Asymmetric aza-Friedel-Crafts reaction of newly developed ketimines: access to chiral indeno[1,2-b]quinoxaline architectures

The functionalized 11-amino-indeno[1,2-b]quinoxaline scaffold is a pivotal structural motif in diverse bioactive compounds. In this study, we developed a chiral phosphoric acid catalysed enantioselective aza-Friedel-Crafts reaction between indeno[1,2-b]quinoxalin-11-imines and indoles. This methodology enables the synthesis of chiral hybrid architectures incorporating both 11-aminoindeno[1,2-b]quinoxaline and indole moieties, achieving exceptional synthetic efficiency (up to 99% yield) with outstanding stereocontrol (up to 99% ee).

Discovery of intermolecular cascade annulation for dihydrobenzo[b][1,8]naphthyridine-ylidene-pyrrolidinetriones

Developing efficient procedures for the synthesis of combinations of pharmacophores continues to be a vital objective in synthetic science. Herein, we report an unprecedented family of dihydrobenzo[b][1,8]naphthyridine-ylidene-pyrrolidinetriones achieved by reacting ortho-halogenated quinolonechalcones with aminomaleimides under metal-free conditions. Among these compounds, several exhibit the potential to serve as fluorescent dyes for biological applications. Mechanistic investigations indicate that the reaction proceeds via a 1,4-Michael addition followed by an intermolecular cascade annulation, which involves aniline fragment transfer and SNAr processes. As far as we know, studies regarding the synthesis of dihydrobenzo[b][1,8]naphthyridine-ylidene-pyrrolidinetriones are rare. This discovery offers great inspiration for a feasible approach toward the creation of more complex and useful molecules.

Design, synthesis, anti-mycobacterial activity, molecular docking and ADME analysis of spiroquinoxaline-1,2,4-oxadiazoles via [3 + 2] cycloaddition reaction under ultrasound irradiation

The development of anti-tuberculosis (anti-TB) drugs has become a challenging task in medicinal chemistry. This is because Mycobacterium tuberculosis (TB), the pathogen that causes tuberculosis, has an increasing number of drug-resistant strains, and existing medication therapies are not very effective. This resistance significantly demands new anti-TB drug profiles. Here, we present the design and synthesis of a number of hybrid compounds with previously known anti-mycobacterial moieties attached to quinoxaline, quinoline, tetrazole, and 1,2,4-oxadiazole scaffolds. A convenient ultrasound methodology was employed to attain spiroquinoxaline-1,2,4-oxadiazoles via [3 + 2] cycloaddition of quinoxaline Schiff bases and aryl nitrile oxides at room temperature. This approach avoids standard heating and column chromatography while producing high yields and shorter reaction times. The target compounds 3a-p were well-characterized, and their in vitro anti-mycobacterial activity (anti-TB) was evaluated. Among the screened compounds, 3i displayed promising activity against the Mycobacterium tuberculosis cell line H37Rv, with an MIC99 value of 0.78 µg/mL. However, three compounds (3f, 3h, and 3o) exhibited potent activity with MIC99 values of 6.25 µg/mL. To further understand the binding interactions, the synthesized compounds were docked against the tuberculosis protein 5OEQ using in silico molecular docking. Moreover, the most active compounds were additionally tested for their cytotoxicity against the RAW 264.7 cell line, and the cytotoxicity of compounds 3f, 3h, 3i, and 3o was 27.3, 28.9, 26.4, and 30.2 µg/mL, respectively. These results revealed that the compounds 3f, 3h, 3i, and 3o were less harmful to humans. Furthermore, the synthesized compounds were tested for ADME qualities, and the results suggest that this series is useful for producing innovative and potent anti-tubercular medicines in the future.

