Mitochondria-targeted ruthenium complexes can be generated in vitro and in living cells to target triple-negative breast cancer cells by autophagy inhibition

Triple-negative breast cancer (TNBC) is the most aggressive type of breast cancer, which owned severe resistance to platinum-based anticancer agents. Herein, we report a new metal-arene complex, Ru-TPE-PPh3, which can be synthesized in vitro and in living cells with copper catalyzed the cycloaddition reaction of Ru-azide and alkynyl (CuAAC). The complex Ru-TPE-PPh3 exhibited superior inhibition of the proliferation of TNBC MDA-MB-231 cells with an IC50 value of 4.0 μM. Ru-TPE-PPh3 could induce the over production of reactive oxygen species (ROS) to initiate the oxidative stress, and further damage the mitochondria both functionally and morphologically, as loss of mitochondrial membrane potential (MMP) and cutting the supply of adenosine triphosphate (ATP), the disappearance of cristae structure. Moreover, the damaged mitochondria evoked the occurrence of mitophagy with the autophagic flux blockage and cell death. The complex Ru-TPE-PPh3 also demonstrated excellent anti-proliferative activity in 3D MDA-MB-231 multicellular tumor spheroids (MCTSs), indicating the potential to inhibit solid tumors in living cells. This study not only provided a potent agent for the TNBC treatment, but also demonstrated the universality of the bioorthogonally catalyzed lethality (BCL) strategy through CuAAC reation.

Halo-1,2,3-triazoles: Valuable Compounds to Access Biologically Relevant Molecules

1,2,3-triazole is an important building block in organic chemistry. It is now well known as a bioisostere for various functions, such as the amide or the ester bond, positioning it as a key pharmacophore in medicinal chemistry and it has found applications in various fields including life sciences. Attention was first focused on the synthesis of 1,4-disubstituted 1,2,3-triazole molecules however 1,4,5-trisubstituted 1,2,3-triazoles have now emerged as valuable molecules due to the possibility to expand the structural modularity. In the last decade, methods mainly derived from the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction have been developed to access halo-triazole compounds and have been applied to nucleosides, carbohydrates, peptides and proteins. In addition, late-stage modification of halo-triazole derivatives by metal-mediated cross-coupling or halo-exchange reactions offer the possibility to access highly functionalized molecules that can be used as tools for chemical biology. This review summarizes the synthesis, the functionalization, and the applications of 1,4,5-trisubstituted halo-1,2,3-triazoles in biologically relevant molecules.

Synthesis of Fluorescent C-C Bonded Triazole-Purine Conjugates

A design toward C-C bonded 2,6-bis(1H-1,2,3-triazol-4-yl)-9H-purine and 2-piperidinyl-6-(1H-1,2,3-triazol-4-yl)-9H-purine derivatives was established using the combination of Mitsunobu, Sonogashira, copper (I) catalyzed azide-alkyne cycloaddition, and SNAr reactions. 11 examples of 2,6-bistriazolylpurine and 14 examples of 2-piperidinyl-6-triazolylpurine intermediates were obtained, in 38-86% and 41-89% yields, respectively. Obtained triazole-purine conjugates expressed good fluorescent properties which were studied in the solution and in the thin layer film for the first time. Quantum yields reached up to 49% in DMSO for bistriazolylpurines and up to 81% in DCM and up to 95% in DMSO for monotriazolylpurines. Performed biological studies in mouse embryo fibroblast, human keratinocyte, and transgenic adenocarcinoma of the mouse prostate cell lines showed that most of obtained triazole-purine conjugates are not cytotoxic. The 50% cytotoxic concentration of the tested derivatives was in the range from 59.6 to 1528.7 µM.

1,2,3-Triazole Hybrids Containing Isatins and Phenolic Moieties: Regioselective Synthesis and Molecular Docking Studies

The synthesis of hybrid molecules is one of the current strategies of drug discovery for the development of new lead compounds. The 1,2,3-triazole moiety represents an important building block in Medicinal Chemistry, extensively present in recent years. In this paper, we presented the design and the synthesis of new 1,2,3-triazole hybrids, containing both an isatine and a phenolic core. Firstly, the non-commercial azide and the alkyne synthons were prepared by different isatines and phenolic acids, respectively. Then, the highly regioselective synthesis of 1,4-disubstituted triazoles was obtained in excellent yields by a click chemistry approach, catalyzed by Cu(I). Finally, a molecular docking study was performed on the hybrid library, finding four different therapeutic targets. Among them, the most promising results were obtained on 5-lipoxygenase, an enzyme involved in the inflammatory processes.

Accelerated Diffusion of a Copper(I)-Functionalized COF Packed Bed Reactor for Efficient Continuous Flow Catalysis

Flow chemistry provides a neo-orientation for the research and development of chemical technology, in which heterogeneous continuous catalysis based on packed beds can realize rapid separation and recycling. However, options for heterogeneous catalysts are still limited. In this work, we gradually grow covalent organic frameworks (COFs, TpBpy) on the surface of a silica gel (SiO2)-supported substrate to obtain a stable copper(I)-chelated high-loading heterogeneous catalyst (SiO2@CuI-TpBpy). SiO2@CuI-TpBpy shows high catalytic activity in three-component Huisgen 1,3-dipolar cycloaddition, giving the corresponding triazoles with excellent yields and reposeful recyclability under batch conditions. The structures of the catalysts remain steady, and the copper contents are basically unchanged after five cycles. Then, the catalysts are successfully applied for three-component heterogeneous catalysis in a one-pot continuous flow to prepare rufinamide in 89% yield for 24 h stably and efficiently with mere traces of copper ions remaining. More importantly, the catalytic system reveals a minuscule effect of catalyst particle size on internal diffusion. This COF encapsulation strategy presents a new possibility for the design of industrial heterogeneous catalysts with high metal loading and low internal diffusion resistance.

Copper phosphorylated cellulose nanofibers mediated azide-alkyne cycloaddition click reaction in water

Heterogenous copper-catalyzed azide-alkyne cycloaddition reaction (CuAAC) was performed by using the phosphorylated carbohydrate-based cellulose nanofibers loaded with copper(II) ions. The copper-containing phosphorylated cellulose nanofibers (here after noted Cu(II)-PCNFs) were prepared in two different morphologies, namely the paper and foam ones and characterized by different techniques, including Scanning Electronic Microscopy (SEM), Energy Dispersive X-ray (EDX), Brauner-Emmett-Teller (BET), FT-IR spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA), X-ray Photoelectron spectroscopy (XPS) and Atomic Force Microscopy (AFM). Cu(II)-PCNFs showed high activity in the CuAAC reaction when applied to the ligation of various organic azides and terminal alkynes without any reducing agent, resulting in the regioselective synthesis of 1,4-disubstituted-1,2,3-triazoles in water at room temperature. These nanofibers were recovered and reused with no significant loss of catalytic activity or selectivity. A carbohydrate-based bio-support cellulose as reliable heterogenous catalyst was efficiently developed in view of taking the click chemistry concept to sustainable chemistry.

CuAAC-Based Synthesis, Copper-Catalyzed Aldehyde-Forming Hydrolytic Fission and Antiproliferative Evaluation of Novel Ferrocenoylamino-Substituted Triazole-Tethered Quinine-Chalcone Hybrids

A series of novel triazole-tethered ferrocenoylamino-substituted cinchona-chalcone hybrids along with two representative benzoylamino-substituted reference compounds were prepared by three methods of CuAAC chemistry. In line with the limited success or complete failure of attempted conversions with low catalyst loadings, by means of DFT modeling studies, we demonstrated that a substantial part of the Cu(I) ions can be chelated and thus trapped in the aroylamino-substituted cinchona fragment and all of the accessible coordinating sites of the chalcone residues. Accordingly, increased amounts of catalysts were used to achieve acceptable yields; however, the cycloadditions with para-azidochalcones were accompanied by partial or complete aldehyde-forming hydrolytic fission of the enone C=C bond in a substituent-, solvent- and copper load-dependent manner. The experienced hydrolytic stability of the hybrids obtained by cycloadditions with ortho-azidochalcones was interpreted in terms of relative energetics, DFT reactivity indices and MO analysis of simplified models of two isomer copper-enone complexes. The novel hybrids were evaluated on HeLa, MDA-MB-231 and A2780 cell lines and showed substantial activity at low-to-submicromolar concentrations. An organometallic model carrying 3,4,5-trimethoxyphenyl residue in the enone part with a para-disubstituted benzene ring in the central skeletal region was identified as the most potent antiproliferative lead, characterized by submicromolar IC50 values measured on the three investigated cells. The biological assays also disclosed that this ferrocenoylamino-containing lead compound displays a ca. two- to five-fold more substantial antiproliferative effect than its benzoylamino-substituted counterpart.

