Synthesis of Bacterial Oligosaccharides from N. meningitidis and Mechanistic Details of Stereoselective Glycosylations Using a Novel Bicyclic Donor

Abstract: This thesis includes two parts. The first part, comprising Chapters 3, 4 and 5, describes the synthesis of bacterial oligosaccharides. In Chapters 3 and 4, the synthesis of branched and phosphorylated oligosaccharide structures corresponding to inner core epitopes of the lipopolysaccharide (LPS) of the Gram-negative bacteria N. meningitidis are discussed. A series of different spacer-equipped, phosphorylated and non-phosphorylated, glycosides has been synthesized as a part of a program involving development of a glycoconjugate-based vaccine against meningitis. Chapter 5 describes the synthesis of a tetrasaccharide corresponding to the repeating unit of the extracellular capsular polysaccharide (CPS) found in S. enteritidis. A short and efficient synthetic route to a trisaccharide acceptor corresponding to the common Gal-Man-Rha backbone found in several Salmonella O-antigen is presented. Further more, the synthesis of a novel tyveloside thioglycoside and the final glycosylation to assemble the complete target tetrasaccharide is reported. The second part, Chapters 6 and 7, describes the development of a novel type of glycosyl donor, a 2N,3O-oxazolidinone protected bicyclic thioglycoside. This donor can be used in stereoselective glycosylations where, by tuning the reaction conditions, either complete α- or β-selectivity can be obtained from the same donor/acceptor system. A mechanistic explanation for this behaviour, involving initial formation of the β-anomer followed by a AgOTf-catalyzed in situ endocyclic anomerization to yield the more stable corresponding α-anomer, has been established. The suggested mechanism was supported by a series of NMR-experiments. Finally, in Chapter 7, the synthesis and use of a galacto-configured 2N,3O-oxazolidinone donor for the synthesis of a serine 2-acetamido 2-deoxy galactoside, a versatile building block for the synthesis of mucin O-glycan core structures, is discussed.