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Protein tracking in living plant cells has become routine with the emergence of reporter genes encoding fluorescent tags. Unfortunately, this imaging strategy is not applicable to glycans because they are not directly encoded by the genome. Indeed, complex glycans result from sequential additions and/or removals of monosaccharides by the glycosyltransferases and glycosidases of the cell's biosynthetic machinery. Currently, the imaging of cell wall polymers mainly relies on the use of antibodies or dyes that exhibit variable specificities. However, as immunolocalization typically requires sample fixation, it does not provide access to the dynamics of living cells. The development of click chemistry in plant cell wall biology offers an alternative for live-cell labeling. It consists of the incorporation of a carbohydrate containing a bio-orthogonal chemical reporter into the target polysaccharide using the endogenous biosynthetic machinery of the cell. Once synthesized and deposited in the cell wall, the polysaccharide containing the analog monosaccharide is covalently coupled to an exogenous fluorescent probe. Here, we developed a metabolic click labeling approach which allows the imaging of cell wall polysaccharides in living and elongating cells without affecting cell viability. The protocol was established using the pollen tube, a useful model to follow cell wall dynamics due to its fast and tip-polarized growth, but was also successfully tested on Arabidopsis root cells and root hairs. This method offers the possibility of imaging metabolically incorporated sugars of viable and elongating cells, allowing the study of the long-term dynamics of labeled extracellular polysaccharides.

Arylborinic acids represent new, efficient, and underexplored hydrogen peroxide-responsive triggers. In contrast to boronic acids, two concomitant oxidative rearrangements are involved in the complete oxidation of these species, which might represent a major limitation for an efficient effector (drug or fluorophore) release. Herein, a comprehensive study of H

Trehalose-based probes are useful tools that allow the detection of the mycomembrane of mycobacteria through the metabolic labeling approach. Trehalose analogues conjugated to fluorescent probes can be used, and other probes are functionalized with a bioorthogonal chemical reporter for a two-step labeling approach. The synthesis of such trehalose-based probes mainly relies on the desymmetrization of natural trehalose using a large number of regioselective protection-deprotection steps to differentiate the eight hydroxyl groups. Herein, in order to avoid these time-consuming steps, we reinvestigated our previously reported tandem protocol mediated by FeCl

Significance Hydrogen peroxide plays an important role in the fine balance between physiological and pathological processes. To detect this diffusible small molecule, we expanded the scope of organic triggers in developing borinic acids as an alternative and more sensitive trigger than the most conventional boronate-based sensors. We discovered that borinic acid is 10,000-fold more reactive than its boronic counterpart toward H 2 O 2 -mediated oxidation. An accurate determination of oxidation kinetic constants and computational experiments corroborate this higher reactivity. This improvement also proved effective for in-cell detection of exogenously as well as endogenously produced H 2 O 2 . We believe borinic acids represent a new and efficient tool allowing for the development of new devices for a better understanding of H 2 O 2 -mediated signaling processes.

International audience; The European Federation for Medicinal chemistry and Chemical biology (EFMC) is a federation of learned societies. It groups organizations of European scientists working in a dynamic field spanning chemical biology and medicinal chemistry. New ideas, tools, and technologies emerging from a wide array of scientific disciplines continuously energize this rapidly evolving area. Medicinal chemistry is the design, synthesis, and optimization of biologically active molecules aimed at discovering new drug candidatesa mission that in many ways overlaps with the scope of chemical biology. Chemical biology is by now a mature field of science for which a more precise definition of what it englobes, in the frame of EFMC, is timely. This article discusses chemical biology as currently understood by EFMC, including all activities dealing with the design and synthesis of biologically active chemical tools and their use to probe, characterize, or influence biological systems.

National audience; Le présent bilan de mandature 2016-2021 de la CPCN (Conférence des présidentes et présidents de sections et de commissions interdisciplinaires du Comité national de la recherche scientifique) a une triple finalité. Il constitue d’abord une forme d’autoévaluation de l’action de la CPCN et, à travers elle, de l’action coordonnée des sections et commissions interdisciplinaires (CID), au cours de cette mandature, en rappelant autant que de besoin le contexte dans lequel cette action s’est inscrite. Il vise également à rendre compte de cette action auprès de la communauté scientifique française à travers une diffusion la plus large possible. Il doit enfin permettre un passage de relais avec les sections et CID et avec la CPCN qui seront mises en place à l’automne 2021.

