Interfering with the Sugar Code: Ten Years Later

Achieving High Affinity for a Bacterial Lectin with Reversible Covalent Ligands

High-affinity monovalent ligands for lectins are challenging to develop due to weak binding interactions. This study investigates the potential of rationally designed covalent ligands targeting the N-terminal domain of BC2L-C lectin from Burkholderia cenocepacia, a pathogen causing severe respiratory infections in immunocompromised patients. Antiadhesion therapy is emerging as a complementary approach against such infections, and bacterial lectins are suitable targets. The fucose-specific BC2L-C-Nt recognizes blood group oligosaccharides on host cells. Using a computational approach, we designed reversible covalent competitive ligands that include a fucoside anchor and a salicylaldehyde warhead targeting Lys108 near the fucose-binding site. Several candidates were synthesized and tested using competition experiments. The most effective ligand improved the IC50 of methyl-fucoside by 2 orders of magnitude, matching the affinity of the native H-type 1 trisaccharide. Control experiments confirmed the importance of both fucose anchor and salicylaldehyde moiety in the ligand's affinity. Mass analysis confirmed the covalent interaction with Lys108.

Expedient Azide-Alkyne Huisgen Cycloaddition Catalyzed by a Combination of VOSO4 with Cu(0) in Aqueous Media

A series of vanadium(III), vanadyl(IV/V) species, inorganic metal oxides, and transition-metal oxides was examined as cocatalysts with Cu(0) powder for copper(I)-catalyzed azide-alkyne cycloaddition. Among them, vanadyl(IV) species bearing acetylacetonate, acetate, and sulfate, vanadyl(V) isopropoxide, and vanadate were suitable for the click reactions of per-acetyl and per-benzyl β-azido glycosides with three different terminal alkynes in CH3CN. Water-soluble vanadyl(IV) sulfate was further selected for efficient click reactions for unprotected β-glycosyl azides and even compatible with a thiol-containing substrate in aqueous media at ambient temperature.

Glycomimetic antagonists of BC2L-C lectin: insights from molecular dynamics simulations

Opportunistic infections from multidrug-resistant pathogens such as Burkholderia cenocepacia are a threatening risk for hospital-bound patients suffering from immunocompromised conditions or cystic fibrosis. B. cenocepacia BC2L-C lectin has been linked to bacterial adhesion and biofilm formation, thus hindering its activity is seen as a promising strategy to reduce the severity of the infection. We recently described the first bifunctional ligands of the trimeric N-terminal domain of BC2L-C (BC2L-C-Nt), capable of simultaneously engaging its fucose-specific sugar binding site and a vicinal region at the interface between two monomers. Here, we report a computational workflow for the study of these glycomimetic bifunctional ligands in complex with BC2L-C-Nt, aimed at investigating the molecular basis of ligand binding and the dynamics of glycomimetic/lectin interactions. In particular, we evaluated the use of molecular docking in the protein trimer, followed by refinement using MM-GBSA re-scoring and MD simulations in explicit water. Computational results were compared to experimental data derived from X-ray crystallography and isothermal titration calorimetry. The computational protocol proved suitable to provide a reliable description of the interactions between the ligands and BC2L-C-Nt, highlighting the contribution of MD simulations in explicit solvent for a good fit with the experimental observations. The information achieved in the study and the whole workflow appear promising for the structure-based design of improved BC2L-C-Nt ligands as novel antimicrobials with antiadhesive properties.

Synthesis of thiodisaccharides related to 4-thiolactose. Specific structural modifications increase the inhibitory activity against E. coli β-galactosidase

In the search for new glycosidase inhibitors, a set of benzyl β-D-Gal-S-(1→4)-3-deoxy-4-thio-α-D-hexopyranosides was synthesized. Diverse configurations were installed at C-2 and C-4 of the glucose residue. The benzyl glycosidic group was kept intact or substituted by an electron-donating or electron-withdrawing group that could also participate in hydrogen bonding. All thiodisaccharides were found to be inhibitors of E. coli β-galactosidase. In general, benzyl thiodisaccharides were better inhibitors than those substituted (NO₂ or NH₂) on the benzyl ring. Thiodisaccharides containing a hexopyranoside, instead of a pentopyranoside, showed a weaker inhibitory activity, except for those having the α-D-xylo configuration, which exhibited inhibition constants of the same order of magnitude. These and previous results indicated that the inhibition process by thiodisaccharides is strongly dependent on the configuration of the 3-deoxy-4-thiopyranoside, as well as its substitution pattern (such as the presence of a benzyl glycoside). The enzyme-inhibitor interaction during the hydrolysis process involves a conformational selection resulting from rotation around the thioglycosidic bond and the flexibility of the terminal six-membered ring. Thus, the mentioned structural features of the inhibitor could give rise to favorable ground state conformations for the interaction with the enzyme, similar to those found for selected thiodisaccharides in the bound state. These studies demonstrated that the performance of thiodisaccharides as enzyme inhibitors could be increased by selecting the appropriate configuration and substitution of the hexopyranoside replacing the glucose moiety of 4-thiolactose.

