Carboxymethyl ß-Cyclodextrin Assistance for the 4-Nitrophenol Reduction Using Cobalt-Based Layered Double Hydroxides.

Cobalt-aluminum-layered double hydroxides containing carboxymethyl ß-cyclodextrin (CMßCD) were synthesized by coprecipitation and evaluated as a cobalt source for the 4-nitrophenol reduction in an aqueous medium. Several physicochemical techniques (XRD, FTIR, TGA) indicated the intercalation of the anionic cyclodextrin without damages to the hydrotalcite-type structure. These lamellar cobalt-aluminum hybrid materials (CoAl_CMßCD) were evaluated in the 4-nitrophenol reduction and showed higher activities in comparison with the CMßCD-free standard material (CoAl_CO3). To rationalize these results, a set of experimental controls going from physical mixtures of CoAl_CO3 with different cyclodextrins to other cobalt-based materials were investigated, highlighting the beneficial effects of both the layered double hydroxide and CMßCD-based hybrid structures. CMßCD also showed a beneficial effect as an additive during the 4-nitrophenol reduction. CoAl_CO3, dispersed in a fresh CMßCD solution could be re-used for five successive cycles without the loss of activity.

Sugar-Based Surfactants: Effects of Structural Features on the Physicochemical Properties of Sugar Esters and Their Comparison to Commercial Octyl Glycosides.

Two series of sugar esters with alkyl chain lengths varying from 5 to 12 carbon atoms, and with a head group consisting of glucose or galactose moieties, were synthesized. Equilibrium surface tension isotherms were measured, yielding critical micellar concentration (CMC) surface tensions at CMC (γcmc) and minimum areas at the air-water interface (Amin). In addition, Krafft temperatures (Tks) were measured to characterize the ability of molecules to dissolve in water, which is essential in numerous applications. As a comparison to widely used commercial sugar-based surfactants, those measurements were also carried out for four octyl d-glycosides. Impacts of the linkages between polar and lipophilic moieties, alkyl chain lengths, and the nature of the sugar head group on the measured properties were highlighted. Higher Tk and, thus, lower dissolution ability, were found for methyl 6-O-acyl-d-glucopyranosides. CMC and γcmc decreased with the alkyl chain lengths in both cases, but Amin did not appear to be influenced. Both γcmc and Amin appeared independent of the ester group orientation. Notably, alkyl (methyl α-d-glucopyranosid)uronates were found to result in noticeably lower CMC, possibly due to a closer distance between the carbonyl function and the head group.

Impact of the chemical structure on amphiphilic properties of sugar-based surfactants: A literature overview.

In this review, structure-property trends are systematically analyzed for four amphiphilic properties of sugar-based surfactants: critical micelle concentration (CMC), its associated surface tension (γCMC), efficiency (pC20) and Krafft temperature (TK). First, the impact on amphiphilic properties of the alkyl chain size and the presence of branching and/or unsaturation is investigated. Then, various polar head parameters are explored, such as the degree of polymerization of the sugar unit (mono- or oligosaccharides), the chemical nature of the linker and the sugar configuration. Some systematic comparisons between ethoxylated surfactants and sugar-based surfactants are also carried out. While some structural trends with the impact of alkyl chain length or the polar head size are now well understood, this analysis points out that systematic studies of more specific effects of alkyl chain (e.g. branching, unsaturation, presence of rings, position on the polar head) and polar head (e.g. linker, anomeric configuration, internal stereochemistry, cyclic vs. acyclic sugar residues) were scarcer or not available to date. This work encourages the use of these structural trends in the perspective of developing new bio-based surfactants and their consideration in predictive models. It also highlights the need of further experimental tests to fill remaining gaps notably to explore some specific structural features (such as the introduction of rings in the alkyl chain or the position of the alkyl chain on the polar head) and towards applicative properties (like foaming capacity or wettability).

Lactose derivatives as potential inhibitors of pectin methylesterases.

The discovery of molecules that can inhibit the action of phytopathogens is essential to find alternative to current pesticides. Pectin methylesterases (PME), enzymes that fine-tune the degree of methylesterification of plant cell wall pectins, play a key role in the pathogenicity of fungi or bacteria. Here we report the synthesis of new lactoside derivatives and their analysis as potential PME inhibitors using three plants and one fungal PME. Because of its structure, abundance and reduced cost, lactose was chosen as a case study. Lactoside derivatives were obtained by TEMPO-mediated oxidation of methyl lactoside, followed by an esterification procedure. Three derivatives were synthesized: sodium (methyl-lactosid)uronate, methyl (methyl-lactosid)uronate and butyl (methyl-lactosid)uronate. The inhibition of the plant and pathogen enzyme activities by lactoside derivatives was measured in vitro, showing the importance of the substitution on lactose: methyl (methyl-lactosid)uronate was more efficient than butyl (methyl-lactosid)uronate. These results were confirmed by docking analysis showing the difference in the interaction between lactoside derivatives and PME proteins. In conclusion, this study identified novel inhibitors of pectin remodeling enzymes.

