Synthesis of the Tetrasaccharide Repeating Unit Corresponding to the O-Antigen of Providencia alcalifaciens O7:H7 Strain

Synthesis of the tetrasaccharide corresponding to the O-an-tigen of Providencia alcalifaciens O7:H7 strain was achieved in satisfacto-ry yield by applying a stereoselective glycosylation strategy. Stereose-lective incorporation of beta-L-rhamnose, alpha-D-glucosamine and alpha-D-glucose moieties in the tetrasaccharide was achieved in very good yield.The D-glucuronic acid moiety in the tetrasaccharide was achieved bylate-stage TEMPO-bis(acetoxy)iodobenzene (BAIB)-mediated regiose-lective oxidation of the primary hydroxyl group of the D-glucose moi-ety. Thioglycosides were used as glycosyl donors in the presence of acombination of N-iodosuccinimide (NIS) and triflic acid (TfOH) as thio-philic promoter.