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

A transition metal-free [3 + 2] cycloaddition approach for the efficient synthesis of trisubstituted pyrrole derivatives from β-chlorovinyl aldehydes

A transition metal-free, Cs2CO3-promoted approach has been devised for the efficient synthesis of nitrile-substituted novel pyrrole derivatives from β-chlorovinyl aldehydes. Interestingly, the strategy was also found to be applicable to the synthesis of chromenone-fused pyrrole derivatives. The reaction proceeded through [3 + 2] cycloaddition between diversely substituted aryl propiolonitriles and toluenesulphonylmethyl isocyanide in DMF at ambient temperature. This approach offers several advantages including the use of inexpensive and readily available starting materials, wide substrate scope, operational simplicity, short reaction times (15 min-1.5 h), high atom economy, sustainable reaction conditions and high product yields. The strategy has been found to be amenable for gram-scale synthesis, and the scope of the strategy has been demonstrated for the synthesis of a diverse library of novel pyrrole derivatives with yields of up to 91%. The generated pyrrole derivatives are amenable for late-stage functionalisation and functional group interconversion.

Quantum Chemical Studies on the Prototropic and Acid/Base Equilibria for 2-Aminopyrrole in Vacuo-Role of CH Tautomers in the Design of Strong Brønsted Imino N-Bases

In the quest of the pivotal origin of the very strong gas-phase proton basicity for some iminopyrrole derivatives, proposed in the literature on the basis of quantum chemical calculations, the full tautomeric and acid/base equilibria were investigated in vacuo for 2-aminopyrrole exhibiting enamino-imino tautomerism. Thermochemistry of these processes investigated at the Density Functional Theory (DFT) level indicates a lower stability for the imino than for the enamino tautomers. However, the imino N atom in the imino forms displays an exceptionally high basicity, particularly in the minor and rare tautomers containing at least one tautomeric proton at the pyrrole C atom. This explains why derivatives of CH tautomers (being free of prototropy) display exceptionally high gas-phase proton basicity. As predicted by the Maksić group using quantum chemical methods, these derivatives can be considered as good organic imino N-superbase candidates. Unfortunately, some other structures of iminopyrrole derivatives (proposed by the same group) possess labile protons, and, thus, exhibit prototropy, resulting in the transformation into the more stable but less basic aminopyrrole derivatives under synthesis conditions or acid/base equilibria measurements.

Cancer Accumulation and Anticancer Activity of "CROX (Cluster Regulation of RUNX)" PIP in HER2-Positive Gastric Cancer Evaluated by Chicken Egg Cancer Model

BACKGROUND

We have focused on pyrrole-imidazole (PI) polyamide compounds, which preferentially bind to their target DNA sequences. To validate our "CROX (Cluster Regulation of RUNX)" strategy, we have created a novel PI polyamide-based inhibitor against RUNX termed Chb-M'. Recently, we have confirmed its cancer-specific uptake in mouse xenograft derived from HER2-positive gastric cancer cells. The accumulation and efficacy of Chb-M' in cancer has not yet been investigated in vivo, which is a simpler and less expensive method other than mouse xenograft models.

METHODS

In the present study, we have employed the simple and versatile experimental system termed CAM (chorioallantoic membrane) model, and evaluated whether Chb-M' could have the cancer accumulation potential and anti-cancer activity.

RESULTS

Based on our present results, gastric cancer MKN45 cells transplanted onto CAM successfully developed cancers, and the intravenously injected FITC-labeled Chb-M' obviously accumulated in these CAM cancers. As expected, the treatment of the CAM cancers with Chb-M' significantly attenuated the growth of the CAM cancers. Our present results were basically identical to those obtained from mouse xenograft model.

CONCLUSION

Our present findings strongly suggest that Chb-M' preferentially accumulates in cancer to suppress its growth, and the CAM model might serve as a valuable and promising platform to rapidly assess the cancer uptake and anti-cancer efficacy of various PI polyamide-based drug candidates.

