Triazole Linker Research Articles

Urea-thiazole/benzothiazole hybrids with a triazole linker: synthesis, antimicrobial potential, pharmacokinetic profile and in silico mechanistic studies.

Some urea-thiazole/benzothiazole hybrids with a triazole linker were synthesized via Cu(I)-catalysed click reaction. After successfully analysed by various spectral techniques including FTIR, NMR and HRMS, antimicrobial screening of the synthesized hybrids along with their precursors was carried out against two Gram (+) bacteria (Staphylococcus aureus and Bacillus endophyticus), two Gram (-) bacteria (Escherichia coli and Pseudomonas fluorescens) and two fungi (Candida albicans and Rhizopus oryzae). All the synthesized compounds (4a-4l) displayed better biological response than the standard fluconazole against both of the tested fungi. Compounds 4h and 4j were found to be the most active compounds against R. oryzae and C. albicans, respectively. Molecular docking of hybrid 4j and its alkyne precursor 1b in the active site of C. albicans target sterol 14-α demethylase was also performed and was also supported by molecular dynamics studies. In silico ADME prediction of synthesized urea-thiazole/benzothiazole hybrids with a triazole linker and their alkyne precursors was also predicted.

A New 1,5-Disubstituted Triazole DNA Backbone Mimic with Enhanced Polymerase Compatibility.

Triazole linkages (TLs) are mimics of the phosphodiester bond in oligonucleotides with applications in synthetic biology and biotechnology. Here we report the RuAAC-catalyzed synthesis of a novel 1,5-disubstituted triazole (TL2) dinucleoside phosphoramidite as well as its incorporation into oligonucleotides and compare its DNA polymerase replication competency with other TL analogues. We demonstrate that TL2 has superior replication kinetics to these analogues and is accurately replicated by polymerases. Derived structure–biocompatibility relationships show that linker length and the orientation of a hydrogen bond acceptor are critical and provide further guidance for the rational design of artificial biocompatible nucleic acid backbones.

Designed Artificial Protein Heterodimers With Coupled Functions Constructed Using Bio-Orthogonal Chemistry.

The formation of protein complexes is central to biology, with oligomeric proteins more prevalent than monomers. The coupling of functionally and even structurally distinct protein units can lead to new functional properties not accessible by monomeric proteins alone. While such complexes are driven by evolutionally needs in biology, the ability to link normally functionally and structurally disparate proteins can lead to new emergent properties for use in synthetic biology and the nanosciences. Here we demonstrate how two disparate proteins, the haem binding helical bundle protein cytochrome b 562 and the β-barrel green fluorescent protein can be combined to form a heterodimer linked together by an unnatural triazole linkage. The complex was designed using computational docking approaches to predict compatible interfaces between the two proteins. Models of the complexes where then used to engineer residue coupling sites in each protein to link them together. Genetic code expansion was used to incorporate azide chemistry in cytochrome b 562 and alkyne chemistry in GFP so that a permanent triazole covalent linkage can be made between the two proteins. Two linkage sites with respect to GFP were sampled. Spectral analysis of the new heterodimer revealed that haem binding and fluorescent protein chromophore properties were retained. Functional coupling was confirmed through changes in GFP absorbance and fluorescence, with linkage site determining the extent of communication between the two proteins. We have thus shown here that is possible to design and build heterodimeric proteins that couple structurally and functionally disparate proteins to form a new complex with new functional properties.

First-in-Class Cyclic Temporin L Analogue: Design, Synthesis, and Antimicrobial Assessment.

The pharmacodynamic and pharmacokinetic properties of bioactive peptides can be modulated by introducing conformational constraints such as intramolecular macrocyclizations, which can involve either the backbone and/or side chains. Herein, we aimed at increasing the α-helicity content of temporin L, an isoform of an intriguing class of linear antimicrobial peptides (AMPs), endowed with a wide antimicrobial spectrum, by the employment of diverse side-chain tethering strategies, including lactam, 1,4-substituted [1,2,3]-triazole, hydrocarbon, and disulfide linkers. Our approach resulted in a library of cyclic temporin L analogues that were biologically assessed for their antimicrobial, cytotoxic, and antibiofilm activities, leading to the development of the first-in-class cyclic peptide related to this AMP family. Our results allowed us to expand the knowledge regarding the relationship between the α-helical character of temporin derivatives and their biological activity, paving the way for the development of improved antibiotic cyclic AMP analogues.

