Design and creativity in synthesis of multivalent neoglycoconjugates

Metallo-Glycodendrimeric Materials against Enterotoxigenic Escherichia coli

Conjugation of carbohydrates to nanomaterials has been extensively studied and recognized as an alternative in the biomedical field. Dendrimers synthesized with mannose at the end group and with entrapped zero-valent copper/silver could be a potential candidate against bacterial proliferation. This study is aimed at investigating the bactericidal activity of metal-glycodendrimers. The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was used to synthesize a new mannosylated dendrimer containing 12 mannopyranoside residues in the periphery. The enterotoxigenic Escherichia coli fimbriae 4 (ETEC:F4) viability, measured at 600 nm, showed the half-inhibitory concentration (IC50) of metal-free glycodendrimers (D), copper-loaded glycodendrimers (D:Cu) and silver-loaded glycodendrimers (D:Ag) closed to 4.5 × 101, 3.5 × 101 and to 1.0 × 10-2 µg/mL, respectively, and minimum inhibitory concentration (MIC) of D, D:Cu and D:Ag of 2.0, 1.5 and 1.0 × 10-4 µg/mL, respectively. The release of bacteria contents onto broth and the inhibition of ETEC:F4 biofilm formation increased with the number of metallo-glycodendrimer materials, with a special interest in silver-containing nanomaterial, which had the highest activity, suggesting that glycodendrimer-based materials interfered with bacteria-bacteria or bacteria-polystyrene interactions, with bacteria metabolism and can disrupt bacteria cell walls. Our findings identify metal-mannose-dendrimers as potent bactericidal agents and emphasize the effect of entrapped zero-valent metal against ETEC:F4.

Synthesis, structural study and antitumor activity of novel alditol-based imidazophenanthrolines (aldo-IPs)

A series of 1H-imidazo [4,5-f][1,10] phenanthroline derivatives functionalized at 2-position with chiral, and conformationally flexible polyhydroxy alkyl chains derived from carbohydrates (alditol-based imidazophenanthrolines, aldo-IPs) is presented herein. These novel glycomimetics showed relevant and differential cytotoxic activity against several cultured tumor cell lines (PC3, HeLa and HT-29), dependent on the nature and stereochemistry of the polyhydroxy alkyl chain. The mannose-based aldo-IP demonstrated the higher cytotoxicity in the series, substantially better than cisplatin metallo-drug in all cell lines tested, and better than G-quadruplex ligand 360A in HeLa and HT29 cells. Cell cycle experiments and Annexin V-PI assays revealed that aldo-IPs induce apoptosis in HeLa cells. Initial study of DNA interactions by DNA FRET melting assays proved that the aldo-IPs produce only a slight thermal stabilization of DNA secondary structures, more pronounced in the case of quadruplex DNA. Viscosity titrations with CT dsDNA suggest that the compounds behave as DNA groove binders, whereas equilibrium dialysis assays showed that the compounds bind CT with Ka values in the range 104-105 M-1. The aldo-IP derivatives were obtained with synthetically useful yields through a feasible one-pot multistep process, by aerobic oxidative cyclization of 1,10-phenanthroline-5,6-diamine with a selection of unprotected aldoses using (NH4)2SO4 as promoter.

Con A lectin binding by synthetic bivalent arabinomannan tri- and pentasaccharides reveals connectivity-dependent functional valencies

Lectin Con A, with specificity to interact with α-d-mannopyranoside, achieves tight binding affinity with the aid of optimal multivalent ligand valencies, distances and orientations between the ligands. A series of synthetic arabinomannans, possessing arabinan core and mannan at the non-reducing ends, is studied to assess the above constraints involved with lectin binding in this report. Trisaccharides, with (1 → 2)(1 → 3), (1 → 2)(1 → 5) and (1 → 3)(1 → 5) glycosidic bond connectivities, and a pentasaccharide with mannopyranosides at the non-reducing ends are synthesized. The binding affinities of the mannose bivalent ligands are studied with tetrameric Con A lectin by isothermal titration calorimetry (ITC). Among the derivatives, trisaccharide with (1 → 2)(1 → 3) glycosidic bond connectivity and the pentasaccharide undergo lectin interaction, clearly fulfilling the bivalent structural and functional valencies. Remaining oligosaccharides exhibit only a functional monovalency, defying the bivalent structural valency. The trisaccharide fulfilling the structural and functional valencies represent the smallest bivalent ligand, undergoing the lectin interaction in a trans-mode.

A brief account of evolution of assays to study carbohydrate-protein interaction

Molecular recognition remains one of the most desirable means of cellular communication. Each cell offers a unique surface pattern of biomolecules that makes it very specific about the nature of molecules that interact with the cell. Protein-glycan interaction has been one of the most common forms of cell signaling. Glycans expressed on the cell surface interact with an exogenous protein, and in many cases lead to a physiological response. These carbohydrate-binding proteins, commonly known as lectins, are very specific to the glycan they bind to. An exogenous lectin interacting with an animal cell surface glycan is generally studied using the classical hemagglutination assay. However, this method presents certain challenges that make it imperative to design and develop novel methods that are more specific and efficient in their interaction. In the last decade, a few methods have been developed to analyze more diverse reactions and use a lesser amount of sample. In some cases, the processing of the sample is also reduced. This review discusses how the methods have evolved over the decades and how they have reduced error while becoming more efficient.

Galectin-3 and Epithelial MUC1 Mucin-Interactions Supporting Cancer Development

Aberrant glycosylation of cell surface proteins is a very common feature of many cancers. One of the glycoproteins, which undergoes specific alterations in the glycosylation of tumor cells is epithelial MUC1 mucin, which is highly overexpressed in the malignant state. Such changes lead to the appearance of tumor associated carbohydrate antigens (TACAs) on MUC1, which are rarely seen in healthy cells. One of these structures is the Thomsen-Friedenreich disaccharide Galβ1-3GalNAc (T or TF antigen), which is typical for about 90% of cancers. It was revealed that increased expression of the T antigen has a big impact on promoting cancer progression and metastasis, among others, due to the interaction of this antigen with the β-galactose binding protein galectin-3 (Gal-3). In this review, we summarize current information about the interactions between the T antigen on MUC1 mucin and Gal-3, and their impact on cancer progression and metastasis.

