Ultrasound-assisted bismuth nitrate-induced green synthesis of novel pyrrole derivatives and their biological evaluation as anticancer agents

Pyrrole: A Decisive Scaffold for the Development of Therapeutic Agents and Structure-Activity Relationship

An overview of pyrroles as distinct scaffolds with therapeutic potential and the significance of pyrrole derivatives for drug development are provided in this article. It lists instances of naturally occurring pyrrole-containing compounds and describes the sources of pyrroles in nature, including plants and microbes. It also explains the many conventional and modern synthetic methods used to produce pyrroles. The key topics are the biological characteristics, pharmacological behavior, and functional alterations displayed by pyrrole derivatives. It also details how pyrroles are used to treat infectious diseases. It describes infectious disorders resistant to standard treatments and discusses the function of compounds containing pyrroles in combating infectious diseases. Furthermore, the review covers the uses of pyrrole derivatives in treating non-infectious diseases and resistance mechanisms in non-infectious illnesses like cancer, diabetes, and Alzheimer's and Parkinson's diseases. The important discoveries and probable avenues for pyrrole research are finally summarized, along with their significance for medicinal chemists and drug development. A reference from the last two decades is included in this review.

Synthesis, Hydrolytic Stability and In Vivo Biological Study of Bioconjugates of the Tetrapeptides FELL Containing Pyrrole Moiety

BACKGROUND

Bioconjugates are promising alternatives for the multiple targeting of any disease. Pyrrole heterocycle is well known with many activities and is a building block of a lot of medical drugs. On the other hand, peptides are short molecules with many advantages such as small size, ability to penetrate the cell membrane and bond-specific receptors, vectorizing potential, etc. Thus, hybrid molecules between peptide and pyrrole moiety could be a promising alternative as an anti-pain tool.

METHODS

New bioconjugates with a general formula Pyrrole (α-/β-acid)-FELL-OH (NH2) were synthesized using Fmoc/OtBu peptide synthesis on solid support. HPLC was used to monitor the purity of newly synthesized bioconjugates. Their structures were proven by electrospray ionization mass spectrometry. The Paw Pressure test (Randall-Selitto test) was used to examinate the analgesic activity. Hydrolytic stability of targeted structures was monitored in three model systems with pH 2.0, 7.4 and 9.0, including specific enzymes by means of the HPLC-UV method.

RESULTS

The obtained results reveal that all newly synthesized bioconjugates have analgesic activity according to the used test but free pyrrole acids have the best analgesic activity.

CONCLUSIONS

Although free pyrrole acids showed the best analgesic activity, they are the most unstable for hydrolysis. Combination with peptide structure leads to the hydrolytic stabilization of the bioconjugates, albeit with slightly reduced activity.

Clauson-Kaas pyrrole synthesis using diverse catalysts: a transition from conventional to greener approach

Pyrrole is an important aromatic heterocyclic scaffold found in many natural products and predominantly used in pharmaceuticals. Continuous efforts are being made to design and synthesize various pyrrole derivatives using different synthetic procedures. Among them, the Clauson-Kaas reaction is a very old and well-known method for synthesizing a large number of N-substituted pyrroles. In recent years, due to global warming and environmental concern, research laboratories and pharmaceutical industries around the world are searching for more environmentally friendly reaction conditions for synthesizing compounds. As a result, this review describes the use of various eco-friendly greener protocols to synthesize N-substituted pyrroles. This synthesis involves the reaction of various aliphatic/aromatic primary amines, and sulfonyl primary amines with 2,5-dimethoxytetrahydrofuran in the presence of numerous acid catalysts and transition metal catalysts. The goal of this review is to summarize the synthesis of various N-substituted pyrrole derivatives using a modified Clauson-Kaas reaction under diverse conventional and greener reaction conditions.

Recent Advances in the Green Synthesis of Active N-Heterocycles and Their Biological Activities

N-heterocyclic scaffolds represent a privileged architecture in the process of drug design and development. It has widespread occurrence in synthetic and natural products, either those that are established or progressing as potent drug candidates. Additionally, numerous novel N-heterocyclic analogues with remarkable physiological significance and extended pharmaceutical applications are escalating progressively. Hence, the classical synthetic protocols need to be improvised according to modern requirements for efficient and eco-friendly approaches. Numerous methodologies and technologies emerged to address the green and sustainable production of various pharmaceutically and medicinally important N-heterocyclic compounds in last few years. In this context, the current review unveils greener alternatives for direct access to categorically differentiated N-heterocyclic derivatives and its application in the establishment of biologically active potent molecules for drug design. The green and sustainable methods accentuated in this review includes microwave-assisted reactions, solvent-free approaches, heterogeneous catalysis, ultrasound reactions, and biocatalysis.

