Synthesis and Preliminary Biological Study of Bisindolylmethanes Accessed by an Acid-Catalyzed Hydroarylation of Vinylindoles

Short Total Synthesis of (+)-Colletotryptins B-D and Mucronatin B Derivative

The short and first total synthesis of (+)-colletotryptins B-D, ent-colletotryptin A, and diastereomer of mucronatin B, which are a group of natural 3-(indol-2-yl)-3-(indol-3-yl)-1,2-propanediol (IIPDO) analogues containing two stereogenic centers at the C8' and C9' positions, isolated from endophytic fungus Colletotrichum sp. SC1355 and Tetrapterys mucronata, respectively, has been successfully accomplished in two and three steps with overall yields ranging from 28 to 54%. Key features of this synthesis include an innovative Bi(OTf)3-catalyzed stereoselective transindolylation of (S)-3,3'-di(1H-indol-3-yl)propane-1,2-diol. The operational simplicity, environmentally friendly catalyst, and broad functional group tolerance of this modular strategy render it suitable for adoption in both academic and industrial settings.

A Tandem Hydroformylation-Organocatalyzed Friedel-Crafts Reaction for the Synthesis of Diindolylmethanes

Herein, we present an efficient and atom-economic tandem hydroformylation organocatalyzed Friedel-Crafts reaction sequence for the synthesis of diindolylmethanes. Classic syntheses have relied on (Lewis) acid activation of aldehydes, which are often not commercially available and rather sensitive in handling. In contrast, the combination of rhodium-catalyzed hydroformylation and subsequent organocatalytic activation of the in-situ formed aldehydes allows the use of readily available and stable alkenes with various functional groups while avoiding acidic conditions to expand the range of available diindolylmethanes. A broad scope of diindolylmethanes was prepared in yields up to 85 % demonstrates the utility of the presented method.

Phosphoric Acid Catalyzed N-Addition/ C-Addition Reaction of 3-Vinyl Indoles with Pyrazole/Pyrazolone to Construct Pyrazole-Substituted 3-(1-Heteroarylethyl)-indole Scaffolds

Developing a highly efficient atom-economic method for the preparation of 3-(1-heteroarylethyl)-indole scaffolds is of significant value in pharmaceutical and agricultural chemistry. Herein, a phosphoric acid-catalyzed N-addition reaction of 3-vinyl indoles with pyrazoles and C-addition reaction of 3-vinyl indoles with pyrazolones were developed. A series of pyrazole-substituted 3-(1-heteroarylethyl)-indole scaffolds were synthesized in excellent yields (up to 99% yield) under mild reaction conditions. A reasonable reaction mechanism was proposed to explain the experimental results.

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.

Efficient Green Synthesis, Anticancer Activity, and Molecular Docking Studies of Indolemethanes Using a Bioglycerol-Based Carbon Sulfonic Acid Catalyst

Indolemethane derivatives are significant molecules in the study of N-heterocyclic chemistry. Herein, we designed and developed a highly efficient green synthesis of indolemethane compounds using a recyclable biodegradable glycerol-based carbon solid acid catalyst under solvent-free conditions at room temperature for 5 min with excellent yields. The synthesized compounds were subjected to cytotoxic activity against prostate (DU145), hepatocellular carcinoma (HepG2), and melanoma (B16) cell lines. The highest cytotoxicity effects were found with 1k (1.09 μM) and 1c (2.02 μM) against DU145, followed by 1a, 1d, 1f, 1n, and 1m between 5.10 and 8.18 μM concentrations. The anticancer activity is validated using molecular docking simulations, and comparing binding energies with the standard drug doxorubicin suggests that the title compounds are well fitted into the active site pocket of the target molecules..

Chiral spirocyclic phosphoric acid-catalyzed enantioselective synthesis of heterotriarylmethanes bearing an amino acid moiety

We present herein an enantioselective protocol for the chiral phosphoric acid-catalyzed addition of 3-arylisoxazol-5-amines to highly reactive 3-methide-3H-pyrroles to provide a diverse range of heterotriarylmethanes bearing an amino acid moiety in good yields (up to 97%) and high enantioselectivities (up to 93% ee) under mild conditions. The chiral spirocyclic phosphoric acid is crucial in converting the initial 1H-pyrrol-3-yl carbinols into reactive 3-methide-3H-pyrroles and obtaining the good enantiocontrol, thereby facilitating the desired enantioselective transformation.

