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PubMed2002

Identification and occurrence of the novel alkaloid pentahydroxypentyl-tetrahydro-beta-carboline-3-carboxylic acid as a tryptophan glycoconjugate in fruit juices and jams.

The novel carbohydrate-derived beta-carboline, 1-pentahydroxypentyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, was identified in fruit- and vegetable-derived products such as juices, jams, and tomato sauces. This compound occurred as two diastereoisomers, a cis isomer (the major compound) and a trans isomer, ranging from undetectable amounts to 6.5 microg/g. Grape, tomato, pineapple, and tropical juices exhibited the highest amount of this alkaloid (up to 3.8 mg/L), whereas apple, banana, and peach juices showed very low or nondetectable levels. This tetrahydro-beta-carboline was also found in jams (up to 0.45 microg/g), and a relative high amount was present in tomato concentrate (6.5 microg/g) and sauce (up to 1.8 microg/g). This beta-carboline occurred in fruit-derived products as a glycoconjugate from a chemical condensation of D-glucose and L-tryptophan that is highly favored at low pH values and high temperature. Production, processing treatments, and storage of fruit juices and jams can then release this beta-carboline. Fruit-derived products and other foods containing this compound might be an exogenous dietary source of this glucose-derived tetrahydro-beta-carboline.

Beverages↗

PubMed2004

Solid-phase synthesis of oligonucleotide glycoconjugates bearing three different glycosyl groups: orthogonally protected bis(hydroxymethyl)-N,N'-bis(3-hydroxypropyl)malondiamide phosphoramidite as key building block.

Diethyl O,O'-(methoxymethylene)bis(hydroxymethyl)malonate (3) was observed to undergo a stepwise aminolysis when treated with 3-aminopropanol. This allowed convenient preparation of bis(hydroxymethyl)-N,N'-bis(3-hydroxypropyl)malondiamide bearing orthogonal levulinyl (Lev) and tert-butyldiphenylsilyl (TBDPS) protections at the two N-hydroxypropyl groups (8). One of the hydroxylmethyl functions was then protected with a 4,4'-dimethoxytrityl (DMTr) group, and the other one was phosphitylated to obtain a methyl N,N-diisopropylphosphoramidite (1). This building block was used for the synthesis of oligonucleotide glycoconjugates (25 and 26) carrying three different sugar units. After conventional phosphoramidite chain assembly of the sequence containing 1, the 5'-terminal DMTr group was removed and an appropriate glycosyl 6-O-phosphoramidite was coupled. The remaining protections of the branching unit were removed in the order of Lev and TBDPS, and the exposed hydroxyl functions were reacted one after another with the desired glycosyl 6-O-phosphoramidites. Global deprotection and cleavage of the conjugate from the support were achieved by conventional ammonolysis.

Catalysis↗

PubMed2003

Creatine phosphate--creatine kinase in enzymatic synthesis of glycoconjugates.

[reaction: see text] Enzymatic production of glycoconjugates is hampered by expensive phosphagens such as acetyl phosphate (AcP) and phosphoenolpyruvate (PEP). Here, we introduce creatine phosphate--creatine kinase system as a novel and practical energy source in carbohydrate synthesis. This system was successfully demonstrated in the production of bioactive oligosaccharides with different sugar nucleotide regeneration systems.

Adenosine Triphosphate↗

PubMed2003

Synthesis of some biologically relevant beta-C-glycoconjugates.

[reaction: see text] An esterification-RCM approach to a variety of biologically relevant beta-C-glycoconjugates is reported herein. A range of carboxylic acids were coupled with several different olefin alcohols 1 to provide esters 3. The esters were then converted to the final ring-closed product 6 in three steps in 49-60% overall yield. The formed compounds are biologically relevant and serve as stable carbohydrate mimics of the corresponding O-glycosides.

Esters↗

PubMed2003

General access to iminosugar C-glycoside building blocks by means of cross-metathesis: a gateway to glycoconjugate mimetics.

[reaction: see text] Cross-metathesis reactions of alpha-1-C-allyl-1-deoxynojirimycin derivatives 7a,b and various functionalized alkenes mediated by Grubbs's catalyst 3 are reported. The reactions showed reasonable to very good yields and excellent E/Z selectivity. This methodology allows the efficient and convergent synthesis of iminosugar C-glycosides with a great degree of structural diversity in the aglycone, opening the way to a variety of new glycoconjugate mimetics of biological interest.

