SYNTHESES OF 3 INTERGLYCOSIDIC ISOMERS OF N-ACETYL-BETA-D-MANNOSAMINYL-L-RHAMNOSES ASSOCIATED WITH O-ANTIGENS OF SEVERAL GRAM-NEGATIVE OPPORTUNISTIC PATHOGENS

We achieved practical, highly stereoselective syntheses of three inter glycosidic isomers of N-acetyl-beta-D-mannosaminyl-L-rhamnoses, among which a beta(1-->4)-isomer corresponds to the repeating unit of the O- antigen of lipopolysaccharide (LPS) from the opportunistic pathogens P seudomonas cepacia O5 and Pseudomonas aeruginosa X (Meitert). The othe r isomers are a beta(1-->2)-disaccharide, a constituent of LPS from Es cherichia coli O1A, and an artificial beta(1-->3)-isomer. The disaccha rides were obtained by simple three-step reaction sequences from 2-(be nzoyloxyimino)-2-deoxyglycosyl halides (mannosamine progenitor). beta- Selective glycosylations of appropriately protected L-rhamnosyl accept ers were performed. Subsequent reduction of the 2-acyloxyimino functio n to an amino group, N-acetylation, and removal of the protecting grou ps provided the target disaccharides. C-13-NMR and nuclear Overhauser effect spectra proved to be useful for structural determination of the positional isomers of the disaccharides.