Biomedical importance of indoles

Pseudo-Natural Products: Expanding chemical and biological space by surpassing natural constraints

This review explores the recent advancements in the design and synthesis of pseudo-natural products (pseudo-NPs) by employing innovative principles and strategies, heralding a transformative era in chemistry and biology. Pseudo-NPs, produced through in silico fragmentation and the de novo recombination of natural product fragments, reveal compounds endowed with distinct biological activities. Their advantage lies in transcending natural product structures, fostering diverse possibilities. Research in this area over the past decade has yielded unconventional combinations of natural product fragments, leading to the identification of novel compounds possessing unique scaffolds and biological significance, thereby contributing to the discovery of new therapeutics. The pseudo-NPs exert potent biological effects through various signaling pathways. In chemical biology and medicinal chemistry, designing pseudo-NPs is an important strategy, harnessing molecular hybridization and bioinspired synthesis to generate diverse compounds with remarkable biological activities, underscoring their immense potential in drug discovery and development.

Preliminary evaluation of antiproliferative and apoptotic activities of novel indolin-2-one derivatives

Indole-based agents are frequently used in targeted or supportive therapy of several cancers. In this study, we investigated the anticancer properties of originally synthesized novel indolin-2-one derivatives (6a-d) against Malignant Mesothelioma, Breast cancer, and Colon Cancer cells. Our results revealed that all derivatives were effectively delayed cell proliferation by inhibiting the ERK1/2, AKT, and STAT3 signaling pathways in a concentration-dependent manner. Additionally, these variants induced cell cycle arrest in the S phase, accompanied by elevated levels of p21 and p27 expressions. Derivatives also initiated mitochondrial apoptosis through the upregulation of Bax and downregulation of Bcl-2 proteins, leading to the activation of caspase 3 and PARP cleavage in exposed cells. Remarkably, three of the indolin-2-one derivatives displayed significant selectivity towards Breast and Colon Cancer cells, with compound 6d promising as the most potent and wide spectral one for all cancer cell lines.

Iodine/Oxone® oxidative system for the synthesis of selenylindoles bearing a benzenesulfonamide moiety as carbonic anhydrase I, II, IX, and XII inhibitors

A wide range of 3-selenylindoles were synthesized via an eco-friendly approach that uses Oxone® as the oxidant in the presence of a catalytic amount of iodine. This mild and economical protocol showed broad functional group tolerance and operational simplicity. A series of novel selenylindoles bearing a benzenesulfonamide moiety were also synthesized and evaluated as carbonic anhydrase inhibitors of the human (h) isoforms hCa I, II, IX, and XII, which are involved in pathologies such as glaucoma and cancer. Several derivatives showed excellent inhibitory activity towards these isoforms in the nanomolar range, lower than that shown by acetazolamide.

Regioselective Brønsted acid catalyzed ring opening of aziridines by phenols and thiophenols; a gateway to access functionalized indolines, indoles, benzothiazines, dihydrobenzo-thiazines, benzo-oxazines and benzochromenes

Brønsted acid catalyzed regioselective ring opening of aziridines by phenols and thiophenols have been reported. Involvement of a series of aziridines with a range of phenols and thiophenols offer the generality of the reported protocol. Completion of the reaction at room temperature within very short time brings the uniqueness of the developed technique. To emphasis on the application of the developed methodology, the products have been used for the further synthesis of a range of useful and novel heterocyclic molecules such as indolines, indoles, benzothiazines, dihydrobenzothiazines, benzo-oxazines and benzochromenes.

Selective Synthesis of 3-(1H-Tetrazol-5-yl)-indoles from 2H-Azirines and Arynes

A new selective synthetic approach to indole derivatives bearing a tetrazole moiety has been developed. Arynes, generated in situ from o-(trimethylsilyl)aryl triflates and KF, reacted smoothly with 2-(2-benzyl-2H-tetrazol-5-yl)-2H-azirines to give 3-(2-benzyl-2H-tetrazol-5-yl)-indole derivatives with high selectivity. Deprotection of the tetrazole moiety gave 3-(1H-tetrazol-5-yl)-indole derivatives.

Nickel-Catalyzed Alkene Isomerization to Access Bench-Stable Enamines and Their [3 + 2] Annulation

Enamines are difficult to prepare on the bench due to their instability, which results in side reactions, decompositions, poor yields, etc. Herein, we developed a simple and effective method for making bench-stable enamines using a very low amount of nickel catalyst loading. The deuterium exchange, competitive reaction, and radical clock experiment have all been found to favor the ionic mechanism of this alkene isomerization. Scale-up and [3 + 2] annulation reaction of enamines with activated cyclopropane to deliver cyclopentane derivatives have shown the value of this method in organic synthesis.

Synthesis and photodynamic activity of new 5-[(E)-2-(3-alkoxy-1-phenyl-1H-pyrazol-4-yl)ethenyl]-2-phenyl-3H-indoles

A series of new indole-pyrazole hybrids 8a-m were synthesized through the palladium-catalyzed ligandless Heck coupling reaction from easily accessible unsubstituted, methoxy- or fluoro-substituted 4-ethenyl-1H-pyrazoles and 5-bromo-3H-indoles. These compounds exerted cytotoxicity to melanoma G361 cells when irradiated with blue light (414 nm) and no cytotoxicity in the dark at concentrations up to 10 µM, prompting us to explore their photodynamic effects. The photodynamic properties of the example compound 8d were further investigated in breast cancer MCF-7 cells. Evaluation revealed comparable anticancer activities of 8d in both breast and melanoma cancer cell lines within the submicromolar range. The treatment induced a massive generation of reactive oxygen species, leading to different types of cell death depending on the compound concentration and the irradiation intensity.

Chemometric profiling and anti-arthritic activity of aerial parts of Glinus oppositifolius (L.) Aug. DC

ETHNOPHARMACOLOGICAL RELEVANCE

Glinus oppositifolius (L.) Aug. DC. belongs to the family Molluginaceae, an annual prostrate herb traditionally used to treat inflammations, arthritis, malarial, wounds, fevers, diarrhoea, cancer, stomach discomfort, jaundice, and intestinal parasites. However, the anti-arthritic activity of the aerial part has still not been reported.

