Thomas Norberg

Thioglycosides as glycosylating agents in oligosaccharide synthesis

A review is given of the use of thioglycosides as glycosyl donors in oligosaccharide synthesis. Both indirect use, by conversion of the thioglycoside into a glycosyl halide and direct use, by electrophilic activation of the thioglycoside, are discussed.

Contulakin-G, an O-glycosylated invertebrate neurotensin

We have purified contulakin-G, a 16-amino acid O-linked glycopeptide (pGlu-Ser-Glu-Glu-Gly-Gly-Ser-Asn-Ala-Thr-Lys-Lys-Pro-Tyr-Ile-Leu-OH, pGlu is pyroglutamate) from Conus geographus venom. The major glycosylated form of contulakin-G was found to incorporate the disaccharide β-d-Galp-(1→3)-α-d-GalpNAc-(1→) attached to Thr10. The C-terminal sequence of contulakin-G shows a high degree of similarity to the neurotensin family of peptides. Synthetic peptide replicates of Gal(β→3) GalNAc(α→)Thr10 contulakin-G and its nonglycosylated analog were prepared using an Fmoc (9-fluorenylmethoxycarbonyl) protected solid phase synthesis strategy. The synthetic glycosylated con- tulakin-G, when administered intracerebroventricular into mice, was found to result in motor control-associated dysfunction observed for the native peptide. Contulakı́n-G was found to be active at 10-fold lower doses than the nonglycosylated Thr10 contulakin-G analog. The binding affinities of contulakin-G and the nonglycosylated Thr10 contulakin-G for a number of neurotensin receptor types including the human neurotensin type 1 receptor (hNTR1), the rat neurotensin type 1 and type 2 receptors, and the mouse neurotensin type 3 receptor were determined. The binding affinity of the nonglycosylated Thr10contulakin-G was approximately an order of magnitude lower than that of neurotensin1–13 for all the receptor types tested. In contrast, the glycosylated form of contulakin-G exhibited significantly weaker binding affinity for all of the receptors tested. However, both contulakin-G and nonglycosylated Thr10 contulakin-G were found to be potent agonists of rat neurotensin receptor type 1. Based on these results, we conclude that O-linked glycosylation appears to be a highly unusual strategy for increasing the efficacy of toxins directed against neurotransmitter receptors.

Derivatization Procedures for Reducing Oligosaccharides, Part 3: Preparation of Oligosaccharide Glycosylamines, and Their Conversion Into Glycosaccharide - Acrylamide Copolymers

Abstract Reducing oligosaccharides were converted in good yields into the corresponding primary glycosylamines by treatment with aqueous ammonium bicarbonate. The glycosylamines were then acryloylated and the obtained oligosaccharide N-acryloyl glycosylamines were copolymerized with acrylamide. High molecular weight, linear copolymers were obtained, which were useful as antigens in immunoassays.

New derivatization and separation procedures for reducing oligosaccharides

Abstract4-Trifluoroacetamidoaniline was reacted with reducing oligosaccharides in the presence of sodium cyanoborohydride to give aminoalditol derivatives, useful for linkage to proteins or solid matrices. A mixture of reducing oligosaccharides, difficult to separate by HPLC, was treated in the same way. The resulting derivatives were easily separated by HPLC.

Synthesis of mono- and disaccharide amino-acid derivatives for use in solid phase peptide synthesis

N-Fluorenylmethyloxycarbonyl-protected serine and threonine derivatives, carryingO-glycosidically α- or β-linked peracetylated β-d-Galp-(1–3)-d-GalNAcp carbohydrate chains, were prepared. These derivatives are intended for use in solid phase glycopeptide synthesis. Suitably protected mono- and disaccharide thioglycosides were used as carbohydrate intermediates. These were activated by treatment with bromine to give the glycosyl bromides, which were then used in silver triflate-promoted glycosidations ofN-fluorenylmethyloxycarbonyl amino-acid phenacyl esters. Removal of the phenacyl esters with zinc gave the target free acids.

Synthesis of a dimeric Lewis X hexasaccharide derivative corresponding to a tumor-associated glycolipid.

