Synthesis of tetrasaccharide repeating unit of the O-antigen from enterohemorrhagic Escherichia coli O157 in the form of its 2-(trimethylsilyl) ethyl glycoside

Two α-linked disaccharide derivatives, ethyl 3,4,6-tri-O-acetyl-2- azido-2-deoxy-α-D-galactopyranosyl-(1 → 2)-4-azido-3-O-benzyl-4,6- dideoxy-1-thio-α-D-mannopyranoside (10) and 2-(trimethylsilyl)ethyl 3-O-acetyl-4-O-benzoyl-2-O-benzyl-α-L-fucopyranosyl-(1 → 4)-2,3-di-O-benzyl-6-O-tert-butyldiphenylsilyl-β-D-glucopyranoside (16), were prepared from appropriate monosaccharide synthons. The disaccharide 16 was deacetylated and debenzoylated to afford the acceptor 17, which was allowed to react with the donor 10 to afford a tetrasaccharide derivative 18. This tetrasaccharide was transformed in three steps into 21, the desired repeating unit of the antigen from enterohemorrhagic E. coli type O157.