Chemical characterization of the oligosaccharides in milk of high Arctic harbour seal (Phoca vitulina vitulina)

Carbohydrates were extracted from high Arctic harbour seal milk, Phoca vitulina vitulina (family Phocidae). Free neutral oligosaccharides were separated by gel filtration and preparative thin layer chromatography, while free sialyl oligosaccharides were separated by gel filtration and then purified by ion exchange chromatography, gel filtration and high performance liquid chromatography. Oligosaccharide structures were determined by ¹H-NMR spectroscopy. The structures of the neutral oligosaccharides were as follows: lactose, 2′-fucosyllactose, lacto-N-neotetraose, lacto-N-neohexaose, monofucosyl lacto-N-neohexaose and difucosyl lacto-N-neohexaose. Thus, all of the neutral saccharides contained lactose or lacto-N-neotetraose or lacto-N-neohexaose as core units and/or non-reducing α(1-2) linked fucose. These oligosaccharides have also been found in hooded seal milk. The structures of the silalyl oligosaccharides were: monosialyl lacto-N-neohexaose, monosialyl monofucosyl lacto-N-neohexaose, monosialyl difucosyl lacto-N-neohexaose and disialyl lacto-N-neohexaose. These oligosaccharides contained lacto-N-neohexaose as core units, and one or two α(2-6) linked Neu5Ac, and/or non-reducing α(1-2) linked Fuc. The Neu5Ac residues were found to be linked to GlcNAc or penultimate Gal residues. The acidic oligosaccharides are the first to have been characterized in the milk of any species of seal.