Copper-catalyzed Azide-alkyne Cycloaddition Research Articles

Layered Copper Hydroxide Salts as Catalyst for the “Click” Reaction and Their Application in Methyl Orange Photocatalytic Discoloration

The 1,2,3-triazoles are an important class of organic compounds that are found in a variety of biologically active compounds. The most usual and efficient methodology to synthetize these compounds is the Copper-catalyzed Azide–Alkyne Cycloaddition (CuAAC), preferably by use of click chemistry principles. Therefore, the development of simple, robust, easily accessible and efficient materials as catalysts for this kind of reaction is highly desirable. In this sense, layered hydroxide salts (LHS) emerge as an interesting alternative for the click reaction. Thus, we describe herein the preparation and characterization of copper (II) layered hydroxide salts and their application as catalysts for the CuAAC reaction under solvent-free conditions. This synthetic methodology of CuAAC reaction is attractive as it follows several concepts of green chemistry, such as being easy to perform, allowing purification without chromatographic column, the process forming no sub-products, affording the desired 1,2,3-traizoles in the specific 1,4-disubstituted position in high yield, and having a short reaction time. Moreover, the photocatalysis for the degradation of methyl orange was also highly efficient using the same catalyst.

Click chemistry: A fascinating, Nobel-winning method for the improvement of biological activity

Click chemistry is totally an approach consisting of efficient and reliable reactions that bind two molecular building blocks and require no complex purification techniques. The aspire of achieving molecules with the desired characteristics and behaviour is the key to the click chemistry concept. In this concept, in order to obtain 1,2,3-triazole products as diversely functionalized molecules, copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has been widely used for years in the field of materials science, organic synthesis and the biochemistry. This review focusses on the importance of click chemistry for obtaining biologically active triazole molecules and therefore the applications of such 1,2,3-triazole derivatives in medicinal chemistry field are highlighted.

Process-Divergent Syntheses of 4- and 5-Sulfur-Functionalized 1,2,3-Triazoles via Copper-Catalyzed Azide-Alkyne Cycloadditions of 1-Phosphinyl-2-sulfanylethynes.

4-Sulfanyl-substituted 1,2,3-triazoles were provided regioselectively with good yields and broad scope via consecutive t-BuOK-promoted dephosphinylation of 1-phosphinyl-2-sulfanylethynes and copper-catalyzed azide-alkyne cycloadditions (CuAAC) with alkyl azides. Unsymmetrically substituted ditriazoles were successfully obtained using a tandem dephosphinylative CuAAC protocol with diazides. Direct CuAAC of the 1-phosphinyl-2-sulfanylethynes with azides afforded regioisomeric mixtures of 4-phosphinyl-5-sulfanyl- and 5-phosphinyl-4-sulfanyl-1,2,3-triazoles that were easily separable from one another. When the phosphinyl- and sulfanyl-substituted triazoles were treated with t-BuOK, the dephosphination proceeded smoothly, yielding the corresponding 5- and 4-sulfanyltriazoles, respectively. 5-(1-Aryl-1-hydroxymethyl)-4-sulfanyltriazoles were synthesized by stepwise treatment of 5-phosphinyl-4-sulfanyltriazole with MeMgBr and arylaldehydes. Additionally, Ph2P(O) and RS groups in the triazoles were easily converted to Ph2P and RSO2 by PhSiH3-reduction and m-CPBA-oxidation, respectively. Following the dephosphinylative CuAAC of 1-phosphinyl-2-(4-t-butylphenylsulfanyl)ethyne with aryl azides and m-CPBA-oxidation, potent antagonists of pregnane X receptor LC-58 and LC-59 were successfully produced.

Decoration of Polyfluorene-Wrapped Carbon Nanotubes with Photocleavable Side-Chains.

Functionalizing polyfluorene-wrapped carbon nanotubes without damaging their properties is effective via Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC). However, the length and nature of polymer side-chains can impact the conductivity of polyfluorene-SWNT films by preventing close contact between the nanotubes. Here, we investigate the functionalization of a polyfluorene-SWNT complex using photocleavable side-chains that can be removed post-processing. The cleavage of the side-chains containing an ortho-nitrobenzyl ether derivative is efficient when exposed to a UV lamp at 365 nm. The photoisomerization of the o-nitrobenzyl ether linker into the corresponding o-nitrosobenzaldehyde was first monitored via UV-Vis absorption spectroscopy and 1H-NMR spectroscopy on the polymer, which showed efficient cleavage after 2 h. We next investigated the cleavage on the polyfluorene-SWNT complex via UV-Vis-NIR absorption spectroscopy. The precipitation of the nanotube dispersion and the broad absorption peaks after overnight irradiation also indicated effective cleavage. In addition, Raman spectroscopy post-irradiation showed that the nanotubes were not damaged upon irradiation. This paper reports a proof of concept that may find applications for SWNT-based materials in which side-chain removal could lead to higher device performance.