1-Deoxynojirimycin↗

PubMed2003

Synthesis of fullerene glycoconjugates through sulfide connection in aqueous media.

[reaction: see text] A thiolate/alkyl halide coupling reaction in aqueous media provides a one-step synthesis of fullerene glycoconjugates bearing five carbohydrate groups in good yield by using stoichiometric amounts of reactants, without recourse to hydroxy group protection. The sulfide-connection methodology is also useful for synthesis of simpler amphiphilic fullerene molecules, such as one bearing five carboxylic acid groups.

Fullerenes↗

PubMed2005

Carbohydrate sulfonyl chlorides for simple, convenient access to glycoconjugates.

[reaction: see text] The use of carbohydrate sulfonyl chlorides is introduced as a new, facile glycoconjugation method which could find broad applications. We demonstrate the approach by synthesizing a number of glycosylated cholesterol absorption inhibitors which display high inhibitory efficacies in our recently established in vitro assay. Furthermore, we highlight an advantage of the electron-withdrawing nature of the sulfonyl linkage which allowed the synthesis of otherwise unstable azetidine conjugates.

Anticholesteremic Agents↗

PubMed1998

Corneal glycoconjugates: an ultrastructural lectin-gold study.

The oligosaccharide chains of cell surface and extracellular matrix glycoconjugates are essential for the biological properties of these molecules. We have, therefore, investigated carbohydrate residues in the rat cornea using biotinylated lectin-gold probes. Fixed corneas were removed and embedded in Lowicryl HM20 or LR White. Ultrathin sections were incubated in one of the lectins: Triticum vulgare (WGA), Canavalia ensiformis (Con A), Griffonia simplicifolia (GS-1), Limax flavus (LFA) and Allomyrina dichotoma (Allo A), followed by streptavidin-gold, or the sections were incubated in cationic colloidal gold. Semi-quantification of gold labelling was determined for corneal endothelium, Descemet's membrane, stroma and epithelium from electron micrographs. WGA and Con A binding sites were expressed either moderately or strongly throughout the cornea, suggesting a preponderance of alpha-mannose and N-acetylglucosamine residues. A particular concentration of these sugars was found in Descemet's membrane. In contrast, GS-1 (specific for alpha-galactose) and Allo A (specific for beta-galactose) labelled all regions weakly. Sialic acid residues, as defined by LFA labelling and the expression of neuraminidase-sensitive cationic colloidal gold binding sites, were sparsely distributed throughout the stroma, Descemet's membrane and endothelium. In contrast, sialoglycoconjugates were found in significant concentrations in the epithelium. Electron microscopy proved useful in providing new information on the cellular and subcellular localization of these lectin binding sites.

Acrylic Resins↗

PubMed1999

Glycoconjugates of the rat ciliary body epithelium: a lectin histochemical and protein blotting study.

The present study sought to identify and partially characterize the glycoconjugates specific to the double-layered ciliary body epithelium of the rat eye by lectin histochemistry and lectin blottings. Hydrated paraffin sections of Carnoy-fixed Sprague-Dawley rat eyes were stained with a panel of 21 different biotinylated lectins, followed by streptavidin-peroxidase and the glucose oxidase-diaminobenzidine-nickel staining procedure. The results of lectin histochemistry revealed that the inner epithelial layer was rich in GlcNAc(beta1,4)GlcNAc, alpha-Gal, Gal(beta1,3)GalNAc, GalNAc(alpha1,3)GalNAc/Gal, GalNAc(alpha1,6)Gal, Fuc(alpha1,2)Gal(beta1,4)GlcNAc and Gal(beta1,4)GlcNAc(beta1,2)Man(alpha1,6) sugar residues as shown by its positive reactivities with S-WGA, PWA, DSA, GS-I-B4, PNA, DBA, SBA, WFA, UEA-I, LTA and PHA-E. The reactivities of GS-I-B4, PNA, DBA and SBA were restricted to the inner layer at the tips of the ciliary processes. On the other hand, the outer epithelial layer was stained evenly by DSA and Jacalin, and partly by MAA, showing that this epithelial layer was rich in GlcNAc(beta1,4)GlcNAc, Gal(beta1,3)GalNAc and NeuAc(alpha2,3)Gal disaccharides. These lectin binding patterns of the ciliary body epithelium suggest a topographical and functional difference in this double cell-layered epithelium. Their possible roles in the secretion of aqueous humour and production of ciliary zonule are discussed. Some identified lectin markers specific to these two cell layers may be useful for further experimental studies. Glycoproteins extracted from the dissected ciliary body were separated by SDS-PAGE electrophoresis and analyzed by protein blottings with 8 different lectins. The results showed that at least 10 major membrane-bound glycoproteins, with molecular weights ranging from 30 to 150 kD, rich in beta-GlcNAc, beta-Gal, alpha/beta-GalNAc and NeuAc(alpha2,6)Gal residues, were present in the microsomal fraction.

