Stereoselective Synthesis of the Gal-α-(1→3)-Gal-ß-(1→3)-GlcNAc Trisaccharide: a new Ligand for DCAR and Mincle C-Type Lectin Receptors.

In this work, we have discovered that the Gal-α-(1→3)-Gal-ß-(1→3)-GlcNAc trisaccharide, a fragment of the B antigen Type-1, is a new ligand of two C-type lectin receptors (CLRs) i. e. DCAR and Mincle which are key players in different types of autoimmune diseases. Accordingly, we report here on a straightforward methodology to access pure Gal-α-(1→3)-Gal-ß-(1→3)-GlcNAc trisaccharide. A spacer with a terminal primary amine group was included at the reducing end of the GlcNAc residue thus ensuring the further functionalization of the trisaccharide Gal-α-(1→3)-Gal-ß-(1→3)-GlcNAc.

Total Synthesis of the Phosphorylated Zwitterionic Trisaccharide Repeating Unit of Photorhabdus temperata cinerea 3240.

Herein, we report the total synthesis of the phosphorylated zwitterionic trisaccharide repeating unit of Photorhabdus temperata subsp. cinerea 3240. The efficient route involves regio- and stereoselective assembly of trisaccharide with rare deoxyamino sugar AAT at the nonreducing end, late stage oxidation, and installation of a phosphate linker on the trisaccharide. The total synthesis was completed via a longest linear sequence of 24 steps in 6.5% overall yield.

Total Synthesis of the Photorhabdus temperata ssp. Cinereal 3240 Zwitterionic Trisaccharide Repeating Unit.

Zwitterionic carbohydrate modifications, such as phosphoethanolamine (PEtN), govern host-pathogen interactions. Whereas it is recognized that these modifications stimulate the host immune system, the purpose of PEtN modification remains largely descriptive. As an enabling step toward studying this carbohydrate modification, we report a synthesis of the P. temperata zwitterionic trisaccharide repeating unit. The 32-step synthesis was enabled by H-phosphonate chemistry to install the PEtN arm on a poorly reactive and sterically hindered C4-alcohol.

The forgotten sugar: A review on multifarious applications of melezitose.

Although, 187 years elapsed after the discovery of melezitose, it is a high time to deduce some solid applications as there are only 13 more years left to celebrate a double century of this sugar. The forgotten sugar has multifarious applications; it is used as a metabolic marker to differentiate melezitose fermenting microorganisms, as a carbon source to culture specific microorganisms, as a potential surfactant and excipient to stabilize pharmaceuticals, as a lyoprotectant or cryoprotectant for several industrial applications, as an edibility enhancer in food industry, as a hair smoothening agent in cosmetic industry, and provide protective & nourishing effects in fisheries and aquaculture industries. In entomological research, it is used to study niche differentiation, increased longevity of insects and also as a biocontrol agent. This review brings out the best possible applications of melezitose and present in the form of a mnemonic to remember this forgotten sugar.

Synthesis and Cell Growth Inhibitory Activity of Six Non-glycosaminoglycan-Type Heparin-Analogue Trisaccharides.

The design and synthesis of heparin mimetics with high anticancer activity but no anticoagulant activity is an important task in medicinal chemistry. Herein, we present the efficient synthesis of five Glc-GlcA-Glc-sequenced and one Glc-IdoA-Glc-sequenced non-glycosaminoglycan, heparin-related trisaccharides with various sulfation/sulfonylation and methylation patterns. The cell growth inhibitory effects of the compounds were tested against four cancerous human cell lines and two non-cancerous cell lines. Two d-glucuronate-containing tetra-O-sulfated, partially methylated trisaccharides displayed remarkable and selective inhibitory effects on the growth of ovary carcinoma (A2780) and melanoma (WM35) cells. Methyl substituents on the glucuronide unit proved to be detrimental, whereas acetyl substituents were beneficial to the cytostatic activity of the sulfated derivatives.

Synthesis of l-glycero- and d-glycero-d-manno-Heptose Building Blocks for Stereoselective Assembly of the Lipopolysaccharide Core Trisaccharide of Vibrio parahemolyticus O2.

Synthesis of bacterial cell surface l-glycero-d-manno-heptose (l,d-Hep)- and d-glycero-d-manno-heptose (d,d-Hep)-containing higher carbon sugars is a challenging task. Here, we report a convenient and efficient approach for the synthesis of the l,d-Hep and d,d-Hep building blocks. Using l-lyxose and d-ribose as starting materials, this approach features diastereoselective Mukaiyama-type aldol reactions as the key steps. On the basis of the synthetic l,d-Hep and d,d-Hep building blocks, we achieved the first stereoselective synthesis of the unique α-l,d-Hep-(1→3)-α-d,d-Hep-(1→5)-α-Kdo core trisaccharide of the lipopolysaccharide of Vibrio parahemolyticus O2.