Fluorescent Gold Nanoparticles in Suspension as an Efficient Theranostic Agent for Highly Radio-Resistant Cancer Cells

Gold nanoparticles are a promising candidate for developing new strategies of therapy against cancer. Due to their high atomic number and relative biocompatibility, they are commonly investigated as radiosensitizers to locally increase the dose of radiotherapy. In order to optimize this radiosensitizing effect, it is necessary to control the positioning of the nanoparticles in the cells. The purpose of this study is to investigate, by means of fluorescent gold nanoparticles in suspension, the dose enhancement on highly radio-resistant cancer cells. These nanoparticles were successfully produced using modern click-chemistry methods, first by attaching a chelating agent Diethylenetriamine pentaacetate benzylamine to L-cysteine, bonding the resulting ligand to a gold core, grafting propargylamine and then utilizing copper-catalyzed azide-alkyne cycloaddition (CuAAC) to fuse AlexaFluor 647 to the ligands. The results of this study prove the success of the reactions to produce a minimally cytotoxic and highly stable nanoparticle suspension that increases the radiosensitivity of gliosarcoma 9L tumor cells, with a 35% increase in cell death using 5 Gy kilovoltage radiation. Their fluorescent functionalization allowed for their simple localization within living cells and detection in vivo post-mortem.

Synthesis and conformational studies of hyperbranched-core star polymers with poly(γ-benzyl-l-glutamate) arms

A general methodology for the synthesis of star polymers with large number of polypeptide arms is described. The synthesis is based on the arm-first step-growth polymerization of bifunctional macromonomers by copper-catalyzed azide-alkyne cycloaddition. Star polymers with up to 18 poly-γ-benzyl-l-glutamate (PBLG) arms have been synthesized and characterized. It is shown that the preferred secondary structure of PBLG is significantly affected by the degree of chain packing/crowding.

PEGylated reduced graphene oxide as nanoplatform for targeted gene and drug delivery

Combination therapies involving anticancer drugs and gene therapy agents have become a potential treatment for different cancer types reducing the side effects of anticancer drugs while enhancing their effectiveness. Here, we improved our previously published strategy that uses multiple pyrene groups of poly(ethylene glycol) (PEG) brushed graft copolymer to enhance the biological use of reduced graphene oxide (rGO) and introduced an azide containing monomer in the copolymer for further modifications to carry hydrophobic drugs like doxorubicin (Dox) along with oligonucleotides such as small interfering RNAs (siRNA). Azide functionality on the side chain of coated copolymer enables not only the conjugation of alkyne end group functional cationic copolymer but also allows the addition of targeting moieties like EPPT1 peptide that selectively binds MUC1, an early hallmark of tumorigenesis. To achieve the outlined carrier, first, a well-defined PEG, pyrene, azide, and methyl methacrylate containing poly[(poly(ethylene glycol) methyl ether methacrylate)-co-(3-azidopropyl methacrylate)-co-(methyl methacrylate)-co-(1-pyrenemethyl methacrylate)] (P(PEGMA-co-AzPMA-co-MMA-co-PMA), PAMP) copolymer was synthesized via ATRP and through its azide group another well-defined, cationic copolymer composed of hexyl methacrylate, 2-dimethyl amino ethyl methacrylate, and N,N,N-trimethylaminoethyl methacrylate iodide (P(HMA-co-DMAEMA-co-TMAEMA) was coupled via copper-catalyzed azide-alkyne cycloaddition (CuAAC). This cationic copolymer was synthesized using a unique ATRP initiator to allow click reaction as described as well as pH-dependent degradation through its hydrazone linkage. The obtained graft copolymer (PAMP-CP) was then coated on a graphene oxide (GO) surface and GO was in situ reduced to rGO (PAMP-CP-rGO) to have an rGO-based PEGylated nanoplatform that can be highly loaded with doxorubicin and successfully condensed with anti-GAPDH siRNA. Consequently, this dual drug delivery nanoplatform showed a controlled drug release that switches between release kinetics by the change of pH and high transfection efficiency regarding targeted GAPDH protein levels. Moreover, in vitro cytotoxicity tests showed that EPPT1-targeted Dox-loaded PAMP-CP-rGO shows concentration-dependent and selective cellular toxicity against cancer cells compared to its non-targeted versions. These results demonstrated the potential of a highly adaptable, multifunctional nanoplatform for safely and selectively transporting different cargoes to the tumor site.

