Click Chemistry for the Generation of Combination of Triazole Core and Thioether Donor Site in Organosulfur Ligands: Applications of Metal Complexes in Catalysis

During the last two decades, organosulfur compounds have been used in the field of transition metal catalysis. Some of such compounds are known for their ability to withstand their exposure to air and moisture. These compounds are very important ligands. They may be obtained using simple and smooth modular synthetic protocols which include nucleophilic substitution reactions. The development of click chemistry represents a new era of innovation. It is a lighthouse of reliable and efficient reactions. In recent past, click chemistry has also been applied for the synthesis of such organosulfur ligands specifically suited for the dynamic field of transition metal catalysis. In order to synthesize novel compounds containing sulfur and triazole ring, click chemistry is an advantageous methodology over other approaches. This article covers the general features and uses of this methodology for the development of catalytically active organosulfur compounds. The significant advances in the design of transition metal catalytic systems utilizing such ligands, their use in the catalysis of many chemical transformations are also covered in this article. Effort has also been made to present a comparative overview of the performances of such catalysts vis-à-vis the catalysts designed commonly used ligands. Catalytic performances have been discussed thoroughly in order to identify the impact of ligand architecture on efficacy of the catalyst. Effect of reaction conditions (such as time, temperature etc.) and mechanistic aspects have also been rationalized.

Active template synthesis

The active template synthesis of mechanically interlocked molecular architectures exploits the dual ability of various structural elements (metals or, in the case of metal-free active template synthesis, particular arrangements of functional groups) to serve as both a template for the organisation of building blocks and as a catalyst to facilitate the formation of covalent bonds between them. This enables the entwined or threaded intermediate structure to be covalently captured under kinetic control. Unlike classical passive template synthesis, the intercomponent interactions transiently used to promote the assembly typically do not 'live on' in the interlocked product, meaning that active template synthesis can be traceless and used for constructing mechanically interlocked molecules that do not feature strong binding interactions between the components. Since its introduction in 2006, active template synthesis has been used to prepare a variety of rotaxanes, catenanes and knots. Amongst the metal-ion-mediated versions of the strategy, the copper(I)-catalysed alkyne-azide cycloaddition (CuAAC) remains the most extensively used transformation, although a broad range of other catalytic reactions and transition metals also provide effective manifolds. In metal-free active template synthesis, the recent discovery of the acceleration of the reaction of primary amines with electrophiles through the cavity of crown ethers has proved effective for forming an array of rotaxanes without recognition elements, including compact rotaxane superbases, dissipatively assembled rotaxanes and molecular pumps. This Review details the active template concept, outlines its advantages and limitations for the synthesis of interlocked molecules, and charts the diverse set of reactions that have been used with this strategy to date. The application of active template synthesis in various domains is discussed, including molecular machinery, mechanical chirality, catalysis, molecular recognition and various aspects of materials science.

Polypeptide-based multilayer nanoarchitectures: Controlled assembly on planar and colloidal substrates for biomedical applications

Polypeptides have shown an excellent potential in nanomedicine thanks to their biocompatibility, biodegradability, high functionality, and responsiveness to several stimuli. Polypeptides exhibit high propensity to organize at the supramolecular level; hence, they have been extensively considered as building blocks in the layer-by-layer (LbL) assembly. The LbL technique is a highly versatile methodology, which involves the sequential assembly of building blocks, mainly driven by electrostatic interactions, onto planar or colloidal templates to fabricate sophisticated multilayer nanoarchitectures. The simplicity and the mild conditions required in the LbL approach have led to the inclusion of biopolymers and bioactive molecules for the fabrication of a wide spectrum of biodegradable, biocompatible, and precisely engineered multilayer films for biomedical applications. This review focuses on those examples in which polypeptides have been used as building blocks of multilayer nanoarchitectures for tissue engineering and drug delivery applications, highlighting the characteristics of the polypeptides and the strategies adopted to increase the stability of the multilayer film. Cross-linking is presented as a powerful strategy to enhance the stability and stiffness of the multilayer network, which is a fundamental requirement for biomedical applications. For example, in tissue engineering, a stiff multilayer coating, the presence of adhesion promoters, and/or bioactive molecules boost the adhesion, growth, and differentiation of cells. On the contrary, antimicrobial coatings should repel and inhibit the growth of bacteria. In drug delivery applications, mainly focused on particles and capsules at the micro- and nano-meter scale, the stability of the multilayer film is crucial in terms of retention and controlled release of the payload. Recent advances have shown the key role of the polypeptides in the adsorption of genetic material with high loading efficiency, and in addressing different pathways of the particles/capsules during the intracellular uptake, paving the way for applications in personalized medicine. Although there are a few studies, the responsiveness of the polypeptides to the pH changes, together with the inclusion of stimuli-responsive entities into the multilayer network, represents a further key factor for the development of smart drug delivery systems to promote a sustained release of therapeutics. The degradability of polypeptides may be an obstacle in certain scenarios for the controlled intracellular release of a drug once an external stimulus is applied. Nowadays, the highly engineered design of biodegradable LbL particles/capsules is oriented on the development of theranostics that, limited to use of polypeptides, are still in their infancy.

One-pot chemo- and photo-enzymatic linear cascade processes

The combination of chemo- and photocatalyses with biocatalysis, which couples the flexible reactivity of the photo- and chemocatalysts with the highly selective and environmentally friendly nature of enzymes in one-pot linear cascades, represents a powerful tool in organic synthesis. However, the combination of photo-, chemo- and biocatalysts in one-pot is challenging because the optimal operating conditions of the involved catalyst types may be rather different, and the different stabilities of catalysts and their mutual deactivation are additional problems often encountered in one-pot cascade processes. This review explores a large number of transformations and approaches adopted for combining enzymes and chemo- and photocatalytic processes in a successful way to achieve valuable chemicals and valorisation of biomass. Moreover, the strategies for solving incompatibility issues in chemo-enzymatic reactions are analysed, introducing recent examples of the application of non-conventional solvents, enzyme-metal hybrid catalysts, and spatial compartmentalization strategies to implement chemo-enzymatic cascade processes.