The anti-Acinetobacter baumannii therapeutic potential of azole hybrids: A mini-review

Acinetobacter baumannii is one of the major causes of severe hospital- and community-acquired infections, posing a significant threat to human lives. A. baumannii has already generated resistance to almost all of the currently available antibiotics, but no new class of antibacterials have been launched for the treatment of infections caused by A. baumannii in the last half century, creating an urgent need to develop novel antibacterials. Azoles as a broad class of five-membered nitrogen-containing aromatic heterocycles are privileged pharmacophores widely found in pharmaceuticals. Azoles could target on diverse enzymes, proteins, and receptors in A. baumannii via various noncovalent interactions. Particularly, azole hybrids have potential advantages in increasing therapeutic efficacy and circumventing drug resistance, representing useful scaffolds for the discovery of novel anti-A. baumannii agents. This review outlines the current scenario of the antibacterial therapeutic potential of azole hybrids against A. baumannii, developed from 2020 onwards, aiming to provide potential candidates for further preclinical/clinical evaluations and facilitate the rational design of more effective candidates.

Ligand-Controlled C2- or C3-Selectivity Switching in the Palladium-Catalyzed C-H Arylation of Nonsubstituted 1H-Pyrrole

The C2- or C3-selective direct C-H arylation of nonsubstituted 1H-pyrrole with aryl chlorides/nonaflates was achieved using catalysts derived from palladium and appropriate phosphine ligands. The site selectivity of the arylation can be switched by changing the ligands, and the C3-selective arylation of nonsubstituted 1H-pyrrole was realized for the first time. tBuOLi played an important role in suppressing N-arylation and accelerating C2- or C3-arylation.

Therapeutic Potental of Quinolin-2H-one Hybrids as Anticancer Agents

The statistical data related to cancer in recent years has shown a great increase in the number of cases and is likely to further increase in the future. Even after seeking thorough knowledge on the aetiology of cancer and related disorders and attempting to cure it by various methods like gene therapy, T cell therapy, chemotherapy, surgery, hormone therapy, and photodynamic therapy, there has always been disappointment concerning the survival rate. Hence, there is still a great urge for the discovery of novel drugs for the treatment of cancer. Chemotherapy being one of the widely used methods, several drug entities possessing anticancer properties are already in the market but none of them is known to show good efficacy which necessitates researchers to design newer drugs for the treatment of cancer. The urge to synthesize novel anticancer entities directed researchers towards molecular hybridization as one of the novel methods for designing newer drugs. Literature reveals wide research carried out on quinolin-2-one hybrids, possessing anticancer properties through different mechanisms. Tipifarnib and Dovitinib are quinolin-2-one hybrids used to treat cancer, possessing imidazole and benzimidazole heterocyclic rings. Different heterocyclic scaffolds such as pyrone, pyrrole, pyrimidine, pyridine, thiazole, and pyrazole in combination with heterocyclic quinolin-2-one have shown high potential to become lead for newer anticancer agents with better and wider therapeutic properties and lesser side effects. The current review presents information on the different quinolin-2-one hybrids and their effect on different cancer cell lines. It also imparts knowledge of the structural requirements for designing novel anticancer agents.

Unlocking the Potential of Pyrrole: Recent Advances in New Pyrrole-Containing Compounds with Antibacterial Potential

Nitrogen heterocycles are valuable structural elements in the molecules of antibacterial drugs approved and used to treat bacterial infections. Pyrrole is a five-atom heterocycle found in many natural compounds with biological activity, including antibacterial activity. Numerous compounds are being develop based on the pyrrole heterocycle as new potential antibacterial drugs. Due to the phenomenon of antibacterial resistance, there is a continuous need to create new effective antibacterials. In the scientific literature, we have identified the most relevant studies that aim to develop new compounds, such as pyrrole derivatives, that are proven to have antibacterial activity. Nature is an endless reservoir of inspiration for designing new compounds based on the structure of pyrrole heterocycles such as calcimycin, lynamycins, marinopyrroles, nargenicines, phallusialides, and others. However, many other synthetic compounds based on the pyrrole heterocycle have been developed and can be optimized in the future. The identified compounds were classified according to the type of chemical structure. The chemical structure-activity relationships, mechanisms of action, and antibacterial effectiveness of the most valuable compounds were highlighted. This review highlights scientific progress in designing new pyrrole-containing compounds and provides examples of lead compounds that can be successfully optimized further.

