Chemical Synthesis and Antigenicity Evaluation of Shigella dysenteriae Serotype 10 O-Antigen Tetrasaccharide Containing a (S)-4,6-O-Pyruvyl Ketal

Abstract

Shigella is the second most common etiologic pathogen responsible for childhood acute diarrhea. An anti-Shigella vaccine is still eagerly awaited due to the increasing drug resistance of this pathogen. The Shigella O-antigen is a promising vaccine target. To identify the immune epitopes of the glycan, the first total synthesis of Shigella dysenteriae serotype 10 O-antigen tetrasaccharide containing a (S)-4,6-O-pyruvyl ketal was completed. The 1,2-trans-β-glycosylation & C2 epimerization and conformational locking strategies facilitated the construction of two 1,2-cis-β-glycosidic linkages. The reactivities of both the glycosyl donor and acceptor were improved by adding electron-donating benzyl groups, enabling an efficient assembly of the tetrasaccharide. The (S)-4,6-Opyruvyl ketal was introduced at the final stage due to its influence on the glycosylation stereospecificity and efficiency. In addition, (R)-4,6-O-pyruvylated and nonpyruvylated tetrasaccharides and three further fragments were synthesized. Glycan microarray screening revealed that the tetrasaccharide repeating unit is the key antigenic epitope of the O-antigen. Moreover, the (S)-4,6-O-pyruvyl ketal is an essential structural feature of this antigen for designing carbohydrate-based vaccines against S. dysenteriae serotype 10. The comparison of the (S)-4,6-O-pyruvylated glycan and its (R)-epimer will set an example for biological evaluation of other bacterial glycans containing pyruvyl ketals.

Immunological Exploration of Helicobacter pylori Serotype O2 O‐Antigen by Using a Synthetic Glycan Library

“…To determine the specificity of glycoconjugates‐elicited IgG antibodies, a glycan microarray was constructed for screening with seven oligosaccharides ( 22 — 28 ) from different organisms, including D‐mannose, N ‐acetyl‐D‐galactosamine (GalNAc), ( S )‐4,6‐ O ‐pyruvylated D‐mannose, disaccharides, trisaccharides and phosphate‐ribosyl‐ribitol (Figure S8). [ 5,35 ] There was almost no cross‐reaction of the post‐immune sera with these oligosaccharides, which confirmed the specificity of these antibodies.…”

Advances in glycoside and oligosaccharide synthesis

“…115,117,[121][122][123][124] Similarly, the choice of hydroxyl protecting groups impacts the synthesis and the order of manipulation is essential for a successful synthesis. [125][126][127][128][129][130] Permanent protecting groups, 131,132 such as benzyl ethers (Fig. 4) stay in place throughout the synthesis and are removed after assembling the target structure.…”

Development in the Concept of Bacterial Polysaccharide Repeating Unit-Based Antibacterial Conjugate Vaccines

“…dysenteriae serotype 10 O-antigen in a stereoselective manner. 165 Additionally, corresponding (R)-4,6-O-pyruvylated and non-pyruvylated tetrasaccharides, as well as (S)-4,6-O-pyruvylated mannose, were also synthesized and analyzed for their antigenicity through glycan microarray screening. The results indicated that the tetrasaccharide repeating unit is a crucial antigenic epitope of the Sh.…”

“…Very recently, Yin and co-workers accomplished the first total synthesis of the tetrasaccharide of Sh. dysenteriae serotype 10 O -antigen in a stereoselective manner . Additionally, corresponding ( R )-4,6- O -pyruvylated and non-pyruvylated tetrasaccharides, as well as ( S )-4,6- O -pyruvylated mannose, were also synthesized and analyzed for their antigenicity through glycan microarray screening.…”