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At least 541 records · Page 30Linked to original sources
PubMed2003

Addition of lithiated C-nucleophiles to 2,3-O-isopropylidene-D-erythronolactone: stereoselective formation of a furanose C-disaccharide.

Addition of PhLi and lithiated dithianes to 2,3-O-isopropylidene-D-erythronolactone affords lactols, which are reduced with Et3SiH to the corresponding C-glycosides, the structures of two of which have been solved by X-ray diffraction. The use of a d-ribose-derived lithiated dithiane nucleophile in this chemistry allows for the convenient construction of a furanose C-disaccharide.

Carbohydrate Conformation↗
PubMed2005

Glycal scavenging in the synthesis of disaccharides using mannosyl iodide donors.

[reaction: see text] High mannose glycans composed of alpha (1-->2) and alpha (1-->6) branched sugars are important components of the HIV-associated envelope glycoprotein, gp120. These substructures can be efficiently prepared in solution from glycosyl iodide precursors requiring only a slight excess of the iodide donor, which offers advantages over solid-phase methods that require more than 5 equiv of donor. During the reaction, excess iodide is converted to a glycal that is not easily separated from the desired disaccharide. To overcome this difficulty, a phase-trafficking methodology that relies upon nucleophilic interception of the 1,2 anhydrosugar resulting from oxidation of the glycal has been developed.

Carbohydrate Sequence↗
PubMed2005

Synthesis and conformational analysis of 6-C-methyl-substituted 2-acetamido-2-deoxy-beta-D-glucopyranosyl mono- and disaccharides.

Several 6-C-substituted 2-acetamido-2-deoxy-beta-D-glucopyranosides (beta-D-GlcNAc monosaccharides 1a-3a and 1,4-linked disaccharides 1b-3b) were studied by solution NMR spectroscopy. Conformational analysis of the (6S)- and (6R)-C-methyl-substituted beta-d-GlcNAc monosaccharides indicates that the stereodefined methyl groups impose predictable conformational biases on the exocyclic C-5-C-6 bond, as determined by (1)H-(1)H and (13)C-(1)H coupling constants. Variable-temperature NMR experiments in methanol-d(4) were performed to determine DeltaDeltaH and DeltaDeltaS values derived from the two lowest energy conformers. These indicate that while the influence of 6-C-methyl substitution on conformational enthalpy is in accord with the classic principles of steric interactions, conformational preference in solution can also be strongly affected by other factors such as solvent-solute interactions and solvent reorganization.

Algorithms↗
PubMed2000

The C-disaccharide alpha-C(1-->3)-mannopyranoside of N-acetylgalactosamine is an inhibitor of glycohydrolases and of human alpha-1,3-fucosyltransferase VI. Its epimer alpha-(1-->3)-mannopyranoside of N-acetyltalosamine is not.

The radical C-glycosidation of (-)-(1S,4R,5R, 6R)-6-endo-chloro-3-methylidene-5-exo-(phenylseleno)-7-ox abi cyclo[2. 2.1]heptan-2-one ((-)-4) with 2,3,4, 6-tetra-O-acetyl-alpha-D-mannopyranosyl bromide gave (+)-(1S,3R,4R, 5R,6R)-6-endo-chloro-5-exo-(phenylseleno)-3-endo-(1',3',4', 5'-tetra-O-acetyl-2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)-7-oxabi cyc lo[ 2.2.1]hept-2-one ((+)-5) that was converted into (+)-(1R,2S,5R, 6R)-5-acetamido-3-chloro-2-hydroxy-6-(1',3',4',5'-tetra-O-acetyl)-2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)cyclohex -3-en- 1-yl acetate ((+)-10) and into (+)-(1R,2S,5R, 6S)-5-bromo-3-chloro-2-hydroxy-6-(1',3',4',5'-tetra-O-acetyl-2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)cyclohex -3-en- 1-yl acetate ((+)-19). Ozonolysis of (+)-10 and further transformations provided 2-acetamido-2,3-dideoxy-3-C-(2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)-D-galac tos e (alpha-C(1-->3)-D-mannopyranoside of N-acetylgalactosamine (alpha-D-Manp-(1-->3)CH(2)-D-GalNAc): 1). Displacement of the bromide (+)-19 with NaN(3) in DMF provided the corresponding azide ((-)-20) following a S(N)2 mechanism. Ozonolysis of (-)-20 and further transformations led to 2-acetamido-2,3-dideoxy-3-C-(2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)-D-talose (alpha-C(1-->3)-D-mannopyranoside of N-acetyl D-talosamine (alpha-D-Manp-(1-->3)CH(2)-D-TalNAc): 2). The neutral C-disaccharide 1 inhibits several glycosidases (e.g., beta-galactosidase from jack bean with K(i) = 7.5 microM, alpha-L-fucosidase from human placenta with K(i) = 28 microM, beta-glucosidase from Caldocellum saccharolyticum with K(i) = 18 microM) and human alpha-1, 3-fucosyltransferase VI (Fuc-TVI) with K(i) = 120 microM whereas it 2-epimer 2 does not. Double reciprocal analysis showed that the inhibition of Fuc-TVI by 1 displays a mixed pattern with respect to both the donor sugar GDP-fucose and the acceptor LacNAc with K(i) of 123 and 128 microM, respectively.