Solvent-Free and Catalyst-Free Synthesis of Cross-Linkable Polyfumaramides via Topochemical Azide-Alkyne Cycloaddition Polymerization

Unsaturated polymers are important materials having a lot of applications. Among polymers, polyamides possess a prime position due to their thermal and chemical stability. Herein, we report a simple, greener, catalyst-free, and solid-state synthesis of two unsaturated polyamides via a topochemical azide-alkyne cycloaddition reaction. Two designed fumaramide monomers M1 and M2, functionalized with complementary azide and alkyne reactive motifs at the termini, reacted upon heating their crystalline powders and resulted in the formation of triazolyl-linked unsaturated polyfumaramides P1 and P2, respectively. We have characterized the reaction using various time-dependent techniques such as NMR, FTIR, PXRD, and DSC measurements. Interestingly, the monomer M1 resulted in 1,5-disubstituted triazole-linked unsaturated polyfumaramide (P1), whereas the monomer M2 polymerized into a polyfumaramide having both 1,4-disubstituted and 1,5-disubstituted triazole linkages (P2). Also, the trans-olefinic bond of both the fumaramide monomers was unaffected in the polymerization process and hence yielded unsaturated polymers having trans-olefin units in the repeating unit. Demonstrating the scope of postsynthetic modification, we have shown that unsaturation can be exploited for cross-linking via a light-induced [2 + 2] cycloaddition reaction. This first report on the solid-state synthesis of unsaturated polyfumaramides will be of great interest.

Synthesis and pharmacological characterization of glucopyranosyl-conjugated benzyl derivatives as novel selective cytotoxic agents against colon cancer.

Glucopyranosyl-conjugated benzyl derivatives containing a [1,2,3]-triazole linker were synthesized. Benzyl served as an important pharmacophore in anti-cancer compounds. Compound 8d inhibited the proliferation of colorectal cancer cells with the potency comparable to 5-fluorouracil (5-FU) with improved selectivity towards cancer cells. The antiproliferative activity of 8d is achieved through triggering apoptotic cell death.

Light-Activated Stress Relaxation, Toughness Improvement, and Photoinduced Reversal of Physical Aging in Glassy Polymer Networks.

A covalent adaptable network (CAN) with high glass transition temperature (Tg ), superior mechanical properties including toughness and ductility, and unprecedented spatio-temporally controlled dynamic behavior is prepared by introducing dynamic moieties capable of reversible addition fragmentation chain transfer (RAFT) into photoinitiated copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC)-based networks. While the CuAAC polymerization yields glassy polymers composed of rigid triazole linkages with enhanced toughness, the RAFT moieties undergo bond exchange leading to stress relaxation upon light exposure. This unprecedented level of stress relaxation in the glassy state leads to numerous desirable attributes including glassy state photoinduced plasticity, toughness improvement during large deformation, and even photoinduced reversal of the effects of physical aging resulting in the rejuvenation of mechanical and thermodynamic properties in physically aged RAFT-CuAAC networks that undergo bond exchange in the glassy state. Surprisingly, when an allyl-sulfide-containing azide monomer (AS-N3 ) is used to form the network, the network exhibits up to 80% stress relaxation in the glassy state (Tg - 45 °C) under fixed displacement. In situ activation of RAFT during mechanical loading results in a 50% improvement in elongation to break and 40% improvement in the toughness when compared to the same network without light-activation of RAFT during the tensile testing.

