Synthesis of the tetrasaccharide related to the repeating unit of the antigen from Shigella dysenteriae type 5 Original Research Article

Starting from l-rhamnose, d-mannose and 2-amino-2-deoxy-d-glucose hydrochloride, two disaccharide blocks, namely, ethyl 2,4-di-O-benzyl-3-O-[(R)-1-(methoxycarbonyl)ethyl]-α-l-rhamnopyranosyl-(1→3)-2-O-acetyl-4,6-di-O-benzyl-1-thio-α-d-mannopyranoside and 2-(trimethylsilyl)ethyl 2-O-acetyl-3,6-di-O-benzyl-α-d-mannopyranosyl-(1→3)-4,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranoside, were synthesised and then allowed to react in the presence of N-iodosuccinimide and trifluoromethane sulfonic acid to give a tetrasaccharide derivative. This compound was converted into 2-(trimethylsilyl)ethyl 2,4-di-O-benzyl-3-O-[(R)-1-(methoxycarbonyl)ethyl]-α-l-rhamno-pyranosyl-(1→3)-2-O-acetyl-4,6-di-O-benzyl-α-d-mannopyranosyl-(1→4)-2-O-acetyl-3,6-di-O-benzyl-α-d-mannopyranosyl-(1→3)-2-acetamido-4,6-di-O-benzyl-2-deoxy-β-d-glucopyranoside, which on hydrogenolysis, afforded the methyl ester 2-(trimethylsilyl)ethyl glycoside of the tetrasaccharide related to the repeating unit of the O-antigen from Shigella dysenteriae type 5.