Nouveaux disaccharides aux propriétés aphicides

Des disaccharides de structure b-D-GlcNAc-(1->4)-a-D-Glc 6-sulfate ont montré précédemment des effets aphicides. Nous avons entrepris la synthèse de disaccharides de même structure substitués ou non par des groupes sulfates ou acétate sur certaines positions pour en étudier les propriétés aphicides. Nous avons donc évalué différentes méthodes de glycosylation afin d obtenir sélectivement cette séquence avec un bon rendement. A partir de ce motif, nous avons synthétisé des disaccharides sulfatés régiosélectivement sur différentes positions. Nous avons ensuite exploré la synthèse de thiodisaccharides sulfatés à partir d'un sulfamidate cyclique. Des tests in vivo sur Myzus persicae, pucerons ravageurs des cultures de pommes de terre, d une partie de ces composés ont montré des effets physiologiques remarquables. La cible biologique potentielle de ces molécules étant les chitinases, nous avons évalué leur activité inhibitrice vis-à-vis des endo et exo chitinases de différentes sources. Certains de ces composés sont des inhibiteurs compétitifs avec des Ki de l ordre du micromolaire. L intérêt majeur de ce travail le développement de ces molécules issues de la biomasse pour la protection des cultures.Some disaccharides with a b-D-GlcNAc-(1->4)-a-D-Glc 6-sulfate structure have previously shown aphicidal effects. We have undertaken the synthesis of disaccharides of the same structure substituted or not by sulfates or acetate on specific positions to study their aphicidal properties. Different methods of glycosylation have been assessed in order to selectively obtain this sequence in good yield. From this sequence, we synthesized regioselectively sulfated disaccharides in different positions. Then we have explored the synthesis of sulfated thiodisaccharides from a cyclic sulfamidate. In vivo tests on Myzus persicae (aphid pests of potatoes) of some of these compounds have shown very good physiological effects. Chitinase are the potential biological target of these molecules, therefore their inhibitory activity of endo and exo chitinases from different sources has been evaluated. Some of these compounds are competitive inhibitors with Ki in the micromolar range. The main interest of this work is the development of molecules derived from biomass in crop protection.AMIENS-BU Sciences (800212103) / SudocSudocFranceF

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

© 2020 John Wiley & Sons A/S. Galectins play key roles in numerous biological processes. Their mode of action depends on their localization which can be extracellular, cytoplasmic, or nuclear and is partly mediated through interactions with β-galactose containing glycans. Galectins have emerged as novel therapeutic targets notably for the treatment of inflammatory disorders and cancers. This has stimulated the design of carbohydrate-based inhibitors targeting the carbohydrate recognition domains (CRDs) of the galectins. Pursuing this approach, we reasoned that linear oligogalactosides obtained by straightforward iterative click chemistry could mimic poly-lactosamine motifs expressed at eukaryote cell surfaces which the extracellular form of galectin-3, a prominent member of the galectin family, specifically recognizes. Affinities toward galectin-3 consistently increased with the length of the representative oligogalactosides but without reaching that of oligo-lactosamines. Elucidation of the X-ray crystal structures of the galectin-3 CRD in complex with a synthesized di- and tri-galactoside confirmed that the compounds bind within the carbohydrate-binding site. The atomic structures revealed that binding interactions mainly occur with the galactose moiety at the non-reducing end, primarily with subsites C and D of the CRD, differing from oligo-lactosamine which bind more consistently across the whole groove formed by the five subsites (A-E) of the galectin-3 CRD

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

© 2020 John Wiley & Sons A/S. Galectins play key roles in numerous biological processes. Their mode of action depends on their localization which can be extracellular, cytoplasmic, or nuclear and is partly mediated through interactions with β-galactose containing glycans. Galectins have emerged as novel therapeutic targets notably for the treatment of inflammatory disorders and cancers. This has stimulated the design of carbohydrate-based inhibitors targeting the carbohydrate recognition domains (CRDs) of the galectins. Pursuing this approach, we reasoned that linear oligogalactosides obtained by straightforward iterative click chemistry could mimic poly-lactosamine motifs expressed at eukaryote cell surfaces which the extracellular form of galectin-3, a prominent member of the galectin family, specifically recognizes. Affinities toward galectin-3 consistently increased with the length of the representative oligogalactosides but without reaching that of oligo-lactosamines. Elucidation of the X-ray crystal structures of the galectin-3 CRD in complex with a synthesized di- and tri-galactoside confirmed that the compounds bind within the carbohydrate-binding site. The atomic structures revealed that binding interactions mainly occur with the galactose moiety at the non-reducing end, primarily with subsites C and D of the CRD, differing from oligo-lactosamine which bind more consistently across the whole groove formed by the five subsites (A-E) of the galectin-3 CRD

Access to Galectin3 Inhibitors from Chemoenzymatic Synthons

International audienceChemo-enzymatic strategies are useful to provide both regio-and stereoselective access to bioactive oligosaccharides. We show herein that a glycosynthase mutant of a Thermus thermophilus -glycosidase can react with unnatural glycosides such as 6-azido-6-deoxy-D-glucose/glucosamine to lead to -D-galactopyranosyl-D-glucopyranoside or -D-galactopyranosyl-2-acetamido-2-deoxy-D-glu-copyranoside derivatives bearing a unique azide function. Taking advantage of the orthogonality between the azide and the hydroxyl functional groups, the former was next selectively reacted to give rise to a library of galectin-3 inhibitors. Combining enzyme substrate promiscuity and bioorthogonality thus appears as a powerful strategy to rapidly access to sugar-based ligands

