Efficient synthesis of water-soluble calixarenes using click chemistry

[reaction: see text] Several water-soluble calix[4]arenes were synthesized via Huisgen 1,3-dipolar cycloaddition between azides and alkynes. Cationic, anionic, and nonionic calixarenes were prepared from a common azidocalixarene intermediate. Azidocalixarenes performed better than alkynylcalixarenes as precursors. The aggregation behavior of the water-soluble calixarenes was studied by (1)H NMR spectroscopy.     

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.     

Efficient microwave-assisted synthesis of multivalent dendrimeric peptides using cycloaddition reaction (click) chemistry

Multivalent dendrimeric peptides were synthesized via a microwave-assisted Huisgen 1,3-dipolar cycloaddition between azido peptides and dendrimeric alkynes in yields ranging from 46 to 96%.     

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).     

Modular synthesis of photocleavable peptides using click chemistry

A modular synthesis of photocleavable peptides was developed. Peptide based kinase substrates were modified on solid support with a traceless linker derived from 1-(2-nitrophenyl)propargyl alcohol and coupled to azide functionalized cell-penetrating peptides using Cu(I) catalyzed click chemistry.     

Efficient synthesis of multifunctional polymers via thiol-epoxy "click" chemistry

We demonstrate high efficiency and simplicity of the thiol-epoxy reaction towards preparation of a wide range of main-chain as well as end-chain multifunctional polymers.     

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.     

Thiophene donor-acceptor [2]rotaxanes

A series of the thiophene donor-acceptor [2]rotaxanes have been synthesized based on the inclusion complexes of cyclobis(paraquat- p-phenylene) (CBPQT4+) with thiophene, bithiophene, and terthiophene. The maximum wavelength of the charge-transfer band strongly depends on the number of thiophene units, while the association constant does not. These donor-acceptor pairs will be fascinating constituents for optoelectronic and electromechanical materials.     

One-pot synthesis of donor-acceptor [2]rotaxanes based on cryptand-paraquat recognition motif

Two novel cryptand-based [2]rotaxanes were synthesized by a facile one-pot reaction from three neutral precursors: easily accessible cryptand host 1 and commercially available 4,4'-bipyridine and 3,5-di-tert-butylbenzyl bromide. Their structures were confirmed by (1)H NMR, 2D NMR, HRMS and X-ray analysis. Moreover, two [2]pseudorotaxanes based on the same cryptand hosts and dibenzyl viologen guest 3 were also demonstrated both in solution and in the solid state, which are different from previously reported [3]pseudorotaxane-like complexes formed by dimethyl viologen guest 2 and the cryptands.     

