Copper-catalyzed Azide-alkyne Click Research Articles

Oxidation-Controlled, Strain-Promoted Tellurophene-Alkyne Cycloaddition (OSTAC): A Bioorthogonal Tellurophene-Dependent Conjugation Reaction.

Tellurophene-bearing small molecules have emerged as valuable tools for localizing cellular activities in vivo using mass cytometry. To broaden the utility of tellurophenes in chemical biology, we have developed a bioorthogonal reaction to facilitate tagging of tellurophene-bearing conjugates for downstream applications. Using TePhe, a tellurophene-based phenylalanine analogue, labeled recombinant proteins were generated for reaction development. Using these proteins, we demonstrate an oxidation-controlled, strain-promoted tellurophene-alkyne cycloaddition (OSTAC) reaction. Mild oxidation of the tellurophene ring with N-chlorosuccinimide produces a reactive Te(IV) species which undergoes rapid (k > 100 M-1 s-1) cycloaddition with bicyclo[6.1.0]nonyne (BCN) yielding a benzo-fused cyclooctane. Selective labeling of TePhe-containing proteins can be achieved in complex protein mixtures and on fixed cells. OSTAC reactions can be combined with strain-promoted azide alkyne cycloaddition (SPAAC) and copper-catalyzed azide alkyne click (CuAAC) reactions. Demonstrating the versatility of this approach, we observe the expected staining patterns for 5-ethynyl-2'-deoxyuridine (DNA synthesis-CuAAC) and immunohistochemistry targets in combination with TePhe (protein synthesis-OSTAC) in fixed cells. The favorable properties of the OSTAC reaction suggest its broad applicability in chemical biology.

Synthetic approach to new 2H-benzo[b] [1,4]oxazin-3-one derivatives containing 1,2,3-triazole by click chemistry

Owing to the biological importance of 1,2,3-triazoles and benzoxazine-3(4H)-ones scaffolds, we have attempted to design and synthesize novel 1,2,3-traizoles linked to benzoxazin-3-one moiety. Indeed, a novel series of 1,4-disubstituted 1,2,3-triazoles containing 2H-1,4-benzoxazin-3-(4H)-one were synthesized. The 1,2,3-triazoles were obtained in high yields by a double copper-catalyzed azide-alkyne click chemistry reaction between azides and corresponding propargylated benzoxazin-3-ones. These compounds incorporate both the 2H-benzo[b] (Rao et al., 2019; Fringuelli et al., 2009) [1,4]oxazin-3-one motif and two 1,2,3-triazole heterocycles. The synthesized molecules were characterized by spectroscopic techniques such 1H NMR, 13C NMR, FT-IR and elemental analysis.

Ionizable Lipids from Click Reactions for Lipid Nanoparticle Assembling and mRNA Delivery.

Ionizable lipid-containing lipid nanoparticles (LNPs) are regarded as promising nonviral vectors for gene therapy delivery systems. Rationale design of the ionizable lipid structure based on initial screening of ionizable lipid molecule libraries combined with systematic comparison and analysis on the physical chemical parameters related to delivery efficiency greatly accelerated the discovery of novel LNP candidates for delivering various nucleic acid therapeutics like mRNAs (mRNAs). Based on the copper-catalyzed azide-alkyne click reaction, which is highly efficient and biocompatible, we were able to obtain the lipid molecule library containing a common triazole moiety between different lipid tails and various substituents as hydrophilic head groups. Herein, we systematically investigated the change of pKa values of different ionizable lipid molecules with different substituents as head groups in the click-based lipid library, mapping the pKa value change to different steps in the process of the LNP assembly and mRNA delivery. Systematic analyses on the data including the pKa value of the ionized lipids and the encapsulation and delivery efficiency of mRNA in LNPs with these ionized lipids provided the possibility of rational design on the head and tail structure for the triazole containing ionized lipids to realize highly efficient delivery of different mRNAs.

Synthesis of Fluorescent, Dumbbell-Shaped Polyurethane Homo- and Heterodendrimers and Their Photophysical Properties.

