Cu(I)-catalyzed Azide-alkyne Cycloaddition Research Articles

Microwave-assisted synthesis of new pyrazole derivatives bearing 1,2,3-triazole scaffold as potential antimicrobial agents

A new series of (E)-3-(3-(4-substituted phenyl)-1-phenyl-1H-pyrazol- 4-yl)-1-(2-hydroxy-4-((1-aryl-1H-1-2,3-triazol-4-yl)methoxy)phenyl)- prop-2-en-1-one derivatives was synthesized. The synthesis of the title compounds involved the 1,3-dipolar Cu(I)-catalyzed alkyne?azide cycloaddition (CuAAC) reaction of (E)-3-(3-(4-substituted phenyl)-1-phenyl-1H-pyrazol-4- -yl)-1-(2-hydroxy-4-(prop-2-yn-1-yloxy)phenyl)prop-2-en-1-ones with aromatic azides. The structures were confirmed by NMR, FT-IR, mass and elemental analysis. All the synthesized compounds (6a?j) were evaluated for their antimicrobial activity. Compounds 6a, 6d and 6e demonstrated promising inhibitory effects on both bacterial and fungal strains.

Fluorescent labeling of Taqman oligonucleotide probes via Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click chemistry

We describe an approach to the synthesis of TaqMan oligonucleotide probes that is based on Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click chemistry when oligonucleotides containing an internal alkynyl group at the pyrimidine position are labeled post-synthetically with a f luorescent azide. TaqMan probes were constructed with f luorescein in different internal positions and a BHQ1 quencher on the 3′-end. Our previously designed alkynylated deoxyuridine or deoxycytidine phosphoramidites have been employed for the synthesis of alkynyl oligonucleotides. It was demonstrated that the synthesized TaqMan probes can detect accumulation of PCR product in real-time. The closer to the label the 3′-terminal quencher, the higher the quenching efficiency, but the efficiency of probe hybridization to DNA template is reduced in this case.

Reversible photoreduction of Cu(ii)-coumarin metal-organic polyhedra.

We report a new approach for photoinduced reduction of Cu2+ that will enrich the structural diversity of coordination complexes and be a valuable contributor to the development of Cu+/Cu0-based catalysts. To realize controlled Cu2+ reduction, coumarin as a triplet quencher of excited benzophenone was tethered to Cu(ii)-metal-organic polyhedra (MOPs). The photoinduced catalytic activity of the coumarin-MOPs was also examined in a Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC).

Syntheses of metallo-pseudorotaxanes, rotaxane and post-synthetically functionalized rotaxane: a comprehensive spectroscopic study and dynamic properties.

Herein, a bis-amido tris-amine macrocycle and five bipyridine-based bidentate chelating ligands were investigated towards various divalent transition metal ion (NiII, CoII, CuII, and ZnII)-templated syntheses of metallo [2]pseudorotaxanes. The formation of these ternary complexes was elucidated via different spectroscopic techniques such as ESI-MS, absorption spectroscopy, EPR spectroscopy, and single-crystal X-ray diffraction studies wherever possible. Azide-terminated NiII, CoII, CuII, ZnII-templated [2]pseudorotaxanes were explored to generate [2]rotaxane, ROT, via reaction with an alkyne-terminated triphenylene unit as a stopper under the mild reaction condition of the CuI-catalyzed azide-alkyne cycloaddition reaction. NiII-templated [2]pseudorotaxane was found to be the best precursor towards the high-yield synthesis of ROT. The interpenetrative nature of the center piece in metal-free rotaxane was also established through various spectroscopic techniques such as ESI-MS and 1D and 2D (COSY, NOESY, ROESY, and DOSY) NMR spectroscopy. Furthermore, ROT was functionalized via tri-acetylation as AcROT to incorporate three tertiary amides at the tris-amine centers; this AcROT exhibited rotamer-induced molecular motions in an interpenetrated system via the formation of multiple conformers/co-conformers. Additionally, the existence of multiple rotamers was established via variable-temperature NMR spectroscopic studies. Li+ and 12-crown-4 were found to be suitable for the reversible conformation/co-conformation fixation of tri-acetylated bis-amido tris-amine macrocyclic wheel-based rotaxane.