Enhancing the biological properties of zinc complexes with bis(indolyl)methane groups: Synthesis, characterization, DNA interaction, and biocide activity

The unprecedented mononucleated ligand (6,6-di(1H-indol-3-yl)-N,N-bis(pyridin-2-ylmethyl)hexan-1-amine (L^C5) with an N₃-donor set and its complexes [Zn(L^C5)Cl₂] • 2CH₃OH (1) and [Zn(L^C5)₂](ClO₄)₂ (2), were successfully prepared. All compounds were fully characterized by a suite of physicochemical methods. Fluid ¹H and ¹³C NMR spectroscopy, as well as DFT and TD-DFT calculations, were carried out to propose a viable structural arrangement for both complexes. The interaction between these compounds and DNA was monitored in the UV region where binding constants (K_b) were estimated (2 > 1 > L^C5). These data were corroborated by DNA cleavage assays using groove binders, circular dichroism, and docking studies. Both complexes confirmed their biocide activity against selected microorganisms: Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria, the filamentous fungi A. fumigatus and S. cerevisiae. Finally, the cytotoxic activities of 1 and 2 were tested against the erythroleukemia K562 cell line. For all biological studies, it was probed that the presence of the indole moieties and the zinc atoms in the chemical composition of the complexes studied could increase the magnitude of the activity following the order: 2 > 1 > L^C5, where a linear relationship between the biological activity upon K562 cells (IC₅₀) and DNA binding studies (K_b) was found.

K2S2O8-glucose mediated oxidative coupling of alcohols with indoles for synthesis of Bis(indolyl)methanes in water

The use of inexpensive K2S2O8 in water at room temperature for synthesis of bis(indolyl)methanes (BIMs) from simple indoles and alcohols is reported. The key step involves the conversion of alcohols...

Chiral Iridium Complexes of Anionic NCP Pincer Ligand for Asymmetric Transfer Hydrogenation of 1,1-Diarylethenes with Ethanol

Chiral iridium complexes ligated by anionic oxazoline-bearing NCP-type pincer ligands were developed and applied to the asymmetric transfer hydrogenation (ATH) of diarylethenes using environmentally benign ethanol as the hydrogen donor. High enantioselectivities could be achieved for substrates bearing ortho-Me, ortho-Cl, or ortho-Br substituents on one of the aryl groups. The ATH of ortho-Br-substituted diarylethenes is particularly attractive due to the propensity of the C_(aryl)-Br bond to undergo various new bond-forming events.

Short Total Synthesis of (±)-Gelliusine E and 2,3'-Bis(indolyl)ethylamines via PTSA-Catalyzed Transindolylation

A first and short total synthesis of the marine sponge 2,3'-bis(indolyl)ethylamine (2,3'-BIEA) alkaloid (±)-gelliusine E was performed in both a three-step divergent approach and a one-pot three-component approach with an overall yield of up to 58%. A key feature of the novel strategy is PTSA-catalyzed transindolylation of the readily synthesized 3,3'-BIEAs with tryptamine derivatives. The structure of the isolated natural product is revised as protonated (±)-gelliusine E (4'). By design, this modular route allows the rapid synthesis of other members of the 2,3'-BIEA family, for example, (±)-6,6'-bis-(debromo)-gelliusine F and analogues with step economy, operational simplicity, and reduced waste. Furthermore, their cytotoxicity in breast cancer cells was investigated.

Mahardhika A, L. Wendt L, E. Müller C. Iodine-catalyzed electrophilic substitution of indoles: Synthesis of (un)symmetrical diindolylmethanes with a quaternary carbon center

A novel, versatile approach for the synthesis of unsymmetrical 3,3'-diindolylmethanes (DIMs) with a quaternary carbon center has been developed via iodine-catalyzed coupling of trifluoromethyl(indolyl)phenylmethanols with indoles. In contrast to previously reported methods, the new procedure is characterized by chemoselectivity, mild conditions, high yields, and scalability to obtain gram amounts for biological studies. Selected compounds were found to display affinity for cannabinoid receptors, which are promising drug targets for the treatment of inflammatory and neurodegenerative diseases.

Nickel-Catalyzed Asymmetric Hydroarylation of Vinylarenes: Direct Enantioselective Synthesis of Chiral 1,1-Diarylethanes

The enantioselective hydroarylation of vinylarenes catalyzed by a chiral, non-racemic nickel catalyst is presented as a facile method to generate chiral 1,1-diarylethanes. These reactions proceed via formation of a chiral, non-racemic nickel benzyl intermediate. Transmetalation with arylboron nucleophiles and subsequent reductive elimination enable the formation of a variety of chiral 1,1-diarylethanes. The 1,1-diarylethane products from reactions of arylboronic acids containing electron-donating substituents are formed with typically greater than 90% ee, while the 1,1-diarylethanes generated from reactions of arylboronic acids containing electron-withdrawing groups are generated with typically less than 80% ee. These results are consistent with the rate of transmetalation with an arylboron nucleophile playing a key role in the enantioselectivity of these hydroarylation reactions. This mechanistic insight has led to the development of reactions of neo-pentylglycolate esters of arylboronic acids with vinylarenes that occur with higher enantioselectivities based on increased rates of transmetalation.

