Chemical Synthesis of a Complex-Type N-Glycan Containing a Core Fucose

A chemical synthesis of a core fucose containing N -glycan was achieved. Asparagine was introduced at an early stage of the synthesis, and the sugar chain was convergently elongated. As for the fragment synthesis, we reinvestigated α-sialylation, β-mannosylation, and N -glycosylation to reveal that precise temperature control was essential for these glycosylations. Intermolecular hydrogen bonds involving acetamide groups were found to reduce the reactivity in glycosylations: the protection of NHAc as NAc 2 dramatically improved the reactivity. The dodecasaccharide–asparagine framework was constructed via the (4 + 4) glycosylation and the (4 + 8) glycosylation using the tetrasaccharide donor and the tetrasaccharide–asparagine acceptor. An ether-type solvent enhanced the yields of these key glycosylations between large substrates. After the whole deprotection of the dodecasaccharide, the target N -glycan was obtained.