Mannosyl glycodendritic structure inhibits DC-SIGN-mediated Ebola virus infection in cis and in trans

We have designed a glycodendritic structure, BH30sucMan, that blocks the interaction between dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) and Ebola virus (EBOV) envelope. BH30sucMan inhibits DC-SIGN-mediated EBOV infection at nanomolar concentrations. BH30sucMan may counteract important steps of the infective process of EBOV and, potentially, of microorganisms shown to exploit DC-SIGN for cell entry and infection.

Direct chemical synthesis of the beta-mannans: linear and block syntheses of the alternating beta-(1-->3)-beta-(1-->4)-mannan common to Rhodotorula glutinis, Rhodotorula mucilaginosa, and Leptospira biflexa

Two stereocontrolled syntheses of a methyl glycoside of an alternating beta-(1-->4)-beta-(1-->3)-mannohexaose, representative of the mannan from Rhodotorula glutinis, Rhodotorula mucilaginosa, and Leptospira biflexa, are described. Both syntheses employ a combination of 4,6-O-benzylidene- and 4,6-O-p-methoxybenzylidene acetal-protected donors to achieve stereocontrolled formation of the beta-mannoside linkage. The first synthesis is a linear one and proceeds with a high degree of stereocontrol throughout and an overall yield of 1.9%. The second synthesis, a block synthesis, makes use of the coupling of two trisaccharides, resulting in a shorter sequence and an overall yield of 4.4%, despite the poor selectivity in the key step.

Phosphated crosslinked guar for colon-specific drug delivery. I. Preparation and physicochemical characterization

Guar gum (GG) was crosslinked with increasing amounts of trisodium trimetaphosophate (STMP) to reduce its swelling properties for use as a vehicle in oral delivery formulations, especially drug delivery systems aimed at localizing drugs in the distal portions of the small bowel. Swelling of GG in artificial gastrointestinal fluids was reduced from 100 to 120-fold (native GG) to 10-35-fold depending on the amount of crosslinker used, showing a bell-shape dependency. As a result of the crosslinking procedure GG lost its non-ionic nature and became negatively charged. This was demonstrated by methylene blue (MB) adsorption studies and swelling studies in sodium chloride solutions with increasing concentrations in which the hydrogels' network collapsed. The adsorption of MB was also used to characterize the degree of the GG crosslinking, from which the effective network density was calculated. In addition, effective network density was calculated from elasticity measurements. Both measurements showed that the crosslinking density (but not swelling) of the new products was linearly dependent on the amount of STMP used in the reaction.

Glycodendritic structures based on Boltorn hyperbranched polymers and their interactions with Lens culinaris lectin

Multivalent scaffolds bearing carbohydrates have been prepared to mediate biological processes where carbohydrates are involved. These systems consist of dendritic structures based on Boltorn H20 and H30 hyperbranched polymers to which carbohydrates are linked through a convenient spacer. Mannose has been chosen as a sugar unit to test the viability of this strategy. These glycodendritic compounds have been prepared in a few steps with good yields, showing a high solubility in physiological media and low toxicity. The binding of these dendritic polymers to the mannose-binding lectin Lens culinaris (LCA) was studied using STD-NMR experiments and quantitative precipitation assays. The results demonstrate the existence of a clear interaction between the mannose derivative systems and the Lens lectin where the dendritic scaffold does not have an important role in mannose binding but supplies the necessary multivalence for lectin cluster formation. These glycodendritic structures are able to interact with a receptor, and therefore they can be considered as promising tools for biological studies.

Direct chemical synthesis of the beta-D-mannans: the beta-(1-->2) and beta-(1-->4) series

The direct syntheses of a beta-(1-->2)-mannooctaose and of a beta-(1-->4)-mannohexaose are reported by means of 4,6-O-benzylidene-protected beta-mannosyl donors. The synthesis of the (1-->2)-mannan was achieved by means of the sulfoxide coupling protocol, whereas the (1-->4)-mannan was prepared using the analogous thioglycoside/sulfinamide methodology. In the synthesis of the (1-->4)-mannan, the glycosylation yields and stereoselectivities remain approximately constant with increasing chain length, whereas those for the (1-->2)-mannan consist of two groups with the formation of the tetra- and higher saccharides giving yields and selectivities consistently lower than those of the lower homologues. The decrease in yield after the trisaccharide in the (1-->2)-mannan synthesis is attributed to steric interference by the n-3 residue and is consistent with the collapsed, disordered structure predicted by early computational work. The consistently high yields and selectivities seen in the synthesis of the (1-->4)-mannan are congruent with the more open, ordered structure originally predicted for this polymer. The lack of order in the structure of the (1-->2)-mannan, as compared to the high degree of order in the (1-->4)-mannan, is also evident from a comparison of the NMR spectra of the two polymers and even from their physical nature: the (1-->2)-mannan is a gum and the (1-->4)-mannan is a high melting solid.

