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.

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Starting from a tumor-associated synthetic MUC1-derived peptide MUC1a' and using a completely enzymatic approach for the synthesis of the core-2 sialyl Lewis X glycopart, the following glycopeptide was synthesized:First, polypeptide N-acetylgalactosaminyltransferase 3 was used to site-specifically glycosylate MUC1a' to give MUC1a'-GalNAc. Then, in a one-pot reaction employing b-galactosidase and core-2 b6-N-acetylglucosaminyltransferase the core-2 O-glycan structure was prepared. The core-2 structure was then sequentially galactosylated, sialylated, and fucosylated by making use of b4-galactosyltransferase 1, a3-sialyltransferase 3, and a3-fucosyltransferase 3, respectively, resulting in the sialyl Lewis X glycopeptide. The overall yield of the final compound was 23% (3.2 mg, 1.4 µmol). During the synthesis three intermediate glycopeptides containing O-linked GalNAc, Gal(b1-4)GlcNAc(b1-6)[Gal(b1-3)]GalNAc, and Neu5Ac(a2-3)Gal(b1-4)GlcNAc(b1-6)[Gal(b1-3)]GalNAc, respectively, were isolated in mg quantities. All products were characterized by mass spectrometry and NMR spectroscopy.