Chemical synthesis of the O-antigen repeating unit of Actinobacillus actinomycetemcomitans serotype f

Herein, we report the total synthesis of the trisaccharide repeating unit of the O-antigen of Actinobacillus actinomycetemcomitans serotype f. The trisaccharide comprising of alpha-(1-2) and alpha-(1-3)-linked L-rhamnopyranosides backbone with the latter rhamnose containing a branching N-acetyl-D-galactosaminopyranoside at the C2-O via a beta-glycosidic bond was synthesized by two methods. Initially, the protected trisaccharide has been synthesized by step-wise assembly of the monosaccharide building blocks and subsequently the former was synthesized by the one-pot assembly of the latter components. The synthesized trisaccharide contains an aminoethyl linker appended as an O-glycoside at the reducing end, thereby providing scope for further conjugation for different applications.