The assembly of oligosaccharides from "standardized intermediates": beta-(1----3)-linked oligomers of D-galactose.
Several 2-O-benzoyl-4,6-di-O-benzyl-3-O-R-alpha-D-galactopyranosyl chlorides, designed as general precursors of beta-linked, interior D-galactopyranosyl residues in oligosaccharides, were tested in a sequential synthesis of the galactotriose beta-D-Galp-(1----3)-beta-D-Galp-(1----3)-D-Gal (19). The chlorides having R = tetrahydro-2-pyranyl and tert-butyldimethylsilyl gave excellent results, whereas those having R = 3-benzoylpropionyl and chloroacetyl were unsatisfactory. An activated disaccharide block (17), having R = 2,3-di-O-benzoyl-4,6-di-O-benzyl-beta-D-galactopyranosyl, was also prepared and tested as a glycosyl donor. The coupling of 17 to 1-propenyl 2-O-benzoyl-4,6-di-O-benzyl-alpha-D-galactopyranoside (14), in the molar ratio 1.13:1, gave 64% of a trisaccharide derivative (18) that could be converted into 19. This latter synthesis of 19 is efficient because all three galactose units are derived from 14 or its immediate precursor.
D002236:Carbohydrate Conformation; D005690:Galactose; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D009844:Oligosaccharides / Q000138:chemical synthesis*; D009904:Optical Rotation; D010084:Oxidation-Reduction
D007202:Indicators and Reagents; D009844:Oligosaccharides; D005690:Galactose