Glutathione Mediates Control of Dual Differential Bio-orthogonal Labelling of Biomolecules

Traditional approaches to bio-orthogonal reaction discovery have focused on developing reagent pairs that react with each other faster than they are metabolically degraded. Glutathione (GSH) is typically responsible for the deactivation of most bio-orthogonal reagents. Here we demonstrate that GSH promotes a Cu-catalysed (3+2) cycloaddition reaction between an ynamine and an azide. We show that GSH acts as a redox modulator to control the Cu oxidation state in these cycloadditions. Rate enhancement of this reaction is specific for ynamine substrates and is tuneable by the Cu:GSH ratio. This unique GSH-mediated reactivity gradient is then utilised in the dual sequential bio-orthogonal labelling of peptides and oligonucleotides via two distinct chemoselective (3+2) cycloadditions.

Glutathione Mediates Control of Dual Differential Bio-orthogonal Labelling of Biomolecules

Traditional approaches to bio-orthogonal reaction discovery have focused on developing reagent pairs that react with each other faster than they are metabolically degraded. Glutathione (GSH) is typically responsible for the deactivation of most bio-orthogonal reagents. Here we demonstrate that GSH promotes a Cu-catalysed (3+2) cycloaddition reaction between an ynamine and an azide. We show that GSH acts as a redox modulator to control the Cu oxidation state in these cycloadditions. Rate enhancement of this reaction is specific for ynamine substrates and is tuneable by the Cu:GSH ratio. This unique GSH-mediated reactivity gradient is then utilised in the dual sequential bio-orthogonal labelling of peptides and oligonucleotides via two distinct chemoselective (3+2) cycloadditions.

Design, synthesis, conformational analysis, and biological activity of Cα1-to-Cα6 1,4- and 4,1-disubstituted 1H-[1,2,3]triazol-1-yl-bridged oxytocin analogues

Oxytocin (OT) is a neurohypophyseal peptide hormone containing a disulphide-bridged pseudocyclic conformation. The biomedical use of OT peptides is limited amongst others by disadvantageous pharmacokinetic parameters. To increase the stability of OT by replacing the disulphide bridge with the stable and more rigid [1,2,3]triazol-1-yl moiety, we employed the Cu2+-catalysed side chain-to-side chain azide-alkyne 1,3-cycloaddition. Here we report the design, synthesis, conformational analysis, and in vitro pharmacological activity of a homologous series of Cα1-to-Cα6 side chain-to-side chain [1,2,3]triazol-1-yl-containing OT analogues differing in the length of the bridge, location, and orientation of the linking moiety. Exploiting this macrocyclisation approach, it was possible to generate a systematic series of compounds providing interesting insight into the structure-conformation-function relationship of OT. Most analogues were able to adopt similar conformation to endogenous OT in water, namely, a type I β-turn. This approach may in the future generate stabilised pharmacological peptide tools to advance understanding of OT physiology.

New Carboxytriazolyl Amphiphilic Derivatives of Calix[4]arenes: Aggregation and Use in CuAAC Catalysis

This work focuses on the synthesis of a new series of amphiphilic derivatives of calix[4]arenes for the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The aggregation properties of synthesized calix[4]arenes were studied using various techniques (fluorescence spectroscopy, nanoparticle tracking analysis, and dynamic light scattering). Increasing the length of the alkyl substituent led to stronger hydrophobic interactions, which increased polydispersity in solution. The zwitterionic nature of the synthesized calix[4]arenes was established using different types of dyes (Eosin Y for anionic structures and Rhodamine 6G for cationic structures). The synthesized calix[4]arenes were used as organic stabilizers for CuI. The catalytic efficiency of CuI-calix[4]arene was compared with that of the phase transfer catalyst tetrabutylammonium bromide (TBAB) and the surfactant sodium dodecyl sulfate (SDS). For all calixarenes, the selectivity in the CuAAC reaction was higher than that observed when TBAB and SDS were estimated.

Growing Impact of Intramolecular Click Chemistry in Organic Synthesis

Click Chemistry, a modular, rapid, and one of the most reliable tool for the regioselective 1,2,3-triazole forming [3+2] reaction of organic azide and terimal alkyne is widely explored in various emerging domains of research ranging from chemical biology to catalysis and medicinal chemistry to material science. This regioselective reaction from a diverse range of azido-alkyne scaffolds has been well performed in both intermolecular as well as intramolecular fashions. In comparison to the intermolecular metal (Cu/Ru/Ni) variant of 'Click Chemistry', the intramolecular click tool is little addressed. The intramolecular click chemistry is exemplified as a mordern tool of cyclization which involves metal-catalyzed (CuAAC/RuAAC) cyclization, organo-catalyzed cyclization, and thermal-induced topochemical reaction. Thus, we report herein the recent approaches on intramolecular azide-alkyne cycloaddition 'Click Chemistry' with their wide-spread emerging applications in the developement of a diverse range of molecules including fused-heterocycles, well-defined peptidomemics, and macrocyclic architectures of various notable features.

Click Chemoselective Probe with a Photoswitchable Handle for Highly Sensitive Determination of Steroid Hormones in Food Samples

Residues of endocrine disrupting steroid hormones in food might cause various diseases like cardiovascular diseases and breast and prostate cancers. Monitoring steroid hormone levels plays a vital role in ensuring food safety and exploring the pathogenic mechanism of steroid hormone-related diseases. Based on the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction, a novel chemoselective probe, Azo-N3, which contains a reactive site N3, an imidazolium salt-based MS tag, and an azobenzene-based photoswitchable handle, was designed and synthesized to label ethynyl-bearing steroid hormones. The probe Azo-N3 was applied for the highly selective and sensitive detection of four ethynyl-bearing steroid hormones in food samples (milk, egg, and pork) by using ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The ionization efficiency of the labeled analytes could be increased by 6-105-fold, and such a labeled method exhibited satisfactory detection limits (0.04-0.2 μg/L), recovery (80.6-122.4%), and precision (RSDs% lower than 6.9%). Interestingly, the efficient immobilization of the probe Azo-N3 onto α-cyclodextrin (α-CD)-modified magnetic particles to construct a solid supported chemoselective probe Fe3O4-CD-Azo-N3 and UV light-controlled release of the labeled analytes from a magnetic support can be achieved by taking advantage of the photoswitched host-guest inclusion between the azobenzene unit and α-CD. The potential applications of Fe3O4-CD-Azo-N3 for labeling, capturing, and the photocontrolled release of the labeled steroid hormones were fully investigated by mass spectrometry imaging analysis. This work not only provides a sensitive and accurate method to detect steroid hormones in food but also opens a new avenue in designing solid supported chemoselective probes.

