Chemical synthesis of the pentasaccharide repeating unit of the O-specific polysaccharide from Escherichia coli O132 in the form of its 2-aminoethyl glycoside

Abstract

The total chemical synthesis of the pentasaccharide repeating unit of the O-polysaccharide from E. coli O132 is accomplished in the form of its 2-aminoethyl glycoside. The 2-aminoethyl glycoside is particularly important as it allows further glycoconjugate formation utilizing the terminal amine without affecting the stereochemistry of the reducing end. The target was achieved through a [3 + 2] strategy where the required monosaccharide building blocks are prepared from commercially available sugars through rational protecting group manipulation. The NIS-mediated activation of thioglycosides was used extensively for the glycosylation reactions throughout.

Chemical Synthesis of β-l-Rhamnose Containing the Pentasaccharide Repeating Unit of the O-Specific Polysaccharide from a Halophilic Bacterium Halomonas ventosae RU5S2EL in the Form of Its 2-Aminoethyl Glycoside

“…Considering the low yield with the picoloyl-induced HAD, we explored the remote participation of the 6-O-acyl group for α-selectivity. 24 When the known trichloroacetimidate derivative 9 25 was reacted with the same rhamnosyl acceptor 10 21 in the presence of TMSOTf, the sole α-linked disaccharide 4 was obtained in 65% yield (Method II, Scheme 4). Therefore, the remote participation of the 6-O-acyl group 26 was found to be more effective for the α-selective glucosylation in this particular case.…”

“…The reaction resulted in the formation of the desired sole α-linked disaccharide 25 in 38% yield only (Method I, Scheme ), and the acceptor and hemiacetal of the donor were recovered by flash chromatography. Considering the low yield with the picoloyl-induced HAD, we explored the remote participation of the 6- O -acyl group for α-selectivity . When the known trichloroacetimidate derivative 9 was reacted with the same rhamnosyl acceptor 10 in the presence of TMSOTf, the sole α-linked disaccharide 4 was obtained in 65% yield (Method II, Scheme ).…”

Chemical Synthesis of the Linker‐Armed Trisaccharide Repeating Unit of the O‐Antigen from Pseudomonas putida BIM B‐1100

“…[32] Next, the C-6 position of the reducing end ManpNAc moiety was oxidized by TEMPO in the presence of iodosobenzene diacetate (IDBA) [33] to furnish the corresponding β-ManpNAcA unit. Zemplén de-O-acetylation [34] using NaOMe in MeOH followed by hydrogenolysis using 10 % Pd(OH) 2 /C in methanol at ambient temperature with a H 2 balloon [35] afforded the target trisaccharide 1 in 62 % overall yield (Scheme 5).…”