Synthesis and Evaluation of Gallotannin Derivatives as Antioxidants and α-Glucosidase Inhibitors

Gallotannins are phenolic natural products containing galloyl moieties connected to polyhydric alcohol cores, e.g., D-glucose. Some gallotannins are reported to have antidiabetic properties, such as alpha-glucosidase inhibitory activity. In this study, fourteen unnatural gallotannin derivatives with 1,5-anhydroalditol and inositol as the cyclic polyol cores were synthesized to investigate how their structures affected antioxidative and alpha-glucosidase inhibitory activities. Tannic acid demonstrated the most potent antioxidative activity (EC50 = 2.84 mu M), with potency increasing proportionally to the number of galloyl moieties. Synthetic inositol derivatives outperformed 1,5-anhydroalditol derivatives in rat alpha-glucosidase inhibitory activity. Pentagalloyl glucose, a natural compound, demonstrated the highest activity (IC50 = 0.336 mu M).