Exploring the Influence of Spacers in EDTA-β-Cyclodextrin Dendrimers: Physicochemical Properties and In Vitro Biological Behavior

The synthesis of a new family of ethylenediaminetetraacetic acid (EDTA) core dimers and G0 dendrimers end-capped with two and four β-cyclodextrin (βCD) moieties was performed by click-chemistry conjugation, varying the spacers attached to the core. The structure analyses were achieved in DMSO-d6 and the self-inclusion process was studied in D2O by 1H-NMR spectroscopy for all platforms. It was demonstrated that the interaction with adamantane carboxylic acid (AdCOOH) results in a guest-induced shift of the self-inclusion effect, demonstrating the full host ability of the βCD units in these new platforms without any influence of the spacer. The results of the quantitative size and water solubility measurements demonstrated the equivalence between the novel EDTA-βCD platforms and the classical PAMAM-βCD dendrimer. Finally, we determined the toxicity for all EDTA-βCD platforms in four different cell lines: two human breast cancer cells (MCF-7 and MDA-MB-231), human cervical adenocarcinoma cancer cells (HeLa), and human lung adenocarcinoma cells (SK-LU-1). The new EDTA-βCD carriers did not present any cytotoxicity in the tested cell lines, which showed that these new classes of platforms are promising candidates for drug delivery.

Automated solid-phase synthesis of metabolically stabilized triazolo-peptidomimetics

The use of 1,4-disubstituted 1,2,3-triazoles as trans-amide bond surrogates has become an important tool for the synthesis of metabolically stabilized peptidomimetics. These heterocyclic bioisosters are generally incorporated into the peptide backbone by applying a diazo-transfer reaction followed by CuAAC (click chemistry) with an α-amino alkyne. Even though the manual synthesis of backbone-modified triazolo-peptidomimetics has been reported by us and others, no procedure has yet been described for an automated synthesis using peptide synthesizers. In order to efficiently adapt these reactions to an automated setup, different conditions were explored, putting special emphasis on the required long-term stability of both the diazo-transfer reagent and the Cu(I) catalyst in solution. ISA·HCl is the reagent of choice to accomplish the diazo-transfer reaction; however, it was found instable in DMF, the most commonly used solvent for SPPS. Thus, an aqueous solution of ISA·HCl was used to prevent its degradation over time, and the composition in the final diazo-transfer reaction was adjusted to preserve suitable swelling conditions of the resins applied. The CuAAC reaction was performed without difficulties using [Cu (CH3 CN)4 ]PF6 as a catalyst and TBTA as a stabilizer to prevent oxidation to Cu(II). The optimized automated two-step procedure was applied to the synthesis of structurally diverse triazolo-peptidomimetics to demonstrate the versatility of the developed methodology. Under the optimized conditions, five triazolo-peptidomimetics (8-5 amino acid residues) were synthesized efficiently using two different resins. Analysis of the crude products by HPLC-MS revealed moderate to good purities of the desired triazolo-peptidomimetics (70-85%). The synthesis time ranged between 9 and 12.5 h.

Synthesis of 1,2,3-Triazole-Containing Methoxylated Cinnamides and Their Antileishmanial Activity against the Leishmania braziliensis Species

Leishmaniasis is a group of infectious diseases caused by protozoan parasites that belong to the genus Leishmania. Currently, there is no human vaccine, and the available treatments are associated with toxicity, high cost, and the emergence of resistant strains. These factors highlight the need to identify new antileishmanial candidates. In this study, we synthesized twenty-four methoxylated cinnamides containing 1,2,3-triazole fragments and evaluated their antileishmanial activity against the Leishmania braziliensis species, which is the main etiological agent responsible for American Tegumentary Leishmaniasis (ATL). The cinnamides were synthetically prepared using nucleophilic acyl substitution and copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions. The compounds were characterized using infrared, nuclear magnetic resonance, and high-resolution mass spectrometry techniques. We performed preliminary studies to evaluate the biological activity of these compounds against L. braziliensis promastigotes and axenic amastigotes. Compound 28, N-((1-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)-1H-1,2,3-triazole-4-yl) methyl)-3,4-dimethoxy cinnamide, demonstrated relevant antileishmanial activity with low toxicity in murine cells. The selectivity index values for this compound were superior compared with data obtained using amphotericin B. Furthermore, this cinnamide derivative reduced the infection percentage and number of recovered amastigotes in L. braziliensis-infected macrophages. It also induced an increase in reactive oxygen species production, depolarization of the mitochondrial potential, and disruption of the parasite membrane. Taken together, these findings suggest that this synthetic compound holds potential as an antileishmanial candidate and should be considered for future studies in the treatment of ATL.

Synthesis of Multifunctional Protein-Polymer Conjugates via Oxygen-tolerant, Aqueous Copper-Mediated Polymerization, and Bioorthogonal Click Chemistry

Oxygen-tolerant, aqueous copper-mediated polymerization approaches are combined with click chemistry in either a sequential or a simultaneous manner, to enable the synthesis of multifunctional protein-polymer conjugates. Propargyl acrylate (PgA) and propargyl methacrylate (PgMA) grafting from a bovine serum albumin (BSA) macroinitiator is thoroughly optimized to synthesize chemically addressable BSA-poly(propargyl acrylate) and BSA-poly(propargyl methacrylate) respectively. The produced multifunctional bioconjugates bear pendant terminal 1-alkynes which can be readily post-functionalized via both [3+2] Huisgen cycloaddition and thiol-yne click chemistry under mild reaction conditions. Simultaneous oxygen-tolerant, aqueous copper-catalyzed polymerization, and click chemistry mediate the in situ multiple chemical tailoring of biomacromolecules in excellent yields.

Radiofluorination of an Anionic, Azide-Functionalized Teroligomer by Copper-Catalyzed Azide-Alkyne Cycloaddition

This study describes the synthesis, radiofluorination and purification of an anionic amphiphilic teroligomer developed as a stabilizer for siRNA-loaded calcium phosphate nanoparticles (CaP-NPs). As the stabilizing amphiphile accumulates on nanoparticle surfaces, the fluorine-18-labeled polymer should enable to track the distribution of the CaP-NPs in brain tumors by positron emission tomography after application by convection-enhanced delivery. At first, an unmodified teroligomer was synthesized with a number average molecular weight of 4550 ± 20 Da by free radical polymerization of a defined composition of methoxy-PEG-monomethacrylate, tetradecyl acrylate and maleic anhydride. Subsequent derivatization of anhydrides with azido-TEG-amine provided an azido-functionalized polymer precursor (o14PEGMA-N₃) for radiofluorination. The ¹⁸F-labeling was accomplished through the copper-catalyzed cycloaddition of o14PEGMA-N₃ with diethylene glycol-alkyne-substituted heteroaromatic prosthetic group [¹⁸F]2, which was synthesized with a radiochemical yield (RCY) of about 38% within 60 min using a radiosynthesis module. The ¹⁸F-labeled polymer [¹⁸F]fluoro-o14PEGMA was obtained after a short reaction time of 2-3 min by using CuSO₄/sodium ascorbate at 90 °C. Purification was performed by solid-phase extraction on an anion-exchange cartridge followed by size-exclusion chromatography to obtain [¹⁸F]fluoro-o14PEGMA with a high radiochemical purity and an RCY of about 15%.

Harnessing the power of PLA-PEG Nanoparticles for Linezolid delivery against Methicillin-Resistant Staphylococcus aureus

This study deals with the development of novel poly(lactic acid-co-polyethylene glycol) nanoparticles (PLA-PEG NPs) for the efficient and prolonged delivery of Linezolid (LNZ), a synthetic antibacterial agent used against methicillin-resistant Staphylococcus aureus (MRSA). A two-step synthetic strategy based on carbodiimide coupling and copper-catalyzed azide-alkyne cycloaddition was first exploited for the conjugation of PLA with PEG. The encapsulation of LNZ into medium-molecular-weight PLA-PEG NPs was carried out by different methods including nanoprecipitation and dialysis. The optimal PLA-PEG@LNZ nanoformulation resulted in 3.5% LNZ payload (15% encapsulation efficiency, with a 10:3 polymer to drug ratio) and sustained release kinetics with 65% of entrapped antibiotic released within 80 h. Moreover, the zeta potential values (from -31 to -39 mV) indicated a good stability without agglomeration even after freeze-drying and lyophilization. The PLA-PEG@LNZ NPs exerted antimicrobial activity against a panel of Gram-positive bacteria responsible for human infections, such as S. aureus, MRSA, S. epidermidis, S. lugdunensis and vancomycin resistant Enterococcus faecium (VRE). Moreover, PLA-PEG@LNZ NPs showed inhibitory activity on both planktonic growth and preformed biofilm of MRSA. The antibacterial activity of LNZ incorporated in polymeric NPs was well preserved and the nanosystem served as an antibiotic enhancer with a potential role in MRSA-associated infections management.

