Structures of monosialyl oligosaccharides isolated from the respiratory mucins of a non-secretor (O, Lea+b−) patient suffering from chronic bronchitis. Characterization of a novel type of mucin carbohydrate core structure

Mucin glycopeptides were prepared from the respiratory mucus of a non-secretor, chronic bronchitis patient with blood group O, Lea+b−. Oligosaccharides were released by alkaline borohydride treatment and purified by anionexchange chromatography, size-exclusion chromatography and high-performance liquid chromatography on a silica-bonded alkylamine column. Structural studies employed 500-MHz 1H-NMR spectroscopy and fast atom bombardment-mass spectrometry. Twenty-six monosialyl oligosaccharides ranging in size from di- to octasaccharide, were fully characterized in this study. The sialic acid occurs either α(2←3)- or α(2←6)-linked to a galactosyl residue, or α(2←6)-linked to GalNAc-ol. In keeping with the nonsecretor status of the patient, no structures with an α(1←2)-linked fucose residue were found. Nine of the structures had fucose present in α(1←3) linkage, either in the Lex determinant or in the sialyl-Lex determinant, or both (structure 11). Only one oligosaccharide (structure 3b) was seen with fucose α(1←4)-linked in the Lea determinant. Eight structures isolated from the mucins of the non-secretor patient had not been found previously in the respiratory mucins of secretor individuals; they are Listed below. Among these, structure 4α represents a novel type of mucin carbohydrate core structure.