“Click Chemistry” Inspired Synthesis of pseudo-Oligosaccharides and Amino Acid Glycoconjugates

In Vitro and In Vivo Antiviral Studies of New Heteroannulated 1,2,3-Triazole Glycosides Targeting the Neuraminidase of Influenza A Viruses

There is an urgent need to develop and synthesize new anti-influenza drugs with activity against different strains, resistance to mutations, and suitability for various populations. Herein, we tested in vitro and in vivo the antiviral activity of new 1,2,3-triazole glycosides incorporating benzimidazole, benzooxazole, or benzotriazole cores synthesized by using a click approach. The Cu-catalyzation strategy consisted of 1,3-dipolar cycloaddition of the azidoalkyl derivative of the respective heterocyclic and different glycosyl acetylenes with five or six carbon sugar moieties. The antiviral activity of the synthesized glycosides against wild-type and neuraminidase inhibitor resistant strains of the avian influenza H5N1 and human influenza H1N1 viruses was high in vitro and in mice. Structure–activity relationship studies showed that varying the glycosyl moiety in the synthesized glycosides enhanced antiviral activity. The compound (2R,3R,4S,5R)-2-((1-(Benzo[d]thiazol-2-ylmethyl)-1H-1,2,3-triazol-4-yl)methoxy)tetrahydro-2H-pyran-3,4,5-triyl triacetate (Compound 9c) had a 50% inhibitory concentration (IC50) = 2.280 µM and a ligand lipophilic efficiency (LLE) of 6.84. The compound (2R,3R,4S,5R)-2-((1-((1H-Benzo[d]imidazol-2-yl)methyl)-1H-1,2,3-triazol-4-yl)methoxy)tetrahydro-2H-pyran-3,4,5-triyl triacetate had IC50 = 2.75 µM and LLE = 7.3 after docking analysis with the H5N1 virus neuraminidase. Compound 9c achieved full protection from H1N1 infection and 80% protection from H5N1 in addition to a high binding energy with neuraminidase and was safe in vitro and in vivo. This compound is suitable for further clinical studies as a new neuraminidase inhibitor.

Click chemistry based synthesis, cytotoxic activity and molecular docking of novel triazole-thienopyrimidine hybrid glycosides targeting EGFR

In the current study, new thienopyrimidine conjugates bearing 1,2,3-triazole core and different sugar moieties have been designed and synthesized by Cu(I)-catalysed click dipolar cycloaddition. The cytotoxic activity of the synthesised conjugates 2, 5, 7, and 13-18 was studied against HCT-116 and MCF-7 cell lines by the MTT assay. The triazole glycosides 16 and 18 provided significant cytotoxic activities against HCT-116 cell lines comparable to that of doxorubicin and other studied compounds. The cytotoxic behaviour against MCF-7 exhibited that all the investigated compounds were more potent than doxorubicin. Moreover, all screened targets were evaluated against mutant EGFR kinase type L858R and the results revealed that the acetylated 1,2,3-triazole glycosides 13-18 exhibited excellent EGFR inhibitory activity in comparison with gefitinib. Furthermore, molecular modelling studies were performed to investigate the binding affinity of the most active compounds to EGFR enzyme.

Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications

Copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes, commonly known as CuAAC or click chemistry, has been identified as one of the most successful, versatile, reliable, and modular strategies for the rapid and regioselective construction of 1,4-disubstituted 1,2,3-triazoles as diversely functionalized molecules. Carbohydrates, an integral part of living cells, have several fascinating features, including their structural diversity, biocompatibility, bioavailability, hydrophilicity, and superior ADME properties with minimal toxicity, which support increased demand to explore them as versatile scaffolds for easy access to diverse glycohybrids and well-defined glycoconjugates for complete chemical, biochemical, and pharmacological investigations. This review highlights the successful development of CuAAC or click chemistry in emerging areas of glycoscience, including the synthesis of triazole appended carbohydrate-containing molecular architectures (mainly glycohybrids, glycoconjugates, glycopolymers, glycopeptides, glycoproteins, glycolipids, glycoclusters, and glycodendrimers through regioselective triazole forming modular and bio-orthogonal coupling protocols). It discusses the widespread applications of these glycoproducts as enzyme inhibitors in drug discovery and development, sensing, gelation, chelation, glycosylation, and catalysis. This review also covers the impact of click chemistry and provides future perspectives on its role in various emerging disciplines of science and technology.

