Synthesis of a set of di- and tri-sulfated galabioses

Among cell-adhesion molecules, L-selectin recognizes sulfated sLe^x with relatively low affinity. Here, we aimed at artificial mimics by synthesizing a set of di- and tri-sulfated galabioses, which may surpass the affinity of sulfated sLe^x. As a strategy to obtain 3′,6′,6-tri-O-sulfogalabioses, regioselective reductive cleavage of 4,6- and 4′,6′-di-O-benzylidenegalabioses was employed. Two suitably protected galactose precursors were conjugated to yield α and β anomers (48 and 18%, respectively) by using a pentenyl galactoside donor and iodinium di-sym-collidine perchlorate as the catalyst. For synthesizing the 3′,6-di-O-sulfogalabiose, however, a trichloroacetimidate donor was superior (52%) to the pentenyl one (30%).