges for the development of a bioactive heterocycle framework with maximum productivity and minimum side products. A few decades ago, novel tools for manufacturing fused heterocycles had a huge impact on organic chemistry. Subsequently, the preparation of fused heterocycles through a synthetically efficient and environmentally benign route is the important purpose of modern synthetic chemistry. Methods: This review consists of green synthetic strategies for the synthesis of N/O-containing various bio-active fused heterocyclic compounds using modern organic transformations including: cyclocondensation, cycloaddition, one-pot, multi-components, and other modular reactions. Some greener unconventional techniques such as ultrasound and microwave-assisted method, green solvent and solventfree reaction medium are important modes adopted towards sustainability. Objective: This review aims to reflect the sustainability scope in green approaches to the synthesis of N/O-containing bio-active fused heterocyclic compounds so that economically and environmentally viable synthetic methodologies may be selectively identified and applied in academia and industries. Conclusion: In this review, we have discussed the recent advancements in green and eco-friendly tools for the synthesis of N/O-based bio-active fused heterocyclic compounds that will lead to further research in this field.

Deep eutectic solvents (DESs) are a mixture of two or more chemicals (hydrogen bond donors and acceptors) that are solid at room temperature, but combined at a unique molar ratio, presenting a melting point recession and becoming liquid. These solvents emerged as an alternative to hazardous solvents employed in various organic transformations and fulfilled the green chemistry concept. The convenience of synthesis, recyclability, inexpensiveness, non-toxicity, high solvent capacity, high biodegradation, low volatile organic character, and environmentally benign nature give DESs an edge over other solvents. Due to the numerous benefits to present environmental concerns and the necessity to replace hazardous solvents, the DESs solvent system is appealing to chemists in recent decades. The most important role played by the DESs showed component interactions via covalent or ionic bonds, and is thus considered a good candidate to replace ionic liquids or traditional solvents. The present review article focuses mainly on recent highlights of DESs, preparation, properties and applications to various heterocyclic molecule construction for the period 2012 to 2022.

The wide pharmaceutical activity of the bioactive heterocycles, which include nitrogen, oxygen, and sulphur and comprise five- and six-membered rings, has drawn the attention of medicinal chemists for several years. The therapeutic potential of bioactive heterocycles for a variety of disorders lies in their medicinal effects. The most prominent of them is Alzheimer's disease (AD), a neurodegenerative disorder that impairs memory and causes other psychiatric problems. Globally, there are around 54 million cases, and by 2050, that number is predicted to rise by 131 million. So far, donepezil, galantamine, and rivastigmine have indeed received FDA approval for use in the treatment of AD. In this regard, the pharmacophoric properties of heterocycle molecules are equivalent to those of galantamine mimics. Therefore, it is beneficial to create novel compounds containing these moieties and test their ability to inhibit acetyl and butyl cholinesterase. Diverse heterocyclic scaffolds may now have therapeutic potential for Alzheimer's disease. Recently, greener and more expeditious synthesis of bioactive heterocycles has drawn much attention because of the utilisation of environmentally benign protocols, thereby diminishing the usage of hazardous chemicals. In this review, we discuss the most pertinent findings about the "green" synthesis of heterocycles and their possible anti-activity against Alzheimer's.

Synthesis of heterocyclic scaffolds by microwave irradiation is a green and clean process. The organic transformation induced by microwave irradiation, as an alternative source of energy, has been of great interest due to the high efficiency, yield, and short reaction time with minimum by-product production. Heterocyclic compounds, an important skeleton for pharmaceuticals, are the most privileged and prevalent class of organic chemistry. They have enormous medicinal value and pharmaceutical potential. This review demonstrates the effectiveness of microwave heating for the synthesis of heterocyclic compounds. The eco-friendly microwave-induced synthesis of five-membered heterocyclic systems covering recent literature is highlighted in this article.

In this review, we report green transformations of biologically active heterocycles catalyzed by Citric acid. Citric acid is found naturally in citrus fruits, especially lemons and limes. Citric acid is soluble in water used as a highly efficient and biodegradable catalyst for multi-component transformations, biomimetic reactions, and C-C bond formation. It has been applicable for the multicomponent synthesis of pyrano[2, 3-e]pyrimidin, pyrano[2, 3-d]pyrazol-amines, amidoalkyl naphthols, tetrahydropyridines, indazolo[ 2,1-b]phthalazine-triones, indazolo[2,1-b]phthalazine-triones, indazolo[2,1-b]phthalazine-triones, ethyl 3-methyl-4,5-dioxo-1,2-diphenylpyrrolidine-3-carboxylate and 2,4-disubstituted thiazoles from ketones via C-Br, C-S, and C-N Bond Formations. Citric acid is also used in combination with ultrasound for the synthesis of biologically active pyrazolyl-bis coumarinyl methanes and pyrrolidinone. Citric acid is used in the generation of nanocatalysts, mesoporous carbon materials (OMCs) as well as polymerization reactions by the reaction of resorcinol/formaldehyde resin. Citric acid is also used in the generation of fluorescent 1,4-disubstituted-1,2,3-triazoles1,8-dioxo-decahydroacridines by Hantzsch condensation.

Accumulation of pharmaceuticals in the environment due to slow mineralization in nature is a growing pollution problem affecting organisms and animals and humans in the long run. When pharmaceuticals are antibiotics, the problem is twofold since the buildup of such compounds in the environment also fuels the development of antibiotic resistance. Building weak structures of biologically active compounds is one way of facilitating the quicker degradation of the drug in the environment after the drug has been excreted from the patient subsequently performing its function. The emergence of the process of photodegradation post-excretion of the pharmaceutical from the patient is one method that is under development, which will facilitate a quicker breakdown of the drug. Another method to enable this is hydrolysis, which is pH-dependent and involves making up of compounds that hydrolyze quicker under certain pH conditions. To enable the ongoing efforts in making pharmaceuticals to be more benign, this focused review showcases examples from research on antimicrobial agents and anticancer agents.