Macrocyclic Peptidomimetics Prepared by Ring-Closing Metathesis and Azide–Alkyne Cycloaddition

Macrocycles are finding increasing use as a means to define the backbone geometries of peptides and peptidomimetics. Ring-closing metathesis and CuI-catalyzed azide–alkyne cycloaddition are particularly useful for introducing such rings and they do so in high yield and with a good functional group tolerance and compatibility. Here, we present an overview of the use of these two methods, with reference to selected examples and particular reference to β-strand peptidomimetics for use as protease inhibitors.

Modifying graphene oxide with short peptide via click chemistry for biomedical applications

In this article, the synthesis, cytocompatibility and antibacterial properties of short peptide modified graphene oxide (GO) were presented. The materials were prepared via Cu (I)-catalyzed azide-alkyne cycloaddition (CUAAC) click reaction. Click reaction is an efficient synthesis method without damaging the bioactivity of grafted short peptide. Two different peptides (RGD (arginine-glycine-aspartic acid) and AMP (antimicrobial peptide)) were used to modify GO in this work. Compared with pristine GO, the RGD modified GO was endowed with better biocompatibility, while the AMP modified GO performed excellent sterilization property. This report of short peptide modified GO materials may provide an innovative strategy for the biomedical applications of GO.

Synthesis of Fluorinated Triazole and Isoxazole Derivatives By Electrochemical Fluorination

Partially fluorinated triazole derivatives were synthesized through anodic fluorination of alkynes having arylthio group and following Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) with benzyl azide. The other route toward the fluorinated triazoles, namely the anodic fluorination of triazole derivatives once prepared by advanced CuAAC of the alkyne and azide above was also investigated. Furthermore, Cu(I)-catalyzed isoxazole synthesis of fluorinated alkynes and imidoyl chloride was also successfully demonstrated. Figure 1

Microwave-assisted synthesis, anti-inflammatory and anti-proliferative activities of new maslinic acid derivatives bearing 1,5- and 1,4-disubstituted triazoles

In this work, 40 analogs with a natural maslinic acid core (from Olea europaea L.) and various aromatic azides were synthesized. A regiospecific, facile and practical synthesis of 1,5-triazolyl derivatives by Ru(II)-catalyzed azide-alkyne cycloaddition (RuAAC), and mono-, bis- and tri-1,4-triazolyl derivatives by Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) was described. All the reactions were assisted by microwave irradiation avoiding toxic reagents and solvents. The new products were obtained from the reaction mixture by simple purification in almost quantitative yields and the reaction times were in general shorter than those reported in the literature. Their chemical structures were elucidated on the basis of extensive spectroscopic methods including ESI-HRMS, 1D and 2D-NMR. Most of the compounds were evaluated for their anti-inflammatory activity using LPS-stimulated human peripheral blood mononuclear cells (PBMCs) and antiproliferative effects towards cultured murine EMT-6 (Breast) and human SW480 (colon) cancer cell lines.

Synthesis of fluorinated triazole and isoxazole derivatives by electrochemical fluorination

Partially fluorinated triazole derivatives were synthesized through anodic fluorination of alkynes having arylthio group and following Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) with benzyl azide. The other route toward the fluorinated triazoles, namely the anodic fluorination of triazole derivatives once prepared by advanced CuAAC of the alkyne and azide above was also investigated. It was shown that these two routes are mutually complementary methodology for the synthesis of new mono- and difluoromethyltriazole derivatives. Furthermore, Cu(I)-catalyzed isoxazole synthesis from fluorinated alkynes and imidoyl chloride was demonstrated.

Synthesis and reaction of block copolymer composed of independently clickable segments via monomer-selective living copolymerization

Living anionic copolymerizations of silyl-protected propargyl acrylate (TMS-PA) and 6-chlorohexyl methacrylate (CHMA) were conducted in the presence of ethylaluminum bis(2,6-di-tert-butylphenoxide) [EtAl(ODBP)2], a bulky aluminum Lewis acid, in toluene at ź60 °C. The polymerization proceeded in a monomer-selective manner, where the acrylate, TMS-PA, was selectively activated by EtAl(ODBP)2 and polymerized preferentially over to the methacrylate, CHMA, and the polymerization of CHMA followed after the complete consumption of TMS-PA to afford a block copolymer with narrow molecular weight distribution. The blocky sequence was confirmed with 1H NMR spectrum, while the peak shift of size exclusion chromatograms (SECs) from low to high molecular weights as well as the progressive monomer consumptions also supported the monomer-selective living copolymerization. The obtained block copolymer could be functionalized with respect to each segment independently via a repeated Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry; the alkynyl (propargyl) group was deprotected with tetrabutylammonium fluoride (TBAF) in acetic acid, and the subsequent CuAAC reaction with benzyl azide allowed quantitative and selective modification of the polyacrylate block. Subsequently, the 6-chlorohexyl group was azidated with sodium azide, and the CuAAC reaction with phenylacetylene resulted in complete modification on the polymethacrylate segment. Since CuAAC reaction is selective, quantitative and tolerant to various functional groups, this procedure, that is a combination of monomer-selective copolymerization of reactive monomers with a click chemistry, can provide a facile pathway for the preparation of a block copolymer with a variety of combination of functional pendants groups.

