Synthesis Of 1,1’-Disaccharides Modulated By Organic Reagents And Lev Controlled Glycosylation Via Remote Participation

1,1’-disaccharides,as structural units of various natural products,have unique structures and biological activities.Therefore,the synthesis of 1,1’-disaccharides and their derivatives has been widely concerned,committed to the development of new glycosylation methods for more efficient,mild,and high stereoselective synthesis of1,1’-disaccharides.This thesis mainly focuses on the methodology of the stereoselective construction of 1,1’-O-glycosidic bonds and 2-amino-1,1’-S-disaccharides using organic reagents.Ynamide are a kind of special alkyne amines with electron-withdrawing groups attached to nitrogen atom,the dual chemical characteristics of electrophilicity and nucleophilicity endow ynamide with rich and diverse reactivity.We introduced ynamide as a leaving group in the glycosylation process,which has good leaving performance and successfully mediated the synthesis of 1,1’-O-disaccharides by a onepot method from glycosyl hemiacetals.Using this strategy,most of the hemiacetal substrates can obtain the corresponding 1,1’-O-disaccharide products in good yield and stereoselectivity,moreover,rhamnose and 2-NPhth-peracetylglucose hemiacetal can generate single configuration 1,1’-O-disaccharide with excellent yield and stereoselectivity.After that,based on our group’s interest in organothiourea catalysts and 2-amino-1,1’-S-disaccharides,we have developed a bifunctional organothiourea catalysis method for the stereoselective synthesis of 2-amino-1,1’-S-disaccharides using 2-nitroglycals.The method has the characteristics of mild reaction conditions,good stereoselectivity,high yield and wide substrate range.In addition,the method was successfully applied on the synthesis of the thiolated 2,2’-diamino-1,1’-disaccharide fragment of bioactive nature product tunicamy-cins.In addition,convergent synthesis is a common and efficient strategy in oligosaccharide synthesis,but the selectivity and yield of the glycosylation products are often disappointing due to the complex stereo structure of oligosaccharide donor and receptor.It is important to develop more efficient stereoselective glycosylation.Therefore,this Thesis explores the stereoselective glycosylation of disaccharide donors controlled by remote participation of levulinoyl(Lev)group via hydrogen bond.The β-selectivity was significantly improved by this method and the problem in glycosylation of high branched galactose acceptors and donors was solved.