Showing papers on "Click chemistry published in 2018"

SuFEx Click Chemistry Enabled Late-Stage Drug Functionalization

Abstract: Sulfur(VI) Fluoride Exchange (SuFEx) is a new family of click chemistry transformations which relies on readily available materials to produce compounds bearing the SVI–F motif The potential of SuFEx in drug discovery has just started to be explored We report the first method of SuFEx chemistry for the conversion of phenolic compounds to their respective arylfluorosulfate derivatives in situ in 96-well plates This method is compatible with automated synthesis and screening to quickly assess the biological activities of the in situ generated, crude products Using this method, we perform late-stage functionalization of a panel of known anticancer drugs to generate the corresponding arylfluorosulfates These in situ generated arylfluorosulfates are directly tested in a cancer-cell growth inhibition assay in parallel with their phenolic precursors We discover three arylfluorosulfates that exhibit improved anticancer cell proliferation activities compared to their phenol precursors Among these three comp

Visualizing biologically active small molecules in cells using click chemistry

Abstract: Natural products and synthetic small molecules can be used to perturb, dissect and manipulate biological processes, thereby providing the basis for drug development. Over the past decades, the evolution of molecular biology protocols and microscopy techniques has made it possible to visually detect proteins in living systems with valuable spatiotemporal resolution, in which dynamic topological information has proved to be insightful. By contrast, although small molecules have become essential for biological studies, general methods to track them in cells remain underexplored. In this Review, we discuss how bioorthogonal chemistry, and click chemistry in particular, can be exploited to label and visualize almost any biologically active small molecule in cells and tissues. We review recent developments, highlighting cases in which visualizing small molecules has provided crucial mechanistic insights. This methodology is facile to implement, is versatile and is illuminating. Click chemistry enables efficient chemical labelling of small molecules in cells, providing a powerful method to visualize almost any biologically active compound. This versatile methodology can provide valuable information about the mechanisms of action of small molecules in various biological settings.

An Organometallic Cu20 Nanocluster: Synthesis, Characterization, Immobilization on Silica, and "Click" Chemistry.

Abstract: The development of atomically precise nanoclusters (APNCs) protected by organometallic ligands, such as acetylides and hydrides, is an emerging area of nanoscience. In principle, these organometallic APNCs should not require harsh pretreatment for activation toward catalysis, such as calcination, which can lead to sintering. Herein, we report the synthesis of the mixed-valent organometallic copper APNC, [Cu20(CCPh)12(OAc)6)] (1), via reduction of Cu(OAc) with Ph2SiH2 in the presence of phenylacetylene. This cluster is a rare example of a two-electron copper superatom, and the first to feature a tetrahedral [Cu4]2+ core, which is a unique "kernel" for a Cu-only superatom. Complex 1 can be readily immobilized on dry, partially dehydroxylated silica, a process that cleanly results in release of 1 equiv of phenylacetylene per Cu20 cluster. Cu K-edge EXAFS confirms that the immobilized cluster 2 is structurally similar to 1. In addition, both 1 and 2 are effective catalysts for [3+2] cycloaddition reactions between alkynes and azides (i.e., "Click" reactions) at room temperature. Significantly, neither cluster requires any pretreatment for activation toward catalysis. Moreover, EXAFS analysis of 2 after catalysis demonstrates that the cluster undergoes no major structural or nuclearity changes during the reaction, consistent with our observation that supported cluster 2 is more stable than unsupported cluster 1 under "Click" reaction conditions.

Biosynthesis and Characterization of Copper Nanoparticles Using Shewanella oneidensis: Application for Click Chemistry.

Abstract: Copper nanoparticles (Cu-NPs) have a wide range of applications as heterogeneous catalysts. In this study, a novel green biosynthesis route for producing Cu-NPs using the metal-reducing bacterium, Shewanella oneidensis is demonstrated. Thin section transmission electron microscopy shows that the Cu-NPs are predominantly intracellular and present in a typical size range of 20-40 nm. Serial block-face scanning electron microscopy demonstrates the Cu-NPs are well-dispersed across the 3D structure of the cells. X-ray absorption near-edge spectroscopy and extended X-ray absorption fine-structure spectroscopy analysis show the nanoparticles are Cu(0), however, atomic resolution images and electron energy loss spectroscopy suggest partial oxidation of the surface layer to Cu2 O upon exposure to air. The catalytic activity of the Cu-NPs is demonstrated in an archetypal "click chemistry" reaction, generating good yields during azide-alkyne cycloadditions, most likely catalyzed by the Cu(I) surface layer of the nanoparticles. Furthermore, cytochrome deletion mutants suggest a novel metal reduction system is involved in enzymatic Cu(II) reduction and Cu-NP synthesis, which is not dependent on the Mtr pathway commonly used to reduce other high oxidation state metals in this bacterium. This work demonstrates a novel, simple, green biosynthesis method for producing efficient copper nanoparticle catalysts.