Here, we present a 3D localization-based super-resolution technique providing a slowly varying localization precision over a 1 μm range with precisions down to 15 nm. The axial localization is performed through a combination of point spread function (PSF) shaping and supercritical angle fluorescence (SAF), which yields absolute axial information. Using a dual-view scheme, the axial detection is decoupled from the lateral detection and optimized independently to provide a weakly anisotropic 3D resolution over the imaging range. This method can be readily implemented on most homemade PSF shaping setups and provides drift-free, tilt-insensitive and achromatic results. Its insensitivity to these unavoidable experimental biases is especially adapted for multicolor 3D super-resolution microscopy, as we demonstrate by imaging cell cytoskeleton, living bacteria membranes and axon periodic submembrane scaffolds. We further illustrate the interest of the technique for biological multicolor imaging over a several-μm range by direct merging of multiple acquisitions at different depths., 3D single molecule localization microscopy suffers from several experimental biases that degrade the resolution or localization precision. Here the authors present a dual-view detection scheme combining supercritical angle fluorescence and astigmatic imaging to obtain precise and unbiased 3D super resolution images.

International audience; The [Re(bpy)(CO)3Cl] catalyst pioneered by Lehn for the two-electron reduction of CO2 has constantly revealed unique facets in the mechanistic understanding of the selective transformation of CO2. A novel triazole-linked ruthenium photosensitizer and a rhenium catalyst dyad was synthesized and investigated for photo-induced charge accumulation using time-resolved absorption spectroscopy. The triazole bridging ligand promoted weak electronic communication between the two units, resulting in an anodic shift of the reduction potentials of the Re moiety. Upon excitation of the photosensitizer, the first reduction of the catalyst occurred with a fast apparent rate of >5×107 s−1. Using a double-excitation nanosecond pump-pump-probe setup to track the second electron accumulation on the catalytic unit was not conclusive as no observable absorption changes occurred upon the second excitation, suggesting a pathway for an efficient intramolecular reverse electron transfer preventing the two-electron accumulation at the catalyst under our experimental conditions. Nevertheless, under continuous irradiation and with the use of sacrificial electron donors, photocatalytic CO2 reduction assays showed good turnover numbers, hinting at the non-innocent role of byproducts in solution.

International audience; Although their impact in biology and cellular communication are now well established, in situ visualization of glycans has long remained elusive due to the lack of suitable and general imaging techniques. Twenty years ago, the bioorthogonal chemical reporter strategy based on chemoselective and biocompatible reactions has emerged to become the state-of-the-art labeling technology for studying glycans. In this chapter, after providing an update on recent developments in bioorthogonal chemistry, we review how this strategy can be implemented to the visualization and biochemical analysis of different glycans in the bacterial cell envelope.

DAISY combined Supercritical Angle Fluorescence (SAF) detection in order to provide an absolute axial reference to a point spread function engineering approach . The dual view optical setup permits to introduce a strong astigmatism and decouple lateral and axial information, thus extending the axial performances without degrading the lateral precision. This technique provides 3D absolute information over a 1-µm capture range above the glass coverslip and an axial localization precision down to 15 nm with minimal loss of lateral resolution and little sensitivity to field aberrations. We will present sequential and simultaneous up to 3 color 3D imaging in cells.

Detection of hydrogen peroxide (H2O2), which is responsible for numerous damages when overproduced, is crucial for a better understanding of H2O2-mediated signalling in physiological and pathological processes. For this purpose, various“off-on” small fluorescent probes relying on a boronate trigger have been developed. However, they suffer from low kinetics and do not allow forH2O2-detectionwith a short response time. Therefore, more reactive sensors are still awaited. To address this issue, we have successfully developed the first generation of borinic-based fluorescent probes containing a coumarin-scaffold. We determined the in vitrokinetic constants of the probe toward H2O2-promotedoxidation. We measured 1.9x104m-1.s-1as a second order rate constant, which is 10 000 faster than its boronic counterpart (1.8 m-1.s-1). This remarkable reactivity was also effective in a cellular context, rendering the borinic trigger an advantageous new tool for H2O2detection.

In this study, we report the first synthesis of an alkyne-based trehalose monomycolate probe containing a β-hydroxylated fatty acid and an α-branched chain similar to those of the natural mycolic acid. We demonstrate its utility for the labeling of the mycomembrane of Corynebacteria as well as for the study of mycoloyltransferases.

