Secondary Metabolites from Dovyalis Abyssinica (A. Rich.) Warb Fruits and their Antioxidant Effects

Abstract

One of the main underlying causes of modern diseases is oxidative stress, an imbalance between radicals and antioxidants in living organisms. Its causative agents, unquenched radicals that outnumber antioxidants, remain challenging due to industrialization and modern lifestyles. In humans, these free radicals continue to harm fatty tissues, DNA, and proteins, which results in a multitude of diseases, including cancer, neurological, and cardiovascular diseases. There is, therefore, a need to document and add sources of natural antioxidants. Traditional medicine has long used extracts from D. abyssinica to treat certain human pathogens. Scientific research has demonstrated the efficacy of several secondary metabolites isolated from its leaves, roots, and bark against human infections. However, no investigation on the fruits of this plant has yet been reported. This research, therefore, studied the antioxidant capacities and total phenolic content of fruit extracts of D. abyssinica and isolated three known secondary metabolites from its fruits. Ripe fruits were collected from Egerton University botanic garden, freeze-dried, and ground into fine powder. Solvent extraction was done to obtain hexane, methylene chloride, ethyl acetate, and methanol crude extracts. Samples of these four crude extracts were subjected to the folin-ciocalteu method and DPPH assay to determine their total phenolic content and antioxidant capacities, respectively. The methanol extract gave 921.79 ± 1.63×10-³ mg GAE/100g (mg of gallic acid equivalents per 100g of extract), whereas the ethyl acetate extract gave 517.95 ± 1.4×10-³ mg GAE/100g phenolic content. In contrast, the methylene chloride and hexane extracts gave 261.54 ± 1.0×10-⁴ mg GAE/100g and 24.36 ± 8.2×10-⁴ mg GAE/100g respectively. From these extracts, data on IC50 showed a significant radical scavenging capacity in the methanol extract (4.4 g/mL) than those of ethyl acetate, methylene chloride, and hexane extracts (8.4 g/mL, 28.8 g/mL, and 55.8 g/mL respectively). Subsequently, methanol and ethyl acetate crude extracts were subjected to column, thin layer, and ultimately preparative thin layer chromatographic techniques for separation and purification. 1-D and 2-D NMR spectroscopic analysis revealed three known compounds: betulinic acid (31), sitosterol (32), and 3,4-bis(4-hydroxybenzoyl)-1,5-anhydro-Dglucitol (41), and the compounds are new reports from the fruits of D. abyssinica. This research showed that the studied fruits of D. abyssinica exhibited a substantial phenolic content and antioxidant capacity, providing a source of natural antioxidants and hence contributing to SDGs 2.1 and 3.7 on improved nutrition and well-being promotion.