Cellulose Acetate-Supported Copper as an Efficient Sustainable Heterogenous Catalyst for Azide-Alkyne Cycloaddition Click Reactions in Water

A new sustainable heterogeneous catalyst for copper-catalyzed azide-alkyne cycloaddition reaction (CuAAC) was investigated. The preparation of the sustainable catalyst was carried out through the complexation reaction between the polysaccharide cellulose acetate backbone (CA) and copper(II) ions. The resulting complex [Cu(II)-CA] was fully characterized by using different spectroscopic methods such as Fourier-transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Ultraviolet-visible (UV-vis), and Inductively Coupled Plasma (ICP) analyses. The Cu(II)-CA complex exhibits high activity in the CuAAC reaction for substituted alkynes and organic azides, leading to a selective synthesis of the corresponding 1,4-isomer 1,2,3-triazoles in water as a solvent and working at room temperature. It is worth noting that this catalyst has several advantages from the sustainable chemistry point of view including no use of additives, biopolymer support, reactions carried out in water at room temperature, and easy recovery of the catalyst. These characteristics make it a potential candidate not only for the CuAAC reaction but also for other catalytic organic reactions.

Monodisperse Hyperbranched Polytriazoles as Unimolecular Nanocontainers for Encapsulation of Functional Payloads

In this work, we developed a series of polytriazole-based unimolecular nanocontainers (UNs) with good water solubility, uniformity, and colloidal stability via a bottom-up chain-growth copper-catalyzed azide-alkyne cycloaddition (co)polymerization that featured tunable size, degree of branching (DB), and functionality of the UNs. A broad selection of hydrophobic payload molecules, including Nile red (NR), camptothecin, pyrene, 1-pyrenemethanol, and IR676, were successfully encapsulated to demonstrate the high versatility of these polymers as UNs. Using NR as a probe guest, the relationship between the encapsulation performance and the structural properties of UNs, including size and DB, was investigated. Furthermore, the localization and dispersity of encapsulated NR were explored and the dependence of payload's dispersity on the DB of UNs was revealed. The payload encapsulated in UNs exhibited tunable release kinetics, determined by either adjusting release conditions or including pH-responsive structural units in the UNs. Meanwhile, the dyes encapsulated in UNs exhibited improved photostability and stronger resistance to photobleaching. We expect these explorations addressed the size and stability issues widely encountered in current drug/dye nanocarriers and provided a versatile platform of polytriazole-based UNs for suitable payloads in various applications, including drug delivery and bio-imaging. This article is protected by copyright. All rights reserved.

Peptide-Resorcinarene Conjugates Obtained via Click Chemistry: Synthesis and Antimicrobial Activity

Antimicrobial resistance (AMR) is one of the top ten threats to public health, as reported by the World Health Organization (WHO). One of the causes of the growing AMR problem is the lack of new therapies and/or treatment agents; consequently, many infectious diseases could become uncontrollable. The need to discover new antimicrobial agents that are alternatives to the existing ones and that allow mitigating this problem has increased, due to the rapid and global expansion of AMR. Within this context, both antimicrobial peptides (AMPs) and cyclic macromolecules, such as resorcinarenes, have been proposed as alternatives to combat AMR. Resorcinarenes present multiple copies of antibacterial compounds in their structure. These conjugate molecules have exhibited antifungal and antibacterial properties and have also been used in anti-inflammatory, antineoplastic, and cardiovascular therapies, as well as being useful in drug and gene delivery systems. In this study, it was proposed to obtain conjugates that contain four copies of AMP sequences over a resorcinarene core. Specifically, obtaining (peptide)₄-resorcinarene conjugates derived from LfcinB (20-25): RRWQWR and BF (32-34): RLLR was explored. First, the synthesis routes that allowed obtaining: (a) alkynyl-resorcinarenes and (b) peptides functionalized with the azide group were established. These precursors were used to generate (c) (peptide)₄-resorcinarene conjugates by azide-alkyne cycloaddition CuAAC, a kind of click chemistry. Finally, the conjugates' biological activity was evaluated: antimicrobial activity against reference strains and clinical isolates of bacteria and fungi, and the cytotoxic activity over erythrocytes, fibroblast, MCF-7, and HeLa cell lines. Our results allowed establishing a new synthetic route, based on click chemistry, for obtaining macromolecules derived from resorcinarenes functionalized with peptides. Moreover, it was possible to identify promising antimicrobial chimeric molecules that may lead to advances in the development of new therapeutic agents.

Aminooxy Click Modification of a Periodate-Oxidized Immunoglobulin G: A General Approach to Antibody-Drug Conjugates with Dye-Mediated Expeditious Stoichiometry Control

A universal approach to the construction of antibody-drug conjugates (ADCs) has been developed. It relies on periodate oxidation of naturally present glycans of immunoglobulin G, followed by oxime ligation and, optionally, copper(I)-catalyzed alkyne-azide cycloaddition for conjugation with a toxic payload. The introduction of highly absorbing cyanine dyes into the linker allows for facile determination of the drug-antibody ratio. We applied this methodology to the synthesis of cytotoxic conjugates of an antibody against the tumor-associated antigen PRAME with doxorubicin and monomethyl auristatin E (MMAE). The resultant conjugates retained their affinity to a large extent, yet their cytotoxicity in vitro varied dramatically: while the doxorubicin-based conjugate did not produce any effect on cells, the MMAE-based one demonstrated specific activity against PRAME-expressing cancer cell lines. Importantly, the latter conjugate constitutes the first reported example of a PRAME-targeting ADC.

Functionalization of Bacterial Cellulose and Related Surfaces Using a Facile Coupling Reaction by Thermoresponsive Catalyst

Recently, bacterial cellulose and related materials attracted significant attention for applications such as leather-like materials, wound healing materials, etc., due to their abundance in pure form and excellent biocompatibility. Chemical modification of bacterial cellulose further helps to improve specific properties for practical utility and economic viability. However, in most cases, chemical modification of cellulose materials involves harsh experimental conditions such as higher temperatures or organic solvents, which may destroy the 3-dimensional network of bacterial cellulose, thereby altering its characteristic properties. Hence, in this work, we have adopted the Suzuki coupling methodology, which is relatively unexplored for chemically modifying cellulose materials. As the Suzuki coupling reaction is tolerable against air and water, modification can be done under mild conditions so that the covalently modified cellulose materials remain intact without destroying their 3-dimensional form. We performed Suzuki coupling reactions on cellulose surfaces using a recently developed thermoresponsive catalyst consisting of poly(N-isopropylacrylamide) (PNIPAM)-tagged N-heterocyclic carbene (NHC)-based palladium(II) complex. The thermoresponsive nature of the catalyst particularly helped to perform reactions in a water medium under mild conditions considering the biological nature of the substrates, where separation of the catalyst can be easily achieved by tuning temperature. The boronic acid derivatives have been chosen to alter the wettability behavior of bacterial cellulose. Bacterial cellulose (BC) obtained from fermentation on a lab scale using a cellulose-producing bacterium called Gluconacetobacter kombuchae (MTCC 6913) under Hestrin-Schramm (HS) medium, or kombucha-derived bacterial cellulose (KBC) obtained from kombucha available in the market or cotton-cellulose (CC) was chosen for the surface functionalization to find the methodology's diversity. Movie files in the Supporting Information and figures in the manuscript demonstrated the utility of the methodology for fluorescent labeling of bacterial cellulose and related materials. Finally, contact angle analysis of the surfaces showed the hydrophobic natures of some functionalized BC-based materials, which are important for the practical use of biomaterials in wet climatic conditions.

