Synthesis and biological evaluation of a new sialyl Lewis X mimetic derived from lactose

Synthesis and Antibody Binding Studies of Schistosome-Derived Oligo-α-(1-2)-l-Fucosides

Schistosomiasis is caused by blood-dwelling parasitic trematodes of the genus Schistosoma and is classified by the WHO as the second most socioeconomically devastating parasitic disease, second only to malaria. Schistosoma expresses a complex array of glycans as part of glycoproteins and glycolipids that can be targeted by both the adaptive and the innate part of the immune system. Some of these glycans can be used for diagnostic purposes. A subgroup of schistosome glycans is decorated with unique α-(1-2)-fucosides and it has been shown that these often multi-fucosylated fragments are prime targets for antibodies generated during infection. Since these α-(1-2)-fucosides cannot be obtained in sufficient purity from biological sources, we set out to develop an effective route of synthesis towards α-(1-2)-oligofucosides of varying length. Here we describe the exploration of two different approaches, starting from either end of the fucose chains. The oligosaccharides have been attached to gold nanoparticles and used in an enzyme-linked immunosorbent assay ELISA and a microarray format to probe antibody binding. We show that binding to the oligofucosides of antibodies in sera of infected people depends on the length of the oligofucose chains, with the largest glycans showing most binding.

Lactose esters: synthesis and biotechnological applications

Biodegradable nonionic sugar esters-based surfactants have been gaining more and more attention in recent years due to their chemical plasticity that enables the various applications of these molecules. In this review, various synthesis methods and biotechnological implications of lactose esters (LEs) uses are considered. Several chemical and enzymatic approaches are described for the synthesis of LEs, together with their applications, i.e. function in detergents formulation and as additives that not only stabilize food products but also protect food from undesired microbial contamination. Further, this article discusses medical applications of LEs in cancer treatment, especially their uses as biosensors, halogenated anticancer drugs, and photosensitizing agents for photodynamic therapy of cancer and photodynamic inactivation of microorganisms.

Stereospecific, High-Yielding, and Green Synthesis of β-Glycosyl Esters

A new method of synthesizing β-glycosyl esters stereospecifically has been developed by treating O-benzyl-protected glycosyl chlorides with Cs2CO3, tetrabutylammomium bromide (TBAB), a carboxylic acid, water, and granular polytetrafluoroethylene (PTFE) at 80 °C under mechanical agitation. D-Glucosyl, D-xylosyl, and D-galactosyl chlorides and 20 carboxylic acids were used to demonstrate the scope of the reaction. Control experiments showed that the water and granular PTFE had indispensable roles. Water-soluble TBAB has been found to be as efficient as N-methyl-N,N,N-trioctyloctan-1-ammonium chloride (Aliquat 336) in the reactions. After scaling up to 5-12 g, all of the products were obtained quantitatively via simple filtration and no organic solvents or chromatography was needed for the entire process.

Chemical Synthesis of the Tumor-Associated Globo H Antigen

A derivative of the tumor-associated globo H antigen, a complex hexasaccharide, was synthesized by a convergent and efficient [3+2+1] strategy using various glycosylation methods. All glycosylation reactions afforded good to excellent yields and outstanding stereoselectivity, including the installation of cis α-linked D-galactose and L-fucose. The longest linear sequence for this synthesis was 11 steps from a galactose derivative 11 to give an overall yield of 2.6%. The synthetic target had a free and reactive amino group at the glycan reducing end, facilitating its conjugation with other molecules for various applications.

Lactosyl derivatives function in a rat model of severe burn shock by acting as antagonists against CD11b of integrin on leukocytes

Severe burn shock remains an unsolved clinical problem with urgent needs to explore novel therapeutic approaches. In this study, the in vivo bioactivity of a series of synthetic lactosyl derivatives (oligosaccharides) was assessed on rats with burn shock to elucidate the underlying mechanisms. Administration of An-2 and Gu-4, two lactosyl derivatives with di- and tetravalent beta-D: -galactopyranosyl-(1-4)-beta-D: -glucopyranosyl ligands, significantly prolonged the survival time (P < 0.05 vs. saline), stabilized blood pressure and ameliorated the injuries to vital organs after burn. Flow chamber assay displayed that An-2 and Gu-4 markedly decreased the adhesion of leukocytes to microvessel endothelial cells. Competitive binding assay showed that a CD11b antibody significantly interrupted the interaction of An-2 and Gu-4 with leukocytes from rats with burn shock. With fluorescent microscopy, we further found that the oligosaccharides were selectively bound to leukocytes and with a colocalization of CD11b on the cell membrane. Interestingly, the lectin domain-deficient form of CD11b failed to bind with An-2 and Gu-4. The results suggest that both An-2 and Gu-4 significantly inhibit the adhesion of leukocytes to endothelial cells by binding to CD11b and thereby exert protective effects on severe burn shock.