Acetylgalactosamine↗

PubMed2001

Schistosome glycoconjugates in host-parasite interplay.

Schistosomes are digenetic trematodes which cause schistosomiasis, also known as bilharzia, one of the main parasitic infections in man. In tropical and subtropical areas an estimated 200 million people are infected and suffer from the debilitating effects of this chronic disease. Schistosomes live in the blood vessels and strongly modulate the immune response of their host to be able to survive the hostile environment that they are exposed to. It has become increasingly clear that glycoconjugates of schistosome larvae, adult worms and eggs play an important role in the evasion mechanisms that schistosomes utilise to withstand the immunological measures of the host. Upon infection, the host mounts innate as well as adaptive immune responses to antigenic glycan elements, setting the immunological scene characteristic for schistosomiasis. In this review we summarise the structural data now available on schistosome glycans and provide data and ideas regarding the role that these glycans play in the various aspects of the glycobiology and immunology of schistosomiasis.

Animals↗

PubMed2004

Analysis of GM3-Gg3 interaction using clustered gycoconjugate models constructed from glycolipid monolayers and artificial glycoconjugate polymers.

Carbohydrate-carbohydrate interactions between clustered GM3 on the Langmuir monolayer and clustered Gg3 trisaccharide along a polystyrene chain were investigated using surface pressure-area (pi-A) isotherms and surface plasmon resonance (SPR). The pi-A isotherm of the GM3 monolayer was expanded substantially and specifically by the Gg3-trisaccharide-bearing glycoconjugate polystyrene [PN(Gg3)] even at 10(-12) M. The PN(Gg3)-induced expansion of the GM3 monolayer required no calcium ion, and the expansion was strongly inhibited in the presence of urea and acetamido sugars. SPR studies of the GM3-Gg3 interaction were carried out to estimate the affinity constant and specificity of the interaction quantitatively. PN(Gg3) was adsorbed onto the GM3 monolayer strongly and specifically with an apparent affinity constant of Ka = 2.5 x 10(6) M(-1). The mechanism of the GM3-Gg3 interaction was discussed on the basis of the relationship between affinity and structure. We found that the NHAc groups of N -acetylneuraminic acid in GM3 and of GalNAc in Gg3 play an important role in the GM3-Gg3 interaction and that PN(Gg3) recognizes not only some specified portions of GM3 but also the trisaccharide as a whole. Published in 2003.

G(M3) Ganglioside↗

PubMed2003

Depletion of anti-Gal antibodies by the intravenous infusion of Gal type 2 and 6 glycoconjugates in baboons.

BACKGROUND: Natural anti-Gal antibodies (NAb) to Gal epitopes play a key role in the rejection of pig cells or organs transplanted into primates. We have investigated the effect on NAb return after extracorporeal immunoadsorption (EIA) of the continuous intravenous (i.v.) infusion of (i) bovine serum albumin conjugated to Gal type 6 oligosaccharides (BSA-Gal) or (ii) a poly l-lysine backbone conjugated to Gal type 2 or 6 oligosaccharides (PLL-Gal). METHODS: Porcine mobilized peripheral blood progenitor cells (PBPC) obtained by leukapheresis from MHC-inbred miniature swine (n = 9) were infused intravenously (i.v.) into baboons: Group 1 baboons (n = 4) received whole body and thymic irradiation, splenectomy, antithymocyte globulin, cobra venom factor, cyclosporine, mycophenolate mofetil, anti-CD154mAb, porcine hematopoietic growth factors, and EIA before transplantation of high doses (2 to 4 x 1010 cells/kg) of PBPC; Group 2 baboons (n = 3) received the Group 1 regimen plus a continuous i.v. infusion of BSA-Gal for up to 30 days; Group 3 baboons (n = 5) received the Group 1 regimen plus a continuous i.v. infusion of PLL-Gal type 2 (n = 2) or both PLL-Gal types 2 and 6 (n = 3) for up to 30 days. RESULTS: Group 1: NAb returned to pre-PBPC levels within 20-30 days, but there was no induction of antibody to Gal or non-Gal determinants; Group 2: NAb was undetectable or at very low level during BSA-Gal therapy. In one baboon, however, IgG to Gal type 2, but not to type 6, returned during BSA-Gal therapy; Group 3: NAb was undetectable or at very low level during PLL-Gal therapy. In two baboons that received PLL-Gal type 2, NAb to Gal type 6, but not to type 2, returned during PLL-Gal treatment. Two of five baboons, however, developed systemic infection. Four of five baboons died within 14 days; autopsy revealed focal hemorrhagic injury to their hearts, lungs, and small intestines, with histologic abnormalities that varied between animals from hemorrhage and/or thrombosis in some organs (heart, lungs, or intestine) to signs of infections (bacteria in intestine, cytomegalovirus in liver). CONCLUSIONS: (i) BSA-Gal and PLL-Gal therapy maintained depletion of NAb. (ii) Some heterogeneity in specificity of NAb was identified, indicating that the infusion of a combination of Gal type 2 and 6 glycoconjugates may be required. (iii) The addition of PLL-Gal to the immunosuppressive regimen was associated with a high incidence of morbidity and mortality without a clear histopathologic entity underlying the cause of death.

