Oligosaccharides related to tumor‐associate 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‐GalpNAc‐(1→3)‐β‐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 (Scheme 1). 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 (Scheme 2). 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.