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

Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC)-Mediated Macrocyclization of Peptides: Impact on Conformation and Biological Activity.

The long-lasting impetus to design novel modes of macrocyclization, and their implementation into a wide range of bioactive peptides, originates from their contributions to the restriction of conformational space and the stabilization of preferential bioactive conformations that support higher efficacy and binding affinity to cognate macromolecular targets, improved specificity and lowering susceptibility to enzymatic degradation processes. Introducing CuI-catalyzed azide-alkyne cycloaddition (CuAAC), a prototypical click reaction, to the field of peptide sciences as a bio-orthogonal reaction that generates a disubstituted-[1,2,3]triazol-1-yl moiety as a pseudopeptidic bond that is peptidomimetic in nature, paved the way to its widespread application as a new and promising mode of macrocyclization. This review presents the state-of-art of CuAAC-mediated macrocyclization as it applies to an expansive range of bioactive peptides and explores the relationship among the structural diversity of CuAACmediated cyclizations, biological activities and conformations.

Facile Fabrication of 10-Hydroxycamptothecin-Backboned Amphiphilic Polyprodrug with Precisely Tailored Drug Loading Content for Controlled Release.

Polymeric prodrugs with precisely controlled drug loading content (DLC) and rapid intracellular destabilization generally require complicated chemistry that hinders large-scale manufacture. For this purpose, we reported in this study a facile construction of reduction-sensitive amphiphilic polyprodrugs with an anticancer drug, 10-hydroxycamptothecin (HCPT), and a hydrophilic poly(ethylene oxide) (PEG) moiety as the alternating building blocks of the multiblock copolymer using Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAc) click coupling between azide-SS-HCPT-SS-azide and alkyne-PEG-alkyne. Adoption of PEGs with two different molecular weights (MWs) of 400 and 1450 Da (PEG400 and PEG1450) afforded two polyprodrugs with different DLCs. Both formulations can self-assemble into spherical micelles with hydrodynamic diameter smaller than 200 nm, and exhibit glutathione (GSH)-triggered degradation for promoted drug release. A further comparison study revealed that the PEG1450-based polyprodrug is a better formulation than the analogue constructed from PEG400 in terms of in vitro drug release behaviors, and cytotoxicity. This work thus provides a facile yet efficient strategy toward polymeric prodrugs with precisely controlled DLC and reduction-triggered degradation for enhanced anticancer drug delivery.

ROMP synthesis of 1,2,3-triazolyl dendronized polymers with triethylene glycol branches as recyclable nanoreactors for Cu(I) “click” catalysis reaction in water

The design and construction of high-efficiency nanoreactor systems have attracted a great deal of attention for their potential applications in materials science, biomedicine and catalysis. Especially, understanding the relationship between the precise internal structure of nanoreactors and their catalytic performance is essential for catalyst design. Here we report two bulky G2 dendronized norbornene macromonomers 8 and 13 containing nine hydrophilic triethylene glycol (TEG) termini with three and nine, respectively, 1,2,3-triazole (trz) rings, and their controlled polymerizations via the ring-opening metathesis polymerization (ROMP) technique using Grubbs' third-generation olefin metathesis catalyst. The self-assemblies of the obtained dendronized polymers (DPs) 9 and 14 in water then yield novel micellar nanoreactors with different location distribution of the coordinative intradendritic trz ligands. The recyclable nanoreactors are used to support CuI ion generated by in situ reduction of CuSO4·5H2O via sodium ascorbate, and strongly activate the CuI-catalyzed azide alkyne cycloaddition (CuAAC) “click” reactions in water, leading to exceptional TONs up to 250 000 and TOFs up to 16 670 h−1. Remarkably, when the amount of CuI catalysts is less than 50 ppm, 9a-CuI exhibits considerably higher catalytic efficiency than 14a-CuI, which is attributed to the architectural difference of the two used DPs 9 and 14. This work highlights the role of the location of trz ligands in DPs nanoreactors on the catalytic efficiency of CuI catalyst, and the unique advantage of DP-type nanoreactors by less steric inhibition, compared to the congested dendrimers nanoreactors, and also rationalizes optimization in catalyst engineering.