Unlocking the potential of iridium and ruthenium arene complexes as anti-tumor and anti-metastasis chemotherapeutic agents

It is a major challenge to design novel multifunctional metal-based chemotherapeutic agents for anti-tumor and anti-metastasis applications. Two complexes (OA-Ir and OA-Ru) were synthesized via CuAAC (copper-catalyzed azide-alkyne cycloaddition) reaction from nontoxic Ir-N₃ or Ru-N₃ species and low toxic alkynyl precursor OA-Alkyne, and exhibited satisfactory anti-tumor and anti-metastasis pharmacological effects. Conjugation of Oleanolic acid (OA) and metal-arene species significantly enhanced the cytotoxicity in A2780 cells compared to the precursors through mitochondrial-induced autophagy pathway. Moreover, the two complexes could inhibit the cell metastasis and invasion through damage of actin dynamics and down-regulation of MMP2/MMP9 proteins. Combination of two precursors improved the lipophilicity and biocompatibility, simultaneously enhanced the cell uptake and the mitochondrial accumulation of metal-arene complexes, which caused mitochondrial membrane potential damage, oxidative phosphorylation, ATP depletion and autophagy. Besides, OA-Ir and OA-Ru displayed excellent activity to disintegrate the 3D multicellular tumor spheroids, showing potential for the treatment of solid tumors. This work provides a new way for developing novel metal-based complexes via CuAAC reaction for simultaneously inhibiting tumor proliferation and metastasis.

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

Among all the available approaches in organic synthesis, the "click chemistry" protocol is very common nowadays to covalently connect two diverse moieties in a single framework. Therefore, this review focuses on the synthesis and photophysical studies of β- and meso-substituted and 1,2,3-triazole-fused porphyrin conjugates. All of the porphyrin conjugates discussed here are synthesized via a copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction between an azide and a terminal alkyne, also popular as "click reaction" or CuAAC reaction. Moreover, the 1,2,3-triazole ring also serves as a spacer and an electron transfer bridge between the porphyrin and the attached chromophores. In order to provide a critical overview of the synthesis and properties of various porphyrin-triazole hybrids, this review will discuss some of the key reactions involved in the preparation of triazole-linked porphyrin conjugates.

Radiochemical Synthesis of 4-[18F]FluorobenzylAzide and Its Conjugation with EGFR-Specific Aptamers

Central nervous system tumors related to gliomas are of neuroectodermal origin and cover about 30% of all primary brain tumors. Glioma is not susceptible to any therapy and surgical attack remains one of the main approaches to its treatment. Preoperative tumor imaging methods, such as positron emission tomography (PET), are currently used to distinguish malignant tissue to increase the accuracy of glioma removal. However, PET is lacking a specific visualization of cells possessing certain molecular markers. Here, we report an application of aptamers to enhancing specificity in imaging tumor cells bearing the epidermal growth factor receptor (EGFR). Glioblastoma is characterized by increased EGFR expression, as well as mutations of this receptor associated with active division, migration, and adhesion of tumor cells. Since 2021, EGFR has been included into the WHO classification of gliomas as a molecular genetic marker. To obtain conjugates of aptamers GR20 and GOL1-specific to EGFR, a 4-[¹⁸F]fluorobenzylazide radiotracer was used as a synthon. For the production of the synthon, a method of automatic synthesis on an Eckert & Ziegler research module was adapted and modified using spirocyclic iodonium ylide as a precursor. Conjugation of 4-[¹⁸F]fluorobenzylazide and alkyne-modified aptamers was carried out using Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) with/without the TBTA ligand. As a result, it was possible to obtain ¹⁸F-labelled conjugates with 97% radiochemical purity for [¹⁸F]FB-GR20 and 98% for [¹⁸F]FB-GOL1. The obtained conjugates can be used for further studies in PET analysis on model animals with grafted glioblastoma.

Post-Functionalization of Organometallic Complexes via Click-Reaction

CuAAC (Cu catalyzed azide-alkyne cycloaddition) click-reaction is a simple and powerful method for the post-synthetic modification of organometallic complexes of transition metals. This approach allows the selective introduction of additional donor sites or functional groups to the periphery of the ligand environment. This is especially important if a metalloligand with free donor sites, which are of the same nature as the primary site for the coordination of the primary metal, has to be created. The concept of post-synthetic modification of organometallic complexes by click-reaction is relatively recent and the currently available experimental material does not yet allow us to identify trends and formulate recommendations to address specific problems. In the present study, we have applied the CuAAC reaction for the post-synthetic modification of diimine mononuclear complexes Re(I), Pt(II) and Ir(III) with C≡C bonds at the periphery of the ligand environment and demonstrated that click-chemistry is a powerful tool for the tunable chemical post-synthetic modification of coordination compounds.

Three-armed RGD-decorated starPLA-PEG nanoshuttle for docetaxel delivery

A novel star-shaped amphiphilic copolymer based on three poly(lactide)-block-poly(ethylene glycol) (PLA-PEG) terminal arms extending from a glycerol multifunctional core was newly synthesized and decorated with the tumor-targeting ligand cyclic-RGDyK peptide (Arg-Gly-Asp-D-Tyr-Lys) to be eventually formulated in polymeric micelles incorporating a suitable anticancer drug (i.e., Docetaxel, DTX; drug loading 16 %, encapsulation efficiency 69 %). The biological profile of unloaded micelles (RGD-NanoStar) was studied on Human Adipose-derived Mesenchymal Stem Cells (Ad-MSCs) as health control, pointing out the absence of toxicity. Surprisingly, an unprecedented effect on cell viability was exerted by RGD-NanoStar, comparable to that of the free DTX, on tumoral MDA-MB 468 Human Breast Adenocarcinoma cells, specifically starting from 48 h of culture (about 40 % and 60 % of dead cells at 48 and 72 h, respectively, at all tested concentrations). RGD-NanoStar reduced the cell viability also of tumoral U87 Human Glioblastoma cells, compared to cells only, at 72 h (about 25 % of dead cells) demonstrating a time-dependent effect exerted by the highest concentrations. The effects of DTX-loaded micelles (RGD-NanoStar/DTX) on U87 and MDA-MB 468 cell lines were evaluated by MTT, cell morphology analysis, and scratch test. A compromised cell morphology was observed without significant difference between DTX-treated and RGD-NanoStar/DTX - treated cells, especially in U87 cell line. Although no apparent benefit emerged from the drug incorporation into the nanosystem by MTT assay, the scratch test revealed a statistically significant inhibition of tumoral cell migration on both cell lines, confirming the well-known role of DTX in inhibiting cell movements even when loaded on polymeric micelles. Specifically, only 43 μm distance was covered by U87 cells after 30 h culture with RGD-NanoStar/DTX (30 μg/mL) compared to 73 μm in the presence of free DTX at the same concentration; more interestingly, a total absence of MDA-MB 468 cell movements was detected at 30 h compared to about 50 μm distance covered by cells in the presence of free DTX (10 μg/mL). The stronger inhibitory activity on cell migration of RGD-NanoStar/DTX compared to the free drug in both cell lines at 30 h attested for a good ability of the drug-loaded nanocarrier to reduce tumor propagation and invasiveness, enhancing the typical effect of DTX on metastatization.