Synthesis and characterization of a small library of bisglucosides: Influence of the nature of the diol/diphenol used in O-glucosylation

In this paper, the synthesis of different bisglucosides is investigated through the reaction of two acetylated glucose units with a diol (or diphenol) in order to develop a versatile molecular platform for the future development of bio-based polymers. A panel of five diols and one diphenol is initially used in order to examine the influence of their chemical skeleton on the reaction yield and both nature and proportion of formed species. Reaction products are identified using ¹H and ¹³C NMR spectroscopies completed by MALDI-TOF MS technique. The nucleophilicity of these dihydroxy compounds is identified as being the main factor that governs the reaction characteristics. In particular, the best selectivity is obtained with the use of hydroquinone. Inversely, by-products (oligomers, deacetylated compounds) are observed with the diols defined by higher nucleophilicity despite the choice of stereoselective pathway using acyl protecting groups.

Synthesis and Cytotoxic Activity of New 1,3,4-Thiadiazole Thioglycosides and 1,2,3-Triazolyl-1,3,4-Thiadiazole N-glycosides

New 1,3,4-thiadiazole thioglycosides linked to substituted arylidine systems were synthesized via glycosylation of the prepared 1,3,4-thiadiazole thiol compounds. Click strategy was also used for the synthesis of new 1,3,4-thiadiazole and 1,2,3-triazole hybrid glycosides by reaction of the acetylenic derivatives with different glycosyl azids followed by deacetylation process. The cytotoxic activities of the prepared compounds were studied against HCT-116 (human colorectal carcinoma) and MCF-7 (human breast adenocarcinoma) cell lines using the MTT assay. The results showed that the key thiadiazolethione compounds 2 and 3, the triazole glycosides linked to p-methoxyarylidine derivatives 14 and 15 in addition to the free hydroxyl glycoside 20 were found potent in activity comparable to the reference drug doxorubicin against MCF-7 human cancer cells. The acetylenic derivative 2 and glycoside 20 were also found highly active against HCT-116 cell lines.

Synthesis and anti-H5N1 virus activity of triazole- and oxadiazole-pyrimidine hybrids and their nucleoside analogs

New 1,2,3-triazole glycosides and 1,2,4-thioglycosides incorporating a substituted pyrimidinedione ring system were synthesized via click dipolar cycloaddition and heterocyclization of hydrazine-1-carbodithioate derivatives, respectively. The sugar hydrazine derivatives linked aminodimethyluracil were also prepared. In addition, the oxadiazoline substituted with acyclic sugar moieties linked to the pyrimidinedione as acyclic nucleoside analogs were synthesized. The antiviral activity of the synthesized compounds against avian influenza H5N1 virus was investigated and compounds 18, 13 and 19 showed good activities against the virus strains.

A synthetic approach to 'click' neoglycoprotein analogues of EPO employing one-pot native chemical ligation and CuAAC chemistry

The clinical significance of batch-wise variability on the pharmacokinetics and potency of commercial erythropoietin (EPO), prepared recombinantly as a heterogeneous mixture of glycoforms, necessitates the development of synthetic strategies to afford homogenous EPO formulations. Herein we present a previously unexplored and divergent route towards 'click' neoglycoprotein analogues of EPO, employing one-pot native chemical ligation (NCL) of alkynylated peptides and copper-catalysed azide-alkyne cycloaddition (CuAAC) with azido monosaccharides. By design, our synthetic platform permits glycosylation at virtually any stage, providing flexibility for the synthesis of various glycoforms for biological analysis. Insights obtained from attempted folding of our 'click' neoglycoprotein EPO analogue, bearing four different neutral sugar moieties, highlight the important role played by the charged oligosaccharides present in native EPO glycoproteins.

Using gene expression database to uncover biology functions of 1,4-disubstituted 1,2,3-triazole analogues synthesized via a copper (I)-catalyzed reaction

We have synthesized bioactive 1,4-disubstituted 1,2,3-triazole analogues containing 2H-1,4-benzoxazin-3-(4H)-one derivatives via 1,3-dipolar cycloaddition in the presence of CuI. All the reactions proceeded smoothly and afforded its desired products in excellent yields. Among these analogues, 3y exhibited a better cytotoxic effect on human hepatocellular carcinoma (HCC) Hep 3B cells and displayed less cytotoxicity on normal human umbilical vein endothelial cells, compared with Sorafenib, a targeted therapy for advanced HCC. 3y also induced stronger apoptosis and autophagy. Addition of curcumin enhanced 3y-induced cytotoxicity by further induction of autophagy. Using gene expression signatures of 3y to query Connectivity Map, a glycogen synthase kinase-3 inhibitor (AR-A014418) was predicted to display similar molecular action of 3y. Experiments further demonstrate that AR-A014418 acted like 3y, and vice versa. Overall, our data suggest the chemotherapeutic potential of 3y on HCC.