Compartmentalized Intracellular Click Chemistry with Biodegradable Polymersomes.

Polymersome nanoreactors that can be employed as artificial organelles have gained much interest over the past decades. Such systems often include biological catalysts (i.e., enzymes) so that they can undertake chemical reactions in cellulo. Examples of nanoreactor artificial organelles that acquire metal catalysts in their structure are limited, and their application in living cells remains fairly restricted. In part, this shortfall is due to difficulties associated with constructing systems that maintain their stability in vitro, let alone the toxicity they impose on cells. This study demonstrates a biodegradable and biocompatible polymersome nanoreactor platform, which can be applied as an artificial organelle in living cells. The ability of the artificial organelles to covalently and non-covalently incorporatetris(triazolylmethyl)amine-Cu(I) complexes in their membrane is shown. Such artificial organelles are capable of effectively catalyzing a copper-catalyzed azide-alkyne cycloaddition intracellularly, without compromising the cells' integrity. The platform represents a step forward in the application of polymersome-based nanoreactors as artificial organelles.

Waste-minimized continuous flow copper-catalyzed azide-alkyne cycloaddition with low metal contamination

Metal contamination is a waste-generating and serious issue in the synthesis of chemicals, in particular in the case of products with biological activity. The appropriate selection of operating conditions plays a crucial role in the abatement of metal leaching in solution and associated wastes. Herein we report a waste-minimized continuous flow process for the synthesis of 1,4-disubstituted β-keto 1,2,3-triazoles exploiting the use of a copper tube flow reactor (CTFR). The selection of the proper azeotropic mixture allowed an almost quantitative recovery of the reaction medium greatly influencing the E-factor of the protocol. A thorough understanding of the main parameters affecting the waste generation was given by calculation of the E-factor distribution for different work-up tested under batch and flow conditions. Furthermore, the measurement of different green metrics (AE: Atom Economy, SF: Stoichiometric Factor, RME: Reaction Mass Efficiency, and MRP: Mass Recover Parameter) clearly demonstrated the benefits of the flow scale-up that allowed to perform a low environmental footprint CuAAC reaction.

Hybrids of thiazolidinone with 1,2,3-triazole derivatives: design, synthesis, biological evaluation, in silico studies, molecular docking, molecular dynamics simulations, and ADMET profiling

A new series of thiazolidinone linked 1,2,3-triazole hybrids 5a-h was designed and synthesized using the copper-catalyzed Huisgen azide-alkyne cycloaddition (CuAAC) between thiazolidinone linked alkyne and aromatic azides. The structures of the newly synthesized compounds were established by NMR (1H and 13C) and HRMS. The targeted thiazolidinone-1,2,3-triazole hybrids were evaluated for their cytotoxic activity against four human cancer cell lines, including fibrosarcoma (HT-1080), lung carcinoma (A-549), and breast carcinoma (MCF-7 and MDA-MB-231) using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliun bromide (MTT). The obtained data showed that most of these compounds have moderate anti-proliferative activity with IC50 values between 10.26 ± 0.71 and 53.93 ± 1.20 μM. The compound 5a exhibited higher activity with an IC50 value of 10.26 ± 0.71 µM, compared to 5d with an IC50 value of 11.56 ± 1.98 µM for the HT-1080 and MCF-7 cancer cells line, respectively. Moreover, Annexin-V apoptosis was assessed by flow cytometry for hybrid compounds 5a and 5d against HT-1080 and MCF-7 competitor cell lines, as they increase the level of active caspase 3/7. The experimental results were further confirmed by docking studies followed by molecular dynamic simulations. Both the potent derivatives i.e. 5a and 5d have comparable docking scores and MD simulations results showed that the docked complex of 5a is somewhat more stable than 5d primarily for protein p53. The ADMET profile of both derivatives established their safety zone and drug-like potential. Communicated by Ramaswamy H. Sarma

In Situ Analysis of Mitochondrial DNA Synthesis Using Metabolic Labeling Coupled to Fluorescence Microscopy.

