Mannosylated G(0) Dendrimers with Nanomolar Affinities toEscherichia coli FimH

FimH antagonists: bioisosteres to improve the in vitro and in vivo PK/PD profile

Urinary tract infections (UTIs), predominantly caused by uropathogenic Escherichia coli (UPEC), belong to the most prevalent infectious diseases worldwide. The attachment of UPEC to host cells is mediated by FimH, a mannose-binding adhesin at the tip of bacterial type 1 pili. To date, UTIs are mainly treated with antibiotics, leading to the ubiquitous problem of increasing resistance against most of the currently available antimicrobials. Therefore, new treatment strategies are urgently needed. Here, we describe the development of an orally available FimH antagonist. Starting from the carboxylate substituted biphenyl α-d-mannoside 9, affinity and the relevant pharmacokinetic parameters (solubility, permeability, renal excretion) were substantially improved by a bioisosteric approach. With 3'-chloro-4'-(α-d-mannopyranosyloxy)biphenyl-4-carbonitrile (10j) a FimH antagonist with an optimal in vitro PK/PD profile was identified. Orally applied, 10j was effective in a mouse model of UTI by reducing the bacterial load in the bladder by about 1000-fold.

Inhibition of type 1 fimbriae-mediated Escherichia coli adhesion and biofilm formation by trimeric cluster thiomannosides conjugated to diamond nanoparticles

Recent advances in nanotechnology have seen the development of a number of microbiocidal and/or anti-adhesive nanoparticles displaying activity against biofilms. In this work, trimeric thiomannoside clusters conjugated to nanodiamond particles (ND) were targeted for investigation. NDs have attracted attention as a biocompatible nanomaterial and we were curious to see whether the high mannose glycotope density obtained upon grouping monosaccharide units in triads might lead to the corresponding ND-conjugates behaving as effective inhibitors of E. coli type 1 fimbriae-mediated adhesion as well as of biofilm formation. The required trimeric thiosugar clusters were obtained through a convenient thiol-ene "click" strategy and were subsequently conjugated to alkynyl-functionalized NDs using a Cu(I)-catalysed "click" reaction. We demonstrated that the tri-thiomannoside cluster-conjugated NDs (ND-Man3) show potent inhibition of type 1 fimbriae-mediated E. coli adhesion to yeast and T24 bladder cells as well as of biofilm formation. The biofilm disrupting effects demonstrated here have only rarely been reported in the past for analogues featuring such simple glycosidic motifs. Moreover, the finding that the tri-thiomannoside cluster (Man3N3) is itself a relatively efficient inhibitor, even when not conjugated to any ND edifice, suggests that alternative mono- or multivalent sugar-derived analogues might also be usefully explored for E. coli-mediated biofilm disrupting properties.

Plasmonic photothermal destruction of uropathogenic E. coli with reduced graphene oxide and core/shell nanocomposites of gold nanorods/reduced graphene oxide

The selective photothermal destruction of E. coli is shown.

Synthesis of novel types of polyester glycodendrimers as potential inhibitors of urinary tract infections

Syntheses of highly mannosylated polyester dendrimers with 2, 4, 8, and 16 α-d-mannopyranose residues on their peripheries connected by different linker arms are presented.

Fucofullerenes as tight ligands of RSL and LecB, two bacterial lectins

A series of water-soluble glycofullerenes containing up to 24 fucose residues were tested against the two bacterial lectins LecB and RSL, and C60(E)12 bearing 24 fucose residues appeared to be the best known inhibitor of both lectins to date.

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.

Synthesis and solvodynamic diameter measurements of closely related mannodendrimers for the study of multivalent carbohydrate-protein interactions

This paper describes the synthesis of three closely related families of mannopyranoside-containing dendrimers for the purpose of studying subtle structural parameters involved in the measurements of multivalent carbohydrate-protein binding interactions. Toward this goal, two trimers 5 and 9, three 9-mers 12, 17, 21, and one 27-mer 23, varying by the number of atoms separating the anomeric and the core carbons, were synthesized using azide-alkyne cycloaddition (CuAAc). Compound 23 was prepared by an efficient convergent strategy. The sugar precursors consisted of either a 2-azidoethyl (3) or a prop-2-ynyl α-D-mannopyranoside (7) derivative. The solvodynamic diameters of 9-mer 12, 17, and 21 were determined by pulsed-field-gradient-stimulated echo (PFG-STE) NMR experiments and were found to be 3.0, 2.5, and 3.4 nm, respectively.

