Phytochemical, Antioxidant, and Flavonoid Investigation of Methanolic Leaf Extract of Piliostigma thonningii (Schum.)

Abstract

Piliostigma thonningii (Milne-Redhead, Fabaceae) is used for various medicinal purposes in African countries with some pharmacological activities established from the crude extracts including antibacterial, antihelminthic, anti-inflammatory, and antilipidemic activities. In the present study, crude methanolic extract of Piliostigma thonningii was examined for its antioxidant activity and phytochemical constituents. The antioxidant assay was determined by the free radicals scavenging activity measured in terms of hydrogen donation or radical scavenging ability using the stable radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) and determined by UV spectrophotometer at 517 nm. The concentration of the plant crude methanolic extract required for 50% inhibition of DPPH radical scavenging effect (IC₅₀) was recorded as 0.02 mg/ml as against a value of 0.015 mg/ml recorded for vitamin C used as standard. The crude methanolic extract showed potent inhibition of DPPH radical scavenging activity which is quite comparable to that of the Vitamin C standard. Qualitative phytochemical screening of the crude extract showed that it tested positive for saponins, flavonoids, terpenoids, steroids, alkaloids, and phenols indicating the presence of these phytochemicals, while tannins, phlobatannins, glycosides, triterpenoids, carbohydrates, resins, and anthraquinones were absent. Quantitative phytochemical analysis revealed that the crude extract contained 3.2% saponins, 1.6% flavonoids, 1.8% alkaloids, and 0.7% phenols. Bioassay-guided fractionation of the extract yielded five flavonoids which were identified by spectral analysis as piliostigmin (1), myricetin (2), kaempferide-3-O-β-D-glucoside (3), quercetin-3-O-β-glucoside (4), and quercetin-3-O-β-rhamnoside (5). The results of this study shows that extracts of Piliostigma thonningii could be a potent therapeutic agent for various diseases.