Animals↗
PubMed2005

Dehydration damage of domain-exhibiting supported bilayers: an AFM study on the protective effects of disaccharides and other stabilizing substances.

Atomic force microscopy (AFM) has been applied to characterize hydrated sphingomyelin/dioleoylphosphatidylcholine/cholesterol supported bilayers, after dehydration either in the absence or in the presence of several stabilizing substances. Such a study provides information about the effect of extreme environmental conditions on biological membranes and, in particular, on lipidic microdomains. Dehydration stress, indeed, is thought to cause both macroscopical damage and alterations of microdomains in biomembranes, leading to deleterious effects. These phenomena can be avoided if disaccharides are added during dehydration. In this work, we apply AFM imaging to directly visualize damage caused to supported lipid bilayers by water removal. We compare the efficiency of sucrose, trehalose, dextran, dimethyl sulfoxide, and glucose in preserving the structural integrity of domain-exhibiting model membranes. Finally, in addition to confirming previous findings, our results provide further insight into damage and alteration of microdomains in membranes as a consequence of stressful drying conditions.

Disaccharides↗
PubMed2001

A convergent strategy for the synthesis of beta-carba-galacto-disaccharides.

[reaction in text] A convergent strategy for the synthesis of beta-carba-galacto-disaccharides is illustrated by the preparation of 1 and 4, from a central "glycone" component 22, and the corresponding "aglycone" segments, monosaccharide alcohols, 23a or 23b. The key step is the formation of the carbasugar ring via an oxocarbenium ion-enol ether cyclization.

Cyclization↗
PubMed2002

Galacto, gluco, manno, and disaccharide-based C-glycosides of 2-amino-2-deoxy sugars.

[reaction: see text] Starting from readily available precursors, selenoglycosides derived from GalNAc, GlcNAc, and ManNAc were prepared by either a one- or a two-step process. The anomeric selenides underwent facile C-Se homolysis to provide the corresponding anomeric radicals, which were trapped with alkenes to give C-glycosides. This provides a general entry to alpha-C-glycosides based on 2-amino-2-deoxy sugars that is also applicable to disaccharide variants.

Amino Sugars↗
PubMed2003

Stereoselective entry to beta-linked C-disaccharides using a carbon-Ferrier reaction.

[structure: see text] The synthesis of unsaturated beta-linked C-disaccharides by the Lewis acid-mediated reaction of 3-O-acetylated glycals with monosaccharide-derived alkenes is described. Deprotection and selective hydrogenation of an exocyclic carbon-carbon double, in the presence of an endocyclic double bond, for representative targets is also illustrated.

Acetylation↗
PubMed2003

Nitrone cycloadditions to isolevoglucosenone: ready access to a new class of directly linked (1-->3)-imino-C-disaccharides.

Straightforward access to a new class of d-gulo- and d-allo-derived directly linked (1-->3)-imino-C-disaccharides by means of cycloaddition reactions of enantiopure polyhydroxylated pyrroline N-oxides with isolevoglucosenone is reported. The cycloaddition reactions display a high level of double asymmetric induction, which allows a partial kinetic resolution of a racemic nitrone. [reaction: see text]

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed2004

Novel efficient routes to heparin monosaccharides and disaccharides achieved via regio- and stereoselective glycosidation.

A new methodology for the synthesis of heparin building blocks has been developed. We describe novel efficient routes to both L-iduronic acid and D-glucuronic acid acceptors. Glycosylation with thioglycosides donors gave corresponding disaccharides in a regio- and stereoselective fashion. An improved approach to synthesizing azido-glucose thioglycoside donor to render azido-sugar from mannose via nucleophilic substitution is described. [reaction: see text]

Carbohydrate Sequence↗
PubMed1999

A new, lipophilic p-alkoxybenzyl ether protecting group and its use in the synthesis of a disaccharide.