Targeted delivery of oligonucleotides using multivalent protein-carbohydrate interactions

Cell surface protein-carbohydrate interactions are essential for tissue-specific recognition and endocytosis of viruses, some bacteria and their toxins, and many glycoproteins. Often protein-carbohydrate interactions are multivalent - multiple copies of glycans bind simultaneously to multimeric receptors. Multivalency enhances both affinity and binding specificity, and is of interest for targeted delivery of drugs to specific cell types. The first such example of carbohydrate-mediated drug delivery to reach the clinic is Givosiran, a small interfering ribonucleic acid (siRNA) that is conjugated to a trivalent N-acetylgalactosamine (GalNAc) ligand. This ligand enables efficient uptake of the nucleic acid by the asialoglycoprotein receptor (ASGP-R) on hepatocytes. Synthetic multivalent ligands for ASGP-R were among the first 'cluster glycosides' developed at the birth of multivalent glycoscience around 40 years ago. In this review we trace the history of 'GalNAc targeting' from early academic studies to current pharmaceuticals and consider what other opportunities could follow the success of this delivery technology.

Multivalent glycosystems for human lectins

Human lectins are involved in a wide variety of biological processes, both physiological and pathological, which have attracted the interest of the scientific community working in the glycoscience field. Multivalent glycosystems have been employed as useful tools to understand carbohydrate-lectin binding processes as well as for biomedical applications. The review shows the different scaffolds designed for a multivalent presentation of sugars and their corresponding binding studies to lectins and in some cases, their biological activities. We summarise this research by organizing based on lectin types to highlight the progression in this active field. The paper provides an overall picture of how these contributions have furnished relevant information on this topic to help in understanding and participate in these carbohydrate-lectin interactions.

Targeting a Multidrug-Resistant Pathogen: First Generation Antagonists of Burkholderia cenocepacia's BC2L-C Lectin

Multidrug-resistant pathogens such as Burkholderia cenocepacia have become a hazard in the context of healthcare-associated infections, especially for patients admitted with cystic fibrosis or immuno-compromising conditions. Like other opportunistic Gram-negative bacteria, this pathogen establishes virulence and biofilms through lectin-mediated adhesion. In particular, the superlectin BC2L-C is believed to cross-link human epithelial cells to B. cenocepacia during pulmonary infections. We aimed to obtain glycomimetic antagonists able to inhibit the interaction between the N-terminal domain of BC2L-C (BC2L-C-Nt) and its target fucosylated human oligosaccharides. In a previous study, we identified by fragment virtual screening and validated a small set of molecular fragments that bind BC2L-C-Nt in the vicinity of the fucose binding site. Here, we report the rational design and synthesis of bifunctional C- or N-fucosides, generated by connecting these fragments to a fucoside core using a panel of rationally selected linkers. A modular route starting from two key fucoside intermediates was implemented for the synthesis, followed by evaluation of the new compounds as BC2L-C-Nt ligands with a range of techniques (surface plasmon resonance, isothermal titration calorimetry, saturation transfer difference NMR, differential scanning calorimetry, and X-ray crystallography). This study resulted in a hit molecule with an order of magnitude gain over the starting methyl fucoside and in two crystal structures of antagonist/lectin complexes.

Synthesis of Oligosaccharides Containing the S-Galp(α1 → 3)Galp Unit, Glycomimetic of the Epitope Recognized by Lytic Antibodies

Two important activities take place in the surface of Trypanosoma cruzi, the agent of Chagas disease: the trans-sialidase (TcTS) catalyzes the transfer of sialic acid from the host glycoconjugates to the mucin-like glycoproteins from the parasite and the presence of lytic antibodies recognize the epitope α-Galp(1 → 3)-β-Galp(1 → 4)-α-GlcNAcp. This antigenic structure is known to be present in the parasite mucins; however, in order to be substrates of trans-sialidase, some of the galactose residues should be in the β-Galp configuration. To study the interaction between both activities, it is important to count the synthetic structures as well as the structural-related glycomimetics. With this purpose, we addressed the synthesis of a trisaccharide and two isomeric tetrasaccharides containing the 1-S-α-Galp(1 → 3)-β-Galp motif, the thio analog of the epitope recognized by lytic antibodies. Starting with a common lactose precursor, the sulfur function was incorporated by double inversion of the configuration of the galactose residue that was further glycosylated using different activated donors. Both tetrasaccharides were good acceptors of sialic acid in the reaction catalyzed by TcTS, as determined by high-performance anion exchange chromatography.

C-Glycosylcrotylboronates for the Synthesis of Glycomimetics

The stereoselective synthesis of E- and Z- isomers of a C- mannosyl crotylpinacolboronate via Ni-promoted reactions on an allylic acetate and a diene precursor, respectively, is described. The E- and Z- isomers reacted with 1,2-O-isopropylidene glyceraldehyde in the presence or absence of (R)- and (S)- TRIP catalysts, to give predominantly 3,4-anti and 3,4-syn crotylation products, respectively, with moderate to high facial selectivity. These products were transformed to biologically relevant C-manno-disaccharides.

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.

One pot synthesis of thio-glycosides via aziridine opening reactions

thio-Glycosides with a pseudo-disaccharide structure are synthesized via aziridine opening reactions starting from glycosyl thioacetates with a one-pot protocol, which affords glycomimetics equipped for easy and stable conjugation to aglycones.