AIM OF THE STUDY

To investigate the antioxidant and anti-arthritic activity of G. oppositifolius in Complete Freund's Adjuvant (CFA) induced rats.

MATERIALS AND METHODS

The dried aerial parts of this plant material were defatted with n-hexane and extracted by methanol using a soxhlet apparatus. The in vitro anti-arthritic activity of methanolic extract of G. oppositifolius (MEGO) was evaluated in protein denaturation, membrane stabilization, and inhibition of proteinase assay at 25, 50, 100, 200, and 400 μg/ml concentrations. Female Wistar rats were immunized sub-dermally into the right hind paw with 0.1 ml of CFA. Rats were administered with MEGO at doses of 200 and 400 mg/kg once daily for fourteen days after arthritis induction. Assessment of arthritis was performed by measuring paw diameter, arthritic index, arthritic score, body weight, organ weight, and hematological and biochemical parameters, followed by the analysis of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), interleukin-1-beta (IL-1β), cyclooxygenase-2 (COX-2), interleukin 13 (IL-13) and interleukin 10 (IL-10) and histopathological study. In vivo antioxidant effect was investigated in enzymatic assays. The presence of phytoconstituents was analyzed by Gas Chromatography-Mass Spectrometry (GC-MS) and Liquid Chromatography-Mass Spectrometry (LC-MS), respectively. In silico molecular docking study of the compounds was carried out against COX-2, IL-1β, IL-6, and TNF-α using AutoDock 4.2 and BIOVIA-Discovery Studio Visualizer software.

RESULTS

MEGO's in vitro anti-arthritic activity showed dose-dependent inhibition of protein denaturation, membrane stabilization, and proteinase inhibition, followed by significant in vivo anti-arthritic activity. The rats treated with MEGO showed tremendous potential in managing arthritis-like symptoms by restoring hematological, biochemical, and histological changes in CFA-induced rats. MEGO (200 and 400 mg/kg) showed a significant alleviation in the levels of hyper expressed inflammatory mediators (TNF-α, IL-1β, and IL-6) and oxidative stress (SOD, CAT, GSH, and LPO) in CFA-induced rats. Spergulagenin-A as identified by LC-MS analysis, exhibited the highest binding affinity against COX-2 (-8.6), IL-1β (7.2 kcal/mol), IL-6 (-7.4 kcal/mol), and TNF-α (-6.5 kcal/mol).

CONCLUSIONS

Provided with the comprehensive investigation, methanolic extract of G. oppositifolius against arthritic-like condition is a proof of concept that revalidates its ethnic claim. The presence of Spergulagenin-A might be responsible for the anti-arthritic activity.

Ruthenium-catalyzed C-H functionalization of indoles and indolines with 7-azabenzonorbornadienes: access to aminodihydronaphthyl indoles and indolines

Indoles, indolines and hydronaphthylamines are ubiquitous structural motifs in natural products, pharmaceuticals, and biologically active molecules. In this paper, we report the synthesis of aminodihydronaphthyl-substituted indoles and indolines via a Ru-catalyzed carbamoyl-directed C-H functionalization of indoles and indolines with 7-azabenzonorbornadienes. In the presence of Cu(OAc)2 and AgSbF6, [Ru(p-cymene)Cl2]2 catalyzes the reaction of 1-carbamoylindoles with 7-azabenzonorbornadienes to produce 2-(1-amino-1,2-dihydronaphthalen-2-yl)indoles. Under the same conditions, the reaction of 1-carbamoylindolines with 7-azabenzonorbornadienes affords 7-(1-amino-1,2-dihydronaphthalen-2-yl)indolines. In both cases, the reactions yield cis-configured products.

Site-selective synthesis of indanyl-substituted indole derivatives via 1,3-dithiane induced Nazarov cyclization

We report an efficient site-selective synthetic method to C2 and C3 indanyl-substituted indole derivatives via 1,3-dithianyl induced Nazarov-type cyclization. In particular, C2-selective indanyl-substituted indoles were directly obtained by a BF3·Et2O-promoted sequence of intramolecular C3-C2 migration and Nazarov-type cyclization process.

Anticancer perspectives of monocarbonyl analogs of curcumin: A decade (2014-2024) review

Monocarbonyl analogs of curcumin (MACs) represent structurally modified versions of curcumin. The existing literature indicates that MACs exhibit enhanced anticancer properties compared with curcumin. Numerous research articles in recent years have emphasized the significance of MACs as effective anticancer agents. This review focuses on the latest advances in the anticancer potential of MACs, from 2014 to 2024, including discussions on their mechanism of action, structure-activity relationship (SAR), and in silico molecular docking studies.

Abiotic/Biotic Stress and Substrate Dictated Metabolic Diversity of Azotobacter Chroococcum: Synthesis of Alginate, Antifungal n-Alkanes, Lactones, and Indoles

The current paper deals with new metabolites of different groups produced by Azotobacter chroococcum XU1. The strain's metabolic diversity is strongly altered by different factors, and some secondary metabolites are being reported for the first time for this species. As an abiotic/biotic stress response, the strain produced a broad spectrum of indole ring-containing compounds, n-alkanes (eicosane, heneicosane, docosane, tetracosane, and hexacosane), alkanes (7-hexyl eicosane and 2-methyloctacosane), saturated fatty acids (hexanoic and octanoic acids), esters (hexadecanoic acid methyl and pentadecanoic acid-14-methyl-methyl esters), and amides (9-Octadecenamide, (Z)- and 13-Docosenamide, (Z)-). Furthermore, to mitigate the abiotic stress the strain actively produced exopolysaccharide (EPS) to biosorb the Na+ ions. Apart from these metabolites, A. chroococcum XU1 synthesized lactones, namely 1,5-d-gluconolactone and d, l-mevalonic acid lactone in response to carbon source modification.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-024-01212-x.