Efficient chemoenzymatic synthesis of fluorinated sialyl Thomsen-Friedenreich antigens and investigation of their characteristics.

A set of fluorinated sialyl-T derivatives were efficiently synthesized using one-pot multi-enzyme (OPME) chemoenzymatic approach. The P. multocida α2-3-sialyltransferase (PmST1) involved in the synthesis showed extremely flexible donor and acceptor substrate specificities. These sialosides have been successfully investigated with stability towards Clostridium perfringens sialidase substrate specificity assay using 1H NMR spectroscopy. Hydrolysis studies monitored by 1H NMR clearly demonstrated that the fluorine substitution obviously reduced hydrolysis rate of Clostridium perfringens sialidase. To further investigate the fluorine influence, structure-dependent variation of sialoside-lectin binding was observed for MAL and different sialoside-immobilized surfaces. Subtle changes on the ligand of carbohydrate-binding protein were distinguished by SPR. These fluorinated sialyl-T derivatives obtained are valuable probes for further biological studies or antitumor drug design.

New synthesis of 6″-[18 F]fluoromaltotriose for positron emission tomography imaging of bacterial infection.

6″-[18 F]fluoromaltotriose is a positron emission tomography tracer that can differentiate between bacterial infection and inflammation in vivo. Bacteria-specific uptake of 6″-[18 F]fluoromaltotriose is attributed to the targeting of maltodextrin transporter in bacteria that is absent in mammalian cells. Herein, we report a new synthesis of 6″-[18 F]fluoromaltotriose as a key step for its clinical translation. In comparison with the previously reported synthesis, the new synthesis features unambiguous assignment of the fluorine-18 position on the maltotriose unit. The new method utilizes direct fluorination of 2″,3″,4″-tri-O-acetyl-6″-O-trifyl-α-D-glucopyranosyl-(1-4)-O-2',3',6'-tri-O-acetyl-α-D-glucopyranosyl-(1-4)-1,2,3,6-tetra-O-acetyl-D-glucopyranose followed by basic hydrolysis. Radiolabeling of the new maltotriose triflate precursor proceeds using a single HPLC purification step, which results in shorter reaction time in comparison with the previously reported synthesis. Successful synthesis of 6″-[18 F]fluoromaltotriose has been achieved in 3.5 ± 0.3% radiochemical yield (decay corrected, n = 7) and radiochemical purity above 95%. The efficient radiosynthesis of 6″-[18 F]fluoromaltotriose would be critical in advancing this positron emission tomography tracer into clinical trials for imaging bacterial infections.

An efficient assay for identification and quantitative evaluation of potential polysialyltransferase inhibitors.

The polysialyltransferases (polySTs) catalyse the polymerisation of polysialic acid, which plays an important role in tumour metastasis. While assays are available to assess polyST enzyme activity, there is no methodology available specifically optimised for identification and quantitative evaluation of potential polyST inhibitors. The development of an HPLC-fluorescence-based enzyme assay described within includes a comprehensive investigation of assay conditions, including evaluation of metal ion composition, enzyme, substrate and acceptor concentrations, temperature, pH, and tolerance to DMSO, followed by validation using known polyST inhibitors. Thorough analysis of each of the assay components provided a set of optimised conditions. Under these optimised conditions, the experimentally observed Ki value for CMP, a competitive polyST inhibitor, was strongly correlated with the predicted Ki value, based on the classical Cheng-Prusoff equation [average fold error (AFE) = 1.043]. These results indicate that this assay can provide medium-throughput analysis for enzyme inhibitors with high accuracy, through determining the corresponding IC50 values with substrate concentration at the KM, without the need to perform extensive kinetic studies for each compound. In conclusion, an in vitro cell-free assay for accurate assessment of polyST inhibition is described. The utility of the assay for routine identification of potential polyST inhibitors is demonstrated, allowing quantitative measurement of inhibition to be achieved, and exemplified through assessment of full competitive inhibition. Given the considerable and growing interest in the polySTs as important anti-metastatic targets in cancer drug discovery, this is a vital tool to enable preclinical identification and evaluation of novel polyST inhibitors.

Trisaccharide Sulfate and Its Sulfonamide as an Effective Substrate and Inhibitor of Human Endo-O-sulfatase-1.

