Synthesis of 2 -Azidoethyl Trisaccharide,$\alpha-D-Gal-(1\righarrow2)-6d-\alpha-D- Altro-Hepp-(1\rightarrow3)-\beta$-D-GlcNAc, an O-Antigenic Repeating Unit of C.jejuni O:23 and O:36

A trisaccharide, the O-antigenic repeating unit of C. jejuni serotype O:23 and O:36, was synthesized as a 2 -azidoethyl glycoside by block addition of perbenzylated thiogalactoside donors to $\alpha$-altroHepp-(1$\rightarrow$3)-GlcNPhth disaccharide acceptor in presence of IDCP promoter. The $\alpha$-linked altroheptopyranoside moiety in the glycosyl acceptor was effectively prepared by Swern oxidation of $\alpha$-mannohepp-(1$\rightarrow$3)-GlcNPhth disaccharide followed by mild reduction with1 $NaCNBH_3$.