Easy Access to Functionalized Indolines and Tetrahydroquinolines via a Photochemical Cascade Cyclization Reaction

Herein, the development of a light-mediated synthesis of functionalized indolines and tetrahydroquinolines is reported. These structural motifs are considered as highly valuable targets, attributed to their widespread occurrence in pharmaceuticals and natural products. The gold-mediated approach offers a direct route to functionalized indolines in yields of up to 81% under mild photochemical conditions. Thereby, easily accessible Boc-protected N-aryl-allylamine and homoallylamine derivatives were reacted with sp3-hybridized haloalkanes in an intermolecular cascade cyclization reaction. A broad scope of substrates, including a variety of different substituents on the aromatic backbone as well as various haloalkanes, could be utilized. Indoline derivatives, which are functionalized in position 2, are also accessible by applying ortho-allylic anilines. Moreover, the synthetic appeal was demonstrated for a total synthesis of the anti-inflammatory agent AN669 in three reaction steps in an overall yield of 64%.

K2CO3-mediated annulation of 1,3-acetonedicarboxylates with 2-fluoro-1-nitroarenes: synthesis of indoles

The K2CO3-mediated one-pot reaction of 1,3-acetonedicarboxylates with 2 equiv. of substituted 2-fluoro-1-nitrobenzenes has been developed to synthesize various 2,3-dicarboxylate indoles via a tandem annulation pathway. In the effective reaction, one carbon-carbon double bond, one carbon-carbon single bond and one carbon-nitrogen single bond are formed under open-vessel conditions. DFT calculations are used to rationalize the plausible mechanisms.

Organoselenium-Catalyzed C2,3-Diarylation of N-H Indoles

An organoselenium-catalyzed C2,3-diarylation of unprotected N-H indoles with electron-rich aromatics has been developed. This one-pot multicomponent tandem cross-dehydrogenation coupling reaction allows for the incorporation of two different aromatic groups to indoles. More importantly, this approach offers significant advantages, including a high atom and step economy, eliminating the need for prepreparation of the reaction substrates, streamlining the synthetic process and enhancing its practicality. Overall, this organoselenium-catalyzed C2,3-diarylation reaction presents an efficient and versatile strategy for the functionalization of indole derivatives.

Indole as a Versatile Building Block in Cycloaddition Reactions: Synthesis of Diverse Heterocyclic Frameworks

Indole, a ubiquitous and structurally versatile aromatic compound, has emerged as a key player in the synthesis of diverse heterocyclic frameworks via cycloaddition reactions. These reactions are completely atom-economical and, hence, are considered as green reactions. This review article provides a comprehensive overview of the pivotal role played by indole in the construction of complex and biologically relevant heterocyclic compounds. Here we explore the chemistry of indole-based cycloadditions, highlighting their synthetic utility in accessing a wide array of heterocyclic architectures, including cyclohepta[b]indoles, tetrahydrocarbazoles, tetrahydroindolo[3,2-c]quinoline, and indolines, among others. Additionally, we discuss the mechanistic insights that underpin these transformations, emphasizing the strategic importance of indole as a building block. The content of this article will certainly encourage the readers to explore more work in this area.

Discovery of a New Polymorph of 5-Methoxy-1H-Indole-2-Carboxylic Acid: Characterization by X-ray Diffraction, Infrared Spectroscopy, and DFT Calculations

This study presents a new 5-methoxy-1H-indole-2-carboxylic acid (MI2CA) polymorph investigated by single-crystal X-ray diffraction, infrared spectroscopy, and density functional theory (ωB97X-D) calculations employing two basis sets (6-31++G(d,p) and aug-cc-pVTZ). The compound crystallizes in the monoclinic system, space group P21/c (a = 4.0305(2) Å, b = 13.0346(6) Å, c = 17.2042(9) Å, β = 91.871(5)°, Z = 4). In the crystalline structure, the formation of cyclic dimers via double hydrogen bonds O-H⋯O between MI2CA molecules was observed. Interactions between the NH groups of the indole rings and the adjacent methoxy groups, as well as C-H⋯O contacts, significantly influence the spatial arrangement of molecules. The results from DFT calculations, including dimeric and trimeric structures, agree well with the experimental structural and spectroscopic data. Analysis of the infrared spectra confirms the conclusions drawn from X-ray diffraction studies and reveals differences between the IR spectra of the newly obtained polymorph and that reported earlier in the literature. This comprehensive study sheds some light on the MI2CA polymorphism and is important for a potential pharmacological applications of this compound.

Mechanochemical C-H Arylation and Alkylation of Indoles Using 3 d Transition Metal and Zero-Valent Magnesium

Although the 3 d transition-metal catalyzed C-H functionalization have been extensively employed to promote the formation of valuable carbon-carbon bonds, the persistent problems, including the use of sensitive Grignard reagents and the rigorous operations (solvent-drying, inert gas protection, metal pre-activation and RMgX addition rate control), still leave great room for further development of sustainable methodologies. Herein, we report a mechanochemical technology toward in-situ preparation of highly sensitive organomagnesium reagents, and thus building two general 3 d transition-metal catalytic platforms that enables regioselective arylation and alkylation of indoles with a wide variety of halides (including those containing post transformable functionalities and heteroaromatic rings). This mechanochemical strategy also brings unique reactivity and high step-economy in producing functionalized N-free indole products.

Synthetic account on indoles and their analogues as potential anti-plasmodial agents

Malaria caused by P. falciparum, has been recognized as one of the major infectious diseases causing the death of several patients as per the reports from the World Health Organization. In search of effective therapeutic agents against malaria, several research groups have started working on the design and development of novel heterocycles as anti-malarial agents. Heterocycles have been recognized as the pharmacophoric features for the different types of medicinally important activities. Among all these heterocycles, nitrogen containing aza-heterocycles should not be underestimated owing to their wide therapeutic window. Amongst the aza-heterocycles, indoles and fused indoles such as marinoquinolines, isocryptolepines and their regioisomers, manzamines, neocryptolenines, and indolones have been recognized as anti-malarial agents active against P. falciparum. The present work unleashes the synthetic attempts of anti-malarial indoles and fused indoles through cyclocondensation, Fischer-indole synthesis, etc. along with the brief discussions on structure-activity relationships, in vitro or in vivo studies for the broader interest of these medicinal chemists, working on their design and development as potential anti-malarial agents.