Intramolecular Copper-Containing Hyperbranched Polytriazole Assemblies for Label-Free Cellular Bioimaging and Redox-Triggered Copper Complex Delivery.

Intramolecular Cu-containing amphiphilic hyperbranched polytriazoles are purposefully designed and synthesized via a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, and are self-assembled into spherical assemblies. Based on the metal coordination ability of triazole groups, the copper catalyst can be intramolecularly coordinated with triazole groups in the CuAAC, producing the copper-triazole coordination polyprodrugs. Unexpectedly, the amphiphilic hyperbranched polytriaozle assemblies can also be applied as fluorescent nanoprobes with aggregation-induced emission enhancement. The cellular uptake verifies their functional application for cellular bioimaging. Furthermore, the results of cell viability indicate that the mPEG-hb-S-S-PTAs assemblies are effective copper delivery systems for cancer therapy by releasing the anticancer copper-triazole coordination complexes. Therefore, the amphiphilic hyperbranched polytriazoles may have very promising applications in complex copper delivery and label-free cellular bioimaging.

Ternary mixed-mode silica sorbent of solid-phase extraction for determination of basic, neutral and acidic drugs in human serum.

In this study, a ternary mixed-mode silica sorbent (TMSS) with octamethylene, carboxyl, and amino groups was prepared via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction and a subsequent reduction of azide to primary amine. While used in solid-phase extraction (SPE), the retention behavior of TMSS towards a total of nine kinds of basic, neutral, and acidic drugs was investigated in detail. The results revealed that hydrophobic, ion-exchange interaction, and electrostatic repulsion between TMSS and the analytes were closely related to the retention behavior of TMSS. Besides, the log Kow value of the analyte was also a factor influencing the retention behavior of analytes on TMSS. The nine analytes could be retained by TMSS simultaneously and then, were eluted into two fractions according to the acid-base property of the analytes for further determinations. The acidic and neutral analytes were in one fraction, and the basic ones in the other fraction. When used to treat the human serum spiked with the nine drugs, TMSS offered higher recoveries than BakerBond CBA and comparable recoveries to Oasis WCX. It should be noted TMSS had better purifying capability for human serum than Oasis WCX. Under the optimized SPE conditions, a method of SPE hyphenated to high-performance liquid chromatography-ultraviolet detection (HPLC-UV) for determination of the basic, neutral, and acidic drugs spiked in human serum was established. For the nine drugs, the linear ranges were all between 5.0 and 1000μgL-1 with correlation coefficients (R2) above 0.9990, and the limits of detection (LODs) were in the range of 0.8-2.3μgL-1. The intra-day and inter-day relative standard deviations (RSDs) were less than 5.3 and 8.8%, respectively. Graphical abstract Treating drugs in human serum by SPE with ternary mixed-mode silica sorbent.

Insulin-like Growth Factor 1 Analogs Clicked in the C Domain: Chemical Synthesis and Biological Activities.

Human insulin-like growth factor 1 (IGF-1) is a 70 amino acid protein hormone, with key impact on growth, development, and lifespan. The physiological and clinical importance of IGF-1 prompted challenging chemical and biological trials toward the development of its analogs as molecular tools for the IGF-1 receptor (IGF1-R) studies and as new therapeutics. Here, we report a new method for the total chemical synthesis of IGF-1 analogs, which entails the solid-phase synthesis of two IGF-1 precursor chains that is followed by the CuI-catalyzed azide-alkyne cycloaddition ligation and by biomimetic formation of a native pattern of disulfides. The connection of the two IGF-1 precursor chains by the triazole-containing moieties, and variation of its neighboring sequences (Arg36 and Arg37), was tolerated in IGF-1R binding and its activation. These new synthetic IGF-1 analogs are unique examples of disulfide bonds' rich proteins with intra main-chain triazole links. The methodology reported here also presents a convenient synthetic platform for the design and production of new analogs of this important human hormone with non-standard protein modifications.