Cu-Catalyzed Click Reaction in Carbohydrate Chemistry

Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), popularly known as the "click reaction", serves as the most potent and highly dependable tool for facile construction of simple to complex architectures at the molecular level. Click-knitted threads of two exclusively different molecular entities have created some really interesting structures for more than 15 years with a broad spectrum of applicability, including in the fascinating fields of synthetic chemistry, medicinal science, biochemistry, pharmacology, material science, and catalysis. The unique properties of the carbohydrate moiety and the advantages of highly chemo- and regioselective click chemistry, such as mild reaction conditions, efficient performance with a wide range of solvents, and compatibility with different functionalities, together produce miraculous neoglycoconjugates and neoglycopolymers with various synthetic, biological, and pharmaceutical applications. In this review we highlight the successful advancement of Cu(I)-catalyzed click chemistry in glycoscience and its applications as well as future scope in different streams of applied sciences.

Cholesterol appended bis-1,2,3-triazoles as simple supramolecular gelators for the naked eye detection of Ag+, Cu2+ and Hg2+ ions

Cholesterol coupled bis-1,2,3-triazoles have been designed and synthesized. Their gelation abilities and cation responsive behaviors are documented.

Design and synthesis of multivalent neoglycoconjugates by click conjugations

A highly stereoselective BF₃∙OEt₂-promoted tandem hydroamination/glycosylation on glycal scaffolds has been developed to form propargyl 3-tosylamino-2,3-dideoxysugars in a one-pot manner. Subsequent construction of multivalent 3-tosylamino-2,3-dideoxyneoglycoconjugates with potential biochemical applications was presented herein involving click conjugations as the key reaction step. The copper-catalyzed regioselective click reaction was tremendously accelerated with assistance of microwave irradiation.

“One-pot” access to α-d-mannopyranosides from glycals employing ruthenium catalysis

An efficient and convenient one-pot method for the preparation of α-d-mannopyranosides from glycal is described.

Synthesis of sulfonamide-conjugated glycosyl-amino acid building blocks

The efficient synthesis of novel glycoconjugate amino acid building blocks wherein the amino acid and carbohydrate moieties are linked via a sulfonamide functional group is reported. The general reaction sequence consists of coupling a glycosyl thioacetate to an amino acid methyl ester followed by oxidation and deprotection of the carbohydrate moiety. We demonstrate the synthesis of derivatives from a range of amino acids, with reaction at either the α-amino group of amino acid precursors or the sidechain ε-amino group of lysine precursors.

Multivalent glycoconjugate syntheses and applications using aromatic scaffolds

Glycan-protein interactions are of utmost importance in several biological phenomena. Although the variety of carbohydrate residues in mammalian cells is limited to less than a dozen different sugars, their spatial topographical presentation in what is now associated as the "glycocodes" provides the fundamental keys for specific and high affinity "lock-in" recognition events associated with a wide range of pathologies. Toward deciphering our understanding of these glycocodes, chemists have developed new creative tools that included dendrimer chemistry in order to provide monodisperse multivalent glycoconjugates. This review provides a survey of the numerous aromatic architectures generated for the multivalent presentation of relevant carbohydrates using covalent attachment or supramolecular self-assemblies. The basic concepts toward their controlled syntheses will be described using modern synthetic procedures with a particular emphasis on powerful organometallic methodologies. The large variety of dendritic aromatic scaffolds, together with a brief survey of their unique biophysical and biological properties will be critically reviewed. The distinctiveness of the resulting multivalent glycoarchitectures, encompassing glycoclusters, glycodendrimers and molecularly defined self-assemblies, in forming well organized cross-linked lattices with multivalent carbohydrate binding proteins (lectins) together with their photophysical, medical, and imaging properties will also be briefly highlighted. The topic will be presented in increasing order of aromatic backbone complexities and will end with fullerenes together with self-assembled nanostructures, thus complementing the various scaffolds described in this special thematic issue dedicated to multivalent glycoscience.

