Deprotection Of The 2, 2, 2-trichloroethyl Group At The Anomeric Oxygen Of Carbohydrates And Stereoselective Synthetic Studies On β-glycosyl Fluorides

The thesis includes two parts:1. deprotection of the 2,2,2-trichloroethyl group at the anomeric oxygen of carbohydrates.2. synthetic studies onβ-glycosyl fluorides.1. The 2,2,2-trichloroethyl (TCE) moiety has been the most widely used haloethyl protecting group for carbon, sulfuric and phosphorus acids as a result of the mild, nonhydrolytic conditions used for their cleavage. It has been successfully used for protection of the anomeric centre against standard reaction conditions in the synthesis of oligosaccharides and glycoconjugates. However, only a few methods are available for its removal. We have demonstrated a facile, highly efficient removal of TCE protecting groups in the presence of either acetyl or benzyl protected TCE O-glycosides (15 examples) with the Zn dust and ammonium chloride in acetonitrile. The time required for the desired deprotective compounds is remarkably short (5min) and the yield of the deprotection reaction is exceptionally high (≥95%). The applied reagents, zinc dust doesn't need to be activated before use. Furthermore, the reaction could be done in neutral media and in large scales (10mmol). Thus, we expect that this methodology will find widespread use in the deprotection of this class of protecting group.2. Glycosyl fluorides, which are substituted in anomeric carbon, are important materials for the synthesis of glycosides and oligosaccharides, and they are a very valuable and versatile group of synthetic intermediates widely used in the field of carbohydrate chemistry. Moreover,β-glycosyl fluorides can be used as a donor in the synthesis ofα-glycosides. However, there were few good methods of the direct conversion of lactols intoβ-glycosyl fluorides. We have demonstrated a highly efficient stereoselective synthesis ofβ-glycosyl fluorides from lactols with the 5-Iodooctafluoro-3-oxapentanesulphonyl fluoride as the fluorinating agent in the presence of DBU as the base. Nineβ-glycosyl fluorides have been synthesized through this method. The advantages of the present procedure are:the method is simple, the time required for this reaction is short, moreover the reactions precede with highly stereoselectivities with acetyl and benzyl protections, which make this idea more worthy for further research.