Molecular Weight and Charge Density Effects of Guanidinylated Biodegradable Polycarbonates on Antimicrobial Activity and Selectivity.

Six guanidine functionalized aliphatic biodegradable polycarbonates with varying molecular weights and charge densities were synthesized via postsynthesis modification of alkyne containing polycarbonates using Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry. The concept of passive diluting group was to modify the cationic charge density of the polycarbonate without changing its hydrophilicity. Within the molecular weight range from 8000 to 30000 g mol-1, these guanidine polycarbonates exhibited broad-spectrum biocidal activity with low toxicity to red blood cells (RBCs). The lowest molecular weight homopolymer sample (PG-8k-100) showed the best antimicrobial activity (MIC = 40 μg/mL against Escherichia coli and MIC = 20 μg/mL against Staphylococcus epidermidis) and least RBC toxicity (0.6% hemolysis at MIC). Within the three guanidine charge densities from 20% to 70%, the low to medium dilution samples (PG-8k-7030 and PG-8k-5050) had no obvious loss in antimicrobial activities compared to the nondiluted control sample PG-8k-100. However, upon further dilution, PG-8k-2080 gave the lowest antimicrobial activity.

Polymeric Chemosensors: A Conventional Platform with New Click Chemistry

Abstract Polymers are a good platform for the production of various functional materials, since functional moieties can be introduced into both the main chain backbone and side chain pendants by elegant molecular design and utilizing efficient synthetic protocols. Highly colored and fluorescent π-systems have often been employed as ion sensing units especially when heteroaromatic rings are included. The heteroaromatic rings can form supramolecular complexes with metal ions or anions, resulting in the visual color changes of absorption and fluorescence. Conjugated polymers have been traditionally employed to this end, because they are highly emissive and very sensitive to various ions. However, most of such conjugated polymers are synthesized by costly cross-coupling polycondensations, which do not meet the green chemistry concepts of this century. Click chemistry is a new concept representing an efficient and atom-economic synthesis, and one of the most common reactions is the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) yielding 1,2,3-triazole rings. The 1,2,3-triazole derivatives are electronically almost inert, but they possess fluorescent chemosensor properties. Recent examples of polymeric chemosensors based on the 1,2,3-triazole derivatives are introduced. Furthermore, an emerging click chemistry reaction, i.e., the alkyne-acceptor click chemistry, is also introduced. This reaction produces highly colored donor-acceptor (D-A) chromophores on a polymer platform, enabling visual detection of the ion sensing behavior. The polymeric chemosensors with the D-A chromophores show a specific discrimination between hard and soft metal ions by different color changes. These polymers are also useful for anion sensing.

Longitudinally Controlled Modification of Cylindrical and Conical Track-Etched Poly(ethylene terephthalate) Pores Using an Electrochemically Assisted Click Reaction.

In this study, the longitudinally controlled modification of the inner surfaces of poly(ethylene terephthalate) (PET) track-etched pores was explored using an electrochemically assisted Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. Cylindrical or conical PET track-etched pores were first decorated with ethynyl groups via the amidation of surface -COOH groups, filled with a solution containing Cu(II) and azide-tagged fluorescent dye, and then sandwiched between comb-shaped and planar gold electrodes. Cu(I) was produced at the comb-shaped working electrode by the reduction of Cu(II); it diffused along the pores toward the other electrode and catalyzed CuAAC between an azide-tagged fluorescent dye and a pore-tethered ethynyl group. The modification efficiency of cylindrical pores (ca. 1 μm in diameter) was assessed from planar and cross-sectional fluorescence microscope images of modified membranes. Planar images showed that pore modification took place only above the teeth of the comb-shaped electrode with a higher reaction yield for longer Cu(II) reduction times. Cross-sectional images revealed micrometer-scale gradient modification along the pore axis, which reflected a Cu(I) concentration profile within the pores, as supported by finite-element computer simulations. The reported approach was applicable to the asymmetric modification of cylindrical pores with two different fluorescent dyes in the opposite directions and also for the selective visualization of the tip and base openings of conical pores (ca. 3.5 μm in base diameter and ca. 1 μm in tip diameter). The method based on electrochemically assisted CuAAC provides a controlled means to fabricate asymmetrically modified nanoporous membranes and, in the future, will be applicable for chemical separations and the development of sequential catalytic reactors.