Metabolic labeling with the nucleoside analog 5-ethynyl-2'-deoxyuridine (EdU) enables the selective labeling of DNA synthesis in live cells. Newly synthesized EdU-containing DNA can be covalently modified after extraction or in fixed cells using copper-catalyzed azide-alkyne cycloaddition "click chemistry" reactions, enabling bioconjugation to various substrates including fluorophores for imaging studies. While often used to study nuclear DNA replication, EdU labeling can also be leveraged to detect the synthesis of organellar DNA in the cytoplasm of Eukaryotic cells. In this chapter, we outline methods for the application of EdU labeling to the study of mitochondrial genome synthesis in fixed cultured human cells, using fluorescent labeling and superresolution light microscopy.

Tetracopper(I) thiolate- and amido-(SNS) complexes and copper-catalyzed azide-alkyne cycloaddition in water.

Two tetranuclear Cu(I) complexes bearing thiolate- and amido-SNS ligands were characterized by X-ray diffraction and mass spectrometry. Although the amido ligand undergoes irreversible N-protonation by the copper-bound alkyne, the thiolate complex demonstrates good activity in the copper-catalyzed azide-alkyne cycloaddition reaction with a variety of substrates. The base-free reactions are performed in water and afford excellent yields over 2 h at 70 °C. DFT calculations suggest a proton-shuttle role for the thiolate donor in formation of the initial dicopper σ,π-alkynyl intermediate.

A bioorthogonal chemistry approach to detect the K1 polysialic acid capsule in Escherichia coli.

Most Escherichia coli strains associated with neonatal meningitis express the K1 capsule, a sialic acid polysaccharide that is directly related to their pathogenicity. Metabolic oligosaccharide engineering (MOE) has mostly been developed in eukaryotes, but has also been successfully applied to the study of several oligosaccharides or polysaccharides constitutive of the bacterial cell wall. However, bacterial capsules are seldom targeted despite their important role as virulence factors, and the K1 polysialic acid (PSA) antigen that shields bacteria from the immune system still remains untackled. Herein, we report a fluorescence microplate assay that allows the fast and facile detection of K1 capsules with an approach that combines MOE and bioorthogonal chemistry. We exploit the incorporation of synthetic analogues of N-acetylmannosamine or N-acetylneuraminic acid, metabolic precursors of PSA, and copper-catalysed azide-alkyne cycloaddition (CuAAC) as the click chemistry reaction to specifically label the modified K1 antigen with a fluorophore. The method was optimized, validated by capsule purification and fluorescence microscopy, and applied to the detection of whole encapsulated bacteria in a miniaturized assay. We observe that analogues of ManNAc are readily incorporated into the capsule while those of Neu5Ac are less efficiently metabolized, which provides useful information regarding the capsule biosynthetic pathways and the promiscuity of the enzymes involved. Moreover, this microplate assay is transferable to screening approaches and may provide a platform to identify novel capsule-targeted antibiotics that would circumvent resistance issues.

Late-stage diversification strategy for synthesizing ynamides through copper-catalyzed diynylation and azide-alkyne cycloaddition.

A late-stage diversification strategy for synthesizing ynamides has been developed. This strategy was enabled by the copper-catalyzed direct electrophilic diynylation of sulfonamides with a novel triisopropylsilyl diynyl benziodoxolone, deprotection, and the late-stage chemoselective copper-catalyzed azide-alkyne cycloaddition sequence, which yields various complex molecule-derived ynamides with pyrene, amino acid, nucleoside, and N-acetylglucosamine as substituents.

Chromene-dihydropyrimidinone and xanthene-dihydropyrimidinone hybrids: design, synthesis, and antibacterial and antibiofilm activities

A series of chromene-dihydropyrimidinone and xanthene-dihydropyrimidinone hybrid compounds were easily synthesized through a multicomponent reaction followed by the copper-catalyzed alkyne–azide cycloaddition reaction.

Synthesis and evaluation of photophysical, electrochemical, and ROS generation properties of new chalcogen-naphthoquinones-1,2,3-triazole hybrids.

This study presents a comprehensive analysis encompassing the synthesis, structural elucidation, photophysical behavior, and electrochemical properties of a novel series of chalcogen-naphthoquinone-1,2,3-triazole hybrids. Employing a meticulously designed protocol, the synthesis of these hybrids, denoted as 11a-j, was achieved with remarkable efficiency (yielding up to 81%). This synthesis used a regioselective copper-catalyzed azide-alkyne cycloaddition reaction (CuAAC). Furthermore, a detailed investigation into the photophysical characteristics, TDDFT calculations, electrochemical profiles, and photobiological attributes of compounds 11a-j was conducted. This exploration aimed to unravel insights into the excited state behaviors of these molecules, as well as their redox properties. Such insights are crucial for future applications of these derivatives in diverse biological assays.

