ParaCEST MRI contrast agents capable of derivatization via"click" chemistry

A comprehensive series of lanthanide chelates has been prepared with a tetrapropargyl DOTAM type ligand. The complexes have been characterized by a combination of (1)H NMR, single-crystal X-ray crystallography, CEST and relaxation studies and have also been evaluated for potential use as paramagnetic chemical exchange saturation transfer (ParaCEST) contrast agents in magnetic resonance imaging (MRI). We demonstrate the functionalization of several chelates by means of alkyne-azide "click" chemistry in which a glucosyl azide is used to produce a tetra-substituted carbohydrate-decorated lanthanide complex. The carbohydrate periphery of the chelates has a potent influence on the CEST properties as described herein.     

Synthesis of ferrocene conjugates with di- and triterpenes by click chemistry method

Reactions of propargyl dehydroabietate with ferrocenylalkyl azides led to the formation of substituted 1,2,3-triazoles. The corresponding 1,2,3-triazoles formed in the reaction of ferrocenylalkyl azides with propargyl betulonic ester.     

A comparison investigation on the solubilization of betulin and betulinic acid in cyclodextrin derivatives

Betulin (BET) and betulinic acid (BA) are naturally occurring pentacyclic lupane triterpenes, exhibit great promise as bioactive agents for the treatment of many diseases. The poor solubilities of BET and BA in water have limited their applications. In the present work, BET and BA were selected as guest molecules, three hydrophilic gamma-cyclodextrin (CD) thioethers were synthesized and selected as host molecules. beta-, Hydroxypropyl-beta-CD, (HP-beta-CD), gamma-CD and HP-gamma-CD were also investigated as hosts in order to compare the solubilization abilities of these host molecules. The solubilities of BET and BA were estimated from 1H NMR measurements by comparing the relative integral areas of the proton signals between CDs and guests. gamma-CD thioethers 5-7solubilized BET and BA to much higher extends than other host molecules. The obtained maximal solubilities of BET and BA were 5.2 and 4.5 mM, respectively. The topographies of the inclusion compounds were determined by ROESY NMR spectroscopy.     

Functionalization of polymers with phosphorescent iridium complexes via click chemistry

We report a simple yet highly efficient route to prepare polymers with a variety of pendant iridium complexes as potential materials in organic light-emitting diodes by employing click chemistry.     

Creation of 3,4-bis-triazolocoumarin-sugar conjugates via flourogenic dual click chemistry and their quenching specificity with silver(I) in aqueous media

Fluorogenic click chemistry has recently emerged as an ingenious and powerful tool toward numerous biochemical purposes. We describe herein the use of dual click chemistry toward the fluorescence restoration of a fluorogenic coumarin on epimeric dipropargyl sugar scaffolds and their practical utility in selective metal ion detection. The dual click reactions were smoothly proceeded under microwave irradiation between silylated 3,4-di-O-propynyl gluco- or galactoside and 3-azidocoumarin, forming fluorescently reactivated bis-triazolocoumarins on sugar templates. Subsequent desilylation resulted in the OH-glycosides with desired water solubility. The following photochemical study disclosed that their fluorescence could be uniquely quenched by silver(I) in aqueous media with very minor responses to the addition of other metal ions. This research would presumably prompt the efficient creation of water soluble and potentially low toxic chemosensors via the fluorogenic dual click chemistry in using the universally existent sugars as the central scaffold.     

Synthesis of unsymmetrical sulfamides and polysulfamides via SuFEx click chemistry

As hydrogen-bond donors and acceptors, N,N′-disubstituted sulfamides have been used in a range of applications from medicinal chemistry to anion-binding catalysis. However, compared to ureas or thioureas, the utilization of this unique moiety remains marginal, in part because of a lack of general synthetic methods to access unsymmetrical sulfamides. Specifically, polysulfamides are a virtually unknown type of polymer despite their potential utility in non-covalent dynamic networks, an intense area of research in materials science. We report herein a practical and efficient process to prepare unsymmetrical sulfamides via Sulfur(vi)-Fluoride Exchange (SuFEx) click chemistry. This process was then applied to synthesize polysulfamides. Thermal analysis showed that this family of polymers possess high thermal stability and tunable glass transition temperatures. Finally, hydrolysis studies indicated that aromatic polysulfamides could be recycled back to their constituting monomers at the end of their life cycle.

