Aqueous methanolysis of an α-D-N-acetylneuraminyl pyridinium zwitterion: solvolysis occurs with no intramolecular participation of the anomeric carboxylate group†

The synthesis of 3,4-dihydro-2H-pyrano[3,2-c]pyridinium α-D-N-acetylneuraminoate (4), the subsequent rate constants for aqueous methanolysis and the associated reaction products are reported. When compared with the analogous 2-deoxyglucopyranosyl 4′-bromoisoquinolinium salt (11), the rate of solvolysis of 4 displays a reduced sensitivity towards the ionizing power of the solvent. Solvolysis product analysis showed that substitution occurs predominantly with inversion of configuration. Hence it can be concluded that the methanolysis reactions of 4 proceed via dissociative transition states with no intramolecular nucleophilic participation by the anomeric carboxylate group. Copyright © 2004 John Wiley & Sons, Ltd.