Nitroxide supported on nanometric metal oxides as new hybrid catalysts for selective sugar oxidation.

A new series of supported organocatalysts, prepared by a simple method, were used for selective sugar oxidation. This approach is based on the immobilization of a nitroxide derivative through a carboxylic function on nanometric metal oxides (TiO2, Al2O3 and CeO2), allowing the recovery of the catalyst. These hybrid materials were carefully characterized by Diffuse Reflectance FT-IR spectroscopy (DRIFT), ThermoGravimetric Analysis (TGA), X-Ray Diffraction (XRD), Brunauer-Emmet-Teller surface area measurements (B.E.T.), elemental and electrochemical analyses, showing different characteristics and behaviors depending on the nature of the metal oxide used. The activity of the supported nitroxide catalyst was evaluated on methyl α-d-glucoside oxidation, used as model reaction. In all cases, high catalytic activity was highlighted, with up to 25 times less nitroxyl radical required for complete conversion than under homogeneous conditions. The influence of several experimental conditions such as the use of phosphate buffer and recyclability of the catalyst were also investigated.

Catalytic Synthesis of a New Series of Alkyl Uronates and Evaluation of Their Physicochemical Properties.

Large quantities (>3 g) of a new series of alkyl uronates were synthesized in two steps from commercial methyl hexopyranosides. Firstly, several tens of grams of free methyl α-d-glucopyranoside were selectively and quantitatively oxidized into corresponding sodium uronate using 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO)-catalyzed oxidation. Hydrophobic chains of different length were then introduced by acid-mediated esterification with fatty alcohols (ethyl to lauryl alcohol) leading to the desired alkyl glucuronates with moderate to good yields (49%-72%). The methodology was successfully applied to methyl α-d-mannopyranoside and methyl ß-d-galactopyranoside. Physicochemical properties, such as critical micelle concentration (CMC), equilibrium surface tension at CMC (γcmc), solubility, and Krafft temperature were measured, and the effect of structural modifications on surface active properties and micelle formation was discussed.

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.

Quantitative analysis (K(d) and IC(50)) of glycoconjugates interactions with a bacterial lectin on a carbohydrate microarray with DNA Direct Immobilization (DDI).

Nowadays, there is a great interest for understanding the structure/function relationship governing recognition of carbohydrates by their receptors for the design of new treatments. Indeed, carbohydrates and glycoconjugates play a major role in key biological events such as cell-cell recognition, pathogenesis inflammation, and host pathogen interactions. Pseudomonas aeruginosa (PA) is one of the predominant bacterium encountered in nosocomial infections. PA infections often lead to chronic inflammation and eventually to death despite aggressive antibiotic therapy: the emergence of resistant strains and biofilm formation seems to give a selective advantage to the bacterium. A promising approach is to inhibit the virulence factors of PA such as PA-IL which is a galactose specific lectin. Herein, we develop a microarray to probe the binding of six galacto-conjugates to PA-IL differing by their spatial configuration and geometry. This microsystem is made of 40 independent microwells in which 64 spots of glycoconjugates probes are arrayed by using DNA Directed Immobilization (DDI). This microsystem allows, in a multiplex fashion, qualitative information on the binding by direct fluorescence readout as well as quantitative information by the determination of IC(50) values in a competition assay and surface dissociation constants (K(d)). According to our data, direct fluorescent signals (FI(635)), IC(50) and K(d) values provided similar ranking for glycoconjugates with respect to PA-IL binding thus affording a general tool for the selection of galacto-conjugates displaying the best affinities toward PA-IL.

Synthesis of homo- and heterofunctionalized glycoclusters and binding to Pseudomonas aeruginosa lectins PA-IL and PA-IIL.

Homo- and heterofunctionalized glycoclusters with galactose and/or fucose residues targeting both PA-IL and PA-IIL lectins of Pseudomonas aeruginosa were synthesized using "Click" chemistry and DNA chemistry. Their binding to lectins (separately or in a mixture) was studied using a DNA Directed Immobilization carbohydrate microarray. Homoglycoclusters bind selectively to their lectin while the heteroglycocluster binds simultaneously both lectins with a slight lower affinity.