Rational Design of Novel, Potent Small Molecule Pan-Selectin Antagonists

This report describes the first results of a rational hit-finding strategy to design novel small molecule antiinflammatory drugs targeting selectins, a family of three cellular adhesion molecules. Based on recent progress in understanding of molecular interaction between selectins and their natural ligands as well as progress in clinical development of synthetic antagonists like 1 (bimosiamose, TBC1269), this study was initiated to discover small molecule selectin antagonists with improved pharmacological properties. Considering 1 as template structure, a ligand-based approach followed by focused chemical synthesis has been applied to yield novel synthetic small molecules (MWr < 500) with a trihydroxybenzene motif, bearing neither peptidic nor glycosidic components, with nanomolar in vitro activity. Biological evaluation involves two kinds of in vitro assays, a static molecular binding assay, and a dynamic HL-60 cell attachment assay. As compared to controls, the novel compounds showed improved biological in vitro activity both under static and dynamic conditions.

Synthesis of a 2,3,4-Triglycosylated Rhamnoside Fragment of Rhamnogalacturonan-II Side Chain A Using a Late Stage Oxidation Approach

Pectic polysaccharide RG-II, a key component of plant primary cell walls, is known to exist as a dimer formed by means of borate diester cross-links between apiosyl residues of one of its constituent side-chain oligosaccharides. Described herein is the strategy for the synthesis of the branched tetrasaccharide alpha-d-GalA-(1-->2)-[beta-D-GalA-(1-->3)]-[alpha-L-Fuc-(1-->4)]-alpha-L-Rha-OMe, an RG-II fragment that is linked to the apiosyl residue that is thought to be responsible for the borate complexation in RG-II dimer. Iterative glycosylation of the rhamnoside acceptors derived from the key 2,3-orthoacetate of methyl 4-O-methoxybenzyl-alpha-d-rhamnopyranoside afforded the protected tetrasaccharide. The target dicarboxylic acid saccharide was subsequently prepared by removal of protecting groups followed by TEMPO-mediated oxidation of galactopyranosyl residues to galactopyranosyluronic acids.

High-throughput identification of fucosyltransferase inhibitors using carbohydrate microarrays

A noncovalent carbohydrate microarray was used to screen for possible inhibitors to fucosyltransferases, which are critical to the synthesis of inflammation mediators like sialyl Lewis x (SLe(x)). Inhibition was followed by observation of the transferred fucose on the carbohydrate array with the lectin Tetragonolobus purpureas. Of these compounds, four inhibitors with nanomolar Ki(s) were discovered, with three of the top five inhibitors exhibiting a common architecture.

Stereoselective Synthesis of α- and β-l-C-Fucosyl Aldehydes and Their Utility in the Assembly of C-Fucosides of Biological Relevance

An efficient synthesis of O-benzylated derivatives of the title sugar aldehydes via thiazole addition to tri-O-benzyl-l-fuconolactone followed by highly stereoselective deoxygenation of the resulting thiazolylketose and thiazole to formyl transformation is described. Wittig olefination of these aldehydes with galactopyranose and glucopyranose 6-phosphoranes and reduction of the resulting alkenes afforded alpha- and beta-linked (1-->6)-L-C-fucosyl disaccharides, namely, beta-L-C-Fuc-(1-->6)-alpha-D-Gal, alpha-L-C-Fuc-(1-->6)-alpha-D-Gal, and alpha-L-C-Fuc-(1-->6)-alpha-d-Glc. The alpha-anomer of the above C-fucosyl aldehydes was transformed into a C-fucosylmethyl triphenylphosphonium iodide from which the corresponding C-fucosylmethylene phosphorane was generated upon treatment with BuLi. This phosphorane reacted with the Garner aldehyde (N-Boc D-serinal acetonide) and its one-carbon higher homologue to give alkenes whose reduction and unveiling of the glycinyl group from the oxazolidine ring afforded C-fucosyl alpha-amino acids, namely alpha-L-linked C-fucosyl serines and C-fucosyl asparagines. As a final test of the synthetic utility of the title aldehydes, the beta-anomer was employed as starting material in the stereoselective synthesis of both R- and S-epimer L-C-fucosyl phenylhydroxy acetates. One epimer was obtained by reaction of the sugar aldehyde with phenylmagnesium bromide, oxidation of the resulting alcohol to ketone, addition of 2-lithiothiazole to the latter, and transformation of the thiazole ring into the carboxyl group through an aldehyde intermediate. The other epimer was obtained by the same procedure and inverting the timing of phenyl and thiazolyl group addition. In both routes, the key step establishing the configuration of the quaternary carbon atom of the aliphatic chain was the highly stereoselective addition of the organometal to the ketone intermediate.

Two New Galloylglucosides from the Leaves of Mallotus furetianus

Two new galloylglucosides, mallophenols A (1) and B (2), were isolated from the leaves of Mallotus furetianus (Euphorbiaceae), together with seven known compounds, (6S,9R)-roseoside (3), aviculin (4), (+)-lyoniresinol-3alpha-O-alpha-L-rhamnopyranoside (5), (Z)-3-hexenyl-beta-D-glucopyranoside (6), 3,3,8,9,10-pentahydroxydibenzo[b,d]pyran-6-one (7), 3-hydroxy-4,5(R)-dimethyl-2(5H)-furanone (8) and gallic acid (9). The stereostructures of 1 and 2 were elucidated on the basis of spectroscopic analysis and chemical evidence.