Recent trends for chemoselectivity modulation in one-pot organic transformations

In organic reactions, chemoselectivity refers to the selective reactivity of one functional group in the presence of another. This can be more successful if the reagent and reaction parameters are appropriately chosen. One-pot reactions have been shown to be an effective structural variety technique for the development of novel heterocyclic or carbocyclic compounds. This review article focuses on recent efforts by researchers from around the world to synthesise novel organic molecules utilising these methodologies (2013-2024), as well as their mechanism insights. The substrate, catalyst, solvent, and temperature conditions all have a significant impact on chemoselectivity in the organic reactions described here. The manipulation of chemoselectivity in organic processes creates new potential for the production of novel heterocycles and carbocycles.

I2-Mediated Site-Selective C-H Functionalization: Access to p-Amino-Substituted Unsymmetrical Benzils and Quinoxalines from Sulfoxonium Ylides

An I2-mediated approach for selective C-H functionalization of unprotected aniline derivatives for synthesizing benzils and quinoxaline derivatives from sulfoxonium ylides has been described. Aniline derivatives and sulfoxonium ylides ornamented with different functional groups showed good compatibility. They afforded the corresponding products with moderate to high yields via a mild and simple procedure. Finally, we validated the practicality of this method by scaling up the reaction and further conversion of the synthesized derivatives into other valuable molecules.

Synthesis of functionalized tetrahydrodibenzo[b,g][1,8]naphthyridin-1(2H)-ones through base-promoted annulation of quinoline-derived dipolarophiles and cyclic enaminones

An eco-friendly and metal-free method for the synthesis of tetrahydrodibenzo[b,g][1,8]naphthyridin-1(2H)-ones was established. Quinoline-derived dipolarophiles and cyclic enaminones as starting materials undergo a 1,4-Michael addition/SNAr tandem annulation reaction affording the target products. This approach features transition metal-free conditions, good functional group tolerance and operational simplicity.

Molecular orientation rules the efficiency of immobilized antioxidants

Tannic acid (TA) and glutathione (GSH) are important molecular antioxidants against reactive oxygen species. Their efficiency is limited by low solubility and high sensitivity, which may be solved by confinement in composite materials. Here, effect of immobilization of these antioxidants on their radical scavenging activity was investigated using layered double hydroxide (LDH) nanoparticles as hosts. Different preparation methods were applied to build composite systems leading to variations in the molecular orientation of both TA and GSH on the surface or among the layers of LDHs. Systematic combination of spectroscopy (FT-IR, Raman, UV-VIS-NIR-DRS), diffraction (XRD) and microscopy (SEM) methods revealed perpendicular or parallel orientation of TA on the surface of LDH depending on the preparation approach applied. Immobilization of GSH protected the antioxidant molecules from degradation. Radical scavenging tests evidenced that the activity of the antioxidants strongly depends on the molecular orientation. The LDH supported GSH and TA proved as durable and reusable antioxidant agents to be applied as radical scavengers in medical therapies or in industrial processes.

Discovery, synthesis and in silico approach of pyrrolo [3,4-c]pyrroles as SARS-CoV-2 mpro inhibitors

A new coronavirus has been identified as the contributing agent of the severe acute respiratory syndrome (SARS). The main viral protease (Mpro), which controls the activities of the coronavirus replication complex, which is an essential target for the treatment of coronavirus disease. With the primary objective of targeting this receptor, we designed a new series of pyrrolo [3,2-c] pyrroles, synthesized and characterized using various analytical techniques including FT-IR, UV-Vis and NMR spectroscopic studies. The biological descriptors of the synthesized compounds were investigated using DFT calculation. The mode of binding and reactivity of the target compounds with SARS-CoV-2 main protease (Mpro) were studied using molecular docking and molecular dynamics (MD) simulation. Molecular docking of the compounds (4a and 5a) showed a promising binding affinity towards Mpro protein with the binding energy of -7.8 kcal/mol and -7.0 kcal/mol, respectively. The results of MD simulation and prime MM-GBSA calculation were consistent with molecular docking. The absorption, distribution, metabolism and excretion (ADME) properties of the compounds are in the acceptable range, as they are orally active and obey Lipinski's rule of five without violation. In addition, in silico toxicity prediction using the Pro-Tox II revealed the non-toxic nature of the compounds. Hence the obtained results suggest that these compounds could be a possible anti-viral candidate and highlight this series of compounds for further drug design and development against SARS-CoV-2.Communicated by Ramaswamy H. Sarma.

