Synthesis of a Trisaccharide and a Tetrasaccharide from the Cell-Wall Lipopolysaccharides of Azospirillum brasilense S17

A trisaccharide containing a d-mannosamine moiety and a tetrasaccharide containing an l-rhamnan chain that are found in the cell walls of Azospirillum brasilense S17 were synthesized concisely and in excellent yields. The key features of the synthetic strategy were stereoselective glycosylations and a minimum number of protecting-group manipulations.