Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications

Ag2O-mediated Tandem Reaction between Terminal Alkyne and o-Iodibenzoic Acid: Construction of 3-Ethylideneisobenzofuran-1(3H)-ones

Taking aryl propargyl ether and o-iodibenzoic acid as substrates, a series of aryl cyclolactones bearing an exocyclized C=C bond were constructed with moderate to good yields. Diverse substituent groups could be tolerant in the reaction, which indicated excellent compatibility of the reaction. In this tandem reaction, Ag2O was employed as the media and Et3N was screened as the base to facilitate the reaction. A concise mechanism was proposed on the basis of the expansion of the substrates and theoretical analysis. Sonogashira type coupling coupled with intramolecular nucleophilic addition in one pot to construct the product, 3-ethylideneisobenzofuran-1(3H)-one.

Enantioselective Propargylation of Oxonium Ylide with α-Propargylic-3-Indolymethanol: Access to Chiral Propargylic Indoles

An enantioselective three-component reaction of α-propargylic-3-indolymethanol with diazoindolinone and alcohol under cocatalysis of Rh(II) and chiral phosphoric acid (CPA) has been reported. It proceeds through the regio- and enantiospecific addition of the in situ formed oxonium ylide to the α-propargylic indole iminium ion that is generated from 3-indolyl propargylic alcohol with CPA. This work features an asymmetric counteranion-directed propargylation of oxonium ylide, and provides an efficient access to chiral propargylic indole derivatives with high yields and enantioselectivities.

Inverting Conventional Chemoselectivity in the Sonogashira Coupling Reaction of Polyhalogenated Aryl Triflates with TMS-Arylalkynes

A newly developed phosphine ligand with a C2-cyclohexyl group on the indole ring was successfully applied in a chemoselective Sonogashira coupling reaction with excellent chemoselectivity, affording an inversion of the conventional chemoselectivity order of C-Br > C-Cl > C-OTf. This study also provided an efficient approach to the synthesis of polycyclic aromatic hydrocarbons (PAHs) and the natural product analogue trimethyl-selaginellin L by merging of chemoselective Sonogashira and Suzuki-Miyaura coupling reactions.

Green synthesis of triazolo-nucleoside conjugates via azide–alkyne C–N bond formation

Modified nucleosides are the core precursors for the synthesis of artificial nucleic acids, and are important in the field of synthetic and medicinal chemistry. In order to synthesize various triazolo-compounds, copper and ruthenium catalysed azide–alkyne 1,3-dipolar cycloaddition reactions also known as click reaction have emerged as a facile and efficient tool due to its simplicity and convenient conditions. Introduction of a triazole ring in nucleosides enhances their therapeutic value and various photophysical properties. This review primarily focuses on the plethora of synthetic methodologies being employed to synthesize sugar modified triazolyl nucleosides, their therapeutic importance and various other applications.

The Role of Triazole and Glucose Moieties in Alkali Metal Cation Complexation by Lower-Rim Tertiary-Amide Calix[4]arene Derivatives

The binding of alkali metal cations with two tertiary-amide lower-rim calix[4]arenes was studied in methanol, N,N-dimethylformamide, and acetonitrile in order to explore the role of triazole and glucose functionalities in the coordination reactions. The standard thermodynamic complexation parameters were determined microcalorimetrically and spectrophotometrically. On the basis of receptor dissolution enthalpies and the literature data, the enthalpies for transfer of reactants and products between the solvents were calculated. The solvent inclusion within a calixarene hydrophobic basket was explored by means of ¹H NMR spectroscopy. Classical molecular dynamics of the calixarene ligands and their complexes were carried out as well. The affinity of receptors for cations in methanol and N,N-dimethylformamide was quite similar, irrespective of whether they contained glucose subunits or not. This indicated that sugar moieties did not participate or influence the cation binding. All studied reactions were enthalpically controlled. The peak affinity of receptors for sodium cation was noticed in all complexation media. The complex stabilities were the highest in acetonitrile, followed by methanol and N,N-dimethylformamide. The solubilities of receptors were greatly affected by the presence of sugar subunits. The medium effect on the affinities of calixarene derivatives towards cations was thoroughly discussed regarding the structural properties and solvation abilities of the investigated solvents.

