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Capsular polysaccharides (CPS) of Acinetobacter baumannii is a virulence factor with diverse structures. CPS are produced by the CPS biosynthesis gene cluster in their K locus (KL). However, CPS variations may occur due to insertion of additional genes from external sources, e.g., prophages. Recently, the CPS structure from a clinical isolate, BAL062 which includes KL58 locus, was found to have a pseudaminic acid isomer (8ePse5NAc7NAc) as a result of prophage inserted epaA/epaB genes. Here, we report a CPS structure produced by A. baumannii strain MRSN31468 which also belongs to a KL58 type. The K58 CPS structure was determined by 1D and 2D NMR analysis of the oligosaccharides derived from the CPS by a phage depolymerase, and supported by the sugar composition analysis. The K58 CPS structure has the following tetra saccharide repeating unit. [Display omitted] The K58 CPS differs from the CPS from BAL062 only by replacing 8-epimerized β-8ePse5NAc7NAc with β-Pse5NAc7NAc. Acinetobacter baumannii K58 Capsular polysaccharide. [Display omitted] • Acinetobacter baumannii strain MRSN31468 has K58 capsule polysaccharide with structural similarities to K2 and K98. • The strain MRSN31468 CPS has a similar structure to BAL062, but the Pse is not epimerized at its C-8 position. • A new method for CPS extraction from A. baumannii using 90 % phenol is effective. [ABSTRACT FROM AUTHOR]

Photoredox catalysis has recently emerged as a powerful approach for preparing oligosaccharides because it uses mild conditions, is compatible with partially or completely unprotected carbohydrate substrates, and exhibits impressive regio‐ and stereo‐selectivity and high functional group tolerance. However, most catalytic photoredox reactions require an external photocatalyst (organic dye or expensive transition-metal complex) to deliver key glycosyl radicals. Several photocatalyst-free photocatalytic reactions that avoid the use of expensive metal salts or organic-dye additives have received significant attention. In this review, we highlight the most recent developments in photocatalyst-free light-promoted carbohydrate synthesis and modification, which is expected to inspire broad interest in further innovations in the green synthesis of saccharides. In this review, we highlight the most recent developments in photocatalyst-free light-promoted carbohydrate synthesis and modification, which is expected to inspire broad interest in further innovations in the green synthesis of saccharides. [Display omitted] • Avoid using expensive metal catalysts or additive organic dye, photocatalyst-free photocatalysis provides an innovative and sustainable approach for glycochemists. • Photocatalyst-free light-promoted carbohydrate synthesis and modification have received widespread attention in glycochemistry. • Compared to traditional photocatalytic methods, photocatalyst-free photocatalysis offers an atom-economic and eco-friendly method for the synthesis and modification of carbohydrates. [ABSTRACT FROM AUTHOR]

In this study, the mechanism and nature of mechanical force-induced conformational transitions of alginate oligomers with different ratios of β- d -mannuronic acid (M unit) and α- l -guluronic acid (G unit) units were investigated. The influence of the type of glycosidic linkage in either homo- or heterooligomers on the nature of conformational transitions was also considered. For this purpose, two different theoretical methods were used: quantum mechanics (QM) at the DFT level with the EGO (Enforced Geometry Optimization) approach previously tested also for other saccharide systems, and molecular dynamics (MD) simulations within hybrid interaction potentials, which take into account both the ab initio (QM) level of theory and classical molecular mechanics (MM) force fields. This allowed to characterize in detail the structural and energetic properties of the conformational transition occurring upon the influence of external, mechanical forces (e.g. ring conformations at the path of ring-inversion process as well as the energies corresponding to initial, final and intermediate states). The results indicate qualitatively various responses against the applied force, depending on the G:M ratio, which have their source in differing topologies of glycosidic linkage in either G or M units. This is of potential relevance for determining the content of naturally heterogeneous alginate chains by the AFM experimental studies. The effects of explicit solvent and non-zero temperature are not of primarily importance in the context of determined stretching properties. [Display omitted] • Conformational transition in alginates can be induced by external forces. • Type of the glycosidic linkage influences the response to a tensile force. • Solvent effect is not of primary importance during the stretching of saccharides. [ABSTRACT FROM AUTHOR]

The physicochemical properties and biological activities of polysaccharides depend on their structures. Monosaccharide composition analysis is indispensable for the structural characterization of polysaccharides and is helpful in the quality control of polysaccharide preparation. Here, using a model mixture and tamarind seed polysaccharide as examples, we demonstrated that a quantitative 2D NMR method, gsHSQC i (three gradient-selective Heteronuclear Single Quantum Coherence spectra acquired with incremented repetition times, i = 1, 2, 3) can directly quantify a variety of monosaccharides in solution with adequate precision and accuracy, requiring no derivatization, postprocessing steps and column separation. Both anomeric and non-anomeric signals of monosaccharides can be utilized for content determination. More accurate quantification of fructose in a mixture containing nine monosaccharides is obtained, which is difficult to achieve by quantitative 1D 1HNMR and the common PMP-HPLC method (high-performance liquid chromatography through pre-column derivatization with 1-phenyl-3-methyl-5-pyrazolone) due to the peak overlapping and the poor derivatization efficiency, respectively. The results also revealed that Na[Fe(EDTA)] can serve as a proper relaxation-enhancing agent for saccharide samples to save experimental time. We expect that this approach can be applied as an alternative to analyzing the monosaccharide composition and be helpful in interpreting the structure of polysaccharides. [Display omitted] • Direct quantification of a variety of monosaccharides in the mixture without derivatization and column separation • Measure the monosaccharide mixture directly without a pre-established standard curve for each monosaccharide • More non-anomeric signals can be utilized for quantification in gsHSQC i compared with qHNMR • Na[Fe(EDTA)] is used as a proper relaxation-enhancing agent to save experimental time • DMSO 2 is used as an internal reference for quantitation. [ABSTRACT FROM AUTHOR]

