Investigation of antioxidant compounds from the berries of teclea simplicifolia (engl.) i. verd. and ziziphus mucronata willd.

Abstract

Life threatening diseases like, cancer, diabetes, cardiovascular and neurodegenerative diseases have been linked to oxidative stress in the human body. Oxidative stress results from the uncontrolled generation of reactive oxygen species (ROS) in the body. Naturally, the normal body regulates ROS through in situ production of antioxidants. However, the human body is not capable of quenching ROS exceeding a certain level and this can result in oxidative stress. Hence the need of exogenous antioxidants arises and it is in this regard that this study was designed to find novel antioxidant compounds from medicinal plants. The main objective of the study was to investigate the antioxidant compounds present in the berries of Teclea simplicifolia and Ziziphus mucronata from Kenya. The berries of T. simplicifolia and Z. mucronata were separately collected, dried, pulverized and extracted using sequential extraction of cyclohexane, ethyl acetate and methanol. The crude extracts were tested for antioxidant activity using DPPH (2,2-diphenyl-1-picrylhydrazyl) method and ascorbic acid was used as the standard. The responsible compounds were purified via activity guided chromatography. The chemical structures of the purified compounds were determined using nuclear magnetic resonance (NMR) 1-D and 2-D experiments. For T. simplicifolia the IC50 value for cyclohexane extract was 135,897.6 μg/mL, for ethyl acetate extract it was 32,989.1μg/mL and for methanol extract it was 1,152.1 μg/mL. For Z. mucronata the IC50 value for cyclohexane extract was 44,466.5 μg/mL, for ethyl acetate extract it was 214.9 μg/mL and for methanol extract it was 8.9 μg/mL. Z. mucronata showed stronger antioxidant activity hence it was pursued for antioxidant compounds. A total of 22 compounds were purified but 19 of them were unstable and decomposed on transit to United Kingdom for NMR experiments. Full NMR spectra to allow structure elucidation was gotten for three compounds, namely: ursolic acid, betulin and betulinic acid. The three compounds are known compounds with antioxidant activity reported in the literature. This work has established that the berries of T. simplicifolia and Z. mucronata possess antioxidant compounds hence verifying their beneficial use as potent sources of antioxidants.