Development of new spiro[1,3]dithiine-4,11'-indeno[1,2-b]quinoxaline derivatives as S. aureus Sortase A inhibitors and radiosterilization with molecular modeling simulation

Multi-drug resistant microbes have become a severe threat to human health and arise a worldwide concern. A total of fifteen spiro-1,3-dithiinoindenoquinoxaline derivatives 2-7 were synthesized and evaluated for their biological activities against five standard and MDRB pathogens. The MIC and MBC/MFC for the most active derivatives were determined in vitro via broth microdilution assay. These derivatives showed significant activity against the tested strains with microbicidal behavior, with compound 4b as the most active compound (MIC range between 0.06 and 0.25 µg/mL for bacteria strains and MIC = 0.25 µg/mL for C. albicans). The most active spiro-1,3-dithiinoindenoquinoxaline derivatives were able to inhibit the activity of SrtA with IC₅₀ values ranging from 22.15 ± 0.4 µM to 37.12 ± 1.4 µM. In addition, the active spiro-1,3-dithiinoindenoquinoxaline attenuated the in vitro virulence-related phenotype of SrtA by weakening the adherence of S. aureus to fibrinogen and reducing the biofilm formation. Surprisingly, compound 4b revealed potent SrtA inhibitory activity with IC₅₀ = 22.15 µM, inhibiting the adhesion of S. aureus with 39.22 ± 0.15 % compared with untreated 9.43 ± 1.52 %, and showed a reduction in the biofilm biomass of S. aureus with 32.27 ± 0.52 %. We further investigated the effect of gamma radiation as a sterilization method on the microbial load and found that a dose of 5 kGy was sufficient to eradicate the microbial load. The quantum chemical studies exhibited that the tested derivatives have a small energy band gap (ΔE = -2.95 to -3.61 eV) and therefore exert potent bioactivity by interacting with receptors more stabilizing.

The crystal structure of dimethylammonium 8-[(7,9-dioxo-6,10-dioxaspiro[4.5]decan-8-ylidene)methyl]-9-oxo-6,10-dioxaspiro[4.5]dec-7-en-7-olate, C19H25NO8

C19H25NO8, monoclinic, P21/n (no. 14), a = 10.149(2) Å, b = 12.338(3) Å, c = 15.898(3) Å, β = 97.58(3)°, V = 1973.2(7) Å3, Z = 4, R gt (F) = 0.0581, wR ref (F 2) = 0.1842, T = 293(2) K.

Recent updates on the anticancer activity of quinoxaline hybrids (Jan. 2017-Jan. 2022)

Abstract:

Cancer as one of the leading causes of death among non-communicable diseases has already posed a heavy burden on the world health system. Chemotherapy is one of the most effective approaches for cancer treatment, but multidrug resistance, lack of efficacy, and toxic side effects hamper efficacious cancer chemotherapy, creating an urgent need to develop novel, more effective and less toxic anticancer therapeutics. Quinoxalines as fascinating structures constitute an important class of heterocycles in drug discovery. Quinoxaline hybrids could exert anticancer activity through diverse mechanisms and possess profound in vitro and in vivo efficacy against various cancers including multidrug-resistant forms. Thus, quinoxaline hybrids represent useful templates for the control and eradication of cancer. The purpose of the present review article is to provide an emphasis on the recent developments (Jan. 2017-Jan. 2022) in quinoxaline hybrids with insights into their in vitro and in vivo anticancer potential as well as structure-activity relationships (SARs) to facilitate further rational design of more effective candidates.

An overview of quinoxaline synthesis by green methods: recent reports

Quinoxalines and their derivatives belong to an important class of bicyclic aromatic heterocyclic system, also known as benzopyrazines, containing a benzene ring and a pyrazine ring. They have attracted considerable attention over the years due to their potential biological and pharmaceutical properties. A wide range of synthetic strategies is reported in this significant area of research. The present review showcases recent research advances in the synthesis of quinoxaline derivatives following environmentally benign approaches.

