New antioxidants incorporating indole and indoline chromophores

Transition-metal-free and additive-free intermolecular hydroarylation of alkenes with indoles in hexafluoroisopropanol

Hydroarylation of alkenes is one of the most straightforward and atom-economical strategy for the construction of multi-aryl-substituted alkanes, but systematic studies have been limited to transition metal catalysis. Here we report a hexafluoroisopropanol (HFIP)-promoted hydroarylation of alkenes with indoles without the presence of transition metal catalysts or any additive. HFIP was the only reagent used in this work, and could be easily removed via evaporation, and recovered via distillation in industry settings. This reaction was shown to provide an efficient, clean and operationally simple procedure with a remarkable substrate scope and versatile transformations, delivering a variety of multi-aryl alkanes incorporating the indole motif. In preliminary studies, several of these products showed biologically activity against cells from an array of human cancer cell lines. A mechanistic study was also carried out and suggested that the quinone methide might be the key intermediate. And in contrast to the conclusions of a previous report, the current work suggested that protonation by HFIP might not be the rate-determining step.

Visible-Light-Induced Intramolecular Tandem Cyclization of Unactivated Indoloalkynes for the Synthesis of Sulfonylated and Selenylated Indolo[1,2-a]quinolines

A convenient and efficient visible-light-induced method has been developed for the construction of sulfonated and selenylated indolo[1,2-a]quinolines through sulfonyl or selenyl radical-initiated tandem cyclization of unactivated alkynes with sodium sulfinates or diaryl diselenides under mild conditions. This protocol, which simply utilizes visible light as the safe and eco-friendly energy source and an inexpensive and nontoxic organic dye as a photocatalyst without the aid of an external photocatalyst, provides various sulfonyl- and selenyl-containing indolo[1,2-a]quinolines in moderate to good yields.

Catalyst-free direct synthesis of indeno[1,2-b]indol-5(4bH)-yl benzimidamides

A new series of indeno[1,2-b]indol-5(4bH)-ylbenzimidamide derivatives 3a–3j has been synthesized as potential casein kinase II (CK2) inhibitors. A convenient and straightforward synthesis protocol was used via a reaction of β-enaminones 1a–1j with ninhydrin 2. This transformation proceeds under mild conditions (boiling ethanol, 0.5 h) in absence of catalyst in good to excellent yields (66–86%). The new compounds have been characterized by NMR, HRMS and IR spectra.

Entropy-Induced Selectivity Switch in Gold Catalysis: Fast Access to Indolo[1,2-a]quinolines

New N-heterocyclic compounds for organic functional materials and their efficient syntheses are highly demanded. A surprising entropy-induced selectivity switch in the gold-catalyzed intramolecular hydroarylation of 2-ethynyl N-aryl indoles was found and its exploitation led to straightforward syntheses of indolo[1,2-a]quinolines. Experimental and computational mechanistic investigations gave insight into this uncommon selectivity phenomenon and into the special reactivity of the indolo[1,2-a]quinolines. The high functional group tolerance of this methodology enabled access to a diverse scope with high yields. In addition, bidirectional approaches, post-functionalization reactions, and π-extension of the core structure were feasible. An in-depth study of the photophysical properties explored the structure-effect relationship for different derivatives and revealed a high potential of these compounds for future applications as functional materials.

Methane Monooxygenase Mimic Asymmetric Oxidation: Self-Assembling μ-Hydroxo, Carboxylate-Bridged Diiron(III)-Catalyzed Enantioselective Dehydrogenation

Mimicking naturally occurring metalloenzymes to enrich the diversity of catalytic asymmetric oxidation reactions is a long-standing goal for modern chemistry. Toward this end, a range of methane monooxygenase (MMO) mimic chiral carboxylate-bridged (μ-hydroxo) diiron(III) dimer complexes using salan as basal ligand and sodium aryl carboxylate as additive have been designed and synthesized. The chiral diiron complexes exhibit efficient catalytic reactivity in dehydrogenative kinetic resolution of indolines using environmentally benign hydrogen peroxide as oxidant. In particular, complex C9 bearing sterically encumbered salan ligands and a 2-naphthoate bridge is identified as the optimal catalyst in terms of chiral recognition. Further investigation reveals that this MMO mimic chiral catalyst can be readily generated by self-assembly under the dehydrogenation conditions. The self-assembling catalytic system is applicable to a series of indolines with multiple stereocenters and diverse substituent patterns in high efficiency with a high level of chiral recognition (selectivity factor up to 153). Late-stage dehydrogenative kinetic resolution of bioactive molecules is further examined.

