The structure of the repeating oligosaccharide unit of the pneumococcal capsular polysaccharide type 18C

The structure of the repeating oligosaccharide of the pneumococcal capsular polysaccharide type 18C has been investigated. The repeating oligosaccharide, isolated from an aqueous hydrofluoric acid hydrolyzate of the polysaccharide, was shown, by fast atom bombardment-mass spectrometry, to have a molecular weight of 928, and to contain an O-acetyl group and a glycerol residue. Information about the sequence in the per-O-methylated oligosaccharide was derived from electron-impact mass spectrometry. Supporting data were obtained from methylation analysis, periodate and chromium trioxide oxidations, and enzymic and acid hydrolyses of the oligosaccharide. These studies indicated that the polysaccharide consists of the following pentasaccharide repeating unit. (formula see text)