Animals↗

PubMed1998

Meaning and therapeutic potential of microbial recognition of host glycoconjugates.

The microbe-host interface is currently in focus because of attempts to develop infection therapy in humans based on either natural receptor saccharide (respiratory and gastrointestinal disease) or sophisticated sialic acid analogues designed from crystal structures (influenza). Most of the known host receptors for microbes are glycoconjugates, and the diversity and selectivity of host tissue glycosylation allow for the tropism of infections. However, among the many binding specificities detected so far, the biological role has been proven only in a few infectious model systems. The existence of multiple specificities of a single microbe is both a complicating factor and a challenge, requiring expanded research with a special demand on glycoscience.

Animals↗

PubMed2000

Characterisation of glycoconjugate sugar residues in the vomeronasal organ of the armadillo Chaetophractus villosus (Mammalia, Xenarthra).

Conventional carbohydrate histochemistry and the binding patterns of 21 lectins were analysed to characterise the glycoconjugate content in the components of the vomeronasal organ of the armadillo Chaetophractus villosus. The mucomicrovillous complex of the sensory epithelium bound most of the lectins studied. No reaction was observed with Con A, PSA, S-Con A and SBA, and the sustentacular cells were-stained with UEA-I, DSL, LEL, STL and Con A. The vomeronasal receptor neurons were labelled with S-WGA, WGA, PNA, UEA-I, STL, Con A, S-Con A, ECL and RCA120. The basal cell layer reacted with S-WGA, WGA, LCA, UEA-I, DSL, LEL, STL, Con A, JAC and VVA. The nonsensory epithelium exhibited a differential staining in relation to the different components. The mucociliary complex stained with ECL, DBA, JAC, RCA120, STL, LCA, PHA-E, PHA-L, LEL, BSL-I and VVA. However, SJA and UEA-I stained the mucus complex lining a subpopulation of columnar cells. The cytoplasm and cell membranes of columnar cells was labelled with DBA, DSL and LCA. The apical region of these cells exhibited moderate reactivity with LEL and SJA. None of the lectins bound specifically to secretory granules of the nonsecretory cells. Basal cells of the nonsensory epithelium were labelled with DSL, LEL, LCA, BSL-I and STL. The vomeronasal glands showed a positive reaction with WGA, DSL, LEL, LCA, DBA, PNA, RCA120 and SBA. Subpopulations of acinar cells were observed with ECL, S-WGA, Con A, S-Con A and DBA. PNA and RCA120 stained the cells lining the glandular ducts. In comparison with previous results obtained in the olfactory mucosa of the same group of armadillos, the carbohydrate composition of the vomeronasal organ sensory epithelium differed from the olfactory sensory epithelium. This is probably related to the different nature of molecules involved in the perireceptor processes.

Animals↗

PubMed2000

The cytolytic effect of a glycoconjugate extracted from corms of saffron plant (Crocus sativus) on human cell lines in culture.