Human endo-O-sulfatases (Sulf-1 and Sulf-2) are extracellular heparan sulfate proteoglycan (HSPG)-specific 6-O-endosulfatases, which regulate a multitude of cell-signaling events through heparan sulfate (HS)-protein interactions and are associated with the onset of osteoarthritis. These endo-O-sulfatases are transported onto the cell surface to liberate the 6-sulfate groups from the internal d-glucosamine residues in the highly sulfated subdomains of HSPGs. In this study, a variety of HS oligosaccharides with different chain lengths and N- and O-sulfation patterns via chemical synthesis were systematically studied about the substrate specificity of human Sulf-1 employing the fluorogenic substrate 4-methylumbelliferyl sulfate (4-MUS) in a competition assay. The trisaccharide sulfate IdoA2S-GlcNS6S-IdoA2S was found to be the minimal-size substrate for Sulf-1, and substitution of the sulfate group at the 6-O position of the d-glucosamine unit with the sulfonamide motif effectively inhibited the Sulf-1 activity with IC50 = 0.53 µM, Ki = 0.36 µM, and KD = 12 nM.

Total Synthesis of the Lipid-Anchor-Attached Core Trisaccharides of Lipoteichoic Acids of Streptococcus pneumoniae and Streptococcus oralis Uo5.

Herein we report an efficient total synthesis of lipid-anchor-appended core trisaccharides of lipoteichoic acids of Streptococcus pneumoniae and Streptococcus oralis Uo5. The key features include the expedient synthesis of the rare sugar 2,4,6-trideoxy-2-acetamido-4-amino-d-Galp building block via one-pot sequential SN2 reactions and the α-selective coupling of d-thioglucoside with the diacyl glycerol acceptor to construct a common disaccharide acceptor, which was utilized in the total synthesis of target molecules 1 and 2.

Synthesis of a Di-Mycoloyl Tri-Arabinofuranosyl Glycerol Fragment of the Mycobacterial Cell Wall, Based on Synthetic Mycolic Acids.

Fragments of mycobacterial cell walls such as arabinoglycerol mycolate and dimycoloyl diarabinoglycerol, comprising complex mixtures of mycolic acids, have immunostimulatory and antigenic properties. A related di-mycoloyl tri-arabinofuranosyl glycerol fragment has been isolated from cell wall hydrolysates. An effective stereoselective synthesis of tri-arabinofuranosyl glycerol, followed by coupling with stereochemically defined mycolic acids of different structural classes, to provide unique di-mycoloyl tri-arabinofuranosyl glycerols is now described.

Total Synthesis of the Congested, Bisphosphorylated Morganella morganii Zwitterionic Trisaccharide Repeating Unit.

Zwitterionic polysaccharides (ZPSs) activate T-cell-dependent immune responses by major histocompatibility complex class II presentation. Herein, we report the first synthesis of a Morganella morganii ZPS repeating unit as an enabling tool in the synthesis of novel ZPS materials. The repeating unit incorporates a 1,2-cis-α-glycosidic bond; the problematic 1,2-trans-galactosidic bond, Gal-ß-(1 → 3)-GalNAc; and phosphoglycerol and phosphocholine residues which have not been previously observed together as functional groups on the same oligosaccharide. The successful third-generation approach leverages a first in class glycosylation of a phosphoglycerol-functionalized acceptor. To install the phosphocholine unit, a highly effective phosphocholine donor was synthesized.

Kilogram scale chemical synthesis of 2'-fucosyllactose.

A scalable synthetic procedure to high quality 2'-fucosyllactose, the most abundant oligosaccharide in human breast milk, has been designed and validated in kilogram scale. The synthetic route has been developed to suit industrial environment and contains only a single chromatographic purification step.

2,4-Dinitrobenzenesulfonamide-Directed SN2-Type Displacement Reaction Enables Synthesis of ß-d-Glycosaminosides.

An efficient protocol to construct ß-d-gluco-/galactosaminosyl linkages was established using nonparticipating and strong electron-withdrawing C-2-2,4-dinitrobenzenesulfonamide (DNsNH)-directed SN2-like glycosylation of glycosyl ortho-hexynylbenzoates. The reaction is applicable to a wide range of O-, N-, and C-nucleophiles and features convenient conversion of DNsNH into AcNH in high yield under mild conditions. Oligomerization-ready trisaccharide, composed of ß-d-(1→3)-glucosamino residues, has been achieved, setting a solid foundation for the synthesis of oligosaccharides associated with Neisseria meningitidis capsular polysaccharide.

A metal free mild and green approach for tandem opening of 4,6-O-benzylidene acetals to their corresponding 6-O-acetyl derivatives: Application in the synthesis of a trisaccharide using one-pot glycosylation reactions.

