Chemical synthesis of the tumor-associated globo H antigen†
A derivative of the tumor-associated globo H antigen, a complex hexasaccharide, was synthesized by a convergent and efficient [3 + 2 + 1] strategy using various glycosylation methods. All glycosylation reactions afforded good to excellent yields and outstanding stereoselectivity, including the installation of cis α-linked D-galactose and L-fucose. The longest linear sequence for this synthesis was 11 steps from a galactose derivative 11 to give an overall yield of 2.6%. The synthetic target had a free and reactive amino group at the glycan reducing end, facilitating its conjugation with other molecules for various applications.