Received: May 31, 2020 Accepted: June 04, 2020 Published: June 04, 2020
The objective of this research work was to isolate the anti-diabetic principle of the leaves of Aspilia africana through bioassay guided phytochemical investigation. The methanol extract previously screened for anti-diabetic activity was partitioned successively with n-Hexane, CH2Cl2, EtOAc and n-BuOH. The butanol fraction, the only fraction that responded positively to in-vitro anti-diabetic tests (like the crude methanol extract) was treated with diethyl ether to precipitate the saponins. The crude saponin was hydrolyzed with 4M HCl and the organic part subjected to silica gel chromatography which on further purification through gel filtration and prep TLC afforded a compound which was identified using melting point determination, extensive nuclear magnetic resonance spectroscopy (1D, 2D, COSY, HMBC, HQMC), Fourier Transform- Infra-red (FT-IR) spectroscopy and basic chemical reactions. The isolated compound was identified as 2-hydroxyolean-12-en-28-oic acid or oleanolic acid. The in vitro anti-diabetic assays showed inhibition of α-amylase and α-glucosidase with the following IC50: in α-amylase assay: crude methanol 96.40±0.2 mg/mL, butanol fraction 72.50±0.65 mg/mL, isolated compound 25.45±0.45 μg/mL, compared to the reference drug (acarbose) 46.31±0.58 μg/mL; in the α-glucosidase assay crude methanol 95.10±0.20 mg/mL, butanol fraction 72.65±3.20 mg/mL, isolated compound 47.57±0.40 μg/mL, compared to the reference drug (acarbose), 48.10±0.13 μg/mL. Based on these findings the compound responsible for the anti-diabetic activity of Aspilia africana is 2-hydroxyolean-12-en-28-oic acid.