Large Scale Synthesis of Two Trisaccharide Spacer Glycosides Corresponding to the Blood Group A and B Determinants Using Thioglycosides and Dimethyl(Thiomethyl)Sulfonium Tetrafluoroborate (DMTSB) as Promoter

Two trisaccharide spacer glycosides, p-trifluoroacetamidophenylethyl 3-O-(2-acetamido-2-deoxy-α-D-galactopyranosyl) — 2 — O — (α-l-fucopyranosyl)-β-d-galactopyranoside and p-trifluoroacetamidophenylethyl 2-O-(α-l-fucopyranosyl)-3-O-(α-d-galactopyranosyl)-β-d-galactopyranoside, corresponding to the human blood group A and B determinants, were synthesized. A key fucosylgalactosyl disaccharide derivative was glycosylated with galactos-aminyl or galactosyl donors, respectively. Dimethyl(thiomethyl)sulfonium tetrafluoroborate was used for thioglycoside activation in all but one coupling reaction. The small scale procedure was further developed for use in a large scale (10–100 g final product) synthesis. Large scale syntheses of some crystalline thioglycoside building blocks are also described.