Abstract
Chemoenzymatic synthesis, which combines the structural flexibility of organic synthesis and high specificity and efficacy of enzymatic synthesis, is applied in this research to synthesize oligosaccharides effectively. Herein, tumor-associated carbohydrate antigens SSEA-3, DSGb5, and multisialylated oligosaccharides library were synthesized by chemoenzymatic strategy. The syntheses of tumor-associated antigens were performed by first using enzymes GalK, and RmlA to generate UDP-Gal and LgtC to catalyze the formation of Gal-1,4-Lac linkage to give trisaccharide-Gb3. Following by chemical glycosylation of protected Gb3 with disaccharide and stepwise deprotection, SSEA-3 was acquired in 10 steps from Gb3 with total yield 23%. Then, SSEA-3 underwent chemical sialylation giving monosialylayed hexasaccharide and then enzymatic transformation by gave 2,3- sialyltransferase renal carcinoma antigen DSGb5 to accomplish the first total synthesis of DSGb5. In the construction of multisialylated oligosaccharide library, the core structure, Gal-1,3-GalNAc, was sialylated by chemoenzymatic strategy. The library was composed of seven oligosaccharides differed by the number (or position) of sialylated sites. These oligosaccharides will be immobilized on microarray slide and their binding affinities with Siglecs are undergoing.