Hetero-Diels-Alder and CuAAC Click Reactions for Fluorine-18 Labeling of Peptides: Automation and Comparative Study of the Two Methods

Radiolabeled peptides are valuable tools for diagnosis or therapies; they are often radiofluorinated using an indirect approach based on an F-18 prosthetic group. Herein, we are reporting our results on the F-18 radiolabeling of three peptides using two different methods based on click reactions. The first one used the well-known CuAAC reaction, and the second one is based on our recently reported hetero-Diels-Alder (HDA) using a dithioesters (thia-Diels-Alder) reaction. Both methods have been automated, and the 18F-peptides were obtained in similar yields and synthesis time (37-39% decay corrected yields by both methods in 120-140 min). However, to obtain similar yields, the CuAAC needs a large amount of copper along with many additives, while the HDA is a catalyst and metal-free reaction necessitating only an appropriate ratio of water/ethanol. The HDA can therefore be considered as a minimalist method offering easy access to fluorine-18 labeled peptides and making it a valuable additional tool for the indirect and site-specific labeling of peptides or biomolecules.

Tetrabutylammonium iodide-catalyzed oxidative α-azidation of β-ketocarbonyl compounds using sodium azide

We herein report the oxidative α-azidation of carbonyl compounds by using NaN3 in the presence of dibenzoyl peroxide catalyzed by tetrabutylammonium iodide (TBAI). By utilizing these readily available bulk chemicals a variety of cyclic β-ketocarbonyl derivatives can be efficiently α-azidated under operationally simple conditions. Control experiments support a mechanistic scenario involving in situ formation of an ammonium hypoiodite species which first facilitates the α-iodination of the pronucleophile, followed by a phase-transfer-catalyzed nucleophilic substitution by the azide. Furthermore, we also show that an analogous α-nitration by using NaNO2 under otherwise identical conditions is possible as well.

1,5-disubstituted 1,2,3-triazolylated carbohydrates and nucleosides

In general, 1,5-disubstituted 1,2,3-triazolyl moiety is much less common in the synthesis and applications in comparison to its regioisomeric counterpart. Moreover, the synthesis of 1,5-disubstituted 1,2,3-triazoles are not so straightforward as is the case for copper catalyzed strategy of 1,4-disubstituted 1,2,3-triazoles. The preparation of 1,5-triazolylated carbohydrates and nucleosides are even more complex because of the difficulties in accessing the appropriate starting materials as well as the compatibility of reaction conditions with the various protecting groups. 1,5-Disubstitution regioisomeric triazoles of carbohydrates and nucleosides were traditionally obtained as minor products through straightforward heating of the mixture of azides and terminal alkynes. However, the separation of isomers was tedious or in some cases futile. On the other hand, regioselective synthesis using ruthenium catalysis triggered serious concern of residual metal content in therapeutically important ingredients. Therefore, serious efforts are being made by several groups to develop non-toxic metal based or completely metal-free synthesis of 1,5-disubstituted 1,2,3-triazoles. This article strives to summarize the pre-Click era as well as the post-2001 reports on the synthesis and potential applications of 1,5-disubstituted 1,2,3-triazoles in biological systems.

Synthesis of PEGylated amphiphilic block copolymers with pendant linoleic moieties by combining ring-opening polymerization and click chemistry

This study focused on synthesizing and characterizing PEGylated amphiphilic block copolymers with pendant linoleic acid (Lin) moieties as an alternative to enhance their potential in drug delivery applications. The synthesis involved a two-step process, starting with ring-opening polymerization of ε-caprolactone (CL) and propargylated cyclic carbonate (MCP) to obtain PEG-b-P(CL-co-MCP) copolymers, which were subsequently modified via click chemistry. Various reaction conditions were explored to improve the yield and efficiency of the click chemistry step. The use of anisole as a solvent, N-(3-azidopropyl)linoleamide as a substrate, and a reaction temperature of 60°C proved to be highly efficient, achieving nearly 100% conversion at a low catalyst concentration. The resulting copolymers exhibited controlled molecular weights and low polydispersity, confirming the successful synthesis. Furthermore, click chemistry allows for the attachment of Lin moieties to the copolymer, enhancing its hydrophobic character, as deduced from their significantly lower critical micelle concentration than that of traditional PEG-b-PCL systems, which is indicative of enhanced stability against dilution. The modified copolymers exhibited improved thermal stability, making them suitable for applications that require high processing temperatures. Dynamic light scattering and transmission electron microscopy confirmed the formation of micellar structures with sizes below 100 nm and minimal aggregate formation. Additionally, 1H NMR spectroscopy in deuterated water revealed the presence of core-shell micelles, which provided higher kinetic stability against dilution.

Fifty Shades of Phenanthroline: Synthesis Strategies to Functionalize 1,10-Phenanthroline in All Positions

1,10-Phenanthroline (phen) is one of the most popular ligands ever used in coordination chemistry due to its strong affinity for a wide range of metals with various oxidation states. Its polyaromatic structure provides robustness and rigidity, leading to intriguing features in numerous fields (luminescent coordination scaffolds, catalysis, supramolecular chemistry, sensors, theranostics, etc.). Importantly, phen offers eight distinct positions for functional groups to be attached, showcasing remarkable versatility for such a simple ligand. As a result, phen has become a landmark molecule for coordination chemists, serving as a must-use ligand and a versatile platform for designing polyfunctional arrays. The extensive use of substituted phenanthroline ligands with different metal ions has resulted in a diverse array of complexes tailored for numerous applications. For instance, these complexes have been utilized as sensitizers in dye-sensitized solar cells, as luminescent probes modified with antibodies for biomaterials, and in the creation of elegant supramolecular architectures like rotaxanes and catenanes, exemplified by Sauvage's Nobel Prize-winning work in 2016. In summary, phen has found applications in almost every facet of chemistry. An intriguing aspect of phen is the specific reactivity of each pair of carbon atoms ([2,9], [3,8], [4,7], and [5,6]), enabling the functionalization of each pair with different groups and leading to polyfunctional arrays. Furthermore, it is possible to differentiate each position in these pairs, resulting in non-symmetrical systems with tremendous versatility. In this Review, the authors aim to compile and categorize existing synthetic strategies for the stepwise polyfunctionalization of phen in various positions. This comprehensive toolbox will aid coordination chemists in designing virtually any polyfunctional ligand. The survey will encompass seminal work from the 1950s to the present day. The scope of the Review will be limited to 1,10-phenanthroline, excluding ligands with more intracyclic heteroatoms or fused aromatic cycles. Overall, the primary goal of this Review is to highlight both old and recent synthetic strategies that find applicability in the mentioned applications. By doing so, the authors hope to establish a first reference for phenanthroline synthesis, covering all possible positions on the backbone, and hope to inspire all concerned chemists to devise new strategies that have not yet been explored.

