Total synthesis of 6-O-sulfo-sialylparagloboside: a widely useful glycoprobe for biochemical research

The total synthesis of 6-O-sulfo-sialylparagloboside is described. A suitably protected β-d-GlcpNAc-(1→3)-β-d-Galp-(1→4)-d-GlcpOSE derivative was glycosylated with an α-d-Neup5Ac-(2→3)-d-Galp derived imidate to give the corresponding protected α-d-Neup5Ac-(2→3)-β-d-Galp-(1→4)-β-d-GlcpNAc-(1→3)-β-d-Galp-(1→4)-d-GlcpOSE pentasaccharide derivative. Proper manipulation of the protecting groups of the pentasaccharide afforded the corresponding glycosyl imidate, which was coupled with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol. Selective reduction of the azido group, N-acylation with octadecanoic acid, 6-O-sulfation of the GlcpNAc residue, and complete removal of the protecting groups gave the desired 6-O-sulfo-sialylparagloboside.