Indole-Based Compounds in the Development of Anti-Neurodegenerative Agents

Neurodegeneration is a gradual decay process leading to the depletion of neurons in both the central and peripheral nervous systems, ultimately resulting in cognitive dysfunctions and the deterioration of brain functions, alongside a decline in motor skills and behavioral capabilities. Neurodegenerative disorders (NDs) impose a substantial socio-economic strain on society, aggravated by the advancing age of the world population and the absence of effective remedies, predicting a negative future. In this context, the urgency of discovering viable therapies is critical and, despite significant efforts by medicinal chemists in developing potential drug candidates and exploring various small molecules as therapeutics, regrettably, a truly effective treatment is yet to be found. Nitrogen heterocyclic compounds, and particularly those containing the indole nucleus, which has emerged as privileged scaffold, have attracted particular attention for a variety of pharmacological applications. This review analyzes the rational design strategy adopted by different research groups for the development of anti-neurodegenerative indole-based compounds which have the potential to modulate various molecular targets involved in NDs, with reference to the most recent advances between 2018 and 2023.

Indole-based NNN donor Schiff base ligand and its complexes: Sonication-assisted synthesis, characterization, DNA binding, anti-cancer evaluation and in-vitro biological assay

A novel indole based NNN donor Schiff base ligand and its Ni(II), Zn(II) and Cd(II) complexes have been synthesized using sonication-assisted method which is a highly efficient eco-friendly mechanism. The synthesized complexes have been characterized using elemental analysis, UV-Vis spectroscopy, mass spectrometry, FT-IR, and NMR and are optimized using DFT approach, which provided their theoretical framework. The stoichiometry between the ligand and the metal ions was also determined using Job's method. The thermogravimetric (TGA/DSC) analyses confirm the stability for all complexes at room temperature followed by thermal decomposition in different steps. DNA binding activities have been assessed by employing UV-visible and fluorescence spectra using the CT-DNA. The estimated intrinsic binding constant (Kb) for NiL, ZnL, and CdL complexes was 6.00 × 105, 5.58 × 105, and 4.7 × 105, respectively. In accordance with the Kb value, the quenching constant (Ksv) values of NiL, ZnL, and CdL are 5.59 × 105 M-1, 4.3 × 105 M-1, and 4.08 × 105 M-1 respectively. The anticancer properties have been assessed using MTT Assay. It has been found that the Ni(II) complex (NiL) is the most potent among the series with IC50 of 169 µg/mL. An in-vitro antioxidant experiment using DPPH was used to evaluate the synthesizedcomplexes' ability to scavenge free radicals. The findings indicated that the complexes exhibited notable antioxidant properties. The antioxidant property ZnL has been found to be the highest with an IC50 of 2.91 µg/mL and it follows the order is ZnL > NiL > CdL > L. Using the egg albumin denaturation technique, the anti-inflammatory property have been assessed, and the amount of protein denaturation inhibition has been computed. NiL has the highest % inhibition among the series studied. Comparatively, the metal complexes have been reported to exhibit higher biological activities than the prepared Schiff base ligand. The reason for the excellent biological properties observed in the metal complexes could be attributed to the incorporation of the electron-withdrawing CH3COO- during complexation. Molecular docking studies have been performed on the 2GYT protein and it has been found that the complexes have excellent binding affinity, with NiL having the lowest binding energy of -6.93 Kcal mol-1. The values suggested that NiL is more effective against HePG2 cancer cells, which is also in accordance with the MTT Assay results.

HFIP-mediated C-3-alkylation of indoles and synthesis of indolo[2,3-b]quinolines & related natural products

An expeditious metal free C-3 alkylation of indoles and its NIS-mediated deviation to indolo[2,3-b]quinolines is reported. This protocol, executed in aqueous HFIP has broad substrate scope and is well inclined towards the ideas of sustainable chemistry. Applications of these strategies in accessing bioactive natural products like vibrindole, norcryptotakeine, neocryptolepine and indenoindolone scaffolds has also been demonstrated.

Carbonylative synthesis and functionalization of indoles

Carbonylation processes have become widely recognized as a versatile, convenient, and low-cost method for the synthesis of high-value compounds. Given the great importance of heterocyclic compounds, the carbonylative approach has become increasingly important for their synthesis. In this mini-review, as a class of benzo-fused nitrogen-containing heterocyclic compounds, we summarized and discussed the recent achievements on the synthesis and functionalization of indole derivatives via carbonylative approaches.

Diversity-Oriented Synthesis of Indole-Fused Polycyclic Scaffolds via Rhodium-Catalyzed NH-Indole-Directed C-H Coupling of 2-Phenyl-1H-indoles with Propargylic Alcohol Derivatives

Diversity-oriented synthesis strategy for the efficient assembly of indole-fused polycyclic scaffolds via rhodium-catalyzed NH-indole-directed C-H coupling with propargylic alcohol derivatives in a regioselective manner was developed. Five 2-phenyl-1H-indole-embedded core skeletons were synthesized. In particular, three different indole-fused exo-olefin-containing polycycles were realized, which may be manipulated for further chemistry.

Reaction Pattern and Mechanistic Aspects of Iodine and Iodine-Based Reagents in Selenylation of Aliphatic, Aromatic, and (Hetero)Cyclic Systems