Fluorescent dendrimers have wide applications in biomedical and materials science. Here, we report the synthesis of fluorescent polyurethane homodendrimers and Janus dendrimers, which often pose challenges due to the inherent reactivity of isocyanates. Polyurethane dendrons (G1-G3) were synthesized via a convergent method using a one-pot multicomponent Curtius reaction as a crucial step to establish urethane linkages. The alkyne periphery of the G1-G3 dendrons was modified by a copper catalyzed azide-alkyne click reaction (CuAAC) to form fluorescent dendrons. In the reaction of the surfaces functionalized two different dendrons with a difunctional core, a mixture of three dendrimers consisting of two homodendrimers and a Janus dendrimer were obtained. The Janus dendrimer accounted for a higher proportion in the products' distribution, being as high as 93% for G3. The photophysical properties of Janus dendrimers showed the fluorescence resonance energy transfer (FRET) from one to the other fluorophore of the dendrimer. The FRET observation accompanied by a large Stokes shift make these dendrimers potential candidates for the detection and tracking of interactions between the biomolecules, as well as potential candidates for fluorescence imaging.

Multimodal 4-arylchromene derivatives with microtubule-destabilizing, anti-angiogenic, and MYB-inhibitory activities.

Aim: Efficient and readily available anticancer drugs are sought as treatment options. For this reason, chromene derivatives were prepared using the one-pot reaction and tested for their anticancer and anti-angiogenic properties. Methods: 2-Amino-3-cyano-4-(aryl)-7-methoxy-4H-chromene compounds (2A-R) were repurposed or newly synthesized via a three-component reaction of 3-methoxyphenol, various aryl aldehydes, and malononitrile. We performed assays to study the inhibition of tumor cell growth [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromid (MTT) assay], effects on microtubules (immunofluorescence), cell cycle (flow-activated cell sorting analysis), angiogenesis (zebrafish model), and MYB activity (luciferase reporter assay). Fluorescence microscopy was applied for localization studies via copper-catalyzed azide-alkyne click reaction of an alkyne-tagged drug derivative. Results: Compounds 2A-C and 2F exhibited robust antiproliferative activities against several human cancer cell lines (50% inhibitory concentrations in the low nanomolar range) and showed potent MYB inhibition. The alkyne derivative 3 was localized in the cytoplasm after only 10 min of incubation. Substantial microtubule disruption and G2/M cell-cycle arrest were observed, where compound 2F stood out as a promising microtubule-disrupting agent. The study of anti-angiogenic properties showed that 2A was the only candidate with a high potential to inhibit blood vessel formation in vivo. Conclusion: The close interplay of various mechanisms, including cell-cycle arrest, MYB inhibition, and anti-angiogenic activity, led to identifying promising multimodal anticancer drug candidates.

Rose Bengal Immobilized on Cellulose Paper for Sustainable Visible‐Light Photocatalysis

This work reports the heterogenization of Rose Bengal dye on simple cellulose paper sheets (Cell-RB) through copper-catalyzed azide-alkyne click ligation. The photocatalytic properties of Cell-RB under green LED irradiation were evaluated in a series of dehydrogenative transformations for the functionalization of N-aryltetrahydroisoquinolines and quinoxalin-2(1H)-ones. The excellent photocatalytic activities observed, associated to the ease of recovery with simple tweezers, highlight the strong assets of Cell-RB with respect to traditional homogeneous organic photocatalysts.

Cyclophane-based two-dimensional polymer formed by an interfacial click reaction

Two-dimensional polymers (2DPs) that incorporate molecular hosts offer a distinctive combination of properties, including covalent connectivity, structural regularity, chemical stability, permanent porosity, and molecular recognition. These features make these topologically planar macromolecular sheets promising in relation to applications, including those that appear in sensors, organic electronics, and nanofiltration membranes. Here, we use copper-catalyzed azide-alkyne click chemistry to construct a cyclophane-based 2DP at a liquid-liquid interface by polymerizing a bisazide-functionalized tetracationic cyclophane monomer with a 1,3,5-triethynylbenzene node. The 2DP prepared by employing this strategy is observed to be crystalline porous sheets by a combination of synchrotron X-ray diffraction, transmission electron microscopy, electron diffraction, and nitrogen porosimetry. When employed as the active layer in nanofiltration membranes, this 2DP exhibits excellent rejection performance of a dye, Brilliant Blue G, with 99% of the dye being removed after each cycle. Our findings could lead to the broad application of interfacial click polymerizations to produce 2DPs.

Exfoliated black phosphorous-mediated CuAAC chemistry for organic and macromolecular synthesis under white LED and near-IR irradiation.