Unraveling Tetrazine-Triggered Bioorthogonal Elimination Enables Chemical Tools for Ultrafast Release and Universal Cleavage

Abstract: Recent developments in bond cleavage reactions have expanded the scope of bioorthogonal chemistry beyond click ligation and enabled new strategies for probe activation and therapeutic delivery. These applications, however, remain in their infancy, with further innovations needed to achieve the efficiency required for versatile and broadly useful tools in vivo. Amongst these chemistries, the tetrazine/trans-cyclooctene click-to-release reaction has exemplary kinetics and adaptability but achieves only partial release and is incompletely understood, which has limited its application. Investigating the mechanistic features of this reaction’s performance, we discovered profound pH sensitivity, exploited it with acid-functionalized tetrazines that both enhance and markedly accelerate release, and ultimately uncovered an unexpected dead-end isomer as the reason for poor release. Implementing facile methods to prevent formation of this dead end, we have achieved exceptional efficiency, with essentially complete ...

The [2+2] Cycloaddition-Retroelectrocyclization (CA-RE) Click Reaction: Facile Access to Molecular and Polymeric Push-Pull Chromophores.

Abstract: The [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction between electron-rich alkynes and electron-deficient alkenes is an efficient procedure to create nonplanar donor-acceptor (D-A) chromophores in both molecular and polymeric platforms. They feature attractive properties including intramolecular charge-transfer (ICT) bands, nonlinear optical properties, and redox activities for use in next-generation electronic and optoelectronic devices. This Review summarizes the development of the CA-RE reaction, starting from the initial reports with organometallic compounds to the extension to purely organic systems. The structural requirements for rapid, high-yielding transformations with true click chemistry character are illustrated by examples that include the broad alkyne and alkene substitution modes. The CA-RE click reaction has been successfully applied to polymer synthesis, with the resulting polymeric push-pull chromophores finding many interesting applications.

Injectable and Degradable pH-Responsive Hydrogels via Spontaneous Amino–Yne Click Reaction

Abstract: Injectable hydrogels have attracted increasing attention in tissue regeneration and local drug delivery applications. Current click reactions for preparing injectable hydrogels often require a photoinitiator or catalyst, which may be toxic and may involve complex synthesis of precursors. Here, we report a facile and inexpensive method to prepare injectable and degradable hydrogels via spontaneous amino-yne click reaction without using any initiator or catalyst under physiological conditions based on telechelic electron-deficient dipropiolate ester of polyethylene glycol and water-soluble commercially available carboxymethyl chitosan (CMC). The gelation time, mechanical property, and degradation rate of the hydrogels could be adjusted by varying CMC concentrations and stoichiometric ratios. The reversible pH-induced sol-gel transitions of the hydrogel are presented and the pH-controlled drug release behaviors are demonstrated, of which the mechanism is discussed. In vitro cytotoxicity assays and in vivo in situ injection study of the CMC-based hydrogels showed favorable gel formation, nontoxicity, and good tissue biocompatibility. Therefore, these biodegradable and injectable hydrogels prepared by spontaneous amino-yne click reaction hold potential for tissue engineering and other biomedical applications.

Click Chemistry-Based Injectable Hydrogels and Bioprinting Inks for Tissue Engineering Applications.