Organoselenium compounds have been the subject of extensive research since the discovery of the biologically active compound ebselen. Ebselen has recently been found to show activity against the main protease of the virus responsible for COVID-19. Other organoselenium compounds are also well-known for their diverse biological activities, with such compounds exhibiting interesting physical properties relevant to the fields of electronics, materials, and polymer chemistry. In addition, the incorporation of selenium into various organic molecules has garnered significant attention due to the potential of selenium to enhance the biological activity of these molecules, particularly in conjunction with bioactive heterocycles. Iodine and iodine-based reagents play a prominent role in the synthesis of organoselenium compounds, being valued for their cost-effectiveness, non-toxicity, and ease of handling. These reagents efficiently selenylate a broad range of organic substrates, encompassing alkenes, alkynes, and cyclic, aromatic, and heterocyclic molecules. They serve as catalysts, additives, inducers, and oxidizing agents, facilitating the introduction of different functional groups at alternate positions in the molecules, thereby allowing for regioselective and stereoselective approaches. Specific iodine reagents and their combinations can be tailored to follow the desired reaction pathways. Here, we present a comprehensive review of the progress in the selenylation of organic molecules using iodine reagents over the past decade, with a focus on reaction patterns, solvent effects, heating, microwave, and ultrasonic conditions. Detailed discussions on mechanistic aspects, such as electrophilic, nucleophilic, radical, electrochemical, and ring expansion reactions via selenylation, multiselenylation, and difunctionalization, are included. The review also highlights the formation of various cyclic, heterocyclic, and heteroarenes resulting from the in situ generation of selenium intermediates, encompassing cyclic ketones, cyclic ethers, cyclic lactones, selenophenes, chromones, pyrazolines, pyrrolidines, piperidines, indolines, oxazolines, isooxazolines, lactones, dihydrofurans, and isoxazolidines. To enhance the reader's interest, the review is structured into different sections covering the selenylation of aliphatic sp2/sp carbon and cyclic sp2 carbon, and then is further subdivided into various heterocyclic molecules.

Divergent Electrochemical Synthesis of Indoles through pKa Regulation of Amides: Synthetic and Mechanistic Insights

A divergent synthetic approach to access highly substituted indole scaffolds is illustrated. By virtue of a tunable electrochemical strategy, distinct control over the C-3 substitution pattern was achieved by employing two analogous 2-styrylaniline precursors. The chemoselectivity is governed by the fine-tuning of the acidity of the amide proton, relying on the appropriate selection of N-protecting groups, and assisted by the reactivity of the electrogenerated intermediates. Detailed mechanistic investigations based on cyclic voltametric experiments and computational studies revealed the crucial role of water additive, which assists the proton-coupled electron transfer event for highly acidic amide precursors, followed by an energetically favorable intramolecular C-N coupling, causing exclusive fabrication of the C-3 unsubstituted indoles. Alternatively, the implementation of an electrogenerated cationic olefin activator delivers the C-3 substituted indoles through the preferential nucleophilic nature of the N-acyl amides. This electrochemical approach of judicious selection of N-protecting groups to regulate pKa/E° provides an expansion in the domain of switchable generation of heterocyclic derivatives in a sustainable fashion, with high regio- and chemoselectivity.

Nickel(II)-Catalyzed Formal [3+2] Cycloadditions between Indoles and Donor-Acceptor Cyclopropanes

This article describes the development of a nickel-catalyzed regio- and diastereoselective formal [3+2] cycloaddition between N-substituted indoles and donor-acceptor cyclopropanes to synthesize cyclopenta[b]indoles. Optimized reaction conditions provide the desired nitrogen-containing cycloadducts in up to 93% yield and dr 8.6:1 with complete regioselectivity. The substrate scope showed high tolerance to various substituted indoles and cyclopropanes, resulting in the synthesis of six new cyclopenta[b]indoles and the isolation of five derivatives previously reported in the literature. In addition, a mechanistic proposal for the reaction was studied through online reaction monitoring by ESI-MS, allowing for the identification of the reactive intermediates in the Ni(II) catalyzed process. X-ray crystallography confirmed the structure and relative endo stereochemistry of the products. This method enables the fast and efficient construction of fused indolines from readily accessible starting materials.

Synthesis of Indolyl Phenyl Diketones through Visible-Light-Promoted Ni-Catalyzed Intramolecular Cyclization/Oxidation Sequence of Ynones

The combination of visible light catalysis and Ni catalysis has enabled the synthesis of indolyl phenyl diketones through the cyclization/oxidation process of ynones. This reaction proceeded under mild and base-free conditions and showed a broad scope and feasibility for gram-scale synthesis. Several natural products and biologically interesting molecules could be readily postfunctionalized by this method.

Design, synthesis, and anticancer evaluation of 1-benzo[1,3]dioxol-5-yl-3-N-fused heteroaryl indoles

A series of 1-benzo[1,3]dioxol-5-yl-indoles bearing 3-N-fused heteroaryl moieties have been designed based on literature reports of the activity of indoles against various cancer cell lines, synthesized via a Pd-catalyzed C-N cross-coupling, and evaluated for their anticancer activity against prostate (LNCaP), pancreatic (MIA PaCa-2), and acute lymphoblastic leukemia (CCRF-CEM) cancer cell lines. A detailed structure-activity relationship study culminated in the identification of 3-N-benzo[1,2,5]oxadiazole 17 and 3-N-2-methylquinoline 20, whose IC50 values ranged from 328 to 644 nM against CCRF-CEM and MIA PaCa-2. Further mechanistic studies revealed that 20 caused cell cycle arrest at the S phase and induced apoptosis in CCRF-CEM cancer cells. These 1-benzo[1,3]dioxol-5-yl-3-N-fused heteroaryl indoles may serve as a template for further optimization to afford more active analogs and develop a comprehensive understanding of the structure-activity relationships of indole anticancer molecules.

Enzymatic Synthesis of Indole-Based Imidazopyridine using α-Amylase

The imidazo[1,2-a]pyridine scaffold has gained significant attention due to its presence as a lead structure in several commercially available pharmaceuticals like zolimidine, zolpidem, olprinone, soraprazan, etc. Further, indole-based imidazo[1,2-a]pyridine derivatives have been found interesting due to their anticancer and antibacterial activities. However, limited methods have been reported for the synthesis of indole-based imidazo[1,2-a]pyridines. In this study, we have successfully developed a biocatalytic process for synthesizing indole-based imidazo[1,2-a]pyridine derivatives using the α-amylase enzyme catalyzed Groebke-Blackburn-Bienayme (GBB) multicomponent reaction of 2-aminopyridine, indole-3-carboxaldehyde, and isocyanide. The generality and robustness of this protocol were shown by synthesizing differently substituted indole-based imidazo[1,2-a]pyridines in good isolated yields. Furthermore, to make α-amylase a reusable catalyst for GBB multicomponent reaction, it was immobilized onto magnetic metal-organic framework (MOF) materials [Fe3 O4 @MIL-100(Fe)] and found reusable up to four consecutive catalytic cycles without the significant loss in catalytic activity.