Synthesis and evaluation of 1,5-dithialaminaribiose and -triose tetravalent constructs

We report the synthesis of novel tetravalent glucoclusters containing 1,5-dithia mimetics of laminaribiose and triose. The new constructs were evaluated for their ability to inhibit anti-CR3 fluorescent staining of human neutrophils, for which they showed moderate affinity. Evaluation of the synthesized glycoclusters for their ability to inhibit anti-Dectin-1 fluorescent staining of mouse macrophages revealed little to no affinity for Dectin-1.

Catanionic Vesicles as a Facile Scaffold to Display Natural N-Glycan Ligands for Probing Multivalent Carbohydrate-Lectin Interactions

Multivalent interactions are a key characteristic of protein-carbohydrate recognition. Phospholipid-based liposomes have been explored as a popular platform for multivalent presentation of glycans, but this platform has been plagued by the instability of typical liposomal formulations in biological media. We report here the exploitation of catanionic vesicles as a stable lipid-based nanoparticle scaffold for displaying large natural N-glycans as multivalent ligands. Hydrophobic insertion of lipidated N-glycans into the catanionic vesicle bilayer was optimized to allow for high-density display of structurally diverse N-glycans on the outer membrane leaflet. In an enzyme-linked competitive lectin-binding assay, the N-glycan-coated vesicles demonstrated a clear clustering glycoside effect, with significantly enhanced affinity for the corresponding lectins including Sambucus nigra agglutinin (SNA), concanavalin A (ConA), and human galectin-3, in comparison with their respective natural N-glycan ligands. Our results showed that relatively low density of high-mannose and sialylated complex type N-glycans gave the maximal clustering effect for binding to ConA and SNA, respectively, while relatively high-density display of the asialylated complex type N-glycan provided maximal clustering effects for binding to human galectin 3. Moreover, we also observed a macromolecular crowding effect on the binding of ConA to high-mannose N-glycans when catanionic vesicles bearing mixed high-mannose and complex-type N-glycans were used. The N-glycan-coated catanionic vesicles are stable and easy to formulate with varied density of ligands, which could serve as a feasible vehicle for drug delivery and as potent inhibitors for intervening protein-carbohydrate interactions implicated in disease.

Validation of Selective Capture of Fimbriated Uropathogenic Escherichia coli by a Label-free Engineering Detection System Using Mannosylated Surfaces

Label-free detection of pathogens is of major concern to the microbiologist community. Most procedures require several steps and amplification techniques. Carbohydrates are well-established receptors for host-pathogen interactions, which can be amplified using glycodendritic architectures on the basis of multivalent binding interactions. Given that uropathogenic Escherichia coli bacterial FimH is based on such mannopyranoside-binding interactions, we demonstrate herein that synthetic monomeric and trimeric thiolated α-d-mannosides can be effectively bound to gold substrate-functionalized self-assembled monolayers (SAMs) preactivated with maleimide functionalities. Mannosides grafted onto SAMs were followed using Quartz Crystal Microbalance with Dissipation (QCM-D). Binding recognition efficiency was first evaluated using the plant lectin from Canavalia ensiformis (ConA) also using QCM-D. We showed a direct correlation between the amount of mannoside bound and the lectin attachment. Even though there was less trimer bound (nM/cm²) to the surface, we observed a 7-fold higher amount of lectin anchoring, thus further demonstrating the value of the multivalent interactions. We next examined the relative fimbriated E. coli selective adhesion/capture to either the monomeric or the trimeric mannoside bound to the surface. Our results established the successful engineering of the surfaces to show E. coli adhesion via specific mannopyranoside binding but unexpectedly, the monomeric derivative was more efficient than the trimeric analog, which could be explained by steric hindrance. This approach strongly suggests that it could be broadly applicable to other Gram-negative bacteria sharing analogous carbohydrate-dependent binding interactions.

Extending the in vivo persistence of synthetic glycoconjugates using a serum-protein binder

Synthetic glycoconjugates are used in the development of vaccines and the design of inhibitors for glycan-protein interactions. The in vivo persistence of synthetic glycoconjugates is an important factor in their efficacy, especially when prolonged interactions with specific cell types may be required. In this study, we applied a strategy for non-covalent association of an active compound with serum proteins for extension of glycoconjugate half-life in serum. The small molecule, AG10, has previously been used to extend the half-life of small molecules through its high affinity for transthyretin (TTR), a serum protein. Using a tetravalent polyethylene glycol (PEG)-based scaffold we developed a synthetic strategy for glycoconjugates that allowed for controlled addition of multiple tags, such as a TTR affinity tag or fluorophore. We designed a version of AG10 modified at the pyrazole core, named GD10, amenable to our conjugation strategy and introduced to glycoconjugates using a tri-functional linker. This approach allowed for attachment of GD10 and fluorophore tags, as well as carbohydrate antigens. We then tested the influence of the GD10 tag on glycoconjugate half-life in vivo using a mouse model. Our results suggest that the combination of the GD10 tag and the PEG scaffold extended the half-life of glycoconjugates by as much as 10-fold when compared to proteins of similar molecular weight. The GD10 tag was able to extend the half-life of similar glycoconjugates by as much as 2-fold. We observed a role for the terminal saccharide residue of the carbohydrate antigen and confirmed that conjugates were able to penetrate multiple compartments in vivo including bone marrow, lymph nodes, and other organs. The introduction of the GD10 tag did not obstruct the ability of conjugates to interact with lectin receptors. We conclude that serum protein binders can be used to extend the persistence of glycoconjugates in vivo.

