Synthesis of inner core antigens related to Chlamydia, Pseudomonas and Acinetobacter LPS

Abstract

Chemical syntheses of inner core determinants have been performed to provide defined artificial antigens (BSA-glycoconjugates) for characterization of monoclonal antibodies directed against important epitopes residing in the inner core of bacterial lipopolysaccharides. Efficient block synthesis of Kdo oligosaccharides has been employed to prepare the allyl glycoside [5] corresponding to the Chlamydia-specific Kdo trisaccharide epitope, to be used in crystallization and NMR (transfer NOe) experiments. Human pathogenic strains of Pseudomonas aeruginosa of RNA group I contain a highly phosphorylated heptose region with a 7- O-carbamoyl L- glycero-D- mannoheptose moiety which may be exploited as immunochemical marker for pathogenic Pseudomonas species. The 7- O-carbamoyl-substituted heptoside [12] as well as the disaccharides 7- O-carbamoyl-L- gro-α-D- manHep p- (1→3)-L- gro-α-D- manHep p-(1→O-Allyl) [23] and α-D-Gal pNAc-(1→3)-L- gro-α-D- manHep p-(1→O-Allyl) [30] were synthesized via regioselective formation of a 6′,7′- O-carbonate group followed by ring opening with NH3/NH4HCO3 to give the 7- O-carbamate in high yields. Finally, glycosides of the Kdo-isosteric D- glycero-D- talo-2-octulosonic acid (Ko) occurring in Acinetobacter spp. have been prepared via intermediate orthoester formation and TMSO-triflate-catalyzed rearrangement into α-ketosides. Coupling with a Kdo bromide donor and deblocking afforded the disaccharide α-Kdo-(2→4)-α-Ko-(2→O-Allyl) [43].