Synthesis of a library of fucosylated glycoclusters and determination of their binding toward Pseudomonas aeruginosa lectin B (PA-IIL) using a DNA-based carbohydrate microarray.

Pseudomonas aeruginosa (PA) is a Gram negative opportunistic pathogen and is the major pathogen encounter in the cystic fibrosis (CF) lung airways. It often leads to chronic respiratory infection despite aggressive antibiotic therapy due to the emergence of resistant strains and to the formation of biofilm. The lectin PA-IIL (LecB) is a fucose-specific lectin from PA suspected to be involved in host recognition/adhesion and in biofilm formation. Thus, it can be foreseen as a potential therapeutic target. Herein, 16 fucosylated glycoclusters with antenna-like, linear, or crown-like spatial arrangements were synthesized using a combination of DNA solid-phase synthesis and alkyne azide 1,3-dipolar cycloaddition (CuAAC). Their binding properties toward PA-IIL were then evaluated based on DNA directed immobilization (DDI) carbohydrate microarray. Our results suggested that the antenna-like scaffold was preferred to linear or crown-like glycoclusters. Among the crown-like carbohydrate centered fucosylated glycoclusters, mannose-based core was better than glucose- and galactose-based ones. The influence of the linker arm was also evaluated, and long linkers between fucoses and the core led to a slight better binding than the short ones.

Multiplexed binding determination of seven glycoconjugates for Pseudomonas aeruginosa lectin I (PA-IL) using a DNA-based carbohydrate microarray.

The binding of seven multivalent glycoconjugates displaying linear or antenna-like structures and different electronic environments were evaluated towards PA-IL on a DNA-based carbohydrate microarray. The affinity can be modulated by the charge and the topology of the galactosylated derivatives.

Measurement of enzymatic activity and specificity of human and avian influenza neuraminidases from whole virus by glycoarray and MALDI-TOF mass spectrometry.

Influenza neuraminidases hydrolyze the ketosidic linkage between N-acetylneuraminic acid and its adjacent galactose residue in sialosides. This enzyme is a tetrameric protein that plays a critical role in the release of progeny virions. Several methods have been described for the determination of neuraminidase activity, usually based on colorimetric, fluorescent, or chemiluminescent detection. However, only a few of these tests allow discrimination of the sialyl-linkage specificity (i.e., α2-3- versus α2-6-linked sialyllactosides) of the neuraminidase. Herein we report a glycoarray-based assay and a MALDI-TOF study for assessing the activity and specificity of two influenza neuraminidases on whole viruses. The human A(H3N2) and avian A(H5N2) neuraminidase activities were investigated. The results from both approaches demonstrated that α2-3 sialyllactoside was a better substrate than α2-6 sialyllactoside for both viruses and that H5N2 virus had a lower hydrolytic activity than H3N2.

Synthesis of a glycomimetic oligonucleotide conjugate by 1,3-dipolar cycloaddition.

A glycomimetic oligonucleotide conjugate bearing four galactose residues on a mannose core is -synthesized using oligonucleotide solid-phase synthesis and Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC, or "click" chemistry). To achieve this purpose, new building blocks (including the solid support and phosphoramidites) are synthesized and used on a DNA synthesizer to generate a tetraalkyne oligonucleotide, which is then conjugated with a galactose azide derivative by click chemistry to afford the desired 3'-tetragalactosyl-mannose oligonucleotide conjugate. The procedures described in this chapter provide a general approach for the synthesis of novel glycoconjugates that can be immobilized to a DNA chip via DNA-directed immobilization to study, for example, their multivalent interactions with lectins in cellular targeting/uptake, etc.

Oligonucleotide carbohydrate-centered galactosyl cluster conjugates synthesized by click and phosphoramidite chemistries.

Oligonucleotide glycoconjugates with a mannose or galactose core bearing four galactose residues introduced by phosphoramidite chemistry and copper catalyzed azide alkyne 1,3-dipolar cycloaddition (click chemistry) have been synthesized. A first click reaction allowed the introduction on a solid support of a mannose core on which four pentynyl linkers were introduced using a phosphoramidite derivative. After the elongation of the oligonucleotide, a second click reaction performed either on solid support or in solution allowed the introduction of four galactose azide derivatives. Repeating the phosphoramidite and click chemistries afforded an oligonucleotide glycoconjugate dendrimer bearing 16 galactoses on its periphery.