A general, practical, and efficient synthesis of N,N′-disubstituted sulfamides has been developed and applied to the preparation of polysulfamides, a virtually unknown class of polymers.     

Synthesis of degradable model networks via ATRP and click chemistry

A simple scheme involving atom transfer radical polymerization (ATRP) from a bifunctional initiator, conversion of the bromine end groups of the resulting telechelic polymer to azides, and cross-linking of this azido-telechelic macromonomer with multi-acetylene functionalized small molecules via copper-catalyzed azide-alkyne cycloaddition was employed to prepare the first tert-butyl acrylate model networks. This general scheme is wide in scope, enabling synthesis of model networks possessing defined pore size from any monomer polymerizable by ATRP. Introduction of an olefin moiety into the ATRP initiator enabled degradation of the materials by ozonolysis to yield star polymer products bearing three or four arms depending on which cross-linker was employed in the parent network. Size-exclusion chromatography of the ozonolysis products confirmed the pore size of the parent network and yielded insight into the number of unreacted functionalities. Model networks derived from a trifunctional alkyne were found to be more completely cross-linked than those derived from a tetrafunctional alkyne, presumably due to less steric hindrance in the former system.     

Synthesis of peptide dendrimers with polyhedral oligomeric silsesquioxane cores via click chemistry

Inorganic polyhedral oligomeric silsesquioxane (POSS) was used as the core for the synthesis of poly(Llysine) peptide dendrimer via copper-catalyzed azide-alkyne click chemistry. The inorganic/organic composite dendrimer was characterized by MS, 1H NMR, FTIR, GPC and DLS.     

Facile synthesis of polymer–peptide conjugates via direct amino acid coupling chemistry

Polymer–peptide conjugates (also known as biohybrids) are attracting considerable attention as injectable materials owing to the self‐assembling behavior of the peptide and the ability to control the material properties using the polymer component. To this end, a simple method for preparing poly(ethylene oxide)‐oligophenylalanine polymer–peptide conjugates (mPEO_m‐F_n‐OEt) using isobutylchloroformate as the activating reagent has been identified and developed. The synthetic approach reported employs an industrially viable route to produce conjugates with high yield and purity. Moreover, the approach allows judicious selection of the precursor building blocks to produce libraries of polymer–peptide conjugates with complete control over the molecular composition. Control over the molecular make‐up of the conjugates allows fine control of the physicochemical properties, which will be exploited in future studies into the prominent self‐assembling behavior of such materials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4853–4859     

Synthesis and photophysical properties of chiral dendrimers with quinoline surface group via click chemistry

Synthesis of some novel chiral dendrimers containing quinoline as surface group and 1,2,3-triazole as branching unit is described. The chiroptical property exhibits the widening of the torsional angle in the BINOL core as the generation increases. The photophysical properties indicate an increase in the molar extinction coefficient and fluorescence intensity and a decrease in quantum yield and lifetime as the generation of the dendrimer increases.     

Modular synthesis of a block copolymer with a cleavable linkage via click chemistry

A diblock copolymer poly(ethylene glycol)-block-polystyrene or PEG-b-PS with an olefinic double bond at the PEG and PS junction has been prepared by modular synthesis viaclickchemistry.This involved the synthesis of PS by atom transfer radical polymerization and the nucleophilic substitution of the terminal bromide group with azide to yield azide-terminated PS. PEG with an alkynyl terminal group was prepared from reacting carboxyl-end-functionalized PEG with 4-hydroxybut-2-enyl prop-2-ynyl succinate,which c...     