FeCl3·6H2O as a Mild Catalyst for Nucleophilic Substitution of Symmetrical Bis(indoyl)methanes

In this paper, unsymmetrical bis(indolyl)methane (BIM) and 3-alkylindole derivatives are smoothly synthesized from symmetrical BIMs with a variety of nucleophiles including heteroaromatic/aromatic compounds, allylsilane and alkynylsilane. FeCl₃·6H₂O is found to be a mild and highly effective catalyst for this nucleophilic substitution reaction in which N-methyl-2-phenylindole behaves as a good leaving group in the C_sp³-C_sp² bond cleavage reaction. The operational ease, nonexpensive and environmentally friendly catalyst, mild reaction conditions, broad functional group tolerance, and scalability of this reaction strategy are advantages of the present procedure.

Selectivity Control in Gold-Catalyzed Hydroarylation of Alkynes with Indoles: Application to Unsymmetrical Bis(indolyl)methanes

Gold-catalyzed hydroarylation of unactivated alkynes with indoles have previously been reported to proceed with double indole addition to produce symmetrical bis(indolyl)methanes (BIMs). We demonstrate for the first time that the selectivity of the gold-catalyzed reaction can be fully switched to allow for isolation of the vinylindole products instead. Furthermore, this selective reaction can be utilized to synthesize the more difficult to access unsymmetrical BIMs from readily available starting materials.

Synthesis of Chiral Bis(3-indolyl)methanes Bearing a Trifluoromethylated All-Carbon Quaternary Stereocenter via Nickel-Catalyzed Asymmetric Friedel-Crafts Alkylation Reaction

Bis(3-indolyl)methanes are well-known natural products with a broad range of important biological functions including cancer cell growth inhibition and antimicrobial activity. Incorporation of a trifluoromethyl group is known to have a profound effect on the parent compound's biological activities. Here, an efficient method for the synthesis of chiral trifluoromethylated bis(3-indolyl)methanes via a catalytic asymmetric Friedel-Crafts (F-C) alkylation reaction has been established. Both enantiomers of the catalysis products can be obtained by tuning the chiral substituents of the catalyst. With 5 mol % of the Ni(II)/(imidazoline-oxazoline) complex as the catalyst, the F-C reaction of indoles with β-CF₃-β-(3-indolyl)nitroalkenes proceeded well to afford a series of chiral bis(3-indolyl)methanes bearing a trifluoromethylated all-carbon quaternary stereocenter in generally good yields with excellent enantioselectivities (up to 98% yield and 94% ee). Furthermore, by interchanging the indole moieties of the two reactants, indole vs β-CF₃-β-(3-indolyl)nitroalkene in the F-C reaction, both enantiomers of a given trifluoromethylated bis(3-indolyl)methane were obtained with high enantioselectivities (89-94% ee) upon removal of the indole N-protecting group in the F-C products. The current work represents the first general catalytic enantioselective approach to the important class of trifluoromethylated bis(3-indolyl)methanes.

Lewis Acid Catalyzed Transfer Hydromethallylation for the Construction of Quaternary Carbon Centers

The design and gram-scale synthesis of a cyclohexa-1,4-diene-based surrogate of isobutene gas is reported. Using the highly electron-deficient Lewis acid B(C6 F5 )3 , application of this surrogate in the hydromethallylation of electron-rich styrene derivatives provided sterically congested quaternary carbon centers. The reaction proceeds by C(sp3 )-C(sp3 ) bond formation at a tertiary carbenium ion that is generated by alkene protonation. The possibility of two concurrent mechanisms is proposed on the basis of mechanistic experiments using a deuterated surrogate.

Protocols for the Syntheses of 2,2'-Bis(indolyl)arylmethanes, 2-Benzylated Indoles, and 5,7-Dihydroindolo[2,3-b]carbazoles

The electrophilic substitution reaction of 4,7-dihydroindole with aryl-aldehydes as an electrophilic partner followed by an oxidation step to deliver 2,2'-bis(indolyl)arylmethanes was studied for the first time. The reaction afforded regioselectivity at the 2,2'-positions of indole in an operationally simple and inexpensive procedure with a variety of substrates. To the best of our knowledge, this is the first set of examples of 2,2'-bis(indolyl)arylmethanes obtained in a substituent-free manner. A facile method from dipyrromethanes to the corresponding 2-benzylindoles was also reported. In addition, 2,2'-bis(indolyl)arylmethanes were converted to 5,7-dihydroindolo[2,3-b]carbazoles.