One-Pot Three-Component Synthesis of Indolyl-4H-chromene-3-sulfonyl Fluoride: A Class of Important Pharmacophore

A one-pot, sequential three-component reaction between salicylaldehyde, indole, and 2-bromoprop-2-ene-1-sulfonyl fluoride (BPESF) has been demonstrated for the synthesis of sulfonyl fluoride substituted 4H-chromene derivatives in moderate to excellent yields (45%-94%). This one-pot sequential method features easily available starting materials, wide substrate scope, mild conditions, and great efficiency.

Unlocking Diversity: From Simple to Cutting-Edge Synthetic Methodologies of Bis(indolyl)methanes

From a synthetic perspective, bis(indolyl)methanes have undergone extensive investigation over the past two to three decades owing to their remarkable pharmacological activities, encompassing anticancer, antimicrobial, antioxidant, and antiinflammatory properties. These highly desirable attributes have spurred significant interest within the scientific community, leading to the development of various synthetic strategies that are not only more efficient but also ecofriendly. This synthesis-based literature review delves into the advancements made in the past 5 years, focusing on the synthesis of symmetrical as well as unsymmetrical bis(indolyl)methanes. The review encompasses a wide array of methods, ranging from well-established techniques to more unconventional and innovative approaches. Furthermore, it highlights the exploration of various substrates, encompassing readily available chemicals such as indole, aldehydes/ketones, indolyl methanols, etc. as well as the use of some specific compounds as starting materials to achieve the synthesis of this invaluable molecule. By encapsulating the latest developments in this field, this review provides insights into the expanding horizons of bis(indolyl)methane synthesis.

Hybrid Heterocycles: Ag(I)-Catalyzed C-C/C-N/C-O Coupled Cascade Dual Cyclization to Valuable Indolo-4H-indolones and Indolo-4H-chromenes

Herein, we report a highly efficient Ag(I)-catalyzed indolyzation with Friedel-Crafts alkylation through a cascade cyclization strategy for accessing valuable hybrid heterocycles for the first time. This general strategy consists of forming four C-C/C-N/C-O bonds toward dual annulation reactions of 2-alkynylanilines with methyl benzoate-2-carboxaldehydes and aromatic amines, as well as with salicylaldehydes and malononitrile. Variably substituted new indolo-4H-phthalimidines and indolo-4H-chromenes were synthesized with excellent yields (85-93%) under mild reaction conditions.

Regioselective C3Alkylation of Indoles for the Synthesis of Bis(indolyl)methanes and 3-Styryl Indoles

Herein, we describe an efficient transition-metal-free regioselective C3alkylation of indoles for the synthesis of bis(indolyl)methanes and 3-styryl indoles. Nitrobenzene is employed as the oxidant to oxidize the alcohols in the presence of a strong base and the reaction avoids the use of transition metals such as Ru and Mn. The protocol provides a favorable route to access biologically active compounds such as arundine, vibrindole A, and turbomycin B.

Facile Synthesis of Some New Peptidomimetic β3 -and β2,3 -Amino Alcohols Possessing Pyridyl Moiety via Reductive Ring Opening of Pyridyl-isoxazolidines

Regio- and stereoselective 1,3-dipolar cycloadditions of C-(3-pyridyl)-N-phenylnitrone (2) with variedly substituted dipolarophiles (3, 4) were carried out to obtain substituted pyridyl-isoxazolidines (5-8). Reductive cleavage of pyridyl-isoxazolidines (5-8) with ammonium formate, methanol-THF solvents, at ambient temperature, in the presence of Pd/C provided a facile route for the synthesis of β3 -and β2,3 -amino alcohols (9-12), with a substitution pattern having pronounced influence on torsional angles. The obtained compounds (9-12) are valuable scaffolds which can be utilized for peptidomimetics. Thus, the present methodology for reductive opening of isoxazolidine ring avoids the disadvantages of using expensive apparatus and hazards involved in the use of hydrogen gas. The preferential formation of amino-alcohols in case of bicyclic isoxazolidines (8a-c), which precludes any recyclization is rationalized by DFT calculations.

Nitro Indole Derivatives as Novel Dual-Polarity Matrices for MALDI Mass Spectrometry and Imaging with Broad Applications

A new matrix framework is presented in this study for the improved ionization efficiency of complex mixtures by matrix-assisted laser desorption ionization (MALDI) mass spectrometry/imaging. Five nitro indole (NI) derivatives [3-methyl-4-nitro-1H-indole (3,4-MNI), 3-methyl-6-nitro-1H-indole (3,6-MNI), 2,3-dimethyl-4-nitro-1H-indole (2,3,4-DMNI), 2,3-dimethyl-6-nitro-1H-indole (2,3,6-DMNI), and 4-nitro-1H-indole (4-NI)] were synthesized and shown to produce both positive and negative ions with a broad class of analytes as MALDI matrices. NI matrices were compared to several common matrices, such as 2,5-dihydroxybenzoic acid (DHB), alpha-cyano-4-hydroxylcinnamic acid (CHCA), sinapinic acid (SA), 1,5-diaminonaphthelene (1,5-DAN), and 9-aminoacridine (9-AA), for the analysis of lipid, peptide, protein, glycan, and perfluorooctanesulfonic acid (PFOS) compounds. 3,4-MNI demonstrated the best performance among the NI matrices. This matrix resulted in reduced ion suppression and better detection sensitivity for complex mixtures, for example, egg lipids/milk proteins/PFOS in tap water, while 2,3,6-DMNI was the best matrix for blueberry tissue imaging. Several important aspects of this work are reported: (1) dual-polarity ion production with NI matrices and complex mixtures; (2) quantitative analysis of PFOS with a LOQ of 0.5 ppb in tap water and 0.05 ppb in MQ water (without solid phase extraction enrichment), with accuracy and precision within 5%; (3) MALDI imaging with 2,3,6-DMNI as a matrix for plant metabolite/lipid identification with ionization enhancement in the negative ion mode m/z 600-900 region; and (4) development of a thin film deposition under/above tissue method for MALDI imaging with a vacuum sublimation matrix on a high-vacuum MALDI instrument.

