Oligosaccharides related to tumor-associated antigens. Part 3. Synthesis of the propyl glycosides of the trisaccharide β-D-Galp-(1 → 3)-β-D-GalpNAc-(1 → 3)-α-D-Galp and of the tetrasaccharide α-L-Fucp-(1 → 2)-β-D-Galp-(1 → 3)-β-D-GalpNAc-(1 → 3)-α-D-Galp, components of a tumor antigen recognized by the antibody MBr1

The synthesis of the trisaccharide β-D-Galp-(1 → 3)-β-D-GalpNAc-(1 → 3)-α-D-Galp-1-OPr (2) and of the tetrasaccharide α-L-Fucp-(1 → 2)-β-D-Galp-(1 → 3)-β-D-GalpNAc-(1 → 3)-α-D-Galp-1-OPr (3), starting from the disaccharidic dihydrooxazole donor 5, is described. Glycosylation of 5 with 6 in the presence of Me₃SiOTf gave the trisaccharide 7 which was deprotected with standard methods to give, via 8, compound 2. Alternatively, protection of 8 as the 4',6'-O-benzylidene derivative 9 followed by glycosylation with 10 and by standard deprotection afforded the tetrasaccharide 3. Biological testing showed that trisaccharide 2 is unable to inhibit the binding of the monoclonal antibody MBr1 to the target tumor cells MCF7, while tetrasaccharide 3 inhibits the binding in ca. 7-fold extent with respect to the previously tested trisaccharide α-L-Fucp-(1 → 2)-β-D-Galp-(1 → 3)-β-D-GalpNAc-1-OPr. These results indicate that the galactose corresponding to the unit D of compound 1 plays an important role in defining the MBr1-recognized epitope and confirm the essential role of fucose for MAb recognition.