Abstract: The tissue engineering and regenerative medicine approach require biomaterials which are biocompatible, easily reproducible in less time, biodegradable and should be able to generate complex three-dimensional (3D) structures to mimic the native tissue structures. Click chemistry offers the much-needed multifunctional hydrogel materials which are interesting biomaterials for the tissue engineering and bioprinting inks applications owing to their excellent ability to form hydrogels with printability instantly and to retain the live cells in their 3D network without losing the mechanical integrity even under swollen state. In this review, we present the recent developments of in situ hydrogel in the field of click chemistry reported for the tissue engineering and 3D bioinks applications, by mainly covering the diverse types of click chemistry methods such as Diels–Alder reaction, strain-promoted azide-alkyne cycloaddition reactions, thiol-ene reactions, oxime reactions and other interrelated reactions, excluding enzyme-based reactions. The click chemistry-based hydrogels are formed spontaneously on mixing of reactive compounds and can encapsulate live cells with high viability for a long time. The recent works reported by combining the advantages of click chemistry and 3D bioprinting technology have shown to produce 3D tissue constructs with high resolution using biocompatible hydrogels as bioinks and in situ injectable forms. Interestingly, the emergence of click chemistry reactions in bioink synthesis for 3D bioprinting have shown the massive potential of these reaction methods in creating 3D tissue constructs. However, the limitations and challenges involved in the click chemistry reactions should be analyzed and bettered to be applied to tissue engineering and 3D bioinks. The future scope of these materials is promising, including their applications in in situ 3D bioprinting for tissue or organ regeneration.

Splicing Nanoparticles-Based "Click" SERS Could Aid Multiplex Liquid Biopsy and Accurate Cellular Imaging.

Abstract: Here, a completely new readout technique, so-called “Click” SERS, has been developed based on Raman scattered light splice derived from nanoparticle (NP) assemblies The single and narrow (1–2 nm) emission originating from triple bond-containing reporters undergoes dynamic combinatorial output, by means of controllable splice of SERS-active NPs analogous to small molecule units in click chemistry Entirely different to conventional “sole code related to sole target” readout protocol, the intuitional, predictable and uniquely identifiable “Click” SERS is relies on the number rather than the intensity of combinatorial emissions By this technique, 10-plex synchronous biomarkers detection under a single scan, and accurate cellular imaging under double exposure have been achieved “Click” SERS demonstrated multiple single band Raman scattering could be an authentic optical analysis method in biomedicine

Highly Stable Copper(I)-Based Metal–Organic Framework Assembled with Resorcin[4]arene and Polyoxometalate for Efficient Heterogeneous Catalysis of Azide–Alkyne “Click” Reaction

Abstract: A new highly stable copper(I)-based metal–organic framework (MOF), namely, [CuI4(SiW12O40)(L)]·6H2O·2DMF (1), was synthesized by incorporating Keggin-type polyoxometalate (POM) anions and a functionalized wheel-like resorcin[4]arene-based ligand (L) under sovothermal condition. 1 exhibits a charming 3D supramolecular architecture sandwiched by the POM anions. Noticeably, 1 has exceptional chemical stability, especially in organic solvents or aqueous solutions with a wide range of pH values. Considering the catalytically active Cu(I) sites in 1, the azide–alkyne cycloaddition (AAC) reaction was studied by employing 1 as the heterogeneous catalyst. Most strikingly, 1 exhibits excellent catalytic activity as well as recyclability for the AAC reaction.

Visible Light-Initiated Bioorthogonal Photoclick Cycloaddition.

Abstract: Here we report a visible light-triggered, catalyst free bioorthogonal reaction that proceeds via a distinct pathway from reported bioorthogonal reactions. The prototype of this bioorthogonal reaction was the photocycloaddition of 9,10-phenanthrenequinone with electron-rich alkenes to form fluorogenic [4+2] cycloadducts. The bioorthogonal photoclick cycloaddition was readily initiated using a conventional visible light source such as a hand-held LED lamp. The reaction proceeded rapidly under biocompatible conditions, without observable competition from side reactions such as nucleophilic additions by water or common nucleophilic species. The bioorthogonal functionality in this reaction did not cross react with various alkynes and electron-deficient alkenes such as monomethyl fumarate. We demonstrated orthogonal labeling of two proteins using this reaction together with a strain promoting azide–alkyne click reaction or the UV-triggered reaction of tetrazole with monomethyl fumarate. The application of this ...

