Structure determination of five sialylated trisaccharides with core types 1, 3 or 5 isolated from bovine submaxillary mucin

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Abstract
In this study we have investigated the structures of five sialylated trisaccharides released from bovine submaxillary mucin by alkaline borohydride treatment and isolated by high-performance liquid chromatography. Three of the trisaccharides contained NeuAc while two contained NeuGc. One oligosaccharide contained core-type 1, two contained core-type 3 and two contained core-type 5. The structures, determined by a combination of one- and two-dimensional 1H-NMR spectroscopy at 270 MHz and methylation analysis involving gas-liquid chromatography/mass spectrometry, were as follows: A4b, GalNAcα(1 → 3)[NeuAcα(2 → 6)]GalNAcol; A4c, GlcNAcβ(1 → 3)[NeuAcα(2 → 6)]GalNAcol; A4d, Galβ(1 → 3)[NeuAcα(2 → 6)]GalNAcol; A4e, GalNAcα(1 → 3)-[NeuGcα(2 → 6)]GalNAcol; A4f, GlcNAcβ(1 → 3)[NeuGcα(2 → 6)]GalNAcol. The oligosaccharides occurred in the approximate molar ratios 1.0:12.0:0.3:0.2:2.0. This is the first report of oligosaccharides containing core-type 5 and of the occurrence of oligosaccharides A4b, A4e, and A4f in bovine submaxillary mucin. 1H-NMR data for structure A4e, which is a novel structure, are presented for the first time.

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