Studies on the Thioglycosides ofN-Acetylneuraminic Acid 10: Synthesis ofS-(α-Sialosyl)-(2→6)-O-2-acetamido-2-deoxy-β-D-Hexopyranosyl Ceramide and Its Related Compounds

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Abstract
Sialosylglycolipids in which 2-thio-N-acetylneuraminic acid (2-thio-Neu5Ac) is linked as the a-glycoside at C-6 of N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc) residue, and ceramide or 2-(2-tetradecylhexadecanamido)-ethanol is contained as the lipophilic part, have been synthesized. Coupling of the sodium salt (11) of α-2-thio-Neu5Ac with 2-azidoethyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-6-O-tosyl-β-D-glucoside (6) or -β-D-galactoside (10), which are prepared via condensation of the oxazoline derivative of GlcNAc or GalNAc with 2-azidoethanol, O-deacetylation, 6-O-tosylation and O-acetylation gave the corresponding β-thioglycosides (12 and 16), respectively. The β-thioglycosides obtained were converted via selective reduction of the azide group, condensation with 2-tetradeCylhexadecanoic acid (20) and removal of the protecting groups, into the end products (15 and 19). On the other hand, glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-l,3-diol (22) with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-D-glucopyranosyl bromide gave the β-glycoside, which was transformed via O-deacetylation, conversion of the phthalimide group to N-acetyl, selective 6-O-tosylation, coupling with 11, reduction of the azide group, condensation with octadecanoic acid and removal of the protecting groups, into the title compound 29.