Unusual lactam formation occurring in the synthesis of a biotinylated T-antigen—serine derivative

Synthesis of the biotinylated T-antigens, linked to a serine by an α (7α) or a β (7β) 2-acetamido-2-deoxy-d-galactoside bond, is described. These derivatives were needed for the detection of a specific endogenous lectin at the surface and/or on the migration pathway of melanoma cells. In the course of the synthesis, an unusual lactam formation was observed with the β anomer of the azido-disaccharide 5β.