Design, Synthesis, Biological Evaluation, 2D-QSAR Modeling, and Molecular Docking Studies of Novel 1H-3-Indolyl Derivatives as Significant Antioxidants

Novel candidates of 3-(4-(thiophen-2-yl)-pyridin/pyran/pyrimidin/pyrazol-2-yl)-1H-indole derivatives (2–12) were designed by pairing the pyridine/pyrane/pyrimidine/pyrazole heterocycles with indole and thiophene to investigate their potential activities as (2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) inhibitors. The purpose of these derivatives’ modification is to create high-efficiency antioxidants, especially against ABTS, as a result of the efficiency of this set of key heterocycles in the inhibition of ROS. Herein, 2D QSAR modeling was performed to recommend the most promising members for further in vitro investigations. Furthermore, the pharmacological assay for antioxidant activity evaluation of the yielded indole-based heterocycles was tested against ABTS (2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid); by utilizing ascorbic acid as the standard. Candidate 10 showed higher antioxidant activity (IC₅₀ = 28.23 μg/mL) than ascorbic acid itself which achieved (IC₅₀ = 30.03 μg/mL). Moreover, molecular docking studies were performed for the newly designed and synthesized drug candidates to propose their mechanism of action as promising cytochrome c peroxidase inhibitors compared to ascorbic acid as a reference standard. Our findings could be promising in the medicinal chemistry scope for further optimization of the newly designed and synthesized compounds regarding the introduced structure-activity relationship study (SAR) in order to get a superior antioxidant lead compound in the near future.

Cleavage and Reassembly of the C═O Bond of 2-Alkynylbenzaldehydes: A Metal-Free Access to Inden-1-ones

A metal-free approach to inden-1-ones from 2-alkynylbenzaldehydes mediated by pyrrolidine has been developed. The reaction proceeds under mild conditions in a step- and atom-economy process by cleaving the C═O bond and constructing new C-C as well as C═O bonds. Oxygen-18 and deuterium labeling experiments revealed an aza-Petasis-Ferrier rearrangement of an intermediate 1-amino-3-methylene-dihydroisobenzofuran.

Cu(II) complex with auxin (3-indoleacetic acid) and an aromatic planar ligand: synthesis, crystal structure, biomolecular interactions and radical scavenging activity

A novel water soluble ternary copper(II) complex,-[Cu₂(phen)₂(3-IAA)₂(H₂O)](ClO₄)₂·H₂O-(phen: 1,10-phenanthroline, 3-IAA: 3-indoleacetic acid), has been synthesized and characterized by elemental CHN analysis, ESI-TOF, FTIR and single-crystal X-ray diffraction techniques. Interaction of the complex with calf thymus DNA (CT-DNA) has been investigated by absorption spectral titration, ethidium bromide (EB) and Hoechst 33258 displacement assay. The interactions between the complex and bovine serum albumin (BSA) were investigated by electronic absorption and fluorescence spectroscopy methods. The experimental results indicate that the fluorescence quenching mechanism between the complex and BSA is a static quenching process. The Stern-Volmer constants, binding constants, binding sites and the corresponding thermodynamic parameters (ΔG, ΔH, ΔS) of BSA + complex systems were determined at different temperatures. The binding distance between the complex and BSA was calculated according to Förster non-radiation energy transfer theory (FRET). The effect of the complex on the conformation of BSA was also examined using synchronous, two dimensional (2D) and three dimensional (3D) fluorescence spectroscopy. Furthermore, the oxygen radical scavenging activity of the complex was determined in terms of IC₅₀, using the DPPH and H₂O₂ method, to show that it particularly enables electron loss from radical species. This study highlights the importance of indole and moieties in the development of antioxidant agents. A potent drug candidate novel water soluble ternary copper(II) complex,-[Cu₂(phen)₂(3-IAA)₂(H₂O)] (ClO₄)₂·H₂O-(phen: 1,10-phenanthroline, 3-IAA: 3-indoleacetic acid), has been synthesized and characterized by elemental CHN analysis, FTIR, ESI-MS and single-crystal X-ray diffraction techniques. The complex has been tested for in vitro biomacromolecular interactions by spectroscopic methods. Furthermore, radical scavenging activities of the complex were also investigated.

