Executive Summary : | Cell-surface carbohydrates in the form of glycoconjugates play important roles in vital life processes such as infections and immune respsonse. Several bacterial glycoconjugates are comprised of rare D- and L-deoxy amino sugars which are not present in human hosts. This peculiar structural difference allows discrimination between the pathogen and the host cell and thus offers avenues for target-specific therapeutics and carbohydrate-based vaccine development. However, these oligosaccharides cannot be isolated with sufficient purity and in acceptable amounts from nature, and therefore chemical synthesis is a crucial step toward the development of these immunologically potent molecules. Towards this end, we recently established a short and convenient methodology for the synthesis of orthogonally protected rare D- and L-deoxy amino sugars, which are difficult to synthesize otherwise. The key building blocks can be assembled together to gain access to precious glycoconjugates. Through this proposal we plan to achieve total synthesis of four biologically important glycans 1-4. The trisaccharide repeating units of Pseudomonas aeruginosa and Staphylococcus aureus type 5, 8 and strain M are very important from the perspective of vaccine development against the ESKAPE pathogen. In fact, a conjugate vaccine, StaphVAXTM that includes the two most prevalent capsular polysaccharides, types 5 and 8, has been developed in a recent phase III clinical study in hemodialysis patients, and it was shown to prevent S. aureus bacteremia for up to 10 months following a single immunization. Moreover, it has also been reported that a bivalent vaccine of S. aureus capsular polysaccharide types 5 and 8 conjugated to Pseudomonas aeruginosa exotoxin A (rEPA) elicit strong bactericidal immune responses in volunteers and give limited (60%) protection for renal disease patients. Therefore, synthesis of the trisaccharide repeating units of Pseudomonas aeruginosa O11 and S. aureus strains is highly warranted. Herein we propose a chemical synthesis of orthogonally protected rare deoxy amino sugars and their stereoselective assembly to construct conjugation-ready oligosaccharides of ESKAPE pathogens P. aeruginosa and S. aureus for further vaccine development. The challenges include, 1. procurement of the appropriately functionalized rare monosaccharide building blocks 2. Installation of consecutive 1,2-cis glycosidic linkages, and, 3. functional group interconversion as well as global deprotection. The availability of linker attached trisaccharides will allow their conjugation to protein and further immunological studies leading to development of vaccines. |