International audience; Lipo-chitotetrasaccharide analogues where one central GlcNAc residue was replaced by a triazole unit have been synthesized from a derivative obtained by chitin depolymerization and a functionalized N-acetyl-glucosamine via the copper-catalyzed azide-alkyne cycloaddition. Their evaluation in a binding assay using LYR3, a putative lipo-chitooligosaccharide receptor in Medicago truncatula, shows a complete loss of binding.

A new synthesis of the fungal lipo-chitooligosaccharide Myc-IV (C16:0, S), which was recently reported to be a major symbiotic signalling molecule in arbuscular mycorrhiza, is described. Key steps include the oxidative cleavage of a 4,6-O-benzylidene acetal to prepare a disaccharidic glycosyl acceptor, and stereoselective glycosylations with 2-methyl-5-tert-butylphenyl thioglycosyl donors.

International audience; The human lectin galectin-1 (hGal-1) translates sugar signals, that is, beta-galactosides, into effects on the level of cells, for example, growth regulation, and has become a model for studying binding of biopharmaceutically relevant derivatives. Bound-state conformations of Gal beta-C-(1 -> 3)-Glc beta-OMe (1) and its beta Gal-(1 -> 3)-beta Glc-OMe disaccharide parent compound were studied by using NMR spectroscopy (transferred (TR)-NOESY data), assisted by docking experiments and molecular dynamics (MD) simulations. The molecular recognition process involves a conformational selection event. Although free C-glycoside access four distinct conformers in solution, hGal-1 recognizes shape of a local minimum of compound 1, the syn-Phi/syn-Psi conformer, not the structure at global minimum. MD simulations were run to explain, in structural terms, the observed geometry of the complex

International audience; Click chemistry was used as an efficient method to covalently attach a chromophore to an amino acid. Such easily prepared model systems allow for time-resolved studies of one-electron oxidation reactions by the excitation of the chromophore by a laser flash. The model complex ruthenium-tryptophan (Ru-Trp) has been synthesised and studied for its photophysical and electrochemical properties. Despite a small driving force of less than 100 meV, excitation with a laser flash results in fast internal electron transfer leading to the formation of the protonated radical (Trp˙H(+)). At neutral pH electron transfer is followed by deprotonation to form the neutral Trp˙ radical with the rate depending on the concentration of water acting as the proton acceptor. The formation of the tryptophan radical was confirmed by EPR.

In plants, 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) is a monosaccharide that is only found in the cell wall pectin, rhamnogalacturonan-II (RG-II). Incubation of 4-day-old light-grown Arabidopsis seedlings or tobacco BY-2 cells with 8-azido 8-deoxy Kdo (Kdo-N3 ) followed by coupling to an alkyne-containing fluorescent probe resulted in the specific in muro labelling of RG-II through a copper-catalysed azide-alkyne cycloaddition reaction. CMP-Kdo synthetase inhibition and competition assays showing that Kdo and D-Ara, a precursor of Kdo, but not L-Ara, inhibit incorporation of Kdo-N3 demonstrated that incorporation of Kdo-N3 occurs in RG-II through the endogenous biosynthetic machinery of the cell. Co-localisation of Kdo-N3 labelling with the cellulose-binding dye calcofluor white demonstrated that RG-II exists throughout the primary cell wall. Additionally, after incubating plants with Kdo-N3 and an alkynated derivative of L-fucose that incorporates into rhamnogalacturonan I, co-localised fluorescence was observed in the cell wall in the elongation zone of the root. Finally, pulse labelling experiments demonstrated that metabolic click-mediated labelling with Kdo-N3 provides an efficient method to study the synthesis and redistribution of RG-II during root growth.

