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At least 847 records · Page 47Linked to original sources
PubMed1996

Synthesis of glycyrrhizin analogues containing fluorinated beta(1-->2)-linked disaccharides.

For studies on the recognition mechanisms for Glycyrrhizin-induced biological activities, seven Glycyrrhizin analogues with 3'-, 4'-, 6'-, 3-, and 4-fluorinated 2-O-beta-D-glucopyranosyl-beta-D-glucopyranoses (1-5) and 3- and 4-fluorinated 2-O-beta-D-glucopyranuronosyl-beta-D-glucopyranoses (6 and 7) were synthesized through a stepwise glycosylation procedure. 1,2-Di-O-acetyl-4,6-di-O-benzyl-3-deoxy-3-fluoro- (13) and 1,2-di-O-acetyl-3,6-di-O-benzyl-4-deoxy-4-fluoro-D-glucopyranose (14) were employed for the first beta-glycosylation of methyl glycyrrhetate, promoted with trimethylsilyl trifluoromethanesulfonate.

Carbohydrate Conformation↗
PubMed1980

Enzymatic synthesis and carbon-13 nuclear magnetic resonance conformational studies of disaccharides containing beta-D-galactopyranosyl and beta-D-[1-13C]galactopyranosyl residues.

Partially purified UDPgalactosyltransferase (EC 2.4.1.22) from bovine milk has been used to synthesize millimolar amounts of compounds such as Gal beta (1 leads to 4)Glc, Gal beta (1 leads to 4)GlcNAc-beta-hexanolamine, and Gal beta (1 leads to 4)GlcNAc beta (1 leads to 4)GlcNAc. The same method has been used to prepare similar compounds containing 13C-enriched galactopyranosyl moieties. Gal beta (1 leads to 4)GlcNAc-beta-hexanolamine was also synthesized in a solid-phase system in which the GlcNAc-beta-hexanolamine glycoside was covalently linked to agarose beads. At pH 7.0 and at 1--5 mM Mn2+ the yields of the galactosyl saccharides are greater than 90% by using 10% excess of UDPGal donor. The use of a 90% enriched [1-13C]galactosyl residue allowed the determination of the most abundant conformer about the galactopyranosyl--glycoside linkage by analysis of the carbon--carbon coupling constants from C1 of Gal to the C3', C4, and C5' of GlcNAc or Glc.

Animals↗
PubMed2002

Characterization of a novel endo-beta-galactosidase specific for releasing the disaccharide GlcNAc alpha 1-->4Gal from glycoconjugates.

In contrast to the beta-linked GlcNAc, the alpha-linked GlcNAc has not been commonly found in glycoconjugates. We have recently revealed the presence of an unusual endo-beta-galactosidase (Endo-beta-Gal(GnGa)) in Clostridium perfringens capable of releasing GlcNAcalpha1-->4Gal from glycans expressed in the gastric mucous cell-type mucin [Ashida, H., Anderson, K., Nakayama, J., Maskos, K., Chou, C.-W., Cole, R. B., Li, S.-C., and Li, Y.-T. (2001) J. Biol. Chem. 276, 28226-28232]. To characterize Endo-beta-Gal(GnGa), we have cloned its gene, gngC, from the genomic DNA library prepared from C. perfringens ATCC10543. The gene encodes 420 amino acid residues including a 17-residue signal peptide at the N-terminus. Using pUC18, we were able to prepare 25 mg of the fully active and pure recombinant Endo-beta-Gal(GnGa) from 1 L of Escherichia coli DH5alpha culture, which was 170 times higher than that produced by the original clostridial strain. Endo-beta-Gal(GnGa) shares a low but significant sequence similarity with two other endo-beta-galactosidases (16-21% amino acid identity). It also shows some similarity with bacterial 1,3-1,4-beta-glucan 4-glucanohydrolases of the glycoside hydrolase family 16. Endo-beta-Gal(GnGa) was found to contain the EXDX(X)E sequence (Glu-168 to Glu-173), that has been identified as the catalytic motif of families 16 and 7 retaining glycoside hydrolases. We have used site-directed mutagenesis to show that Glu-168 and Glu-173 were essential for the Endo-beta-Gal(GnGa) activity. By NMR spectroscopy, Endo-beta-Gal(GnGa) was found to act as a retaining enzyme.

Amino Acid Sequence↗
PubMed2006

Synthesis of sulfonium sulfate analogues of disaccharides and their conversion to chain-extended homologues of salacinol: new glycosidase inhibitors.

Four chain extended homologues of salacinol, a naturally occurring glycosidase inhibitor, were prepared for evaluation as inhibitors of glucosidase enzymes involved in the breakdown of carbohydrates. The syntheses involved the reactions of 1,4-anhydro-2,3,5-tri-O-benzyl-4-thio-D-arabinitol with cyclic sulfate derivatives of different monosaccharides. Debenzylation of the products afforded the novel sulfonium sulfate derivatives of D-glucose, D-galactose, D-arabinose, and D-xylose that are of interest in their own right as glycosidase inhibitors. Reduction to the corresponding alditols then afforded the homologues of salacinol containing polyhydroxylated, acyclic chains of 5- and 6-carbons, differing in stereochemistry at the stereogenic centers. Three of the chain-extended homologues inhibited recombinant human maltase glucoamylase, one of the key intestinal enzymes involved in the breakdown of glucose oligosaccharides in the small intestine, with Ki values in the low micromolar range, of approximately the same magnitude as salacinol, thus providing lead candidates for the treatment of Type 2 diabetes.

Alkylation↗
PubMed2000

Synthesis of the ezomycin nucleoside disaccharide.

[equation--see text] A protected ezomycin octosyl nucleoside was glycosylated at O-6' with a protected ezoaminuroic acid donor to afford, following several functional group modifications, the title compound 1 ( identical with 4-desamino-4-oxoezomycin A(2)).

Aminoglycosides↗
PubMed2001

Efficient syntheses of beta-cyanosugars using glycosyl iodides derived from per-O-silylated mono- and disaccharides.

[reaction: see text] Reported herein is a general method for the efficient syntheses of a variety of beta-cyano glycosides through the activation of per-O-trimethylsilyl glycosides with TMSI to form alpha-glycosyl iodides, which undergo S(N)2-type displacement when treated with tetrabutylammonium cyanide. The cyanoglycosides were reduced under mild conditions using NaBH(4) in the presence of catalytic CoCl(2)(H(2)O)(6) in THF/H(2)O to give the corresponding aminomethyl glycosides.

Disaccharides↗
PubMed2005

Rigid spacer-mediated synthesis of bis-spiroketal ring systems: stereoselective synthesis of nonsymmetrical spiro disaccharides.

The application of the "rigid spacer-mediated linkage between nonreacting centers" concept to the preparation of nonsymmetrical bis-spiroketal structures is demonstrated by the stereoselective synthesis of the bis-spiro fructodisaccharide 1, a minor component of industrial caramels. An o-xylylene bridge has been used to limit the conformational space during the intramolecular glycosylation-spirocyclization reaction of a difructopyranose precursor, thus controlling both the ring size and the stereochemistry at the spiro centers. [Structure: see text]

Carbohydrate Conformation↗