Biocatalytic decarboxylative Michael addition for synthesis of 1,4-benzoxazinone derivatives

The Candida antarctica lipase B (Novozym 435) is found to catalyze a novel decarboxylative Michael addition in vinylogous carbamate systems for the synthesis of 1,4-benzoxazinone derivatives. The reaction goes through Michael addition, ester hydrolysis and decarboxylation. A possible mechanism is suggested, with simultaneous lipase-catalyzed Michael addition and ester hydrolysis. The present methodology offers formation of complex products through multi-step reactions in a one pot process under mild and facile reaction conditions with moderate to high yields (51–90%) and no side product formation. The reaction seems to be is a great example of enzymatic promiscuity.

Sonochemical Protocols for Heterocyclic Synthesis: A Representative Review

In the present era of the industrial revolution, we all are familiar with ever-increasing environmental pollution released from various chemical processes. Chemical production has had a severe impact on the environment and human health. For the betterment of our environment, the chemical community has turned their interest to developing green, harmless and sustainable synthetic processes. To accomplish these goals of green chemistry, the extraordinary properties of sonication play an important role. It is well known that sonochemistry can make decisive contributions to creating high pressures of almost 1000 atm and very high temperatures in the range of 4500-5000 °C. The implementation of ultrasound in chemical transformations somehow fulfils the measures of green chemistry, as it reduces energy consumption, enhances product selectivity, and uses lesser amounts of hazardous chemicals and solvents. Furthermore, heterocyclic synthesis under ultrasonication offers several environmental and process-related advantages compared with conventional methods. The remarkable contribution of ultrasonics to the development of green and sustainable synthetic routes inspired us to write this article. Herein, we have discussed only some of the various synthetic methodologies developed for the construction of heterocyclic cores under ultrasonic irradiation, accompanied by mechanistic insights. In some cases, a comparison between sonochemical conditions and conventional conditions has also been investigated. We emphasized principally 'up to date' developments on various sono-accelerated chemical transformations comprising aza-Michael, aldol reactions, C-C couplings, oxidation, cycloadditions, multi-component reactions, etc. for the synthesis of heterocycles.

Green and four-component cyclocondensation synthesis and in silico docking of new polyfunctionalized pyrrole derivatives as the potential anticholinesterase agents

Synthesis of new substituted pyrrole scaffolds containing substituted thiadiazol-2-amine moiety was successfully developed through one-pot and multi-component tandem condensation reaction utilizing of triethyl ammonium hydrogen sulfate ([Et3NH][HSO4]) ionic liquid as a green media under solvent-free conditions. The chemical structures of all newly synthesized compounds were fully characterized by spectroscopic methods (IR, ¹H NMR, ¹³C NMR) and elemental analyzes. The molecular docking studies were also performed to predict the possible binding sites of the derivatives on the active site gorge of cholinesterase enzymes (AChE and BuChE). The results showed that all the seventeen derivatives interact with the enzymes with high affinity and among them 7d and 7f possess the greatest ability to bind to AChE and BuChE, respectively.

Artificial sugar saccharin and its derivatives: role as a catalyst

The primary objective of this review was to demonstrate the significance of artificial sugar saccharin and its derivatives as catalysts for a wide variety of organic transformations. The application of saccharin and its derivatives represents a greener and superior catalytic approach for reactions. In particular, we were interested in bringing together the literature pertaining to these saccharin derivatives from a catalysis perspective. The present review reports synthesis of saccharin and its derivatives such as saccharin-N-sulfonic acid, sodium saccharin, N-halo saccharin, saccharin lithium-bromide, N-formyl saccharin, N-acyl saccharin, N-nitrosaccharin, N-SCF₃ saccharin, N-fluorosultam, N-phenylselenosaccharin, N-thiocyanatosaccharin palladium saccharin, DMAP-saccharin, and [Bmim]Sac. This catalytic application of saccharin and its derivatives includes reactions such as the Biginelli reaction, Paal-Knorr pyrrole synthesis, azo-coupling reaction, halogenations, domino Knoevenagel, Michael, deoximation reaction, catalytic condensation, functional group protection and oxidation etc. Also, these saccharin derivatives act as a source of CO, NH₂, SCN, SCF₃ and nitro groups. We reported all the available data on saccharin and its derivatives acting as a catalyst from 1957 to date.

