Synthetic strategies and pharmacological activities of chromene and its derivatives: An overview

p-Toluenesulfonic acid-promoted organic transformations for the generation of molecular complexity

Since the beginning of this century, p-toluenesulfonic acid (p-TSA) catalysed organic transformations have been an active area of research for developing efficient synthetic methodologies. Often, catalysis using p-TSA is associated with many advantages, such as operational simplicity, high selectivity, excellent yields, and ease of product isolation, which make organic synthesis convenient and versatile. Notably, p-TSA is a non-toxic, commercially available, inexpensive solid organic compound that is soluble in water, alcohols, and other polar organic solvents. p-TSA is a strong acid compared to many protic or mineral acids and its high acidity helps activate different organic functional groups. p-TSA-promoted conversions are fast, have a high atom and pot economy, and feature a multiple bond-forming index. Therefore, the utilization of p-TSA enables the synthesis of many important structural scaffolds without any hazardous metals, making it desirable in numerous applications of sustainable and green chemistry. Recently, this emerging area of research has become one of the pillars of synthetic organic chemistry to synthesise biologically relevant, complex carbocycles and heterocycles. This study provides a comprehensive summary of methods, applications, and mechanistic insights into p-TSA-catalysed organic transformations, covering the literature reports that have appeared since 2012.

L-Proline-catalysed synthesis of 2-aryl-2H,5H-thiopyrano[2,3-b] thiochromen-5-ones from 4-hydroxydithiocoumarins and cinnamaldehyde derivatives

The hitherto unreported synthesis of 2-aryl-2H,5H-thiopyrano[2,3-b]thiochromen-5-one derivatives was achieved from 4-hydroxydithiocoumarin and cinnamaldehyde using 20 mol% L-proline, an environmentally benign organocatalyst in methanol under reflux conditions. The current approach involves imine formation, followed by a Mannich reaction, instead of a 1,4-addition or thia-Michael reaction, and finally, cyclization. The salient features of this method are mild reaction conditions, broad substrate scope, good yield, atom economy, and shorter reaction time.

How Can Deep Eutectic Systems Promote Greener Processes in Medicinal Chemistry and Drug Discovery?

Chemists in the medicinal chemistry field are constantly searching for alternatives towards more sustainable and eco-friendly processes for the design and synthesis of drug candidates. The pharmaceutical industry is one of the most polluting industries, having a high E-factor, which is driving the adoption of more sustainable processes not only for new drug candidates, but also in the production of well-established active pharmaceutical ingredients. Deep eutectic systems (DESs) have emerged as a greener alternative to ionic liquids, and their potential to substitute traditional organic solvents in drug discovery has raised interest among scientists. With the use of DESs as alternative solvents, the processes become more attractive in terms of eco-friendliness and recyclability. Furthermore, they might be more effective through making the process simpler, faster, and with maximum efficiency. This review will be focused on the role and application of deep eutectic systems in drug discovery, using biocatalytic processes and traditional organic chemical reactions, as new environmentally benign alternative solvents. Furthermore, herein we also show that DESs, if used in the pharmaceutical industry, may have a significant effect on lowering production costs and decreasing the impact of this industry on the quality of the environment.

Neuroprotective potential of formononetin, a naturally occurring isoflavone phytoestrogen

The increased prevalence of neurological illnesses is a burgeoning challenge to the public healthcare system and presents greater financial pressure. Formononetin, an O-methylated isoflavone, has gained a lot of attention due to its neuroprotective potential explored in several investigations. Formononetin is widely found in legumes and several types of clovers including Trifolium pratense L., Astragalus membranaceus, Sophora tomentosa, etc. Formononetin modulates various endogenous mediators to confer neuroprotection. It prevents RAGE activation that results in the inhibition of neuronal damage via downregulating the level of ROS and proinflammatory cytokines. Furthermore, formononetin also increases the expression of ADAM-10, which affects the pathology of neurodegenerative disease by lowering tau phosphorylation, maintaining synaptic plasticity, and boosting hippocampus neurogenesis. Besides these, formononetin also increases the expression of antioxidants, Nrf-2, PI3K, ApoJ, and LRP1. Whereas, reduces the expression of p65-NF-κB and proinflammatory cytokines. It also inhibits the deposition of Aβ and MAO-B activity. An inhibition of Aβ/RAGE-induced activation of MAPK and NOX governs the protection elicited by formononetin against inflammatory and oxidative stress-induced neuronal damage. Besides this, PI3K/Akt and ER-α-mediated activation of ADAM10, ApoJ/LRP1-mediated clearance of Aβ, and MAO-B inhibition-mediated preservation of dopaminergic neurons integrity are the major modulations produced by formononetin. This review covers the biosynthesis of formononetin and key molecular pathways modulated by formononetin to confer neuroprotection.

