Carbohydrate-protein interactions are important for the tuning of many
biological processes. Tools are required to investigate the carbohydrate
recognition domains. Several examples are presented in this work.
The first project consists in the synthesis of neoglycoconjugates for binding studies. Here a simple and efficient route to functionalise chitobiose, chitotriose and chitotetraose with a suitable linker avoiding protecting group chemistry is described. Unprotected chitooligomeres were used as starting material. After amination of the anomeric position of the saccharides, the linker was attached by amide formation. An amide bond was chosen to mimic the peptide bond.
Two projects discuss the synthesis of a pentasaccharide and a heptasaccharide. Using as many identical building and reactions as possible in both the synthesis, the oligosaccharides was assembled following a linear pathway. For the pentasaccharide synthesis, a convergent pathway was attempted first. Starting respectively with a monosaccharide or a disaccharide, each sugar was added after the other, usually followed by a protecting group manipulation. Experience gained
during the pentasaccharide synthesis for protecting group manipulation, strategic group pattern and glycosylation was used for the heptasaccharide synthesis. 1,2-cis glycosylation was improved via a new one-pot procedure. At the end, a hydrogenolysis provided the fully deprotected target molecule.
The last project deals with selenoglycosides. They are intended to improve structure elucidation of lectins by X-Ray crystallography. Since both a and β selenoglycosides are of interest, a route to the two anomers using a common precursor was investigated. The β-selenoglycosides of common mono- and disaccharides were prepared. The respective glycosyl halides were added to the "in situ" reduced dimethyldiselenide. The anomerisation of the β anomers were performed using BF3·OEt2• This route was applied on a H1/Lewisb determinant as well. The major problem in this part of the project was to obtain the β orientation of the selenomethyl group without using a participating group. A solution was eventually found by employing a large excess of the reducing agent during the introduction of the seleno group as a smaller excess led to an a/β mixture.