Efficient and tunable synthesis of new polydentate bifunctional chelating agents using click chemistry

Two novel bifunctional chelating agents, which are bistriazole-based polyaminocarboxylic acids, have been designed and synthesised in high yields. An elegant synthetic approach using the Cu-catalysed azide-alkyne cycloaddition has been developed. This convenient route could be employed for the synthesis of a variety of polydentate bifunctional chelators.     

Covalent immobilization of horseradish peroxidase via click chemistry and its direct electrochemistry

A simple and versatile approach for covalent immobilization of redox protein on solid surface via self-assembled technique and click chemistry is reported. The alkynyl-terminated monolayers are obtained by self-assembled technique, then, azido-horseradish peroxidase (azido-HRP) was covalent immobilized onto the formed monolayers by click reaction. The modified process is characterized by reflection absorption infrared spectroscopy (RAIR), surface-enhanced Raman scattering spectroscopy (SERS) and electrochemical methods. All the experimental results suggest that HRP is immobilized onto the electrode surface successfully without denaturation. Furthermore, the immobilized HRP shows electrocatalytic reduction for H₂O₂, and the linear range is from 5.0 to 700 μM. The heterogeneous electron transfer rate constant k_s is 1.11 s⁻¹ and the apparent Michaelis-Menten constant is calculated to be 0.196 mM.     

Non-nucleoside building blocks for copper-assisted and copper-free click chemistry for the efficient synthesis of RNA conjugates

Novel non-nucleoside alkyne monomers compatible with oligonucleotide synthesis were designed, synthesized, and efficiently incorporated into RNA and RNA analogues during solid-phase synthesis. These modifications allowed site-specific conjugation of ligands to the RNA oligonucleotides through copper-assisted (CuAAC) and copper-free strain-promoted azide-alkyne cycloaddition (SPAAC) reactions. The SPAAC click reactions of cyclooctyne-oligonucleotides with various classes of azido-functionalized ligands in solution phase and on solid phase were efficient and quantitative and occurred under mild reaction conditions. The SPAAC reaction provides a method for the synthesis of oligonucleotide-ligand conjugates uncontaminated with copper ions.     

Facile decoration of functionalized single-wall carbon nanotubes with phthalocyanines via "click chemistry"

We describe the functionalization of single-wall carbon nanotubes (SWNTs) with 4-(2-trimethylsilyl)ethynylaniline and the subsequent attachment of a zinc-phthalocyanine (ZnPc) derivative using the reliable Huisgen 1,3-dipolar cycloaddition. The motivation of this study was the preparation of a nanotube-based platform which allows the facile fabrication of more complex functional nanometer-scale structures, such as a SWNT-ZnPc hybrid. The nanotube derivatives described here were fully characterized by a combination of analytical techniques such as Raman, absorption and emission spectroscopy, atomic force and scanning electron microscopy (AFM and SEM), and thermogravimetric analysis (TGA). The SWNT-ZnPc nanoconjugate was also investigated with a series of steady-state and time-resolved spectroscopy experiments, and a photoinduced communication between the two photoactive components (i.e., SWNT and ZnPc) was identified. Such beneficial features lead to monochromatic internal photoconversion efficiencies of 17.3% when the SWNT-ZnPc hybrid material was tested as photoactive material in an ITO photoanode.     

Supramolecular structures based on dimeric combinations of cyclodextrin and adamantane via click chemistry

