A Versatile Strategy for the Synthesis of N-Acetyl-bacillosamine-Containing Disaccharide Building Blocks Related to Bacterial O-Antigens

A N-phenyltrifluoroacetimidate glycosyl donor of bacillosamine, a 2,4-diaminosugar contained in several O-antigens from pathogenic bacteria, was synthesized starting from the known peracetylated d-fucal and was demonstrated to be effective for the high-yield coupling to bacillosamine-containing disaccharides. The stereoselectivity of the glycosylations was from moderate to very good depending on the solvent and glycosyl acceptor. The synthetic path was then slightly modified to obtain a similar glycosyl donor with an axial acetyl group on position 4. This building block could be coupled to give a disaccharide, that after five steps (azido reduction, acetylation, O-deacetylation, mesylation, and azide substitution) afforded a bacillosamine-containing disaccharide with differently protected amino functions, in order to provide access to all the currently known structural features of bacillosamine-containing disaccharides known to date contained in natural polysaccharides.