The glycosylation reaction is a pivotal reaction in creating new and complex oligosaccharides. These biologically relevant compounds must be obtained in enough quantity and in pure, well... Show moreThe glycosylation reaction is a pivotal reaction in creating new and complex oligosaccharides. These biologically relevant compounds must be obtained in enough quantity and in pure, well-defined form. Organic synthesis can provide these compounds, but efficient methods regarding their selective synthesis are often absent. Every saccharide building block is coupled to another in a glycosylation reaction, which must be both regioselective and stereoselective. For the stereoselectivity of this reaction common protocols are not generally applicable. This thesis investigates the stereoselectivity of the glycosylation reaction from the standpoint of the sugar acceptor, rather than from the sugar donor which has been the focal point for many decades. The results obtained showed that a scale of selectivities can be obtained by changing the reactivity of the acceptor. The trends within the acceptor reactivity are valid for all donors studied, but some donors are more susceptible than others to changes in acceptor reactivity. In the second part of this thesis the spatial identity of intermediates in the glycosylation reaction are investigated. Experimental and computational techniques combined resulted in an effective model to understand the glycosylation reaction on the SN1-side of the reaction spectrum when different functional groups are located on the carbohydrate donor. Show less
This Thesis reports on research aimed at the assembly of acidic and zwitterionic polysaccharides of bacterial origin, using suitably protected 1-thioglycoside residues. Thioglycosides are... Show moreThis Thesis reports on research aimed at the assembly of acidic and zwitterionic polysaccharides of bacterial origin, using suitably protected 1-thioglycoside residues. Thioglycosides are attractive monosaccharide building blocks because of their high stability towards the diverse reaction conditions used in functional group manipulations. Recently, the use of 1-thioglycosides has been stimulated by the advent of the 1-benzenesulfinylpiperidine (BSP)/triflic anhydride (Tf2O) and the diphenylsulfoxide (Ph2SO)/Tf2O activator system. These sulfonium ion based activators proved to be efficient promoters for glycosylations in which inreactive (disarmed) 1-thioglycosides are employed. Furthermore, one-pot orthogonal and chemoselective oligosaccharide synthesis strategies that involve the use of 1-thioglycosides in combination with the above mentioned sulfonium based activator systems have proven to be feasible. Show less
