Abstract
A synthesis of the title trisaccharide (14) is reported. The first step of the synthetic route is stereospecific condensation of 2-acetamido-1, 6-anhydro-3-O-benzyl-2-deoxy-β-D-glucopyranose with 2-methyl-(3, 4, 6-tri-O-acetyl-1, 2-dideoxy-α-D-glucopyrano)-[2', 1' : 4, 5]-2-oxazoline to yield a fully protected β-D-(1→4)-linked disaccharide (8) bearing 2-acetamido-2-deoxy-D-glucopyranose (GlcNAc) at the non-reducing residue. After acetolysis of the 1, 6-anhydro ring of 8, the resulting fully-protected disaccharide is debenzylated to yield chitobiose heptaacetate (10) having a free hydroxyl group at the C-3 position of the reducing GlcNAc. Compound 10 is glycosylated with 2, 3, 4-tri-O-benzyl-α-L-fucopyranosyl bromide by a bromide ion-catalyzed reaction. After removing the protecting groups of the resulting trisaccharide by debenzylation and de-O-acetylation, an anomeric mixture of 14 is obtained as an amorphous solid. CMR spectral data for 14 are also presented.