A Recent Overview of 1,2,3-Triazole-Containing Hybrids as Novel Antifungal Agents: Focusing on Synthesis, Mechanism of Action, and Structure-Activity Relationship (SAR)

A pharmacophore system has been found as 1,2,3-triazole, a five-membered heterocycle ring with nitrogen heteroatoms. These heterocyclic compounds can be produced using azide-alkyne cycloaddition processes catalyzed by ruthenium or copper. The bioactive compounds demonstrated antitubercular, antibacterial, anti-inflammatory, anticancer, antioxidant, antiviral, and antidiabetic properties. This heterocycle molecule, in particular, with one or more 1,2,3-triazole cores has been found to have the most powerful antifungal effects. The goal of this review is to highlight recent developments in the synthesis and structure-activity relationship (SAR) investigation of this prospective fungicidal chemical. Also there have been explained drugs and mechanism of action of a triazole compound with antifungal activity. This review will be useful in a variety of fields, including medicinal chemistry, organic chemistry, mycology, and pharmacology.

Consecutive 2-azidoallylation/click cycloaddition of active methylene for synthesis of functionalized hepta-1,6-dienes with a bis-1,2,3-triazole scaffold

A tandem 2-azidoallylation/click cycloaddition reaction to access novel hepta-1,6-diene skelecton can be successfully accomplished with methylene compounds, phenolic substituted vinyl azide and alkynes in one pot.

Synthesis and structural features of a series of Cu(i) furan-2-thiocarboxylate complexes: efficient “click” catalysts for the synthesis of glycoconjugates and glycocluster

A series of phosphinecopper(i) thiocarboxylates have been synthesized and characterized structurally. These complexes act as efficient catalysts for the 'click' azide–alkyne cycloaddition leading to glycoconjugates and a glycocluster.

Readily accessible azido-alkyne-functionalized monomers for the synthesis of cyclodextrin analogues using click chemistry

A set of linear and cyclic oligomers were synthesized starting from a suitable azido-alkyne monomer through click oligomerization. The synthesis of these monomers starting from bromobenzene features an enzymatic dihydroxylation...

Development of sustainable synthesis of glucuronic acid glycodendrimers using ball milling and microwave-assisted CuAAC reaction

Two green strategies for CuAAC reaction based on two activation pathways, solvent free mechanochemistry and microwave irradiation using a recycable biosolvent, are reported for the synthesis of glucuronic acid glycodendrimers with good conversión.

Organocatalytic asymmetric synthesis of quaternary α-isoxazole–α-alkynyl amino acid derivatives

Chiral phosphoric acid catalyzed enantioselective addition of 5-amino-isoxazoles with β,γ-alkynyl-α-ketimino esters provided good yields and excellent enantioselectivities.

Copper supported silica-based nanocatalysts for CuAAC and cross-coupling reactions

Recent advances in Cu/SiO2-based heterogeneous catalysts for click reaction, C–N, C–S, and C–O coupling reactions are reviewed and summarized.

Terminal and Internal Alkyne Complexes and Azide-Alkyne Cycloaddition Chemistry of Copper(I) Supported by a Fluorinated Bis(pyrazolyl)borate

Copper plays an important role in alkyne coordination chemistry and transformations. This report describes the isolation and full characterization of a thermally stable, copper(I) acetylene complex using a highly fluorinated bis(pyrazolyl)borate ligand support. Details of the related copper(I) complex of HC≡CSiMe₃ are also reported. They are three-coordinate copper complexes featuring η²-bound alkynes. Raman data show significant red-shifts in C≡C stretch of [H₂B(3,5-(CF₃)₂Pz)₂]Cu(HC≡CH) and [H₂B(3,5-(CF₃)₂Pz)₂]Cu(HC≡CSiMe₃) relative to those of the corresponding alkynes. Computational analysis using DFT indicates that the Cu(I) alkyne interaction in these molecules is primarily of the electrostatic character. The π-backbonding is the larger component of the orbital contribution to the interaction. The dinuclear complexes such as Cu₂(μ-[3,5-(CF₃)₂Pz])₂(HC≡CH)₂ display similar Cu-alkyne bonding features. The mononuclear [H₂B(3,5-(CF₃)₂Pz)₂]Cu(NCMe) complex catalyzes [3 + 2] cycloadditions between tolyl azide and a variety of alkynes including acetylene. It is comparatively less effective than the related trinuclear copper catalyst {μ-[3,5-(CF₃)₂Pz]Cu}₃ involving bridging pyrazolates.