Tetravalent glycocyclopeptide with nanomolar affinity to wheat germ agglutinin

A series of tetravalent glycocyclopeptides functionalized with GlcNAc was synthesized using copper(i)-catalysed alkyne-azide cycloaddition, oxime ligation and thiol-ene coupling. The binding ability of these compounds towards wheat germ agglutinin was studied by a competitive ELLA test and ITC experiments. While all compounds were able to inhibit WGA binding to GlcNAc-polymer coated surfaces at low concentrations, derivative 17 having an aliphatic spacer and thioether linkage was 4.9 × 10(6) times more potent on a per sugar basis than GlcNAc. This remarkably strong effect was confirmed by ITC experiments as these revealed an association constant of 9 nM for this compound, therefore presenting a gain of 200,000 times over GlcNAc. These results for compound 17 represent the highest binding properties reported for WGA.

Fullerene sugar balls: a new class of biologically active fullerene derivatives

Among the large variety of bioactive C60 derivatives, fullerene derivatives substituted with sugar residues, that is, glycofullerenes, are of particular interest. The sugar residues are not only solubilizing groups; their intrinsic biological properties also provide additional appealing features to the conjugates. The most recent advances in the synthesis and the biological applications of glycofullerenes are summarized in the present review article with special emphasis on globular glycofullerenes, that is, fullerene sugar balls, constructed on a hexa-substituted fullerene scaffold. The high local concentration of carbohydrates around the C60 core in fullerene sugar balls is perfectly suited to the binding of lectins through the "glycoside cluster effect", and these compounds are potential anti-adhesive agents against bacterial infection. Moreover, mannosylated fullerene sugar balls have shown antiviral activity in an Ebola pseudotyped infection model. Finally, when substituted with peripheral iminosugars, dramatic multivalent effects have been observed for glycosidase inhibition. These unexpected observations have been rationalized by the interplay of interactions involving the catalytic site of the enzyme and non-glycone binding sites with lectin-like abilities.

A multivalent inhibitor of the DC-SIGN dependent uptake of HIV-1 and Dengue virus

DC-SIGN is a C-type lectin receptor on antigen presenting cells (dendritic cells) which has an important role in some viral infection, notably by HIV and Dengue virus (DV). Multivalent presentation of carbohydrates on dendrimeric scaffolds has been shown to inhibit DC-SIGN binding to HIV envelope glycoprotein gp120, thus blocking viral entry. This approach has interesting potential applications for infection prophylaxis. In an effort to develop high affinity inhibitors of DC-SIGN mediated viral entry, we have synthesized a group of glycodendrimers of different valency that bear different carbohydrates or glycomimetic DC-SIGN ligands and have studied their DC-SIGN binding activity and antiviral properties both in an HIV and a Dengue infection model. Surface Plasmon Resonance (SPR) competition studies have demonstrated that the materials obtained bind efficiently to DC-SIGN with IC50s in the μm range, which depend on the nature of the ligand and on the valency of the scaffold. In particular, a hexavalent presentation of the DC-SIGN selective antagonist 4 displayed high potency, as well as improved accessibility and chemical stability relative to previously reported dendrimers. At low μm concentration the material was shown to block both DC-SIGN mediated uptake of DV by Raji cells and HIV trans-infection of T cells.