One-Pot, Three-Step Reaction of 5-[(Trimethylsilyl)ethynyl]pyrrolidin-2-one with Azides Catalyzed by CuI: Synthesis of a Novel Class of 1,4-Disubstituted 1,2,3-Triazoles

A very fast, easy and efficient synthesis is described for a novel and biologically important class of 1,4-disubstituted-4-(5-pyrrolidin-2-one)-1,2,3-triazoles by an ultrasound-assisted one-pot, three-step click reaction sequence of 5-[(trimethylsilyl)ethynyl]pyrrolidin-2-one with organic azides mediated by catalytic CuI salts.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for the period 2005-2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI-TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI-MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate-protein complexes and glycodendrimers are highlighted in this final section.

Nicotinic acid adenine dinucleotide phosphate analogues containing substituted nicotinic acid: effect of modification on Ca(2+) release

Analogues of nicotinic acid adenine dinucleotide phosphate (NAADP) with substitution at either the 4- or the 5-position position of the nicotinic acid moiety have been synthesized from NADP enzymatically using Aplysia californica ADP-ribosyl cyclase or mammalian NAD glycohydrolase. Substitution at the 4-position of the nicotinic acid resulted in the loss of agonist potency for release of Ca(2+)-ions from sea urchin egg homogenates and in potency for competition ligand binding assays using [(32)P]NAADP. In contrast, several 5-substituted NAADP derivatives showed high potency for binding and full agonist activity for Ca(2+) release. 5-Azido-NAADP was shown to release calcium from sea urchin egg homogenates at low concentration and to compete with [(32)P]NAADP in a competition ligand binding assay with an IC(50) of 18 nM, indicating that this compound might be a potential photoprobe useful for specific labeling and identification of the NAADP receptor.

Azide-alkyne "click" conjugation of 8-aza-7-deazaadenine-DNA: synthesis, duplex stability, and fluorogenic dye labeling

The internal dye labeling of DNA by the Huisgen-Meldal-Sharpless "click" reaction is described. Fluorogenic 9-azidomethyl anthracene 2 and 3-azido-7-hydroxycoumarin 3 were employed in the postsynthetic functionalization of oligonucleotides incorporating octa-(1,7)-diynyl-8-aza-7-deaza-2'-deoxyadenosine 1. Nucleoside 1 was prepared by Sonogashira cross coupling from the corresponding 7-iodo compound, converted into the corresponding phosphoramidite, and oligonucleotides were synthesized. To evaluate the influence of ligands on the oligonucleotide duplex stability, benzyl azide 4 (nonpolar), and 2',3'-dideoxy azidothymidine 5 (AZT) (polar) were introduced along with the fluorogenic dyes 2 and 3. DNA duplexes with octa-1,7-diynyl side chains (i.e., containing 1) are more stable than oligonucleotides containing 8-aza-7-deaza-2'-deoxyadenosine, unveiling that this side chain has steric freedom. A single conjugation by an anthracene residue led to a 9 °C T(m) increase of duplex melting. Contrary to 7-deazaadenine dye conjugates, the 8-aza-7-deazaadenine conjugates show virtually no fluorescence quenching, thereby developing almost as strong fluorescence as side chain click derivatives (32 and 33) in the absence of 8-aza-7-deazaadenine moiety. Duplexes containing the 8-aza-7-deazaadenine dye conjugate show increased fluorescence over single-stranded DNA. Mismatches with dA, dG, and dC develop reduced fluorescence compared to the fully matched base pair. Molecular dynamics simulations revealed that the bulky dye molecules are accommodated well in duplex DNA.

Synthesis of function-oriented 2-phenyl-2H-chromene derivatives using L-pipecolinic acid and substituted guanidine organocatalysts

Organocatalytic domino oxa-Michael/aldol reactions between salicylaldehyde with electron deficient olefins are presented. We screened guanidine, 1,1,3,3-tetramethylguanidine (TMG) and L-pipecolinic acid as organocatalysts for this transformation. 3-Substituted 2-phenyl-2H-chromene derivatives are synthesized with high yields and with poor enantioselectivity (5-17% ee) using L-pipecolinic acid while TMG works well with cinnamaldehyde without using co-catalyst. These 3-substituted-2-phenyl-2H-chromene derivatives are further derivatized to synthesize triazole and biotin-containing chromene derivatives, to facilitate purification of protein targets.