Porcine submaxillary mucin contains α2→3‐ and α2→6‐linked N‐acetyl‐ and N‐glycolyl‐neuraminic acid

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Abstract
Four acidic trisaccharides have been obtained by alkaline borohydride reductive cleavage (β‐elimination) of a fraction of porcine submaxillary mucin precipitating at 60 – 75% ethanol. Their structures have been investigated using the techniques of methylation analysis involving gas‐liquid chromatography/mass spectrometry along with high‐resolution 1H‐NMR analysis. Two of the four oligosaccharides, B1 – B4, contain N‐acetylneuraminic acid (NeuAc) while two contain N‐glycolylneuraminic acid (NeuGc). The following structures are proposed for the acidic trisaccharide fraction: (B1) NeuAcα(2→3)Galβ(1→3)GalNAcol, (B2) NeuGcα(2→3)Galβ(1→3)GalNAcol, (B3)Galβ(1→3)[NeuAcα(2→6)]GalNAcol and (B4) Galβ(1→3)[NeuGcα(2→6)]GalNAcol, (GalNAcol = reduced N‐acetylgalactosamine. These oligosaccharides were present in a molar ratio of 69:22:4:5. Although oligosaccharide B4 has previously been found in porcine submaxillary mucin B1, B2 and B3 have not. Furthermore, oligosaccharide B2 is a novel structure.