Structure binding relationship of galactosylated Glycoclusters toward Pseudomonas aeruginosa lectin LecA using a DNA-based carbohydrate microarray

Pseudomonas aeruginosa (PA) is a major public health issue due to its impact on nosocomial infections as well as its impact on cystic fibrosis patient mortality. One of the main concerns is its ability to develop antibiotic resistance. Therefore, inhibition of PA virulence has been proposed as an alternative strategy to tackle PA based infections. LecA (or PA-IL), a galactose binding lectin from PA, is involved in its virulence. Herein, we aimed at designing high affinity synthetic ligands toward LecA for its inhibition and at understanding the key parameters governing the binding of multivalent galactosylated clusters. Twenty-five glycoclusters were synthesized and their bindings were studied on a carbohydrate microarray. Monosaccharide centered clusters and linear comb-like clusters were synthesized with different linkers separating the core and the galactosyl residues. Their length, flexibility, and aromaticity were varied. Our results showed that the binding profile of LecA to galactosylated clusters was dependent on both the core and the linker and also that the optimal linker was different for each core. Nevertheless, an aryl group in the linker structure drastically improved the binding to LecA. Our results also suggest that optimal distances are preferred between the core and the aromatic group and the core and the galactose.

Branched α-d-mannopyranosides: a new class of potent FimH antagonists

We report branched α-d-mannopyranosides as potent FimH antagonists that exploit the previously unexplored lipophilic region formed by Phe142 and Ile13.

Validation of Reactivity Descriptors to Assess the Aromatic Stacking within the Tyrosine Gate of FimH

Antagonists of the FimH adhesin, a protein almost universally present at the extremity of type-1 fimbriae expressed by Escherichia coli, have been abundantly in the spotlight as alternative treatments of urinary tract infections. The antagonists function as bacterial antiadhesives through highly specific α-d-mannose binding in a charged and polar pocket at the tip of the FimH lectin domain and by the stacking of alkyl or aromatic moieties substituted on the mannose with two tyrosine residues (Tyr48 and Tyr137) at the entrance of the mannose-binding pocket. Using high-resolution crystal data, interaction energies are calculated for the different observed aromatic stacking modes between the tyrosines and the antagonist. The dispersion component of the interaction energy correlates with the observed electron density. The quantum chemical reactivity descriptors local hardness and polarizability were successfully validated as prediction tools for ligand affinity in the tyrosine gate of FimH and therefore have potential for rapid drug screening.

Effect of Aminophenyl and Aminothiahexyl α-D-Glycosides of the Manno-, Gluco-, and Galacto-Series on Type 1 Fimbriae-Mediated Adhesion of Escherichia coli

Adhesion of bacteria to the glycosylated surface of their target cells is typically mediated by fimbrial lectins, exposed on the bacterial surface. Among the best-investigated and most important fimbriae are type 1 fimbriae, for which α-d-mannopyranoside-specificity has been described. This carbohydrate specificity is mediated by the type 1 fimbrial lectin FimH. In this account, we have employed four different set-ups to assay type 1 fimbriae-mediated bacterial adhesion, including tailor-made glycoarrays. The focus of our study was on testing FimH specificity with regard to the glycone part of a glycosidic ligand by testing a series of synthetic α-mannosides, as well as α-glucosides and α-galactosides. Unexpectedly, it was found that in solution all tested aminothiahexyl glycosides inhibit bacterial adhesion but that this effect is unspecific. Instead it is due to cytotoxicity of the respective glycosides at high mm concentrations.

Multivalent glycoconjugates as anti-pathogenic agents

Multivalency plays a major role in biological processes and particularly in the relationship between pathogenic microorganisms and their host that involves protein-glycan recognition. These interactions occur during the first steps of infection, for specific recognition between host and bacteria, but also at different stages of the immune response. The search for high-affinity ligands for studying such interactions involves the combination of carbohydrate head groups with different scaffolds and linkers generating multivalent glycocompounds with controlled spatial and topology parameters. By interfering with pathogen adhesion, such glycocompounds including glycopolymers, glycoclusters, glycodendrimers and glyconanoparticles have the potential to improve or replace antibiotic treatments that are now subverted by resistance. Multivalent glycoconjugates have also been used for stimulating the innate and adaptive immune systems, for example with carbohydrate-based vaccines. Bacteria present on their surfaces natural multivalent glycoconjugates such as lipopolysaccharides and S-layers that can also be exploited or targeted in anti-infectious strategies.

