Acid-Catalyzed Hydrolysis and Lactonization of α2,8-Linked Oligosialic Acids

Polysialic acids (PSA) exist mainly on the surface of mammalian cells and certain bacteria and are involved in many important biological roles.1 For example, the R2,8-PSA chain is expressed in neural cell adhesion molecules (N-CAM) in a developmentally regulated manner. The homopolymers of N-acetylneuraminic acids have been implicated in altering the shape and movement of cells because PSA can attenuate adhesion forces and modulate overall cell surface interaction.2 There are two distinct features of PSA in relation to its critical physiological roles: intramolecular lactonization and the lability of glycosidic linkages. The former influences the charge distribution and tertiary structure of PSA, and the latter varies the size of PSA-containing biopolymers. Of all the glycosidic linkages found in oligosaccharides, those of polysialic acids are remarkbly labile.3 R-2,8Polysialic acid has been noted for its degradation in prolonged freezer storage4 and in the preparation of N-CAM for SDS gel anlaysis.5 Acid-catalyzed cleavage of the R2,8-linkage in oligoand polysialic acids (OSA/ PSA) was reported to occur preferentially at the linkage between two internal sialic acid residues. The cleavage of the internal R2,8-linkages in PSA is much easier as a