Isolation and characterization of antidiabetic constituents of Bridelia Micrantha

Abstract

Bridelia micrantha (Hochst) Baill (B. micrantha) is a South African medicinal plant used by traditional healers in the treatment of different human ailments including diabetes, gastrointestinal ailments, joint aches, cough, conjunctivitis, skin problems and malaria. Previous studies have demonstrated the antidiabetic activities of B. micrantha crude extracts in in vivo studies. However, there are no studies on the compounds responsible for the antidiabetic activity of the plant. The purpose of this study was to isolate and characterize the antidiabetic constituents from B. micrantha. Materials and methods Crude methanolic extracts of root, stem and leaf were investigated using in vitro antidiabetic enzyme assays. Antioxidant activities were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing power assays. The isolation of the antidiabetic constituents was carried out using column chromatography on silica gel. Purification of the active fraction was carried out using preparative thin layer chromatography (pTLC). Structure elucidation of the compound was carried out using Nuclear Magnetic Resonance (NMR) spectroscopy and by comparison with literature. Results The results obtained in this study indicated that root, stem and leaf extracts exhibited high inhibition activity against α-glucosidase (98.52, 98.62 and 81.62% respectively). A moderate inhibition against α-amylase enzyme was observed for root (65.62%) and stem (61.86%) extracts. Leaf fraction LFR5 exhibited a high inhibition activity of 96.19% against α-glucosidase. Moreover, the isolated compound showed 96.74% inhibition against α-glucosidase. DPPH results revealed that antioxidant activity of crude extracts was not significantly different and they were concentration-dependent. Reducing power results revealed that stem (119.31 μg/mL) extract had higher activities compared to root (125.17 μg/mL) and leaf (291.88 μg/mL) extracts. Conclusion Quercetin-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnoside was successfully isolated from B. micrantha leaves. Furthermore, quercetin-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnoside demonstrated the ability to inhibit significantly the carbohydrate hydrolysing enzyme α-glucosidase and therefore validate the ethnomedicinal use of B. micrantha in the management of diabetes