Metabolic glycan labeling has recently emerged as a very powerful method for studying cell-surface glycans, which has applications that range from imaging glycans in living multicellular organisms, such as zebrafish or mice, to the identification of metastasis-associated cell-surface sialoglycoproteins. This strategy relies on the cellular biosynthetic machinery assimilating a modified monosaccharide that contains a bioorthogonal chemical reporter. The metabolic incorporation of this reporter into glycans can be further visualized by chemical ligation with a label, such as a fluorescent probe. Somewhat surprisingly, previous studies have mainly focused on the labeling of vertebrate glycans by using derivatives of common monosaccharides, such as Nacetyl neuraminic acid (or its N-acetylmannosamine precursor), N-acetylglucosamine, N-acetylgalactosamine, and fucose. In spite of a much higher degree of diversity in their monosaccharide building blocks as well as an essential role in bacterium–host interactions and bacterial virulence, bacterial polysaccharides have been poorly explored in terms of in vivo structural modifications. Bacteria are divided into Grampositive and Gram-negative bacteria. Whereas Gram-positive bacteria are surrounded by a peptidoglycan cell wall, Gramnegative bacteria are covered by a dense layer of lipopolysaccharides that are embedded in their outer membrane. These lipopolysaccharides are involved in the structural integrity of the cell and are often considered as determinants of pathogenicity. Although lipopolysaccharides appear to be an interesting target for specific and well-defined glycan metabolic labeling in Gram-negative bacteria, attempts to achieve this goal have been limited to the introduction of modified l-fucose derivatives into a customized, genetically engineered strain of Escherichia coli. Although it is a very interesting proof of concept, this l-fucose-based approach has some limitations as l-fucose is not generally present within the lipopolysaccharides of all Gram-negative bacteria, but is found in the O-antigens of specific strains. Secondly, free lfucose is not an intermediate in the normal E. coli “de novo” pathway and, therefore, should not be directly activable into a nucleotide-sugar donor without the introduction of an alternative pathway, known as the “salvage pathway”, into the organism of interest by genetic engineering (metabolic pathway engineering). Furthermore, once activated in the form of a modified guanosine-5’-diphosphate–fucose (GDP– Fuc), the l-fucose analogue might be transformed into a correspondingly modified GDP–mannose (GDP–Man) by the reverse de novo pathway, and potentially further metabolized into various other compounds, a process which could result in the chemical reporter being spread through other pathways of sugar metabolism or beyond. As a result of all of these limitations, and as our goal was labeling the lipopolysaccharides of bacteria with no genetic modification, we investigated whether another sugar could be used as a target for the metabolic modification of glycans. From all of the potential targets, 3-deoxy-d-mannooctulosonic acid (KDO) appears to be a very attractive candidate. Indeed, KDO is a specific and essential component of the inner core of lipopolysaccharides, and has long been considered as being present in the lipopolysaccharides of almost all Gram-negative species (as well as higher plants and algae), in which at least one residue is directly connected to lipid A (Scheme 1a). Because of its vital importance, KDO has been considered as a determinant for the characterization of Gram-negative bacteria, and the KDO pathway as a potential target for the development of new antibacterial compounds. In the KDO pathway (Scheme 1b), arabinose5-phosphate (arabinose-5-P) is condensed with phosphoenolpyruvate (PEP) to give KDO-8-phosphate (KDO-8-P), which is then transformed into free KDO, and further activated to form the cytidine monophosphate (CMP)–KDO donor prior to lipopolysaccharide elaboration. For all of these reasons, we hypothesized that the KDO pathway, as a lipopolysaccharidespecific pathway, may be tolerant enough to incorporate a modified analogue of KDO, such as 8-azido-8-deoxy-KDO (1, Scheme 2), into the core of E. coli lipopolysaccharides, and potentially other Gram-negative bacteria. Given the presence of free KDO as an intermediate in the pathway, we postulated that if the cell penetration of this analogue of KDO was sufficient, it could then be directly activated, partially replace endogenous KDO in lipopolysaccharides, and be detected on the cell surface by azide–alkyne click chemistry (Figure S1 in the Supporting Information). Moreover, modification of the C8-position of KDOwith a bioorthogonal azido group should prevent reverse metabolism by KDO-8-P [*] Dr. A. Dumont, Dr. S. Dukan Aix Marseille Universit , Laboratoire de Chimie Bact rienne (UMR 7283), Institut de Microbiologie de la M diterran e (IMM), CNRS, 31 Chemin Joseph Aiguier 13402 Marseille (France) E-mail: sdukan@imm.cnrs.fr

