Methods Development for the Glycosylation and Microarraying of L-Rhamnose with Applications Toward the Automated Solution-Phase Synthesis of Homogalacturonan and Rhamnogalacturonan I

Nagappayya, Sahana
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This dissertation highlights the concept of glycosylation reaction in carbohydrate synthesis and the effect of electron withdrawing protecting groups on the a/b selectivity at the anomeric center of the L-rhamnose donor for glycosolsytion with L-rhamnose acceptor. Obtaining a b-linkage in the glycosylation reaction of L-rhamnose is a challenging problem and the role and choice of the electron-withdrawing participating and non-participating groups in this regard are highlighted.

The approach of solution phase automated oligosaccharide synthesis is described, with its application to synthesize plant polysaccharides homogalacturonan and rhamnogalacturonan-I. The synthesis of the various building blocks to make these backbones is described with a discussion of the a/b selectivity of galacturonic acid, and the choice of protecting groups on these building blocks. The automated solution phase synthesis is based on fluorous-tagging of the oligosaccharide chain and purification at each step is perfomed by the Fluorous Solid Phase Extraction (FSPE). The application of FSPE to purify the growing oligosaccharide chain on the automated solution phase platform is explained in detail.

Finally, the development of a new fluorous ditag for carbohydrate microarray is described along with its application to carbohydrate microarrays to analyze the binding ability of the fluorous-tagged carbohydrate with plant lectin on fluorous coated glass slides. This new flourous tag developed is tagged to simple monosaccharides and its performance on microarray studies is described. A comparative study to test the potency of the traditional flourous tag and a di-tag is carried out for the microarray of simple monosaccharide, which showed that the di-tag was superior in microarray formation.

Fluorous, Glycosylation, Homogalacturonan, L-Rhamnose, Microarray, Rhamnogalacturonan