Synthesis and in Vitro Antiproliferative Evaluation of C-13 Epimers of Triazolyl-d-Secoestrone Alcohols: The First Potent 13α-d-Secoestrone Derivative.

The syntheses of C-13 epimeric 3-[(1-benzyl-1,2,3-triazol-4-yl)methoxy]-d-secoestrones are reported. Triazoles were prepared from 3-(prop-2-inyloxy)-d-secoalcohols and p-substituted benzyl azides via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The antiproliferative activities of the products and their precursors were determined in vitro against a panel of human adherent cervical (HeLa, SiHa and C33A), breast (MCF-7, MDA-MB-231, MDA-MB-361 and T47D) and ovarian (A2780) cell lines by means of MTT assays. The orientation of the angular methyl group and the substitution pattern of the benzyl group of the azide greatly influenced the cell growth-inhibitory potential of the compounds. The 13β derivatives generally proved to be more potent than their 13α counterparts. Introduction of a benzyltriazolylmethyl group onto the 3-OH position seemed to be advantageous. One 13α compound containing an unsubstituted benzyltriazolyl function displayed outstanding antiproliferative activities against three cell lines.

Efficient One-Pot Synthesis of Alkyl 3-[4-(Aryl or Heteroaryl)-1H-1,2,3-triazol-1-yl]thieno[3,2-b]pyridine-2-carboxylates by ‘Click’ Cu(I)-Catalyzed Azide–Alkyne Cycloaddition

An efficient one-pot synthesis of several new alkyl 3-[4-(aryl or heteroaryl)-1 H -1,2,3-triazol-1-yl]thieno[3,2- b ]pyridine-2-carboxylates has been performed by in situ azidation of alkyl 3-aminothieno[3,2- b ]pyridine-2-carboxylates followed by Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). Both reactions were carried out at room temperature, the first using tert -butyl nitrite and TMSN 3 in MeCN for 2 hours and the latter using several (hetero)arylalkynes, CuI, and Et 3 N in MeCN for very short reaction times (15–30 min). The active Cu(I) species was used directly, instead of the commonly employed Cu(II) species (CuSO 4 ) with a reducing agent (sodium ascorbate) to generate Cu(I) in situ, which did not work in our case. This one-pot process showed wide scope and the products, which may have biological activity, were obtained in good to high yields with no need for chromatographic purification, thus fulfilling the criteria of ‘click’ chemistry. To our knowledge it is the first time that this methodology, using these conditions, has been applied to a heterocyclic moiety.

The synthesis and photoactive properties of cyclic amphiphilic polymers with azobenzene in main chain

ABSTRACTThe cyclic amphiphilic polymers with azobenzene in main chain, cyclic azobenzene tetraethylene glycol polystyrene (cyclic‐Azo‐TEG‐PS) with different molecular weights, were successfully synthesized by combining atom transfer radical polymerization (ATRP) and Cu (I)‐catalyzed azide/alkyne cycloaddition (CuAAC). Gel permeation chromatography (GPC), proton nuclear resonance (1H NMR), Fourier transform‐infrared (FT‐IR), and matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectrometry were used to prove the complete conversion from linear polymers to cyclic ones. The thermal properties and photoisomerization behaviors of obtained cyclic polymers have been investigated by comparison with the linear analogues. The cyclic polymer displayed a higher glass transition temperature compared with the linear one, measured by differential scanning calorimetry (DSC). It was found that the trans‐to‐cis and cis‐to‐trans isomerization of cyclic polymers was both slower than that of their respective linear counterparts upon irradiation by UV/visible light. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1834–1841

Nanohybrid polymer brushes on silica for bioseparation.