An efficient and high yielding reaction for tandem opening of 4,6-O-benzylidene derivatives (gluco, galacto, manno, 2-phthalimido-2-deoxy glucosides) to their corresponding 6-O-acetyl derivatives has been established under metal free condition using 60% solution of aqueous acetic acid (v/v). The reaction is equally pertinent for large scale synthesis and also for disaccharide glycosides. Its application for the construction of a building block towards synthesis of a trisaccharide part related to Pseudomonas aeruginosa utilizing one-pot glycosylation reactions has also been described.

Development of α-Gal-Antibody Conjugates to Increase Immune Response by Recruiting Natural Antibodies.

Cancer treatment with antibodies (Abs) is one of the most successful therapeutic strategies for obtaining high selectivity. In this study, α-gal-Ab conjugates were developed that dramatically increased cellular cytotoxicity by recruiting natural Abs through the interaction between α-gal and anti-gal Abs. The potency of the α-gal-Ab conjugates depended on the amount of α-gal conjugated to the antibody: the larger the amount of α-gal introduced, the higher the level of cytotoxicity observed. The conjugation of antibodies with an α-gal dendrimer allowed the introduction of large amounts of α-gal to the Ab, without loss of affinity for the target cell. The method described here will enable the re-development of Abs to improve their potency.

Total Synthesis of the Trisaccharide Antigen of the Campylobacter jejuni RM1221 Capsular Polysaccharide via de Novo Synthesis of the 6-Deoxy-d- manno-heptose Building Blocks.

A de novo approach utilizing the d-proline-catalyzed and LDA-promoted aldol reactions as key steps for the preparation of differentiated-protected 6-deoxy-d- manno-heptose building blocks was developed. PPh3AuBAr4F-catalyzed glycosylation with the 6-deoxy-d- manno-heptosyl o-hexynylbenzoate as donor was demonstrated as a direct and practical method for the stereoselective synthesis of the ß-linked 6-deoxy-d- manno-heptoside as the major product. Coupling of the 6-deoxy-α-d- manno-heptosyl H-phosphonate with the 3-hydroxyl disaccharide acceptor based on H-phosphonate chemistry was described for the construction of the trisaccharide skeleton with the acid-labile phosphodiester linkage. Finally, first total synthesis of the unique trisaccharide antigen of the capsular polysaccharide of Campylobacter jejuni RM1221 that belongs to HS:53 serotype complex was accomplished for further evaluation as vaccine candidate against C. jejuni RM1221 infection.

A chemo-enzymatic approach for the synthesis of human milk oligosaccharide backbone structures.

The ability of an engineered ß-N-acetylhexosaminidase to utilize a reactive oxazoline as donor molecule for transglycosylation reaction to synthesize human milk oligosaccharide backbone structures was studied. The human milk oligosaccharide precursor lacto-N-triose II and three regioisomers could be synthesized using the oxazoline, which was either in situ-generated resulting in a chemo-enzymatic sequential cascade or was used as a purified compound. The highest observed concentration of overall transglycosylation products in a cascade reaction was 13.7 mM after 18.5 h, whereas the use of purified oxazoline resulted in 25.0 mM of transglycosylation products after 6.5 h. Remarkably, the in situ-generated oxazoline could be used without any further purification and it was shown that the used enzyme tolerated significant amounts of reagents such as triethylamine, which is reported for the first time for an enzyme from the glycoside hydrolase family 20.

4,6- O-Pyruvyl Ketal Modified N-Acetylmannosamine of the Secondary Cell Wall Polysaccharide of Bacillus anthracis Is the Anchoring Residue for Its Surface Layer Proteins.

The secondary cell wall polysaccharide (SCWP) of Bacillus anthracis plays a key role in the organization of the cell envelope of vegetative cells and is intimately involved in host-guest interactions. Genetic studies have indicated that it anchors S-layer and S-layer-associated proteins, which are involved in multiple vital biological functions, to the cell surface of B. anthracis. Phenotypic observations indicate that specific functional groups of the terminal unit of SCWP, including 4,6- O-pyruvyl ketal and acetyl esters, are important for binding of these proteins. These observations are based on genetic manipulations and have not been corroborated by direct binding studies. To address this issue, a synthetic strategy was developed that could provide a range of pyruvylated oligosaccharides derived from B. anthracis SCWP bearing base-labile acetyl esters and free amino groups. The resulting oligosaccharides were used in binding studies with a panel of S-layer and S-layer-associated proteins, which identified structural features of SCWP important for binding. A single pyruvylated ManNAc monosaccharide exhibited strong binding to all proteins, making it a promising structure for S-layer protein manipulation. The acetyl esters and free amine of SCWP did not significantly impact binding, and this observation is contrary to a proposed model in which SCWP acetylation is a prerequisite for association of some but not all S-layer and S-layer-associated proteins.