Glycan-functionalized diamond nanoparticles as potent E. coli anti-adhesives

Bacterial attachment and subsequent biofilm formation on biotic surfaces or medical devices is an increasing source of infections in clinical settings. A large proportion of these biofilm-related infections are caused by Escherichia coli, a major nosocomial pathogen, in which the major adhesion factor is the FimH adhesin located at the tip of type 1 fimbriae. Inhibition of FimH-mediated adhesion has been identified as an efficient antibiotic-alternative strategy to potentially reduce E. coli-related infections. In this article we demonstrate that nanodiamond particles, covently modified with mannose moieties by a "click" chemistry approach, are able to efficiently inhibit E. coli type 1 fimbriae-mediated adhesion to eukaryotic cells with relative inhibitory potency (RIP) of as high as 9259 (bladder cell adhesion assay), which is unprecedented when compared with RIP values previously reported for alternate multivalent mannose-functionalized nanostructures designed to inhibit E. coli adhesion. Also remarkable is that these novel mannose-modified NDs reduce E. coli biofilm formation, a property previously not observed for multivalent glyco-nanoparticles and rarely demonstrated for other multivalent or monovalent mannose glycans. This work sets the stage for the further evaluation of these novel NDs as an anti-adhesive therapeutic strategy against E. coli-derived infections.

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.

Templating gold surfaces with function: a self-assembled dendritic monolayer methodology based on monodisperse polyester scaffolds

The antibiotic resistance developed among several pathogenic bacterial strains has spurred interest in understanding bacterial adhesion down to a molecular level. Consequently, analytical methods that rely on bioactive and multivalent sensor surfaces are sought to detect and suppress infections. To deliver functional sensor surfaces with an optimized degree of molecular packaging, we explore a library of compact and monodisperse dendritic scaffolds based on the nontoxic 2,2-bis(methylol)propionic acid (bis-MPA). A self-assembled dendritic monolayer (SADM) methodology to gold surfaces capitalizes on the design of aqueous soluble dendritic structures that bear sulfur-containing core functionalities. The nature of sulfur (either disulfide or thiol), the size of the dendritic framework (generation 1-3), the distance between the sulfur and the dendritic wedge (4 or 14 Å), and the type of functional end group (hydroxyl or mannose) were key structural elements that were identified to affect the packaging densities assembled on the surfaces. Both surface plasmon resonance (SPR) and resonance-enhanced surface impedance (RESI) experiments revealed rapid formation of homogenously covered SADMs on gold surfaces. The array of dendritic structures enabled the fabrication of functional gold surfaces displaying molecular covering densities of 0.33-2.2 molecules·nm(-2) and functional availability of 0.95-5.5 groups·nm(-2). The cell scavenging ability of these sensor surfaces for Escherichia coli MS7fim+ bacteria revealed 2.5 times enhanced recognition for G3-mannosylated surfaces when compared to G3-hydroxylated SADM surfaces. This promising methodology delivers functional gold sensor surfaces and represents a facile route for probing surface interactions between multivalently presented motifs and cells in a controlled surface setting.

Synthetic glycopeptides and glycoproteins with applications in biological research

Over the past few years, synthetic methods for the preparation of complex glycopeptides have been drastically improved. The need for homogenous glycopeptides and glycoproteins with defined chemical structures to study diverse biological phenomena further enhances the development of methodologies. Selected recent advances in synthesis and applications, in which glycopeptides or glycoproteins serve as tools for biological studies, are reviewed. The importance of specific antibodies directed to the glycan part, as well as the peptide backbone has been realized during the development of synthetic glycopeptide-based anti-tumor vaccines. The fine-tuning of native chemical ligation (NCL), expressed protein ligation (EPL), and chemoenzymatic glycosylation techniques have all together enabled the synthesis of functional glycoproteins. The synthesis of structurally defined, complex glycopeptides or glyco-clusters presented on natural peptide backbones, or mimics thereof, offer further possibilities to study protein-binding events.