[formula: see text] In contrast to major advances in the chemical synthesis of oligosaccharides, the methods of purification of the intermediates are essentially the same as they were decades ago. Here, the synthesis of p-(dodecyloxy)benzyl chloride is described and it is demonstrated that the new p-(dodecyloxy)benzyl ether protecting group can render a protected disaccharide sufficiently lipophilic for selective adsorption on C18 silica, thus sidestepping the expensive silica gel chromatography traditionally used for the isolation of protected oligosaccharides.

Benzyl Compounds↗
PubMed1997

Recombinant factor VIII SQ--inactivation kinetics in aqueous solution and the influence of disaccharides and sugar alcohols.

PURPOSE: To investigate the influence of various nonreducing disaccharides and sugar alcohols on the inactivation kinetics of recombinant factor VIII SQ (r-VIII SQ) in aqueous solution not containing albumin as a stabiliser. METHODS: The stability of r-VIII SQ was followed using measurement of activity (VIII:C) and HPLC gel filtration at different temperatures. The thermal stability was investigated using differential scanning calorimetry (DSC). RESULTS: The decline in VIII:C followed pseudo-first order kinetics. However, the Arrhenius plot was not linear for formulations without carbohydrate, demonstrating a distinct, reproducible curvature. The reaction rate at 5 degrees C was faster than expected from the Arrhenius kinetics. The energy of activation (Ea) for formulations without added carbohydrates, derived from the linear part of the Arrhenius plot, varied between 77 and 86 kJ/mole in the temperature range 20-37 degrees C. The addition of 600 mg/ml sucrose increased the Ea to 104 kJ/mole. DSC measurements showed that Tm' was 64.2 +/- 0.2 degrees C for r-VIII SQ without stabiliser. This value increased linearly with increasing concentrations of carbohydrate. This stabilising effect is most probably explained by the theory of preferential hydration. CONCLUSIONS: The inactivation kinetics of r-VIII SQ in aqueous solution without addition of carbohydrates followed pseudo-first order kinetics but the Arrhenius plot was nonlinear. Sucrose and sorbitol both had highly stabilising effects on r-VIII SQ at concentrations above 300 mg/ml. The preparation containing 600 mg/ml sucrose was stable for at least 12 months at 5 degrees C and 6 months at 25 degrees C.

Animals↗
PubMed2002

Disaccharide nucleosides and oligonucleotides on their basis. New tools for the study of enzymes of nucleic acid metabolism.

The main structural features of an important group of natural compounds, disaccharide nucleosides, are reviewed. The synthesis and properties of modified oligonucleotides on their basis as well as the methods of introduction of reactive aldehyde groups are described. The last part is devoted to the application of these compounds for studies of enzymes of nucleic acid metabolism.

Aldehydes↗
PubMed2004

Indigestible disaccharides open tight junctions and enhance net calcium, magnesium, and zinc absorption in isolated rat small and large intestinal epithelium.

The effects of three indigestible disaccharides on net calcium (Ca), magnesium (Mg), and zinc (Zn) transport in isolated rat jejunal, ileal, cecal, and colonic epithelium were determined. Permeability of fluorescein isothiocynate-dextran-4 (FD4) and transepithelial electrical resistance (TEER), which vary according to tight junction (TJ) activity in the intestinal mucosa, were also determined. The addition of 1-100 mM melibiose, difructose anhydride (DFA) III, or DFA IV to the mucosal medium increased the net absorption of the three minerals and FD4 permeability, while decreasing TEER dose dependently in the four intestinal portions. Positive linear relations were found between the net transport of the three minerals and FD4 passage in all portions of the intestine, whereas negative linear relations were observed between net absorption of the three minerals and TEER. We concluded that the three indigestible saccharides directly affect the epithelial tissue and open TJs, thereby promoting Ca, Mg, and Zn absorption in the small and large intestine in vitro.

Animals↗
PubMed1979

Excretion and synthesis of basement membrane disaccharide units in Masugi nephritis.

During nephrotoxic nephritis in the rat, an increased urinary excretion of glucosyl-galactosyl hydroxylysine and of galactosyl-hydroxylysine has been observed in the autologous phase of the disease. This due mainly to an elevation of the polypeptide-bound fraction of these hydroxylysyl glucosides with a molecular weight over 1,000 daltons. The levels of both urinary hydroxylysyl glucosides were correlated with proteinuria. Their increased excretion appears to originate in the lysed glomerular basement membrane. At the same stage of nephrotoxic nephritis, an increased glucosyl transferase activity could be demonstrated in the isolated glomeruli, correlated with albuminuria, attesting a higher turn-over of the disaccharide units of the glomerular basement membrane.

Albuminuria↗