Corms of Crocus sativus L. (Iridaceae) contain a glycoconjugate that shows cytotoxic activity on tumoral cells in culture. Studies of intracellular calcium fluctuations, and release of lactate dehydrogenase in human cervical epitheloid carcinoma cells, showed that this compound caused plasma membrane damage, allowing movements of both calcium and macromolecules, and leading to cell lysis. Analysis of DNA fragmentation showed that cell death was not mediated by apoptosis. This molecule is active against human tumoral cells derived from fibrosarcoma, cervical epithelioid carcinoma and breast carcinoma, with IC50 values of 7, 9 and 22 micrograms/ml, respectively. The proteoglycan is about 8 times more cytotoxic for malignant cells than for their normal counterparts. In addition, 100 micrograms/ml of proteoglycan produced 50% in vitro lysis of normal human erythrocytes, whereas 320 micrograms/ml induced about 60% cell death on cultured human hair follicles. Altogether, these results suggests a distinctive cytotoxic activity of this molecule on different human cell types.

Antineoplastic Agents, Phytogenic↗

PubMed1992

Glycoconjugates as positive and negative modulators of embryo implantation.

A variety of studies indicate that complex glycoproteins participate in or modulate adhesive interactions occurring during embryo implantation. In particular, proteoglycans and proteins that bind proteoglycans are involved at multiple stages of this process. Identification of these binding proteins and the molecular controls over glycoconjugate expression are required to develop a comprehensive understanding of the implantation process.

Animals↗

PubMed2005

The asialoglycoprotein receptor clears glycoconjugates terminating with sialic acid alpha 2,6GalNAc.

Endogenous ligands have not, to date, been identified for the asialoglycoprotein receptor (ASGP-R), which is abundantly expressed by parenchymal cells in the liver of mammals. On the basis of the rapid clearance of BSA bearing multiple chemically coupled sialic acid (Sia)alpha2,6GalNAcbeta1,4GlcNAcbeta1,2Man tetrasaccharides (SiaGGnM-BSA) from the circulation, and the ability of the ASGP-R hepatic lectin-1 subunit to bind SiaGGnM-BSA, we previously proposed that glycoproteins modified with structures terminating with Siaalpha2,6GalNAc may represent previously unrecognized examples of endogenous ligands for this receptor. Here, we have taken a genetic approach using wild-type and ASGP-R-deficient mice to determine that the ASGP-R in vivo does indeed account for the rapid clearance of glycoconjugates terminating with Siaalpha2,6GalNAc. We have also determined that the ASGP-R is able to bind core-substituted oligosaccharides with the terminal sequence Siaalpha2,6Galbeta1,4GlcNAc but not those with the terminal Siaalpha2,3Galbeta1,4GlcNAc. We propose that glycoproteins bearing terminals Siaalpha2,6GalNAc and Siaalpha2,6Gal are endogenous ligands for the ASGP-R, and that the ASGP-R helps to regulate the relative concentration of serum glycoproteins bearing alpha2,6-linked Sia.

Acetylgalactosamine↗

PubMed2000

Lipophosphoglycan is a virulence factor distinct from related glycoconjugates in the protozoan parasite Leishmania major.

Protozoan parasites of the genus Leishmania undergo a complex life cycle involving transmission by biting sand flies and replication within mammalian macrophage phagolysosomes. A major component of the Leishmania surface coat is the glycosylphosphatidylinositol (GPI)-anchored polysaccharide called lipophosphoglycan (LPG). LPG has been proposed to play many roles in the infectious cycle, including protection against complement and oxidants, serving as the major ligand for macrophage adhesion, and as a key factor mitigating host responses by deactivation of macrophage signaling pathways. However, all structural domains of LPG are shared by other major surface or secretory products, providing a biochemical redundancy that compromises the ability of in vitro tests to establish whether LPG itself is a virulence factor. To study truly lpg(-) parasites, we generated Leishmania major lacking the gene LPG1 [encoding a putative galactofuranosyl (Gal(f)) transferase] by targeted gene disruption. The lpg1(-) parasites lacked LPG but contained normal levels of related glycoconjugates and GPI-anchored proteins. Infections of susceptible mice and macrophages in vitro showed that these lpg(-) Leishmania were highly attenuated. Significantly and in contrast to previous LPG mutants, reintroduction of LPG1 into the lpg(-) parasites restored virulence. Thus, genetic approaches allow dissection of the roles of this complex family of interrelated parasite virulence factors, and definitively establish the role of LPG itself as a parasite virulence factor. Because the lpg1(-) mutant continue to synthesize bulk GPI-anchored Gal(f)-containing glycolipids other than LPG, a second pathway distinct from the Golgi-associated LPG synthetic compartment must exist.

Animals↗