Bioassay-guided fractionation and identification of α-amylase inhibitors from Syzygium cumini leaves
2017
Poongunran, Jeyakumaran | Perera, Handunge Kumudu Irani | Jayasinghe, Lalith | Fernando, Irushika Thushari | Sivakanesan, Ramaiah | Araya, Hiroshi | Fujimoto, Yoshinori
Context: Pancreatic α-amylase and α-glucosidase inhibitors serve as important strategies in the management of blood glucose. Even though Syzygium cumini (L.) Skeels (Myrtaceae) (SC) is used extensively to treat diabetes; scientific evidence on antidiabetic effects of SC leaves is scarce. Objective: SC leaf extract was investigated for α-amylase inhibitory effect and continued with isolation and identification of α-amylase inhibitors. Materials and methods: Bioassay-guided fractionation was conducted using in vitro α-amylase inhibitory assay (with 20–1000 μg/mL test material) to isolate the inhibitory compounds from ethyl acetate extract of SC leaves. Structures of the isolated inhibitory compounds were elucidated using ¹H NMR and ¹³C NMR spectroscopic analysis and direct TLC and HPLC comparison with authentic samples. Study period was from October 2013 to October 2015. Results: An active fraction obtained with chromatographic separation of the extract inhibited porcine pancreatic α-amylase with an IC₅₀ of 39.9 μg/mL. Furthermore, it showed a strong inhibition on α-glucosidase with an IC₅₀ of 28.2 μg/mL. The active fraction was determined to be a 3:1 mixture of ursolic acid and oleanolic acid. Pure ursolic acid and oleanolic acid showed IC₅₀ values of 6.7 and 57.4 μg/mL, respectively, against α-amylase and 3.1 and 44.1 μg/mL respectively, against α-glucosidase. Discussion and conclusions: The present study revealed strong α-amylase and α-glucosidase inhibitory effects of ursolic acid and oleanolic acid isolated from SC leaves for the first time validating the use of SC leaves in antidiabetic therapy.
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