Synthesis, Cytotoxicity and Antiproliferative Effect of New Pyrrole Hydrazones

Novel pyrrole-based carbohydrazide (1) and hydrazones (1A-D) were synthesized, characterized, and subjected to spectroscopic studies. The hydrazones were obtained by reacting a pyrrole hydrazide with substituted pyrrole aldehydes. The initial carbohydrazide was prepared by selective hydrazinolysis of the obtained N-pyrrolylcarboxylic acid ethyl ester. The biological activity of the newly synthesized compounds was investigated in vitro on a panel of tumor and non-tumor cell lines. Mouse embryonic fibroblasts BALB 3T3 clone A31 were used in the safety test (BALB 3T3 NRU-assay). Antiproliferative activity was determined on keratinocytes (HaCaT) and melanoma (SH-4) cells by MTT dye reduction assay. The safety test of the compounds showed low cytotoxicity and absence of phototoxic potential. Among our novel pyrrole hydrazones, 1C was the most selective (SI = 3.83) in human melanoma cells and exhibited very good antiproliferative activity (IC50 = 44.63 ± 3.51 μM). The cytotoxic effect of 1C correlates with its ability to induce apoptosis and to cause cell cycle arrest in the S phase. In addition, the results show that hydrazones obtained by condensation with β-aldehydes are more bioactive than those obtained by condensation with α-aldehydes.

Indium(III)-Catalyzed Synthesis of Pyrroles and Benzo[g]indoles by Intramolecular Cyclization of Homopropargyl Azides

Pyrroles, privileged structural motifs in drug and material science, have been synthesized by indium(III)-catalyzed intramolecular cyclization of homopropargyl azides. This methodology exhibits a broad substrate scope, providing substituted pyrroles and bispyrroles in good yields. Furthermore, an atom-economical sequential method for the synthesis of benzo[g]indoles has been discovered from azido-diynes using InCl3 as catalyst. The method involves two successive intramolecular indium-catalyzed 5-endo-dig alkyne hydroamination and a hydroarylation reactions with 6-endo-dig regioselectivity.

Synthesis of chiral systems featuring the pyrrole unit: a review

Synthetic strategies towards pyrroles within chiral frameworks are summarised, focussing on reports published 2010-2023. The synthesis of pyrroles featuring substituents bearing chiral centres are summarised, as are those whereby pyrroles are located within axially chiral systems courtesy of restricted bond rotation.

Visible-light-induced redox-neutral difunctionalization of alkenes and alkynes

The twelve principles of green chemistry illuminate the pathway in the direction of sustainable and eco-friendly synthesis, marking a fundamental shift in synthetic organic chemistry paradigms. In this realm, harnessing the power of visible light for the difunctionalization of various skeletons without employing any external oxidant or reductant, specifically termed as redox-neutral difunctionalization, has attracted tremendous interest from synthetic organic chemists due to its low cost, easy availability and environmentally friendly nature in contrast to traditional metal-catalyzed difunctionalizations. This review presents an overview of recent updates on visible-light-induced redox-neutral difunctionalization reactions with literature coverage up to May 2024.

2,4-Diarylpyrroles: synthesis, characterization and crystallographic insights

Three 2,4-diarylpyrroles were synthesized starting from 4-nitrobutanones and the crystal structures of two derivatives were analysed. These are 4-(4-methoxyphenyl)-2-(thiophen-2-yl)-1H-pyrrole, C15H13NOS, and 3-(4-bromophenyl)-2-nitroso-5-phenyl-1H-pyrrole, C16H11BrN2O. Although pyrroles without substituents at the α-position with respect to the N atom are very air sensitive and tend to polymerize, we succeeded in growing an adequate crystal for X-ray diffraction analysis. Further derivatization using sodium nitrite afforded a nitrosyl pyrrole derivative, which crystallized in the triclinic space group P-1 with Z = 6. Thus, herein we report the first crystal structure of a nitrosyl pyrrole. Interestingly, the co-operative hydrogen bonds in this NO-substituted pyrrole lead to a trimeric structure with bifurcated halogen bonds at the ends, forming a two-dimensional (2D) layer with interstitial voids having a radius of 5 Å, similar to some reported macrocyclic porphyrins.

