Herein we report an efficient total synthesis of lipid-anchor-appended core trisaccharides of lipoteichoic acids of Streptococcus pneumoniae and Streptococcus oralis Uo5. The key features include the expedient synthesis of the rare sugar 2,4,6-trideoxy-2-acetamido-4-amino-D-Galp building block via one-pot sequential S N 2 reactions and the α-selective coupling of D-thioglucoside with the diacyl glycerol acceptor to construct a common disaccharide acceptor, which was utilized in the total synthesis of target molecules 1 and 2.B acteria often contain unique deoxy amino glycans on their surfaces that are absent in host cells. 1 The bacterial raresugar-containing carbohydrates play important roles in the bacterial growth, survival and motility, entry of pathogen, infection, as well as the immune response. 2 For example, the Gram-positive bacteria Streptococcus pneumoniae and Streptococcus oralis Uo5 both contain lipoteichoic acids (LTAs) as major components of the cell wall, with core trisaccharides 1 and 2 composed of a common disaccharide unit containing a rare 2,4,6-trideoxy-2-acetamido-4-amino-D-Galp (AAT) sugar unit α-linked to diacylglycerol (Figure 1). 3 Streptococcus pneumoniae causes a variety of life-endangering diseases such as severe infection in the upper respiratory track, pneumonia, bacteremia, and meningitis, thereby resulting in high mortality rates. 4−6 The teichoic acid of Streptococcus pneumoniae performs a crucial role in cell division, cation homeostasis, and the regulation of cell-wall elongation. 7,8 Moreover, the

First total synthesis of the conjugation-ready pentasaccharide repeating unit of Plesiomonas shigelloides strain 302-73 (serotype O1) is reported. The complex target pentasaccharide is composed of all-rare amino sugars such as orthogonally functionalized D-bacillosamine, L-fucosamine, and L-pneumosamine linked through four consecutive α-linkages. The poor nucleophilicity of axial 4-OH of L-fucosamine and stereoselective glycosylations are the key challenges in the total synthesis, which was completed via a longest linear sequence of 27 steps in 3% overall yield.

An efficient total synthesis of a conjugation-ready trisaccharide repeating unit of Staphylococcus aureus strain M is reported here. The main challenges involved in this synthesis are the procurement of rare sugars (d-FucNAc and d-GalNAcA) and installation of consecutive 1,2-cis-glycosidic linkages between them. Stereoselective 1,2-cis glycosylation with the linker acceptor was achieved with easily accessible benzylidene protected d-galactosamine thioglycoside by employing a DMF modulated preactivation glycosylation method. The consecutive 1,2-cis linkages were installed with the help of solvent participation. The carboxylic acid functionality was introduced via postglycosylation oxidation on the disaccharide moiety. The total synthesis of trisaccharide repeating unit was accomplished with the longest linear sequence of 24 steps in 4.5% overall yield.