Isolation and structural characterization of the smaller‐size oligosaccharides from desialylated human κ‐casein

Abstract

Alkaline borohydride reductive cleavage (β‐elimination) of desialylated human κ‐caseinoglycopeptide resulted in the release of a series of oligosaccharides. The smaller‐size compounds among them were purified to virtual homogeneity by gel filtration followed by high‐performance liquid chromatography. The structures of 9 oligosaccharides were determined by ¹H‐NMR spectroscopy in conjunction with sugar analysis. The tetrasaccharide Galβ(1→3)[Galβ(1→4)GlcNAcβ(1→6)]GalNAc‐ol and various partial structures thereof were characterized. Notably, the disaccharide GlcNAcβ(1→6)GalNAc‐ol and the trisaccharide Galβ(1→4)GlcNAcβ(1→6)GalNAc‐ol were identified; they represent a novel type of core structure for mucin‐type carbohydrate chains, namely a peptide‐linked GalNAc that is mono‐substituted at C‐6. In addition, some oligosaccharides ending in GlcNAc‐ol could be characterized. Their possible origin is discussed.