Total Synthesis of the Repeating Unit of Zwitterionic Polysaccharide Sp1.

Reported herein is the total synthesis of the trisaccharide repeating unit of zwitterionic polysaccharide Sp1 containing a rare sugar, 2-acetamido-4-amino-2,4,6-trideoxy-d-galactose (AAT), and three consecutive 1,2--glycosidic linkages. The total synthesis was completed via highly stereoselective glycosylations and late-stage oxidation as key steps involving a longest linear sequence of 21 steps with 4.4% overall yield.