Total synthesis of the trisaccharide repeating unit of the O-polysaccharide of Pragia fontium 97U124

Herein, we report the first total synthesis of a densely functionalized trisaccharide repeating unit of Pragia fontium 97U124. The presence of rare deoxy amino sugars namely C4-N-glyceroyl-d-bacillosamine and l-fucosamine, two consecutive 1,2-cis linkages, five nitrogen dispensed over three rings and orthogonal functionality of amines makes the trisaccharide synthesis a challenging task. The total synthesis of target molecule was completed via a longest linear sequence of 22 steps in 5.1 % overall yield starting from d-mannose.