Efficient synthesis of the tetrasaccharide repeating unit corresponding to the cell wall O-antigen of Proteus vulgaris O8 strain.

An acidic tetrasaccharide repeating unit corresponding to the cell wall O-antigen of Proteus vulgaris O8 strain has been synthesized in very good yield applying [2 + 2] block glycosylation strategy. Stereoselective α-glycosylated products were obtained using ether-based solvents in glycosylation reactions. The incorporation of the d-glucuronic acid moiety in the tetrasaccharide was achieved by glycosylation with d-glucose intermediate and TEMPO-Bis(acetoxy)iodobenzene (BAIB) mediated oxidation at the late stage. Non-participating groups (e.g. N3 and benzyl) were placed at C-2 position of the glycosyl donor for the preparation of the 1,2-cis-glycosylated products. The yields of the reactions were very good.