Strong Binding Affinity of d-Allulose and Allulosides to Boronic Acids and the Structural Characterization of Their Sugar-boronate Complexes

As sugars form complexes with boronic acids, some sugars are used as additives for boron-containing pharmaceuticals. The binding constants of the rare sugar d-allulose with boronic acids were measured, and these showed the highest hitherto reported binding-affinity values for sugars. An NMR study clarified that d-allulose in aqueous solution forms complexes exclusively via the reaction of the 2,3-hydroxy groups of α-allulofuranose. Conversely, in organic solvents, d-allulose forms a single complex derived from the 3,5-hydroxy groups of β-allulopyranose. The binding constants of the rare sugar d-allulose with boronic acids were measured, and these showed the highest hitherto reported binding-affinity values for sugars. d-Allulose in aqueous solution forms complexes exclusively via the reaction of the 2,3-hydroxy groups of α-allulofuranose. Conversely, in organic solvents, d-allulose forms a single complex derived from the 3,5-hydroxy groups of β-allulopyranose.