Click‐Connected 2‐(Hydroxyimino)aldehydes for the Design of UV‐Responsive Functional Molecules

AbstractClick chemistry is used to functionalize simple lipophilic and water‐soluble molecules, a complex PEGylated phospholipid (DSPE‐PEG2000), and two benzylic substrates with the 2‐(hydroxyimino)aldehyde (HIA) group. To this end, two terminal alkynes bearing the HIA moiety were synthesized and coupled to different azides through copper(I)‐catalyzed azide alkyne cycloaddition (CuAAC). Norrish–Yang photoisomerization (λ= 365 nm, LED source) is successfully obtained, with no interference by the triazole linker, except when the forbidden n‐π* carbonyl transition is screened by a remote substituent such as salicylaldehyde. UV‐Vis spectrometry suggests a specific interaction of HIAs with Cu(II), whereas no such evidence is found with Cu(I). We thereby show that the CuAAC methodology can be used successfully to obtain HIA‐based UV‐responsive hydrophilic or lipophilic ligands, phospholipidic components for the construction of liposomes, and macrocycle precursors.

Peptide Nucleic Acid with Double Face: Homothymine-Homocytosine Bimodal Cα-PNA (bm-Cα-PNA) Forms a Double Duplex of the bm-PNA2:DNA Triplex.

Cα-bimodal peptide nucleic acids (bm-Cα-PNA) are PNAs with two faces and are designed homologues of PNAs in which each aminoethylglycine (aeg) repeating unit in the standard PNA backbone hosts a second nucleobase at Cα through a spacer chain with a triazole linker. Such bm-Cα-PNA with mixed sequences can form double duplexes by simultaneous binding to two complementary DNAs, one to the base sequence on t-amide side and the other to the bases on the Cα side chain. The synthesis of bm-Cα-PNA with homothymine (T7) on the t-amide face and homocytosine (C5) on the Cα side chain through the triazole linker was achieved by solid phase synthesis with the global click reaction. In the presence of complementary DNAs dA8 and dG6 at neutral pH, bm-Cα-PNA 1 forms a higher order pentameric double duplex of a triplex composed of two bm-Cα-PNA-C5:dG5 duplexes built on a core (bm-Cα-PNA-T7)2:dA8 triplex. Circular dichroism studies showed that assembly can be achieved by either triplex first and duplex later or vice versa. Isothermal titration calorimetry data indicated that the assembly is driven by favorable enthalpy. These results validate concurrent multiple complex formation by bimodal PNAs with additional nucleobases at Cα or Cγ on the aeg-PNA backbone and open up ways to design programmed supramolecular assemblies.

Design, synthesis and biological activity of 1,4-quinone moiety attached to betulin derivatives as potent DT-diaphorase substrate

In this research, betulin derivatives were bonded to the 1,4-quinone fragment by triazole linker. Furthermore, the enzymatic assay used has shown that these compounds are a good DT-diaphorase (NQO1) substrates as evidenced by increasing enzymatic conversion rates relative to that of streptonigrin. The anticancer activities of the hybrids were tested against a panel of human cell lines, like: melanoma, ovarian, breast, colon, and lung cancers. The structure–activity relationship showed that the activity depends on the type of 1,4-quinone moiety and the tumor cell lines used. It was also found that the anticancer effects were increasing against the cell line with higher NQO1 protein level, like: breast (T47D, MCF-7), colon (Caco-2), and lung (A549) cancers. The transcriptional activity of the gene encoding a proliferation marker (H3 histone), cell cycle regulators (p53 and p21) and apoptosis pathway (BCL-2 and BAX) for selected compounds were determined. The molecular docking study was carried out to examine the interaction between the hybrids and NQO1 enzyme. The computational simulation showed that the type of the 1,4-quinone moiety influences location of the compound in the active site of the enzyme. It is worth noting that the study of new hybrids of betulin as substrate for NQO1 protein may lead to new medical therapeutic applications in the future.

