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.     

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.     

Tunable threading/dethreading efficiency of the pseudorotaxane by ether chain length

A series of axles containing the tetraethyl ester calix[4]arene derivative unit and 1,5-dioxynaphthalene (DNP) unit, with different lengths of ether chains, have been synthesized. Complexation of the axles and the cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺) has been investigated by UV-vis and ¹H NMR spectra. The effect of the length of ether chain on the threading/dethreading processes has also been demonstrated, which indicated that the efficiency of threading/dethreading process decreases with the extension of ether chain.     

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.     

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.     

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.     

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.     

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 C8-C8/C2-C8-linked triazolo pyrrolobenzodiazepine dimers by employing ‘click’ chemistry and their DNA-binding affinity

A series of 1,2,3-triazole-containing pyrrolo[2,1-c][1,4]benzodiazepine dimers have been prepared efficiently by employing a ‘click’ chemistry protocol. This method involves 1,3-dipolar cycloaddition of terminal alkynes with organic azides using a Cu(I)-catalyst. Further, these molecules exhibited interesting DNA-binding affinity profiles.     

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.     

A simplified green chemistry approach to the Biginelli reaction using ‘Grindstone Chemistry’

Grindstone Chemistry--a greatly evolved version of Toda’s method of grinding solids together for solvent-free chemical reactions--has been described and its usefulness illustrated by the successful application of this technique to a simplified process for conducting the multi-component Biginelli reaction for the synthesis of physiologically active tetrahydropyrimidinones.     

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.     

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.     

N-(Propargyl)diazenecarboxamides for ‘click’ conjugation and their 1,3-dipolar cycloadditions with azidoalkylamines in the presence of Cu(II)

Propargyl functionalized diazenes 1 were prepared by two different approaches and were examined as alkyne click components in copper-catalyzed azide-alkyne cycloadditions (CuAAC) with 2-(azidomethyl)pyridine 5a and four α-azido-ω-aminoalkanes C2-C5 (5b-e). Whereas the reactions with azidoalkylamines 5b-e reached completion with copper(II) sulfate without the need of reducing agent typically in no more than few minutes, 2-(azidomethyl)pyridine 5a required the addition of metallic copper and much longer reaction times (2-24 h). This difference in the reactivity was studied and addressed in terms of base effect and proximity effect to CuAAC.     

Synthesis of glycidyl triazolyl polymers using click chemistry

The glycidyl azide polymers converted easily to glycidyl 1,2,3-triazolyl polymers by the click chemistry in good to high yields. These reactions are affected deeply by the electron effects. The electron donating groups made the reaction faster.     

Synthesis of new copper(I)-complexed rotaxanes via click chemistry

The Cu(I)-catalyzed dipolar cycloaddition of azides and terminal alkynes (‘click’ chemistry) has been used as a mild and efficient stoppering reaction for the preparation of new copper(I)-complexed rotaxanes.     

Efficient synthesis of a labile copper(I)-rotaxane complex using click chemistry

Copper(I)-induced threading of 5,5′-diazidomethyl-2,2′-bipyridine through a coordinating ring followed by reaction of a propargyl ether attached to a stopper group leads to the desired rotaxane in 62% yield. The reaction is carried out under the ‘click chemistry’ conditions with 0.75 equiv of additional copper(I).     

Synthesis of a fully functionalized pillar[5]arene by ‘click chemistry’ and its effective binding toward neutral alkanediamines

A fully functionalized pillar[5]arene was synthesized by ‘click chemistry’ and the possible synthetic strategies have been discussed. The host showed effective binding affinities toward neutral alkanediamines (K_a >10³ M⁻¹), which are much larger than those observed for simple methyl-substituted pillar[5]arene.     

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.     

Microwave-assisted synthesis of a triazole-linked 3′-5′ dithymidine using click chemistry

Synthesis of a triazole-linked 3′-5′ thymidine dimer making use of 1,3-dipolar cycloaddition is described. The azido-precursor was obtained by regioselective chlorination of thymidine, followed by azidation. The second precursor, a propargyl derivative, was obtained by selective 3′-O-alkylation of thymidine. Two ‘click systems’ were compared to obtain the desired dimer. These reactions were performed by microwave irradiation.