Antioxidant and α-glucosidase inhibitory potential of the pollen of Hibiscus spp.

Hibiscus species are flowering plants of the Malvaceae family. Hibiscus are widely distributed in tropical and subtropical regions and play an important role not only in ornamental aspects but also traditional medicine. In this study, seven compounds, mukungarrole ( 1 ), a new compound and six known flavonoid derivatives ( 2 – 7 ) were isolated from Hibiscus syriacus pollen. Among the isolated compounds, kaempferol ( 2 ) and vincetoxicoside B ( 3 ) showed antioxidant activity. Additonally, the new compound, mukungarrole ( 1 ), along with kaempferol ( 2 ) and isorhamnetin-7- O -rhamnoside ( 5 ), showed α-glucosidase inhibitory activity and its interaction with α-glucosidase was confirmed using molecular docking analysis. Further comparison of five varieties of Hibiscus spp. showed that all five species contained vincetoxicoside B ( 3 ) and kaempferol-7- O -rhamnoside ( 4 ) as major components and exhibited antioxidant and α-glucosidase inhibitory activities. However, there was differences in the content of vincetoxicoside B ( 3 ) and kaempferol-7- O -rhamnoside ( 4 ) and minor components depending on of Hibiscus variety, which contributed to differences in efficacy. This study proves that H. syriacus pollen and its constituents have antioxidant and α-glucosidase inhibitory potentials and the content and efficacy vary depending on Hibiscus species.