3-Deoxy-D-manno-octulosonic acid (Kdo) is a key component of lipopolysaccharides (LPS) found in all gram-negative bacteria. The Kdo sugar exists almost exclusively in alpha-glycoside form and is essential for bacterial survival.
Previously the Ling group has shown that a 1-C-aryl-3,4;6,7-diisopropylidenated heptose glycal can be a versatile donor for the synthesis beta-Kdo glycosides. The glycosylation was accomplished with high regio- and stero- selectivities by using N-iodosuccinimide (NIS). It was postulated that the reason for the observed beta-glycosylyation results arose from the presence of a fused isopropylidene ring on the top face of the glycal therefore directing via steric repulsion the formation of a the beta-Kdo glycoside.
The goal of this thesis was to exchange the fused isopropylidene rings on the glycal with acyclic protecting groups so as to test if glycosylation results could be made to favor formation of a more stable and desired alpha-Kdo glycoside.
Chapter 1 gives a brief introduction of bacterial polysaccharides, in particular, lipopolysaccharides (LPSs) produced by gram-negative bacteria and also Kdo monosaccharide. The biological functions and biosynthetic pathway of LPSs are also summarized. Chapter 2 provides detailed reviews on chemical methodologies reported in the literature for the synthesis of Kdo. Chapter 3 details the work of this thesis towards the development and synthesis of a per-O-benzylated 1-C-aryl-heptose glycal and its properties in glycosylations. The experimental procedures and spectroscopic data of all synthesized compounds are given in Chapter 4.