Bambus[4,6]urils as Dual Scaffolds for Multivalent Iminosugar Presentation and Ion Transport: Access to Unprecedented Glycosidase-Directed Anion Caging Agents

Bambusurils, BU[4] and BU[6], were used for the first time as multivalent scaffolds to link glycosidases inhibitors derived from 1-deoxynojirimycin (DNJ). Two linear DNJ ligands having six or nine carbon alkyl azido linkers or a trivalent DNJ dendron were grafted onto octapropargylated BU[4] and dodecapropargylated BU[6] using copper-catalyzed cycloaddition (CuAAC) to yield corresponding neoglycobambus[4] and neoglycobambus[6]urils bearing 8 to 24 iminosugars. The inhibition potencies of neoglycoBU[4], neoglycoBU[6] and neoglycoBU[6] caging anions were evaluated against Jack Bean α-mannosidase and compared to monovalent DNJ derivatives. Strong affinity enhancements per inhibitory head were obtained for the clusters holding trivalent dendrons with inhibitory constants in the nanomolar range (K_i = 24 nM for BU[4] with 24 DNJ units). Interestingly, the anion (bromide or iodide) encapsulated inside the cavity of BU[6] does not modify the inhibition potency of neoglycoBU[6], opening the way to water-soluble glycosidase-directed anion caging agents that may find applications in important fields such as bio(in)organic chemistry or oncology.

Click Isotope Mass Probe for Highly Selective Determination of Trace Steroid Hormones in Food Samples

Matrix effects are a great challenge for the quantitative analysis of complex food samples by liquid chromatography-tandem mass spectrometry analysis (LC-MS/MS). Stable isotope labeling (SIL) has been widely used as an effective strategy to eliminate matrix effects. Herein, a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click-reaction-based SIL method was proposed for a highly sensitive and selective determination of six synthetic steroid hormones in three different food samples (milk, yogurt, and eggs) by high-performance liquid chromatography (HPLC)-MS/MS. A pair of novel SIL agents, N-(2-azidyl ethyl) aniline (d₀-AEA) and d₅-N-(2-azidyl ethyl) aniline (d₅-AEA) were synthesized to label steroid hormones in the samples and standard solution, respectively. The reaction accomplishes in 30 min at 60 °C. The heavy labeled standards were used as internal standards (ISs), which experience the identical ionization processes with light labeled samples to minimize matrix effects. After derivatization, the ionization efficiencies of steroid hormones were greatly improved by 2-54-folds, and the matrix effects ranged from 88.6 to 99.8%. The established method achieved satisfactory detection limits (0.1-2.5 μg L^-1) and high recoveries (85-102%). These results demonstrated that the proposed method holds unique advantages for trace steroid hormones analysis in foodstuffs.

Benchmarking Cleavable Biotin Tags for Peptide-Centric Chemoproteomics

Click chemistry─specifically the copper-catalyzed azide-alkyne cycloaddition─has enabled the development of a wide range of chemical probes to analyze subsets of the functional proteome. The "clickable" proteome can be selectively enriched by using diverse cleavable biotin tags, but the direct identification of probe/tag-modified peptides (or peptide-centric analysis) remains challenging. Here, we evaluated the performance of five commercially available cleavable biotin tags in three most common chemoproteomic workflows, resulting in a comparative analysis of 15 methods. An acid-cleavable biotin tag with a dialkoxydiphenylsilane moiety, in combination with the protein "click", peptide "capture" workflow, outperforms all other methods in terms of enrichment efficiency, identification yield, and reproducibility, although its performance may be slightly compromised by the formation of an unwanted formate product revealed by blind search. Despite being inferior, photocleavable, and reduction-cleavable, biotin tags can also find their applicable sceneries, especially when dealing with acid-sensitive probes or probe-derived modifications. Furthermore, the systematic comparison of LC-MS/MS characteristics of tag-modified peptides provides valuable information for the future development of cleavable biotin reagents. Taken together, our data provides a much-needed practical guidance for researchers interested in developing and/or applying an ideal cleavable biotin tag to peptide-centric chemoproteomics.

On-DNA-1,2,3-Triazole Formation via Click Reaction

Copper-catalyzed azide-alkyne cycloaddition (CuAAC) provides a simple and convenient strategy to synthesize diverse 1,2,3-triazoles for drug discovery. Described herein is a protocol for the CuSO₄-catalyzed cycloaddition between alkynes and DNA-appended azides.

Design and Synthesis of Novel Podophyllotoxins Hybrids and the Effects of Different Functional Groups on Cytotoxicity

Development of novel anticancer therapeutic candidates is one of the key challenges in medicinal chemistry. Podophyllotoxin and its derivatives, as a potent cytotoxic agent, have been at the center of extensive chemical amendment and pharmacological investigation. Herein, a new series of podophyllotoxin-N-sulfonyl amidine hybrids (4a–4v, 5a–5f) were synthesized by a CuAAC/ring-opening procedure. All the synthesized podophyllotoxins derivatives were evaluated for in vitro cytotoxic activity against a panel of human lung (A-549) cancer cell lines. Different substituents’, or functional groups’ antiproliferative activities were discussed. The –CF₃ group performed best (IC₅₀: 1.65 μM) and exhibited more potent activity than etoposide. Furthermore, molecular docking and dynamics studies were also conducted for active compounds and the results were in good agreement with the observed IC₅₀ values.

NHC Polymeric Particles Obtained by Self-Assembly and Click Approach of Calix[4]Arene Amphiphiles as Support for Catalytically Active Pd Nanoclusters

A new polymeric NHC carrier was synthesized by sequential supramolecular self-assembly and copper-catalyzed azide-alkyne cycloaddition (CuAAC) of amphiphilic imidazolium calix[4]arenes with octyl lipophilic fragments. Obtained polytriazole-imidazolium particles were found as monodisperse submicron particles, with the average diameter of 236 ± 34 nm and average molecular weight of 1380 ± 96 kDa. Successful CuAAC polymerization has been proved using IR spectroscopy and high-resolution ESI mass spectrometry. Polymeric particles, as well as aggregates made from precursor macrocycles, were decorated by Pd clusters (2 nm) for further catalytic investigations. Pd nanoclusters, supported on the polymeric surface, were found highly catalytically active in the model reduction of p-nitrophenol, giving reaction rates an order of magnitude higher compared to literature examples. The reaction was recycled using the same catalyst five times without any loss of activity.

Click reaction triggered turn-on fluorescence strategy for highly sensitive and selective determination of steroid hormones in food samples

The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction has becoming noticeable in the field of analytical chemistry. Mild reaction conditions, simple operation, high efficiency, and good regioselectivity make this classical click reaction a perfect strategy for chemical derivatization. Herein, we proposed a promising click fluorescent labeling method with high selectivity for the determination of five steroid hormones in food samples. The labeling strategy depends on the reaction between 3-Azido-7-hydroxycoumarin and the alkynyl group of steroid hormones, which shows a turn-on fluorescence response in the presence of copper (I). The formed fluorescent products were detected by HPLC-FLD. Under the optimized conditions, the proposed method presented excellent performance with good linearity (R² ≥ 0.9998) and low detection limit (1.8-7.3 μg L^-1). Further, satisfactory recoveries were obtained to be 82-107% in spiked meats with relative standard deviations (RSDs) ≤ 5.7%. Finally, the established method was successfully applied for the determination of steroid hormones in meat, indicating the potential prospect of the click reaction in chemical derivatization.

Molecular Brushes with a Polyimide Backbone and Poly(ε-Caprolactone) Side Chains by the Combination of ATRP, ROP, and CuAAC

An approach to the synthesis of the novel molecular brushes with a polyimide (PI) backbone and poly(ε-caprolactone) (PCL) side chains was developed. To obtain such copolymers, a combination of various synthesis methods was used, including polycondensation, atom transfer radical polymerization (ATRP), ring opening polymerization (ROP), and Cu (I)-catalyzed azide-alkyne Huisgen cycloaddition (CuAAC). ATRP of 2-hydroxyethyl methacrylate (HEMA) on PI macroinitiator followed by ROP of ε-caprolactone (CL) provided a “brush on brush” structure PI-g-(PHEMA-g-PCL). For the synthesis of PI-g-PCL two synthetic routes combining ROP and CuAAC were compared: (1) polymer-analogous transformations of a multicenter PI macroinitiator with an initiating hydroxyl group separated from the main chain by a triazole ring followed by ROP of CL, or (2) a separate synthesis of macromonomers with the desirable functional groups (polyimide with azide groups and PCL with terminal alkyne groups), followed by a click reaction. Results showed that the first approach allows to obtain graft copolymers with a PI backbone and relatively short PCL side chains. While the implementation of the second approach leads to a more significant increase in the molecular weight, but unreacted linear PCL remains in the system. Obtained macroinitiators and copolymers were characterized using ¹H NMR and IR spectroscopy, their molecular weight characteristics were determined by SEC with triple detection. TGA and DSC were used to determine their thermal properties. X-ray scattering data showed that the introduction of a polyimide block into the polycaprolactone matrix did not change the degree of crystallinity of PCL.

