Stereoselective Study On O-glycosidation With Lewis Acid System:SnCl4/CF3COOAg And Microwave Assisted Technology In Glycochemistry

Saccharides play a very important role in life sciences. As known, a variety of biological recognition events such as bacterial and viral infection, cancer metastasis and inflammatory reactions are dependent upon carbohydrates. Up to date, the saccharide study on novel medicines and biotechnology has become one of hot areas, especially developing biological glycoconjugates with activity.In this dissertation, we studied the-reaction conditions for regioselective deacetylation on the C-2position of glucopyranoside, and propossing the mechanism of anomeric effect on the process of O-glycosidation the configuration at the position of anomeric carbon was proposed when alcohols participated as a ligand. Additionally, the microwave-assisted technology was introduced into O-glycosidation as a green synthesis for arbino and its analogouses.1. In glycochemistry, the region-and stereo-selctivity for free hydroxyl groups has become a very important issue, which is involed in the structure design of carbohydrates, the synthesis of nature carbohydrate, and the introducing of pharmacophore. Moreover, it’s important to the synthesis of oligosaccharides and the configuration inversion of hydroxyl group. Since acetyl group has been widely used as a protecting group for hydroxyl groups in carbohydrate chemisty, we focused on the regioselective deacetylations. We choosed penta-acetate glucose with Lewis acids as a catalyst to successfully realize the regioselective deacetylation of C-2position with the highest yield (47%) under mild condition. the mechanism of C-2deacetyaltion and the effect of diffient Lewis acids were discussed. In addition,2-deoxy sugar based on the former research was synthesized.2. In carbohydrate chemistry, the configurations of C-X (X=C, O, N, S) bond at the position of anomeric carbon have a great effect on the stabiliby of the physical characteristics, biological nature and activity. Exactly, the two isomers with the only difference in anomeric carbon positon can show completely different properties from physics to biology. In this dissertation, we well discussed anomeric effect on the synthesis of O-glycosation using two catalyst systems (AgOTfa/SnCl4and SnCl4). Two mechanisms are propersed for the kind of reactions and the catalyst system. Interestingly, the alcohol structure plays role in the configuration at the position of anomeric carbon. In contast with the reported mechanism by Kishi. We propose a new explanation for this kind of reaction with similar reaction condition.3. As a green technology, the microwave-assisted technology was widely used in the organic synthesis. For glycochemisty, it’s was also proved to be an effiective condition to distintly shorten the reaction time and increase yield in the synthesis of arbino analogouses has several shortages, such as expensive, too long time, low yield. By using the microwave-assisted technology, we have successfully increased the yield of the analogouses (compound43,44) from17.6%to38.4%. Moreover, we directly synthesized arbino with Montmeonrilonite as a reusable solid acid catalyst by using the microwave-assisted technology.