Clicked graphene oxide as new support for the immobilization of peroxophosphotungstate: Efficient catalysts for the epoxidation of olefins

Peroxophosphotungstate (PW) anions were successfully immobilized on the surface of clicked graphene oxides and used as heterogeneous catalysts for the epoxidation of various olefins using H2O2 as oxidant. Graphene oxide (GO) was functionalized with azide groups through both grafting and tethering methods Then, supported ionic liquids were formed on the surface of GO through the Cu (I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The clicked GO supported ionic liquids were used as appropriate supports for the immobilization of PW anions. Characterization of the prepared materials by various physicochemical methods showed that PW anions have been successfully immobilized on the surface of clicked GOs. Catalytic activities of these heterogeneous catalysts were evaluated in the epoxidation of olefins which showed that not only the catalysts are active, but also they could be reused several times without significant loss of their activities.

Tuning the functionalization degree of amylose and amylopectin with photochromic spiropyran by CuAAc reaction

Amylose and amylopectin were functionalized with an alkynyl derivative of spiropyran (SPCC) and/or propargyl alcohol by a two step procedure consisting in the derivatization of glucopyranose units with azide at the C6 position followed by Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAc). Substitution degrees with spiropyran (DSSP) between 0.10 and 0.95 were achieved by simply modulating the molar ratio between alkyne species and polysaccharide in the CuAAc reaction, as it was confirmed by FT-IR and NMR spectroscopy characterizations. The UV–Vis spectra of SPCC-modified amylose in DMF solution kept in the dark exhibited an absorbance band with maximum at ∼346 nm, ascribed to spiropyran units. The intensity of the absorbance was found to increase linearly with DSSP. Upon irradiation with UV light, a band at ∼560 nm appeared, due to the conversion of spiropyran to zwitterionic merocyanine, its intensity linearly increasing with DSSP too. ICP-MS analysis showed the presence of a small amount (<270 ppm) of residual Cu from the catalyst in the functionalized polysaccharides. However, EPR spectroscopy indicated that Cu2+ species are bonded to different moieties and they do not significantly interfere with the optical behaviour. These findings indicate that the proposed synthetic strategy can be exploited to prepare photochromic materials with the desired signal intensity by using natural amylose as raw material.

Colorimetric Ion Sensors Based on Polystyrenes Bearing Side Chain Triazole and Donor-Acceptor Chromophores.

Side chain clicked polystyrene derivatives formed by the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction showed colorimetric ion sensing behaviors when donor-acceptor chromophores, prepared by a [2+2] cylcoladdition-retroelectrocyclization between electron-rich alkynes and tetracyanoethylene (TCNE)/7,7,8,8-tetracyanoquinodimethane (TCNQ), were attached to the triazole rings. The metal ion sensing behaviors could be explained according to the theory of hard and soft acids and bases (HSAB). Hard acidic metal ions were mainly recognized by the hard basic anilino-nitrogen moieties, resulting in a decrease in the charge-transfer (CT) bands. In contrast, soft acidic metal ions led to a bathochromic shift in the CT bands due to the selective interactions with the soft basic cyano-nitrogen atoms. With the triazole spacers, more soft (and/or borderline) metal ions were recognized by the donor-acceptor chromophores probably due to more space for the various sized metal ions. The chemodocimetric anion sensing behaviors of the clicked polystyrenes were almost the same as those of the counter polystyrenes without the triazole spacers. Overall, the triazoles in this study do not serve as colorimetric sensor units towards both metal ions and anions, but they are effective spacers between the polymer main chain and ion sensing donor-acceptor side chain chromophores.

