Convergent Synthesis of a Pentasaccharide Containing a Rare Sugar 4‐amino‐4‐deoxy‐D‐fucose Related to the Cell Wall O‐polysaccharide of Acinetobacter baumannii 90

Abstract A convenient synthetic strategy has been developed for the synthesis of a pentasaccharide related to the cell wall O ‐polysaccharide of Acinetobacter baumannii ( A. baumannii ) 90 in very good yield applying a stereoselective [3+2] block glycosylation reaction. The synthesis of the target pentasaccharide was challenging due to the presence of a rare sugar, 4‐amino‐4‐deoxy‐D‐fucose and several α‐glycosidic linkages in it. The construction of 1,2‐ cis glycosyl linkages were achieved using a combination of copper(II) bromide and tetra‐ n ‐butylammonium bromide (TBAB) or a combination of N ‐iodosuccinimide (NIS) and trimethylsilyl trifluoromethanesulfonate (TMSOTf) as thiophilic glycosylation activator. Perchloric acid supported over silica (HClO 4 ‐SiO 2 ) mediated orthogonal glycosylation reaction has been carried out using glycosyl trichloroacetimidate derivative as donor and thioglycoside as acceptor.