Synthesis of the tetrasaccharide repeating unit of the O-glycan from the polar flagellum flagellin of Azospirillum brasilense Sp7.

Chemical synthesis of the tetrasaccharide repeating unit of the O-glycan from the polar flagellum flagellin of Azospirillum brasilense Sp7 in the form of its p-methoxyphenyl glycoside is reported. The required glycosidic linkages have been accomplished by activation of thioglycosides with N-iodosuccinimide in the presence of H2SO4-silica. H2SO4-silica was found to be an effective alternative to the classical acid promoters like TfOH or TMSOTf and it can lead to the formation of both 1,2-cis and 1,2-trans glycosidic linkages depending on the protecting group manipulation and control of the reaction condition.