α-Glucosidase inhibitory activity from ethyl acetate extract of Antidesma bunius (L.) Spreng stem bark containing triterpenoids

Background: Buni (Antidesma bunius [L.] Spreng) has been used as a traditional antidiabetic agent in Asia. Objective: The mechanism of antidiabetic properties was studied in this study by determine its α-glucosidase inhibitory activity. Method: Inhibition of α-glucosidase was performed in all fraction of Buni stem bark with acarbose and miglitol as standards. The half maximal inhibitory concentration (IC₅₀) value of acarbose and miglitol was 5.75 and 59.76 μg/mL respectively while ethyl acetate (EtOAc) fraction was the most active fraction with IC₅₀of 19.33 μg/mL. Three isolates (B1, B2, and B3) were found in the EtOAc fraction and elucidated by infrared, ¹hydrogen-nuclear magnetic resonance, ¹³carbon-nuclear magnetic resonance, and two-dimensional nuclear magnetic resonance. Result: The chemical structures of the isolates were identified by the spectrum then compared with literature which concluded that B1 is friedelin, B2 is β-sitosterol, and B3 is betulinic acid. Inhibition of the α-glucosidase assay showed IC₅₀values of B1, B2, and B3 were 19.51, 49.85, and 18.49 μg/mL, respectively.