Efficient synthesis of the tetrasaccharide repeating unit of the O-antigen of Escherichia coli O174 strain

• A tetrasaccharide corresponding to the O-antigen of E. coli O174 has been synthesized.
• Nitrosyl tetrafluoroborate mediated glycosyl trichloroacetimidate activation was applied.
• Thioglycoside derivative has been used as glycosyl donor in the glycosylation reaction.
• Removal of benzyl ether was done using catalytic transfer hydrogenation.
• A late stage oxidation has been carried out using TEMPO and BAIB.

The tetrasaccharide repeating unit of the O-antigen of Escherichia coli O174 strain was synthesized applying sequential glycosylations of suitably functionalized monosaccharide intermediates. Activation of glycosyl trichloroacetimidate derivatives using nitrosyl tetrafluoroborate (NOBF4) has been used during the synthesis. The glycosylation steps were high yielding with satisfactory stereo outcome.

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