Synthesis of the Tetrasaccharide Repeating Unit from Acinetobacter baumannii Serogroup O18 Capitalizing on Phosphorus-Containing Leaving Groups

摘要

The first convergent synthesis of the tetrasaccharide repeating unit of the polymeric O antigen isolated from Acinetobacter baumannii serogroup O18 has been achieved: The ManNAc beta 1 -> 4Gal and GalNAc beta 1 -> 3Gal units were successfully obtained through beta-selective glycosylation with 2-azido-4,6-O-benzylidene-2-deoxymannosyl diphenyl phosphate and Tf2NH-promoted glycosylation with 2-acetamido-2-deoxygalactosyl diethyl phosphite, respectively. The disaccharide units could be coupled with the aid of TMSClO4 as an activator of the diphenyl phosphate leaving group, and global deprotection, completed the synthesis of the tetrasaccharide.