An Organogermanium Compound Enhances the Initial Reaction Rate of Alkaline Isomerization of an Aldose into a Ketose through Enediol Complex Formation

Abstract

We previously demonstrated that the organogermanium compound 3-(trihydroxygermyl)propanoic acid (THGP) enhances the enzymatic and alkaline isomerization of an aldose to a ketose through cis -diol complex formation by multiple mechanisms. Its higher affinity for the ketose than the aldose protects the ketose complex from alkaline decomposition. Furthermore, it has been reported that the aldose-ketose alkaline isomerization pathway includes 1,2-enediol. Therefore, we speculated that the complex-forming ability of THGP could also be applied to enediol, a transient intermediate of alkaline isomerization. To test this prediction, we analyzed the initial rates of glucose or lactose isomerization in a region where there was no substantial difference in pH with and without THGP addition. The results showed that THGP enhanced the rate of fructose or lactulose formation per unit time by approximately 2-fold compared to the control. This finding indicated that THGP could form a complex with the transition state of aldose-ketose alkaline isomerization.

Interaction of Organogermanium Compounds with Saccharides in Aqueous Solutions: Promotion of Aldose-to-ketose Isomerization and Its Molecular Mechanism

“…In addition, the rate of fructose formation during the initial stage of the reaction, where the reduction in pH and degradation of sugars were negligible, approximately doubled in the presence of THGP. 35) These results indicate that organogermanium compounds with the THGP structure promote the alkaline glucose-fructose isomerization reaction, inhibit the degradation of sugars that occurs during this reaction, and suppress the resulting reduction in pH. 71) These effects likely arise from the negative charge of the sugar-THGP complex.…”

“…In the initial reaction region, where the reduction in pH and degradation of sugar were negligible, the lactulose production rate was approximately doubled in the presence of THGP. 35) …”

“…(D) Alkaline isomerization via an enediol intermediate exists in the cis -enediol form (5) in the presence of THGP. 32) 35) The dehydration reaction proceeds via a cis -enediol intermediate (6), stabilizing the transition state. (E) Alkaline isomerization via hydride transfer performed in the presence of THGP, 35) which produces the cis conformation (7).…”

“… 32) 35) The dehydration reaction proceeds via a cis -enediol intermediate (6), stabilizing the transition state. (E) Alkaline isomerization via hydride transfer performed in the presence of THGP, 35) which produces the cis conformation (7). The dehydration process stabilizes the hydride transfer in the transition state (8).…”

“…23) 24) 25) 26) 27) 28) 29) 30) 31) The present work has identified the effect of organogermanium compounds on sugar isomerization, the affinity of these compounds toward sugars and, consequently, their ability to form organogermanium-sugar complexes as well as the mechanism by which the isomerization reaction can be promoted. 32) 33) 34) 35) The influence of organogermanium compounds on the enzymatic and alkaline isomerization reactions between aldoses and ketoses was investigated by considering their affinity for saccharides with the 3-(trihydroxygermyl)propanoic acid (THGP) structure. The complexation of ketoses with various cis -diol structures and organogermanium compounds with the THGP structure was also evaluated using 1 H-nuclear magnetic resonance (NMR) spectroscopy.…”