Abstract
Capsular polysaccharides of pathogenic bacteria have been reported to be effective vaccines against diseases caused by them. Providencia stuartii is a class of enterobacteria of the family Providencia that is responsible for several antibiotic resistant infections, particularly urinary tract infections of patients with prolonged catheterization in hospital settings. Towards the goal of development of vaccine candidates against this pathogen, we herein report the total synthesis of a trisaccharide repeating unit of the O-antigen polysaccharide of the P. stuartii O49 serotype containing the →6)-β-ᴅ-Galp-(1→3)-β-ᴅ-GalpNAc(1→4)-α-ᴅ-Galp(1→ linkage. The synthesis of the trisaccharide repeating unit was carried out first by a linear strategy involving the [1 + (1 + 1 = 2)] assembly, followed by a one-pot synthesis involving [1 + 1 + 1] strategy from the corresponding monosaccharides. The one-pot method provided a higher yield of the protected trisaccharide intermediate (73%) compared to the two step synthesis (66%). The protected trisaccharide was then deprotected and N-acetylated to finally afford the desired trisaccharide repeating unit as its α-p-methoxyphenyl glycoside.
Highlights
O-antigens or O-specific polysaccharides are one of the important constituents of the surface lipopolysaccharides (LPS) of the cell wall of Gram-negative bacteria
In 2017, Kulkarni and co-worker accomplished the total synthesis of a O-polysaccharide of Providencia alcalifaciens O22 via a one pot assembly of the oligosaccharide unit [36]
We demonstrated a follow-up one-pot synthesis involving a [1 + 1 + 1] strategy using the corresponding appropriately protected monosaccharides, providing the opportunity for rapid access to the desired target molecule
Summary
O-antigens or O-specific polysaccharides are one of the important constituents of the surface lipopolysaccharides (LPS) of the cell wall of Gram-negative bacteria. The O-antigens consist of polysaccharide repeating units bearing several different monosaccharides. The structure of repeating oligosaccharide units of O-polysaccharides of several Providencia O-serogroups as well as P. stuartii O4 [26], O18 [27], O20
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