International audience; Screening of commercially available fluoro monosaccharides as putative growth inhibitors in Arabidopsis thaliana revealed that 2‐fluoro 2‐l‐fucose (2F‐Fuc) reduces root growth at micromolar concentrations. The inability of 2F‐Fuc to affect an Atfkgp mutant that is defective in the fucose salvage pathway indicates that 2F‐Fuc must be converted to its cognate GDP nucleotide sugar in order to inhibit root growth. Chemical analysis of cell wall polysaccharides and glycoproteins demonstrated that fucosylation of xyloglucans and of N‐linked glycans is fully inhibited by 10 μm 2F‐Fuc in Arabidopsis seedling roots, but genetic evidence indicates that these alterations are not responsible for the inhibition of root development by 2F‐Fuc. Inhibition of fucosylation of cell wall polysaccharides also affected pectic rhamnogalacturonan‐II (RG‐II). At low concentrations, 2F‐Fuc induced a decrease in RG‐II dimerization. Both RG‐II dimerization and root growth were partially restored in 2F‐Fuc‐treated seedlings by addition of boric acid, suggesting that the growth phenotype caused by 2F‐Fuc was due to a deficiency of RG‐II dimerization. Closer investigation of the 2F‐Fuc‐induced growth phenotype demonstrated that cell division is not affected by 2F‐Fuc treatments. In contrast, the inhibitor suppressed elongation of root cells and promoted the emergence of adventitious roots. This study further emphasizes the importance of RG‐II in cell elongation and the utility of glycosyltransferase inhibitors as new tools for studying the functions of cell wall polysaccharides in plant development. Moreover, supplementation experiments with borate suggest that the function of boron in plants might not be restricted to RG‐II cross‐linking, but that it might also be a signal molecule in the cell wall integrity‐sensing mechanism.

Nod factors are lipochitoligosaccharides originally produced by the soil bacteria Rhizobia that are involved in the symbiotic process with leguminous plants. Some synthetic analogs of the Nod factors present a strong biological activity, and the conformational behavior of these molecules is of interest for structure/function studies. Nod factor analogs containing an insertion of a phenyl group in the acyl chain at the oligosaccharidic non-reducing end were previously synthesized (Grenouillat N, Vauzeilles B, Bono J-J, Samain E, Beau J-M. 2004. Simple synthesis of nodulation-factor analogues exhibiting high affinity towards a specific binding protein. Angew Chem Int Ed Engl. 43:4644). Conformational studies of natural compounds and synthetic analogs have been performed combining molecular dynamics simulations in explicit water and NMR. Data revealed that the glycosidic head group can adopt only restricted conformations, whereas chemical modifications of the lipid chains, highly flexible in a water environment, influence the global shape of the molecules. Collected structural data could be used in the future to rationalize and understand their biological activity and affinity toward a putative receptor.

A library of paclitaxel (taxol) mimics was obtained by a straightforward strategy involving rational design and an efficient synthesis of a simplified taxane core substitute, together with a click-chemistry combinatorial search for phenylisoserine side-chain surrogates.

The conformational behaviour of the C-glycoside beta-C-Gal-(1-->3)-beta-Glc-OMe (1) has been studied using a combination of molecular mechanics and NMR spectroscopy (proton-proton coupling constants and nuclear Overhauser effects). It is shown that the C-disaccharide populates two distinctive conformational families in solution, the normal syn-psi conformation, which is the predominating conformation of parent O-glycoside 2, and the anti-psi conformation, which has not been detected for the O-disaccharide.

Lipo-chitin oligosaccharides (Nod and Myc LCOs) are molecules involved in symbiotic phenomena in the plant kingdom. They play a major role in the process of atmospheric nitrogen fixation and mineral soil nutrients uptake both in legumes and in non-legumes, and are active at extremely low concentrations down to the nano- and even picomolar range. These compounds contain various substitutions along the oligosaccharide backbone of the molecule including an essential fatty acid on the non-reducing unit and are considered as environmentally-friendly fertilizers. Currently, chemical synthesis cannot produce precursors of Nod and Myc LCOs at a large scale and an in vitro chemoenzymatic pathway is presented here as a new and efficient method for preparing quantities of these high-value oligosaccharides. VC1280 (Vibrio cholerae) is a chitin deacetylase (CD) capable of regioselectively cleaving an acetate from the non-reducing penultimate N-acetyl-D-glucosaminyl (GlcNAc) unit of chitin oligosaccharides (COs). This provides a free amino group which can be further N-acylated with a fatty-acid chain to give analogues of LCOs. Alternatively, the non-reducing GlcNAc unit can be removed by β-N-acetylglucosaminidase treatment, followed by N-acylation to give natural LCOs. VC1280 CD was produced in the periplasm of E. coli. Under the conditions used, 120 mg of the pure enzyme was recovered from 1 L of culture medium. For the first time, in vitro production of a library of natural LCOs as well as their analogues has been carried out at a preparative scale from biosourced chitin oligosaccharides constituting an approach of major interest for sustainable agriculture.