Recent Progress in the Synthesis of Pyrroles

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Pyrrole derivatives are nitrogen-containing heterocyclic compounds and widely distributed in a large number of natural and non-natural compounds. These compounds possess a broad spectrum of biological activities such as anti-infammatory, antiviral, antitumor, antifungal, and antibacterial activities. Besides their biological activity, pyrrole derivatives have also been applied in various areas such as dyes, conducting polymers, organic semiconductors.

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Due to such a wide range of applicability, access to this class of compounds has attracted intensive research interest. Various established synthetic methods such as Paal-Knorr, Huisgen, and Hantzsch have been modified and improved. In addition, numerous novel methods for pyrrole synthesis have been discovered. This review will focus on considerable studies on the synthesis of pyrroles, which date back from 2014.

Catalytic Applications of Saccharin and its Derivatives in Organic Synthesis

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Saccharin (1,2-benzisothiazol-3(2H)-one-1,1-dioxide) is a very mild, cheap, commercially available, water soluble, environmentally benign and edible Brønsted acidic substance. Recently, with other utilities, saccharin and its derivatives were employed as catalysts for various organic transformations. In this review, catalytic applicability of saccharin and its derivatives under various reaction conditions is summarized.

A robust photoluminescence screening assay identifies uracil-DNA glycosylase inhibitors against prostate cancer

Many cancers have developed resistance to 5-FU, due to removal by the enzyme uracil-DNA glycosylase (UDG), a type of base excision repair enzyme (BER) that can excise uracil and 5-fluorouracil (5-FU) from DNA. However, the development of UDG inhibitor screening methods, especially for the rapid and efficient screening of natural product/natural product-like compounds, is still limited so far. We developed herein a robust time-resolved photoluminescence method for screening UDG inhibitors, which could significantly improve sensitivity over the screening method based on the conventional steady-state spectroscopy, reducing the substantial fluorescence background interference. As a proof-of-concept, two potential UDG inhibitors were identified from a database of natural products and approved drugs. Co-treatment of these two compounds with 5-FU showed synergistic cytotoxicity, providing the basis for treating drug-resistant cancers. Overall, this method provides an avenue for the rapid screening of small molecule regulators of other BER enzyme activities that can avoid false negatives arising from the background fluorescence.

The discovery of UDG inhibitors against prostate cancer by using a robust photoluminescence screening assay that can avoid false negatives arising from the background fluorescence.

Alkaloids for cancer prevention and therapy: Current progress and future perspectives

Alkaloids are important chemical compounds that serve as a rich source for drug discovery. Numerous alkaloids screened from medicinal plants and herbs showed antiproliferative and anticancer effects on wide category of cancers both in vitro and in vivo. Vinblastine, vinorelbine, vincristine, and vindesine have already been successfully developed as anticancer drugs. The available and up-to-date information on the ethnopharmacological uses in traditional medicine, phytochemistry, pharmacology and clinical utility of alkaloids were collected using various resources (PubMed, ScienceDirect, Google Scholar and Springerlink). In this article, we provide a comprehensive and critical overview on naturally-occurring alkaloids with anticancer activities and highlight the molecular mechanisms of action of these secondary metabolites. Furthermore, this review also presents a summary of synthetic derivatives and pharmacological profiles useful to researchers for the therapeutic development of alkaloids. Based on the literature survey compiled in this review, alkaloids represent an important group of anticancer drugs of plant origin with enormous potential for future development of drugs for cancer therapy and management.

FeCl3-Mediated Domino Reaction of Benzoxazinones with Aroylmethylidene Malonates: Synthesis to Functionalized Pyrrolobenzoxazines

An efficient domino approach for the synthesis of pyrrolobenzoxazine derivatives is described. The FeCl₃-promoted domino reaction between aroylmethylidene malonates and benzoxazinones has been successfully established to afford the title compounds in good to excellent yield under mild reaction conditions. The domino protocol provides a concise and straightforward access to highly substituted pyrrolobenzoxazines with high efficiency and excellent functional group tolerance.