Each Interruption is an Opportunity: Novel Synthetic Strategies Explored Through Interrupted Click Reactions

The particular and unique mechanism of the copper-catalyzed reaction between azides and alkynes (CuAAC) has not only allowed for the efficient synthesis of 1,2,3-trisubstituted 1,4-triazoles in excellent yields and under mild conditions, becoming the quintessential click reaction, but it has also enabled the straightforward formation of a metallocycle intermediate, the copper triazolyl. This, under suitable reaction conditions able to suppress its protonolysis, can be used either for the creation of new bicyclic triazolyl structures or for the generation of novel three or four-component reactions. The aim of this review is to rationalize and unify all these transformations, which are collectively referred to as "interrupted click reactions".

Influence of Surface Chemistry on Host/Guest Interactions: A Model Study on Redox-Sensitive β-Cyclodextrin/Ferrocene Complexes

While host/guest interactions are widely used to control molecular assembly on surfaces, quantitative information on the effect of surface chemistry on their efficiency is lacking. To address this question, we combined electrochemical characterization with quartz crystal microbalance with dissipation monitoring to study host/guest interactions between surface-attached ferrocene (Fc) guests and soluble β-cyclodextrin (β-CD) hosts. We identified several parameters that influence the redox response, β-CD complexation ability, and repellent properties of Fc monolayers, including the method of Fc grafting, the linker connecting Fc with the surface, and the diluting molecule used to tune Fc surface density. The study on monovalent β-CD/Fc complexation was completed by the characterization of multivalent interactions between Fc monolayers and β-CD-functionalized polymers, with new insights being obtained on the interplay between the surface chemistry, binding efficiency, and reversibility under electrochemical stimulus. These results should facilitate the design of well-defined functional interfaces and their implementation in stimuli-responsive materials and sensing devices.

Biocompatible strategies for peptide macrocyclisation

Peptides are increasingly important drug candidates, offering numerous advantages over conventional small molecules. However, they face significant challenges related to stability, cellular uptake and overall bioavailability. While individual modifications may not address all these challenges, macrocyclisation stands out as a single modification capable of enhancing affinity, selectivity, proteolytic stability and membrane permeability. The recent successes of in situ peptide modifications during screening in combination with genetically encoded peptide libraries have increased the demand for peptide macrocyclisation reactions that can occur under biocompatible conditions. In this perspective, we aim to distinguish biocompatible conditions from those well-known examples that are fully bioorthogonal. We introduce key strategies for biocompatible peptide macrocyclisation and contextualise them within contemporary screening methods, providing an overview of available transformations.

Design, synthesis, and anticancer evaluation of alkynylated pyrrole derivatives

A series of alkynylated pyrrole derivatives were meticulously designed, drawing inspiration from the structure of 3-alkynylpyrrole-2,4-dicarboxylates, which were synthesized via a cyclization process involving methylene isocyanides and propiolaldehydes under mild conditions. These derivatives were subsequently subjected to evaluation for their anticancer properties against a panel of cell lines, including U251, A549, 769-P, HepG2, and HCT-116. According to the detailed analysis of structure-activity relationship, compound 12l emerged as the most promising molecule, with IC50 values of 2.29 ± 0.18 and 3.49 ± 0.30 μM toward U251 and A549 cells, respectively. Subsequent mechanistic investigations revealed that compound 12l exerts its effects by arresting the cell cycle in the G0/G1 phase and inducing apoptosis specifically in A549 cells. These innovative alkynylated pyrrole derivatives hold the potential to serve as a valuable template for the discovery of novel anticancer molecules.

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.

Synthesis of Novel Fluoro Phenyl Triazoles Via Click Chemistry with or without Microwave Irradiation and their Evaluation as Anti-proliferative Agents in SiHa Cells

AIMS

Perform the synthesis of novel fluoro phenyl triazoles via click chemistry with or without microwave irradiation and their evaluation as anti-proliferative agents in SiHa cells.

BACKGROUND

Triazoles are heterocyclic compounds containing a five-member ring with two carbon and three nitrogen atoms. They are of great importance since many of them have shown to have biological activity as antifungal, antiviral, antibacterial, anti-HIV, anti-tuberculosis, vasodilator, and anticancer agents.

OBJECTIVES

Synthesize novel fluoro phenyl triazoles via click chemistry and evaluate their antiproliferative activity.

METHODS

First, several fluorophenyl azides were prepared. Reacting these aryl azides with phenylacetylene in the presence of Cu(I) catalyst, the corresponding fluoro phenyl triazoles were obtained by two methodologies, stirring at room temperature and under microwave irradiation at 40ºC. In addition, their antiproliferative activity was evaluated in cervical cancer SiHa cells.

RESULTS

Fluoro phenyl triazoles were obtained within minutes by means of microwave irradiation. The compound 3f, containing two fluorine atoms next to the carbon connected to the triazole ring, was the most potent among the fluoro phenyl triazoles tested in this study. Interestingly, the addition of a fluorine atom to the phenyl triazole structure in a specific site increases its antiproliferative effect as compared to parent phenyl triazole 3a without a fluorine atom.

