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

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)Galbeta(1→3)GalNAcol, (B2) NeuGcα(2→3)Galbeta(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