Stereoselective preparation of alkyl glycosides of 2-acetamido-2-deoxy-alpha-D-glucopyranose by nonclassical halide-ion catalysis and synthesis and NMR spectroscopy of alpha-D-Gal p-(1-->3)-alpha-D-Glc pNAc-OMe

Practical de-O-acylation reactions promoted by molecular sieves

Methanol dried extensively over molecular sieves, or methanol in combination with powdered molecular sieves, serves as a good acceptor for acyl transfer reactions. Several O-acetylated and O-benzoylated sugar derivatives were efficiently de-O-acylated using this approach. In the case of per-O-acetylated N-acetylglucosamine, selective anomeric deprotection could be effected in high yield.

Synthesis of two hyaluronan trisaccharides

[formula: see text] The synthesis of two hyaluronan trisaccharides, methyl O-(beta-D-glucopyranosyluronic acid)-(1,3)-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-(1,4)-O-beta-D- glucopyranosiduronic acid and methyl O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-(1,4)-O-beta- D-glycopyranosyluronic acid)-(1,3)-O-(2-acetamido-2-deoxy-beta-D-glucopyranoside, are described. Construction of the target molecules was achieved though a combination of the phenyl sulfoxide and trichloroacetimidate glycosylation methodologies. This is the first report on the synthesis of the beta-methyl derivatives, which represent the smallest fragments that incorporate all the structural features of polymeric hyaluronan.

NMR spectroscopy, molecular dynamics, and conformation of a synthetic octasaccharide fragment of the O-specific polysaccharide of Shigella dysenteriae type 1

A synthetic octasaccharide fragment (2) of the O-specific polysaccharide (1) of Shigella dysenteriae type 1 has been studied as its methyl glycoside by one- and two-dimensional homo- and heteronuclear NMR spectroscopy. Complete 1H and 13C NMR assignments have been generated, and the 13C spin-lattice relaxation times have been measured for the octasaccharide 2. A congener (6) of this octasaccharide containing one D-galactose residue with a specific 13C label at C-1 has been synthesized and used to measure interglycosidic 13C-1H coupling by the 2D J-resolved 1H NMR method. From the NMR data, three types of conformational restraints were developed: (a) 29 inter-residue, distance restraints; (b) 48 intra-residue, ring atom dihedral angle restraints, and (c) one heteronuclear, inter-residue dihedral angle restraint. The use of these restraints in a restrained molecular dynamics computation with simulated annealing yielded a conformation resembling a short, irregular spiral, with methyl substituents on the exterior.

Protein conjugates of synthetic saccharides elicit higher levels of serum IgG lipopolysaccharide antibodies in mice than do those of the O-specific polysaccharide from Shigella dysenteriae type 1

Our development of vaccines to prevent shigellosis is based on the hypothesis that a critical (protective) level of serum IgG to the O-specific polysaccharide (O-SP) domain of Shigella lipopolysaccharide (LPS) confers immunity. The O-SP is a hapten and must be conjugated to a protein to induce serum antibodies. The O-SP of Shigella dysenteriae type 1 (approximately 27 tetrasaccharide repeat units), prepared by acid hydrolysis of the LPS, was bound to human serum albumin (HSA) by multiple point attachment (O-SP-HSA): The molar ratio of HSA to O-SP was 1.0. Synthetic saccharides, composed of one or multiples of the O-SP tetrasaccharide, equipped with a spacer at their reducing end, were bound to HSA by a single point attachment: The average molar ratios of the saccharides to HSA ranged from 4 to 24. Serum IgG anti-LPS, elicited in mice by O-SP-HSA or synthetic tetra-, octa-, dodeca-, and hexadecasaccharide fragments, was measured by ELISA. Outbred 6-week-old female mice were injected s.c. three times at biweekly intervals with 2.5 micrograms of saccharide as a conjugate and were bled 7 days after the second and third injections. Excepting the tetramer, conjugates of the octamer, dodecamer and hexadecamer elicited IgG LPS antibodies after the second injection, a statistically significant rise (booster) after the third injection, and higher levels than those vaccinated with O-SP-HSA (P = 0.0001). The highest geometric mean levels of IgG anti-LPS were elicited by the hexadecamer with 9 chains or 9 moles of saccharide/HSA (15.5 ELISA units) followed by the octamer with 20 chains (11.1 ELISA units) and the dodecamer with 10 chains (9.52 ELISA units). Clinical evaluation of these synthetic saccharides bound to a medically useful carrier is planned.

Synthesis of Glycoconjugate Vaccines against Shigella dysenteriae Type 1

Syntheses of a hexadecasaccharide and smaller fragments corresponding to one-four repeating units of the O-specific polysaccharide of Shigella dysenteriae type 1 are reported in a reactive aglycon-linked from. Two tetrasaccharide donor/acceptor repeating units were assembled from monosaccharide precursors in a stepwise fashion and used in a linear, iterative manner to construct the higher-membered saccharides using Schmidt's glycosylation technique that proved superior to others tested. Single-point attachment of the saccharides to human serum albumin, using a secondary heterobifunctional spacer, afforded a range of glycoconjugates for a detailed evaluation of their immunological characteristics.

Measurement of interglycosidic 3JCH coupling constants of selectively 13C labeled oligosaccharides by 2D J-resolved 1H NMR spectroscopy

Tri-, tetra-, and penta-saccharide fragments of the O-specific polysaccharide of Shigella dysenteriae type 1 have been prepared in which a D-galactose residue of each oligosaccharide methyl glycoside derivative contains a 13C label at C-1. The interglycosidic coupling constants (3JCH) of these 13C nuclei with the H-3 nuclei of the adjacent 2-acetamido-2-deoxy-D-glucose residues have been measured by two-dimensional, J-resolved 1H NMR spectroscopy. The magnitudes of these coupling constants indicate that the trisaccharide is conformationally different to the higher oligosaccharide homologs, in agreement with previous studies of 13C chemical shifts and 1JCH values.