5'-Bis-conjugation of oligonucleotides by amidative oxidation and click chemistry.

A pent-4-ynyl tert-butyl N,N-diisopropyl phosphoramidite was coupled at the 5'-end of oligonucleotides to give a phosphite triester linkage, which forms an H-phosphonate diester linkage during treatment with dichloroacetic acid. Then an amidative oxidation with CCl(4) in the presence of an amine and a 1,3-dipolar cycloaddition with an azide under copper(I) catalysis afforded the bis-conjugated oligonucleotides with high efficiency. The introduction of a bromoalkyl group as a precursor of azidoalkyl by amidative oxidation allowed the performance of two selective 1,3-dipolar cycloadditions.

Carbohydrate-oligonucleotide conjugates.

This unit describes a strategy for attaching two mannose and two galactose residues to an oligonucleotide. This conjugation can be performed at the 5'-end of the oligonucleotide sequence, using modified phosphoramidites. First, the oligonucleotide scaffold is synthesized on solid support using a DNA synthesizer, with commercially available and modified phosphoramidites. After the first "click" reaction with a galactosylated azide derivative on solid support, the bromine atoms are replaced with azides and a second click reaction is performed with propargylated mannose either on solid support or in solution. Additionally, using a monoalkynated solid support, the conjugation with carbohydrate residues can be performed at the 3'-end of the oligonucleotide according to a similar protocol. Curr. Protoc. Nucleic Acid Chem. 39:4.38.1-4.38.25.

Specific recognition of lectins by oligonucleotide glycoconjugates and sorting on a DNA microarray.

Two glycoconjugates bearing different DNA tags are mixed in solution with lectins; both interact with their specific lectin and the resulting complexes are sorted, according to their DNA sequences, at the surface of micro-reactors bearing the immobilised complementary DNA sequences.

Azide solid support for 3'-conjugation of oligonucleotides and their circularization by click chemistry.

A solid support bearing an azido linker was used to synthesize a 3'-azido-alkyl-oligonucleotide by phosphoramidite chemistry. The resulting oligonucleotide was either conjugated by 1,3-dipolar cycloaddition on solid support or in solution with mannose-propargyl derivative and in solution with dansyl propargyl. Besides, after introduction of an alkyne function at the 5'-end, the resulting oligonucleotide bearing both 3'-azide and 5'-alkyne functions was circularized.

Design of triazole-tethered glycoclusters exhibiting three different spatial arrangements and comparative study of their affinities towards PA-IL and RCA 120 by using a dna-based glycoarray.

Sugar-coated chips: Glycoside clusters are valuable tools for carbohydrate-lectin recognition studies. However, the spatial arrangement of the sugar residues is a key issue in the design of high-affinity glycoclusters. Here the affinities of linear and antenna- and calixarene-based galactoside clusters towards two lectins derived from Pseudomonas aeruginosa and Ricinus communis were compared by means of glycoarrays.Interactions between proteins and carbohydrates are involved in a large number of crucial biological events. Many efforts have been devoted to the design and synthesis of unnatural saccharides displaying high affinities towards targeted lectins. Among others, glycoside clusters have proven to be valuable tools for these recognition studies. However, the spatial arrangements of the sugar residues are a key issue in the design of high-affinity glycoclusters. Here, the affinities of linear and antenna- and calixarene-based galactoside clusters against two lectins, derived from Pseudomonas aeruginosa and Ricinus communis, have been compared by means of glycoarrays.

DNA-directed immobilisation of glycomimetics for glycoarrays application: comparison with covalent immobilisation, and development of an on-chip IC50 measurement assay.

Glycoarrays are powerful tools for the understanding of protein/carbohydrate interactions and should find applications in the diagnosis of diseases involving these interactions. Immobilisation of the carbohydrate probe is a key issue in the elaboration of high performance devices. In the present study, we have compared the fluorescent signal intensity and determined the lower detection limit of glycoconjugates immobilised at two concentrations (0.5 and 25 microM) by DNA-directed immobilisation (DDI), to glycoconjugates covalently immobilised on the solid support (borosilicate glass slide). At 0.5 microM, DDI led to a stronger fluorescence signal (by a factor of 4.5) and to a lower detection limit (20 nM) than covalent immobilisation (higher than 200 nM). We also report the development of an IC(50) measurement assay of DDI immobilised glycoconjugates. We found that the relative affinity per galactose residue of RCA 120 for glycoconjugates bearing one or three galactose residues was different by a factor of 23 when measured under IC(50) conditions or by direct fluorescence reading.