Cascade Synthesis of New Indole-Containing Pentacyclic Scaffolds Mediated by Aryl and Iminyl Radicals

A five-step approach, starting from simple 1,5-disubstituted indoles, has been implemented for the synthesis of diversely substituted indole-pyrido-indene pentacyclic compounds up to 54 % yield via domino radical-mediated processes in the presence of the radical reagents DLP/TTMSS and AIBN/TTMSS. Reactions proceeded with diverse key starting radical cyano-precursors strategically synthesized which were subsequently transformed into the target pentacyclic compounds through an aryl/iminyl radical-mediated domino reactions sequence. In addition to the routine spectroscopic techniques, the structure of radical precursors, as well as, the target pentacyclic products were unequivocally established by single crystal X-ray diffraction, confirming the effectiveness of the proposed synthetic sequence.

Heterocyclic-Based Analogues against Sarcine-Ricin Loop RNA from Escherichia coli: In Silico Molecular Docking Study and Machine Learning Classifiers

BACKGROUND

Heterocyclic-based drugs have strong bioactivities, are active pharmacophores, and are used to design several antibacterial drugs. Due to the diverse biodynamic properties of well-known heterocyclic cores, such as quinoline, indole, and its derivatives, they have a special place in the chemistry of nitrogen-containing heterocyclic molecules.

OBJECTIVES

The objective of this study is to analyze the interaction of several heterocyclic molecules using molecular docking and machine learning approaches to find out the possible antibacterial drugs.

METHODS

The molecular docking analysis of heterocyclic-based analogues against the sarcin-Ricin Loop RNA from E. coli with a C2667-2'-OCF3 modification (PDB ID: 6ZYB) is discussed.

RESULTS

Many heterocyclic-based derivatives show several residual interaction, affinity, and hydrogen bonding with sarcin-Ricin Loop RNA from E. coli with a C2667-2'-OCF3 alteration which are identified by the investigation of in silico molecular docking analysis of such heterocyclic derivatives.

CONCLUSION

The dataset from the molecular docking study was used for additional optimum analysis, and the molecular descriptors were classified using a variety of machine learning classifiers, including the GB Classifier, CB Classifier, RF Classifier, SV Classifier, KNN Classifier, and Voting Classifier. The research presented here showed that heterocyclic derivatives may operate as potent antibacterial agents when combined with other compounds to produce highly efficient antibacterial agents.

An Operationally Simple Approach to Indole Derivatives from 2-Alkenylanilines Utilizing an Oxidation-Intramolecular Cyclization-Elimination Sequence

Herein we describe a novel route to indole derivatives from a variety of N-substituted 2-alkenylanilines. This route features three operationally simple steps: (1) oxidation to convert N-substituted 2-alkenylanilines into epoxide intermediates, (2) intramolecular cyclization, and (3) the acid-catalyzed elimination of water.

Amidative Cyclization of Alkynyl Esters to Access Pyrazin-1(2H)-ones: Application to the Synthesis of Peramine and Dibromophakellin

Herein, we report an efficient 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed tandem intermolecular amidation and regioselective intramolecular 6-exo-dig cyclization of alkynyl esters to efficiently access pyrazine-1(2H)-one scaffolds. This organo-catalyzed [5 + 1] annulation features a broad substrate scope concerning both annulating partners. Total syntheses of peramine and formal syntheses of dibromophakellin natural products were achieved to show the application potential of the method.

Synthesis of 3-sulfenylindole derivatives from 4-hydroxy-2H-chromene-2-thione and indole using oxidative cross-dehydrogenative coupling reaction and anti-proliferative activity study of some of their sulfone derivatives

The synthesis of hitherto unreported 3-sulfenylindole derivatives is achieved from 4-hydroxy-2H-chromene-2-thione (1) and indole (2) by employing an oxidative cross-dehydrogenative coupling reaction using a combination of 10 mol% of molecular iodine and 1 equivalent of TBHP in DMSO at room temperature. Then, the 3-sulfenylindole derivatives 3a, 3b, 3d, 3f, 3 h, and 3 k were converted into their corresponding sulfone derivatives because of lead likeness properties. Subsequently, a target prediction and docking study of six sulfone derivatives (5a-f) was performed, and four sulfones, namely 5a, 5d, 5e, and 5f, were selected for further in-vitro studies. The four sulfones mentioned above exhibited prominent anti-proliferative activity on breast cancer (MCF7) cell lines. In addition, this reaction was exergonic through quantum chemical analysis of the mechanistic steps. The salient features of this reaction are mild reaction conditions, good yields, and broad substrate scope.

Heterocyclic and non-heterocyclic arena of monocarboxylate transporter inhibitors to battle tumorigenesis

Monocarboxylate transporters (MCTs) have gained significant attention in cancer research due to their critical role in tumour metabolism. MCTs are legends for transporting lactate molecules in cancer cells, an oncometabolite and waste product of glycolysis, acting as an indispensable factor of tumour proliferation. Targeting MCTs with inhibitors has emerged as a promising strategy to combat tumorigenesis. This article summarizes the most recent research on MCT inhibitors in preventing carcinogenesis, covering both heterocyclic and non-heterocyclic compounds. Heterocyclic and non-heterocyclic compounds such as pteridine, pyrazole, indole, flavonoids, coumarin derivatives and cyanoacetic acid derivatives have been reported as potent MCT inhibitors. We examine the molecular underpinnings of MCTs in cancer metabolism, the design and synthesis of heterocyclic and non-heterocyclic MCT inhibitors, their impact on tumour cells and the microenvironment and their potential as therapeutic agents. Moreover, we explore the challenges associated with MCT inhibitor development and propose future directions for advancing this field. This write-up aims to provide researchers, scientists and clinicians with a comprehensive understanding of the heterocyclic and non-heterocyclic MCT inhibitors and their potential in combating tumorigenesis.

Highly Enantioselective Synthesis of 3a-Fluorofuro[3,2-b]indolines via Organocatalytic Aza-Friedel-Crafts Reaction/Selective C-F Bond Activation

Fluoroalkylated compounds are of high interest in drug discovery and have inspired the evolution of diverse C-F bond activation methodologies. However, the selective activation of polyfluorinated compounds remains challenging. Herein, we describe an unprecedented strategy for synthesizing enantioenriched fluorofuro[3,2-b]indolines through the organocatalytic aza-Friedel-Crafts reaction coupled with selective C-F bond activation. These reactions feature excellent enantioselectivities (≤96% ee) and yields (≤96%) as well as good functional group compatibility. Mechanistic investigations by means of 19F nuclear magnetic resonance experiments provided sufficient support for silica gel as the key medium in this transformation.

