Synthesis of precursors for the dimeric 3-O-SO₃Na Lewis X and Lewis A structures

Stereoselective syntheses of 3-O-SO₃Na-β-Gal-(1 → 4)-β-GlcNAc-(1 → 3)-β-Gal-(1 → 4)GlcNAc-β-OBn (15) and 3-O-SO₃Na-β-Gal-(1 → 3)-β-GlcNAc-(1 → 3)-β-Gal-(1 → 3)-β-GlcNAc-(1 → 3)-β-Gal-(1 → 4)-Glc-β-OBn (25) were accomplished through the use of two novel glycosyl donors, namely, ethyl O-(2,6-di-O-acetyl-3,4-O-isopropylidene-β-D-galactopyranosyl)(1 → 4)-3-O-acetyl-2-deoxy-2-phthalimido-1-thio-6-O-trimethylacetyl-β-D-gl ucopyranoside (8) and ethyl O-(2,6-di-O-acetyl-3,4-O-isopropylidene-β-D-galactopyranosyl)-(1 → 3)-4-O-acetyl-2-deoxy-2-phthalimido-1-thio-6-O-trimethylacetyl-β-D-gl ucopyranoside (18).