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

Starting from L-rhamnose, D-mannose and 2-amino-2-deoxy-D-glucose hydrochlo ride, two disaccharide blocks, namely, ethyl 2,4-di-O-benzyl-3-O-[(R)-1-(me thoxycarbonyl)ethyl]-alpha-L-rhamnopyranosyl-(1-->3)-2-O-acetyl-4,6-di-O-be nzyl-1-thio-alpha-D-mannopyranoside and 2-(trimethylsilyl)ethyl 2-O-acetyl- 3,6-di-0-benzyl-alpha-D-mannopyranosyl- (1-->3)-4,6-di-0-benzyl-2-deoxy-2-p hthalimido-beta-D-glucopyranoside, were synthesised and then allowed to rea ct in the presence of N-iodosuccinimide and trifluoromethane sulfonic acid to give a tetrasaccharide derivative. This compound was converted into 2-(t rimethylsilyl)ethyl 2,4-di-O-benzyl-3-O-[(R)-1-(methoxycarbonyl)ethyl]-alph a-L-rhamno-pyranosyl-(1-->3)-2-O-acetyl-4,6-di-O-benzyl-alpha-D-mannopyrano syl-(1-->4)-2-O-acetyl-3,6-di-O-benzyl-alpha-D-mannopyranosyl-(1-->3)-2-ace tamido-4,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside, which on hydrogenoly sis, afforded the methyl ester 2-(trimethylsilyl)ethyl glycoside of the tet rasaccharide related to the repeating unit of the O-antigen from Shigella d ysenteriae type 5. (C) 2000 Elsevier Science Ltd. All rights reserved.