Electrochemical selenocyclization of 2-ethynylanilines with diselenides: facile and efficient access to 3-selenylindoles

An efficient electrochemical selenocyclization strategy for the synthesis of 3-selenylindoles from 2-ethynylanilines and diselenides has been developed in simple tube- or beaker-type undivided cells under ambient conditions. Notably, these sustainable transformations are completed within a short time with low equivalents of charges, diselenides and electrolytes, exhibiting a broad substrate scope with excellent functional group compatibility. Moreover, a gram-scale electrosynthesis and late-stage functionalization of complex molecules further demonstrate the practical synthetic potential of this facile electrochemical system.

In Vitro and In Vivo Biological Evaluation of Indole-thiazolidine-2,4-dione Derivatives as Tyrosinase Inhibitors

Tyrosinase is an important rate-limiting enzyme in melanin biosynthesis. To find potential tyrosinase inhibitors with anti-melanogenic activity, a series of indole-thiazolidine-2,4-dione derivatives 5a~5z were synthesized by incorporating indole with thiazolidine-2,4-dione into one compound and assayed for their biological activities. All compounds displayed tyrosinase inhibitory activities and 5w had the highest anti-tyrosinase inhibitory activity with an IC50 value of 11.2 μM. Inhibition kinetics revealed 5w as a mixed-type tyrosinase inhibitor. Fluorescence quenching results indicated that 5w quenched tyrosinase fluorescence in a static process. CD spectra and 3D fluorescence spectra results suggested that the binding of 5w with tyrosinase could change the conformation and microenvironment of tyrosinase. Molecular docking also represented the binding between 5w and tyrosinase. Moreover, 5w could inhibit tyrosinase activity and melanogenesis both in B16F10 cells and the zebrafish model. Therefore, compound 5w could serve as a tyrosinase inhibitor with anti-melanogenic activity.

N-Indolyl diiron vinyliminium complexes exhibit antiproliferative effects in cancer cells associated with disruption of mitochondrial homeostasis, ROS scavenging, and antioxidant activity

The indole scaffold has been established as a key organic moiety for developing new drugs; on the other hand, a range of diiron bis-cyclopentadienyl complexes have recently emerged for their promising anticancer potential. Here, we report the synthesis of novel diiron complexes with an indole-functionalized vinyliminium ligand (2-5) and an indole-lacking analogue for comparative purposes (6), which were characterized by analytical and spectroscopic techniques. Complexes 2-6 are substantially stable in DMSO‑d6 and DMEM-d solutions at 37 °C (8% average degradation after 48 h) and display a balanced hydrophilic/lipophilic behaviour (LogPow values in the range -0.32 to 0.47), associated with appreciable water solubility. The complexes display selective antiproliferative potency towards several cancer cells in monolayer cultures, mainly in the low micromolar range, with reduced toxicity towards noncancerous epithelial cells. Thus, the cytotoxicity of the complexes is comparable to or better than clinically used metallopharmaceutical cisplatin. Comparing the antiproliferative activity obtained for complexes containing different ligands, we confirmed the importance of the indolyl group in the mechanism of antiproliferative activity of these complexes. Cell-based mechanistic studies suggest that the investigated diiron vinyliminium complexes (DVCs) show cytostatic rather than cytotoxic effects and subsequently induce a population of cells to undergo apoptosis. Furthermore, the molecular mechanism of action involves interactions with mitochondrial DNA and proteins, the reactive oxygen species (ROS)-scavenging properties and antioxidant activity of these complexes in cancer cells. This study highlights the importance of DVCs to their cancer cell activity and reinforces their prospective therapeutic potential as anticancer agents.

A Tandem Madelung Indole Synthesis Mediated by a LiN(SiMe3)2/CsF System

A tandem Madelung indole synthesis by the reaction of methyl benzoate and N-methyl-o-toluidine has been discovered. The combination of LiN(SiMe3)2 with CsF is the key factor, which secures the high efficiency of such tandem transformations. Simply combining methyl benzoate, N-methyl-o-toluidine LiN(SiMe3)2, and CsF generated a diverse array of N-methyl-2-phenylindoles (31 examples, 50-90% yields). Furthermore, the scalability and the poststructural modifications of this indole synthesis were demonstrated.

Dual Palladium-Photoredox-Mediated Regioselective Acylation of Carbazoles and Indolines

We have described a dual palladium-photoredox-catalyzed highly regioselective acylation of carbazoles and indolines using molecular oxygen as the green oxidant. The reaction shows a broad substrate scope and good functional group tolerance. Late-stage functionalization of a carprofen drug derivative, further manipulation of products, and gram-scale synthesis of the acylated products were illustrated to show the versatility of the method.

A redox-neutral weak carbonyl chelation assisted C4-H allylation of indoles with vinylcyclopropanes

A weak acyl chelation-assisted distal C4-H allylation of indoles has been accomplished using vinylcyclopropanes as an allylating agent under redox-neutral ruthenium(II) catalysis. The regioselectivity, removable directing group, substrate scope and diastereoselectivity are the important practical features.

Consecutive four-component synthesis of trisubstituted 3-iodoindoles by an alkynylation-cyclization-iodination-alkylation sequence

A library of 19 differently substituted 3-iodoindoles is generated by a consecutive four-component reaction starting from ortho-haloanilines, terminal alkynes, N-iodosuccinimide, and alkyl halides in yields of 11-69%. Initiated by a copper-free alkynylation, followed by a base-catalyzed cyclizive indole formation, electrophilic iodination, and finally electrophilic trapping of the intermediary indole anion with alkyl halides provides a concise one-pot synthesis of 3-iodoindoles. The latter are valuable substrates for Suzuki arylations, which are exemplified with the syntheses of four derivatives, some of them are blue emitters in solution and in the solid state, in good yield.