In this paper we present two currents of our research. The first goal was the geometry optimization of the structures of derivatives of the alkyl 3-azido-2,3-dideoxy-D-hexopyranosides. Then, we examine the influence of the applied quantum methods on the values of molecular features describing these structures. We use two methods for geometry optimization: the semi-empirical PM7 method and DFT B3LYP/6–31++G* method. The results of comparison parameters of descriptors indicate that there are no statistical differences obtained from both methods. Thus, we recommend the PM7 method for geometry optimization of the derivatives of the alkyl 3-azido-2,3-dideoxy-D-hexopyranosides due to its time and computer resources requirements. Another part of the research was the examination, which groups of descriptors are the most suitable for identifying the similarities in the configuration, the substituents pattern and the molecular mass of 232 examined structures. To explore relation between configuration changes of the 3-azidosaccharides and influence of these changes on the molecular characteristic, we use hierarchical cluster analysis (HCA), where WHIM, 3D-MORSE, RDF and GETAWAY descriptors were selected. Depending on the group of descriptors, molecules are divided in various ways. In general, saccharide' structures are divided into groups based on the configuration of substituents (combination of epimers) or length of the O -glycoside chain. Never before, these saccharides derivatives, were investigated by chemometric analysis. The most problematic issue in experimental and theoretical research is the configuration of substituents in pyranoside ring. Due to vast number of configurations, it is possible to obtain massive amount of diverse structures. This problem concerns us and opens opportunity in investigation the effect of configuration on the parameter of molecules. Image 1 • The geometry optimization of molecules were performed by two methods: PM7 and DFT B3LYP/6–31++G*. • Comparison of parameters of descriptors, received from PM7 and DFT method was carried out. • Hierarchical cluster analysis (HCA) was implemented for WHIM, 3D-MORSE, RDF and GETAWAY descriptors. • Relation between configuration changes and influence of these changes on the molecular characteristic was discussed. [ABSTRACT FROM AUTHOR]

Abstract The article is devoted to the problem of molecular modeling of tautomeric and epimeric equilibria in aqueous solutions of unfunctionalized d -aldo- and d -ketohexoses. We have applied the computational protocol proposed in our previous article [Gaweda, Plazinski, Phys. Chem. Chem. Phys., 2017, 19, 20760–20772, doi:10.1039/c7cp02920a], originally designed to study the conformational features of saccharides, in order to check whether it can be extended to the case of tautomeric/epimeric equilibria of monosaccharides. The results show that the most important trends are correctly reflected in a qualitative manner, i.e. within the limits of 'chemical accuracy' (∼±4 kJ/mol). Insight into the calculated conformational energies provides a molecular interpretation of the tautomeric preferences of aldohexoses, according to which the pyranose/furanose ratio is determined mainly by the energy level of pyranose forms, whereas the energies of furanose forms are approximately constant along the series. The investigated paths of epimerization suggest that epimerization of aldohexopyranoses at any center favors the equatorial arrangements of the hydroxyl group. The energetic effects of epimerization in furanoses are significantly lower and do not exhibit related systematic trends. Graphical abstract Image 1 Highlights • Tautomeric and epimeric equilibria of saccharides are studied by QM/MM approach. • The experimental data on tautomeric equilibria are correctly reflected. • Tautomeric equilibria is correlated with the pyranose conformational properties. • The equatorial-to-axial rearrangements of the ring substituents were studied. • They result in approximately constant energy contribution on epimerization path. [ABSTRACT FROM AUTHOR]

Abstract By sequential synthesis the four 2,6-dideoxy saccharide moieties of the kijanimicin tetrasaccharide could be stereoselectively assembled. For formation of all required 2-deoxy α-glycoside linkages various S -(hexopyranosyl)-phosphorodithioates as donor structures could be convincingly employed. The terminal 2-deoxy β-glycoside linkage was stereoselectively formed following the dibromomethyl methyl ether approach. The target octadeoxy-tetrasaccha-ride could be obtained via nine subsequent steps in 5% overall yield. Graphical abstract Image 1 Highlights • Stereoselective synthesis of oligodeoxy-oligosaccharides. • Glycosylations employing S -hexopyranosyl phosphorodithioates. • Use of DBE reaction for formation of β-linked 2,6-dideoxy-glycosides. [ABSTRACT FROM AUTHOR]

