Major triterpenes, cycloeucalenone and 31‐norcyclolaudenone as inhibitors against both α‐glucosidase and α‐amylase in banana peel

Abstract

Summary The inhibitory activities of banana peel extract against carbohydrate digestive enzymes were investigated. Cycloeucalenone and 31‐norcyclolaudenone were obtained by bioassay‐guided fractionation as effective inhibitors of α‐glucosidase and α‐amylase. The structure–activity relationships of four triterpenes isolated from banana peel, cycloeucalenone, 31‐norcyclolaudenone and cycloeucalenol and its isomer were investigated. The IC 50 values of cycloeucalenone and 31‐norcyclolaudenone against α‐glucosidase were 31.83 ± 2.46 μ m and 38.85 ± 1.54 μ m , respectively, and their IC 50 values against α‐amylase were 20.33 ± 0.59 μ m and 27.63 ± 0.83 μ m , respectively. In contrast, cycloeucalenol and its isomer had insufficient inhibitory activity against either enzyme. The primary active sites of cycloeucalenone and 31‐norcyclolaudenone are the carbonyl group at C‐3 and the double bond in the side chain. Cycloeucalenone induced a parabolic mixed‐type inhibition with a K i value of 73.86 μ m in the α‐glucosidase inhibitory assay. This study provides new evidence for the potential use of banana peel triterpenes as antidiabetic agents.