Synthesis of acetylated konjac glucomannan and effect of degree of acetylation on water absorbency

Konjac glucomannan was acetylated with acetic anhydride under different conditions to reduce the unusually high water absorbency of native konjac. The dependence of the degree of substitution (DS) on the reaction conditions and the influence of the DS on the water absorbency were investigated. The most efficient method for the acetylation was refluxing konjac in acetic anhydride in the presence of sodium hydroxide catalyst. The water absorbency rapidly decreased with increasing DS. Fully acetylated product was obtained within 12 h, which exhibited 1.0 g/g water absorbency vs the 105.4 g/g absorbency of native konjac. Because of the exponential decrease of water absorbency with increasing DS, a relatively small DS is sufficient to significantly suppress the absorption of water.

Synthesis of di- to hexasaccharide 1,2-linked beta-mannopyranan oligomers, a terminal S-linked tetrasaccharide congener and the corresponding BSA glycoconjugates

Homo oligomers of (1-->2)-beta-D-mannopyranosyl residues have been synthesized in order to study the unique immunological properties of the cell wall mannan of C. albicans. p-Chlorobenzyl-protected ulosyl bromide (2) in combination with the sterically hindered, participating solvent, pivaloyl nitrile, facilitated a new approach for the synthesis of these unique homooligomers ranging from disaccharide up to hexasaccharide. The glycosyl donor 2 demonstrates high diastereoselectivity over both the glycosylation and subsequent reduction step and minimizes the number of protecting group manipulations necessary for the synthesis. Congeners of the (1-->2)-beta-D-mannotetraose were synthesized containing a terminal S-linked (1-->2)-beta-D-mannopyranosyl residue. Deprotection of these compounds afforded the propyl glycosides as well as oligomers with amino terminated aglyconic tethers. The tethers were generated from the oligosaccharide allyl glycosides by photoaddition with 2-aminoethanethiol. The functionalized haptens were coupled to BSA via squarate conjugation, and the degree of incorporation was established by TOF mass spectrometry.

Oligomannan synthesis using ionic liquid supported glycosylation

The synthesis of complex oligosaccharides has been a challenge for researchers. Herein, we describe a strategy for the synthesis of an activated oligomannan 1 that employs ionic liquid (IL) support glycosylation methodology on an IL-tagged mannosyl fluoride donor. This method is capable of rapidly producing linear alpha(1-->6) oligomannan thioglycosides in a convenient and cost-effective manner without the need of column purification after each glycosylation step.

Syntheses and characterization of konjac glucomannan acetate and their thermal and mechanical properties

Fully substituted glucomannan triacetate (GMTAc) (degree of substitution (DS)=3.0) was prepared from konjac glucomannan (KGM) treated with acetic acid and trifluoroacetic anhydride (TFAA). The peaks in the (1)H- and (13)C NMR spectra of GMTAc were assigned in detail based on two-dimensional (DQF-COSY, HSQC and HMBC) NMR analysis. Glucomannan acetate samples (GMAc) with different degrees of substitution (DS=1.3, 1.7, 2.0 and 2.8) were prepared by partial deprotection of GMTAc. Thermal properties of GMAcs including GMTAc were analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Their decomposition temperatures were higher than that of KGM, and increased with increase in DS. DSC measurements revealed that GMAc had a high glass transition temperature in the range of 178-219 °C, which decreased with increase in DS. The samples did not exhibit melting peaks, indicating that the GMAcs were amorphous. All GMAcs formed transparent films upon solvent casting, and tensile tests revealed that GMAc had a higher tensile strength and elongation to break at lower DS (1.3 and 1.7) compared to higher DS (2.0, 2.8 and 3.0). This means that the mechanical properties of GMAc could be controlled by DS.

