Total synthesis of the heptasaccharide repeating unit of the iron-binding exopolysaccharide secreted by Klebsiella oxytoca BAS-10

The first total synthesis of a heptasaccharide found in the iron-binding exopolysaccharide produced by Klebsiella oxytoca BAS-10 has been achieved in excellent yield using a block synthetic strategy. A trisaccharide glycosyl donor was stereoselectively coupled with a tetrasaccharide glycosyl acceptor using the trichloroacetimidate activation procedure. The yields and stereo outcome were excellent in each step of glycosylation. A late stage oxidation protocol was adopted for the oxidation of the primary hydroxyl group to the carboxylic functionality while keeping a secondary hydroxyl group unaffected.