Chemoenzymatic-Chemical Synthesis of a (2-3)-Sialyl T Threonine Building Block and Its Application to the Synthesis of the N-Terminal Sequence of Leukemia-Associated Leukosialin (CD 43)

Protection of all functional groups of the carbohydrate portion of the chemoenzymatically synthesized sialyl T threonine ester 1 (R=R1=H, R2=tBu, Fmoc=9-fluorenylmethoxycarbonyl) and subsequent acidolysis of the tert-butyl ester afforded the building block 2 (R=Ac, R1=Me, R2=H). The latter is a useful tool in the solid-phase synthesis of the N-terminal sequence 3 of the leukemia-associated leukosialin.