Metal ion detection using a fluorogenic ‘click’ reaction

A fluorogenic Cu(I)-catalyzed azide-alkyne cycloaddition reaction (CuAAC) of 3-azido-7-hydroxycoumarin has been used to detect metal ions in solution. The formation of a highly fluorescent triazole product signals the presence of Cu(I) or Cu(II) ions at micromolar concentrations. CuAAC can be modified by using an exogenous ligand like EDTA to detect and quantify Zn(II), Ca(II), and Cd(II) ions at micromolar concentrations by an allosteric mechanism. The increase in the formation of the triazole product is regulated by the release of Cu(II) from the Cu(II)-EDTA complex by the addition of a second metal ion, the allosteric effector.     

Tunable BODIPY derivatives amenable to ‘click’ and peptide chemistry

Novel azido- and amino-functionalised fluorescent probes based on the BODIPY framework have been developed. The probes can be easily and cheaply synthesised, exhibit the highly desirable BODIPY fluorescent properties, and are amenable to ‘click’ and peptide chemistry methodologies. These probes provide a stable and readily available tool amenable for the visualisation of both solution and solid supported events.     

Janus carbosilane/phosphorhydrazone dendrimers synthesized by the ‘click’ Staudinger reaction

The first association of carbosilane dendrons (having a phosphine at the focal point) with phosphorhydrazone dendrons (having a thiophosphoryl azide at the focal point) has been successfully carried out by ‘Staudinger click’ reaction. The corresponding Janus dendrimers possess the characteristics of both components; they are oily as the carbosilane dendrons, and they can be easily functionalized as the phosphorhydrazone dendrons.     

Synthesis of hemicyanine dyes for ‘click’ bioconjugation

A new type of 2-propynyl substituted hemicyanine dyes have been synthesized in a facile route, which have showed superior solubility in water and good optical properties. The terminal alkynyl groups were employed for bioconjugation through a 1,3-dipolar cycloaddition with azides under mild conditions.     

Synthesis of C-linked immobilized analogs of aloisine A by ‘click’ chemistry

An efficient approach for the immobilization of a series of analogs of aloisine A, an in vitro inhibitor of protein kinases, to polymeric supports via a [3+2] cycloaddition reaction is reported.     

A fluorescent hydrogen peroxide probe based on a ‘click’ modified coumarin fluorophore

Herein a water-soluble ‘click’ modified coumarin-based fluorescent probe for hydrogen peroxide is reported. This probe shows significant intensity increases (up to fivefold) in near-green fluorescence upon reaction with hydrogen peroxide, and good selectivity over other reactive oxygen species.     

Polymer thermoreversible gels from organogelators enabled by ‘click’ chemistry

[1,2,3]-Triazole-based polymers made by means of the copper(I)-catalyzed azide-alkyne [3+2] cycloaddition (CuAAC) exhibit selective gelling ability for DMSO and organic solvent mixtures containing at least 80% DMSO by volume. The organogels were characterized by FT-IR, DSC, TEM, and rheology.     

Synthesis of a polypseudorotaxane, polyrotaxane, and polycatenane using ‘click’ chemistry

The synthesis of a polypseudorotaxane, polyrotaxane, and polycatenane containing the electron-deficient cyclophane cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺) subunit in the side chain is described. These interlocked supramolecular polymers have been prepared from an azide-functionalized polystyrene derivative and an acetylene-functionalized [2]rotaxane, [2]catenane and their parent tetracationic cyclophane via Cu(I)-catalyzed 1,3 dipolar cycloadditions (‘click chemistry’). The synthesis and characterization of the polymers and intermediates has been described using IR, ¹H NMR, UV spectroscopies, and voltammetry. We have shown that the CBPQT⁴⁺ unit of the side chain polystyrene derivative has the ability to reversibly undergo complexation with a complementary dialkoxynaphthalene derivative.     

Triazole-linked dendro[60]fullerenes: modular synthesis via a ‘click’ reaction and acidity-dependent self-assembly on the surface

A series of Fréchet-type dendron functionalized [60]fullerene derivatives that bear a 1,2,3-triazole linkage group, referred to as triazole-linked dendro[60]fullerenes, were prepared via a modular synthetic protocol based on a Cu-catalyzed [3+2] cycloaddition (‘click’) reaction. Electronic properties of these dendro[60]fullerenes were investigated by UV-vis spectroscopy and cyclic voltammetry. Interfacial supramolecular self-assembly behavior of these dendro[60]fullerenes was studied using atomic force microscopy (AFM). The resulting self-assemblies showed different nanoscale packing geometries and morphologies on the surface, which are controllable by parameters such as the generation of dendron, the nature of peripheral functionalities, and the experimental conditions (e.g., acidity) applied. Correlations between molecular structure and self-assembling outcome were surveyed and discussed. The results of this study suggest a new avenue to gain better ‘bottom-up’ control over the self-assembly of dendrimer-fullerene hybrid materials in terms of shape and size.     