Recent Progress in 1H-1,2,3-triazoles as Potential Antifungal Agents

The need to overcome ever-increasing cases of antifungal resistance and circumvent side effects and drug interactions related to currently available drugs has impelled the demand to expedite the drug discovery and the development of novel antifungals. 1,4-disubstituted 1,2,3-triazole has gained tremendous interest in the last two decades mainly because of its ease of synthesis via copper( I)-catalyzed azide-alkyne cycloaddition (CuAAC) and its broad spectrum of chemotherapeutic potential. 1,2,3-Triazole is an excellent pharmacophore that has been used as a bioisostere for obtaining libraries of new medicinally important scaffolds. The present review focuses on the recent advances (2016-2021) in 1,2,3-triazole derivatives obtained by CuAAC as potential antifungal agents that may facilitate the triazole-based antifungal development process.

Evaluation of a photo-initiated copper(I)-catalyzed azide-alkyne cycloaddition polymer network with improved water stability and high mechanical performance as an ester-free dental restorative

OBJECTIVE

The objective is to develop and characterize an ester-free ether-based photo-CuAAC resin with high mechanical performance, low polymerization-induced stress compared with common BisGMA/TEGDMA (70/30) resins, and improved water stability in comparison to previously developed urethane-based photo-CuAAC resins.

METHODS

Triphenyl-ethane-centered ether-linked tri-azide monomers were synthesized and co-photopolymerized with ether-linked tri-alkyne monomers under visible light irradiation using a copper(II) pre-catalyst and CQ/EDAB as the initiator. The ether-based CuAAC formulation was investigated for thermo-mechanical properties, polymerization kinetics and shrinkage stress, and flexural properties with respect to a conventional BisGMA/TEGDMA (70/30) dental resin. In addition, both the ether-based CuAAC resin and the urethane-based CuAAC resin were examined for their water stability using the BisGMA/TEGDMA (70/30) resin as a control.

RESULTS

The ether-based CuAAC network (AK/AZ-1) exhibited a slightly lower glass-transition temperature compared with the BisGMA/TEGDMA network (108 °C vs 128 °C), but because of its much sharper glass transition, the AK/AZ-1 CuAAC-network maintained storage modulus higher than 1 GPa up to 100 °C. In addition, the ether-based AK/AZ-1 network exhibited reduced shrinkage stress (0.56 MPa vs 1.0 MPa) and much higher flexural toughness (7.6 MJ/m³vs 1.6 MJ/m³) while showing slightly lower flexural modulus and slightly higher flexural strength compared with the BisGMA/TEGDMA network. Moreover, the ether-based AK/AZ-1 CuAAC network displayed comparable water stability in comparison to the BisGMA/TEGDMA network with slightly higher water sorption (46 μg/mm³vs 38 μg/mm³) and much lower water solubility (2.3 μg/mm³vs 4.4 μg/mm³).

SIGNIFICANCE

Employing the ether-based hydrophobic CuAAC formulation significantly improved the water stability of the CuAAC network compared with previously developed urethane-based CuAAC networks. Furthermore, compared with the conventionally used BisGMA/TEGDMA formulation, the reduced shrinkage stress, comparable flexural strength/flexural modulus, and the superior flexural toughness of the ether-based CuAAC network make it a promising ester-free alternative to the currently widely-used methacrylate-based dental restoratives.

Differential Labeling of Chemically Modified Peptides and Lipids among Cyanobacteria Planktothrix and Microcystis

The cyanoHAB forming cyanobacteria Microcystis and Planktothrix frequently produce high intracellular amounts of microcystins (MCs) or anabaenopeptins (APs). In this study, chemically modified MCs and APs have been localized on a subcellular level in Microcystis and Planktothrix applying copper-catalyzed alkyne-azide cycloaddition (CuACC). For this purpose, three different non-natural amino acids carrying alkyne or azide moieties were fed to individual P. agardhii strains No371/1 and CYA126/8 as well as to M. aeruginosa strain Hofbauer showing promiscuous incorporation of various amino acid substrates during non-ribosomal peptide synthesis (NRPS). Moreover, CYA126/8 peptide knock-out mutants and non-toxic strain Synechocystis PCC6803 were processed under identical conditions. Simultaneous labeling of modified peptides with ALEXA405 and ALEXA488 and lipid staining with BODIPY 505/515 were performed to investigate the intracellular location of the modified peptides. Pearson correlation coefficients (PCC) obtained from confocal images were calculated between the different fluorophores and the natural autofluorescence (AF), and between labeled modified peptides and dyed lipids to investigate the spatial overlap between peptides and the photosynthetic complex, and between peptides and lipids. Overall, labeling of modified MCs (M. aeruginosa) and APs (P. agardhii) using both fluorophores revealed increased intensity in MC/AP producing strains. For Synechocystis lacking NRPS, no labeling using either ALEXA405 or ALEXA488 was observed. Lipid staining in M. aeruginosa and Synechocystis was intense while in Planktothrix it was more variable. When compared with AF, both modified peptides and lipids showed a heterologous distribution. In comparison, the correlation between stained lipids and labeled peptides was not increased suggesting a reduced spatial overlap.

CuAAC mediated synthesis of cyclen cored glycodendrimers of high sugar tethers at low generation

Glycodendrimers are receiving considerable attention to mimic a number of imperative features of cell surface glycoconjugate and acquired excellent relevance to a wide domain of investigations including medicine, pharmaceutics, catalysis, nanotechnology, carbohydrate-protein interaction, and moreover in drug delivery systems. Toward this end, an expeditious, modular, and regioselective triazole-forming CuAAC click approach along with double stage convergent synthetic method was chosen to develop a variety of novel chlorine-containing cyclen cored glycodendrimers of high sugar tethers at low generation of promising therapeutic potential. We developed a novel chlorine-containing hypercore unit with 12 alkynyl functionality originated from cyclen scaffold which was confirmed by its single crystal X-ray data analysis. Further, the modular CuAAC technique was utilized to produce a variety of novel 12-sugar coated (G₀) glycodendrimers 12-15 adorn with β-Glc-, β-Man-, β-Gal-, β-Lac, along with 36-galactose coated (G₁) glycodendrimer 18 in good-to-high yield. The structures of the developed glycodendrimer architectures have been well elucidated by extensive spectral analysis including NMR (¹H & ¹³CNMR), HRMS, MALDI-TOF MS, UV-Vis, IR, and SEC (Size Exclusion Chromatogram) data.

Development of tacrine clusters as positively cooperative systems for the inhibition of acetylcholinesterase

The synthesis of four tetra-tacrine clusters where the tacrine binding units are attached to a central scaffold via linkers of variable lengths is described. The multivalent inhibition potencies for the tacrine clusters were investigated for the inhibition of acetylcholinesterase. Two of the tacrine clusters displayed a small but significant multivalent inhibition potency in which the binding affinity of each of the tacrine binding units increased up to 3.2 times when they are connected to the central scaffold.

