Click chemistry oligomerisation of azido-alkyne-functionalised galactose accesses triazole-linked linear oligomers and macrocycles that inhibit Trypanosoma cruzi macrophage invasion

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.

Growing Impact of Intramolecular Click Chemistry in Organic Synthesis

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

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.

An Overview on Glyco-Macrocycles: Potential New Lead and their Future in Medicinal Chemistry

Macrocycles cover a small segment of molecules with a vast range of biological activity in the chemotherapeutic world. Primarily, the natural sources derived from macrocyclic drug candidates with a wide range of biological activities are known. Further evolutions of the medicinal chemistry towards macrocycle-based chemotherapeutics involve the functionalization of the natural product by hemisynthesis. More recently, macrocycles based on carbohydrates have evolved a considerable interest among the medicinal chemists worldwide. Carbohydrates provide an ideal scaffold to generate chiral macrocycles with well-defined pharmacophores in a decorated fashion to achieve the desired biological activity. We have given an overview on carbohydrate-derived macrocycle involving their synthesis in drug design and discovery and potential role in medicinal chemistry.

Linear triazole-linked pseudo oligogalactosides as scaffolds for galectin inhibitor development

Galectins play key roles in numerous biological processes. Their mode of action depends on their localization which can be extracellular, cytoplasmic, or nuclear and is partly mediated through interactions with β-galactose containing glycans. Galectins have emerged as novel therapeutic targets notably for the treatment of inflammatory disorders and cancers. This has stimulated the design of carbohydrate-based inhibitors targeting the carbohydrate recognition domains (CRDs) of the galectins. Pursuing this approach, we reasoned that linear oligogalactosides obtained by straightforward iterative click chemistry could mimic poly-lactosamine motifs expressed at eukaryote cell surfaces which the extracellular form of galectin-3, a prominent member of the galectin family, specifically recognizes. Affinities toward galectin-3 consistently increased with the length of the representative oligogalactosides but without reaching that of oligo-lactosamines. Elucidation of the X-ray crystal structures of the galectin-3 CRD in complex with a synthesized di- and tri-galactoside confirmed that the compounds bind within the carbohydrate-binding site. The atomic structures revealed that binding interactions mainly occur with the galactose moiety at the non-reducing end, primarily with subsites C and D of the CRD, differing from oligo-lactosamine which bind more consistently across the whole groove formed by the five subsites (A-E) of the galectin-3 CRD.

Galactosyl and sialyl clusters: synthesis and evaluation against T. cruzi parasite

The multivalent effect of carbohydrates (glycoclusters) has been explored to study important biological targets and processes involving Trypanosoma cruzi (T. cruzi) infection. Likewise, CuAAC cycloaddition reactions (click chemistry) have been applied as useful strategy in the discovery of bioactive molecules. Hence, we describe the synthesis of 1,2,3-triazole-based tetravalent homoglycoclusters (1–3) and heteroglycoclusters (4 and 5) of d-galactopyranose (C-1 and C-6 positions) and sialic acid (C-2 position) to assess their potential to inhibit T. cruzi cell invasion and also its cell surface trans-sialidase (TcTS). The target compounds were synthesised in good yields (52–75 %) via click chemistry by coupling azidosugars galactopyranose and sialic acid with alkynylated pentaerythritol or tris(hydroxymethyl)-aminomethane (TRIS) scaffolds. T. cruzi cell invasion inhibition assays showed expressive low parasite infection index values (5.3–6.8) for most compounds. However, most glycoclusters proved to be weak TcTS inhibitors at 1 mM (<17 %), except the tetravalent sialic acid 3 (99 % at 1 mM, IC50 450 μM). Therefore, we assume that T. cruzi cell invasion blockage is not due to TcTS inhibition by itself, but rather by other mechanisms involved in this process. In addition, all glycoclusters were not cytotoxic and had significant trypanocidal activity upon parasite survival of amastigote forms.

Trypanosoma cruzi trans-sialidase alternative substrates: Study of the effect of substitution in C-6 in benzyl β-lactoside

Trypanosoma cruzi trans-sialidase (TcTS) is a cell surface protein that participates in the adhesion and invasion mechanisms of the parasite into the host cells, making it an attractive target for inhibitors design. In order to contribute to the knowledge of the interaction between TcTS and their acceptor substrates, we designed and synthesized a library of 20 benzyl lactosides substituted in C-6 of the glucose residue with a series of 1,2,3-triazole derivatives containing different aromatic substituents in the C-4 position. The library was prepared by alkyne-azide cycloaddition reaction catalyzed by Cu(I) ("click chemistry") between a benzyl β-lactoside functionalized with an azide group in the C-6 position and a series of 2-propargyl phenyl ethers. Herein we analyzed the chromatographic behavior on high performance anion exchange chromatography (HPAEC) of the triazoyl-lactose derivatives and their activity as acceptors of TcTS and inhibitors of the sialylation of N-acetyllactosamine. The triazoyl derivatives were obtained with excellent yields and all of them behaved as moderate alternative substrates. The presence of bulky hydrophobic substituents dramatically increased the retention times in HPAEC but did not affect significantly their acceptor properties toward TcTS.

An eco-compatible strategy for the diversity-oriented synthesis of macrocycles exploiting carbohydrate-derived building blocks

An efficient, eco-compatible diversity-oriented synthesis (DOS) approach for the generation of library of sugar embedded macrocyclic compounds with various ring size containing 1,2,3-triazole has been developed. This concise strategy involves the iterative use of readily available sugar-derived alkyne/azide-alkene building blocks coupled through copper catalyzed azide-alkyne cycloaddition (CuAAC) reaction followed by pairing of the linear cyclo-adduct using greener reaction conditions. The eco-compatibility, mild reaction conditions, greener solvents, easy purification and avoidance of hazards and toxic solvents are advantages of this protocol to access this important structural class. The diversity of the macrocycles synthesized (in total we have synthesized 13 macrocycles) using a set of standard reaction protocols demonstrate the potential of the new eco-compatible approach for the macrocyclic library generation.

Nanotechnology in Glycomics: Applications in Diagnostics, Therapy, Imaging, and Separation Processes

This review comprehensively covers the most recent achievements (from 2013) in the successful integration of nanomaterials in the field of glycomics. The first part of the paper addresses the beneficial properties of nanomaterials for the construction of biosensors, bioanalytical devices, and protocols for the detection of various analytes, including viruses and whole cells, together with their key characteristics. The second part of the review focuses on the application of nanomaterials integrated with glycans for various biomedical applications, that is, vaccines against viral and bacterial infections and cancer cells, as therapeutic agents, for in vivo imaging and nuclear magnetic resonance imaging, and for selective drug delivery. The final part of the review describes various ways in which glycan enrichment can be effectively done using nanomaterials, molecularly imprinted polymers with polymer thickness controlled at the nanoscale, with a subsequent analysis of glycans by mass spectrometry. A short section describing an active glycoprofiling by microengines (microrockets) is covered as well.

Impact of cyclic topology: odd–even glass transition temperatures and fluorescence quantum yields in molecularly-defined macrocycles

The topological structure of cyclic-TPE_n+1 (n = 1–6) induces odd–even effects on the T_g and AIE behavior, arising from the alternation of intermolecular interactions.

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.