Controllable donor-acceptor neutral [2]rotaxanes

In pursuit of a neutral bistable [2]rotaxane made up of two tetraarylmethane stoppers--both carrying one isopropyl and two tert-butyl groups located at the para positions on each of three of the four aryl rings--known to permit the slippage of the pi-electron-donating 1,5-dinaphtho[38]crown-10 (1/5DNP38C10) at the thermodynamic instigation of pi-electron-accepting recognition sites, in this case, pyromellitic diimide (PmI) and 1,4,5,8-naphthalenetetracarboxylate diimide (NpI) units separated from each other along the rod section of the rotaxane's dumbbell component, and from the para positions of the fourth aryl group of the two stoppers by pentamethylene chains, a modular approach was employed in the synthesis of the dumbbell-shaped compound NpPmD, as well as of its two degenerate counterparts, one (PmPmD) which contains two PmI units and the other (NpNpD) which contains two NpI units. The bistable [2]rotaxane NpPmR, as well as its two degenerate analogues PmPmR and NpNpR, were obtained from the corresponding dumbbell-shaped compounds NpPmD, PmPmD, and NpNpD and 1/5DNP38C10 by slippage. Dynamic 1H NMR spectroscopy in CD2Cl2 revealed that shuttling of the 1/5DNP38C10 ring occurs in NpNpR and PmPmR, with activation barriers of 277 K of 14.0 and 10.9 kcal mol(-1), respectively, reflecting a much more pronounced donor-acceptor stabilizing interaction involving the NpI units over the PmI ones. The photophysical and electrochemical properties of the three neutral [2]rotaxanes and their dumbbell-shaped precursors have also been investigated in CH2Cl2. Interactions between 1/5DNP38C10 and PmI and NpI units located within the rod section of the dumbbell components of the [2]rotaxane give rise to the appearance of charge-transfer bands, the energies of which correlate with the electron-accepting properties of the two diimide moieties. Comparison between the positions of the visible absorption bands in the three [2]rotaxanes shows that, in NpPmR, the major translational isomer is the one in which 1/5DNP38C10 encircles the NpI unit. Correlations of the reduction potentials for all the compounds studied confirm that, in this non-degenerate [2]rotaxane, one of the translational isomers predominates. Furthermore, after deactivation of the NpI unit by one-electron reduction, the 1/5DNP38C10 macrocycle moves to the PmI unit. Li+ ions have been found to strengthen the interaction between the electron-donating crown ether and the electron-accepting diimide units, particularly the PmI one. Titration experiments show that two Li+ ions are involved in the strengthening of the donor-acceptor interaction. Addition of Li+ ions to NpPmR induces the 1/5DNP38C10 macrocycle to move from the NpI to the PmI unit. The Li+-ion-promoted switching of NpPmR in a 4:1 mixture of CD2Cl2 and CD3COCD3 has also been shown by 1H NMR spectroscopy to involve the mechanical movement of the 1/5DNP38C10 macrocycle from the NpI to the PmI unit, a process that can be reversed by adding an excess of [12]crown-4 to sequester the Li+ ions.     

Convergent synthesis of PAMAM dendrimers using click chemistry of azide-functionalized PAMAM dendrons

Azide-functionalized PAMAM dendrons containing an azidopropylamine focal point were synthesized by the divergent method and applied for the construction of symmetric PAMAM-like dendrimers containing 1,2,3-triazole rings as connectors via stitching with two different multi-terminal alkynes. The stitching method was based on the click chemistry protocol, i.e., the copper-catalyzed cycloaddition reaction between an alkyne and an azide.     

Segmented block copolyesters using click chemistry

Copper(I) catalyzed azide‐alkyne 1,3‐Huisgen cycloaddition reaction afforded the synthesis of triazole‐containing polyesters and segmented block copolyesters at moderate temperatures. Triazole‐containing homopolyesters exhibited significantly increased (～40 °C) glass transition temperatures (T_g) relative to high temperature, melt synthesis of polyesters with analogous structures. Quantitative synthesis of azido‐terminated poly(propylene glycol) (PPG) allowed for the preparation of segmented polyesters, which exhibited increased solubility and mechanical ductility relative to triazole‐containing homopolyesters. Differential scanning calorimetry demonstrated a soft segment (SS) T_g near ?60 °C for the segmented polyesters, consistent with microphase separation. Tensile testing revealed Young's moduli ranging from 7 to 133 MPa as a function of hard segment (HS) content, and stress at break values approached 10 MPa for 50 wt % HS segmented click polyesters. Dynamic mechanical analysis demonstrated an increased rubbery plateau modulus with increased HS content, and the T_g's of both the SS and HS did not vary with composition, confirming microphase separation. Atomic force microscopy also indicated microphase separated and semicrystalline morphologies for the segmented click polyesters. This is the first report detailing the preparation of segmented copolyesters using click chemistry for the formation of ductile membranes with excellent thermomechanical response. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A facile and regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles using click chemistry

The reaction of α-tosyloxy ketones, sodium azide, and terminal alkynes in presence of copper(I) in aqueous polyethylene glycol afforded regioselectively 1,4-disubstituted 1,2,3-triazoles in good yield at ambient temperature. The one-pot exclusive formation of 1,4-disubstituted 1,2,3-triazoles involves in situ formation of α-azido ketones, followed by cycloaddition reaction with terminal alkyne. The generality of this one-pot method was demonstrated by synthesizing an array of diverse 1,4-disubstituted 1,2,3-triazoles.     

