Convergent chemoenzymatic synthesis of -GalNAc rare cores 5, 7, 8 and their sialylated forms.

All -GalNAc glycans are derived from 8 cores with 2 or 3 monosaccharides linked α- or β-glycosidic bonds. While chemical and chemoenzymatic syntheses of β-linked cores 1-4 and 6 and derived glycans have been well developed, the preparation of α-linked rare cores 5, 7, and 8 is challenging due to the presence of this 1,2-cis linkage. Meanwhile, the biosynthesis and functional roles of these structures are poorly understood.