The development of long-wavelength photoinduced copper-catalyzed azide–alkyne click (CuAAC) reaction routes is attractive for organic and polymer chemistry. In this study, we present a novel synthetic methodology for the photoinduced CuAAC reaction utilizing exfoliated two-dimensional (2D) few-layer black phosphorus nanosheets (BPNs) as photocatalysts under white LED and near-IR (NIR) light irradiation. Upon irradiation, BPNs generated excited electrons and holes on its conduction (CB) and valence band (VB), respectively. The excited electrons thus formed were then transferred to the CuII ions to produce active CuI catalysts. The ability of BPNs to initiate the CuAAC reaction was investigated by studying the reaction between various low molar mass alkyne and azide derivatives under both white LED and NIR light irradiation. Due to its deeper penetration of NIR light, the possibility of synthesizing different macromolecular structures such as functional polymers, cross-linked networks and block copolymer has also been demonstrated. The structural and molecular properties of the intermediates and final products were evaluated by spectral and chromatographic analyses.

Chemoadaptive Polymeric Assemblies by Integrated Chemical Feedback in Self-Assembled Synthetic Protocells.

The design and chemical synthesis of artificial material objects which can mimic the functions of living cells is an important ongoing scientific endeavor. A key challenge necessary for fulfilling the criteria for a system to be living currently regards evolution, which is derived from adaptivity. Integrated chemical loops capable of feedback control are required to achieve chemical systems which exhibit adaptivity. To explore this, we present an integrated, two-component orthogonal chemical process involving reversible addition–fragmentation chain transfer (RAFT) based polymerization-induced self-assembly (PISA) and a copper-catalyzed azide–alkyne click (CuAAC) coupling reaction. The chemical processes are linked through electron transfer from the activated chain-transfer agent (CTA) to the dormant Cu(II) precatalyst. We show that combining these complementary chemistries in a single reaction pot resulted in two primary outcomes: (i) simplification of the PISA process to synthesize the macro-CTA in situ from available nonamphiphilic components and (ii) routes to complexity and adaptation involving population dynamics, morphologies, and dissipative phenomena observed during in situ microscopy analysis.

Redox-Active Vertically Aligned Mesoporous Silica Thin Films as Transparent Surfaces for Energy Storage Applications.

Organic-inorganic hybrid membranes, made of a high density of redox active moieties covalently bonded to the internal surfaces of vertically aligned mesoporous silica thin films, are relevant for applications in transparent energy storage devices. This is demonstrated here on the basis of functionalized transparent mesoporous silica thin films prepared on the indium-tin oxide electrode from the combination of an electrochemically induced self-assembly method (to generate azide-functionalized silica) and a copper-catalyzed azide-alkyne click reaction (to derivatize the material with electroactive groups). The very small thickness (105 nm) and the uniformly distributed vertical mesochannels with ultranarrow diameter (2 nm) make the hybrid film a promising substrate that not only achieves a transparency of 82% but also provides large surface area to accommodate a high density of redox active species such as ferrocene. In such rigid and insulating porous membranes, the charge transfer reactions take place through a pure electron-hopping mechanism between adjacent redox sites, which are favored by the ordered and oriented mesostructure containing large amounts of uniformly distributed ferrocene functions in the mesochannels. Their performance results from both high charge transfer rates (electron hopping) and easy mass transport (fast diffusion of counter ions). The most effective system is the ferrocene-functionalized silica film prepared from 40% organosilane, which is able to deliver a capacity of 105 C cm-3 (1.10 mC cm-2) at a current density of 0.4 A cm-3 (with up to 48% capacity retention achieved at a charging time as short as 2.8 s). Such an electrode can be associated to an electrodeposited graphene anode in a solid-state battery-capacitor hybrid device, which can deliver 0.74 mC cm-2 at a potential scan rate of 20 mV s-1. The azide-functionalized mesoporous silica film is actually a versatile platform that can be functionalized with different redox molecules, as shown here for cobaltocenium moieties, which may broaden its application field.

An Entry of the Chemoselective Sulfo-Click Reaction into the Sphere of Nucleic Acids

We report here the first example of a sulfo-click conjugation reaction to be applied to modified nucleosides. The reaction, which proceeds rapidly (k ∼ 2.0 × 10-1 M-1 s-1 at 25 °C) under aqueous biocompatible conditions in the ribo- and deoxyribonucleoside series, affords the corresponding conjugated products in excellent yields. Furthermore, we demonstrate the orthogonality of the reaction with the copper-catalyzed azide-alkyne click reaction (CuAAC) by performing a one-pot dual labeling of a nucleoside carrying two orthogonal azido groups.

Silver Metallic Cyclodextrin-Core Star mPEG.