Novel Hybrid Molecules Based on triazole-β-lactam as Potential Biological Agents

Triazole ring is a cyclic scaffold containing three heteroatoms of nitrogen. They display a broad variety of biological activities. The uncatalyzed/catalyzed 1,3-dipolar cycloadditions are a chemical reaction between a 1,3-dipole and a dipolarophile to achieve 1,2,3-triazoles. The hybrid approach is an innovative and powerful synthetic tool for the synthesis of two or more distinct entities in one molecule with novel biological activities. Owing to the high potential of β-lactams to display noticeable biological properties, these compounds have been one of the important ingredients in hybrid molecules. The four-membered lactams have been recognized as a part of penicillin. There are various synthetic protocols for the synthesis of β-lactams. Staudinger reaction of the Schiff bases with diphenylketenes is a successful and famous strategy for the synthesis of these products. Even though, the number of heterocyclic compounds is limited, plenty of hybrids based on heterocyclic compounds can be designed and prepared. The synthesis of hybrid products of triazole-β-lactam has proved to be highly challenging. The current review article outlines the diversity and creativity in the elegant synthesis of triazole-β-lactam hybrids as potential biological agents. Molecules including isatin, ferrocene, bile acid, chalcone, and etc were attached to β-lactam with triazole linker, as well.

Rhodium Nanoparticles Stabilized by PEG-Tagged Imidazolium Salts as Recyclable Catalysts for the Hydrosilylation of Internal Alkynes and the Reduction of Nitroarenes

PEGylated imidazolium (bromide and tetrafluoroborate) and tris-imidazolium (bromide) salts containing triazole linkers have been used as stabilizers for the preparation of water-soluble rhodium(0) nanoparticles by reduction of rhodium trichloride with sodium borohydride in water at room temperature. The nanomaterials have been characterized (Transmission Electron Microscopy, Electron Diffraction, X-ray Photoelectron Spectroscopy, Inductively Coupled Plasma-Optical Emission Spectroscopy). They proved to be efficient and recyclable catalysts for the stereoselective hydrosilylation of internal alkynes, in the presence or absence of solvent, and in the reduction of nitroarenes to anilines with ammonia-borane as hydrogen donor in aqueous medium (1:4 tetrahydrofuran/water).

Water-soluble galactosamine derivative of β-cyclodextrin as protective ligand and targeted carrier for delivery of toxic anthracycline drug

β-cyclodextrin modified with an electron-rich aromatic triazole linker and targeting moiety (galactosamine) was synthesized and studied as a carrier for the anticancer drug, doxorubicin (DOX), with the aim of targeting the pathological cells, reducing the cardiotoxic side effects and increasing the binding of the drug to DNA. The β-cyclodextrins modified with galactosamine (βCDGAL) are non-toxic and highly soluble in aqueous medium compared to the native βCD and βCD modified only with aromatic moiety, such as triazole linker. Molecular modelling and NMR study gave a deeper insight into the ligand structure, providing an explanation for its increased solubility, and the drug-ligand interactions. The triazole linker strengthened the drug binding and introduced pH dependence of the complex stability constants for βCDGAL derivative, as confirmed by the voltammetry measurements. Spectroscopic studies have shown that entrapment of the DOX in βCDGAL cavity reduces the stability constant of the DOX:Fe(III) complex responsible for the production of cardiotoxic reactive oxygen species and additionally supports the binding of the drug to the double strand DNA. The MTT assay and confocal microscopy results showed that despite encapsulation of the drug in the cyclodextrin molecule, its cytotoxic effect on the liver cancer cell line (HepG2) is comparable to that of the free, non-protected drug.

2,4,9‐Triazaadamantanes with “Clickable” Groups: Synthesis, Structure and Applications as Tripodal Platforms

2,4,9‐Triazaadamantanes (TRIADs) are promising yet scarcely available, conformationally rigid platforms for potential applications in the design of functional molecules and materials. Here, we report a facile synthesis of various N‐ and C7‐substituted 2,4,9‐triazaadamantanes, starting from amines and 4‐allylhepta‐1,6‐dienes. A focus was placed on the synthesis of 2,4,9‐triazaadamantanes bearing reactive groups (NH2, propargyl, OH) on the bridge nitrogen atoms, which were then used to decorate the 3D scaffold by hydrazone, triazole, and boronate linkages. A reversible opening of the adamantane cage to the acyclic tris‐oxime form was observed for 2,4,9‐triazaadamantanes possessing hydroxy‐groups on the nitrogen atoms (TRIAD‐triols). This process could be controlled by temperature or by complexation of TRIAD‐triol with a boronic acid. The structure of 2,4,9‐triazaadamantanes and the stereodynamics at the bridge nitrogen atoms were studied by X‐ray analysis and DFT calculations.

