Abstract
The glycoconjugates outside the cell membrane play an important role in cell-cell interaction as well as cell recognition1. The bio-functions of virus invasion and tumor proliferation are related to the glycoconjugates which have already been revealed in many studies. Chemical synthesis of glycoconjugates can help establish those bio-functions between cells. The glycoconjugates are composed of saccharide units, such as glucose, idose, galactose, mannose … etc. Saccharide units are connected to one another by glycosidic bond formed between the hemiacetal amomeric center of one sugar and the hydroxyl group of another sugar. However, each saccharide contains multiple hydroxyl groups, so the regioselective protection of hydroxyl groups and the stereoselectivity of glycosidic bond would be the biggest challenges of carbohydrate chemistry.In this thesis, we focus on synthetic chemistry of mannose saccharide unit including one-pot regioselectively protection and deprotection, as well as on glycosylation. There are still some problems which need to be addressed in the synthetic chemistry of mannose, for example: (1) Regioselective formation of acetal protecting groups (the competition among 2,3-acetal formation and the 4,6-acetal formation)；(2) Stereoseletive formation of 2,3-acetal functional groups (the selectivity of exo and endo)；(3) Stereoselective formation of glycosidic bond. In the thesis we use 2,3;4,6-tetrahydroxyl compound 113 as starting material, on acetalization gives 2,3;4,6-dibenzylidene compound 115 94%, The stereoselectivity of the five membered acetal ring is good (exo/endo = 99/1). This dibenzylidene compound was studied for selective acetal ring open reaction. A combination of the two strategies, we successfully developed the one-pot regioselective protection method of mannosides. Finally we studied glycosylation as well, and got α mannosides. The reaction condition including the reagents, catalysts, solvents, and temperature will be discussed in detail, and the identification of stereochemistry of dibenzylidene compound and glycosylation product will be discussed subsequently. We believe our preliminary result can avail synthetic chemistry of mannose in the future.