Supported l-tryptophan on Fe3O4@SiO2 as an efficient and magnetically separable catalyst for one-pot construction of spiro[indene-2,2'-naphthalene]-4'-carbonitrile derivatives

In this work, l-tryptophan functionalized silica-coated magnetic nanoparticles were readily prepared and evaluated as a recyclable magnetic nanocatalyst for the synthesis of spiro[indene-2,2'-naphthalene]-4'-carbonitrile derivatives through the one-pot four-component reaction of malononitrile, cyclohexanone, aromatic aldehydes, and 1,3-indandione. This novel magnetic nanocatalyst was confirmed to be effective and provide products in moderate to excellent yields under reflux conditions. The structure of obtained nanoparticles was characterized using FT-IR, XRD, VSM, EDX, elemental mapping, FE-SEM, and TGA. This synthetic protocol provides several benefits such as excellent yields in short reaction times (64-91%), saving costs, reusability of the catalyst using an external magnet (seven runs), and low catalyst loading.

New Methods for the Synthesis of Spirocyclic Cephalosporin Analogues

Spiro compounds provide attractive targets in drug discovery due to their inherent three-dimensional structures, which enhance protein interactions, aid solubility and facilitate molecular modelling. However, synthetic methodology for the spiro-functionalisation of important classes of penicillin and cephalosporin β-lactam antibiotics is comparatively limited. We report a novel method for the generation of spiro-cephalosporin compounds through a Michael-type addition to the dihydrothiazine ring. Coupling of a range of catechols is achieved under mildly basic conditions (K2CO3, DMF), giving the stereoselective formation of spiro-cephalosporins (d.r. 14:1 to 8:1) in moderate to good yields (28-65%).

Activator free diastereoselective 1,3-dipolar cycloaddition: a quick access to coumarin based spiro multi heterocyclic adducts

A formal diastereoselective 1,3-dipolar cycloaddition of azomethine ylide and coumarin derivatives to construct coumarin based spiro multi heterocyclics has been described. The in situ generation of azo-ylide was achieved for various heterocyclic carbonyls (indenoquinoxaline and isatin). This transformation is also suitable for maleimide dipolarophiles for the synthesis of hydro-maleimide derivatives. These decarboxylative annulations neither required any catalyst nor any activator. Further the pure products were isolated by filtration from the reaction mixture after the reaction under ambient conditions.

A General Method for the Synthesis of 11H-Indeno[1,2-B]Quinoxalin- 11-Ones and 6H-Indeno[1,2-B]Pyrido[3,2-E]Pyrazin-6-One Derivatives Using Mandelic Acid as an Efficient Organo-Catalyst at Room Temperature

Aims:

Synthesis of 11H-indeno[1,2-b]quinoxalin-11-ones as well as 6H-indeno[1,2-b]pyrido[3,2-e]pyrazin-6-one derivatives under greener conditions.

Background:

Quinoxaline and related skeletons are very common in naturally occurring bioactive compounds.

Objective:

Design a facile, green and organo-catalyzed method for the synthesis of 11H-indeno[1,2-b]quinoxalin-11-ones as well as 6H-indeno[1,2-b]pyrido[3,2-e]pyrazin-6-one derivatives.

Methods:

Both the scaffolds were synthesized via the condensation of ninhydrin and o-phenylenediamines or pyridine-2,3-diamines respectively by using a catalytic amount of mandelic acid as an efficient, commercially available, low cost, organo-catalyst in aqueous ethanol at room temperature.

Results:

Mild reaction conditions, use of metal-free organocatalyst, non-toxic solvent, ambient temperature, and no column chromatographic separation are some of the notable advantages of our developed protocol.