Photoswitching Affinity and Mechanism of Multivalent Lectin Ligands

Multivalent receptor–ligand binding is a key principle in a plethora of biological recognition processes. Immense binding affinities can be achieved with the correct spatial orientation of the ligands. Accordingly, the incorporation of photoswitches, which can be used to reversibly change the spatial orientation of molecules, into multivalent ligands is a means to alter the binding affinity and possibly also the binding mode of such ligands. We report a divalent ligand for the model lectin wheat germ agglutinin (WGA) containing an arylazopyrazole photoswitch. This switch, which has recently been introduced as an alternative to the more commonly used azobenzene moiety, is characterized by almost quantitative E/Z photoswitching in both directions, high quantum yields, and high thermal stability of the Z isomer. The ligand was designed in a way that only one of the isomers is able to bridge adjacent binding sites of WGA leading to a chelating binding mode. Photoswitching induces an unprecedentedly high change in lectin binding affinity as determined by isothermal titration calorimetry (ITC). Furthermore, additional dynamic light scattering (DLS) data suggest that the binding mode of the ligand changes from chelating binding of the E isomer to crosslinking binding of the Z isomer.

Homo- and Heterogeneous Glycoconjugates on the Basis of N-Glycans and Human Serum Albumin: Synthesis and Biological Evaluation

Neoglycoconjugates mimicking natural compounds and possessing a variety of biological functions are very successful tools for researchers to understand the general mechanisms of many biological processes in living organisms. These substances are characterized by high biotolerance and specificity, with low toxicity. Due to the difficult isolation of individual glycoclusters from biological objects, special interest has been directed toward synthetic analogs. This review is mainly focused on the one-pot, double-click methodology (containing alkyne–azide click cycloaddition with the following 6π-azaelectrocyclization reactions) used in the synthesis of N-glycoconjugates. Homogeneous (including one type of biantennary N-glycan fragments) and heterogeneous (containing two to four types of biantennary N-glycan fragments) glycoclusters on albumin were synthesized via this strategy. A series of cell-, tissue- and animal-based experiments proved glycoclusters to be a very promising class of targeted delivery systems. Depending on the oligosaccharide units combined in the cluster, their amount, and arrangement relative to one another, conjugates can recognize various cells, including cancer cells, with high selectivity. These results open new perspectives for affected tissue visualization and treatment.

Carbosilane Glycodendrimers for Anticancer Drug Delivery: Synthetic Route, Characterization, and Biological Effect of Glycodendrimer-Doxorubicin Complexes

The complexity of drug delivery mechanisms calls for the development of new transport system designs. Here, we report a robust synthetic procedure toward stable glycodendrimer (glyco-DDM) series bearing glucose, galactose, and oligo(ethylene glycol)-modified galactose peripheral units. In vitro cytotoxicity assays showed exceptional biocompatibility of the glyco-DDMs. To demonstrate applicability in drug delivery, the anticancer agent doxorubicin (DOX) was encapsulated in the glyco-DDM structure. The anticancer activity of the resulting glyco-DDM/DOX complexes was evaluated on the noncancerous (BJ) and cancerous (MCF-7 and A2780) cell lines, revealing their promising generation- and concentration-dependent effect. The glyco-DDM/DOX complexes show gradual and pH-dependent DOX release profiles. Fluorescence spectra elucidated the encapsulation process. Confocal fluorescence microscopy demonstrated preferential cancer cell internalization of the glyco-DDM/DOX complexes. The conclusions were supported by computer modeling. Overall, our results are consistent with the assumption that novel glyco-DDMs and their drug complexes are very promising in drug delivery and related applications.

Critical parameters for design and development of multivalent nanoconstructs: recent trends

A century ago, the groundbreaking concept of the magic bullet was given by Paul Ehrlich. Since then, this concept has been extensively explored in various forms to date. The concept of multivalency is among such advancements of the magic bullet concept. Biologically, the concept of multivalency plays a critical role in significantly huge numbers of biochemical interactions. This concept is the sole reason behind the higher affinity of biological molecules like viruses to more selectively target the host cell surface receptors. Multivalent nanoconstructs are a promising approach for drug delivery by the active targeting principle. Designing and developing effective and target-specific multivalent drug delivery nanoconstructs, on the other hand, remain a challenge. The underlying reason for this is a lack of understanding of the crucial interactions between ligands and cell surface receptors, as well as the design of nanoconstructs. This review highlights the need for a better theoretical understanding of the multivalent effect of what happens to the receptor-ligand complex after it has been established. Furthermore, the critical parameters for designing and developing robust multivalent systems have been emphasized. We have also discussed current advances in the design and development of multivalent nanoconstructs for drug delivery. We believe that a thorough knowledge of theoretical concepts and experimental methodologies may transform a brilliant idea into clinical translation.

Siglecs as Therapeutic Targets in Cancer

Hypersialylation is a common post-translational modification of protein and lipids found on cancer cell surfaces, which participate in cell-cell interactions and in the regulation of immune responses. Sialic acids are a family of nine-carbon α-keto acids found at the outermost ends of glycans attached to cell surfaces. Given their locations on cell surfaces, tumor cells aberrantly overexpress sialic acids, which are recognized by Siglec receptors found on immune cells to mediate broad immunomodulatory signaling. Enhanced sialylation exposed on cancer cell surfaces is exemplified as "self-associated molecular pattern" (SAMP), which tricks Siglec receptors found on leukocytes to greatly down-regulate immune responsiveness, leading to tumor growth. In this review, we focused on all 15 human Siglecs (including Siglec XII), many of which still remain understudied. We also highlighted strategies that disrupt the course of Siglec-sialic acid interactions, such as antibody-based therapies and sialic acid mimetics leading to tumor cell depletion. Herein, we introduced the central roles of Siglecs in mediating pro-tumor immunity and discussed strategies that target these receptors, which could benefit improved cancer immunotherapy.

What is the Sugar Code?