CONCLUSION

Several fluoro phenyl triazoles were obtained by reacting fluoro phenyl azides with phenylacetylene in the presence of copper sulphate, sodium ascorbate and phenanthroline. Preparation of these triazoles with MW irradiation represents a better methodology since they are obtained within minutes and higher yields of cleaner compounds are obtained. In terms of biological studies, the proximity between fluorine atom and triazole ring increases its biological activity.

Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

The synthesis of zwitterionic dithiocarboxylate adducts was achieved by deprotonating various aldiminium or 1,2,3-triazolium salts with a strong base, followed by the nucleophilic addition of the in situ-generated cyclic (alkyl)(amino) or mesoionic carbenes (CAACs or MICs) onto carbon disulfide. Nine novel compounds were isolated and fully characterized by 1H and 13C NMR, FTIR, and HRMS techniques. Moreover, the molecular structures of two CAAC·CS2 and two MIC·CS2 betaines were determined by X-ray diffraction analysis. The analytical data recorded for all these adducts were compared with those reported previously for related NHC·CS2 betaines derived from imidazolinium or (benz)imidazolium salts. Due to the absence of electronic communication between the CS2 unit and the orthogonal heterocycle, all the CAAC·CS2, MIC·CS2, and NHC·CS2 zwitterions displayed similar electronic properties and featured the same bite angle. Yet, their steric properties are liable to ample modifications by varying the exact nature of their cationic heterocycle and its substituents.

Synthetic non-toxic anti-biofilm agents as a strategy in combating bacterial resistance

The tremendous increase in the bacterial resistance to the available antibiotics is a serious problem for the treatment of various infections. Biofilm formation in bacteria significantly contributes to the bacterial survival in host cells, and is considered as an crucial factor, responsible for bacterial resistance. The response of the bacterial cells in the biofilm to antibiotics is completely different from that of the free floating planktonic cells of the same strain. The anti-biofilm agents that could inhibit the biofilm production without affecting the bacterial growth, apply less selective pressure over the bacterial strains than the traditional antibiotics; thus the development of bacterial resistance would be of low incidence. Many attempts have been performed to discover novel agents capable of interfering with the bacterial biofilm life cycle, and several compounds have shown promising activities in suppressing the biofilm production or in dispersing mature existing biofilms. This review describes the different chemical classes that have anti-biofilm effects against different Gram-positive and Gram-negative bacteria without affecting the bacterial growth.

1,2-Bis(triazolyl)tetraphenyldigermanes: Synthesis, Structure and Properties

Using the [3+2] cycloaddition reaction of [HC≡C-GePh2 -]2 (1) and a number of RCH2 N3 , this work described the synthesis of a series of novel heterocyclic digermanes, bitriazoles [1,4-C2 HN3 (CH2 R)GePh2 -]2 , 2-12 (R=Ph, p-Tol, p-C6 H4 NMe2 , p-C6 H4 OMe, p-C6 H4 Br, m-C6 H4 NO2 , 2-Naphth, CH2 -p-OC6 H4 CHO, CH2 -p-OC6 H4 COOMe, CH2 P(O)(OEt)2 , COOEt), difficult to produce by other methods. The structural peculiarities of these compounds were studied in detail by NMR spectroscopy and by XRD analysis (for 6, 9 and 10). The properties of 1-12 were studied by UV/vis and luminescence emission spectroscopy, electrochemistry and DFT calculations, indicating an effective conjugation in their molecules.

Fast synthesis of [1,2,3]-triazole derivatives on a Fe/Cu-embedded nano-catalytic substrate

Triazoles are biologically important compounds that play a crucial role in biomedical applications. In this study, we present an innovative and eco-friendly nanocatalyst system for synthesizing compounds via the click reaction. The system is composed of Arabic gum (AG), iron oxide magnetic nanoparticles (Fe3O4 MNPs), (3-chloropropyl) trimethoxysilane (CPTMS), 2-aminopyridine (AP), and Cu(i) ions. Using AP as an anchor for Cu(i) ions and Fe3O4 MNPs allows facile separation using an external magnet. The hydrophilic nature of the Fe3O4@AG/AP-Cu(i) nanocomposite makes it highly efficient in water as a green solvent. The highest reaction efficiency (95.0%) was achieved in H2O solvent with 50.0 mg of nanocatalyst for 60 min at room temperature. The reaction yield remained consistent for six runs, demonstrating the stability and effectiveness of the catalyst.

Recent advances in synthesis of sugar and nucleoside coumarin conjugates and their biological impact

Naturally occurring coumarin and sugar molecules have a diverse range of applications along with superior biocompatibility. Coumarin, a member of the benzopyrone family, exhibits a wide spectrum of medicinal properties, such as anti-coagulant, anti-bacterial, anti-tumor, anti-oxidant, anti-cancer, anti-inflammatory and anti-viral activities. The sugar moiety functions as the central scaffold for the synthesis of complex molecules, attributing to their excellent biocompatibility, well-defined stereochemistry, benign nature and outstanding aqueous solubility. When the coumarin moiety is conjugated with the sugar or nucleoside molecule, the resulting conjugates exhibit significant biological properties. Due to the remarkable growth of such bioconjugates in the field of science over the last decade, owing to their future prospect as a potential bioactive core, an update to this area is very much needed. The present review focusses on the synthesis, characterization and the various therapeutic applications of coumarin conjugates, i.e., sugar and nucleoside coumarin conjugates along with their perspective for future research.

CuFe2O4@SiO2@L-arginine@Cu(I) as a new magnetically retrievable heterogeneous nanocatalyst with high efficiency for 1,4-disubstituted 1,2,3-triazoles synthesis

A novel magnetic heterogeneous catalyst was synthesized through the immobilization of copper ions onto the l-arginine functionalized CuFe₂O₄@SiO₂. The prepared catalyst was characterized by Fourier Transform Infrared (FT-IR), X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), and Energy Dispersive X-Ray spectroscopy (EDX). The resulting catalyst was used in the ultrasonic-assisted synthesis of 1,2,3-triazoles via a one-pot three-component reaction of alkynes, alkyl halides, and sodium azides under green conditions within a short time. The catalyst reusability was investigated after five cycles and no significant loss of activity was observed.

