First synthesis of 5,6-branched galacto-hexasaccharide, the dimer of the trisaccharide repeating unit of the cell-wall galactans of Bifidobacterium catenulatum YIT 4016

Abstract α- d -Galactopyranosyl-(1→6)-[β- d -galactofuranosyl-(1→5)]-β- d -galactofuranosyl-(1→6)-β- d -galactofuranosyl-(1→5)-[α- d -galactopyranosyl-(1→6)]-β- d -galactofuranose, the dimer of the trisaccharide repeating unit of the cell-wall galactans of Bifidobacterium catenulatum YIT 4016, has been synthesized as its dodecyl glycoside 2 by coupling of 2,3,4,6-tetra- O -benzyl-α- d -galactopyranosyl-(1→6)-[6- O -acetyl-2,3,5-tri- O -benzoyl-β- d -galactofuranosyl-(1→5)]-2- O -acetyl-3- O -benzyl-β- d -galactofuranosyl trichloroacetimidate 14 with dodecyl 2,3,4,6-tetra- O -benzyl-α- d -galactopyranosyl-(1→6)-[2,3,5-tri- O -benzoyl-β- d -galactofuranosyl-(1→5)]-2- O -acetyl-3- O -benzyl-β- d -galactofuranoside 16 . The trisaccharide trichloroacetimidate donor 14 and trisaccharide acceptor 16 were regiospecifically prepared by employing 3- O -benzyl-1,2- O -isopropylidene-α- d -galactofuranose 4 as the glycosyl acceptor, and isopropyl 2,3,4,6-tetra- O -benzyl-1-thio-β- d -galactopyranoside 5 and 6- O -acetyl-2,3,5-tri- O -benzoyl-β- d -galactofuranosyl trichloroacetimidate 9 as glycosyl donors.