Conclusion:

In conclusion, we have developed a simple, mild, facile and efficient method for the synthesis of structurally diverse 11H-indeno[1,2-b]quinoxalin-11-one derivatives via the condensation reactions of ninhydrin and various substituted benzene-1,2-diamines using a catalytic amount of mandelic acid as a commercially available metal-free organo-catalyst in aqueous ethanol at room temperature. Under the same optimized reaction conditions, synthesis of 6H-indeno[1,2-b]pyrido[3,2-e]pyrazin-6-one derivatives was also accomplished with excellent yields by using pyridine-2,3-diamines instead of o-phenylenediamine.

Spirocyclic derivatives as antioxidants: a review

In recent years, spiro compounds have attracted significant interest in medicinal chemistry due to their numerous biological activities attributed primarily to their versatility and structural similarity to important pharmacophore centers. Currently, the development of drugs with potential antioxidant activities is of great importance since numerous investigations have shown that oxidative stress is involved in the development and progression of numerous diseases such as cancer, senile cataracts, kidney failure, diabetes, high blood pressure, cirrhosis, and neurodegenerative diseases, among others. This article provides an overview of the synthesis and various antioxidant activities found in naturally occurring and synthetic spiro compounds. Among the antioxidant activities reviewed are DPPH, ABTS, FRAP, anti-LPO, superoxide, xanthine oxidase, peroxide, hydroxyl, and nitric oxide tests, among others. Molecules that presented best results for these tests were spiro compounds G14, C12, D41, C18, C15, D5, D11, E1, and C14. In general, most active compounds are characterized for having at least one oxygen atom; an important number of them (around 35%) are phenolic compounds, and in molecules where this functional group was absent, aryl ethers and nitrogen-containing functional groups such as amine and amides could be found. Recent advances in the antioxidant activity profiles of spiro compounds have shown that they have a significant position in discovering drugs with potential antioxidant activities.

Ru(II)-Catalyzed Switchable C-H Alkylation and Spirocyclization of 2-Arylquinoxalines with Maleimides via ortho-C-H Activation

A Ru(II)-catalyzed facile and controllable protocol for C-H alkylation and spirocyclization of 2-arylquinoxalines with maleimides has been achieved under ambient air in high yields. Sequential ortho-C-H activation and C-annulation results in the formation of diverse polyheterocycles containing spiro[indeno[1,2-b]quinoxaline-11,3'-pyrrolidine]-2',5'-diones, which are of potent interest in medicinal chemistry. Mechanistic investigations suggest a reversible cleavage of the ortho-C-H bond in the turnover-limiting step.

Recent advancement in the synthesis of diverse spiro-indeno[1,2-b]quinoxalines: a review

The nitrogen-containing indeno[1,2-b]quinoxaline ring is a privileged structurally fused active system and has notable applications in various fields of chemistry.

Chitosan-encapsulated manganese ferrite particles bearing sulfonic acid group catalyzed efficient synthesis of spiro indenoquinoxalines

A simple, highly versatile and efficient synthesis of 5-phenyl-spiro[diindenopyridine-indenoquinoxaline]-diones is achieved through a four-component one pot reaction of ninhydrin, 1,2-diaminobenzene, 1,3-indandione and aniline. This reaction was catalyzed by MnFe₂O₄@CS-Bu-SO₃H MNPs as a very efficient, recyclable heterogeneous catalyst in acetonitrile under reflux conditions. The catalyst can be recovered from the subsequent reaction mixture and reused for at least five cycles without any appreciable loss in its efficiency. The core–shell structure and composition of the produced magnetic nanocatalyst were analyzed using FT-IR, XRD, VSM, SEM, EDX and TGA techniques.

A simply, highly versatile and efficient synthesis of 5-phenyl-spiro [diindeno pyridineindenoquinoxaline]-diones is achieved through five component one pot reaction of ninhydrin, 1,2-diaminobenzene, 1,3-indandione and anilines.