Copper(I)-Catalyzed Alkyne-Azide Cycloaddition (CuAAC) "Click" Reaction: A Powerful Tool for Functionalizing Polyhydroxylated Platforms

Click chemistry is currently one of the most used tools for the generation of complex organic molecules. The advantages of using click chemistry in organic synthesis are remarkable; in many cases, the reactions occur under mild conditions and are free of solvents, with high yields and short reaction times. This makes it an extraordinarily effective and viable alternative for obtaining complex/conjugated molecules. In this review, the use of click chemistry CuAAC is especially emphasized for polyhydroxylated platforms such as resorcinarenes or calixarenes, focusing mainly on aspects of synthesis, specifically conditions, reagents, and methodologies.

Computational studies of the CuAAC reaction mechanism with diimine and phosphorus ligands for the synthesis of 1,4-disubstituted 1,2,3-triazoles

The Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions with diimine and phosphorus ligands have been studied using DFT calculations in order to understand the effect of the nature of the ligands on the catalytic cycle for the formation of the 1,4-regioisomer.

Mechanistic Aspects on [3+2] Cycloaddition (32CA) Reactions of Azides to Nitroolefins: A Computational and Kinetic Study

[3+2] cycloadditions of nitroolefins have emerged as a selective and catalyst-free alternative for the synthesis of 1,2,3-triazoles from azides. We describe mechanistic studies into the cycloaddition/rearomatization reaction sequence. DFT calculations revealed a rate-limiting cycloaddition step proceeding via an asynchronous TS with high kinetic selectivity for the 1,5-triazole. Kinetic studies reveal a second-order rate law, and ¹³ C kinetic isotopic effects at natural abundance were measured with a significant normal effect at the conjugated olefinic centers of 1.0158 and 1.0216 at the α and β-carbons of β-nitrostyrene. Distortion/interaction-activation strain and energy decomposition analyses revealed that the major regioisomeric pathway benefits from an earlier and less-distorted TS, while intermolecular interaction terms dominate the preference for 1,5- over 1,4-cycloadducts. In addition, the major regioisomer also has more favorable electrostatic and dispersion terms. Additionally, while static DFT calculations suggest a concerted but highly asynchronous Ei-type HNO₂ elimination mechanism, quasiclassical direct-dynamics calculations reveal the existence of a dynamic intermediate.

Synthesis, computational study and biological evaluation of 9-acridinyl and 1-coumarinyl-1,2,3-triazole-4-yl derivatives as topoisomerase II inhibitors

Topoisomerase (IIB) inhibitors have been involved in the therapies of tumour progression and have become a major focus for the development of anticancer agents. New three-component hybridised ligands, 1,4-disubstituted-1,2,3-triazoles (8-17), were synthesised via a 1,3-dipolar cycloaddition reaction of 9-azidoacridine/3-azidocoumarin with N/O-propargyl small molecules under click reaction conditions. Cancer cell growth inhibition of the synthesised triazoles was tested against human cell-lines in the NCI-60-cell-panel, and the most active compounds tested against topoisomerase (IIB)-enzymes. The acridinyl ligands (8-10) revealed 60-97% cell growth inhibition in six cancer cell-panels. Cell-cycle analysis of MCF7 and DU-145 cells treated with the active acridinyl ligands exhibited cell-cycle arrest at G2/M phase and proapoptotic activity. In addition, compound 8 displayed greater inhibitory activity against topoisomerase (IIB) (IC50 0.52 µM) compared with doxorubicin (IC50 0.83 µM). Molecular dynamics simulation studies showed the acridine-triazole-pyrimidine hybrid pharmacophore was optimal with respect to protein-ligand interaction and fit within the binding site, with optimal orientation to allow for intercalation with the DNA bases (DG13, DC14, and DT9).

Click Chemistry-Enabled Conjugation Strategy for Producing Dibenzodiazepinone-Type Fluorescent Probes To Target M2 Acetylcholine Receptors

The development of fluorescently labeled receptor-targeting compounds represents a powerful pharmacological tool to study and characterize ligand-receptor interactions. Despite significant advances in developing sub-type-specific antagonists for muscarinic acetylcholine receptors (mAChRs), reports on antagonists feasible for click chemistry are less common. Here, we designed and synthesized an antagonist suitable for probe attachment through click chemistry, namely, dibenzodiazepinone (DIBA)-alkyne, based on a previously reported DIBA scaffold with a high binding affinity to type-2 mAChR (M2R). To demonstrate the versatility of DIBA-alkyne as a building block for bioconjugates, we assembled DIBA-alkyne with Cyanine5 fluorophores (Cy5) and polyethylene glycol (PEG) biomolecules to obtain fluorescent DIBA antagonist (DIBA-Cy5) and fluorescent DIBA PEG derivatives. Flow cytometric analysis showed that DIBA-Cy5 possessed a high binding affinity to M2R (Kd = 1.80 nM), a two-order magnitude higher binding affinity than M1R. Fluorescent DIBA PEG derivatives maintained a potent binding to the M2R (Kd ≤ 4 nM), confirmed by confocal microscopic imaging. Additionally, DIBA-Cy5 can serve as a fluorescent ligand in the receptor-ligand competitive binding assay for other mAChR ligands, an attractive alternative to the traditional radioligand-based assay. The competitive binding mode between DIBA-Cy5 and orthosteric antagonist atropine/allosteric modulator LY2119620 indicated a dualsteric binding mode of the DIBA-type antagonist to M2R. Lastly, we demonstrated the direct staining of DIBA-Cy5 to M2R receptors in the sinoatrial node of a mouse heart. The adaptability of the clickable DIBA antagonist to a wide range of fluorophores and biomolecules can facilitate its use in various biomedical applications such as binding assays that screen compounds for M2R as the receptor target.