Abstract The disaccharide β- d -mannopyranosyl-(1 → 2)- d -mannopyranose obtained by chemical cleavage and enzymatic dephosphorylation of biotechnologically available phosphomannan was transformed over six steps into a biotinylated probe suitable for assessment of carbohydrate specificity of antibodies induced by yeast cell wall preparations. Graphical abstract Image 1 Highlights • Synthetic application of biotechnologically produced β-(1 → 2)-dimannoside is described. • β-(1 → 2)-Dimannoside was transformed in 3-aminopropylglycoside. • Biotinylated probe was synthesized from β-3-aminopropylglycoside. [ABSTRACT FROM AUTHOR]

A fucan sulfate was isolated and purified from the sea cucumber Holothuria albiventer by papain enzymolysis, alkaline hydrolysis and ion-exchange chromatography. The water-soluble polysaccharide had high molecular weight and contained fucose and sulfate in a molar ratio of about 1:0.83. Methylation analysis of the native polysaccharide indicated that its glycosidic linkages and sulfate substituents might be at O- 3 or O -3, 4 or O -2, 3, or O -2, 3, 4 positions. FT-IR and 2D NMR spectroscopies further revealed that the fucan sulfate is characteristically composed of a regular α (1 → 3) linked hexasaccharide repeating unit which is substituted with sulfate esters in a distinctive pattern. Anticoagulant properties of the fucan sulfate and its depolymerized product were assessed in vitro in comparison with a low-molecular-weight heparin. The fucan sulfate exhibits strong APTT and TT prolonging activities and intrinsic factor Xase inhibitory activity, and its molecular size seemed to be required for these activities. [ABSTRACT FROM AUTHOR]

During the past decades, the interaction between boronic acids-functionalized sensors and saccharides is of great interest in the frontier domain of the interdiscipline concerning both biology and chemistry. Various boronic acid-based sensing systems have been developed to detect saccharides and corresponding derivatives in vitro as well as in vivo , which embrace unimolecular sensors, two-component sensing ensembles, functional assemblies, and boronic acid-loaded nanomaterials or surfaces. New sensing strategies emerge in endlessly with excellent selectivity and sensitivity. In this review, several typical sensing systems were introduced and some promising examples were highlighted to enable the deep insight of saccharides sensing on the basis of boronic acids. [ABSTRACT FROM AUTHOR]

Novel teichulosonic acid with the repeating unit →6)-β-D-Glc p NAc-(1→8)-α-Kdn-(2→ has been found in the cell walls of two Arthrobacter strains, VKM Ac-2549 and VKM Ac-2550. The teichulosonic acid was revealed in representatives of the genus Arthrobacter for the first time. Two other polymers identified in the above strains were poly(monoglycosyl 1-phosphate) and poly(diglycosyl 1-phosphate) of hitherto unknown structures, i.e., -6)-α-D-Gal p NAc-(1- P -, and -6)-β-D-Glc p NAc-(1→3)-α-D-Gal p -(1- P- . The structures of all three polymers were established by using chemical, NMR spectroscopic and ESI-MS methods. The strains studied in this work differ in the cell wall composition from the type strain of phylogenetically closely related species A. crystallopoietes which was reported to contain a teichoic acid and supposedly had a glycosyl 1-phosphate polymer. [ABSTRACT FROM AUTHOR]

The stereochemical course of O-glycosidation of 1,2- α -d- anhydrosugars (glycal epoxides) with phenols can be tuned by varying the metal ion of the base. While the reaction of 1,2- α -d- anhydrosugars with phenols mediated by trimethylaluminium leads exclusively to 1,2- ci s- α - O -aryl glycosides, similar reaction mediated by caesium carbonate gives exclusively 1, 2-trans - β - O -aryl glycosides. In contrast, reaction with phenoxides generated from Grignard reagent and calcium salts affords mixture of the anomers. [ABSTRACT FROM AUTHOR]

Gram scale synthesis of A (type 2) and B (type 2) tetrasaccharides in the form of 3-aminopropyl glycosides is proposed starting from 3-O-benzoyl-1,6-anhydro-N-acetylglucosamine. Its galactosylation followed by re-protection gave lactosamine derivative with single free 2′-OH group in total yield 75%. Standard fucosylation and next run of re-protection in total yield 88% gave a trisaccharide Fuc-Gal-anhydroGlcNAc with single free 3′-OH group. Its standard α-galactosylation gave protected B (type 2) tetrasaccharide. For synthesis of correspondent A tetrasaccharide seven different 2-azido-2-deoxygalactosyl (GalN 3 ) donors were tested: 6-O-acetyl-3,4-O-isopropylidene-GalN 3 thioglycoside was shown to provide the best yield (89%) and stereoselectivity (α/β = 24:1). Further 1,6-anhydro cycle opening, spacer-arming and complete deprotection resulted in the target 3-aminopropyl glycosides of A (type 2) and B (type 2) tetrasaccharides, yields 87 and 85% correspondingly. [ABSTRACT FROM AUTHOR]