Boronic acid based affinity materials are of great importance for effective enrichment of biomolecules containing a cis-diol structure, for example glycoproteins. In this work, we developed a new pH- and temperature-responsive boronate affinity material for effective separation of glycoproteins. A nanohybrid material composed of silica cores and flexible polymer brushes, denoted as Si@poly(NIPAm-co-GMA)@APBA, was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP) in combination with Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The size, morphology and composition of the obtained nanohybrid were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis and thermogravimetric analysis (TGA). The density of polymer brushes on the surface of silica nanoparticles was determined to be 0.7 molecules per nm2. The maximum binding capacities of the nanohybrid Si@poly(NIPAm-co-GMA)@APBA for ovalbumin (OVA) and horseradish peroxidase (HRP) were determined to be 87.6 mg g-1 and 22.8 mg g-1, respectively. Glycoprotein binding on the nanohybrid could be controlled by varying the pH of the binding buffer. By increasing the temperature from 20 °C to 35 °C, glycoprotein binding onto the nanohybrid was decreased. This new pH- and temperature-responsive nanohybrid will be useful for a number of biotechnological and biomedical applications, for example, for protein separation and drug delivery.

Azide vs Alkyne Functionalization in Pt(II) Complexes for Post-treatment Click Modification: Solid-State Structure, Fluorescent Labeling, and Cellular Fate.

Tracking of Pt(II) complexes is of crucial importance toward understanding Pt interactions with cellular biomolecules. Post-treatment fluorescent labeling of functionalized Pt(II)-based agents using the bioorthogonal Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has recently been reported as a promising approach. Here we describe an azide-functionalized Pt(II) complex, cis-[Pt(2-azidobutyl)amido-1,3-propanediamine)Cl2] (1), containing the cis geometry and difunctional reactivity of cisplatin, and present a comparative study with its previously described alkyne-functionalized congener. Single-crystal X-ray diffraction reveals a dramatic change in the solid-state arrangement with exchange of the alkyne for an azide moiety wherein 1 is dominated by a pseudo-chain of Pt-Pt dimers and antiparallel alignment of the azide substituents, in comparison with a circular arrangement supported by CH/π(C≡C) interactions in the alkyne version. In vitro studies indicate similar DNA binding and click reactivity of both congeners observed by fluorescent labeling. Interestingly, complex 1 shows in vitro enhanced click reactivity in comparison to a previously reported azide-appended Pt(II) complex. Despite their similar behavior in vitro, preliminary in cellulo HeLa studies indicate a superior imaging potential of azide-functionalized 1. Post-treatment fluorescent labeling of 1 observed by confocal fluorescence microscopy shows nuclear and intense nucleolar localization. These results demonstrate the potential of 1 in different cell line localization studies and for future isolation and purification of Pt-bound targets.

Well-controlled ATRP of 2-(2-(2-Azidoethyoxy)ethoxy)ethyl Methacrylate for High-density Click Functionalization of Polymers and Metallic Substrates.

The combination of atom transfer radical polymerization (ATRP) and click chemistry has created unprecedented opportunities for controlled syntheses of functional polymers. ATRP of azido-bearing methacrylate monomers (e.g. 2-(2-(2-azidoethyoxy)ethoxy)ethyl methacrylate, AzTEGMA), however, proceeded with poor control at commonly adopted temperature of 50 °C, resulting in significant side reactions. By lowering reaction temperature and monomer concentrations, well-defined pAzTEGMA with significantly reduced polydispersity were prepared within a reasonable timeframe. Upon subsequent functionalization of the side chains of pAzTEGMA via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry, functional polymers with number-average molecular weights (Mn) up to 22 kDa with narrow polydispersity (PDI < 1.30) were obtained. Applying the optimized polymerization condition, we also grafted pAzTEGMA brushes from Ti6Al4 substrates by surface-initiated ATRP (SI-ATRP), and effectively functionalized the azide-terminated side chains with hydrophobic and hydrophilic alkynes by CuAAC. The well-controlled ATRP of azido-bearing methacrylates and subsequent facile high-density functionalization of the side chains of the polymethacrylates via CuAAC offers a useful tool for engineering functional polymers or surfaces for diverse applications.