SNAP-tagging live cells via chelation-assisted copper-catalyzed azide-alkyne cycloaddition.

SNAP-tag is a single-turnover enzyme that has become a powerful tool, hence a popular choice, of targeted cellular protein labeling. Three SNAP-tag substrates that carry the copper-chelating 2-picolyl azide moiety are prepared, one of which has an unconventional 5-pyridylmethyl-substituted guanine structure, rather than the usual benzylguanine that is optimized to be accepted by SNAP-tag. All three substrates are effective in transferring a 2-picolyl azide moiety to SNAP-tag in live cells under conventional labeling conditions (30-minute incubation of cells with labeling reagents at 37 °C under 5% CO2). Live cells that are decorated with chelating azido groups on the extracellular side of membranes undergo copper-catalyzed azide-alkyne cycloaddition (CuAAC) with an ethynyl-functionalized fluorophore to accomplish membrane protein labeling by a fluorescent dye. The chelation-assisted CuAAC labeling step is rapid (<1 minute) with a relatively low dose of the copper catalyst (20 μM), and consequently exerts no ill effect on the labeled cells. A SNAP-tag substrate that carries a non-chelating azide moiety, on the other hand, fails to produce satisfactory labeling under the same constraints. The rapid, live cell-compatible SNAP-tag/chelation-assisted CuAAC two-step method expands the utility of SNAP-tag in protein labeling applications.

SYNTHESIS AND ANTICANCER EVALUATION OF NEW 1HNAPHTHO[2,3-D] IMIDAZOLE-4,9-DIONE-1,2,3 TRIAZOLE HYBRIDS

A new series of 1H-naphtho[2,3-d]imidazole-4,9-dione-based 1,2,3-triazole hybrids (10a-10n) were synthesized by the reaction of 1-(prop-2-yn-1-yl)-1H-naphtho[2,3-d]imidazole-4,9-dione with aromatic azides via copper-catalyzed azide-alkyne cycloaddition reactions. All the synthesized compounds are screened for their in vitro anticancer activities against three cancer cell lines namely MCF-7 (breast), HeLa (cervical), and A-549 (lung) using an MTT assay. The results revealed that the compounds 10a,10c,10g, and 10k exhibited promising activity against three cancer cell lines. Especially, compound 10a displayed higher activity against all the cell lines than the standard drug, The molecular docking studies of compounds 10a-10n as EGFR targeting agents were also supported by the observed IC50 data.

Synthesis and Phytotoxic Evaluation of Isatin Derivatives Supported by 3D-QSAR Study.

Concerned about weed infestation, a major threat to food production and herbicide resistance that interferes in the mechanism of action of the main herbicides, we have synthesized eight isatin derivatives using the "Click Chemistry" approach through copper-catalyzed azide-alkyne cycloadditions (CuAAC). Sixteen isatin derivatives were evaluated for their phytotoxic activity against the seed culture of the model plants, Lactuca sativa and Allium cepa. Six of them showed phytotoxic activity similar to the positive control, trifluralin. Hypocotyl length measurement analysis in L. sativa revealed that triazole derivative 8 is more active than trifluralin. For A. cepa, root length measurement analyses revealed that 3, 10, 14, 16, and 17 were similar to the positive control trifluralin. Three-dimensional quantitative structure-activity relationship (3D-QSAR) comparative molecular field analysis (CoMFA) model construction using the acetolactate synthase (ALS) crystallographic structure displayed pki values of predicted inhibitory activity and contour maps revealing sterically bulky groups for 11, the CF3 group in ortho, and for 17, Br in ortho, favoring the inhibitory ALS activity.

Stimuli-Responsive Catenane-Based Catalysts.

Rotaxanes and molecular knots exhibit particular properties resulting from the presence of a mechanical bond within their structure that maintains the molecular components interlocked in a permanent manner. On the other hand, the disassembly of the interlocked architecture through the breakdown of the mechanical bond can activate properties which are masked in the parent compound. Herein, we present the development of stimuli-responsive CuI -complexed [2]catenanes as OFF/ON catalysts for the copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction. The encapsulation of the CuI ion inside the [2]catenanes inhibits its ability to catalyze the formation of triazoles. In contrast, the controlled opening of the two macrocycles induces the breaking of the mechanical bond, thereby restoring the catalytic activity of the CuI ion for the CuAAC reaction. Such OFF/ON catalysts can be involved in signal amplification processes with various potential applications.