The aim of this study is to further the understanding of the mechanisms that govern the hydration behavior of neutral solutes, with respect to the ions' properties that are present in a solution. For that, a systematic volumetric study of saccharides (xylose, glucose and sucrose), in the presence of various electrolytes (LiCl, NaCl, KCl, Na 2 SO 4 , K 2 SO 4 , CaCl 2 , MgCl 2 , MgSO 4 ) has been carried out with density measurements at 298.15 K. From this data, the standard transfer molar volume of the saccharide Δ V ϕ , S 0 , which characterizes the hydration state of the solute, has been determined. Positive and increasing values of Δ V ϕ , S 0 with increasing electrolyte concentrations were obtained. This indicated the dehydration of the saccharide in the presence of the electrolyte, due to the predominance of saccharide/cation interactions. Concerning the influence of the cation, it was shown that saccharides are more dehydrated in the presence of divalent cations than in the presence of monovalent ones. This is because the interactions are stronger between saccharides and divalent cations, in comparison to those with monovalent cations. For a specific cation valence and molality, regardless of the anion, saccharide dehydration increases according to the following sequences: Li + < Na + < K + and Mg 2+ < Ca 2 + . These saccharide dehydration sequences have been explained by the Gibbs free energy of hydration of the cations, reflecting the cation/water interactions. For a specific cation valence, it was concluded that decreasing cation/water interactions induce the increase of saccharide dehydration. Concerning the influence of the anion, it was also observed that saccharides are more dehydrated in the presence of divalent anions than in the presence of monovalent ones. It was stated that saccharide/cation interactions are modulated by the nature of the anion. The anion impact was again attributed to its capacity to interact with water molecules. It was pointed out that anions with increasing values of Gibbs free energy of hydration cause an increase in saccharide/cation interactions or a decrease in saccharide/anion interactions. Therefore, saccharide dehydration increases. [ABSTRACT FROM AUTHOR]

Human UDP-xylose synthase ( h UXS1) exclusively converts UDP-glucuronic acid to UDP-xylose via intermediate UDP-4-keto-xylose (UDP-Xyl-4O). Synthesis of model compounds like methyl-4-keto-xylose (Me-Xyl-4O) is reported to investigate the binding pattern thereof to h UXS1. Hence, selective oxidation of the desired hydroxyl function required employment of protecting group chemistry. Solution behavior of synthesized keto-saccharides was studied without enzyme via 1 H and 13 C NMR spectroscopy with respect to existent forms in deuterated potassium phosphate buffer. Keto-enol tautomerism was observed for all investigated keto-saccharides, while gem-diol hydrate forms were only observed for 4-keto-xylose derivatives. Saturation transfer difference (STD) NMR was used to study binding of synthesized keto-gylcosides to wild type h UXS1. Resulting epitope maps were correlated to earlier published molecular modeling studies of UDP-Xyl-4O. STD NMR results of Me-Xyl-4O are in good agreement with simulations of the intermediate UDP-Xyl-4O indicating a strong interaction of proton H3 with the enzyme, potentially caused by active site residue Ala 79 . In contrast, pyranoside binding pattern studies of methyl uronic acids showed some differences compared to previously published STD NMR results of UDP-glycosides. In general, obtained results can contribute to a better understanding in binding of UDP-glycosides to other UXS enzyme family members, which have high structural similarities in the active site. [ABSTRACT FROM AUTHOR]

Changes in concentration (0.001–0.1 M) of an arabinofuranosyl donor ( 1 ) have been shown to modulate the temperature T at which activation of 1 occurs (from −23 °C to +7 °C), the reaction time (from 1.5 h to 3 days) and the yield of the disaccharide formed (from 14% to 82%). At concentrations exceeding 0.01 M, these parameters, as well as the specific optical rotation of the solution of 1 , virtually do not depend on concentration suggesting formation of reacting species (supramers) of glycosyl donor with similar structures, hence reactivities, but considerably different from those formed in more dilute solutions. The found critical concentration (0.01 M) separates two concentration ranges of reaction solutions corresponding to two types of solution structure that are featured by the presence of fundamentally different supramers of glycosyl donor, which have distinct chemical properties. These results allow a fresh look at the problems of reactivity of chemical compounds and selectivity of the reactions in which they participate. [ABSTRACT FROM AUTHOR]

A series of novel C -glycosyl triazolyl quinoline-based fluorescent sensors have been synthesized via click chemistry. It was found that novel sensors exhibited good selectivity for Hg 2+ over many other metal ions. The glucose framework was introduced to increase the water-solubility of the fluorescent sensors and broaden its application for the detection of Hg(II) in the water-solubility biological systems. The mechanism of the chemodosimetric behavior of the sensors has been attributed to a binding mode of triazolyl quinoline with Hg 2+ which has been characterized by a number of spectroscopic techniques. [ABSTRACT FROM AUTHOR]

A glycosyl-rhodamine fluorescent probe with good water-solubility has been designed and synthesized through click reaction. Compared with control compound 1 , the obtained target compound ( RBGlc-3 ) could be independently applied for the detection of Hg 2+ in water medium, and not disturbed by Ce 3+ , Eu 3+ , Ca 2+ , Cd 2+ , Fe 2+ , Ba 2+ , Co 2+ , Cu 2+ , Zn 2+ , Pb 2+ , Mg 2+ , Ni 2+ , K + , Ag + , Na + , NH 4 + , CH 3 COO − , S 2 O 4 2− , SO 4 2− , SO 3 2− and Cl − . 1:1 Stoichiometry is the most likely recognition mode of RBGlc-3 toward Hg 2+ ion, and the OFF–ON fluorescent mechanism of RBGlc-3 is proposed. [ABSTRACT FROM AUTHOR]