Copper(I)‐Catalyzed One‐Pot Sequential [3+2]/[8+2] Annulations for the (Z)‐Selective Construction of Heterocyclic Diazabicyclo[5.3.0]decatrienes

AbstractAn efficient copper(I)‐catalyzed one‐pot domino reaction for the (Z)‐selective construction of diazabicyclo[5.3.0]decatriene derivatives under mild conditions has been developed. This protocol was initiated by a Cu(I)‐catalyzed azide‐alkyne cycloaddition (CuAAC), followed by a ring opening rearrangement and then subsequent higher‐order [8+2] cycloaddition of azaheptafulvene with ketenimine intermediates at the corresponding C‐2 and N‐3 sites, affording biologically active heterocycles in good to high yields.magnified image

A potential industrialized fiber-supported copper catalyst for one-pot multicomponent CuAAC reactions in water

Abstract A potential industrialized fiber catalyst for “click chemistry” via the one-pot multicomponent Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) for the synthesis of 1,2,3-triazoles in water, is reported. Detailed characterization by appearance, mechanical properties, elemental analysis, FTIR spectroscopy, and SEM confirmed the rangeability of the fiber catalyst during the preparation and utilization processes. Moreover, the fiber catalyst-mediated reactions proceeded smoothly to afford triazoles with nearly quantitative yields in short time (15 min). Furthermore, the fiber catalyst has shown tandem activities and superior recyclability (over 10 cycles), and the procedure is operationally simple and amenable to the gram-scale on a simple fixed-bed reactor.

Design and synthesis of 1,2,3-triazolo-phenanthrene hybrids as cytotoxic agents

A series of new 1,2,3-triazolo-phenanthrene hybrids has been synthesized by employing Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. These compounds were evaluated for their in vitro cytotoxic potential against various human cancer cell lines viz. lung (A549), prostate (PC-3 and DU145), gastric (HGC-27), cervical (HeLa), triple negative breast (MDA-MB-231, MDA-MB-453) and breast (BT-549, 4T1) cells. Among the tested compounds, 7d displayed highest cytotoxicity against DU145 cells with IC50 value of 1.5±0.09µM. Further, the cell cycle analysis shown that it blocks G0/G1 phase of the cell cycle in a dose dependent manner. In order to determine the effect of compound on cell viability, phase contrast microscopy, AO/EB, DAPI, DCFDA and JC-1 staining studies were performed. These studies clearly indicated that the compound 7d inhibited the cell proliferation of DU145 cells. Relative viscosity measurements and molecular docking studies indicated that these compounds bind to DNA by intercalation.

Synthesis of Novel Saccharin Derivatives

The synthesis of saccharin (1,2-benzisothiazol-3-one-1,1-dioxide) derivatives substituted on the benzene ring has seen limited development despite the longevity of this compound’s use as an artificial sweetener. This type of saccharin derivative would however present attractive properties for the development of new bioactive, drug-like small molecule compounds. Here we report the derivatisation of the benzene ring of saccharin using Cu(I)-catalyzed azide alkyne cycloaddition (CuAAC) to synthesise a diverse library of novel saccharin-1,2,3-triazole conjugates. All library compounds retain the capability for interactions with biomolecules via the unmodified sulfonamide and lactam groups of the parent saccharin core heterocycle. The compounds also encompass alternate orientations of the 1,2,3-triazole heterocycle, thus further adding diversity to the potential hydrogen bonding interactions of these compounds with biomolecules of therapeutic interest. Our findings demonstrate that specifically functionalized derivatives of saccharin may be prepared from either saccharin azide or saccharin alkyne building blocks in high yield using CuAAC.

Intermediates Stabilized by Tris(triazolylmethyl)amines in the CuAAC Reaction.

