Synthetic studies toward pyruvate acetal-containing saccharides: En route to the efficient synthesis of Rhizobium-related exopolysaccharide fragments
作者:Elisabeth Eckhardt、Thomas Ziegler
DOI:10.1016/s0008-6215(05)80010-2
日期:1994.11
The disaccharide building block benzyl O-2,3-di-O-benzoyl-4,6-O-[(R)-1-(methoxycarbonyl) ethylidene]-beta-D-galactopyranosyl}-(1 --> 3)-2-O-benzoyl-4,6-O-[(S)-1-(methoxycarbonyl)ethylidene] -alpha-D-glucopyranoside (13), related to a Rhizobium exopolysaccharide, was prepared by coupling various 4,6-O-[(R)-1-(methoxycarbonyl)ethylidene]-D-galactosyl donors (benzoyl-protected chloride 1, pivaloyl-protected chloride 2, and benzoyl-protected fluorides 3 and 4, and trichloroacetimidate 5) with benzyl 2-O-benzoyl-4,6-O-[(S)-1-(methoxycarbonyl)ethylidene]-alpha-D-glucopyranoside (10) and the corresponding 2,3-O-tetraisopropyldisiloxane-protected glucoside 12. The best results, with respect to beta-selectivity and yield of the coupling, were obtained with 5 and 10 in dichloromethane. The beta-linked (13) and alpha-linked (14) disaccharides were efficiently converted via the 1-OH derivatives 17 and 21 into the corresponding trichloroacetimidates 18 and 22. The latter were used for the synthesis of the disaccharide ligands 4,6-(R)-pyruvate-beta-D-Galp-(1 --> 3)-4,6-(S)-pyruvate-beta-D-Glcp-O (CH2)(5)NH2 (20), and 4,6-(R)-pyruvate-alpha-D-Galp-(1 --> 3)-4,6-(S)-pyruvate-beta-D-Glcp-O(CH2)(5)NH2 (24). The corresponding tri- and tetra-saccharide derivatives 4,6-(R)-pyruvate-beta-D-Galp-(1 --> 3)-4,6-(S)-pyruvate-beta-D-Glcp-(1 --> 4)-beta-D-Glcp-O(CH2)(5)NH2 (28) and 4,6-(R)-pyruvate-beta-D-Galp-(1 --> 3)-4,6-(S)-pyruvate-beta-D-Glcp-(1 --> 4)-beta-D-Glcp-(1 --> 4)-beta-D-Glcp-O(CH2)(5)NH2 (36) were obtained similarly.