Eight kestose isomers were isolated from sugar beet molasses by carbon–Celite column chromatography and HPLC. GC–FID and GC–MS analyses of methyl derivatives, MALD-TOF-MS measurements and NMR spectra were used to confirm the structural characteristics of the isomers. The 1 H and 13 C NMR signals of each isomer saccharide were assigned using COSY, E-HSQC, HSQC–TOCSY, HMBC and H2BC techniques. These kestose isomers were identified as α-D-fructofuranosyl-(2- > 2)-α-D-glucopyranosyl-(1 < ->2)-β-D-fructofuranoside, α-D-fructofuranosyl-(2- > 3)-β-D-fructofuranosyl-(2 < ->1)-α-D-glucopyranoside, α-D-fructofuranosyl-(2- > 4)-β-D-fructofuranosyl-(2 < ->1)-α-D-glucopyranoside, β-D-fructofuranosyl-(2- > 4)-β-D-fructofuranosyl-(2 < ->1)-α-D-glucopyranoside, β-D-fructofuranosyl-(2- > 3)-α-D-glucopyranosyl-(1 < ->2)-β-D-fructofuranoside, α-D-fructofuranosyl-(2- > 1)-β-D-fructofuranosyl-(2 < ->1)-α-D-glucopyranoside, α-D-fructofuranosyl-(2- > 6)-α-D-glucopyranosyl-(1 < ->2)-β-D-fructofuranoside, and α-D-fructofuranosyl-(2- > 6)-β-D-fructofuranosyl-(2 < ->1)-α-D-glucopyranoside. The former five compounds are novel saccharides. [ABSTRACT FROM AUTHOR]

The 2-N,N-dibenzylamino glucopyranosyl trichloroacetimidate donor was synthesized and an extensive investigation of its glycosyl donor properties was conducted. Coupling studies incorporated a variety of glycosyl promoters and a range of acceptor alcohols representing different reactivities and protecting group patterns. Various reaction temperatures, solvents and glycosylation protocols were also examined. Exclusive β-stereoselectivity was obtained in moderate to good yields with eight novel glycosides being produced, by probable neighbouring group participation via the formation of an aziridinium ion intermediate. Plausible reaction mechanisms were proposed based on the results obtained. [ABSTRACT FROM AUTHOR]

Carbohydrates have quite complicated micro heterogenic structure which may undergo different structural transitions. Due to their extreme flexibility it is very difficult to investigate such structural changes experimentally. In these studies we want to predict what structural and conformational changes are possible in the carbohydrate glycosylphosphatidylinositol anchor chain (GPI): the tetrasaccharide with the unique sequence Man-α(1 → 2)-Man-α(1 → 6)-Man-α(1 → 4)-GlcN-α. This is a very important biomolecule associated with the processes of transmitting various types of signals in the cells of living organisms. In order to investigate conformational and structural changes in GPI we use in these studies the theoretical Enforced Geometry Optimization (EGO) method. In this method a molecule is exposed to a mechanical stress caused by external forces applied to selected atoms. It turned out that under external stretching forces the mannopyranose unit can change its 4C 1 chair conformation into three different forms: 1S 3 , oS 2 and B 2,5. The initial 4C 1 glucosamine ring can transit into the twisted boat 1S 3 and the boat B o,3 conformations. The obtained results confirm the high flexibility of the GPI anchor sugar chain. [Display omitted] • The proper description of forced conformational transitions even in monosaccharides can be complicated. • The change in the length of the sugar molecule does not always have to be associated with a conformational change. • The results confirm the remarkable conformational diversity of the units forming the GPI anchor's saccharide chain. [ABSTRACT FROM AUTHOR]

Various thiosaccharides and 1-thiotrehaloses were synthesized exploiting salient features of gold-catalyzed glycosidation repertoire using alkynyl 1,2-orthoesters as glycosyl donors. The reaction was found to be general, high yielding, diastereoselective, fast, mild and catalytic. [ABSTRACT FROM AUTHOR]

We describe here an expedient and highly stereoselective procedure for the synthesis of α-glycosyl azides. Treatment of 1,6-anhydrosugars with trimethylsilyl azide in the presence of trimethylsilyl triflate led to the formation of α-glycosyl azides. All the reactions were highly stereoselective and afforded the α-glycosyl azides in good to excellent yields. [ABSTRACT FROM AUTHOR]

New cryptands including bis-azacrown and saccharidic moieties in their structure were prepared in several steps by applying Staudinger–aza-Wittig reaction (SAW). Syntheses have been started from cheap, easily available commercial compounds such as D-glucose, D-cellobiose and D-lactose subsequently transformed into their derivatives in fairly good yields (60–65%) and suitable to give desired final cryptands by direct SAW coupling reactions. [ABSTRACT FROM AUTHOR]

Synthetic methods were elaborated for d -glucals attached to oxadiazoles by a C–C bond. Introduction of the double bond was effected by either DBU induced elimination of PhCOOH from the O -perbenzoylated glucopyranosyl precursors or Zn/ N -methylimidazole mediated reductive elimination from the 1-bromoglucopyranosyl starting compounds. Alternatively, heterocyclizations of 2-deoxy- d - arabino -hex-1-enopyranosyl cyanide were also carried out. Test compounds were obtained by Zemplén debenzoylation, however, none of them showed significant inhibition of rabbit muscle glycogen phosphorylase b . [ABSTRACT FROM AUTHOR]

