An efficient method for the preparation of 1,5-anhydroalditol from unprotected carbohydrates via glycopyranosyl iodide

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 α-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 α-glucosidase inhibitory activities. Tannic acid demonstrated the most potent antioxidative activity (EC₅₀ = 2.84 μM), with potency increasing proportionally to the number of galloyl moieties. Synthetic inositol derivatives outperformed 1,5-anhydroalditol derivatives in rat α-glucosidase inhibitory activity. Pentagalloyl glucose, a natural compound, demonstrated the highest activity (IC₅₀ = 0.336 μM).

Synthesis and Comparative Structure-Activity Study of Carbohydrate-Based Phenolic Compounds as α-Glucosidase Inhibitors and Antioxidants

Twenty-one natural and unnatural phenolic compounds containing a carbohydrate moiety were synthesized and their structure-activity relationship (SAR) was evaluated for α-glucosidase inhibition and antioxidative activity. Varying the position of the galloyl unit on the 1,5-anhydro-d-glucitol (1,5-AG) core resulted in changes in the α-glucosidase inhibitory activity and notably, particularly strong activity was demonstrated when the galloyl unit was present at the C-2 position. Furthermore, increasing the number of the galloyl units significantly affected the α-glucosidase inhibition, and 2,3,4,6-tetra-galloyl-1,5-AG (54) and 2,3,4,6-tetra-galloyl-d-glucopyranose (61) exhibited excellent activities, which were more than 13-fold higher than the α-glucosidase inhibitory activity of acertannin (37). Moreover, a comparative structure-activity study suggested that a hemiacetal hydroxyl functionality in the carbohydrate core and a biaryl bond of the 4,6-O-hexahydroxydiphenoyl (HHDP) group, which are components of ellagitannins including tellimagrandin I, are not necessary for the α-glucosidase inhibitory activity. Lastly, the antioxidant activity increased proportionally with the number of galloyl units.

Triterpenoid glycosides from Ladenbergia hexandra Klotzsch

From the bark of Ladenbergia hexandra Klotzsch, ten triterpenoid glycosides were isolated along with five known compounds, and their structures were determined based on extensive NMR and mass spectroscopic, GC and HPLC analyses. Some triterpenoid glycosides contained 6-deoxy-D-allose or D-allose as a sugar moiety. The absolute stereochemical assignment of the sugars was determined by comparison with synthetic samples, as well as by GC and HPLC analysis.