ZnO-ZnS Heterostructure as a Potent Photocatalyst in the Preparation of Some Substituted Chromenes and Remarkable Antigastrointestinal Cancer Activity

The nanosized hybrid material ZnO-ZnS was synthesized using the well-known sol-gel method, as a simple and environmentally friendly procedure. The material was then characterized using various techniques including FESEM, TEM, UV-vis, DRS, EDS, XRD, and FT-IR. The characterization studies revealed the generation of ZnO-ZnS nanoparticles with a mean size of around 25 nm. Moreover, DRS analysis provided a band gap of 3.05 eV for this nanomaterial. The photocatalytic properties of the ZnO-ZnS heterojunction was investigated in the synthesis of some substituted chromenes under mild reaction conditions. The results showed that the prepared nanophotocatalyst exhibits significantly higher activity compared to its individual components (ZnO and ZnS) and provides 73-87% yield with 0.01 g of ZnO-ZnS after 30 min. In addition, the nanophotocatalyst demonstrated a high reusability in the desired condensation reaction. The enhanced photocatalytic activity of ZnO-ZnS can be attributed to the slower recombination of the electron-hole pairs in this semiconductor material. The reactive species OH•, •O2-, and h+ are believed to play important roles in the photocatalytic system. Furthermore, cellular toxicity of ZnO-ZnS nanoparticles was evaluated on HCT-116 human gastrointestinal cancer cell line by MTT assay. The results proved a distinct reduction of cell viability, proofing cytotoxicity of nanoparticles on the cancer cells. This study highlights the potential of the nanoparticles against gastrointestinal cancer.

Advances in the greener synthesis of chromopyrimidine derivatives by a multicomponent tandem oxidation process

A hydrophilic cobalt/copper heterogeneous bimetallic catalyst named mTEG-CS-Co/Cu-Schiff-base/IL was successfully synthesized from chitosan polysaccharide. The new catalyst was investigated and confirmed using various techniques including FT-IR, FE-SEM, EDX-EDS, XRD, TEM, TGA, AFM, NMR and ICP. The catalyst exhibited powerful catalyst activity for the tandem one pot oxidative chromopyrimidine reaction from benzyl alcohols under mild conditions, utilizing air as a clean source in a green protocol. The catalyst was compatible with a wide range of benzyl alcohols, and aldehydes formed in situ, and bis-aldehydes synthesized were condensed with urea/4‑hydroxycumarin to provide favorable products in good yields for all derivatives (14 new derivatives). The presence of tri-ethylene glycol and imidazolium moieties with hydrophilic properties on the mTEG-CS-Co/Cu-Schiff-base/IL nanohybrid provides dispersion of the nanohybrid particles in water, leading to higher catalytic performance. Furthermore, the reaction exhibited several other notable features, including low catalyst loading, the ability to be recycled for up to 6 stages, high atom economy, a simple work procedure, short reaction time, utilization of an environmentally friendly nanohybrid, and the replacement of volatile and organic solvents with water solvent.

CSA@g-C3N4 as a novel, robust and efficient catalyst with excellent performance for the synthesis of 4H-chromenes derivatives

A pioneering robust and green heterogeneous acidic catalyst (CSA@g-C3N4) was rationally designed via immobilization of camphorsulfonic acid (CSA) on the g-C3N4 surface under mild conditions. Grafting CSA in the g-C3N4 lattice is distinguished as the root cause of facilitating the structure change of g-C3N4, leading to a unique morphology, accordingly the remarkable catalytic efficiency of CSA@g-C3N4. The morphology of new as-prepared nano-catalyst was specified by means of FT-IR, XRD, SEM, EDS, TEM, TGA, and BET. For the first time, it is exhibited that the efficient catalyst CSA@g-C3N4 can productively accomplish the three-component reactions with high yields and also serve as an inspiration for easily performing various sorts of MCRs based on our finding. The recommended synthesis pathway of chromenes derivatives is facile and cost-effective which applies a condensation reaction of salicylaldehyde, thiophenol, and malononitrile followed by ready purification in a benign manner. Moreover, the CSA@g-C3N4 nanocomposite can be promptly reused, illustrating no sensational decrease in the catalytic activity after ten times.

Synthesis of New Chromene Derivatives Targeting Triple-Negative Breast Cancer Cells

Breast cancer continues to be the leading cause of cancer-related deaths among women worldwide. The most aggressive type of breast cancer is triple-negative breast cancer (TNBC). Indeed, not only does TNBC not respond well to several chemotherapeutic agents, but it also frequently develops resistance to various anti-cancer drugs, including taxane mitotic inhibitors. This necessitates the search for newer, more efficacious drugs. In this study, we synthesized two novel chromene derivatives (C1 and C2) and tested their efficacy against a battery of luminal type A and TNBC cell lines. Our results show that C1 and C2 significantly and specifically inhibited TNBC cell viability but had no effect on the luminal A cell type. In addition, these novel compounds induced mitotic arrest, cell multinucleation leading to senescence, and apoptotic cell death through the activation of the extrinsic pathway. We also showed that the underlying mechanisms for these actions of C1 and C2 involved inhibition of microtubule polymerization and disruption of the F-actin cytoskeleton. Furthermore, both compounds significantly attenuated migration of TNBC cells and inhibited angiogenesis in vitro. Finally, we performed an in silico analysis, which revealed that these novel variants bind to the colchicine binding site in β-tubulin. Taken together, our data highlight the potential chemotherapeutic properties of two novel chromene compounds against TNBC.