Thioglycoside-containing trimannose analogs were designed and prepared to mimic the natural N-glycan core trisaccharide α- d -Man-(1→3)-[α- d -Man-(1→6)]- d -Man. (1→6)- S -Linked trimannoside 1 and its trivalent cluster 2 were synthesized in 11 and 15 steps, respectively, taking advantages of the armed mannopyranosyl trichloroacetimidate as glycosyl donor. Hemagglutination inhibition of the two new thiomannotriose analogs was preliminarily examined. Comparing to the parent trimannoside α- d -Man-(1→3)-[α- d -Man-(1→6)]- d -Man-OMe, the cluster mannotrioside 2 presented a comparable binding affinity to Con A, while the monomer 6- S -trimannoside 1 exhibited a slightly lower inhibition ability. [ABSTRACT FROM AUTHOR]

Chemical glycosylation is central to carbohydrate chemistry and is generally recognised as a challenging reaction. This review describes the most reoccurring side reactions of glycosyl donors in glycosylation and how scientists have attempted to explain their observations and in some cases succeeded in solving a particular encountered problem. The topics covered are donor hydrolysis, elimination to form glycals, intermolecular aglycon transfer of thioglycosides and glycosyl imidate rearrangement. [ABSTRACT FROM AUTHOR]

Transformation of 3-O-benzyl-1,2:5,6-di-O-isopropylidene-α- d -glucofuranose into 2,4,6-tri-O-benzoyl-3-O-benzyl glucopyranosyl imidate proceeded efficiently via crystalline benzyl and per-benzoylated derivatives. This imidate glycosylated di-O-isopropylidene-α- d -glucofuranose in high yield and glycosylation of the disaccharide after removal of the 3′-O-benzyl ether afforded the β1,3 linked trisaccharide in excellent yield. Di- and trisaccharides imidates were readily prepared from the furanose terminated glycosylation products but both were unreactive in glycosylation reaction with the debenzylated di- and trisaccharide alcohols. The 3′-O-benzyl perbenzoylated disaccharide pyranose derivative could be selectively debenzoylated and converted to the corresponding perbenzoylated 4,6:4′,6′-di-O-benzylidene derivative. Lewis acid catalyzed glycosidation gave the selectively protected disaccharide ethylthioglycoside in good overall yield. Glycosidation of this thioglycoside donor with 5-methoxycarbonylpentanol gave the disaccharide tether glycoside and after catalytic removal of benzyl ether the resulting disaccharide alcohol was glycosylated by the thioglycoside in a 2+2 reaction to yield a tetrasaccharide. Repetition of selective deprotection of the terminal 3-O-benzyl ether followed by glycosylation by the disaccharide thioglycoside gave a protected hexasaccharide. Hydrogenolysis of this hexasaccharide followed by transesterification and second hydrogenolysis to remove a residual benzyl group gave the target hexasaccharide glycoside 1 as a Dectin-1 ligand functionalized to permit covalent attachment to glycoconjugate vaccines and thereby facilitate improved antigen processing by dendritic cells. [ABSTRACT FROM AUTHOR]

Terahertz time-domain attenuated total reflection measurements of monosaccharide (glucose and fructose) and disaccharide (sucrose and trehalose) solutions from 0.146 M to 1.462 M were performed to evaluate (1) the hydration state and (2) the destructuring effect of saccharide solutes on the hydrogen bond (HB) network. Firstly, the extent of hydration water was determined by the decreased amount of bulk water with picosecond relaxation time that was replaced by that with much longer orientational relaxation time. As a result, we found glucose and trehalose exhibits stronger hydration capacity than fructose and sucrose, respectively, despite of the same number of the hydroxyl groups. For each saccharide, the hydration number tended to decrease with solute concentration. Secondly, the destructuring effect of these saccharide solutes on the HB network of the surrounding bulk water was discussed from the perspective of the fraction of non-hydrogen-bonded (NHB) water isolated from the HB network. We found the fraction of NHB water molecules that are not engaged in the HB network monotonously increased with saccharide concentration, indicating saccharide solutes promote the disruption of the water HB network. However, no noticeable differences were confirmed in the fraction of NHB water between glucose and fructose or between sucrose and trehalose. In contrast to hydration number, the number of NHB water produced by a single saccharide solute was less dependent on solute concentration, and three monosaccharide/disaccharide solutes were found to produce one/two NHB water molecules. [ABSTRACT FROM AUTHOR]

Gemcitabine, 2′-deoxy-2′,2′-difluorocytidine, is currently prescribed against a number of cancers. Here we report a linear synthesis of gemcitabine with a high-yielding direct conversion of 3,5-di- O -benzoyl-2-deoxy-2,2-difluororibose into the corresponding glycosyl urea as the key step, followed by conventional conversion to the cytosine base via the uracil derivative. The process proceeded with modest anomeric selectivity. [ABSTRACT FROM AUTHOR]

A simple synthesis of series of new catalysts derived from chiral bifunctional ureas is described. The aza-Henry reaction of imines with nitromethane was promoted by sugar derived bifunctional organocatalysts to give optically active β-nitroamines. The aza-Henry reaction products were obtained in good yields (35–98%) and ee up to 99%. [ABSTRACT FROM AUTHOR]