Ga(OTf)3-Catalyzed Temperature-Controlled Regioselective Friedel-Crafts Alkylation of Trifluoromethylated 3-Indolylmethanols with 2-Substituted Indoles: Divergent Synthesis of Trifluoromethylated Unsymmetrical 3,3'-and 3,6'-Bis(indolyl)methanes

An unprecedented Ga(OTf)₃-catalyzed, temperature-controlled regiodivergent alkylation of 2-substituted indoles with trifluoromethylated 3-indolylmethanols is described that provides structurally diverse unsymmetrical 3,3'- and 3,6'-bis(indolyl)methanes with a CF₃-containing quaternary carbon center in good to excellent yields under mild conditions. In addition, this present protocol could be successfully extended to the synthesis of difluoromethylated 3,3'- and 3,6'-bis(indolyl)methanes with excellent efficiency.

General Synthesis of Unsymmetrical 3,3'-(Aza)diindolylmethane Derivatives

Diindolylmethane (DIM) and its derivatives have recently been in the focus of interest due to their significant biological activities, specifically in cancer prevention and therapy. Molecular targets of DIM have been identified, e.g., the immunostimulatory G protein-coupled receptor GPR84. However, most of the reported and investigated DIM derivatives are symmetrical because general methods for obtaining unsymmetrical DIMs have been lacking. To optimize the interaction of DIM derivatives with their protein targets, unsymmetrical substitution is required. In the present study we developed a new, mild and efficient access to unsymmetrically substituted 3,3'-DIMs by reaction of (3-indolylmethyl)trimethylammonium iodides with a wide range of substituted indole derivatives. 7-Azaindole also led to the 3,3'-connected DIM analogue, while 4- and 5-azaindoles reacted at the N1-nitrogen atom as confirmed by X-ray crystallography. The reactions were performed in water without the requirement of a catalyst or other additives. Wide substrate scope, operational simplicity, environmentally benign workup, and high yields are further advantages of the new method. The synthetic protocol proved to be suitable for upscaling to yield gram amounts for pharmacological studies. This procedure will allow the preparation of a broad range of novel, unsymmetrical DIM derivatives to exploit their potential as novel drugs.

Asymmetric hydrofunctionalization of minimally functionalized alkenes via earth abundant transition metal catalysis

The development of earth-abundant transition metal-catalysed highly enantioselective hydrofunctionalization of minimally functionalized alkenes was summarized.

Propylsulfonic acid-anchored isocyanurate-based periodic mesoporous organosilica (PMO-ICS-Pr-SO3H): A new and highly efficient recoverable nanoporous catalyst for the one-pot synthesis of bis(indolyl)methane derivatives

A new propylsulfonic acid-anchored isocyanurate bridging periodic mesoporous organosilica (PMO-ICS-Pr-SO₃H) was prepared and shown to be a highly efficient recyclable nanoporous catalyst for the one-pot synthesis of bis(indolyl)methane derivatives in good to excellent yields from indole and different aldehydes in EtOH under mild reaction conditions in short reaction times. Moreover, the nanoporous catalyst was recovered and reused at least four times without significant decrease in its catalytic activity. The PMO-ICS-Pr-SO₃H catalyst was characterizred by Fourier transform infrared (FTIR) spectroscopy, thermogravimetry analysis (TGA) and N₂ adsorption-desorption isotherms techniques as well as field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) spectroscopy. Compared to the classical methodologies, this method illustrated significant advantages including low loading of the catalyst, high to excellent yields, short reaction times, avoiding the use of toxic transition metals or reactive reagents for modification of the catalytic activity, easy separation and purification of the products, and reusability of the catalyst.

Fe3O4@SiO2 supported aza-crown ether complex cation ionic liquids: preparation and applications in organic reactions

A series of aza-crown ether ionic liquids supported on magnetic Fe₃O₄@SiO₂ core–shell particles were designed, synthesized and characterized by elemental analysis, TEM, TG and FT-IR.

A facile one-pot method to synthesise 2-alkylated indole and 2,2′-bis(indolyl)methane derivatives using ketones as electrophiles and their anion sensing ability

Indole derivatives are of great importance because of their biological activity and application in technology.

Efficient hydroarylation and hydroalkenylation of vinylarenes by Brønsted acid catalysis

Brønsted acid Tf₂NH-catalyzed hydroarylation and hydroalkenylation of 4 vinylarenes under mild reaction conditions is herein shown to provide access to 1,1-diarylalkane scaffolds and trans-1,3-diaryl-1-butenes in high yields and with excellent regioselectivity.

Microwave-Assisted Synthesis and Molecular Recognition Properties of Novel Indole Acylhydrazone Receptors

Indole acylhydrazones were synthesised in high yields under microwave irradiation By using indole carboxylic acid and 1,4-benzenedialdehyde as starting materials. Their structures were characterised by 1H NMR, IR, MS spectra and elemental analysis. Selective recognition properties of these receptors have been investigated by UV-Vis spectra titration indicating that these receptors can form 1:1 supramolecular complexes with malic acid, tartaric acid, ascorbic acid and tryptophan.