Synthesis of β-d-Galp-(1→3)-β-d-Galp-(1→6)-[β-d-Galf-(1→4)]-d-GlcNAc, a tetrasaccharide component of mucins of Trypanosoma cruzi

The synthesis of free β-d-Galp-(1→3)-β-d-Galp-(1→6)-[β-d-Galf-(1→4)]-d-GlcNAc and the corresponding alditol which has been previously isolated by reductive β-elimination of Trypanosoma cruzi glycoproteins are described. A convergent route was envisioned by condensing an acceptor derivative of β-d-Galf-(1→4)-d-GlcNAc with a donor derivative of β-d-Galp-(1→3)-d-Galp. The trichloroacetimidate method, as well as SnCl4-promoted condensation were utilized for the introduction of the galactofuranosyl unit. On the other hand, the glycosyl-aldonolactone approach, followed by reduction of the lactone with diisoamylborane, and further isomerization to the galactopyranose configuration gave the donor derivative, which was condensed by the trichloroacetimidate method. Moreover, a synthon for the introduction of the β-d-Galp-(1→3)-d-Galf unit is described.