Synthesized Phosphonium Compounds Demonstrate Resistant Modulatory and Antibiofilm Formation Activities against Some Pathogenic Bacteria

A library of six compounds with new hybrids in a single molecule triazole ring attached to the phosphonium salts was synthesized. Click chemistry was, however, used to synthesize the 1-, 2-, and 3-triazole intermediates as a tether for the hybrid phosphonium salts. Their antibacterial activity against Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), and Mycobacterium smegmatis mc2155 was determined using the HT-SPOTi assay. Compound 2 showed the most effective antimicrobial activity as it inhibited the growth of Pseudomonas aeruginosa and Staphylococcus aureus at 0.0125 µg/mL and 31.25 µg/mL, respectively. From the FICI data, compounds 2ET-TOL (2) and RABYL-TOL (4) successfully modulated the activities of amoxicillin against Pseudomonas aeruginosa and Staphylococcus aureus. All the test compounds exhibited a concentration-dependent biofilm formation inhibition against S. aureus, except P-Z (compound 6). Compounds P-MEOXY (1) and 2ET-TOL (2) exhibited mild activity against P. aeruginosa with compound 4 showing antimycobacterial activity at 500 µg/mL.

Conjugated Block Copolymers for Functional Nanostructures

Conjugated polymers have been actively studied as an alternative to inorganic semiconductors for their unique optical and electrical properties and low-cost solution processability. However, typical conjugated polymer films contain numerous defects that negatively affect their transport properties, which remains a major issue despite much effort to develop ways to improve the molecular packing structure. In principle, conjugated block copolymers (BCPs) composed of a rod-type conjugated polymer and a coil-type insulating polymer can assemble into various types of ordered nanostructures based on the microphase segregation of two polymer blocks. However, such assembly typically requires a relatively large volume fraction of the coil block or modification of the rod block, both of which tend to impede charge transport. As an alternative, we and others have fabricated nanoscale assemblies of conjugated BCPs via solution-phase self-assembly, which can be used as building blocks for construction of extended nanoarrays of conjugated polymers. In particular, BCPs containing poly(3-hexylthiophene) (P3HT), a conjugated polymer widely used for its high hole mobility, form highly ordered and technologically relevant one-dimensional (1D) nanowires with controlled lengths. A range of well-defined assembly structures such as square plates, ribbons, vesicles, and helices have been prepared from various conjugated BCPs, resembling those of peptide self-assembly, forming diverse nanostructures through combinations of π-π stacking, hydrogen bonding, and hydrophobic interactions.When the self-assembly of P3HT BCPs takes place at an air-water interface, the initially formed polymer nanowires further assemble into hierarchical two-dimensional (2D) nanoarrays with solvent evaporation. The fluidic nature of the water subphase allows fabrication of highly ordered assembly structures from P3HT BCPs with high P3HT content. The ultrathin free-standing film integrated in a field effect transistor (FET) showed orders of magnitude higher current and hole mobility compared to that fabricated by conventional spin-coating. Furthermore, binary self-assembly of a P3HT BCP and quantum dots (QDs) at the air-water interface generates well-ordered 2D films of alternating P3HT nanowires and 1D QD arrays. Unlike coil-coil BCP systems, QDs reside at the interface between P3HT and coil blocks for a broad range of QD sizes due to the strong P3HT packing interactions and the flexible water subphase, forming tight p-n junctions for enhanced photocurrent. Incorporation of magnetic nanoparticles can further improve the degree of order, enabling fabrication of long-range order and direction-controlled P3HT nanoarrays through magnetic-field induced self-assembly.The conjugated BCP approach is highly modular and can be combined with various types of functional molecules, polymers, and nanoparticles, offering a powerful platform for fabrication of functional polymer nanostructures with desired morphologies and properties. This Account introduces recent advances in the self-assembly of π-conjugated BCPs, describes how they differ from prototypical coil-coil type BCPs, and discusses current issues and future outlooks.

Catalysis and Electron Transfer in De Novo Designed Metalloproteins

One of the hallmark advances in our understanding of metalloprotein function is showcased in our ability to design new, non-native, catalytically active protein scaffolds. This review highlights progress and milestone achievements in the field of de novo metalloprotein design focused on reports from the past decade with special emphasis on de novo designs couched within common subfields of bioinorganic study: heme binding proteins, monometal- and dimetal-containing catalytic sites, and metal-containing electron transfer sites. Within each subfield, we highlight several of what we have identified as significant and important contributions to either our understanding of that subfield or de novo metalloprotein design as a discipline. These reports are placed in context both historically and scientifically. General suggestions for future directions that we feel will be important to advance our understanding or accelerate discovery are discussed.

SulfoxFluor-enabled deoxyazidation of alcohols with NaN3

Direct deoxyazidation of alcohols with NaN₃ is a straightforward method for the synthesis of widely used alkyl azides in organic chemistry. However, known methods have some limitations such as high reaction temperatures and narrow substrate scope. Herein, a general and practical method for the preparation of alkyl azides from alcohols using NaN₃ has been developed. N-tosyl-4-chlorobenzenesulfonimidoyl fluoride (SulfoxFluor) plays an important role in this deoxyazidation process, which converts a broad range of alcohols into alkyl azides at room temperature. The power of this deoxyazidation protocol has been demonstrated by successful late-stage deoxyazidation of natural products and pharmaceutically relevant molecules.

Synthesis, properties and catalysis of quantum dots in C–C and C-heteroatom bond formations

Luminescent quantum dots (QDs) represent a new form of carbon nanomaterials which have gained widespread attention in recent years, especially in the area of chemical sensing, bioimaging, nanomedicine, solar cells, light-emitting diode (LED), and electrocatalysis. Their extremely small size renders some unusual properties such as quantum confinement effects, good surface binding properties, high surface‐to‐volume ratios, broad and intense absorption spectra in the visible region, optical and electronic properties different from those of bulk materials. Apart from, during the past few years, QDs offer new and versatile ways to serve as photocatalysts in organic synthesis. Quantum dots (QD) have band gaps that could be nicely controlled by a number of factors in a complicated way, mentioned in the article. Processing, structure, properties and applications are also reviewed for semiconducting quantum dots. Overall, this review aims to summarize the recent innovative applications of QD or its modified nanohybrid as efficient, robust, photoassisted redox catalysts in C–C and C-heteroatom bond forming reactions. The recent structural modifications of QD or its core structure in the development of new synthetic methodologies are also highlighted. Following a primer on the structure, properties, and bio-functionalization of QDs, herein selected examples of QD as a recoverable sustainable nanocatalyst in various green media are embodied for future reference.

