Synthesis of Gal-β-(1→4)-GlcNAc-β-(1→6)-[Gal-β-(1→3)]-GalNAc-α-OBn oligosaccharides bearing O-methyl or O-sulfo groups at C-3 of the Gal residue: Specific acceptors for Gal: 3-O-sulfotransferases

Our recent studies have revealed the existence of two distinct Gal: 3-O-sulfotransferases capable of acting on the C-3 position of galactose in a Core 2 branched structure, e.g., Galβ1→4GlcNAcβ1→6(Galβ1→3)GalNacα1→OBenzyl as acceptor to give 3-O-sulfoGalβ1→4GlcNAcβ1→3(Galβ1→3)GalNAcα1→OB 20 and Galβ1→4GlcNAcβ1→6(3-O-sulfoGalβ1→3)GalNAcα1→OB 23. We herein report the synthesis of these two compounds and also that of other modified analogs that are highly specific acceptors for the two sulfotransferases. Appropriately protected 1-thio-glycosides 7, 8, and 10 were employed as glycosyl donors for the synthesis of our target compounds.