Synthesis and evaluation of 17α-triazolyl and 9α-cyano derivatives of estradiol

A variety of 17α-triazolyl and 9α-cyano derivatives of estradiol were prepared and evaluated for binding to human ERβ in both a TR-FRET assay, as well as ERβ and ERα agonism in cell-based functional assays. 9α-Cyanoestradiol (5) was nearly equipotent as estradiol as an agonist for both ERβ and ERα. The potency of the 17α-triazolylestradiol analogs is considerably more variable and depends on the nature of the 4-substituent of the triazole ring. While rigid protein docking simulations exhibited significant steric clashing, induced fit docking providing more protein flexibility revealed that the triazole linker of analogs 2d and 2e extends outside of the traditional ligand binding domain with the benzene ring located in the loop connecting helix 11 to helix 12.

Construction of Functionally Compartmental Inorganic Photocatalyst-Enzyme System via Imitating Chloroplast for Efficient Photoreduction of CO2 to Formic Acid.

Inorganic photocatalyst-enzyme systems are a prominent platform for the photoreduction of CO2 to value-added chemicals and fuels. However, poor electron transfer kinetics and enzyme deactivation by reactive oxygen species in the photoexcitation process severely limit catalytic efficiency. In chloroplast, enzymatic CO2 reduction and photoexcitation are compartmentalized by the thylakoid membrane, which protects enzymes from photodamage, while the tightly integrated photosystem facilitates electron transfer, promoting photocatalysis. By mimicking this strategy, we constructed a novel functionally compartmental inorganic photocatalyst-enzyme system for CO2 reduction to formate. To accomplish efficient electron transfer, we first synthesized an integrated artificial photosystem by conjugation of the cocatalyst (a Rh complex) onto thiophene-modified C3N4 (TPE-C3N4), demonstrating an NADH regeneration rate of 9.33 μM·min-1, 2.33 times higher than that of a homogeneous counterpart. The enhanced NADH regeneration activity was caused by the tightly conjugated structure of the artificial photosystem, enabling rapid electron transfer from TPE-C3N4 to the Rh complex. To protect formate dehydrogenase (FDH) from photoinduced deactivation, FDH was encapsulated into MAF-7, a metal-organic framework (MOF) material, to compartmentalize FDH from the toxic photoexcitation process, similar to the function of the thylakoid membrane. Moreover, the triazole linkers of MAF-7 possess both hydrophilicity and pH-buffering capacity providing a stable microenvironment for FDH, which could enhance enzyme stability in photosynthesis. The synergy between the enhanced electron transfer of TPE-C3N4 for NADH cofactor regeneration and MOF-protection of the redox enzyme enables the construction of a functionally compartmental inorganic photocatalyst-enzyme association system, promoting CO2 photoconversion to formic acid with a yield of 16.75 mM after 9 h of illumination, 3.24 times greater than that of the homogeneous reaction counterpart.

Synthesis of Triazole-Linked SAM-Adenosine Conjugates: Functionalization of Adenosine at N-1 or N-6 Position without Protecting Groups.