A novel silver metallic β-cyclodextrin (β-CD)-core star methoxypolyethylene glycol (mPEG) (SM-CD-SPEG) is presented. For this, a well-defined water-soluble β-CD-core star mPEG with aldehyde groups (CD-star(ald)PEG, III) is first designed and synthesized via the copper-catalyzed azide-alkyne click reaction. Then, silver nanoparticles are formed within III through the oxidation-reduction reaction between the aldehyde groups and silver ions. The oxidation-reduction reaction is characterized by means of 1 H NMR spectra. And the preparation conditions of SM-CD-SPEG are optimized. The resulting SM-CD-SPEG aqueous solutions exhibit good stability and a unimolecular micelle morphology. Significantly, it is able to obtain solid SM-CD-SPEG samples with molecular water-solubility. This is convenient for storage and further application of SM-CD-SPEG. The SM-CD-SPEG samples also show good catalytic performance toward the reduction reaction of methylene blue (MB) by sodium borohydride (NaBH4 ).

Exploring the Graft-To Synthesis of All-Conjugated Comb Copolymers Using Azide–Alkyne Click Chemistry

Copolymers with graft architectures possess interesting material properties distinct from their linear polymer counterparts. The effects of multidimensional architectures on the optoelectronic and physical properties of all-conjugated graft copolymers are not well-known, thus providing a large incentive for their study. In order to readily access these materials (hypothesized to have “comb” architectures), it is extremely important to investigate the methods used in their synthesis. Here we study the graft-to synthesis of comb copolymers composed of polythiophene backbones and polyselenophene side chains and identify the opportunities and challenges associated with copolymer formation. Azide-functionalized polythiophene “backbones” and acetylene-terminated polyselenophene “side chains” were synthesized in a controlled fashion using Kumada catalyst-transfer polycondensation (KCTP) polymerization and grafted together using copper-catalyzed azide–alkyne click chemistry (CuAAC). 1H NMR, GPC, and FTIR results ...

Morphology-Preserving Sensitization of ZnO Nanorod Surfaces via Click-Chemistry.

Films of ZnO nanorods grown by chemical vapor deposition were functionalized with a chromophore in a stepwise process that preserves the surface morphology. In the first step, the ZnO nanorods were functionalized by exposure to prop-2-ynoic acid (propiolic acid) in vacuum, which did bind through the COOH group leading to a ZnO surface functionalized with ethyne moieties (ethyne/ZnO). In the second step, 9-(4-azidophenyl)-2,5-di-tert-butylperylene (DTBPe-Ph-N3) was reacted with the ethyne/ZnO surface via copper-catalyzed azide-alkyne click reaction (CuAAC) in solution to form the DTBPe-functionalized surface (DTBPe/ZnO). The ZnO morphology was preserved after each step, as demonstrated by scanning electron microscopy (SEM). Each step was probed by X-ray photoelectron spectroscopy (XPS), and transient absorption spectroscopy (TA) of the resulting DTBPe/ZnO surface shows interfacial electron transfer following visible light excitation. As expected, attempts to bind the reference compound 1-(4-(8,11-ditert-butylperylen-3-yl)-phenyl)-1H-1,2,3-triazole-4-carboxylic acid (DTBPe-Ph-Tz-COOH) directly from solution lead to etched surfaces (confirmed by SEM) and undefined binding modes (confirmed by TA).

Activated Microglia Targeting Dendrimer-Minocycline Conjugate as Therapeutics for Neuroinflammation.