Click Chemistry Reaction-Triggered 3D DNA Walking Machine for Sensitive Electrochemical Detection of Copper Ion

Abstract: Herein, for the first time, we engineered click chemistry reaction to trigger a 3D DNA walking machine for ultrasensitive electrochemical detection of copper ion (Cu2+), which provided a convenient access to overcome the shortcomings of poor selectivity and limited amplification efficiency in traditional determination of Cu2+. Click chemistry reaction drove azido-S2 to bind with alkynyl-S1 for the formation of a walker probe on aminated magnetic polystyrene microsphere@gold nanoparticles (PSC@Au), which opened the hairpin-locked DNAzyme. In the presence of magnesium ion (Mg2+), the unlocked DNAzyme was activated to cleave the self-strand at the facing ribonucleotide site, accompanied by the release of product DNA (S3) and the walker probe. Therefore, the walker probe was able to open the adjacent hairpin-locked DNAzyme strand and then be released by DNAzyme cleavage along the PSC@Au-DNAzyme track. Eventually, the liberated single-strand S3 induced catalytic hairpin assembly (CHA) recycling, resulting in t...

Enzyme-like Click Catalysis by a Copper-Containing Single-Chain Nanoparticle.

Abstract: A major challenge in performing reactions in biological systems is the requirement for low substrate concentrations, often in the micromolar range. We report that copper cross-linked single-chain nanoparticles (SCNPs) are able to significantly increase the efficiency of copper(I)-catalyzed alkyne–azide cycloaddition (CuAAC) reactions at low substrate concentration in aqueous buffer by promoting substrate binding. Using a fluorogenic click reaction and dye uptake experiments, a structure–activity study is performed with SCNPs of different size and copper content and substrates of varying charge and hydrophobicity. The high catalytic efficiency and selectivity are attributed to a mechanism that involves an enzyme-like substrate binding process. Saturation-transfer difference (STD) NMR spectroscopy, 2D-NOESY NMR, kinetic analyses with varying substrate concentrations, and computational simulations are consistent with a Michaelis–Menten, two-substrate, random-sequential enzyme-like kinetic profile. This gener...

Click-to-Release from trans-Cyclooctenes: Mechanistic Insights and Expansion of Scope from Established Carbamate to Remarkable Ether Cleavage.

Abstract: The bioorthogonal cleavage of allylic carbamates from trans-cyclooctene (TCO) upon reaction with tetrazine is widely used to release amines. We disclose herein that this reaction can also cleave TCO esters, carbonates, and surprisingly, ethers. Mechanistic studies demonstrated that the elimination is mainly governed by the formation of the rapidly eliminating 1,4-dihydropyridazine tautomer, and less by the nature of the leaving group. In contrast to the widely used p-aminobenzyloxy linker, which affords cleavage of aromatic but not of aliphatic ethers, the aromatic, benzylic, and aliphatic TCO ethers were cleaved as efficiently as the carbamate, carbonate, and esters. Bioorthogonal ether release was demonstrated by the rapid uncaging of TCO-masked tyrosine in serum, followed by oxidation by tyrosinase. Finally, tyrosine uncaging was used to chemically control cell growth in tyrosine-free medium.

Mechanistic Investigation into the Selective Anticancer Cytotoxicity and Immune System Response of Surface-Functionalized, Dichloroacetate-Loaded, UiO-66 Nanoparticles

Abstract: The high drug-loading and excellent biocompatibilities of metal–organic frameworks (MOFs) have led to their application as drug-delivery systems (DDSs). Nanoparticle surface chemistry dominates both biostability and dispersion of DDSs while governing their interactions with biological systems, cellular and/or tissue targeting, and cellular internalization, leading to a requirement for versatile and reproducible surface functionalization protocols. Herein, we explore not only the effect of introducing different surface functionalities to the biocompatible Zr-MOF UiO-66 but also the efficacy of three surface modification protocols: (i) direct attachment of biomolecules [folic acid (FA) and biotin (Biot)] introduced as modulators for UiO-66 synthesis, (ii) our previously reported “click-modulation” approach to covalently attach polymers [poly(ethylene glycol) (PEG), poly-l-lactide, and poly-N-isopropylacrylamide] to the surface of UiO-66 through click chemistry, and (iii) surface ligand exchange to postsynth...