Green Synthesis and Anticancer Potential of 1,4-Dihydropyridines-Based Triazole Derivatives: In Silico and In Vitro Study

A library of 1,4-dihydropyridine-based 1,2,3-triazol derivatives has been designed, synthesized, and evaluated their cytotoxic potential on colorectal adenocarcinoma (Caco-2) cell lines. All compounds were characterized and identified based on their 1H and 13C NMR (Nuclear Magnetic Resonance) spectroscopic data. Furthermore, molecular docking of best anticancer hits with target proteins (protein kinase CK2α, tankyrase1, and tankyrase2) has been performed. Our results implicated that most of these compounds have significant antiproliferative activity with IC50 values between 0.63 ± 0.05 and 5.68 ± 0.14 µM. Moreover, the mechanism of action of most active compounds 13ab' and 13ad' suggested that they induce cell death through apoptosis in the late apoptotic phase as well as dead phase, and they could promote cell cycle arrest at the G2/M phase. Furthermore, the molecular docking study illustrated that 13ad' possesses better binding interaction with the catalytic residues of target proteins involved in cell proliferation and antiapoptotic pathways. Based on our in vitro and in silico study, 13ad' was found to be a highly effective anti-cancerous compound. The present data indicate that dihydropyridine-linked 1,2,3-triazole conjugates can be generated as potent anticancer agents.

Pyrazole and Triazole Derivatives as Mycobacterium tuberculosis UDP-Galactopyranose Inhibitors

UDP-galactopyranose mutase (UGM) is an essential enzyme involved in the bacterial cell wall synthesis, and is not present in mammalian cells. Thus, UGM from Mycobacterium tuberculosis (Mtb) represents a novel and attractive drug target for developing antituberculosis agents. A pyrazole-based compound, MS208, was previously identified as a mixed inhibitor of MtbUGM which targets an allosteric site. To understand more about the structure activity relationship around the MS208 scaffold as a MtbUGM inhibitor, thirteen pyrazoles and triazole analogues were synthesized and tested against both MtbUGM and Mycobacterium tuberculosis in vitro. While the introduced structural modifications to MS208 did not improve the antituberculosis activity, most of the compounds showed MtbUGM inhibitory activity. Interestingly, the pyrazole derivative DA10 showed a competitive model for MtbUGM inhibition with improved Ki value of 51 ± 4 µM. However, the same compound did not inhibit the growth of Mycobacterium tuberculosis.

Multinuclear mesoionic 1,2,3-triazolylidene complexes: design, synthesis, and applications

The chemistry of multinuclear metal complexes bearing by N-heterocyclic carbene (NHC) ligands, is an area of fast growing interest in modern organometallic chemistry. In particular, complexes supported by mesoionic (MIC) 1,2,3-triazolylidenes are attracting a great deal attention due to their postulated superior donor capacity compared to classical NHC ligands. Despite the readily available synthetic routes to MIC-based ligand platforms featuring several substitution levels, most of the coordination chemistry of triazolylidenes is still dominated by mononuclear complexes. In this short review article, recent progress on the design and synthesis of multinuclear triazolylidene complexes (ranging from di- to tetranuclear species) is discussed. Special emphasis is placed on their structural features, electronic properties and catalytic applications.

A mesoporous metal–organic framework used to sustainably release copper(ii) into reducing aqueous media to promote the CuAAC click reaction

The mesoporous metal–organic framework Cr-MIL-101-NH₂ (MOF1) has been used to encapsulate, by a simple impregnation method, large amounts of copper sulfate. The resulting loaded material, Cu@MOF1, was successfully employed to slowly release copper(ii) into an appropriate reaction medium in which the reducing agent sodium ascorbate reduces copper(ii) to copper(i), thus allowing the well-known copper(i)-catalyzed alkyne–azide cycloaddition (CuAAC) “click” reaction to proceed in the absence of potentially high local copper(i) concentrations. The use of a MOF-based controlled copper release system such as Cu@MOF1 may be relevant for copper(i)-catalyzed reactions having substrates that could be degraded by potentially high local concentrations of copper(i). The copper chelating ligand TBTA (tris(benzyltriazolylmethyl)amine), a very useful ligand for click chemistry, has been successfully attached to the pores of MOF1. The resulting TBTA-functionalized MOF (MOF3) was compared with its non-functionalized version (MOF1). At copper loadings of ca. 3 mmol g⁻¹, the results revealed that the performances of the two materials are strikingly similar. Upon immersion in methanol/water (95/5) containing sodium ascorbate, both materials slowly released copper encapsulated in their pores and could be recovered and reused efficiently for up to five reaction cycles without reloading with metal ion, while allowing the CuAAC reaction to proceed with excellent conversion rates and yields.

Cr-MIL-101-NH₂ (MOF1) has been used to encapsulate large amounts of copper sulfate and the resulting loaded material, Cu@MOF1, was successfully used to promote the CuAAC click reaction.

Construction of Stable Metal-Organic Framework Platforms Embedding N-Heterocyclic Carbene Metal Complexes for Selective Catalysis

We report a bottom-up approach to immobilize catalysts into MOFs, including copper halides and gold chloride in a predictable manner. Interestingly, the structures of MOFs bearing NHC metal complexes maintained a similar 4-fold interpenetrated cube. They exhibited exceptionally high porosity despite the interpenetrated structure and showed good stability in various solvents. Moreover, these MOFs possess high size activity depending on the size of the substrates in various reactions, compared to homogeneous catalysis. Also, the high catalytic activity of MOFs can be preserved 4 times without significant loss of crystallinity. Incorporation of the various metal complexes into MOFs allows for the preparation of functional MOFs for practical applications.