Tetranuclear and trinuclear copper(I) pyrazolates as catalysts in copper mediated azide-alkyne cycloadditions (CuAAC)

Homoleptic, tetranuclear copper(I) pyrazolates {[3,5-(t-Bu)₂Pz]Cu}₄, {[3-(CF₃)-5-(t-Bu)Pz]Cu}₄, and {[4-Br-3,5-(i-Pr)₂Pz]Cu}₄ are excellent stand-alone catalysts for azide-alkyne cycloaddition reactions (CuAAC). This work demonstrates that a range of pyrazolates, including those with electron donating and electron-withdrawing groups to sterically demanding substituents on the pyrazolyl backbones, can serve as effective ligand supports on tetranuclear copper catalysts. However, in contrast to the tetramers and also highly fluorinated {[3,5-(CF₃)₂Pz]Cu}₃, trinuclear copper(I) complexes such as {[3,5-(i-Pr)₂Pz]Cu}₃ and {[3-(CF₃)-5-(CH₃)Pz]Cu}₃ supported by relatively electron rich pyrazolates display poor catalytic activity in CuAAC. The behavior and degree of aggregation of several of these copper(I) pyrazolates in solution were examined using vapor pressure osmometry. Copper(I) complexes such as {[3,5-(CF₃)₂Pz]Cu}₃ and {[3-(CF₃)-5-(t-Bu)Pz]Cu}₄ with electron withdrawing pyrazolates were found to break up in solution to different degrees producing smaller aggregates while those such as {[3,5-(i-Pr)₂Pz]Cu}₃ and {[3,5-(t-Bu)₂Pz]Cu}₄ with electron rich pyrazolates remain intact. In addition, kinetic experiments were performed to understand the unusual activity of tetranuclear copper(I) pyrazolate systems.

Glycosyl Triazole Ligand for Temperature-Dependent Competitive Reactions of Cu-Catalyzed Sonogashira Coupling and Glaser Coupling

Glycosyl triazoles have been introduced as efficient ligands for the Cu-catalyzed Sonogashira reaction to overcome the challenges of sideways homocoupling reactions in Cu catalysis in this reaction. The atmospheric oxygen in a sealed tube did not affect the coupling, and no need of complete exclusion of oxygen was experienced in the presence of glycohybrid triazole ligand L3. High product yields were obtained at 130 °C for a variety of substrates including aliphatic and aromatic terminal alkynes and differently substituted aromatic halides including 9-bromo noscapine. In contrast, at room temperature, a very low loading of the L3-Cu catalytic system could produce excellent yields in Glaser coupling including homocoupling and heterocoupling of a variety of aliphatic and aromatic alkynes.

Synthetic development of sugar amino acid oligomers towards novel podophyllotoxin analogues

In this work, we have developed an approach for the synthesis of sugar amino acid oligomers based on the glucosamine scaffold. We found that the solid-phase approach was unsuccessful for the preparation of sugar amino acid oligomers and the limitation of the liquid-phase approach revolved around the low solubility of larger oligomers. Nevertheless, this strategy allowed the coupling of alkynylated carbohydrate amino acids with podophyllotoxin-bearing an azide functional group yielding novel podophyllotoxin analogues. Due to their low solubility, the antiproliferative study revealed no anticancer activity of these newly synthesized analogues.

Azide-Alkyne "Click" Reaction in Water Using Parts-Per-Million Amine-Functionalized Azoaromatic Cu(I) Complex as Catalyst: Effect of the Amine Side Arm

A series of Cu(II) complexes, 1-4 and 6, were synthesized through a reaction of amine-functionalized pincer-like ligands, HL^1,2, L^a,b, and a bidentate ligand L¹ with CuCl₂·2H₂O. The chemical reduction of complex 1 using 1 equiv of sodium l-ascorbate resulted in a dimeric Cu(I) complex 5 in excellent yield. All of the complexes, 1-6, were thoroughly characterized using various physicochemical characterization techniques, single-crystal X-ray structure determination, and density functional theory calculations. Ligands HL^1,2 and L^a,b behaved as tridentated donors by the coordination of the amine side arm in their respective Cu(II) complexes, and the amine side arm remained as a pendant in Cu(I) complexes. All of these complexes (1-6) were explored for copper(I)-catalyzed 1,3-dipolar azide-alkyne cycloaddition (CuAAC) reaction at room temperature in water under air. Complex 5 directly served as an active catalyst; however, complexes 1-4 and 6 required 1 equiv of sodium l-ascorbate to generate their corresponding active Cu(I) catalyst. It has been observed that azo-based ligand-containing Cu(I)-complexes are air-stable and were highly efficient for the CuAAC reaction. The amine side arm in the ligand backbone has a dramatic role in accelerating the reaction rate. Mechanistic investigations showed that the alkyne C-H deprotonation was the rate-limiting step and the pendant amine side arm intramolecularly served as a base for Cu-coordinated alkyne deprotonation, leading to the azide-alkyne 2 + 3 cycloaddition reaction. Thus, variation of the amine side arm in complexes 1-4 and use of the most basic diisopropyl amine moiety in complex 4 has resulted in an unique amine-functionalized azoaromatic Cu(I) system for CuAAC reaction upon sodium l-ascorbate reduction. The complex 4 has shown excellent catalysis at its low parts-per-million level loading in water. The catalytic protocol was versatile and exhibited very good functional group tolerance. It was also employed efficiently to synthesize a number of useful functional triazoles having medicinal, catalytic, and targeting properties.

