Synthesis of Pentasaccharide Fragments Related to the O ‐Specific Polysaccharide of Shigella flexneri Serotype 1a

The synthesis of the pentasaccharide 5‐aminopentylglycosides α‐ L ‐Rha p ‐(1→3)‐[α‐ D ‐Glc p ‐(1→4)]‐β‐ D ‐Glc p NAc‐(1→2)‐α‐ L ‐Rha p ‐(1→2)‐α‐ L ‐Rha p ‐1‐ O ‐(CH 2 ) 5 NH 2 ( 29 ) andα‐ L ‐Rha p ‐(1→3)‐α‐ L ‐Rha p ‐(1→3)‐[α‐ D ‐Glc p ‐(1→4)]‐β‐ D ‐Glc p NAc‐(1→2)‐α‐ L ‐Rha p ‐1‐ O ‐(CH 2 ) 5 NH 2 ( 28 ), related to the O ‐specific polysaccharide of Shigella flexneri serotype 1a by coupling of the suitably protected trisaccharides α‐ D ‐Glc p ‐(1→4)‐β‐ D ‐Glc p (1→2)‐α‐ L ‐Rha p ‐1‐ O ‐(CH 2 ) 5 NH 2 ( 23 ) and α‐ L ‐Rha p ‐(1→3)‐[α‐ D ‐Glc p ‐(1→4)]‐β‐ D ‐Glc p ‐1‐SPh ( 26 ) with the corresponding rhamnosyl glycosides α‐ L ‐Rha p ‐(1→3)‐α‐ L ‐Rha p ‐1‐SEt ( 17 ) and α‐ L ‐Rha p ‐(1→3)‐α‐ L ‐Rha p ‐1‐ O ‐(CH 2 ) 5 NH 2 ( 13 ), is described. Building blocks 23 and 26 were prepared by intramolecular glycosylation of an unsymmetrically tethered cellobiosamine derivative. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)