Modified pyridine-triazole and 2,2'-bipyrimidine ligands generating robust titanium complexes constructed around a TiO4N2 core

The synthesis and characterisation of novel chelate nitrogen ligands with phasmidic tails (pyridine-triazole ligand 1b; 2,2'-bipyrimidine ligands 2b and 3b) as well as their titanium(IV) coordination complexes are reported. The analogous ligands 1a, 2a and 3a with methoxy substituents instead of the tails were also synthesized, together with titanium complexes that could be crystallographically characterised. A good agreement is noticed between analytical data of the complexes in solution (NMR) and in the solid state (X-ray diffraction). The complexes are overall robust on phases like alumina or silica, so that they could be characterised by TLC and sometimes chromatographied. Supramolecular architectures were generated from an equimolar solution of titanium(IV) isopropoxide, ligand 1a and a polyphenol ligand 5-H₄, leading to a double-stranded helicate characterised by MS, NMR and crystallography, which was then converted into a trinuclear complex as shown by MS and NMR DOSY data. The liquid-crystalline behaviour of the ligands 1b, 2b and 3b incorporating the long alkyl tails and that of the complexes derived from these ligands have been investigated.

Chemistry on the Complex: Derivatization of TiO4 N2 -Based Complexes and Application to Multi-Step Synthesis

The chemistry on octahedral TiO₄ N₂ -complexes is described. The Ti(IV)-based precursors are composed of two 3,3'-diphenyl-2,2'-biphenolato ligands (1) and one substituted 1,10-phenanthroline ligand (2-5). The application of imine condensation, palladium-catalyzed C-C bond formation or copper-catalysed azide-alkyne cycloaddition allowed the grafting of various new groups onto these species. In particular Sonogashira reactions permitted to observe an excellent conversion of the starting complexes. This systematic study enabled to compile the factors required to preserve the framework of the complexes in the course of a chemical transformation. Thanks to this chemistry realized on the complex, the Ti(1)₂ fragment was used as a protecting group to develop a multi-step synthesis of a bis-phenanthroline compound (12), for which the synthesis without this protection failed. Thus, a dinuclear complex [Ti₂ (1)₄ (12)] was first prepared starting from complex precursor bearing an acetylenic function via a Hay coupling reaction. This was followed by a deprotection step affording 12. Overall, this work illustrates how the Ti(1)₂ fragment could be an useful tool for the preparation of unprecedented diimine compounds.

An IR Spectroscopy Study of the Degradation of Surface Bound Azido-Groups in High Vacuum

Controlled surface functionalization with azides to perform on surface "click chemistry" is desired for a large range of fields such as material engineering and biosensors. In this work, the stability of an azido-containing self-assembled monolayer in high vacuum is investigated using in situ Fourier transform infrared spectroscopy. The intensity of the antisymmetric azide stretching vibration is found to decrease over time, suggesting the degradation of the azido-group in high vacuum. The degradation is further investigated at three different temperatures and at seven different nitrogen pressures ranging from 1 × 10^-6 mbar to 5 × 10^-3 mbar. The degradation is found to increase at higher temperatures and at lower nitrogen pressures. The latter supporting the theory that the degradation reaction involves the decomposition into molecular nitrogen. For the condition with the highest degradation detected, only 63% of azides is found to remain at the surface after 8 h in vacuum. The findings show a significant loss in control of the surface functionalization. The instability of azides in high vacuum should therefore always be considered when depositing or postprocessing azido-containing layers.

Hybrids of 4-hydroxy derivatives of goniothalamin and piplartine bearing a diester or a 1,2,3-triazole linker as antiproliferative agents

A library of nine hybrids of 4-hydroxygoniothalamin (2), 4-hydroxypiplartine (4), monastrol (5) and oxo-monastrol (6) was prepared via a modular synthetic route with a diester or a 1,2,3-triazole as linkers. The compounds were assayed against a panel of human cancer cell lines, including MCF-7 (breast adenocarcinoma), HeLa (cervical adenocarcinoma), Caco-2 (colorectal adenocarcinoma) and PC3 (prostate adenocarcinoma), as well as against normal breast (MCF10A) and prostate (PNT2) cells. In general, hybrids with an ester linker containing 4-hydroxypiplartine (4) were more potent than the corresponding hybrids with 4-hydroxygoniothalamin (2). On the other hand, compounds presenting the 1,2,3-triazole linker displayed enhanced cytotoxicity and selectivity when compared to their corresponding hybrids with the diester linker. The 4-hydroxypiplartine-based hybrids 12 and 22 displayed high cytotoxicity (IC50 values below 10 μM) against all cancer cells studied, especially in MCF-7 cells with IC50 values of 1.7 ± 0.1 and 1.6 ± 0.9 μM, respectively. Furthermore, the 4-hydroxygoniothalamin-monastrol hybrid (compound 21) and the 4-hydroxypiplartine-oxo-monastrol hybrid (compound 25), both bearing a 1,2,3-triazole linker, displayed high selectivity and potency towards breast cancer cell line (MCF-7 vs. MCF10 cells, selectivity index = 15.8 and 7.1, respectively), while the 4-hydroxypiplartine -4-hydroxymethylgoniothalamin hybrid with a diester linker (compound 33) showed high selectivity towards melanoma cancer cells (selectivity index = 9.6). Antiproliferative and pro-apoptotic potential of compounds 12 and 22 against MCF-7 cancer cells were further investigated. Cell cycle studies revealed increased G2/M population in MCF-7 cultures as well as reduced G0/G1 population compared to the control groups indicating cell cycle arrest in G2/M phase. In addition, the frequency of positive cells for annexin V was higher in treated samples suggesting that compounds 12 and 22 induce apoptosis in estrogen-positive MCF-7 cells.