EVIDENCE OF STABLE HYDROGEN-BONDED IONS DURING ISOMERZATION OF HEXOSES IN ALKALI

Article abstract of DOI:10.1016/0008-6215(89)84020-0

Epimeric pairs of aldohexoses and related ketohexose were isomerized in aqueous KOH at various temperatures and pH values, and the mixtures then analyzed by h.p.l.c. on either a cation-exchange resin or a reversed-phase column.It was found that the propertions of starting aldohexoses remaining after several days often exceeded those of the same that were formed from the epimeric aldoses and the corresponding ketoses.The difference with allose, gulose, and mannose was much larger than with other aldohexoses.These differences are rationalized by assuming that anomers having the OH groups attached to C-1, C-2, and C-3 in an axial-equatorial-axial or an equatorial-axial-equatorial arrangement form especially stable, hydrogen-bonded ions or molecular complexes that disturb the equilibrium state and affect the isomerization and mutarotation reactions.