Xanthones with multiple roles against diabetes: their synthesis, structure-activity relationship, and mechanism studies

A four-step synthetic process has been developed to prepare 1,3,5,8-tetrahydroxyxanthone (2a) and its isomer 1,3,7,8-tetrahydroxyxanthone (2b). 25 more xanthones were also synthesized by a modified scheme. Xanthone 2a was identified as the most active inhibitor against both α-glucosidase and aldose reductase (ALR2), with IC₅₀ values of 7.8 ± 0.5 μM and 63.2 ± 0.6 nM, respectively, which was far active than acarbose (35.0 ± 0.1 μM), and a little more active than epalrestat (67.0 ± 3.0 nM). 2a was also confirmed as the most active antioxidant in vitro with EC₅₀ value of 8.9 ± 0.1 μM. Any structural modification including methylation, deletion, and position change of hydroxyl group in 2a will cause an activity loss in inhibitory and antioxidation. By applying a H₂O₂-induced oxidative stress nematode model, it was confirmed that xanthone 2a can be absorbed by Caenorhabditis elegans and is bioavailable to attenuate in vivo oxidative stress, including the effects on lifespan, superoxide dismutase, Catalase, and malondialdehyde. 2a was verified with in vivo hypoglycemic effect and mitigation of embryo malformations in high glucose. All our data support that xanthone 2a behaves triple roles and is a potential agent to treat diabetic mellitus, gestational diabetes mellitus, and diabetic complications.