Adsorption of tannin from aqueous solution by deacetylated konjac glucomannan

Konjac glucomannan treated by alkali solution through deacetylated reaction was used as a new water insoluble adsorbent to remove tannin from aqueous solution. A comprehensive study on adsorption of tannin by deacetylated konjac glucomannan (DKGM) was conducted regarding the effects of initial pH, adsorbent dosage, contact time, temperature and initial tannin concentration. The adsorption process was much dependent on the pH and temperature and was found to follow pseudo-second-order kinetics. The optimum pH value was at pH ranging from 2 to 6. The maximum removal efficiency of tannin from aqueous solution was 90%. Increasing the adsorption temperature would result in lower adsorption capacity, suggesting that adsorption of tannin onto DKGM was exothermic in nature. The adsorption isotherms were measured at various temperatures and correlated to Freundlich isotherms. Adsorption mechanism was confirmed that the interaction of DKGM and tannin was through hydrogen bonding. It was also observed that DKGM possesses excellent reusability for tannin removal.

Synthesis of a beta1,2-mannopyranosyl tetrasaccharide found in the phosphomannan antigen of Candida albicans

The synthesis of a portion of the challenging beta1,2-mannosyl polymer found in the cell walls of Candida albicans was undertaken to develop a conjugate vaccine against C. albicans and to facilitate NMR conformational studies of this unique polysaccharide. The novel approach to the synthesis of tetrasaccharide 1 employed the modified ulosyl bromide 11 as the glycosyl donor which provided high diastereoselectivity. A participating solvent as well as p-chlorobenzyl protection facilitated the new approach.

Preparation, structure and anticoagulant activity of a low molecular weight fraction produced by mild acid hydrolysis of sulfated rhamnan from Monostroma latissimum

A low molecular weight fraction, designated LMWP, was prepared by mild acid hydrolysis of sulfated rhamnan from Monostroma latissimum and purified by anion-exchange and gel-permeation chromatography. Chemical and spectroscopic analyses showed that LMWP was mainly composed of rhamnose, and its molecular weight was about 33.6 kDa. The backbone of LMWP consists of 1,3-linked α-L-rhamnose units with partially sulfate groups at the C-2 position. Approximately 25% of 1,3-linked α-L-rhamnose units is substituted at C-2 by sulfated or non-sulfated 1,3-linked α-L-rhamnose and 1,2-linked α-L-rhamnose units. LMWP effectively prolonged clotting time as evaluated by the activated partial thromboplastin time assay and was a potent thrombin inhibitor mediated by heparin cofactor II. The investigation demonstrated that LMWP is a novel sulfated polysaccharide with anticoagulant activity.

Macrophage mannose receptor-specific gene delivery vehicle for macrophage engineering

Macrophages are the most plastic cells in the hematopoietic system and they exhibit great functional diversity. They have been extensively applied in anti-inflammatory, anti-fibrotic and anti-cancer therapies. However, the application of macrophages is limited by the efficiency of their engineering. The macrophage mannose receptor (MMR, CD206), a C-type lectin receptor, is ubiquitously expressed on macrophages and has a high affinity for mannose oligosaccharides. In the present study, we developed a novel non-viral vehicle with specific affinity for MMR. Mannan was cationized with spermine at a grafted ratio of ∼12% to deliver DNA and was characterized as a stable system for delivery. This spermine-mannan (SM)-based delivery system was evaluated as a biocompatible vehicle with superior transfection efficiency on murine macrophages, up to 28.5-fold higher than spermine-pullulan, 11.5-fold higher than polyethylenimine and 3.0-fold higher than Lipofectamine™ 2000. We confirmed that the SM-based delivery system for macrophages transfection was MMR-specific and we described the intracellular transport of the delivery system. To our knowledge, this is the first study using SM to demonstrate a mannose receptor-specific gene delivery system, thereby highlighting the potential of a novel specific non-viral delivery vehicle for macrophage engineering.

Novel mouse monoclonal antibodies specifically recognize Aspergillus fumigatus galactomannan

A panel of specific monoclonal antibodies (mAbs) against synthetic pentasaccharide β-D-Galf-(1→5)-[β-D-Galf-(1→5)]₃-α-D-Manp, structurally related to Aspergillus fumigatus galactomannan, was generated using mice immunized with synthetic pentasaccharide-BSA conjugate and by hybridoma technology. Two selected mAbs, 7B8 and 8G4, could bind with the initial pentasaccharide with affinity constants of approximately 5.3 nM and 6.4 nM, respectively, based on surface plasmon resonance-based biosensor assay. The glycoarray, built from a series of synthetic oligosaccharide derivatives representing different galactomannan fragments, demonstrated that mAb 8G4 could effectively recognize the parental pentasaccharide while mAb 7B8 recognizes its constituting trisaccharide parts. Immunofluorescence studies showed that both 7B8 and 8G4 could stain A. fumigatus cells in culture efficiently, but not the mutant strain lacking galactomannan. In addition, confocal microscopy demonstrated that Candida albicans, Bifidobacterium longum, Lactobacillus plantarum, and numerous gram-positive and gram-negative bacteria were not labeled by mAbs 7B8 and 8G4. The generated mAbs can be considered promising for the development of a new specific enzyme-linked assay for detection of A. fumigatus, which is highly demanded for medical and environmental controls.