Dynamic Combinatorial Chemistry: Direct detection of imines in water and their adaptive re-equilibration in the presence of a target are possible by simple HPLC analysis. The equilibrating mixture is fixed by a fast drop in the pH during the analytical step. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

International audience; The direct and chemoselective N-transacylation of peracetylated chitooligosaccharides (COSs), readily obtained from chitin, to give per-N-trifluoroacetyl derivatives offers an attractive route to size-defined COSs and derived glycoconjugates. It involves the use of various acceptor building blocks and trifluoromethyl oxazoline dimer donors prepared with efficiency and highly reactive in 1,2-trans glycosylation reactions. This method was applied to the preparation of the important symbiotic glycolipids which are highly active on plants and to the TMG-chitotriomycin, a potent and specific inhibitor of insect, fungal, and bacterial N-acetylglucosaminidases.

The method is developed to prepare the building blocks for the construction of oligosaccharides.

International audience; In this paper we report the synthesis of a chromophore-catalyst assembly designed for the photoreduction of carbon dioxide. The chromophore unit is made up of a ruthenium trisbipyridyl-like unit covalently attached to a nickel cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) via a triazole ring. The intramolecular electron transfer activation of the catalyst unit by visible light was studied by nanosecond flash photolysis and EPR spectroscopy. In aqueous solutions (pH = 6.5), activation of the Ru(II)-Ni(II) modular assembly with 450 nm visible light in the presence of a sacrificial electron donor accomplishes the reduction of CO2 into CO and H2 in a ratio of 2.7 to 1.

International audience; Legionella pneumophila is a pathogenic bacterium involved in regular outbreaks characterized by a relatively high fatality rate and an important societal impact. Frequent monitoring of the presence of this bacterium in environmental water samples is necessary to prevent these epidemic events, but the traditional culture-based detection and identification method requires up to 10 days. Reported herein is a method allowing identification of Legionella pneumophila by metabolic lipopolysaccharide labeling which targets, for the first time, a precursor to monosaccharides that are specifically present within the O-antigen of the bacterium. This new approach allows easy detection of living Legionella pneumophila, while other Legionella species are not labeled.

International audience; Combining triflic acid-catalyzed acetalation, benzylation, reductive ring opening of benzylidene acetal and glycosylation in one-pot transformations leads to a wide range of d-glucosamine building blocks for assembling oligomers.

This review particularly emphasizes synthetic applications resulting from cascade or one-pot transformations and a glycosylation reaction promoted by ferric salts. These easy to handle, cheap and environment-friendly salts have been examined for their ability to induce, as a Lewis acid, fast carbohydrate-based modifications in our laboratories at Orsay and Gif sur Yvette. A short synthetic route to the dihydropyran framework of anti-influenza constructs is reported by coupling the Petasis three-component condensation to an iron(iii)-promoted one-pot cascade of deprotection – C–C double bond isomerization – cyclization - oxazoline formation. We also show that iron(iii) chloride hexahydrate is most appropriate to catalyze a one-pot regioselective protection of mono- and disaccharides. This iron(iii) catalysis renders multi-step routes, such as chemical oligosaccharide syntheses, faster. In the last section, we report a catalytic glycosylation method particularly simple and straightforward leading to the important β-d-GlcNAc motif, in which the more electrophilic iron(iii) triflate activates the readily available peracetate of N-acetyl-β-d-glucosamine. This glycosylation does not necessarily require the formation of the mandatory oxazolinium intermediate.

N-Acetyl glucosamine and chitooligosaccharides are selectively converted into β-glycosides without protection of the other hydroxyl groups by alkylation of the anomeric alkoxides in N,N-dimethylformamide containing lithium bromide. Addition of the lithium salt notably improves the stereoselectivity of the glycosylation of the monomer and the efficiency of the process with higher oligomers.

Several β-C-disaccharides have been selectively synthesized by radical cyclization of two temporarily tethered functionalized monosaccharides. In this process, intramolecular addition of a carbohydrate-derived radical onto an anomeric exomethylene group, followed by axial hydrogen addition, resulted in β stereochemistry.