A dansyl-derivatized phytic acid analogue as a fluorescent substrate for phytases: experimental and computational approach

International audienceA new myo-inositol pentakisphosphate was synthesized, which featured a dansyl group at position C-5. The fluorescent tag was removed from the inositol by a 6-atom spacer to prevent detrimental steric interactions in the catalytic site of phytases. The PEG linker was used in order to enhance hydrophilicity and biocompatibility of the new artificial substrate. Computational studies showed a favorable positioning in the catalytic site of phytases. Enzymatic assays demonstrated that the tethered myo-inositol was processed by two recombinant phytases Phy-A and Phy-C, classified respectively as acid and alkaline phytases, with similar rates of phosphate release compared to their natural substrate

Lactosamine-Based Derivatives as Tools to Delineate the Biological Functions of Galectins: Application to Skin Tissue Repair

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Hexavalent thiofucosides to probe the role of the Aspergillus fumigatus lectin FleA in fungal pathogenicity

International audienceA. fumigatus is a pathogenic fungus infecting the respiratory system and responsible for a variety of life-threatening lung diseases. A fucose-binding lectin named FleA which has a controversial role in A. fumigatus pathogenesis was recently identified. New chemical probes with high affinity and enzymatic stability are needed to explore the role of FleA in the infection process. In this study, we developed potent FleA antagonists based on optimized and non-hydrolysable thiofucoside ligands. We first synthesized a set of monovalent sugars showing micromolar affinity for FleA by isothermal titration calorimetry. The most potent derivative was co-crystallized with FleA to gain insights into the binding mode in operation. Its chemical multimerization on a cyclodextrin scaffold led to an hexavalent compound with a significantly enhanced binding affinity (Kd = 223 ± 21 nM) thanks to a chelate binding mode. The compound could probe the role of bronchial epithelial cells in a FleA-mediated response to tissue invasio

Multivalent Fucosides with Nanomolar Affinity for the Aspergillus fumigatus Lectin FleA Prevent Spore Adhesion to Pneumocytes

FleA (or AFL), a fucose lectin, was recently identified in the opportunistic mold Aspergillus fumigatus, which causes fatal lung infections in immunocompromised patients. We designed di-, hexa- and octavalent fucosides with various spacer arm lengths to block the hexameric FleA through chelation. Microcalorimetry measurements showed that the ethylene glycol (EG) spacer arm length has a strong influence on the binding affinity of the divalent fucosides. The relationship between the EG length and chelate binding efficiency to FleA was explored according to polymer theory. Hexa- and octavalent compounds based on cyclodextrin and octameric silsesquioxane scaffolds were nanomolar FleA inhibitors, surpassing their monovalent fucose analogue by more than three orders of magnitude. Importantly, some of the fucosides were highly efficient in preventing fungal spore adhesion to bronchoepithelial cells, with half maximal inhibitory concentration values in the micromolar range. We propose that the synergistic antiadhesive effect observed can be ascribed to chelate binding to FleA and to the formation of conidium aggregates, as observed by optical microscopy. These fucosides are promising tools that can be used to better understand the role of FleA in conidia pathogenicity and host defenses against invasive aspergillosis

An anionic synthetic sugar containing 6-SO3-NAcGlc mimics the sulfated cruzipain epitope that plays a central role in immune recognition

Cruzipain (Cz), the major cysteine proteinase of Trypanosoma cruzi, is a glycoprotein that contains sulfated high-mannose-type oligosaccharides. We have previously determined that these sulfate groups are targets of specific immune responses. In order to evaluate the structural requirements for antibody recognition of Cz, a systematic structure–activity study of the chemical characteristics needed for antibody binding to the Cz sulfated epitope was performed by immunoassays. With this aim, different synthesized molecules were coupled to the proteins BSA and aprotinin and confronted with (a) mouse sera specific for Cz and its carboxy-terminal (C-T) domain, (b) antibodies raised in rabbits immunized with Cz and its C-terminal domain and (c) IgGs purified from human Chagas disease sera. Our results indicate that a glucosamine containing an esterifying sulfate group in position O-6 and an N-acetyl group was the preferred epitope for the immune recognition of sera specific for Cz and its C-T domain. Although to a minor extent, other anionic compounds bearing sulfate groups in different positions and number as well as different anionic charged groups including carboxylated or phosphorylated monosaccharides, disaccharides and oligosaccharides were recognized. In conclusion, we found that synthetic anionic sugar conjugates containing N-acetyl D-glucosamine-6-sulfate sodium salt (GlcNAc6S) competitively inhibit the binding of affinity purified rabbit anti-C-T IgG to the C-T extension of Cz. Extending these findings to the context of natural infection, immune assays performed with Chagas disease serum confirmed that the structure of synthetic GlcNAc6S mimics the N-glycan-linked sulfated epitope displayed in the C-T domain of Cz