Structural modifications of the leaving group of S-glycosyl O -methyl phenylcarbamothioates (SNea) involving change of substituents that express different electronic effects led to a better understanding of how the reactivity of these glycosyl donors can be modified by changing the structure of their leaving groups. Mechanistic studies involving the isolation of departed aglycones were indicative of the direct activation of both p -methoxy-SNea and p -nitro-SNea leaving groups via the anomeric sulfur rather than the remote nitrogen atom. The presence of an electron donating substituent ( p -methoxy) has a strong effect on the nucleophilicity of the sulfur atom that becomes more susceptible toward the attack of thiophilic reagents, in particular. This key observation allowed to differentiate the reactivity levels of p -methoxy-SNea versus p -nitro-SNea and even unmodified SNea leaving groups. The reactivity difference observed in the series of SNea leaving groups is sufficient to be exploited in expeditious oligosaccharide synthesis via selective activation strategies. [ABSTRACT FROM AUTHOR]

The first synthesis of the outer core fragment of Burkholderia multivorans lipooligosaccharide [β- d -Glc-(1→3)-α- d -GalNAc-(1→3)-β- d -GalNAc-(1→3)- l -Rha] as α-allyl tetrasaccharide was accomplished. The glycosylations involving GalNAc units were studied in depth testing them under several conditions. This allowed the building of both the α- and the β-configured glycosidic bonds by employing the same GalNAc glycosyl donor, thus considerably shortening the total number of synthetic steps. The target tetrasaccharide was synthesized with an allyl aglycone to allow its future conjugation with an immunogenic protein en route to the development of a synthetic neoglycoconjugate vaccine against the Burkholderia cepacia pathogens. [ABSTRACT FROM AUTHOR]

Glycosylation is the key reaction by which our body can produce and modify carbohydrates and their conjugates which are molecules essential for life. The study of the diversity of their functions is a current and ever-expanding topic that requires the ability to provide pure saccharides quickly, efficiently and in a controlled way which can be achieved by chemical synthesis. Although the influence of the donor and the promoter on the outcome of a glycosylation reaction is well documented, the search for new methodologies and new promoters/activators is constantly expanding. In this review, after an introduction dealing with well-known glycosylation strategies, we describe the most recent advances in terms of the use of innovative approaches, focalizing the study on new promoters and leaving groups exploited in the last ten years. [Display omitted] • New methodologies and new reagents in glycosylation reaction. • Discussion on recent promoters derived from transition metals, boron derivatives, and Halogens. • Comparison of the roles of leaving groups from ethers and esters, S-derivatives and N -oxyacetamides for regioselectivity. [ABSTRACT FROM AUTHOR]

The O-specific polysaccharide was isolated from the lipopolysaccharide of Echinicola vietnamensis and studied by chemical methods along with 1 H and 13 C NMR spectroscopy, including 2D 1 H, 1 H COSY, TOCSY, ROESY, 1 H, 13 C HSQC, HMBC, and H2BC experiments. It was found that the polysaccharide is built up of branched tetrasaccharide repeating units, containing 2-acetamido-2-deoxy- d -glucuronic acid (GlcNAcA), 2-acetamido-2-deoxy- d -galactose (GalNAc), and d -glucuronic acid (GlcA) with a terminal residue of 3,6-dideoxy- l -xylo-hexose (colitose, Col) and has the following structure. [ABSTRACT FROM AUTHOR]

An easy and mild method has been developed for the synthesis of mixed glycosyl disulfides/selenenylsulfides from glycosyl halides and diaryl/dialkyl dichalcogenides in the presence of benzyltriethylammonium tetrathiomolybdate [(BnEt 3 N) 2 MoS 4 ]. The salient feature of this method is the sulfur transfer from [BnEt 3 N] 2 MoS 4 to form glycosyl disulfides which with excess tetrathiomolybdate further undergo exchange reaction with other dichalcogenides in a one-pot operation. [ABSTRACT FROM AUTHOR]

The synthesis of biotinylated conjugates of oligomers of the basic repeating unit of chondroitin sulfate E (CS-E) with the sequence [GlcA-4,6-disulfated GalNAc] n is reported herein for the first time. An efficient and stereocontrolled preparation of di-, tetra-, and hexasaccharide derivatives was achieved using a common key disaccharide intermediate in an iterative way. An unexpected and never reported side reaction on the carbonyl group of the levulinate ester was observed during a coupling reaction. These complex molecules should be useful to study their interactions with various proteins. [ABSTRACT FROM AUTHOR]

A concise and practical chemoenzymatic synthesis of lacto- N -tetraose, a major component and one of the most common core structures of human milk oligosaccharides (HMOs) was reported. This convergent synthesis relies on the glycosylation of a readily available lactoside acceptor with a lacto- N -biose donor generated from a highly efficient one-pot two-enzyme synthesis. [ABSTRACT FROM AUTHOR]

Chemical synthesis of the tetrasaccharide repeating unit of the O -glycan from the polar flagellum flagellin of Azospirillum brasilense Sp7 in the form of its p -methoxyphenyl glycoside is reported. The required glycosidic linkages have been accomplished by activation of thioglycosides with N -iodosuccinimide in the presence of H 2 SO 4 –silica. H 2 SO 4 –silica was found to be an effective alternative to the classical acid promoters like TfOH or TMSOTf and it can lead to the formation of both 1,2- cis and 1,2- trans glycosidic linkages depending on the protecting group manipulation and control of the reaction condition. [ABSTRACT FROM AUTHOR]