Chemoenzymatic labeling of RNA to enrich, detect and identify methyltransferase-target sites

The RNA methyltransferase (MTase) complex METTL3-METTL14 transfers methyl groups from S-adenosyl-l-methionine (AdoMet) to the N⁶-position of adenosines within its consensus sequence, the DRACH motif (D=A, G, U; R=A, G; H=A, C, U). Interestingly, this MTase complex shows remarkable promiscuity regarding the cosubstrate. This can be exploited to install nonnatural modifications, like clickable or photocaging groups. Clickable groups are widely used for subsequent functionalization and open a broad range of possibilities for downstream applications. Here, we elaborate on click chemistry for coupling of RNA to biotin to enrich MTase targets via streptavidin-coated magnetic beads. Importantly, after clicking and coupling to beads the modification becomes sterically demanding and stalls reverse transcriptases, leading to termination adjacent to the MTase target site. Using radioactively labeled primers in the reverse transcription, the modified position can be precisely identified on a sequencing gel via phosphor imaging.

Solid-Phase Synthesis of RNA 5'-Azides and Their Application for Labeling, Ligation, and Cyclization Via Click Chemistry

RNAs with 5' functional groups have been gaining interest as molecular probes and reporter molecules. Copper-catalyzed azide-alkyne cycloaddition is one of the most straightforward methods to access such molecules; however, RNA functionalization with azide group has been posing a synthetic challenge. This article describes a simple and efficient protocol for azide functionalization of oligoribonucleotides 5'-end in solid-phase. An azide moiety is attached directly to the C5'-end in two steps: (i) -OH to -I conversion using methyltriphenoxyphosphonium iodide, and (ii) -I to -N₃ substitution using sodium azide. The reactivity of the resulting compounds is exemplified by fluorescent labeling using both copper(I)-catalyzed (CuAAC) and strain-promoted (SPAAC) azide-alkyne cycloaddition reactions, ligation of two RNA fragments, and cyclization of short bifunctionalized oligonucleotides. The protocol makes use of oligoribonucleotides synthesized by standard phosphoramidite approach on solid support, using commercially available 2'-O-PivOM-protected monomers. Such a protection strategy eliminates the interference between the iodination reagent and silyl protecting groups (TBDMS, TOM) commonly used in RNA synthesis by phosphoramidite approach. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Solid-phase synthesis of oligoribonucleotide 5'-azides Basic Protocol 2: CuAAC labeling of oligoribonucleotide 5'-azides in solution Alternate Protocol 1: CuAAC labeling of oligoribonucleotide 5'-azides on solid support Basic Protocol 3: SPAAC labeling of oligoribonucleotide 5'-azides Basic Protocol 4: CuAAC ligation of oligoribonucleotide 5'-azides Basic Protocol 5: CuAAC cyclization of oligoribonucleotide 5'-azides Support Protocol: HPLC Purification.

Development of Diverse Range of Biologically Relevant Carbohydrate-Containing Molecules: Twenty Years of Our Journey*

There is an increasing demand for significant amount of carbohydrate-containing molecules owing to their complete chemical, biological, and pharmacological investigations to better understand their role in many important biological events. Clinical studies of a wide range of simple carbohydrates or their derivatives, glycohybrids, glycoconjugates, and neoglycoconjugates have been conducted worldwide for the successful treatment of various frontline diseases. Herein, a brief perspective of carbohydrate-based molecular scaffolding and my experience during the last 20 years in the area of synthetic carbohydrate chemistry, mainly for their impact in drug discovery & development, is presented.

Metabolic and conformational stabilization of a VEGF-mimetic beta-hairpin peptide by click-chemistry

HPLW is a Vascular Endothelial Growth Factor (VEGF)-mimicking beta-hairpin peptide endowed of proangiogenic effect and showing valuable biomedical application in the proangiogenic therapy. However, the translational potential of HPLW is limited by its low metabolic stability, which would shorten the in vivo efficacy of the molecule. Here, we developed a peptide analog of HPLW, named HPLW2, that retains the structural and biological properties of the original peptide but features an impressive resistance to degradation by human serum proteases. HPLW2 was obtained by covalently modifying the chemical structure of the peptide with molecular tools known to impart protease resistance. Notably, the peptide was cyclized by installing an interstrand triazole bridge through Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) reaction. HPLW2 appears as a novel and promising drug candidate with potential biomedical application in the proangiogenic therapy as a low molecular weight drug, alternative to the use of VEGF. Our work points out the utility of the interstrand triazole bridge as effective chemical platform for the conformational and metabolic stabilization of beta-hairpin bioactive peptides.

Triazole-Modified Peptidomimetics: An Opportunity for Drug Discovery and Development

Peptidomimetics play a fundamental role in drug design due to their preferential properties regarding natural peptides. In particular, compounds possessing nitrogen-containing heterocycles have been intensively studied in recent years. The triazolyl moiety incorporation decreases the molecule susceptibility to enzymatic degradation, reduction, hydrolysis, and oxidation. In fact, peptides containing triazole rings are a typical example of peptidomimetics. They have all the advantages over classic peptides. Both efficient synthetic methods and biological activity make these systems an interesting and promising object of research. Peptide triazole derivatives display a diversity of biological properties and can be obtained via numerous synthetic strategies. In this review, we have highlighted the importance of the triazole-modified peptidomimetics in the field of drug design. We present an overview on new achievements in triazolyl-containing peptidomimetics synthesis and their biological activity as inhibitors of enzymes or against cancer, viruses, bacteria, or fungi. The relevance of above-mentioned compounds was confirmed by their comparison with unmodified peptides.

1,2,3-Triazoles as Biomimetics in Peptide Science

Natural peptides are an important class of chemical mediators, essential for most vital processes. What limits the potential of the use of peptides as drugs is their low bioavailability and enzymatic degradation in vivo. To overcome this limitation, the development of new molecules mimicking peptides is of great importance for the development of new biologically active molecules. Therefore, replacing the amide bond in a peptide with a heterocyclic bioisostere, such as the 1,2,3-triazole ring, can be considered an effective solution for the synthesis of biologically relevant peptidomimetics. These 1,2,3-triazoles may have an interesting biological activity, because they behave as rigid link units, which can mimic the electronic properties of amide bonds and show bioisosteric effects. Additionally, triazole can be used as a linker moiety to link peptides to other functional groups.

Chitotriazolan (poly(β(1-4)-2-(1H-1,2,3-triazol-1-yl)-2-deoxy-d-glucose)) derivatives: Synthesis, characterization, and evaluation of antibacterial activity

Here we describe the first synthesis of a new type of polysaccharides derived from chitosan. In these structures, the 2-amino group on the pyranose ring was quantitively replaced by an aromatic 1,2,3-triazole moiety. The 2-amino group of chitosan and di-TBDMS chitosan was converted into an azide by diazo transfer reaction. The chitosan azide and TBDMS-chitosan azide were poorly soluble but could be fully converted to triazoles by "copper-catalysed Huisgen cycloaddition" in DMF or DMSO. The reaction could be done with different alkynes but derivatives lacking cationic or anionic groups were poorly soluble or insoluble in tested aqueous and organic solvents. Derivatives with N,N-dimethylaminomethyl, N,N,N-trimethylammoniummethyl, sulfonmethyl, and phosphomethyl groups linked to the 4-position of the triazole moiety were soluble in water at neutral or basic conditions and could be analyzed by ¹H, ¹³C APT, COSY, and HSQC NMR. The quaternized cationic chitotriazolan's had high activity against S. aureus and E. coli, whereas the anionic chitotriazolan's lacked activity.

Synthesis and Antiproliferative Activity of Triazoles Based on 2-Azabicycloalkanes

A library of 21 novel chiral 1,2,3-triazole-based 2-azabicycloalkane conjugates was designed and synthesized using the copper(I)-catalyzed click reaction. The obtained hybrids were assessed for their antiproliferative potency against three selected human cancer cell lines: Hs294T (melanoma), MIA PaCa-2 (pancreas tumor) and NCI-H1581 (lung tumor). The majority of the synthesized compounds demonstrated moderate to potent activity, and some of them appeared more selective than cisplatin, with selectivity index exceeding 9.