Oligosaccharides corresponding to biological repeating units of Shigella flexneri variant Y polysaccharide. III: Synthesis and 2D-nuclear magnetic resonance analysis of a heptasaccharide hapten

The synthetic strategy relies on the use of the key trisaccharide intermediate α-L-Rhap-(1→2)-α-L-Rhap-(1→3)-α-L-Rhap, both as a glycosyl acceptor and as a donor. Thus, the trisaccharide bromide in conjunction with the β-D-GlcpNPhth-(1→2)-α-L-Rhap-(1→3)-α-L-Rhap unit under Helferich conditions yielded the blocked heptasaccharide in 86% yield. The latter unit was obtained, in turn, from the key trisaccharide intermediate functioning as an acceptor molecule