| Résumé | Pneumococcal cell wall polysaccharide (C–PS), a contaminant in pneumococcal capsular polysaccharide (Pn-PS) vaccines is degraded by mild deamination of the 4-amino-2-acetamido-2,4,6-tri-deoxy-galactose (AAT) in C–PS, which was carried out by addition of 5% aqueous sodium nitrite to a solution of polysaccharide in 5% aqueous acetic acid. Glycosidic linkage and functional groups such as O-acetates, phosphodiesters, and pyruvates were preserved under the conditions. The small fragments from degraded C–PS were removed by ultrafiltration or dialysis to provide essentially C–PS free Pn-PS. Because of the presence of AAT in its structure the deamination is not suitable for the purification of type 1 Pn-PS. Meanwhile, the mass and NMR spectroscopic analysis on the deamination products suggests that both type 1 Pn-PS and C–PS degraded following a major pathway of 5,4-hydride shift, cleavage of AAT O5-C1 bond, C1 hemiacetal formation, and its hydrolysis to release neighboring GalA- in type 1 Pn-PS and GalNAc(6-O-PCho)- in C–PS. |
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