Zwitterionic polysaccharides (ZPSs) are biologically significant because of their known ability to activate CD4+ T-cells through the MHC II complex in the absence of proteins, peptides or lipids. This feature alone breaks the general paradigm that carbohydrates are T-cell independent antigens. Polysaccharide A1 (PS A1), one of the most well-studied ZPSs, is expressed on the surface of Gram-negative obligate anaerobic bacterium, Bacteroides fragilis ATCC 25285/NCTC 9343. Our research group has been exploiting the T-cell dependent nature of PS A1 as a novel “carrier” in an entirely carbohydrate-based vaccine when conjugated to tumor associated carbohydrate antigens like Tn, TF and STn. However, in order to further our understanding of the key immunological mechanisms, well-characterized and homogeneous synthetic constructs of defined oligomeric length are of high importance. Furthermore, zwitterionic polysaccharide repeating units of defined oligomeric length would be significant in answering questions related to vaccine development. This talk will therefore focus on the trials and tribulations as well as the successes in understanding carbohydrate assembly and highlight solutions to challenging synthetic transformations.

Total synthesis of bacterial polysaccharide PS A1 with alternating charges on adjacent monosaccharides

2019 Spring National Meeting

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