The dimeric Lewis X hexasaccharide p-trifluoroacetamidophenylethyl O-beta-D-galactopyranosyl-(1----4)-O-[alpha-L-fucopyranosyl-(1----3)]-O- (2- acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----3)-O-beta-D-galactopyrano syl- (1----4)-O-[alpha-L-fucopyranosyl-(1----3)]-2-acetamido-2-deoxy-beta-D- glucopyranoside (14), which is a derivative of a tumor-associated glycolipid, was synthesized from thioglycoside intermediates. A protected disaccharide was used as a key-intermediate for synthesis of the p-nitrophenylethyl glycoside of suitably protected O-beta-D-Galp-(1----4)-O-beta-D-GlcpN-(1----3)-O-beta-D-Galp-(1--- -4)-beta-D- GlcpN, which, after selective deblocking, was di-L-fucosylated and deprotected to give 14.

The conformation of Salmonella O-antigenic oligosaccharides of serogroups A, B, and D1 inferred from 1H- and 13C-nuclear magnetic resonance spectroscopy☆

The conformational model derived by the HSEA calculation method was used to interpret the n.m.r. data for solutions of oligosaccharides corresponding to the Salmonella serogroups A, B, and D1 antigenic determinants. The favored conformer, derived by calculation, accounted for the observed, chemical-shift changes and accurately predicted the existence and magnitude of inter-ring proton n.O.e.s. Extensive proton-density and compression of proton, Van der Waals radii were correlated with deshielding of specific proton-resonances. The model of lipopolysaccharide conformation accounts for the known antigenic properties of Salmonella O-antigens.

Synthesis of the methyl and 1-octyl glycosides of the P-antigen tetrasaccharide (globotetraose)

The methyl and 1-octyl beta-glycosides of the P-antigen tetrasaccharide [globotetraose, beta-D-GalpNAc-(1----3)-alpha-D-Galp-(1----4)-beta-D-Galp-(1----4) -D-Glc] were synthesised from a tetrasaccharide precursor, prepared using methyl disaccharide 1-thioglycosides as intermediates. In the key glycosidation with silver triflate, HO-2 was used as an alpha-directing group in the glycosyl bromide.

Ligands of the asialoglycoprotein receptor for targeted gene delivery, part 1: Synthesis of and binding studies with biotinylated cluster glycosides containing N-acetylgalactosamine.

In order to develop the non-viral Bioplex vector system for targeted delivery of genes to hepatocytes, we have evaluated the structure-function relationship for a number of synthetic ligands designed for specific interaction with the hepatic lectin ASGPr. Biotinylated ligand derivatives containing two, three or six beta-linked N-acetylgalactosamine (GalNAc) residues were synthesized, bound to fluorescent-labeled streptavidin and tested for binding and uptake to HepG2 cells using flow cytometry analysis (FACS). Uptake efficiency increased with number of displayed GalNAc units per ligand, in a receptor dependent manner. Thus, a derivative displaying six GalNAc units showed the highest uptake efficacy both in terms of number of internalizing cells and increased amount of material taken up per each cell. However, this higher efficiency was shown to be due not so much to higher number of sugar units, but to higher accessibility of the sugar units for interaction with the receptor (longer spacer). Improving the flexibility and accessibility of a trimeric GalNAc ligand through use of a longer spacer markedly influenced the uptake efficiency, while increasing the number of GalNAc units per ligand above three only provided a minor contribution to the overall affinity. We hereby report the details of the chemical synthesis of the ligands and the structure-function studies in vitro. Published in 2003.

The conformation of Salmonella O-antigenic polysaccharide chains of serogroups A, B, and D1 predicted by semi-empirical, hard-sphere (HSEA) calculations

The preferred conformation of the tetrasaccharide repeating units of Salmonella Serogroups A, B, and D1 have been calculated. The semiempirical calculations used the Hard-Sphere, Exo-Anomeric (HSEA) approach to derive a conformational model, which could be used to assist the interpretation of conformations significantly populated in aqueous solution. The calculated model was extended to include a pentasaccharide repeating unit bearing an alpha-D-glucopyranose-branch point. The 3,6-dideoxyhexose to D-mannose linkage was shown to possess a steep energy surface with a minimum, which results in good exposure of the dideoxyhexose O-2 and O-4 atoms. Stereochemical changes involving the equatorial or axial disposition of these atoms are the distinguishing structural features of the A, B, and D1 serogroups. A lipophilic surface involving the 6-deoxy groups of the dideoxy-D-hexose and L-rhamnose residues was identified, and the possible implications of these features in antigenic determinants is discussed. The preferred conformation predicted by the HSEA method correlates with the known antigenic specificities of polysaccharides belonging to these Salmonella serogroups.