A code is defined by the nature of the symbols, which are used to generate information‐storing combinations (e. g. oligo‐ and polymers). Like nucleic acids and proteins, oligo‐ and polysaccharides are ubiquitous, and they are a biochemical platform for establishing molecular messages. Of note, the letters of the sugar code system (third alphabet of life) excel in coding capacity by making an unsurpassed versatility for isomer (code word) formation possible by variability in anomery and linkage position of the glycosidic bond, ring size and branching. The enzymatic machinery for glycan biosynthesis (writers) realizes this enormous potential for building a large vocabulary. It includes possibilities for dynamic editing/erasing as known from nucleic acids and proteins. Matching the glycome diversity, a large panel of sugar receptors (lectins) has developed based on more than a dozen folds. Lectins ‘read’ the glycan‐encoded information. Hydrogen/coordination bonding and ionic pairing together with stacking and C−H/π‐interactions as well as modes of spatial glycan presentation underlie the selectivity and specificity of glycan‐lectin recognition. Modular design of lectins together with glycan display and the nature of the cognate glycoconjugate account for the large number of post‐binding events. They give an entry to the glycan vocabulary its functional, often context‐dependent meaning(s), hereby building the dictionary of the sugar code.

"Surface Density of Ligands Controls In-Plane and Aggregative Modes of Multivalent Glycovesicle-Lectin Recognitions"

Glycovesicles are ideal tools to delineate finer mechanisms of the interactions at the biological cell membranes.  Multivalency forms the basis which, in turn, should surpass more than one mechanism in order to maintain multiple roles that the ligand-lectin interactions encounter.  Ligand densities hold a prime control to attenuate the interactions.  In the present study, mannose trisaccharide interacting with a cognate receptor, namely, Con A, is assessed at the vesicle surfaces.  A synthetic (1→3)(1→6)-branched mannose trisaccharide is tethered with a diacetylene monomer and glycovesicles of varying sugar densities are prepared.  The polydiacetylene vesicles are prepared by maintaining uniform lipid concentrations.  The interactions of the glycovesicles with the lectin are probed through dynamic light scattering and UV-Vis spectroscopy techniques.  Binding efficacies are assessed by surface plasmon resonance technique.  Aggregative and in-plane modes of interactions follow a ligand density-dependant manner at the vesicle surface. Vesicles with sparsely populated ligands engage lectin in an aggregative mode (trans-), leading to a cross-linked complex formation.  Whereas glycovesicles imbedded with dense ligands engage lectin interaction in an in-plane mode  intramolecularly (cis-).  Sub-nanomolar dissociation constants govern the intramolecular interaction occurring within the plane of the vesicle, relatively more efficacious than the aggregative intermolecular interactions.

Synthesis of regioisomeric maltose-based Man/Glc glycoclusters to control glycoligand presentation in 3D space

The investigation of carbohydrate recognition in a natural environment suffers from the complexity of overlapping functional effects such as multivalency and heteromultivalency effects. Another key factor in carbohydrate recognition is the presentation mode of glycoligands in three-dimensional (3D) space. In order to trace out the effect of 3D ligand presentation, we utilized an oligosaccharide model to precisely control the spatial relation between a mannose ligand (Man) and a glucose moiety (Glc). A disaccharide (maltose) served as a scaffold to alternately conjugate Man and Glc at position 6 and 6' of a synthetic maltoside, resulting in a pair of regioisomeric heterobivalent glycoclusters. The biological effect of this specific structural tuning was tested in a native system employing mannose-specific adhesion of live E. coli cells. Indeed, the variable 3D presentation of the Man ligand resulted in a 2-fold difference between the regioisomeric heterobivalent glycoclusters as inhibitors of bacterial adhesion. This can be considered a remarkable effect, which could be interpreted by computer-aided modelling of the complexes between the bacterial lectin and the synthetic regioisomeric glycoligands.

Recent Development in the Design of Neoglycoliposomes Bearing Arborescent Architectures

This brief review highlights systematic progress in the design of synthetic glycolipid (neoglycolipids) analogs evolving from the conventional architectures of natural glycosphingolipids and gangliosides. Given that naturally occurring glycolipids are composed of only one hydrophilic sugar head-group and two hydrophobic lipid tails embedded in the lipid bilayers of the cell membranes, they usually require extraneous lipids (phosphatidylcholine, cholesterol) to confer their stability. In order to obviate the necessity for these additional stabilizing ingredients, recent investigations have merged dendrimer chemistry with that of neoglycolipid syntheses. This singular approach has provided novel glycoarchitectures allowing reconsidering the necessity for the traditional one to two hydrophilic/hydrophobic ratio. An emphasis has been provided in the recent design of modular arborescent neoglycolipid syntheses coined glycodendrimersomes.

A brief insight to the role of glyconanotechnology in modern day diagnostics and therapeutics

Carbohydrate-protein and carbohydrate-carbohydrate interactions are very important for various biological processes. Although the magnitude of these interactions is low compared to that of protein-protein interaction, the magnitude can be boosted by multivalent approach known as glycocluster effect. Nanoparticle platform is one of the best ways to present diverse glycoforms in multivalent manner and thus, the field of glyconanotechnology has emerged as an important field of research considering their potential applications in diagnostics and therapeutics. Considerable advances in the field have been achieved through development of novel techniques, use of diverse metallic and non-metallic cores for better efficacy and application of ever-increasing number of carbohydrate ligands for site-specific interaction. The present review encompasses the recent developments in the area of glyconanotechnology and their future promise as diagnostic and therapeutic tools.