More than 150 RNA chemical modifications have been identified to date. Among them, methylation of adenosine at the N-6 position (m6A) is crucial for RNA metabolism, stability and other important biological events. In particular, this is the most abundant mark found in mRNA in mammalian cells. The presence of a methyl group at the N-1 position of adenosine (m1A) is mostly found in ncRNA and mRNA and is mainly responsible for stability and translation fidelity. These modifications are installed by m6A and m1A RNA methyltransferases (RNA MTases), respectively. In human, deregulation of m6A RNA MTases activity is associated with many diseases including cancer. To date, the molecular mechanism involved in the methyl transfer, in particular substrate recognition, remains unclear. We report the synthesis of new SAM-adenosine conjugates containing a triazole linker branched at the N-1 or N-6 position of adenosine. Our methodology does not require protecting groups for the functionalization of adenosine at these two positions. The molecules described here were designed as potential bisubstrate analogues for m6A and m1A RNA MTases that could be further employed for structural studies. This is the first report of compounds mimicking the transition state of the methylation reaction catalyzed by m1A RNA MTases.

Synthesis and Anticancer Activity of Dimeric Polyether Ionophores.

Polyether ionophores represent a group of natural lipid-soluble biomolecules with a broad spectrum of bioactivity, ranging from antibacterial to anticancer activity. Three seem to be particularly interesting in this context, namely lasalocid acid, monensin, and salinomycin, as they are able to selectively target cancer cells of various origin including cancer stem cells. Due to their potent biological activity and abundant availability, some research groups around the world have successfully followed semi-synthetic approaches to generate original derivatives of ionophores. However, a definitely less explored avenue is the synthesis and functional evaluation of their multivalent structures. Thus, in this paper, we describe the synthetic access to a series of original homo- and heterodimers of polyether ionophores, in which (i) two salinomycin molecules are joined through triazole linkers, or (ii) salinomycin is combined with lasalocid acid, monensin, or betulinic acid partners to form ‘mixed’ dimeric structures. Of note, all 11 products were tested in vitro for their antiproliferative activity against a panel of six cancer cell lines including the doxorubicin resistant colon adenocarcinoma LoVo/DX cell line; five dimers (14–15, 17–18 and 22) were identified to be more potent than the reference agents (i.e., both parent compound(s) and commonly used cytostatic drugs) in selective targeting of various types of cancer. Dimers 16 and 21 were also found to effectively overcome the resistance of the LoVo/DX cancer cell line.

New glycosylated platinum(II) phthalocyanine containing ribose moiety – synthesis and photophysical properties

The synthesis and spectral characterisation of new glycoconjugated phthalonitrile connected with triazole linker via Cu(II)-mediated click reaction is reported. Treatment of azido derivative of 1-methoxy-2,3- O-isopropylidene-β-d-ribose with 4-O-propargyloxy-substituted phthalonitrile in presence copper(II) sulfate pentahydrate and sodium l-ascorbate in tert-butanol/water gave desired glycophthalonitrile with 84% yield. This precursor underwent mixed-cyclisation with the tert-butyl-substituted phthalonitrile, to afford the mono-glycosylated A3B-type platinum(II) phthalocyanine. Upon irradiation this compound could sensitise the formation of singlet oxygen in acetone, with 0.95 quantum yield by comparative method with use of 1,3-diphenylisobenzofuran (DPBF) as scavenger.

Application and Structural Analysis of Triazole‐Bridged Disulfide Mimetics in Cyclic Peptides

AbstractRuthenium‐catalysed azide–alkyne cycloaddition (RuAAC) provides access to 1,5‐disubstituted 1,2,3‐triazole motifs in peptide engineering applications. However, investigation of this motif as a disulfide mimetic in cyclic peptides has been limited, and the structural consequences remain to be studied. We report synthetic strategies to install various triazole linkages into cyclic peptides through backbone cyclisation and RuAAC cross‐linking reactions. These linkages were evaluated in four serine protease inhibitors based on sunflower trypsin inhibitor‐1. NMR and X‐ray crystallography revealed exceptional consensus of bridging distance and backbone conformations (RMSD<0.5 Å) of the triazole linkages compared to the parent disulfide molecules. The triazole‐bridged peptides also displayed superior half‐lives in liver S9 stability assays compared to disulfide‐bridged peptides. This work establishes a foundation for the application of 1,5‐disubstituted 1,2,3‐triazoles as disulfide mimetics.