Lead optimization studies on FimH antagonists: discovery of potent and orally bioavailable ortho-substituted biphenyl mannosides

Herein, we describe the X-ray structure-based design and optimization of biaryl mannoside FimH inhibitors. Diverse modifications to the biaryl ring to improve druglike physical and pharmacokinetic properties of mannosides were assessed for FimH binding affinity based on their effects on hemagglutination and biofilm formation along with direct FimH binding assays. Substitution on the mannoside phenyl ring ortho to the glycosidic bond results in large potency enhancements several-fold higher than those of corresponding unsubstituted matched pairs and can be rationalized from increased hydrophobic interactions with the FimH hydrophobic ridge (Ile13) or "tyrosine gate" (Tyr137 and Tyr48) also lined by Ile52. The lead mannosides have increased metabolic stability and oral bioavailability as determined from in vitro PAMPA predictive model of cellular permeability and in vivo pharmacokinetic studies in mice, thereby representing advanced preclinical candidates with promising potential as novel therapeutics for the clinical treatment and prevention of recurring urinary tract infections.

Synthesis of heteroglycoclusters by using orthogonal chemoselective ligations

Synthetic heteroglycoclusters are being subjected to increasing interest due to their potential to serve as selective ligands for carbohydrate-binding proteins. In this paper, we describe an expedient strategy to prepare cyclopeptides displaying well-defined distributions and combinations of carbohydrates. By using both oxime ligation and copper(I)-catalyzed alkyne–azide cycloaddition, two series of compounds bearing binary combinations of αMan, αFuc or βLac in an overall tetravalent presentation, and either 2:2 or 3:1 relative proportions, have been prepared.

Diazo transfer and click chemistry in the solid phase syntheses of lysine-based glycodendrimers as antagonists against Escherichia coli FimH

Uropathogenic Escherichia coli infections, ultimately leading to cystitis and pyelonephritis, are initially mediated by the adhesion of the bacterial FimH to the transmembrane glycoprotein uroplakin-1a present at the surface of urothelial cells. The adhesion is based on the recognition and high avidity binding between the high-mannose glycans of the uroplakin and the FimH, a mannose-specific lectin located at the tip of type 1 fimbriae. We found that synthetic multiantennary mannopyranosides glycodendrons, harboring triazole functionality at the anomeric position, were potent hemagglutination inhibitors of guinea pig erythrocytes and E. coli. A mannosylated dendrimer exposing up to sixteen sugar residues showed an HAI titer of 1 μM and was thus 500-fold more potent than the corresponding monovalent methyl α-d-mannopyranoside. The synthesis of the glycodendrons involved highly efficient solid-phase synthesis of branched l-lysine scaffolds, diazo transfer reaction on the terminal amine residues, and 1,3-dipolar copper-catalyzed azide-alkyne cycloaddition using propargyl α-d-mannopyranoside.

Clusters of ligands on dendrimer surfaces

The development of methodology that is designed to allow a significant increase in the patterning and in the functionalization of the dendrimer is the ultimate goal of the research described here. Glycoside clusters based on TRIS were formed using click chemistry and were attached to PAMAM dendrimers. A series of dendrimers bearing tris-mannoside and an ethoxyethanol group was synthesized, and the binding interactions of these dendrimers with Concanavalin A were evaluated using inhibition ELISAs. The results of the inhibition ELISAs suggest that tris-mannoside clusters can replace individual sugars on the dendrimer without loss of function. Since tris-mannoside clustering allows for a redistribution of the dendrimers' surface functionalities, from this chemistry one can envision patterned dendrimers that incorporate multiple groups to increase the function and utility of the dendrimer.

Synthesis of a glycodendrimer incorporating multiple mannosides on a glucoside core

The synthesis of a glycodendrimer by incorporating repetitive mannoside units onto a glucoside core was carried out to multivalently probe fundamental carbohydrate–protein interactions. The dendritic structure was constructed by a modified procedure that utilized multiple glycosylations between a thioether glycosyl donor and five elongated spacer arms of a glycosyl acceptor. The completed dendrimer bears a full carbohydrate structure, and thus should find its potential application in the study of mannose–lectin interactions.