Role of Recent Therapeutic Applications and the Infection Strategies of Shiga Toxin-Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) is a global foodborne bacterial pathogen that is often accountable for colon disorder or distress. STEC commonly induces severe diarrhea in hosts but can cause critical illnesses due to the Shiga toxin virulence factors. To date, there have been a significant number of STEC serotypes have been evolved. STECs vary from nausea and hemorrhoid (HC) to possible lethal hemolytic-based uremic syndrome (HUS), thrombotic thrombocytopenic purpura (TTP). Inflammation-based STEC is usually a foodborne illness with Shiga toxins (Stx 1 and 2) thought to be pathogenesis. The STEC's pathogenicity depends significantly on developing one or more Shiga toxins, which can constrain host cell protein synthesis leading to cytotoxicity. In managing STEC infections, antimicrobial agents are generally avoided, as bacterial damage and discharge of accumulated toxins are thought the body. It has also been documented that certain antibiotics improve toxin production and the development of these species. Many different groups have attempted various therapies, including toxin-focused antibodies, toxin-based polymers, synbiotic agents, and secondary metabolites remedies. Besides, in recent years, antibiotics' efficacy in treating STEC infections has been reassessed with some encouraging methods. Nevertheless, the primary role of synbiotic effectiveness (probiotic and prebiotic) against pathogenic STEC and other enteropathogens is less recognized. Additional studies are required to understand the mechanisms of action of probiotic bacteria and yeast against STEC infection. Because of the consensus contraindication of antimicrobials for these bacterial pathogens, the examination was focused on alternative remedy strategies for STEC infections. The rise of novel STEC serotypes and approaches employed in its treatment are highlighted.

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.

Dendritic-Like Molecules Built on a Pillar[5]arene Core as Hole Transporting Materials for Perovskite Solar Cells

Multi-branched molecules have recently demonstrated interesting behaviour as charge-transporting materials within the fields of perovskite solar cells (PSCs). For this reason, extended triarylamine dendrons have been grafted onto a pillar[5]arene core to generate dendrimer-like compounds, which have been used as hole-transporting materials (HTMs) for PSCs. The performances of the solar cells containing these novel compounds have been extensively investigated. Interestingly, a positive dendritic effect has been evidenced as the hole transporting properties are improved when going from the first to the second-generation compound. The stability of the devices based on the best performing pillar[5]arene material has been also evaluated in a high-throughput ageing setup for 500 h at high temperature. When compared to reference devices prepared from spiro-OMeTAD, the behaviour is similar. An analysis of the economic advantages arising from the use of the pillar[5]arene-based material revealed however that our pillar[5]arene-based material is cheaper than the reference.

Synthesis of Glycodendrimers with Antiviral and Antibacterial Activity

Glycodendrimers are an important class of synthetic macromolecules that can be used to mimic many structural and functional features of cell-surface glycoconjugates. Their carbohydrate moieties perform key important functions in bacterial and viral infections, often regulated by carbohydrate-protein interactions. Several studies have shown that the molecular structure, valency and spatial organisation of carbohydrate epitopes in glycoconjugates are key factors in the specificity and avidity of carbohydrate-protein interactions. Choosing the right glycodendrimers almost always helps to interfere with such interactions and blocks bacterial or viral adhesion and entry into host cells as an effective strategy to inhibit bacterial or viral infections. Herein, the state of the art in the design and synthesis of glycodendrimers employed for the development of anti-adhesion therapy against bacterial and viral infections is described.

Glyconanofluorides as Immunotracers with a Tunable Core Composition for Sensitive Hotspot Magnetic Resonance Imaging of Inflammatory Activity

Nature-inspired nanosized formulations based on an imageable, small-sized inorganic core scaffold, on which biomolecules are assembled to form nanobiomimetics, hold great promise for both early diagnostics and developed therapeutics. Nevertheless, the fabrication of nanobiomimetics that allow noninvasive background-free mapping of pathological events with improved sensitivity, enhanced specificity, and multiplexed capabilities remains a major challenge. Here, we introduce paramagnetic glyconanofluorides as small-sized (<10 nm) glycomimetics for immunotargeting and sensitive noninvasive in vivo¹⁹F magnetic resonance imaging (MRI) mapping of inflammation. A very short T₁ relaxation time (70 ms) of the fluorides was achieved by doping the nanofluorides' solid crystal core with paramagnetic Sm³⁺, resulting in a significant 8-fold enhancement in their ¹⁹F MRI sensitivity, allowing faster acquisition and improved detectability levels. The fabricated nanosized glycomimetics exhibit significantly enhanced uptake within activated immune cells, providing background-free in vivo mapping of inflammatory activity, demonstrated in both locally induced inflammation and clinically related neuropathology animal models. Fabricating two types of nanofluorides, each with a distinct chemical shift, allowed us to exploit the color-like features of ¹⁹F MRI to map, in real time, immune specificity and preferred targetability of the paramagnetic glyconanofluorides, demonstrating the approach's potential extension to noninvasive multitarget imaging scenarios that are not yet applicable for nanobiomimetics based on other nanocrystal cores.

Design, Synthetic Strategies, and Therapeutic Applications of Heterofunctional Glycodendrimers

Glycodendrimers have attracted considerable interest in the field of dendrimer sciences owing to their plethora of implications in biomedical applications. This is primarily due to the fact that cell surfaces expose a wide range of highly diversified glycan architectures varying by the nature of the sugars, their number, and their natural multiantennary structures. This particular situation has led to cancer cell metastasis, pathogen recognition and adhesion, and immune cell communications that are implicated in vaccine development. The diverse nature and complexity of multivalent carbohydrate-protein interactions have been the impetus toward the syntheses of glycodendrimers. Since their inception in 1993, chemical strategies toward glycodendrimers have constantly evolved into highly sophisticated methodologies. This review constitutes the first part of a series of papers dedicated to the design, synthesis, and biological applications of heterofunctional glycodendrimers. Herein, we highlight the most common synthetic approaches toward these complex molecular architectures and present modern applications in nanomolecular therapeutics and synthetic vaccines.

Grafting Dendrons onto Pillar[5]Arene Scaffolds

With their ten peripheral substituents, pillar[5]arenes are attractive compact scaffolds for the construction of nanomaterials with a controlled number of functional groups distributed around the macrocyclic core. This review paper is focused on the functionalization of pillar[5]arene derivatives with small dendrons to generate dendrimer-like nanomaterials and bioactive compounds. Examples include non-viral gene vectors, bioactive glycoclusters, and liquid-crystalline materials.