Hydrogelation and spontaneous fiber formation of 8-aza-7-deazaadenine nucleoside ‘click’ conjugates

Nucleoside hydrogels based on benzyl azide ‘click’ conjugates of 8-aza-7-deaza-2′-deoxyadenosine bearing 7-ethynyl, 7-octa-(1,7-diynyl), and 7-tri-prop-2-ynyl-amine side chains were synthesized (1, 3, 4). The cycloaddition adduct with the shortest linker (1) yields the most powerful hydrogelator forming stable gels at a concentration of 0.3 wt % of 1 in water. One molecule of 1 catches 7500 water molecules. Cycloaddition of the 8-aza-7-deaza-7-azido-2′-deoxyadenosine (9) and 3-phenyl-1-propyne (10) leads to the isomeric conjugate 2, with a C-N connectivity between the nucleobase and triazole moiety. This gel is less stable than that of the adduct 1. Both gels show a similar stability over a wide pH range (4.0-10.0). Xerogels of 1 and 2 studied by scanning electron microscopy (SEM) reveal that both click adducts (1 and 2) form long fibers spontaneously.     

Synthesis of steroidal dendrimers modified by ‘click’ chemistry with PAMAM dendrons as unimolecular micelles

Novel Fréchet–PAMAM hybrid dendrimers linked by triazole units as unimolecular micelles with a hydrophobic core surrounded by a hydrophilic shell were prepared. The dendritic cores with 3 and 6 alkyne terminal groups were synthesized from 1,3,5-tribromomethyl-benzene (tBrMeB), in one case by direct coupling with 17α-ethynylestradiol (EE); in the second one the tBrMeB was reacted with bis(hydroxymethyl) phenol followed by chlorination of the hydroxyl groups and subsequent coupling to EE. With this strategy, the core can be grown by further substitutions of bis(hydroxymethyl) phenol over the halogenated terminals as Fréchet dendrimer. The hydrophilic shells used were PAMAM type dendrons of 0.5 and 1.5 generations with azide as focal point and tert-butyl ester as end groups. The unimolecular micelles were obtained by cycloaddition between an azide in the selected dendron and the alkyne terminal in the hydrophobic core to obtain a 1,4-disubstituted 1,2,3-triazole. Once the coupling was achieved, the tert-butyl ester groups were hydrolyzed in trifluoroacetic acid and the corresponding dendrimers with carboxylic acid as end groups were completely soluble in phosphate buffer solutions of pH 7.0, 7.4, and 8.0. All hybrid dendrimers were characterized by High Resolution Mass Spectrometry, ¹H and ¹³C NMR, and FTIR.     

Designing dendritic frameworks using versatile building blocks suitable for Cu-catalyzed alkyne azide ‘click’ chemistry

Synthesis of molecular building blocks that incorporate azide and alkyne-terminated functionalities suitable for Cu^I-catalyzed cycloaddition between alkynes and azides is reported. Their utility in constructing dendritic frameworks with 4, 6, or 12 peripheral acetylene groups using either the convergent or divergent methodology, and their functionalization with desirable end groups are demonstrated.     

Synthesis of bis-1,2,3-triazolo-bridged unsymmetrical pyrrolobenzodiazepine trimers via ‘click’ chemistry and their DNA-binding studies

New conceivable synthetic approach for the construction of nitrogen-rich 1,2,3-triazolo-pyrrolo[2,1-c][1,4]benzodiazepine (TPBD, 3a-c) trimers has been developed. The first example of a bis-1,2,3-triazolo-bridged unsymmetrical PBD trimer has been successfully synthesized by employing a CuAAC type ‘click’ chemistry protocol. This efficient route generates tri-imine functionality in a single molecule. It has been envisaged that such tri-imine functionalities could bring in efficient interaction with DNA in a sequence-selective manner in the minor groove of duplex DNA. One of the representative analogues 3c has shown improved DNA-binding ability (ΔT_m 23.7 °C) by thermal denaturation studies using CT-DNA and this data is also supported by molecular modeling (MD) studies.     

Efficient post-polymerization functionalization of conducting poly(3,4-ethylenedioxythiophene) (PEDOT) via ‘click’-reaction

The possibility to functionalize polymers after a successful polymerization process is often an important challenge in macromolecular science. Herein, modified electrodes based on azide-containing potentiodynamically electropolymerized PEDOT derivatives are reported. This reactive coatings are subsequently modified under mild heterogeneous conditions by copper-catalyzed Huisgen 1,3-dipolar cycloaddition with terminal alkynes, the so-called ‘click’-reaction. A series of terminal alkynes have been successfully used for the facile immobilization of neutral, electron-accepting and electron-donating units to the conducting PEDOT with high conversion efficiencies showing the broad scope of the strategy. The route is devoid of the limitations generated by the various steric and electronic impacts of the substituents when attached to the monomer before polymerization.     