Palladium(II)-catalyzed tandem cyclization of 2-ethynylaniline tethered cinnamyl acetate for the synthesis of indenoindoles

A palladium(ii)-catalyzed cyclization of 2-ethynylaniline tethered cinnamyl acetate involving aminopalladation/alkene insertion/β-acetoxy elimination cascade processes was established. The new protocol provides efficient access to indenoindoles in moderate to good yields under mild conditions.

The antioxidant and neuroprotective effects of Zolpidem on acrylamide-induced neurotoxicity using Wistar rat primary neuronal cortical culture

Zolpidem is an introduced medication for the therapy of sleeping disorders. Its pharmacological effects are consequently characterized by a quick onset and a half-life of 2.4 h. Previous studies revealed the antioxidant and neuroprotectant effects of zolpidem. In this research, we wanted to demonstrate the exact sub-cellular/molecular mechanism of this medication using the primary neuronal cortical culture. For this purpose, firstly, the cortical neurons were isolated from the postnatal Wistar rat pups. Thereafter, different neural toxicity endpoints caused by acrylamide including ROS formation, lipid peroxidation, mitochondrial membrane potential collapse, lysosomal membrane integrity, and apoptosis were determined. All of these parameters are upstream events of cellular apoptosis which justifies neurodegeneration involved in many diseases such as Alzheimer's and Parkinson's. Our results demonstrated that zolpidem at concentrations of 1 and 2 mM prevented all the acrylamide-induced above referenced neural toxic events leading to neuronal apoptosis. These results revealed that zolpidem has the antioxidant and neuroprotectant properties that make it a promising prophylactic agent for preventing neurodegenerative complications. Considering the important role of oxidative stress in the development or progression of diseases, if the medication used as a treatment of a disease has antioxidant properties at the same time, it will certainly have much greater healing effects.

The structural diversity of heterocycle-fused potassium cyclopentadienides

Cyclopentadienides of d- and f-elements are highly important complexes with undoubted potential for practical applications. Annelation of a heterocyclic fragment with an η5-ring results in substantial improvement of the catalytic properties of these compounds, called "heterocenes"; the investigation of metal coordination with these specific ligands is a highly important problem. We prepared potassium derivatives 5-8 of heterocycle-annelated cyclopentadienes with different structures - derivatives of cyclopenta[1,2-b:4,3-b']dithiophene (1), indeno[2,1-b]indole (2), indeno[1,2-b]indole (3), and indeno[1,2-b]indolizine (4) and studied the crystal and molecular structures of these salts by X-ray diffraction. We found that heterocycle-fused cyclopentadienides demonstrate remarkable diversity in metal-ligand coordination modes and crystal packing, with formation of two-dimensional polymeric (5), linear polymeric (6), tetrameric (7) and monomeric (8) structures. The NMR spectral data and results of DFT modeling indicate an increase in electron density in the cyclopentadienyl fragment, and this effect was found to be larger in the derivative of the new indolizine ligand precursor 4. The results of our study will be used in the design of next-generation catalysts of α-olefin polymerization.

Nickel-Catalyzed Intramolecular Direct Arylation of Imines toward Diverse Indoles

An efficient nickel-catalyzed intramolecular direct arylation of imines with challenging aryl chlorides has been developed. The versatile nickel catalysis made use of easily accessible imines and delivered diversely decorated 2-arylindoles of considerable importance to biological and medicinal chemistry.

Synthesis of cis-5,5a,6,10b-Tetrahydroindeno[2,1-b]indoles through Palladium-Catalyzed Decarboxylative Coupling of Vinyl Benzoxazinanones with Arynes

A novel palladium-catalyzed decarboxylative coupling reaction of vinyl benzoxazinanones with arynes which may feature an intramolecular nucleophilic attack of an amino group at the central carbon of π-allylpalladium intermediate has been developed. The cis-5,5a,6,10b-tetrahydroindeno[2,1-b]indoles were generated in moderate to good yields. One key to the success of the present reaction was to achieve comparable rates for the palladium-catalyzed decarboxylation and aryne formation steps.

Palladium-Catalyzed Alkylation with Alkyl Halides by C(sp3 )-H Activation

Utilizing halogens as traceless directing goups represents an attractive strategy for C-H functionalization. A two C-H alkylation system, initiated by the oxidative addition of organohalides to Pd⁰ , has been developed. The first reaction involves an intermolecular alkylation of palladacycles to form C(sp³ )-C(sp² ) bonds followed by C(sp² )-H activation/cyclization to deliver alkylated benzocyclobutenes as the final products. In the second reaction, two C-C bonds are formed by the reaction of palladacycles with CH₂ Br₂ , and provides a facile and efficient method for the synthesis of indanes. The alkylated benzocyclobutene products can be transformed into tricyclic hyrocarbons, and the indane derivatives are essential structural motifs in bioactive and odorant molecules.