Recent development in the design of small 'drug-like' and nanoscale glycomimetics against Escherichia coli infections

Glycoconjugates are involved in several pathological processes. Glycomimetics that can favorably emulate complex carbohydrate structures, while competing with natural ligands as inhibitors, are gaining considerable attention owing to their improved hydrolytic stability, binding affinity, and pharmacokinetic (PK) properties. Of particular interest are the families of α-d-mannopyranoside analogs, which can be used as inhibitors against adherent invasive Escherichia coli infections. Bacterial resistance to modern antibiotics triggers the search for new alternative antibacterial strategies that are less susceptible to acquiring resistance. In this review, we highlight recent progress in the chemical syntheses of this family of compounds, one of which having reached clinical trials against Crohn's disease (CD).

Synthesis and evaluation of porphyrin glycoconjugates varying in linker length: preliminary effects on the photodynamic inactivation of Mycobacterium smegmatis

Porphyrins have served as common photosensitizing agents in photomedicine due to their unique properties and broad therapeutic potential. While photodynamic therapy (PDT) offers a promising avenue for novel drug development, limitations in application due to selectivity, and the inherent hydrophobicity and poor solubility of porphyrins and other organic photosensitizers has been noted. Porphyrin glycoconjugates have recently gained attention for their potential to overcome these limitations. However, little has been done to explore the effects of the linker between the carbohydrate and porphyrin analog. Here we report the synthesis of over 30 new carbohydrate-porphyrin conjugates which vary in the nature of the sugar (Gal, Glc, GalNAc, GlcNAc, Lac and Tre) and the distance between the porphyrin macrocycle and the carbohydrate. Porphyrin glycoconjugates were synthesized in three steps from a readily available meso-brominated diphenylporphyrin analog by (i) C-O coupling of an appropriate TMS-protected alkynol consisting of two to six carbon spacers (ii) removal of the TMS protecting group, and (iii) CuAAC conjugation with an appropriate glycosyl azide. First studies with trehalose-based glycoporphyrins and M. smeg were used to determine the effects of the linker in photodynamic inactivation (PDI) studies. Preliminary results demonstrated an increase in photodynamic inactivation with a decrease in linker length. Investigations are underway to determine the mechanism for these results.

Non-invasive intranasal administration route directly to the brain using dendrimer nanoplatforms: An opportunity to develop new CNS drugs

There are several routes of administration to the brain, including intraparenchymal, intraventricular, and subarachnoid injections. The blood-brain barrier (BBB) impedes the permeation and access of most drugs to the central nervous system (CNS), and consequently, many neurological diseases remain undertreated. For past decades, to circumvent this effect, several nanocarriers have been developed to deliver drugs to the brain. Importantly, intranasal (IN) administration can allow direct delivery of drugs into the brain through the anatomical connection between the nasal cavity and brain without crossing the BBB. In this regard, dendrimers may possess great potential to deliver drugs to the brain by IN administration, bypassing the BBB and reducing systemic exposure and side effects, to treat diseases of the CNS. In this original concise review, we highlighted the few examples advocated regarding the use of dendrimers to deliver CNS drugs directly via IN. This review highlighed the few examples of the association of dendrimer encapsulating drugs (e.g., small compounds: haloperidol and paeonol; macromolecular compounds: dextran, insulin and calcitonin; and siRNA) using IN administration. Good efficiencies were observed. In addition, we will present the in vivo effects of PAMAM dendrimers after IN administration, globally, showing no general toxicity.

Synthesis of Galectin Inhibitors by Regioselective 3'-O-Sulfation of Vanillin Lactosides Obtained under Phase Transfer Catalysis

Vanillin-based lactoside derivatives were synthetized using phase-transfer catalyzed reactions from per-O-acetylated lactosyl bromide. The aldehyde group of the vanillin moiety was then modified to generate a series of related analogs having variable functionalities in the para- position of the aromatic residue. The corresponding unprotected lactosides, obtained by Zemplén transesterification, were regioselectively 3'-O-sulfated using tin chemistry activation followed by treatment with sulfur trioxide-trimethylamine complex (Men3N-SO3). Additional derivatives were also prepared from the vanillin's aldehyde using a Knoevenagel reaction to provide extended α, β-unsaturated carboxylic acid which was next reduced to the saturated counterpart.

Glycosylated Nanoparticles for Cancer-Targeted Drug Delivery

Nanoparticles (NPs) are novel platforms that can carry both cancer-targeting molecules and drugs to avoid severe side effects due to nonspecific drug delivery in standard chemotherapy treatments. Cancer cells are characterized by abnormal membranes, metabolic changes, the presence of lectin receptors, glucose transporters (GLUT) overexpression, and glycosylation of immune receptors of programmed death on cell surfaces. These characteristics have led to the development of several strategies for cancer therapy, including a large number of carbohydrate-modified NPs, which have become desirable for use in cell-selective drug delivery systems because they increase nanoparticle-cell interactions and uptake of carried drugs. Currently, the potential of NP glycosylation to enhance the safety and efficacy of carried therapeutic antitumor agents has been widely acknowledged, and much information is accumulating in this field. This review seeks to highlight recent advances in NP stabilization, toxicity reduction, and pharmacokinetic improvement and the promising potential of NP glycosylation from the perspective of molecular mechanisms described for drug delivery systems for cancer therapy. From preclinical proof-of-concept to demonstration of therapeutic value in the clinic, the challenges and opportunities presented by glycosylated NPs, with a focus on their applicability in the development of nanodrugs, are discussed in this review.

A Strategy for Tumor Targeting by Higher-Order Glycan Pattern Recognition: Synthesis and In Vitro and In Vivo Properties of Glycoalbumins Conjugated with Four Different N-Glycan Molecules

Natural glycoconjugates that form glycocalyx play important roles in various biological processes based on cell surface recognition through pattern recognition mechanisms. This work represents a new synthesis-based screening strategy to efficiently target the cancer cells by higher-order glycan pattern recognition in both cells and intact animals (mice). The use of the very fast, selective, and effective RIKEN click reaction (6π-azaelectrocyclization of unsaturated imines) allows to synthesize and screen various structurally well-defined glycoalbumins containing two and eventually four different N-glycan structures in a very short time. The importance of glycan pattern recognition is exemplified in both cell- and mouse-based experiments. The use of pattern recognition mechanisms for cell targeting represents a novel and promising strategy for the development of diagnostic, prophylactic, and therapeutic agents for various diseases including cancers.

