Alpha-glucosidase inhibitory prenylated flavonoids from the root bark of Adenodolichos paniculatus hua & hutch (fabaceae): isolation and enzyme kinetics

Adenodolichos paniculatus Hua & Hutch (Fabaceae) is a plant whose root bark was claimed to be used against diabetes mellitus and cancer in traditional medicine. The aim of the study was to evaluate the safety profile, investigate the alpha-glucosidase inhibitory actions and enzyme kinetics of the root bark extracts of A. paniculatus, and isolate its bioactive principles. The powdered root bark of Adenodolichos paniculatus was extracted with dichloromethane via maceration for 72 hours followed by 70 % methanol for 7 days with continuous shaking intermittently to obtain dichloromethane extract (DCM) and hydromethanolic extract (HME) after drying in vacuo respectively. Another fresh portion of the powdered root bark was extracted with distilled water via decoction by boiling in distilled water for 20 minutes and left for 24 hours, lyophilized to obtain lyophilized aqueous extract (AQE). Thereafter, toxicological profile and α-glucosidase inhibitory activity of the extracts were investigated. α-glucosidase inhibitors were isolated from the most active extract via bioassay – guided fractionation using various chromatographic techniques. The spectroscopic analysis of the isolated compounds was determined by using 1D (1H &13C NMR) and HRESIMS. The bioassay-guided isolation reveals that the α-glucosidase inhibitors reside majorly in the hydromethanolic extract and after several chromatographic techniques, four (4) prenylated flavonoids were isolated from polar fraction that was chromatographically tracked with the target activity. They were identified as leachinone G (1), kurarinone (2), kushenol I (3), kushenol K (4). Oral LD 50 in rat was found to be more than 2000 mg/kg and there was no significant difference in haematological parameters between the control and the treated animals. This study justifies the ethnomedical use of A.paniculatus root bark in the management of diabetes mellitus.