International audience; : While chitooligosaccharides (COs) derived from fungal chitin are potent elicitors of defense reactions, structurally related signals produced by certain bacteria and fungi, called lipo-chitooligosaccharides (LCOs), play important roles in the establishment of symbioses with plants. Understanding how plants distinguish between friend and foe through the perception of these signals is a major challenge. We report the synthesis of a range of COs and LCOs, including photoactivatable probes, to characterize a membrane protein from the legume Medicago truncatula. By coupling photoaffinity labeling experiments with proteomics and transcriptomics, we identified the likely LCO-binding protein as LYR3, a lysin motif receptor-like kinase (LysM-RLK). LYR3, expressed heterologously, exhibits high-affinity binding to LCOs but not COs. Homology modeling, based on the Arabidopsis CO-binding LysM-RLK AtCERK1, suggests that LYR3 could accommodate the LCO in a conserved binding site. The identification of LYR3 opens up ways for the molecular characterization of LCO/CO discrimination.

International audience; Lipochitin oligosaccharides (LCOs) are signaling molecules required by ecologically and agronomically important bacteria and fungi to establish symbioses with diverse land plants. In plants, oligo-chitins and LCOs can differentially interact with different lysin motif (LysM) receptors and affect innate immunity responses or symbiosis-related pathways. In animals, oligo-chitins also induce innate immunity and other physiological responses but LCO recognition has not been demonstrated. Here LCO and LCO-like compounds are shown to be biologically active in mammals in a structure dependent way through the modulation of angiogenesis, a tightly-regulated process involving the induction and growth of new blood vessels from existing vessels. The testing of 24 LCO, LCO-like or oligo-chitin compounds resulted in structure-dependent effects on angiogenesis in vitro leading to promotion, or inhibition or nil effects. Like plants, the mammalian LCO biological activity depended upon the presence and type of terminal substitutions. Un-substituted oligo-chitins of similar chain lengths were unable to modulate angiogenesis indicating that mammalian cells, like plant cells, can distinguish between LCOs and un-substituted oligo-chitins. The cellular mode-of-action of the biologically active LCOs in mammals was determined. The stimulation or inhibition of endothelial cell adhesion to vitronectin or fibronectin correlated with their pro- or anti-angiogenic activity. Importantly, novel and more easily synthesised LCO-like disaccharide molecules were also biologically active and de-acetylated chitobiose was shown to be the primary structural basis of recognition. Given this, simpler chitin disaccharides derivatives based on the structure of biologically active LCOs were synthesised and purified and these showed biological activity in mammalian cells. Since important chronic disease states are linked to either insufficient or excessive angiogenesis, LCO and LCO-like molecules may have the potential to be a new, carbohydrate-based class of therapeutics for modulating angiogenesis.

Click chemistry was used to assemble a trimetallic RuII–NiII–RuII complex made up of two tris(bipyridyl)ruthenium(II)-based photosensitisers and a nickel(II)–salen complex. The electrochemical and photophysical properties of the resulting photosensitiser–metal complex are discussed. Photoinduced activation triggered by visible light absorption induces a fast intramolecular charge shift from one of the chromophores to the salen cavity to generate a nickel(III)–salen species.

International audience; A de-O-benzylation reaction induced by I-2-Et3SiH and developed by Iadonisi et al. on mono- and disaccharides was applied to per- or polybenzylated alpha-cyclodextrins to furnish compounds deprotected at position 3 of all sugar units. This methodology allows the straightforward post-functionalisation of the secondary rim of cyclodextrins already functionalised on their primary rim.

In this Communication, we present the synthesis and use of [Ru(bpy)(2)(bpy-CCH)](2+), a versatile synthon for the construction of more sophisticated dyads by means of click chemistry. The resulting chromophore-acceptor or -donor complexes have been studied by flash photolysis and are shown to undergo efficient electron transfer to/from the chromophore. Additionally, the photophysical and chemical properties of the original chromophore remain intact, making it a very useful component for the preparation of visible-light-active dyads.

(IF : 3,45); International audience; A series of neoglycoconjugates derived from deoxynojirimycin has been prepared by click connection with functionalised adamantanes. They have been assayed as glycosidase inhibitors, as inhibitors of the glycoenzymes relevant to the treatment of Gaucher disease, as well as correctors of the defective ion-transport protein involved in cystic fibrosis. We have demonstrated that it is possible to selectively either strongly inhibit ER-α-glucosidases and ceramide glucosyltransferase or restore the activity of CFTR in CF-KM4 cells by varying the length of the alkyl chain linking DNJ and adamantane.