Crystal structures of peanut lectin in the presence of synthetic β-N- and β-S-galactosides disclose evidence for the recognition of different glycomimetic ligands

Carbohydrate-lectin interactions are involved in important cellular recognition processes, including viral and bacterial infections, inflammation and tumor metastasis. Hence, structural studies of lectin-synthetic glycan complexes are essential for understanding lectin-recognition processes and for the further design of promising chemotherapeutics that interfere with sugar-lectin interactions. Plant lectins are excellent models for the study of the molecular-recognition process. Among them, peanut lectin (PNA) is highly relevant in the field of glycobiology because of its specificity for β-galactosides, showing high affinity towards the Thomsen-Friedenreich antigen, a well known tumor-associated carbohydrate antigen. Given this specificity, PNA is one of the most frequently used molecular probes for the recognition of tumor cell-surface O-glycans. Thus, it has been extensively used in glycobiology for inhibition studies with a variety of β-galactoside and β-lactoside ligands. Here, crystal structures of PNA are reported in complex with six novel synthetic hydrolytically stable β-N- and β-S-galactosides. These complexes disclosed key molecular-binding interactions of the different sugars with PNA at the atomic level, revealing the roles of specific water molecules in protein-ligand recognition. Furthermore, binding-affinity studies by isothermal titration calorimetry showed dissociation-constant values in the micromolar range, as well as a positive multivalency effect in terms of affinity in the case of the divalent compounds. Taken together, this work provides a qualitative structural rationale for the upcoming synthesis of optimized glycoclusters designed for the study of lectin-mediated biological processes. The understanding of the recognition of β-N- and β-S-galactosides by PNA represents a benchmark in protein-carbohydrate interactions since they are novel synthetic ligands that do not belong to the family of O-linked glycosides.

Surface Ligand Density Switches Glycovesicles between Monomeric and Multimeric Lectin Recognition

Carbohydrate-protein interactions define a multitude of cellular recognition events. We present herein synthetic glycovesicles as cell-surface mimics in order to switch the nature of lectin recognition. The covalent glycovesicles, constituted with diacetylene monomers of various ligand densities at their surfaces, are prepared through photo-polymerization. Vesicles with sparsely imbedded ligands engage in a lectin interaction leading to the formation of a dense, crosslinked multimeric complex. On the other hand, vesicles with many ligands, or completely covered with them, switch the lectin interaction to form a fully soluble monomeric complex, without crosslinking. Nanomolar dissociation constants govern these interactions, as assessed by a ligand-displacement assay. The study demonstrates the switching nature - between monomeric and multimeric - of the interaction as a function of ligand density in the vesicles; the results are directly relevant to understanding such a phenomenon occurring at cell surfaces.

Concise and Reliable Syntheses of Glycodendrimers via Self-Activating Click Chemistry: A Robust Strategy for Mimicking Multivalent Glycan-Pathogen Interactions

Individual interactions between glycans and their receptors are usually weak, although these weak interactions can combine to realize a strong interaction (multivalency). Such multivalency plays a crucial role in the recognition of host cells by pathogens. Glycodendrimers are useful materials for the reconstruction of this multivalent interaction. However, the introduction of a large number of glycans to a dendrimer core is fraught with difficulties. We herein synthesized antipathogenic glycodendrimers using the self-activating click chemistry (SACC) method developed by our group. The excellent reactivity of SACC enabled the efficient preparation of sialyl glycan and Gb3 glycan dendrimers, which exhibited strong avidity toward hemagglutinin on influenza virus and Shiga toxin B subunit produced by Escherichia coli, respectively. We demonstrated the usefulness of SACC-based glycodendrimers as antipathogenic compounds.

Dendrimers toward Translational Nanotherapeutics: Concise Key Step Analysis

The goal of nanomedicine is to address specific clinical problems optimally, to fight human diseases, and to find clinical relevance to change clinical practice. Nanomedicine is poised to revolutionize medicine via the development of more precise diagnostic and therapeutic tools. The field of nanomedicine encompasses numerous features and therapeutic disciplines. A plethora of nanomolecular structures have been engineered and developed for therapeutic applications based on their multitasking abilities and the wide functionalization of their core scaffolds and surface groups. Within nanoparticles used for nanomedicine, dendrimers as well polymers have demonstrated strong potential as nanocarriers, therapeutic agents, and imaging contrast agents. In this review, we present and discuss the different criteria and parameters to be addressed to prepare and develop druggable nanoparticles in general and dendrimers in particular. We also describe the major requirements, included in the preclinical and clinical roadmap, for NPs/dendrimers for the preclinical stage to commercialization. Ultimately, we raise the clinical translation of new nanomedicine issues.

Synthesis of N-acetylglucosamine and N-acetylallosamine resorcinarene-based multivalent β-thio-glycoclusters: unexpected affinity of N-acetylallosamine ligands towards Wheat Germ Agglutinin

Herein, we report the synthesis of calix[4]resorcinarene-based multivalent ligands bearing β-S-GlcNAc and β-S-AllNAc recognition elements. A clickable β-S-AllNAc derivative was successfully prepared from a β-thioalkynyl GlcNAc precursor, making use of a 2,3-oxazoline intermediate, easily formed by intramolecular displacement of a triflate group located at the 3-position by the 2-N-acetate group. By reaction of these alkynyl-functionalized derivatives with an octaazido-calix[4]resorcinarene macrocycle having undecyl chains, two octavalent glycoclusters exposing the epimeric N-acetylhexosamines were obtained. In addition, a related calix[4]resorcinarene-based glycocluster having methyl groups instead of undecyl chains and β-S-GlcNAc residues was also synthesized. After an initial evaluation of the interaction of the undecyl-functionalized β-S-GlcNAc octavalent derivative with Wheat Germ Agglutinin (WGA) by a turbidimetry experiment, the interaction of the three synthesized glycoclusters towards WGA was studied by Isothermal Titration Calorimetry. The results showed a favorable effect due to the presence of the undecyl chains in terms of affinity. Surprisingly, the β-S-AllNAc octavalent compound showed the highest affinity among the evaluated glycoclusters, showing for the first time that WGA interacts with β-AllNAc-bearing ligands. Molecular docking studies of β-AllNAc with WGA in comparison with β-GlcNAc contributed to the understanding of the atomic interactions responsible for this unexpected affinity.