Organoselenium-chitosan derivative: Synthesis via "click" reaction, characterization and antioxidant activity

The derivatization of chitosan (CS) is widely exploited to endow this polysaccharide with enhanced physicochemical and biological properties. Beyond the synthetic route, the nature of the compounds used to functionalize the CS-derivatives exerts a pivotal role in their final properties. Making use of a simple "click" reaction, we synthesized for the first time an organoselenium-CS derivative through a 1,2,3-triazole formation. The product (CS-TSe) was characterized in detail by FTIR, NMR (¹H, ¹³C, and ⁷⁷Se) and UV-Vis techniques, and SEM microscopy. The antioxidant activity of CS-TSe was examined by ABTS⁺ and DPPH (free radical-scavenging) assays. Experimentally, it was demonstrated that CS-TSe has superior antioxidant activity compared with raw CS and "free" organoselenium compound, suggesting a benign and synergistic effect due to the derivatization. In short, the antioxidant property of CS-TSe combined with the other attractive properties of CS and selenium could be useful in the formulation of advanced materials for biomedical and packaging applications.

Biocompatible photoinduced CuAAC using sodium pyruvate

Sodium pyruvate, a natural intermediate produced during cellular metabolism, is commonly used in buffer solutions and media for biochemical applications. Here we show the use of sodium pyruvate (SP) as a reducing agent in a biocompatible aqueous photoinduced azide-alkyne cycloaddition (CuAAC) reaction. This copper(I)-catalyzed 1,3-dipolar cycloaddition is triggered by SP under UV light irradiation, exhibits oxygen tolerance and temporal control, and provides a convenient alternative to current CuAAC systems, particularly for biomolecular conjugations.

Research fronts of Chemical Biology

Over the past decades, researchers have witnessed substantially increasing and ever-growing interests and efforts in Chemical Biology studies, thanks to the development of genome and epi-genome sequencing (revealing potential drug targets), synthetic chemistry (producing new medicines), bioorthogonal chemistry (chemistry in living systems) and high-throughput screening technologies (in vitro cell systems, protein binding assays and phenotypic assays). This report presents literature search results for current research in Chemical Biology, to explore basic principles, summarize recent advances, identify key challenges, and provide suggestions for future research (with a focus on Chemical Biology in the context of human health and diseases). Chemical Biology research can positively contribute to delivering a better understanding of the molecular and cellular mechanisms that accompany pathology underlying diseases, as well as developing improved methods for diagnosis, drug discovery, and therapeutic delivery. While much progress has been made, as shown in this report, there are still further needs and opportunities. For instance, pressing challenges still exist in selecting appropriate targets in biological systems and adopting more rational design strategies for the development of innovative and sustainable diagnostic technologies and medical treatments. Therefore, more than ever, researchers from different disciplines need to collaborate to address the challenges in Chemical Biology.

Dinuclear Copper(I) Thiodiacetate Complex-Mediated Expeditious Synthesis of the Chlorine-Containing Cyclen-Cored 36-Glucose-Coated Glycodendrimer

High-sugar-tethered glycodendrimers are a remarkable tool in glycobiology for the investigation of carbohydrate-protein interaction using its multivalency property. An enthralling double-stage convergent synthetic approach was selected to build a novel class of chlorine-containing glucose-coated dendrimers using an efficient click catalyst ‘dinuclear copper(I) thiodiacetate complex.’ In this context, cyclen core was developed through a divergent approach, while the glucodendron was developed via a convergent approach independently. Both azide-alkyne partners were coupled through a modular copper azide-alkyne cycloaddition (CuAAC) strategy to afford a high yield of the desired 36-glucose-coated glycodendrimer. The synthesized glycodendrimer has been elucidated by NMR, gel permeation chromatography (GPC), and IR spectral analysis.