Fe3O4@nano-almondshell/Si(CH2)3/2-(1-piperazinyl)ethylamine as an effective magnetite almond shell-based nanocatalyst for the synthesis of dihydropyrano[3,2-c]chromene and tetrahydrobenzo[b]pyran derivatives

The preparation and design of nano-catalysts based on magnetic biopolymers as green and biocompatible nano-catalysts have made many advances. This paper deals with the preparation of magnetite biopolymer-based Brønsted base nano-catalyst from a nano-almond (Prunus dulcis) shell. This magnetite biopolymer-based nano-catalyst was obtained through a simple process based on the core-shelling of nano-almond shell and Fe₃O₄ NPs and then the immobilization of 3-chloropropyltrimethoxysilane as linker and 2-aminoethylpiperazine as a basic section. Structural and morphological analysis of this magnetite biopolymer-based nano-catalyst were done using Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray diffraction, Thermogravimetric analysis, Vibrating sample magnetization, Energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller, and Transmission electron microscopy techniques. The performance of the synthesized Fe₃O₄@nano-almondshell/Si(CH₂)₃/2-(1-piperazinyl)ethylamine as a novel magnetite biopolymer-based nano-catalyst for the synthesis of dihydropyrano[3,2-c]chromene and tetrahydrobenzo[b]pyran was investigated and showed excellent efficiency.

N-, O- and S-Heterocycles Synthesis in Deep Eutectic Solvents

The synthesis of heterocycles is a fundamental area of organic chemistry that offers enormous potential for the discovery of new products with important applications in our daily life such as pharmaceuticals, agrochemicals, flavors, dyes, and, more generally, engineered materials with innovative properties. As heterocyclic compounds find application across multiple industries and are prepared in very large quantities, the development of sustainable approaches for their synthesis has become a crucial objective for contemporary green chemistry committed to reducing the environmental impact of chemical processes. In this context, the present review focuses on the recent methodologies aimed at preparing N-, O- and S-heterocyclic compounds in Deep Eutectic Solvents, a new class of ionic solvents that are non-volatile, non-toxic, easy to prepare, easy to recycle, and can be obtained from renewable sources. Emphasis has been placed on those processes that prioritize the recycling of catalyst and solvent, as they offer the dual benefit of promoting synthetic efficiency while demonstrating environmental responsibility.

Inhibitory Potential of Chromene Derivatives on Structural and Non-Structural Proteins of Dengue Virus

Dengue fever is a mosquito-borne viral disease that has become a serious health issue across the globe. It is caused by a virus of the Flaviviridae family, and it comprises five different serotypes (DENV-1 to DENV-5). As there is no specific medicine or effective vaccine for controlling dengue fever, there is an urgent need to develop potential inhibitors against it. Traditionally, various natural products have been used to manage dengue fever and its co-morbid conditions. A detailed analysis of these plants revealed the presence of various chromene derivatives as the major phytochemicals. Inspired by these observations, authors have critically analyzed the anti-dengue virus potential of various 4H chromene derivatives. Further, in silico, in vitro, and in vivo reports of these scaffolds against the dengue virus are detailed in the present manuscript. These analogues exerted their activity by interfering with various stages of viral entry, assembly, and replications. Moreover, these analogues mainly target envelope protein, NS2B-NS3 protease, and NS5 RNA-dependent RNA polymerase, etc. Overall, chromene-containing analogues exerted a potent activity against the dengue virus and the present review will be helpful for the further exploration of these scaffolds for the development of novel antiviral drug candidates.

Synthesis, Biological Evaluation, and In Silico Studies of Novel Coumarin-Based 4H,5H-pyrano[3,2-c]chromenes as Potent β-Glucuronidase and Carbonic Anhydrase Inhibitors

The search for novel heterocyclic compounds with a natural product skeleton as potent enzyme inhibitors against clinical hits is our prime concern in this study. Here, a simple and facile two-step strategy has been designed to synthesize a series of novel coumarin-based dihydropyranochromenes (12a-12m) in a basic moiety. The synthesized compounds were thus characterized through spectroscopic techniques and screened for inhibition potency against the cytosolic hCA II isoform and β-glucuronidase. Few of these compounds were potent inhibitors of hCA II and β-glucuronidase with varying IC₅₀ values ranging from 4.55 ± 0.22 to 21.77 ± 3.32 μM and 440.1 ± 1.17 to 971.3 ± 0.05 μM, respectively. Among the stream of synthesized compounds, 12e and 12i were the most potent inhibitors of β-glucuronidase, while 12h, 12i, and 12j showed greater potency against hCA II. In silico docking studies illustrated the significance of substituted groups on the pyranochromene skeleton and binding pattern of these highly potent compounds inside enzyme pockets.