Aberrant glycosylation patterns on cancer cells: Therapeutic opportunities for glycodendrimers/metallodendrimers oncology

Despite exciting discoveries and progresses in drug design against cancer, its cure is still rather elusive and remains one of the humanities major challenges in health care. The safety profiles of common small molecule anti-cancer therapeutics are less than at acceptable levels and limiting deleterious side-effects have to be urgently addressed. This is mainly caused by their incapacity to differentiate healthy cells from cancer cells; hence, the use of high dosage becomes necessary. One possible solution to improve the therapeutic windows of anti-cancer agents undoubtedly resides in modern nanotechnology. This review presents a discussion concerning multivalent carbohydrate-protein interactions as this topic pertains to the fundamental aspects that lead glycoscientists to tackle glyconanoparticles. The second section describes the detailed properties of cancer cells and how their aberrant glycan surfaces differ from those of healthy cells. The third section briefly describes the immune systems, both innate and adaptative, because the numerous displays of cell surface protein receptors necessitate to be addressed from the multivalent angles, a strength full characteristic of nanoparticles. The next chapter presents recent advances in glyconanotechnologies, including glycodendrimers in particular, as they apply to glycobiology and carbohydrate-based cancer vaccines. This was followed by an overview of metallodendrimers and how this rapidly evolving field may contribute to our arsenal of therapeutic tools to fight cancer. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Precipitation-free high-affinity multivalent binding by inline lectin ligands

Multivalent ligand-protein interactions are a key concept in biology mediating, for example, signalling and adhesion. Multivalent ligands often have tremendously increased binding affinities. However, they also can cause crosslinking of receptor molecules leading to precipitation of ligand-receptor complexes. Plaque formation due to precipitation is a known characteristic of numerous fatal diseases limiting a potential medical application of multivalent ligands with a precipitating binding mode. Here, we present a new design of high-potency multivalent ligands featuring an inline arrangement of ligand epitopes with exceptionally high binding affinities in the low nanomolar range. At the same time, we show with a multi-methodological approach that precipitation of the receptor is prevented. We distinguish distinct binding modes of the ligands, in particular we elucidate a unique chelating binding mode, where four receptor binding sites are simultaneously bridged by one multivalent ligand molecule. The new design concept of inline multivalent ligands, which we established for the well-investigated model lectin wheat germ agglutinin, has great potential for the development of high-potency multivalent inhibitors as future therapeutics.

How galectins have become multifunctional proteins

Having identified glycans of cellular glycoconjugates as versatile molecular messages, their recognition by sugar receptors (lectins) is a fundamental mechanism within the flow of biological information. This type of molecular interplay is increasingly revealed to be involved in a wide range of (patho)physiological processes. To do so, it is a vital prerequisite that a lectin (and its expression) can develop more than a single skill, that is the general ability to bind glycans. By studying the example of vertebrate galectins as a model, a total of five relevant characteristics is disclosed: i) access to intra- and extracellular sites, ii) fine-tuned gene regulation (with evidence for co-regulation of counterreceptors) including the existence of variants due to alternative splicing or single nucleotide polymorphisms, iii) specificity to distinct glycans from the glycome with different molecular meaning, iv) binding capacity also to peptide motifs at different sites on the protein and v) diversity of modular architecture. They combine to endow these lectins with the capacity to serve as multi-purpose tools. Underscoring the arising broad-scale significance of tissue lectins, their numbers in terms of known families and group members have steadily grown by respective research that therefore unveiled a well-stocked toolbox. The generation of a network of (ga)lectins by evolutionary diversification affords the opportunity for additive/synergistic or antagonistic interplay in situ, an emerging aspect of (ga)lectin functionality. It warrants close scrutiny. The realization of the enormous potential of combinatorial permutations using the five listed features gives further efforts to understand the rules of functional glycomics/lectinomics a clear direction.

Preparation and in vivo evaluation of glyco-gold nanoparticles carrying synthetic mycobacterial hexaarabinofuranoside

A number of bacterial glycans are specific markers for the detection and the serological identification of microorganisms and are also widely used as antigenic components of vaccines. The use of gold nanoparticles as carriers for glyco-epitopes is becoming an important alternative to the traditional conjugation with proteins and synthetic polymers. In this study, we aimed to prepare and evaluate in vivo glyco-gold nanoparticles (glyco-GNPs) bearing the terminal-branched hexaarabinofuranoside fragment (Ara₆) of arabinan domains of lipoarabinomannan and arabinogalactan, which are principal polysaccharides of the cell wall of Mycobacterium tuberculosis, the causative agent of tuberculosis. In particular, we were interested whether the antibodies generated against Ara₆-GNPs would recognize the natural saccharides on the cell surface of different mycobacterial strains. Two synthetic Ara₆ glycosides with amino-functionalized spacer aglycons differing in length and hydrophilicity were directly conjugated with spherical gold nanoparticles (d = 15 nm) to give two sets of glyco-GNPs, which were used for the immunization of rabbits. Dot assays revealed cross-reactions between the two obtained antisera with the hexaarabinofuranoside and the 2-aminoethyl aglycon used for the preparation of glyco-GNPs. Both antisera contained high titers of antibodies specific for Mycobacteria as shown by enzyme-linked immunosorbent assay using M. bovis and M. smegmatis cells as antigens while there was only a weak response to M. phlei cells and no interaction with E. coli cells. The results obtained suggest that glyco-GNPs are promising agents for the generation of anti-mycobacterial antibodies.