Synthesis of benzofuro[3,2-b]indoline amines via deamination-interrupted Fischer indolization and their unexpected reactivity towards nucleophiles

We report the access to the benzofuro[3,2-b]indoline framework via an interrupted Fischer indolization and its unexpected reactivity towards allyl nucleophiles.

Lactic acid-catalyzed fusion of ninhydrin and enamines for the solvent-free synthesis of hexahydroindeno[1,2-b]indole-9,10-diones

The lactic acid-catalyzed reactions of ninhydrin and secondary enaminones were conducted by solvent-free grinding at room temperature to yield polycyclic 4b,9b-dihydroxy-4b,5,6,7,8,9b-hexahydroindeno[1,2-

Pd-catalyzed dehydrogenative C–H activation of iminyl hydrogen with the indole C3–H and C2–H bond: an elegant synthesis of indeno[1,2-b]indoles and indolo[1,2-a]indoles

This synthetic protocol describes two sequential C–H activation route towards indeno[1,2-b]indoles. Indolo[1,2-a]indoles were also synthesized by activating indole C2–H bond.

Oxidative Reaction of Oxindole-3-acetic Acids

The oxindole-3-acetic acids, oxidative metabolites of indole-3-acetic acid, were isolated from a byproduct of a corn starch manufacturing plant, and were further converted to the 3-hydroxyl derivatives in the presence of metal ion. The mechanical study was followed by a chemical analysis including other byproducts, and suggested the presence of an intermediate that had a radical at the C-3 position of oxindole-3-acetic acids.

Indenoindoles and cyclopentacarbazoles as bioactive compounds: synthesis and biological applications

Indenoindoles and their isomers cyclopentacarbazoles represent a wide class of synthetic and natural compounds. The great interest of these structures in (bio)organic chemistry is due to the use of various building blocks to get the elemental four ring structure. Depending on the synthetic route chosen, the chemists can achieve a large number of regioisomers. Each regioisomer can be considered as a template for specific functionalizations. Therefore, this mini-review aims (i) to present an overview on how to access this large family of heterocyclic compounds and (ii) to discuss their various biological applications and drug development in oncology (e.g. kinases), in CNS disorders (e.g. Alzheimer's disease), in endocrinology (e.g. hormone replacement therapy) and oxidative stress (e.g. organ preservation). Past and present works will be presented through the systems 6-5-5-6 and 6-5-6-5 (combination of 6-membered and 5-membered rings).

Synthesis, Antioxidant, Antimicrobial, Antimycobacterial, and Cytotoxic Activities of Azetidinone and Thiazolidinone Moieties Linked to Indole Nucleus

2-N-(2-Phenyl-1H-indol-3-yl)imino-4-arylthiazoles (3a–c) were used as key synthons for the preparation of (4-arylthiazol-2-yl)-4-(2-phenyl-1H-indol-3-yl)azetidin-2-ones (4a–c) and 3-(4-arylthiazol-2-yl)-2-(2-phenyl-1H-indol-3-yl)thiazolidin-4-ones (5a–c). These newly synthesized compounds have been characterized with the help of IR,1H NMR,13C NMR, and mass spectral studies. All compounds were screened for their antioxidant, antimicrobial, antimycobacterial, and cytotoxic activities. Some of the compounds displayed excellent activity.

Synthesis of a fluorogenic cyclooctyne activated by Cu-free click chemistry

Cyclooctyne-based probes that become fluorescent upon reaction with azides are important targets for real-time imaging of azide-labeled biomolecules. The concise synthesis of a coumarin-conjugated cyclooctyne, coumBARAC, that undergoes a 10-fold enhancement in fluorescence quantum yield upon triazole formation with organic azides is reported. The design principles embodied in coumBARAC establish a platform for generating fluorogenic cyclooctynes suited for biological imaging.

Palladium-catalyzed hydrofunctionalization of vinyl phenol derivatives with heteroaromatics

A hydroheteroarylation reaction of vinyl phenols using an alkyl chloride as the sacrificial hydride source is reported. The method tolerates a wide range of heterocycles as the exogenous nucleophile including indoles and pyrroles. The resulting products are easily processed to biologically relevant scaffolds.