A novel substrate directed multicomponent reaction for the syntheses of tetrahydro-spiro[pyrazolo[4,3-f]quinoline]-8,5'-pyrimidines and tetrahydro-pyrazolo[4,3-f]pyrimido[4,5-b]quinolines via selective multiple C-C bond formation under metal-free conditions

A versatile and substrate oriented multicomponent reaction for the syntheses of novel highly diastereoselective tetrahydro-1'H-spiro[pyrazolo[4,3-f]quinoline-8,5'-pyrimidine]-2',4',6'(3'H)-triones (d.r. up to 20 : 1 (syn : anti)) and tetrahydro-8H-pyrazolo[4,3-f]pyrimido[4,5-b]quinoline-8,10(9H)-diones via formation of selective multiple C-C bonds under identical reaction conditions (viz. ethanol as a reaction medium and deep eutectic mixture as a catalyst) is demonstrated. Both approaches involve mild reaction conditions, use of non-hazardous solvents, and facilitate good to excellent reaction yields of the target compounds.

The crystal structure of 3-(4-hydroxybenzyl)-1,5-dioxaspiro[5.5]undecane-2,4-dione, C16H18O5

C16H18O5, monoclinic, P21/c (no. 14), a = 11.281(2) Å, b = 12.321(3) Å, c = 10.630(2) Å, β = 101.07(3)°, V = 1450.1(5) Å3, Z = 4, R gt(F) = 0.0421, wR ref(F 2) = 0.1123, T = 293(2) K.

An expedient synthesis of novel spiro[indenoquinoxaline-pyrrolizidine]-pyrazole conjugates with anticancer activity from 1,5-diarylpent-4-ene-1,3-diones through the 1,3-dipolar cycloaddition/cyclocondensation sequence

A highly regio- and stereoselective two-stage route for the synthesis of spiro[indenoquinoxaline-pyrrolizidine]-pyrazole hybrids with anticancer activity has been developed.

Recent applications of ninhydrin in multicomponent reactions

Ninhydrin (1,2,3-indanetrione hydrate) has a remarkable breadth in different fields, including organic chemistry, biochemistry, analytical chemistry and the forensic sciences. For the past several years, it has been considered an important building block in organic synthesis. Therefore, there is increasing interest in ninhydrin-based multicomponent reactions to rapidly build versatile scaffolds. Most of the works described here are simple reactions with readily available starting materials that result in complex molecular architectures. Some of the synthesized compounds exhibit interesting biological activities and constitute a new hope for anticancer agents. The present review aims to highlight the multicomponent reactions of ninhydrin towards diverse organic molecules during the period from 2014 to 2019.

This article aims to review recent multicomponent reactions of ninhydrin towards diverse organic scaffolds, such as indeno-fused heterocycles, spiro-indeno heterocycles, quinoxalines, propellanes, cage-like compounds, and dispiro heterocycles.

Crystal structure of 8-(3,4-dimethylbenzylidene)-6,10-dioxaspiro[4.5]decane-7,9-dione, C17H18O4

C17H18O4, monoclinic, P21/c (no. 14), a = 8.6020(17) Å, b = 14.835(3) Å, c = 11.624(2) Å, β = 90.07(3), V = 1483.3(5) Å3, Z = 4, R gt(F) = 0.0474, wR ref(F 2) = 0.1439, T = 293(2) K.

Coumarin based hydrazone as an ICT-based fluorescence chemosensor for the detection of Cu2+ ions and the application in HeLa cells

We have constructed a new coumarin based fluorescence probe BENZPYR with ICT character through condensation of N, N-diethylamino-3-acetyl coumarin with 2-hydrazinobenzothiazole. The absorbance and fluorescence spectral characteristics of BENZPYR revealed that the chemosensor can specifically detect for Cu²⁺ ions over other different metal ions and the lowest limit of detection was found in nano molar range. The turn off sensor of BENZPYR is related to chelation enhanced quenching (CHEQ) and intramolecular charge transfer (ICT) processes were serve as excellent fluorescent detection of Cu²⁺ ions in DMF medium. Fluorescence microscopy experiments revealed that probe BENZPYR may have application as a fluorophore to detect the Cu²⁺ in living cells. The simulated DFT analysis of electronic and structural properties and also UV-vis absorption spectra are in well accordance with the experimental UV-vis absorption spectra.