Synthesis of the Sda determinant and two analogous tetrasaccharides

To contribute to the possibility of studying in greater detail the biological significance of Sda-containing glycans as occur in Tamm-Horsfall glycoprotein, the following three spacerlinked tetrasaccharides have been synthesized: the Sda determinant α-Neu p5Ac-(2 → 3)-[β-d-GalpNAc-(1 → 4)]-β-d-Galp-(1 → 4)-β-d-GlcpNAc-(1 → O)(CH2)5NH2 (1), the Gal-analogue α-Neu p5Ac-(2 → 3)- [β-d-Galp-(1 → 4)]-β-d-Galp-(1 → 4)-β-d-GlcpNAc-(1 → O)(CH2)5NH2 (2), and the GlcNAc-analogue α-Neu p5Ac-(2 → 3)-[β-d-GlcpNAc-(1 → 4)]-β-d-Galp-(1 → 4)-β-d-GlcpNAc-(1 → O)(CH2)5NH2 (3). The general trisaccharide acceptor 5-azidopentyl (methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-non-2-ulopyranosylonate)-(2 → 3)-(2,6-di-O-benzyl-β-d-galactopyranosyl)-(1 → 4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranoside was prepared, using methyl (phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-d-glycero-d-galacto-non-2-ulopyranosid)-onate as the sialyl donor. For the syntheses of 1, 2, and 3 the glycosyl donors 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-α-d-galactopyranosyl bromide, 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide, and 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl trichloroacetimidate, respectively, proved to be the most suitable.