Sialyliation Study Of Electron Rich Sialic Acid With The Aid Of C-1 Group Participation

N-acetylneuraminic acid(Neu5Ac)is mainly occurred on the cell surface.Neu5Ac and its derivatives have a relevant with the recognition.binding and dissociation of cell membrane.Moreover,Neu5Ac is mostly linked to other sugars in the form of a-sialosidic bonds.and constructing the a-sialosidic bonds is difficult due to the influence of its anomeric effect and the?-configuration is relatively stable.In addition,Neu5Ac has a methylene moiety at the C-3 position,so the neighbor participation effect which often used in glycosylation is not available.Electron-donating groups can stabilize the positively charged pyranoside ring;electron-withdrawing groups is not conducive to the positive charge on the ring.In the synthesis of oligosaccharides.the acetyl group is an electron-withdrawing protecting group.and the benzyl group is an electron-donating protecting group.By using benzyl protection,we can construct a sialic acid donor with better activity at low temperature.At the same time.we introduced a certain modification to the carboxyl group at position C-1,allowing the modified group to participate in the glycosylation reaction.We hope that through the form of the SN2 reaction mechanism,the hydroxyl group of the acceptor can attack the C-2 position of N-acetylneuraminic acid to afford a configuration.Previously,most researches were focused on electron-withdrawing groups such as acetyl.For electron-donating groups such as benzyl or benzyloxymethyl ether,there is no detailed research report yet.In this essay,the first chapter mainly introduces sialic acid and its derivatives.The functions of sialic acid,such as the identification of pathogen lectins,and the development of the brain of the fetus are briefly introduced.At the same time.the construction methods of the currently popular sialic acid donors and the achievements of predecessors in this area are also described.In Chapters 2 and 3.we constructed a variety of sialic acid donors with electron rich protecting groups and conducted in-depth studies on their glycosylation reactions.The donor we constructed with electron donating group and C-1 participating group can indeed improve the yield and selectivity.After continuous efforts to optimize the reaction conditions?the final sialic acid donor D3 we constructed with good yield and selectivity of several corresponding natural linkages.We finally adopted p-TolSCl/AgOTf as the activation conditions.In the subsequent glycosidylation reaction,we obtained good results:The donor showed good results in construction of natural primary and secondary alcohol linkages,and it was also demonstrated that benzyl-protected ethyl thiosialic acid donors had better activity and selectivity than benzyloxomethyl ether-protected p-toluene thiosialic acid donors.