Studies On Gold(?)-Catalyzed Steroselective Glycosylation With Kdo O-alkynyl Benzoate As Donor

The outer membrane of the Gram-negative bacteria is an asymmetric liposome bilayer,including glycerol phosphate in the inner layer of the membrane and lipopolysaccharide(LPS)of the outer layer.The core structure of the LPS always has at least one Kdo that can maintain the integrity of the cell membrane by attacking foreign chemical substances and is essential in the normal growth of bacterial cells.Moreover,Kdo,as a unique eight-carbon sugar unit that exists only in the bacterial and plant surface structures,has a strong immunological activity and has great potential to be developed as antimicrobial vaccines and diagnostic tools.Natural Kdo glycosides have both a and ? configurations.Although ?-Kdo glycosides are rare in nature,they still be found on the cell surface polysaccharides of E.coli,Campylobacter jejuni,Haemophilus influenzae,Neisseria meningitidis,Pasteurella and other Gram-negative bacterial.So it is important to synthesize ?-Kdo glycosides?In this paper,o-alkynyl benzoate was used as the Kdo leaving group.By exploring the glycosylation conditions in which Kdo o-alkynyl benzoate was coupled with alcohol,the best conditions could be screened out.Then the Kdo o-alkynyl benzoate was glycosylated with various alcohols and ?-Kdo glycosides could be obtained with high stereoselectivity.Based on this method,we synthesized the Kdo monosaccharide which reducting end is C5-linker and it could be further linked to the carrier protein and the surface of the chip for biological studies.This glycosylation method laid the foundation for the future synthesis of ?-Kdo oligosaccharides.