Chemoenzymatic and Protecting-Group-Free Synthesis of 1,4-Substituted 1,2,3-Triazole-α-d-glucosides with Potent Inhibitory Activity toward Lysosomal α-Glucosidase

α-Glucosyl triazoles have rarely been tested as α-glucosidase inhibitors, partly due to inefficient synthesis of their precursor α-d-glucosylazide (αGA1). Glycosynthase enzymes, made by nucleophile mutations of retaining β-glucosidases, produce αGA1 in chemical rescue experiments. Thermoanaerobacterium xylanolyticus glucosyl hydrolase 116 β-glucosidase (TxGH116) E441G nucleophile mutant catalyzed synthesis of αGA1 from sodium azide and pNP-β-d-glucoside (pNPGlc) or cellobiose in aqueous medium at 45 °C. The pNPGlc and azide reaction product was purified by Sephadex LH-20 column chromatography to yield 280 mg of pure αGA1 (68% yield). αGA1 was successfully conjugated with alkynes attached to different functional groups, including aryl, ether, amine, amide, ester, alcohol, and flavone via copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry reactions. These reactions afforded the 1,4-substituted 1,2,3-triazole-α-d-glucoside derivatives AGT2-14 without protection and deprotection. Several of these glucosyl triazoles exhibited strong inhibition of human lysosomal α-glucosidase, with IC50 values for AGT4 and AGT14 more than 60-fold lower than that of the commercial α-glucosidase inhibitor acarbose.

CuAAC mediated synthesis of cyclen cored glycodendrimers of high sugar tethers at low generation

Glycodendrimers are receiving considerable attention to mimic a number of imperative features of cell surface glycoconjugate and acquired excellent relevance to a wide domain of investigations including medicine, pharmaceutics, catalysis, nanotechnology, carbohydrate-protein interaction, and moreover in drug delivery systems. Toward this end, an expeditious, modular, and regioselective triazole-forming CuAAC click approach along with double stage convergent synthetic method was chosen to develop a variety of novel chlorine-containing cyclen cored glycodendrimers of high sugar tethers at low generation of promising therapeutic potential. We developed a novel chlorine-containing hypercore unit with 12 alkynyl functionality originated from cyclen scaffold which was confirmed by its single crystal X-ray data analysis. Further, the modular CuAAC technique was utilized to produce a variety of novel 12-sugar coated (G0) glycodendrimers 12-15 adorn with β-Glc-, β-Man-, β-Gal-, β-Lac, along with 36-galactose coated (G1) glycodendrimer 18 in good-to-high yield. The structures of the developed glycodendrimer architectures have been well elucidated by extensive spectral analysis including NMR (1H & 13CNMR), HRMS, MALDI-TOF MS, UV-Vis, IR, and SEC (Size Exclusion Chromatogram) data.

Trichloroacetimidate-Triggered Expeditious and Novel Synthesis of N-Acylbenzotriazoles

A facile route for the synthesis of a diverse range of N-acylbenzotriazole derivatives from the corresponding carboxylic acids has been established through a carbonyl activation pathway. In this method, trichloroacetonitrile is performed as an effective reagent for an easy access of N-acylbenzotriazoles which was simply proceeded through the activation of carboxylic acids via in situ imidate formation in anhydrous 1,2-dichloroethane followed by addition of 1H-benzotriazole at 80 °C for 3–4 h. Easy handling, one-pot, and metal-free conditions demonstrate the notable merits of the devised protocol.

d-Glucosamine as the Green Ligand for Cu(I)-Catalyzed Regio- and Stereoselective Domino Synthesis of (Z)-3-Methyleneisoindoline-1-ones and (E)-N-Aryl-4H-thiochromen-4-imines

d-Glucosamine, a natural, inexpensive, and conveniently accessible sugar, has been explored as an efficient ligand for the Cu(I)-catalyzed regio- and stereoselective synthesis of an array of (Z)-3-methyleneisoindoline-1-ones and (E)-N-aryl-4H-thiochromen-4-imines in good-to-excellent yield in a tandem fashion via the reaction of 2-halobenzamide and 2-halobenzothioamide with terminal alkynes, respectively. The water solubility and biocompatible nature of the ligand offer easy separation of the catalytic system toward the aqueous phase as well as change in the reaction path in terms of the product also demonstrated the variation of the reaction temperature. The domino reaction proceeds by the Sonogashira and Ullmann type cross-coupling reaction, followed by Cu(I)-promoted additive cyclization of heteroatom to the triple bond. In addition, d-glucosamine causes successful Glaser-Hay coupling of terminal alkynes under Cu catalysis to produce a high yield of respective 1,3-diynes.