Tris(triazolylmethyl)amine ligands (TL) are widely used to accelerate the CuI -catalyzed azide-alkyne cycloaddition (CuAAC) reaction, but its mechanistic role remains unclear. Using electrospray ionization mass spectrometry, we detected for the first time the trinuclear TL-CuI3 -acetylide and the dinuclear TL-CuI2 -acetylide complexes in aqueous solution. The apparent second-order rate constants of their reaction with an azide were 27 and 783 m-1 ⋅s-1 when the alkyne was tethered to TL. In the catalytic system without the tether, the rate constant increased to >146 m-1 ⋅s-1 for the TL-CuI3 -acetylide, but dropped about 14-fold to approximately 55 m-1 ⋅s-1 for the TL-CuI2 -acetylide. The results indicated that TL accelerated the reaction by stabilizing the CuI2 - and CuI3 -acetylide and their azide-adduct intermediates, but this role is largely weakened by excess alkyne and other competing ligands under catalytic conditions.

Temperature and pH Dual-Responsive Core-Brush Nanocomposite for Enrichment of Glycoproteins.

In this report, we present a novel modular approach to the immobilization of a high density of boronic acid ligands on thermoresponsive block copolymer brushes for effective enrichment of glycoproteins via their synergistic multiple covalent binding with the immobilized boronic acids. Specifically, a two-step, consecutive surface-initiated atom transfer radical polymerization (SI-ATRP) was employed to graft a flexible block copolymer brush, pNIPAm-b-pGMA, from an initiator-functionalized nanosilica surface, followed by postpolymerization modification of the pGMA moiety with sodium azide. Subsequently, an alkyne-tagged boronic acid (PCAPBA) was conjugated to the polymer brush via a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction, leading to a silica-supported polymeric hybrid material, Si@pNIPAm-b-pBA, with a potent glycol binding affinity. The obtained core-brush nanocomposite was systematically characterized with regard to particle size, morphology, organic content, brush density, and number of immobilized boronic acids. We also studied the characteristics of glycoprotein binding of the nanocomposite under different conditions. The nanocomposite showed high binding capacities for ovalbumin (OVA) (98.0 mg g-1) and horseradish peroxidase (HRP) (26.8 mg g-1) in a basic buffer (pH 9.0) at 20 °C. More importantly, by adjusting the pH and temperature, the binding capacities of the nanocomposite can be tuned, which is meaningful for the separation of biological molecules. In general, the synthetic approach developed for the fabrication of block copolymer brushes in the nanocomposite opened new opportunities for the design of more functional hybrid materials that will be useful in bioseparation and biomedical applications.

Tethering antimicrobial peptides onto chitosan: Optimization of azide-alkyne “click” reaction conditions

Antimicrobial peptides (AMP) are promising alternatives to classical antibiotics, due to their high specificity and potency at low concentrations, and low propensity to elicit pathogen resistance. Immobilization of AMP onto biomaterials is an emergent field of research, towards creation of novel antimicrobial materials able to avoid formation of biofilms on the surfaces of medical devices. Herein, we report the chemical route towards one such material, where chitosan was used as biocompatible carrier for the covalent grafting of Dhvar-5, a well-known potent AMP, via the chemoselective (“click”) Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The material’s structure, as well as peptide loading, were confirmed by Fourier-transformed infra-red (FT-IR) and X-ray photoelectron (XPS) spectroscopies, and by Amino Acid Analysis (AAA), respectively. Results herein reported demonstrate that, with proper optimization, the “click” CuAAC is an attractive approach for the tethering of AMP onto chitosan, in order to create novel antimicrobial materials potentially valuable for biomedical applications.

Recent advances of CuAAC click reaction in building cyclic polymer

Cyclic polymers have attracted more and more attentions in recent years because of their unique topological structures and characteristic properties in both solution and bulk state. There are relatively few reports on cyclic polymers, partly because of the more demanding synthetic procedures. In recent years, “click” reaction, especially Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC), has been widely utilized in the synthesis of cyclic polymer materials because of its high efficiency and low susceptibility to side reactions. In this review, we will focus on three aspects: (1) Constructions of monocyclic polymer using CuAAC “click” chemistry; (2) Formation of complex cyclic polymer topologies through CuAAC reactions; (3) Using CuAAC “click” reaction in the precise synthesis of molecularly defined macrocycles. We believe that the CuAAC click reaction is playing an important role in the design and synthesis of functional cyclic polymers.