Modification of alkyne-functionalized asymmetric phthalocyanines by CuI-catalyzed azide-alkyne cycloaddition

The use of asymmetric phthalocyanines (Pcs) as platforms for the preparation of several asymmetric hexatriazolyl-monohydroxyphthalocyanines via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was investigated. Asymmetric Pcs 5a and 5b were prepared through statistical macrocyclization of phthalonitriles (Pns) 1a and 2 to give PMB-protected 4a and 4b, which afforded asymmetric Pcs 5a and 5b after acidic cleavage. The ‘ROMP-Capture-Release’ method as a synthetic approach to prepare asymmetric Pc 5b was also evaluated. TIPS-protection of the terminal alkynes was necessary to prevent cross-coupling during the ring-opening metathesis polymerization (ROMP) step. Zinc Pc 5b was successfully used as a scaffold for functional modification under CuAAC conditions using several azides bearing hydrophobic, photo-crosslinkable, or electroactive moieties. Monitoring the CuAAC reaction by both UV/Vis and FTIR spectroscopies provided insight into the role of azide equivalent, reaction time, and catalyst on reaction progress.

Click chemistry for targeted protein ubiquitylation and ubiquitin chain formation

Herein we describe a simple protocol for the efficient generation of site-specific ubiquitin-protein conjugates using click chemistry. By using two different methods to expand the genetic code, the two bio-orthogonal functionalities that are necessary for Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC), an alkyne and an azide, are co-translationally incorporated into the proteins of interest with unnatural amino acids. Protein ubiquitylation is subsequently carried out with the purified proteins in vitro by CuAAC. In addition, we provide a protocol for the incorporation of two unnatural amino acids into a single ubiquitin, resulting in a 'bifunctional' protein that contains both an alkyne and an azide functionality, thereby enabling assembly of free ubiquitin chains as well as ubiquitin chains conjugated to a target protein. Our procedure enables the synthesis of nonhydrolyzable ubiquitin-protein conjugates within 1 week (given that the relevant cDNAs are at hand), and it yields conjugates in milligram quantities from 1-liter expression cultures. The approach described herein is faster and less laborious than other methods, and it requires only standard molecular biology equipment. Moreover, the protocol can be readily adapted to achieve conjugation at any site of any target protein, which facilitates the generation of custom-tailored ubiquitin-protein conjugates.

1,2,3-Triazole Stabilized Neurotensin-Based Radiopeptidomimetics for Improved Tumor Targeting.

Neurotensin (NT) is a regulatory peptide with nanomolar affinity toward NT receptors, which are overexpressed by different clinically relevant tumors. Its binding sequence, NT(8-13), represents a promising vector for the development of peptidic radiotracers for tumor imaging and therapy. The main drawback of the peptide is its short biological half-life due to rapid proteolysis in vivo. Herein, we present an innovative strategy for the stabilization of peptides using nonhydrolizable 1,4-disubstituted, 1,2,3-triazoles as amide bond surrogates. A "triazole scan" of the peptide sequence yielded novel NT(8-13) analogues with enhanced stability, retained receptor affinity, and improved tumor targeting properties in vivo. The synthesis of libraries of triazole-based peptidomimetics was achieved efficiently on solid support by a combination of Fmoc-peptide chemistry, diazo transfer reactions, and the Cu(I)-catalyzed alkyne azide cycloaddition (CuAAC) employing methods that are fully compatible with standard solid phase peptide synthesis (SPPS) chemistry. Thus, the amide-to-triazole substitution strategy may represent a general methodology for the metabolic stabilization of biologically active peptides.

Postpolymerization Modification of Poly(dihydropyrimidin-2(1H)-thione)s via the Thiourea-Haloalkane Reaction to Prepare Functional Polymers.

A highly reactive thiourea-contained polycondensate, poly(dihydropyrimidin-2(1H)-thione) (poly(DHPMT)) has been facilely synthesized via the Biginelli polycondensation using thiourea and a difunctional compound containing benzaldehyde and β-keto ester groups as monomers. The thiourea moiety in the polymer structure has similar reactivity as the thiourea, thus the poly(DHPMT) is an excellent polymer precusor for preparing new functional polymers through the postpolymerization modification (PPM) strategy. After simple reaction with functional haloalkanes, the parent poly(DHPMT) could be almost completely converted (>99%) to daughter polymers containing alkene or alkyne side groups. Then, the daughter polymers have been further transferred to granddaughter polymers through another PPM via thiol-ene or Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions. Besides, when 3-phenylpropargyl chloride was used as the reactant, a bright yellow fluorescent polymer could be simply achieved due to the in situ formed conjugated heterocycle in the polymer structure, further demonstrating the diversity of the functional polymers through PPM. Considering the easily available monomers, simple polycondensation, and the excellent reactivity of the thiourea moiety in the polymer structure, this thiourea-contained Biginilli polycondensate might be a versatile platform for new functional polymer preparation.