Structure-activity relationship (SAR) study and design strategies of nitrogen-containing heterocyclic moieties for their anticancer activities

The present review article offers a detailed account of the design strategies employed for the synthesis of nitrogen-containing anticancer agents. The results of different studies describe the N-heterocyclic ring system is a core structure in many synthetic compounds exhibiting a broad range of biological activities. Benzimidazole, benzothiazole, indole, acridine, oxadiazole, imidazole, isoxazole, pyrazole, triazoles, quinolines and quinazolines including others drugs containing pyridazine, pyridine and pyrimidines are covered. The following studies of these compounds suggested that these compounds showed their antitumor activities through multiple mechanisms including inhibiting protein kinase (CDK, MK-2, PLK1, kinesin-like protein Eg5 and IKK), topoisomerase I and II, microtubule inhibition, and many others. Our concise representation exploits the design and anticancer potency of these compounds. The direct comparison of anticancer activities with the standard enables a systematic analysis of the structure-activity relationship among the series.

Base-mediated regiospecific cascade synthesis of N-(2-pyridyl)pyrroles from N-propargylic β-enaminones

Two birds with one stone: two classical heterocycles, pyrrole and pyridine, were simultaneously installed from one acyclic enaminone precursor for the preparation of N-(2-pyridyl)pyrroles.

An expeditious green route toward 2-aryl-4-phenyl-1H-imidazoles

Background

Azaheterocycles are an important class of compounds because of their highly potent medicinal activities, and the imidazole subcategory is of special interest in regard to drug discovery research.

Findings

An expeditious synthetic protocol of 2-aryl-4-phenyl-1H-imidazoles has been accomplished by reacting phenylglyoxal monohydrate, ammonium acetate, and aldehyde under sonication. Following this green approach a series of 2-aryl-4-phenyl-1H-imidazoles has been synthesized using diversely substituted aldehydes.

Conclusions

A rapid and simple synthetic procedure to synthesize diversely substituted 2-aryl-4-phenyl-1H-imidazoles has been reported. Other salient features of this protocol include milder conditions, atom-economy, easy extraction, and minimum wastes. The present procedure may find application in the synthesis of biologically active molecules.

Pyrrole: a resourceful small molecule in key medicinal hetero-aromatics

Pyrrole is widely known as a biologically active scaffold which possesses a diverse nature of activities.

Bismuth nitrate-induced novel nitration of estradiol: an entry to new anticancer agents

Direct nitration of estradiol was carried out using metal nitrates on solid surfaces under mild condition, and a combination of bismuth nitrate pentahydrate impregnated KSF clay was found to be the best reagent to synthesize 2- and 4-nitroestradiol effectively. Furthermore, various basic side chains were introduced, through O-linker at C-3, to these nitroestradiols. The ability of these derivatives to cause cytotoxicity in Estrogen Receptor (ER)-positive and ER-negative breast cancer cell lines, as well as cancer cell lines of other origins, was examined. Qualitative structure activity relationship (SAR) has also been studied. We found that a basic side chain containing either a piperidine or morpholine ring, when conjugated to 2-nitroestradiol, was particularly effective at causing cytotoxicity in each of the cancer cell lines examined. Surprisingly, this effective cytotoxicity was even seen in ER-negative breast cancer cells.

Nano CoFe2O4 supported antimony(iii) as an efficient and recyclable catalyst for one-pot three-component synthesis of multisubstituted pyrroles

A novel magnetic nano-CoFe₂O₄ supported Sb ([CoFe₂O₄@SiO₂-DABCO-Sb]) was successfully constructed and identified as an efficient catalyst for synthesis of multisubstituted pyrroles via one-pot three-component reaction of amines, nitroolefin and 1,3-dicarbonyl compounds.

A green approach toward quinoxalines and bis-quinoxalines and their biological evaluation against A431, human skin cancer cell lines

Background: The objective of this study was to develop a practical green procedure to synthesize quinoxalines and bis-quinoxalines and evaluate their inhibitory effects on the viability of A431 human epidermoid carcinoma cells. Method: A series of quinoxaline and bis-quinoxaline derivatives have been designed and synthesized following a microwave-assisted and bismuth nitrate-catalyzed eco-friendly route. A detailed comparison has been made between microwave-induced protocol with the reactions occurred at room temperature. The structure of the compounds have been elucidated by various spectroscopic methods and finally confirmed by x-ray crystallographic analyses. Results: Two quinoxaline derivatives, compounds 6 and 12 have demonstrated inhibitory effects on the viability of A431 human epidermoid carcinoma cells when compared with HaCaT nontumorigenic human keratinocyte cells. Conclusion: Notably, compound 6 inhibits Stat3 phosphorylation/activation in A431 skin cancer cells.