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.

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 (HClO4‐SiO2) mediated orthogonal glycosylation reaction has been carried out using glycosyl trichloroacetimidate derivative as donor and thioglycoside as acceptor. [ABSTRACT FROM AUTHOR]