Efficient Synthesis of Antigenic Trisaccharides Containing N-Acetylglucosamine: Protection of NHAc as NAc2

The antigenic trisaccharides, alpha-gal epitope and H antigen, containing N-acetyl-d-glucosamine (GlcNAc) were synthesized using a diacetyl strategy, in which NHAc is tentatively converted to NAc2 during oligosaccharide construction. Acetylation of NHAc in GlcNAc significantly improved the reactivity in glycosylation reactions. The diacetyl strategy allowed to achieve the efficient synthesis of alpha-gal through a sequential one-pot and one-flow procedure. Meanwhile, H antigen was synthesized by stepwise elongation from the reducing end side of GlcNAc. The enhancement of the reactivity by NAc2 protection was observed in both glycosylations at proximal and distal positions to GlcNAc. This diacetyl strategy is expected to be applicable to the synthesis of a wide range of glycans.