Synthesis of an S-(alpha-sialosyl)-(2----9)-O-(alpha-sialosyl)-(2----3')-beta-lactos ylceramide

9-O Acetylated Gangliosides in Health and Disease

Glycosphingolipids comprise a lipid class characterized by the presence of sugar moieties attached to a ceramide backbone. The role of glycosphingolipids in pathophysiology has gained relevance in recent years in parallel with the development of analytical technologies. Within this vast family of molecules, gangliosides modified by acetylation represent a minority. Described for the first time in the 1980s, their relation to pathologies has resulted in increased interest in their function in normal and diseased cells. This review presents the state of the art on 9-O acetylated gangliosides and their link to cellular disorders.

Synthesis of LewisX-O-Core-1 threonine: A building block for O-linked LewisX glycopeptides

LewisX (LeX) is a branched trisaccharide Galβ1→4(Fucα1→3)GlcNAc that is expressed on many cell surface glycoproteins and plays critical roles in innate and adaptive immune responses. However, efficient synthesis of glycopeptides bearing LeX remains a major limitation for structure-function studies of the LeX determinant. Here we report a total synthesis of a LeX pentasaccharide 1 using a regioselective 1-benzenesulfinyl piperidine/triflic anhydride promoted [3 + 2] glycosylation. The presence of an Fmoc-threonine amino acid facilitates incorporation of the pentasaccharide in solid phase peptide synthesis, providing a route to diverse O-linked LeX glycopeptides. The described approach is broadly applicable to the synthesis of a variety of complex glycopeptides containing O-linked LeX or sialyl LewisX (sLeX).

Imposing the trans/gauche conformation on a sialic acid donor with a 5-N,7-O-oxazinanone group: effect on glycosylation stereoselectivity

A 5-N,7-O-oxazinanone derivative of a thiosialic acid ester has been synthesized and investigated for the effect of conformational restriction on glycosylation. The cyclic group is found to be powerfully disarming, but to have no beneficial effect on reaction stereoselectivity.

A synthetic approach to polysialogangliosides containing alpha-sialyl-(2-->8)-sialic acid: total synthesis of ganglioside GD3

A stereocontrolled, facile total synthesis of ganglioside GD3 is described as an example of a proposed systematic approach to the preparation of gangliosides containing an alpha-sialyl-(2-->8)-sialic acid unit alpha-glycosidically linked to O-3 of a D-galactose residue in their oligosaccharide chains. Glycosylation of 2-(trimethylsilyl)ethyl 6-O-benzoyl-, 3-O-benzoyl-, or 3-O-benzyl-beta-D-galactopyrano-sides, or 2-(trimethylsilyl)ethyl 2,3,6,2',6'-penta-O-benzyl-beta-lactoside (7), with methyl [phenyl 5- acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D- glycero-alpha-D-galacto-2-nonulopyranosylono-1',9 lactone)- 4,7-di-O-acetyl-3,5-dideoxy-2-thio-D-glycero-D-galacto-2-nonulopyrano sid] onate (3), using N-iodosuccinimide-trifluoromethanesulfonic acid as a promoter, gave the corresponding alpha glycosides 8 (32%), 13 (33%), 14 (48%), and 17 (31%), respectively. The glycosyl donor 3 was prepared from O-(5-acetamido-3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosy lonic acid)-(2-->8)-5-acetamido-3,5- dideoxy-D-glycero-D-galacto-2-nonulopyranosonic acid by treatment with Amberlite IR-120 (H+) in methanol, O-acetylation, and subsequent replacement of the anomeric acetoxy group with phenylthio. Compound 8 was converted into the methyl beta-thioglycoside via O-benzoylation, replacement of the 2-(trimethylsilyl)ethyl group by acetyl, and introduction of the methylthio group by reaction with methylthiotrimethylsilane. Compound 17 was converted, via O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and reaction with trichloroacetonitrile, into the alpha-trichloroacetimidate, which was coupled with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol to give the beta-glycoside. This glycoside was easily transformed, via selective reduction of the azido group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester and lactone functions, into ganglioside GD3.