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A convergent [4+2] stereoselective block glycosylation strategy has been developed for the synthesis of the hexasaccharide repeating unit of the capsular polysaccharide of Klebsiella K19 strain in very good yield. The p-methoxybenzyl (PMB) group was used as a temporary alkyl protecting group, which was removed by tuning the glycosylation conditions. A thioglycoside was used as a glycosyl acceptor in an orthogonal glycosylation reaction. A late-stage TEMPO-mediated selective oxidation of a primary hydroxyl group into carboxylic acid allowed incorporation of the d-glucuronic acid moiety in the hexasaccharide. A combination of N-iodosuccinimide (NIS) and perchloric acid supported over silica (HClO4–SiO2) was used as a thiophilic promoter for the activation of thioglycosides. HClO4–SiO2 was also used as a solid acid activator for a glycosyl trichloroacetimidate derivative.

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Synthesis of the octasaccharide repeating unit of the K55 capsular polysaccharide of Acinetobacter baumannii BAL_204 strain has been achieved in very good yield using a convergent [5+3] block glycosylation strategy. The pentasaccharide and trisaccharide components were synthesized using sequential stereoselective glycosylations. The p-methoxybenzyl (PMB) group was used as temporary alkyl protecting group, which was removed under the thiophilic glycosylation condition by raising the temperature. A late-stage TEMPO-mediated selective oxidation of primary hydroxyl group into carboxylic acid allowed getting the d-glucuronic acid moiety in the octasaccharide. A combination of N-iodosuccinimide (NIS) and perchloric acid supported over silica (HClO4­-SiO2) was used as a thiophilic promoter for the activation of thioglycosides. HClO4-SiO2 was also used as a solid acid activator for glycosyl trichloroacetimidate derivative.

No abstract