Convergent synthesis of a beta-(1-->3)-mannohexaose

An as yet unknown beta-(1-->3)-mannohexaose has been synthesized by a block route involving the coupling of two trisaccharides. Comparison of three closely related attempted mannohexaose syntheses reinforces the influence of subtle matching and/or mismatching interactions on the outcome of convergent oligosaccharide synthesis.

Lysosomal-enzyme targeting: the phosphorylation of synthetic D-mannosyl saccharides by UDP-N-acetyl-glucosamine:lysosomal-enzyme N-acetylglucosamine-phosphotransferase from rat-liver microsomes and fibroblasts

Phosphorylation of the D-mannose residues of lysosomal enzymes is essential for the uptake and intracellular transport of these enzymes to lysosomes. The GlcNAc-P-transferase which is involved in the phosphorylation reaction seems to recognize a signal, probably a protein conformation, common to many lysosomal enzymes. To evaluate the role of the carbohydrate portion of the enzyme in these phosphorylation reactions, the acceptor specificity of GlcNAc-P-transferase from rat-liver microsomes and fibroblasts was examined with the aid of synthetic D-mannosyl disaccharides and derivatives that are closely related to the high-mannose type of oligosaccharides. Four methyl D-mannobiosides were synthesized, and their structures were established by 13C-n.m.r. spectroscopy. Of all the D-mannosyl saccharides tested, alpha-D-Man-(1----2)-alpha-D-Man-(1----OMe) was found to be the best acceptor, thereby suggesting that oligosaccharide structure may also have a role to play in recognition by this enzyme.

Effect of carboxymethylation on rheological and drug release characteristics of locust bean gum matrix tablets

This study was undertaken to investigate correlation between the carboxymethylation-induced rheological changes and drug release characteristics of locust bean gum (LBG) matrix tablets. LBG was derivatized to carboxymethyl LBG (CMLBG) and characterized by (13)C NMR, FTIR and elemental analyses. Rheological studies revealed that LBG, in contact with water, produced a strong elastic gel which swelled less due to lower penetration of water resulting in slower drug release. On the other hand, CMLBG formed a viscous polymer solution through which higher influx of water resulted in rapid swelling of the matrix and faster drug release. Although the release from a particular matrix was dependent on drugs' solubilities, CMLBG matrix tablet produced faster release of all the drugs than LBG matrix tablets. In conclusion, rheological study appeared to be an useful tool to predict release of drugs from polysaccharide matrix tablets.

Synthesis and characterization of konjac glucomannan-graft-polyacrylamide via gamma-irradiation

The synthesis of konjac glucomannan-graft-polyacrylamide (KGM-g-PAM) was carried out at 25°C by γ-irradiation under a N₂ atmosphere. The effects of absorbed radiation dosage and monomer concentration on grafting yield and water absorbency were studied. The grafted copolymers were characterized using Fourier Transform Infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), x-ray diffraction (XRD), thermogravimetric analysis (TGA) and gel permeation chromatography (GPC). The grafting yield was observed to increase with increasing absorbed dosage and monomer concentration. Compared with the original KGM, the grafted copolymers exhibited better thermal stability and water absorbency. The results suggest that γ-irradiation is convenient and efficient for inducing graft copolymerization of KGM and acrylamide (AM).

The stepwise synthesis of oligo(glycosyl phosphates) via glycosyl hydrogenphosphonates. The chemical synthesis of oligomeric fragments from Hansenula capsulata Y-1842 exophosphomannan and from Escherichia coli K51 capsular antigen

A stepwise approach has been used in the syntheses of pentamannosyl tetraphosphate HO-[-6Man(alpha)-PO4-]4-6Man(alpha)-OMe and tetra(N-acetylglucosaminyl) triphosphate HO-[-3GlcNAc(alpha)-PO4]3- 3GlcNAc(beta)-OC6H4NO2, which are fragments of the yeast and bacteria extracellular phosphoglycans. Elongation of the chain was performed with the use of suitably protected glycosyl hydrogenphosphonate derivatives for successive introduction of glycosyl phosphate residues. Partially protected monosaccharide derivatives and oligomeric blocks served as hydroxylic components.

