| In Nature, GT-B glycosyltransferase enzymes catalyze the transfer of carbohydrates from sugar nucleotide donors to natural product acceptors with exquisite chemo-, regio-, and stereoselectivity, invoking interest in using these biocatalysts in glycosylation engineering. One major limitation to investigating the scope and synthetic utility of these enzymes remains poor access to sugar nucleotide substrates, as these compounds are notoriously difficult to chemically synthesize and purify.;In this thesis, an improved synthetic route to the 2,6-dideoxysugar L-digitoxose and its conversion to UDP-alpha/beta-L-digitoxose are described. Furthermore, the chemical synthesis and purification of eleven non-deoxy- and 6-deoxysugar nucleotides via the indirect coupling of sugar-1-phosphates with N-methylimidazole-activated nucleoside 5'-monophosphates, as well as the direct coupling of glycosyl iodides and bromides with nucleoside 5'-diphosphates, is discussed. Of particular importance is the development of the first stereoselective chemical synthesis of the biologically relevant sugar nucleotides GDP-alpha-D-mannose and GDP-beta- L-fucose via coupling of nucleoside 5'-diphosphates and acylated glycosyl bromides using neighbouring group participation. In addition, the enzymatic synthesis of sugar nucleotides is investigated using three wild-type thymidylyltransferase enzymes, resulting in the preparation of fifteen sugar nucleotides. The broad substrate flexibility demonstrated by these biocatalysts in initial assays provides impetus to further examine their synthetic potential. |
