One‐Pot Synthesis of a Tetrasaccharide Repeating Unit of O‐Antigen from Escherichia coli O33

A tetrasaccharide repeating unit of the O‐antigen from Escherichia coli O33 has been synthesized for the first time using a chemoselective [1+1+2] one‐pot glycan assembly strategy. The phosphoglycerol moiety was installed by using the phosphoramidite method with benzylidene‐protected glycerol 2‐phosphoramidite as the reagent. Overall, the target tetrasaccharide was synthesized from monosaccharide building blocks in 12 linear steps, resulting in a satisfactory yield of 28%.