Oligosaccharides Corresponding to Biological Repeating Units of Shigella flexneri Variant Y Polysaccharide. 2. Synthesis and Two-Dimensional NMR Analysis of a Hexasaccharide Hapten

Article abstract of DOI:10.1021/jo00272a038

The block synthesis of a hexasaccharide portion of the biological repeating unit, <2)-α-L-Rhap-(1->2)-α-L-Rhap-(1->3)-α-L-Rhap-(1->3)-β-D-GlcpNAc-(1->, of the Shigella flexneri variant Y polysaccharide is described.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, as a glycosyl donor.Thus, the trisaccharide bromide in conjunction with the β-D-GlcpNPhth-(1->2)-α-L-Rhap-(1->2)-α-L-Rhap unit under Helferich conditions yielded the blocked hexasaccharide in 85percent yield.Attempts at coupling thetetrasaccharide donor, α-L-Rhap-(1->2)-α-L-Rhap-(1->3)-α-L-Rhap-(1->3)-β-D-GlcpNPhth, with the disaccharide acceptor, α-L-Rhap-(1->2)-α-L-Rhap, to give the hexasaccharide under a variety of conditions were unsuccessful.The blocked derivatives were synthesized as their allyl glycosides.Removal of the blocking groups, hydrogenation of the allyl group, and N-acetylation yielded the hexasaccharide hapten, α-L-Rhap-(1->2)-α-L-Rhap-(1->3)-α-L-Rhap-(1->3)-β-D-GlcpNAc-(1->2)-α-L-Rhap-(1->2)-α-L-Rhap, as its propyl glycoside, for use in inhibition studies with complementary monoclonal antibodies, and in NMR and X-ray studies.The detailed NMR analysis of the protected and deprotected hexasaccharides by use of two-dimensional NMR techniques is also described.