The Polysaccharides from Pinellia ternata and Their Derivatives: Preparation, Structure Characteristics, and Activities in Vitro

Three polysaccharides, PTC, PTH, and PTB, were extracted from Pinellia ternata using three different extraction conditions: room temperature water, hot water, and 2 % Na2CO3 solution. PTC and PTH were composed of rhamnose, glucose, galactose, mannose, glucuronic acid, galacturonic acid, and arabinose, which combine to form complex structures. PTB was composed solely of glucose and rhamnose. Further analysis indicated that PTC and PTB exhibited triple-helix structures. PTC showed the highest scavenging capacity against DPPH, superoxide anion, and hydroxyl radicals, with half maximal inhibitory concentrations (IC50) of 1004.1, 1584.1, and 1584.1 μg/mL, respectively. Additionally, PTC, PTH, and PTB were subjected to sulfation, phosphorylation, and selenization, resulting in the production of nine derivates. The distinctive absorptive bands of these derivates were determined through infrared spectroscopy. Selenized and sulfated derivates have shown significant antitumor and immunoenhancing properties. Our findings revealed that at 400 μg/mL, the inhibition rate of selenated PTB on HeLa cells was 54.2 % and that on HepG2 cells was 43.1 %. Additionally, selenized PTC displayed significant immunoenhancing activity, with a proliferation rate of 63.7 % at 400 μg/mL in RAW264.7 cells. These results provide valuable evidence supporting the consideration of polysaccharides from Pinellia ternata as a potential candidate for the development of antineoplastic drugs.

In silico evaluation of potential breast cancer receptor antagonists from GC-MS and HPLC identified compounds in Pleurotus ostreatus extracts

Introduction: Pharmacotherapeutic targets for breast cancer include the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor (EGFR). Inhibitors of these receptors could be interesting therapeutic candidates for the treatment and management of breast cancer (BC). Aim: This study used GC-MS and HPLC to identify bioactive compounds in Pleurotus ostreatus (P. ostreatus) extracts and applied in silico methods to identify potent EGFR, ER, and PR inhibitors from the compounds as potential drug candidates. Method: GC-MS and HPLC were used to identify bioactive chemicals in P. ostreatus extracts of aqueous (PO-A), methanol (PO-M), ethanol (PO-E), chloroform (PO-C), and n-hexane (PO-H). The ER, PR, and EGFR model optimization and molecular docking of compounds/control inhibitors in the binding pocket were simulated using AutoDock Vina in PyRx. The drug-likeness, pharmacokinetic, and pharmacodynamic features of prospective docking leads were all anticipated. Result: The results indicated the existence of 29 compounds in PO-A, 36 compounds in PO-M and PO-E, 42 compounds in PO-C, and 22 compounds in PO-H extracts. With ER, only o-tolylamino-acetic acid (4-nitro-benzylidene)-hydrazide (-7.5 kcal mol-1) from the ethanolic extract could bind to the receptor. PR and EGFR, on the other hand, identified several compounds with higher binding affinities than the control. Ergotaman-3',6',18-trione (-8.1 kcal mol-1), 5,10-diethoxy-2,3,7,8-tetrahydro-1H,6H-dipyrrolo[1,2-a:1',2'-d]pyrazine (-7.8 kcal mol-1) from the aqueous extract; o-tolylamino-acetic acid (4-nitro-benzylidene)-hydrazide (-8.4 kcal mol-1) from the ethanolic extract had better binding affinity compared to progesterone (-7.7 kcal mol-1). Likewise, ergotaman-3',6',18-trione (-9.7 kcal mol-1) from the aqueous extract and phenol, 2,4-bis(1,1-dimethyl ethyl) (-8.2 kcal mol-1) from the chloroform extract had better binding affinities compared to the control, gefitinib (-7.9 kcal mol-1) with regards to EGFR. None of the PO-H or PO-M extracts outperformed the control for any of the proteins. Phenols and flavonoids such as quercetin, luteolin, rutin, chrysin, apigenin, ellagic acid, and naringenin had better binding affinity to PR and EGFR compared to their control. Conclusion: The identified compounds in the class of phenols and flavonoids were better lead molecules due to their ability to strongly bind to the proteins' receptors. These compounds showed promising drug-like properties; they could be safe and new leads for creating anticancer medicines.

Functionalized 2,3'-Bipyrroles and Pyrrolo[1,2-c]imidazoles from Acylethynylpyrroles and Tosylmethylisocyanide

An efficient method for the synthesis of pharmaceutically prospective but still rare functionalized 2,3'-bipyrroles (in up to 80% yield) by the cycloaddition of easily available acylethynylpyrroles with tosylmethylisocyanide (TosMIC) has been developed. The reaction proceeds under reflux (1 h) in the KOH/THF system. In the t-BuONa/THF system, TosMIC acts in two directions: along with 2,3'-bipyrroles, the unexpected formation of pyrrolo[1,2-c]imidazoles is also observed (products ratio~1:1).