Electrochemically Promoted Tyrosine-Click-Chemistry for Protein Labeling

Abstract: The development of new bio-orthogonal ligation methods for the conjugation of native proteins is of particular importance in the field of chemical biology and biotherapies. In this work, we developed a traceless electrochemical method for protein bioconjugation. The electrochemically promoted tyrosine-click (e-Y-CLICK) allowed the chemoselective Y-modification of peptides and proteins with labeled urazoles. A low potential is applied in an electrochemical cell to activate urazole anchors in situ and on demand, without affecting the electroactive amino acids from the protein. The versatility of the electrosynthetic approach was shown on biologically relevant peptides and proteins such as oxytocin, angiotensin 2, serum bovine albumin, and epratuzumab. The fully conserved enzymatic activity of a glucose oxidase observed after e-Y-CLICK further highlights the softness of the method. The e-Y-CLICK protocols were successfully performed in pure aqueous buffers, without the need for co-solvents, scavenger or oxid...

Assembly of PEG Microgels into Porous Cell-Instructive 3D Scaffolds via Thiol-Ene Click Chemistry.

Abstract: The assembly of microgel building blocks into 3D scaffolds is an emerging strategy for tissue engineering. A key advantage is that the inherent microporosity of these scaffolds provides cells with a more permissive environment than conventional nanoporous hydrogels. Here, norbornene-bearing poly(ethylene glycol) (PEG) based microgels are assembled into 3D cell-instructive scaffolds using a PEG-dithiol linker and thiol-ene click photopolymerization. The bulk modulus of these materials depends primarily on the crosslink density of the microgel building blocks. However, the linker and initiator concentrations used during assembly have significant effects on cell spreading and proliferation when human mesenchymal stem cells (hMSCs) are incorporated in the scaffolds. The cell response is also affected by the properties of the modular microgel building blocks, as hMSCs growing in scaffolds assembled from stiff but not soft microgels activate Yes-associated protein signaling. These results indicate that PEG microgel scaffolds assembled via thiol-ene click chemistry can be engineered to provide a cell-instructive 3D milieu, making them a promising 3D platform for tissue engineering.

Application of click chemistry in nanoparticle modification and its targeted delivery.

Abstract: Click chemistry is termed as a group of chemical reactions with favorable reaction rate and orthogonality. Recently, click chemistry is paving the way for novel innovations in biomedical science, and nanoparticle research is a representative example where click chemistry showed its promising potential. Challenging trials with nanoparticles has been reported based on click chemistry including copper-catalyzed cycloaddition, strain-promoted azide-alkyne cycloaddition, and inverse-demand Diels-Alder reaction. Herein, we provide an update on recent application of click chemistry in nanoparticle research, particularly nanoparticle modification and its targeted delivery. In nanoparticle modification, click chemistry has been generally used to modify biological ligands after synthesizing nanoparticles without changing the function of nanoparticles. Also, click chemistry in vivo can enhance targeting ability of nanoparticles to disease site. These applications in nanoparticle research were hard or impossible in case of traditional chemical reactions and demonstrating the great utility of click chemistry.

Identification and characterization of nucleobase-modified aptamers by click-SELEX

Abstract: Aptamers are single-stranded oligonucleotides that are in vitro-selected to recognize their target molecule with high affinity and specificity. As they consist of the four canonical nucleobases, their chemical diversity is limited, which in turn limits the addressable target spectrum. Introducing chemical modifications into nucleic acid libraries increases the interaction capabilities of the DNA and thereby the target spectrum. Here, we describe a protocol to select nucleobase-modified aptamers by using click chemistry (CuAAC) to introduce the preferred chemical modification. The use of click chemistry to modify the DNA library enables the introduction of a wide range of possible functionalities, which can be customized to the requirements of the target molecule and the desired application. This protocol yields modified DNA aptamers with extended interaction properties that are not accessible with the canonical set of nucleotides. After synthesis of the starting library containing a commercially available, alkyne-modified uridine (5-ethynyl-deoxyuridine (EdU)) instead of thymidine, the library is functionalized with the modification of choice by CuAAC. The thus-modified DNA is incubated with the target molecule and the best binding sequences are recovered. The chemical modification is removed during the amplification process. Therefore, this protocol is compatible with conventional amplification procedures and avoids enzymatic incompatibility problems associated with more extensive nucleobase modifications. After single-strand generation, the modification is reintroduced into the enriched library, which can then be subjected to the subsequent selection cycle. The duration of each selection cycle as outlined in the protocol is ∼1 d.