The cyclic starches α-, β-, and γ-cyclodextrins (CDs) readily form inclusion complexes (ICs) with a large variety of polymers. In polymer-CD-ICs, the CD hosts are threaded by the guest polymers, which must be highly extended, and stacks of polymer threaded host CDs pack closely together and crystallize. When guest polymers are coalesced from their CD-IC crystals, by washing with a solvent good, bad for CD, polymer, or treatment with an amylase enzyme, the guest polymers coalesce into bulk samples whose structures, morphologies, and even conformations are distinct from bulk samples made from their solutions and melts. We generally observe (i) crystallizable homopolymers coalesced from their CD-ICs to evidence increased levels of crystallinity, unusual polymorphs, and higher melting, crystallization, and decomposition temperatures, while coalesced amorphous homopolymers exhibit higher glass-transition temperatures, than samples consolidated from their disordered solutions and melts; (ii) molecularly mixed, intimate blends of two or more polymers that are normally believed to be immiscible can be achieved by coalescence from their common CD-IC crystals, (iii) the phase segregation of incompatible blocks can be controlled (suppressed or increased) when block copolymers are coalesced from their CD-IC crystals, and (iv) the thermal and temporal stabilities of the coalesced and well-mixed homopolymer blends and block copolymers appear to be substantial, thereby suggesting retention of as-coalesced structures and morphologies under normal thermal processing conditions. Furthermore, CDs may be covalently incorporated in polymers both during and after their syntheses, thereby providing a broad range of new functionalities for delivery of additives or to act as sensors or filters. Alternatively, additive-CD-ICs or additives rotaxanated with CDs may be effectively delivered to polymers. As an example, TiO₂—filled polypropylene fibers may be readily dyed in aqueous solution using water soluble CD-rotaxanated azo-dyes.     

Functionalized ionic liquids with highly polar polyhydroxylated appendages and their rapid synthesis via thiol-ene click chemistry

The thiol-ene ‘click’ reaction of 1-thioglycerol with ionic liquids incorporating cations bearing appended vinyl- and/or allyl groups is a versatile, single-step means for their conversion into derivatives bearing up to eight hydroxyl groups per cation.     

Synthesis of degradable molecular brushes via a combination of ring-opening polymerization and click chemistry

Acid-degradable molecular brushes with polycarbonate backbone and densely grafted side chains (∼1.9 SCs per backbone repeating unit) were synthesized for the first time using the grafting-onto method. Extremely efficient copper-catalyzed azide-alkyne cycloaddition click reactions between the polycarbonate backbone containing two pendant azido groups per backbone unit and alkynyl-terminated poly (methyl acrylate) (ay-PMA₇₂, average degree of polymerization DP = 72) SCs were demonstrated to finish in 10 min with a quantitative conversion of the azido groups. Similar grafting efficiencies were also achieved when using alkynyl-terminated polystyrene (ay-PS), poly(ethylene oxide) (ay-PEO), and poly (t-butyl acrylate)-b-polystyrene (ay-PtBA-b-PS) to successfully prepare molecular brushes with high grafting density (>1.8 SCs per backbone repeating unit). Under acidic condition, the polycarbonate backbones were completely degradable and the final degraded product of the molecular brushes was a linear polymer chain with molecular weight two times of the SCs. When a mixture of hydrophobic ay-PS and hydrophilic ay-PEO chains was used, amphiphilic heterobrushes PC-g-(PS-co-PEO) were synthesized, which could self-assemble into micelles or vesicles in selective solvents, depending on the ratio of the two SCs in the brush. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 239–248     

A potent and highly selective inhibitor of human alpha-1,3-fucosyltransferase via click chemistry

Potent inhibitors of fucosyltransferases, and glycosyltransferases in general, have been elusive due to the inherent barriers surrounding the family of glycosyltransfer reactions. The problems of weak substrate affinity and low catalytic proficiency of fucosyltransferase was offset by recruiting additional binding features, in this case hydrophobic interactions, to produce a high affinity inhibitor, 24, with Ki = 62 nM. The molecule was identified from a GDP-triazole library of 85 compounds, which was produced by the Cu(I)-catalyzed [2 + 3] cycloaddition reaction between azide and acetylene reactants, followed by in situ screening without product isolation.     

Design and characterization of an electrochemical peptide-based sensor fabricated via"click" chemistry

We report an electrochemical peptide-based sensor fabricated via'click' chemistry for detection of anti-p24 antibodies. Our results also allude to a signaling mechanism similar to that of the linear probe electrochemical DNA sensor.