PEGylation of porous silicon using click chemistry

Porous silicon has received considerable interest in recent years in a range of biomedical applications, with its performance determined by surface chemistry. In this work, we investigate the PEGylation of porous silicon wafers using click chemistry. The porous silicon wafer surface chemistry was monitored at each stage of the reaction via photoacoustic Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, whereas sessile drop contact angle and model protein adsorption measurements were used to characterize the final PEGylated surface. This work highlights the simplicity of click-chemistry-based functionalization in tailoring the porous silicon surface chemistry and controlling protein-porous silicon interactions.     

Solid-state structures and superstructures of two charged donor-acceptor rotaxanes

Two [2]rotaxanes and a [2]pseudorotaxane containing 1,5-dioxynaphthalene recognition sites located in the middle of their dumbbell and thread components, respectively, and encircled by single cyclobis(paraquat-p-phenylene) rings have been synthesized under template control and their solid-state (super)structures have been solved. The investigations revealed that the stoppers on the dumbbell components, the solvents, and the counterions can affect the conformations adopted by the [2]rotaxanes and [2]pseudorotaxane in the solid state.     

Synthesis of well-defined hydrogel networks using click chemistry

New PEG-based hydrogel materials have been synthesized by Click chemistry and shown to result in well-defined networks having significantly improved mechanical properties; the selectivity of the azide/acetylene coupling reaction also allows for the incorporation of various additives and functional groups leading to chemical tailoring of the hydrogels.     

Generation of profluorescent isoindoline nitroxides using click chemistry

Novel profluorescent nitroxides bearing a triazole linker between the coumarin fluorophore and an isoindoline nitroxide were prepared in good yields using the copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition reaction (CuAAC). Nitroxides containing 7-hydroxy and 7-diethylamino substitution on their coumarin rings displayed significant fluorescence suppression, and upon reaction with methyl radicals, normal fluorescence emission was returned. The fluorescence emission for the 7-hydroxycoumarin nitroxide and its diamagnetic analogue was found to be strongly influenced by pH with maximal fluorescence emission achieved in basic solution. Solvent polarity was also shown to affect fluorescence emission. The significant difference in fluorescence output between the nitroxides and their corresponding diamagnetic analogues makes these compounds ideal tools for monitoring processes involving free-radical species.     

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.     

Theory and experiment in concert: templated synthesis of amide rotaxanes, catenanes, and knots

The synthesis of amide rotaxanes, amide catenanes, and trefoil amide knots is based on template effects mediated by hydrogen bonds. While a large body of experimental data is available, in-depth theoretical studies of these template syntheses are virtually unavailable, although they would provide a more profound insight into the exact details of the hydrogen-bonding patterns involved in the formation of these mechanically interlocked species. In this article we present a density functional study of the conformational properties of tetralactam macrocycles and the threading mechanism that produces the immediate precursor for rotaxane and catenane formation. Predictions of the geometries and relative energies made on the basis of semi-empirical AM1 calculations are compared with these results in order to judge the reliability of the simpler approach. Since these calculations yield good agreement with the structural features, they have been used to extend the calculations in order to understand the mechanism of formation of a trefoil dodecaamide knot that has recently been synthesized. The inherent topological chirality of the knot is reflected in the intermediates generated during its formation; these involve helical loops. These loops parallel the rotaxane and catenane wheels with respect to the arrangement of the functional groups that mediate the template effect and may well serve as wheel analogues through which one of the precursor molecules can be threaded. This threading step finally results in the knotted structure. Good agreement between the results of the calculations presented here and experimental findings is achieved.     

“点击”反应在制备环状聚合物中的应用

环状聚合物具有不同于线性高分子的独特性质,是一类具有应用前景的新型聚合物材料,但复杂的结构导致其合成过程复杂繁琐.＂点击＂化学由于其高效、可靠、高选择性的特点已成为拓扑高分子合成的新方法,活性自由基聚合（ATRP、RAFT和NMP）具有聚合物结构可控等特点,二者联用为环状聚合物的合成拓宽了思路.本文就近几年＂点击＂反应、＂点击＂反应与活性自由基聚合联用以及其他方法联用在环状聚合物中的应用进行综述.＂点击＂反应与这些方法的结合将在功能性环状聚合物的设计与合成中发挥积极的作用.