Plesiomonas shigelloides, a pathogen responsible for frequent outbreaks of severe travelers' diarrhea, causes grave extraintestinal infections. Sepsis and meningitis due to P. shigelloides are associated with a high mortality rate as antibiotic resistance increases and vaccines are not available. Carbohydrate antigens expressed by pathogens are often structurally unique and are targets for developing vaccines and diagnostics. Here, we report a total synthesis of the highly functionalized trisaccharide repeating unit 2 from P. shigelloides serotype 51 from three monosaccharides. A judicious choice of building blocks and reaction conditions allowed for the four amino groups adorning the sugar rings to be installed with two N-acetyl (Ac) groups, rare acetamidino (Am), and d-3-hydroxybutyryl (Hb) groups. The strategy for the differentiation of amino groups in trisaccharide 2 will serve well for the syntheses of other complex glycans.
The gut pathogen Clostridium bolteae has been associated with the onset of autism spectrum disorder (ASD). To create vaccines against C. bolteae,itisimportant to identify exact protective epitopes of the immunologically active capsular polysaccharide (CPS). Here,aseries of C. bolteae CPS glycans,u pt oa no ctadecasaccharide,w as prepared. Keyt o achieving the total syntheses is a[2+ +2] coupling strategy based on a b-d-Rhap-(1!3)-ad -Manp repeating unit that in turn was accessed by astereoselective b-d-rhamnosylation. The 4,6-O-benzylidene-induced conformational locking is ap owerful strategy for forming a b-d-mannose-type glycoside.Anindirect strategy based on C2 epimerization of b-d-quinovoside was efficiently achieved by Swern oxidation and borohydride reduction. Sequential glycosylation, and regioselective and global deprotection produced the disaccharide and tetrasaccharide,u pt ot he octadecasaccharide.G lycan microarray analysis of sera from rabbits immunized with inactivated C. bolteae bacteria revealed ahumoral immune response to the diand tetrasaccharide,b ut none of the longer sequences.T he tetrasaccharide may be ak ey motif for designing glycoconjugate vaccines against C. bolteae.
Helicobacter pylori, a widespread gastric bacterial pathogen that infects 90 % of the population in developing countries, causes chronic gastritis, peptic ulcers and gastric cancer. Battling H. pylori infection is a serious challenge due to the increased resistance to antibiotics and the lack of vaccines. The lipopolysaccharide covering the H. pylori cell-surface outer membrane is an attractive target for the development of a glycoconjugate vaccine. Here, we report a [3+5] convergent synthesis of an outer core octasaccharide of H. pylori employing just three orthogonally protected building blocks. A synergistic glycosylation strategy enables the creation of five pivotal 1,2-cis-α-glucosidic bonds consist of four types of linkages using just three monomers. This strategy can be expanded to many 1,2-cis-α-gluoside-containing oligosaccharides both in solution and solid phase.
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