Synthesis and Antigenic Evaluation of Oligosaccharide Mimics of Vi Antigen from Salmonella typhi.

Salmonella typhi is responsible for typhoid fever, which is a serious health threat in developing countries. As a virulent factor of Salmonella typhi, the purified Vi polysaccharide (Vi PS) has become an effective vaccine to combat typhoid fever. The chemical synthesis can provide homogeneous and well-defined molecules for the development of Vi-based vaccines. However, the synthesis of Vi oligosaccharides in high yields and with exclusive α-stereoselectivities remains very challenging. In this paper, a series of Vi pseudooligosaccharides, including pseudo tetra-, hexa-, and octa-saccharides were efficiently synthesized. These oligosaccharide analogues were conjugated by carbon chain tether through olefin cross metathesis or by the 1,2,3-triazole moiety through copper (I)-catalyzed alkyne-azide cycloaddition reaction (CuAAC). The binding affinities of these oligosaccharide mimics to anti-Vi antibodies were investigated. These results will be beneficial to the further development of Vi-based oligosaccharide vaccines.