Brain-related disorders have outmatched cancer and cardiovascular diseases worldwide as the leading cause of morbidity and mortality. The lack of effective therapies and the relatively dry central nervous system (CNS) drug pipeline pose formidable challenge. Superior, targeted delivery of current clinically approved drugs may offer significant potential. Minocycline has shown promise for the treatment of neurological diseases owing to its ability to penetrate the blood-brain barrier (BBB) and potency. Despite its potential in the clinic and in preclinical models, the high doses needed to affect a positive therapeutic response have led to side effects. Targeted delivery of minocycline to the injured site and injured cells in the brain can be highly beneficial. Systemically administered hydroxyl poly(amidoamine) (PAMAM) generation-6 (G6) dendrimers have a longer blood circulation time and have been shown to cross the impaired BBB. We have successfully prepared and characterized the in vitro efficacy and in vivo targeting ability of hydroxyl-G6 PAMAM dendrimer-9-amino-minocycline conjugate (D-mino). Minocycline is a challenging drug to carry out chemical transformations due to its inherent instability. We used a combination of a highly efficient and mild copper catalyzed azide-alkyne click reaction (CuAAC) along with microwave energy to conjugate 9-amino-minocycline (mino) to the dendrimer surface via enzyme responsive linkages. D-mino was further evaluated for anti-inflammatory and antioxidant activity in lipopolysaccharides-activated murine microglial cells. D-mino conjugates enhanced the intracellular availability of the drug due to their rapid uptake, suppressed inflammatory cytokine tumor necrosis factor α (TNF-α) production, and reduced oxidative stress by suppressing nitric oxide production, all significantly better than the free drug. Fluorescently labeled dendrimer conjugate (Cy5-D-mino) was systematically administered (intravenous, 55 mg/kg) on postnatal day 1 to rabbit kits with a clinically relevant phenotype of cerebral palsy. The in vivo imaging study indicates that Cy5-D-mino crossed the impaired blood-brain barrier and co-localized with activated microglia at the periventricular white matter areas, including the corpus callosum and the angle of the lateral ventricle, with significant implications for positive therapeutic outcomes. The enhanced efficacy of D-mino, when combined with the inherent neuroinflammation-targeting capability of the PAMAM dendrimers, may provide new opportunities for targeted drug delivery to treat neurological disorders.

Boron-containing phenolic–siloxane hybrid polymers through facile click chemistry route

Realization of easily processable, tough phenolic functional polymer materials is of high demand for composite applications. Herein, we report the synthesis of boron-containing phenolic–siloxane hybrid polymers through a facile copper-catalysed azide–alkyne click chemistry (CuAAC) approach. For this, phenolic resoles incorporated with boron (PFB) was propargyl-derivatized and then bridged through triazole moieties using telechelic α, ω azidated polydimethylsiloxane (AZ-PDMS). The propargylated boronated PF (PFBPr) resins exhibited high heat of reaction during thermal cure due to the prevalence of multiple reactions. PFBPr-siloxane hybrid co-polymers exhibited glass transitions in the ranges – 100 to – 75 °C and at 25–35 °C corresponding to soft segment and hard segments. Pyrolysed PFBPr-siloxane products showed mixed phase heterogeneous systems of B and SiC. Introduction of boron and silicon improved the degree of graphitization and reduced the graphite crystallite size of the carbonization products. The pyrolysed compounds of silicon and boron formed during high temperature were conducive for creating a layer of void-free graphitic ordered carbon that improved with boron and silicon content, as revealed by SEM images.

Highly sensitive and selective detection of mercury (II) based on a zirconium metal-organic framework in aqueous media

A novel metal-organic framework (MOF) fluorescent probe UiO-66-PSM is obtained by the copper-catalyzed azide-alkyne click (CuAAC) reaction of UiO-66-N3 with phenylacetylene. The click-generated triazole unit can act as the metal binding site to coordinate with Hg2+, which exhibits the most pronounced fluorescence response (rapid response, excellent selectivity, and high sensitivity) over other metal ions. Moreover, it is capable of detecting Hg2+ in environmental water samples without any structural disintegration of the framework, indicating its high potential in practical applications.

Determining the Origin of Rate-Independent Chemoselectivity in CuAAC Reactions: An Alkyne-Specific Shift in Rate-Determining Step.

We report a kinetic and spectroscopic analysis of alkyne-dependent chemoselectivity in the copper-catalyzed azide-alkyne click (CuAAC) reaction. Studies of six alkyne subtypes reveal that the rate-determining step (RDS) of an aromatic ynamine class is shifted from acetylide formation to the azide ligation/migratory insertion event allowing chemoselectivity independent of overall rate.

Arginine side-chain modification that occurs during copper-catalysed azide-alkyne click reactions resembles an advanced glycation end product.

Dehydroascorbate is a by-product of copper-catalysed azide-alkyne click (CuAAC) reactions and also forms advanced glycation end products (AGEs) in tissues undergoing oxidative stress. Here we isolate and characterize an arginine-dehydroascorbate adduct formed during CuAAC reactions, investigate strategies for preventing its formation, and propose its biological relevance as an AGE.

A dicationic, podand-like, ionic liquid water system accelerated copper-catalyzed azide-alkyne click reaction

In this work, an effective, task specific, dicationic, podand-like ionic liquid was synthesized and applied to improve the capability features of click reaction. Moreover, to broaden the scope and decreasing the serious limitations of preparation methods of organic azides, a simple green procedure for the preparation of alkyl azides, the fundamental starting materials in click reactions, from alcohols under solvent-free conditions and microwave irradiation has been reported, for the first time.