The tetrasaccharide repeating unit of the O -antigen of Escherichia coli O174 strain was synthesized applying sequential glycosylations of suitably functionalized monosaccharide intermediates. Activation of glycosyl trichloroacetimidate derivatives using nitrosyl tetrafluoroborate (NOBF 4 ) has been used during the synthesis. The glycosylation steps were high yielding with satisfactory stereo outcome. [ABSTRACT FROM AUTHOR]

A convergent strategy has been developed for the synthesis of the tetrasaccharide repeating unit of the O -antigen from Edwardsiella tarda PCM 1156. Sequential glycosylations of a series of rationally protected monosaccharide intermediates were achieved either by the activation of thioglycosides using N-iodosuccinimide (NIS) in conjunction with H 2 SO 4 –silica or by activation of trichloroacetimidate by H 2 SO 4 –silica only. All glycosylation reactions resulted in the formation of the desired linkage with absolute stereoselectivity and yielded the required derivatives in good to excellent yields. Both azido and phthalimido groups have been used as the precursor of the desired acetamido group depending on the requirement of 1,2- cis - or 1,2- trans -glycosidic linkage. [ABSTRACT FROM AUTHOR]

Activated by NBS, readily available 1,2- trans -1-dihydroxyboryl benzyl S -glycosides served as glycosyl donors and reacted with certain simple alcohol acceptors to produce pure 1,2- cis - O -glycosides in moderate yields. The boronic acid moiety was revealed essential in the glycosylation for product formation and good anomeric ratio. The preliminary model reactions suggested that glycosyl aryl boronic acids could be used for stereoselective glycosylation. [ABSTRACT FROM AUTHOR]

Protected sulfate groups may be used as an alternative tool to provide sulfate esters at hydroxyl and amino groups, particularly on complex glycans. We examined 2,2,2-trichloroethoxysulfation at the mono-, di-, and trihydroxyl groups of saccharide moieties to show regioselective sulfation. We found some side reactions including inter- and intramolecular nucleophilic reactions with 2,2,2-trichloroethoxysulfates. [ABSTRACT FROM AUTHOR]

Water-soluble graphene nanosheets (GNS) were fabricated via functionalization of graphene oxide (GO) with mono and disaccharides on the basal plane and edges using Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition of azides and terminal alkynes (Click chemistry). To graft saccharides onto the plane of GO, it was reacted with sodium azide to introduce azide groups on the plane. Then, it was treated with alkyne-modified glucose, mannose, galactose, and maltose. In the next approach, we attached 1,3-diazideoprop-2-ol onto the edges of GO and it was subsequently clicked with alkyne-glucose. The products were analyzed by Fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy, thermogravimetric analysis (TGA), and X-ray diffraction spectrometry. FTIR and TGA results showed both sugar-grafted GO sheets were reduced by sodium ascorbate during click-coupling reaction which is an advantage for this reaction. Besides, glycoside-grafted GNS were easily dispersed in water and stable for two weeks. [ABSTRACT FROM AUTHOR]

Chemical synthesis of the tetrasaccharide related to the exocellular polysaccharide from Rhodococcus sp. RHA1 is reported. The stereoselective glycosylations were achieved by activation of the thioglycoside donors using N-iodosuccinimide in the presence of La(OTf)3 varying temperature per the need of 1,2-cis or 1,2-trans glycosylations. The target tetrasaccharide is reported in the form of its p-methoxyphenyl glycoside that can be cleaved selectively from the per-O-acetylated derivative allowing further glycoconjugate formation using trichloroacetimidate chemistry. [ABSTRACT FROM AUTHOR]

Chiral ureas containing glycosyl and diphenylphosphinyl scaffolds were found to be an effective organocatalyst. They were synthesised in high yields by a one-pot tandem Staudinger/aza-Wittig coupling reaction. The first attempts of using them in asymmetric synthesis are presented. Yields of the Morita-Baylis-Hillman reaction were moderate with an enantiomeric excess of up to 80%. [ABSTRACT FROM AUTHOR]

Highlights: [•] This research aimed to specifically detect ribofuranoside carbohydrates. [•] Fluorescent boronic acid probes identified that specifically detect ribofuranoside. [•] Concentration dependent detection of ribofuranoside with 3-biphenylboronic acid. [•] Determination of the affinity of the probe for ribofuranoside. [ABSTRACT FROM AUTHOR]

Highlights: [•] A pentasaccharide corresponding to the O-antigen of E. coli O13 has been synthesized. [•] Thioglycoside derivatives were used as glycosyl donor in all glycosylation reactions. [•] Benzylidene acetal, benzyl ether were removed by catalytic transfer hydrogenation. [•] Conformational analysis was done by 2D ROESY and MD simulation techniques. [ABSTRACT FROM AUTHOR]

Highlights: [•] A pentasaccharide analog has been synthesized for the first time. [•] The plant growth regulation activity of this analog was studied. [•] The activity data shows the analog can stimulate the growth of wheat coleoptile. [Copyright &y& Elsevier]