Synthesis of the trisaccharide repeating unit of the K-antigen from Klebsiella type-63

The benzyl substituted ethyl thioglycoside of L-fucose was found to be a more reactive donor compared to 2-O-benzyl substituted p-tolyl thioglycoside of D-galactose. Using the benzyl substituted ethyl thioglycoside of L-fucose (8), as a donor and the suitably substituted p-tolyl thioglycoside of D-galactose (7) as acceptor, the p-tolyl thioglycoside of the disaccharide, 9, was prepared. This disaccharide donor was allowed to react with a suitably protected galactopyranosyluronic acid acceptor, 16, to give the trisaccharide repeating unit of the K-antigen from Klebsiella type 63.