Enzymatic synthesis of mannobioses and mannotrioses by reverse hydrolysis using alpha-mannosidase from Aspergillus niger

Various manno-oligosaccharides including alpha-D-man-(1 --> 2)-D man and alpha-D-man-(1 --> 2)-alpha-D-man-(1 --> 2)-D-man were formed when a highly concentrated mannose solution was incubated in the presence of alpha-mannosidase from Aspergillus niger. alpha-D-Man-(1 --> 2)-D-man and alpha-D- man-(1 --> 2)-alpha-D-man-(1 --> 2)-D-man were isolated by activated carbon chromatography followed by high performance liquid chromatography using an amino-silica column. In addition to the above oligosaccharides, alpha-D-man-(1 --> 3)-D-man, alpha-D-man-(1 --> 6)-D-man, and alpha-D-man-(1 --> 2)-alpha-D-man-(1 -->6)-D-man were also isolated.

Chemical synthesis of a comb-shaped, branched stereoregular polysaccharide, 4-O-alpha-D-mannopyranosyl-(1-->6)-alpha-D-mannopyranan

4-O-alpha-D-Mannopyranosyl-(1-->6)-alpha-D-mannopyranan (7) was prepared via ring-opening polymerization of 1,6-anhydro-2,3-di-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-alpha-D- mannopyranosyl)-beta-D-mannopyranose (5) using phosphorus pentafluoride as initiator in dichloromethane at -60 degrees C, followed by debenzylation. Compound 5 was obtained via glycosidation of 1,6-anhydro-2,3-O- isopropylidene-beta-D-mannopyranose (1) with 2,3,4,6-tetra-O-benzyl-1-O-trichloroacetimidoyl-alpha-D-mannopyran ose (2) using p-toluenesulfonic acid as catalyst and subsequent transformation of the protecting groups of the resulting 1,6-anhydro-4-O-(2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranosyl)-2,3- O-isopropylidene-beta-D-mannopyranose (3).

Sonochemical synthesis of gum guar biopolymer stabilized copper oxide on exfoliated graphite: Application for enhanced electrochemical detection of H2O2 in milk and pharmaceutical samples

A novel and cost-effective synthesis of biopolymer-based organic and inorganic composite materials have received substantial attention in a broad range application including electroanalysis of small molecules. In this perspective, we report the synthesis of gum guar (guar) biopolymer stabilized cupric oxide decorated on exfoliated graphite (GR-guar/CuO) composite. Different physicochemical characterization methods were used to confirm the successful exfoliation of graphite and formation of the GR-guar/CuO composite. A simple sonochemical method has been used for the preparation of guar stabilized exfoliated graphite (GR-guar). The flower-like CuO on GR-guar and guar stabilized CuO (CuO-guar) composites were synthesized using a hydrothermal method. Cyclic voltammetric studies revealed that the GR-guar/CuO composite modified screen-printed carbon electrode (SPCE) had enhanced electro-reduction ability towards H₂O₂ than GR-guar and pristine graphite/CuO-guar modified SPCEs. Under optimized experimental conditions, the GR-guar/CuO composite modified electrode detects H₂O₂ in the response ranges from 0.02 to 1296.6 µM. The sensor shows a lower detection limit of 5.8 nM with high sensitivity. The as-prepared GR-guar/CuO composite sensor is highly reproducible and had excellent selectivity and practicality towards the detection of H₂O₂. Consequently, the fabricated sensor can be used for the accurate detection of H₂O₂ in real samples.

A strong inhibition of HIV-induced cytopathic effects by synthetic (1----6)-alpha-D-mannopyranan sulfate

The anti-HIV effects of mannopyranan sulfate (1) were investigated by using MT-4 cells, namely, an HTLV-I-carrying CD-4 positive cell-line, in vitro. Stereoregular (1----6)-alpha-D-mannopyranan, which had been synthesized by ring-opening polymerization of a 1,6-anhydromannose derivative, was sulfated with piperidine-N-sulfonic acid to provide 1. N.m.r. analysis of 1 indicated that the reactivity of hydroxyl groups was in the order, 3-OH greater than 2-OH much greater than 4-OH. Mannopyranan sulfate having degree of substitution (d.s.) of 1.19-1.83 effectively inhibited HIV-induced cytopathic effects at a concentration of greater than 3.3 micrograms/mL. The anticoagulant activity and the adsorption on concanavalin A of 1 indicated the possibility of selective binding of 1 having d.s. of 1.19-1.83 to HIV-protein.