Study On The Reaction Of Kdo Acetylate And Iodine Glycosides

3-Deoxy-D-manno-octulosonic acid(Kdo)is an indispensable constituent of the cell wall lipopolysaccharides(LPS)of Gram-negative bacteria.It plays a vital role in growth and pathogenicity of bacteria.Natural Kdo glycosides exist in either ?-and?-anomeric configurations.It is important to stereoselectively construct Kdo glycosides for the research and development of antibacterial vaccines,antibiotics and immunology.The presence of the electron withdrawing carboxylate group at the C2 position leads to the higher steric hindrance at C2 position and less stability of oxocarbenium when generated.Due to the absence of a hydroxyl group at the C3 position,the Kdo donor is easy to undergo the elimination to form Kdo glycal,thus reducing the yield of glycosylation.Furthermore,no neighboring group participation is applicable to ensure the high steroselectivity for Kdo glycosylation,thus usually producing a mixture of ?/?isomers.So it is a challenge to synthetize Kdo glycosides with high steroselectivity.Therefore,it is necessary to develop a new and efficient method for the Kdo glycosides.This dissertation includes two major sections:1).Glycosylation using Kdo glycosyl alkynyl esters as donors;2).Glycosylation using Kdo glycosyl iodides as donors.In the the first section,alkynyl esters have been explored as leaving group for Kdo glycosylation.The followings have been done:a).Preparation of three types of Kdo donors;b).Investigation on the glycosylation using different alkynyl ester donors;c).Studies of the substrate scopes with the use of alkynylbenzoate as a glycosyl donor.The results revealed that alkynlbenzoate donor undergoes glycosylation faster than the other donors as well as higher ?-selectivity.Low reaction temperature is beneficial to the ?-selectivity and glycosylation yield and vice versa.In the second section,Kdo glycosylation has been done using Kdo glycosyl iodide as a donor.The followings have been studied:a).Preparation of Kdo ortho-alkynlphenyl thioglycosides;b).Preparation of Kdo glycosyl iodides by treatment of ortho-alkynlphenyl thioglycosides with I2;c).Exploration of glycosylation using the Kdo glycosyl iodides.The glycosylation of Kdo glycosyl iodide with(-)-menthol proceeded smoothly to provide the desired product with high ?-selectivity.