Sulfonium alkylation followed by ‘click’ chemistry for facile surface modification of proteins and tobacco mosaic virus

Alkylsulfonium salts (ASS) have been shown to act as powerful alkylating agents. However, few studies have addressed the application of sulfonium salts to the modification of biomolecules such as nucleic acids and proteins. Since these large biomolecules play important roles in biological processes, a convenient and fast method for their modification is greatly needed. In this work, for the first time, we used a tandem method of sulfonium alkylation and click chemistry (CuAAC) for modification of biomolecules. Fluorescent labeling of proteins and tobacco mosaic virus were successfully performed after simple incubation of biomolecules with sulfonium salts followed by azido-containing compound at room temperature. This facile bioconjugation assay based on ASS-CuAAC reactions should be useful in protein chemistry and bionanoscience.     

Expedient synthesis of 1,2,3-triazole-fused tetracyclic compounds by intramolecular Huisgen (‘click’) reactions on carbohydrate-derived azido-alkynes

An efficient, practical and convenient synthesis of 1,2,3-triazole-fused tetracyclic compounds was achieved by intramolecular 1,3-dipolar cycloaddition of carbohydrate-derived azido-alkynes.     

Synthesis of (±)-1,2,3-triazolo-3′-deoxy-4′-hydroxymethyl carbanucleosides via ‘click’ cycloaddition

The synthesis of 1,2,3-triazolo-3′-deoxy-4′-hydroxymethyl carbanucleosides with different reaction conditions and diverse modulations on the heterocycle residues was developed. Heterocycle moieties were efficiently introduced on the pseudo-sugar either via nucleophilic substitution or via 1,3-dipolar Huisgen cycloaddition. With this latter approach, 1,4-disubstituted and 1,4,5-trisubstituted-(±)-[1,2,3]-triazolo-3′-deoxy-4′-hydroxymethyl carbanucleosides were prepared from the corresponding azido-carbocycle and various terminal or internal alkynes. Antiviral activities and cellular toxicities of the final compounds were evaluated as smallpox inhibitors. Unfortunately, at concentrations up to 100 mM, none of them inhibited production of vaccinia virus (Lister strain) or cowpox virus (Brighton strain) in vero cells.     

Synthesis of azide-alkyne fragments for ‘click’ chemical applications; formation of oligomers from orthogonally protected trialkylsilyl-propargyl azides and propargyl alcohols

A series of orthogonally protected 1,4-disubstituted-1,2,3-triazoles were prepared from the corresponding alkynols and trialkylsilyl-propargyl azides via 1,3-dipolar cycloaddition. These cycloadducts were selectively deprotected and extended in a stepwise fashion via further ‘click’ reactions to form oligomeric peptidomimetic compounds. This methodology gives access to triazole-based peptidomimetics in a controlled fashion and lays the foundation for a fragment-based approach to drug discovery.     

BODIPY based ‘click on’ fluorogenic dyes: application in live cell imaging

The design, synthesis, and photophysical properties of new BODIPY-based fluorogenic ‘click on’ dyes are reported. CuAAC reaction of non-fluorescent BODIPY azide with a series of non-fluorescent alkyne molecules resulted in fluorescent triazoles which displayed up to 532-fold enhancement of fluorescence in the red region. Imaging studies confirmed the general trend of cell permeability and a cholesterol linked derivative exhibited selective localization into intracellular membranes.     

Synthesis and ‘double click’ density functionalization of 8-aza-7-deazaguanine DNA bearing branched side chains with terminal triple bonds

The 7-[di(prop-2-ynl)amino]prop-1-ynyl derivative of 8-aza-7-deaza-2′-deoxyguanosine (1) was synthesized from 7-iodo-8-aza-7-deaza-2′-deoxyguanosine (7) by Sonogashira cross-coupling and converted into the phosphoramidite building block 10. Oligonucleotides bearing branched side chains with terminal triple bonds were prepared by solid-phase synthesis containing single or multiple residues of 1 as 2′-deoxyguanosine surrogates. T_m measurements demonstrate that compound 1 has a positive effect on duplex stability, which is comparable to the stabilizing effect of the octa-1,7-diynylated non-branched nucleoside 2. Nucleoside 1 and corresponding oligonucleotides were functionalized by the Cu(I)-mediated 1,3-dipolar cycloaddition ‘double click’ reaction with diverse ligands (AZT 3, benzyl azide 4, 11-azidoundecanol 5 and m-dPEG™₄-azide 6). The conjugation reactions were carried out in solution and on solid support. Nucleoside 1 allowed ‘double’ functionalization of a single residue with two reporter groups. The ‘double click’ reaction proceeded smoothly even when two residues of nucleoside 1 were arranged in proximal positions. Hybridization with complementary strands led to a stable oligonucleotide duplex. Molecular modeling indicates that inspite of the crowded steric situation with four AZT ligands within closest proximal positions, all ligands are well accommodated in the major groove not disturbing the DNA helix.