Phytochemical Constituents and Comparative Antioxidative Effects of Some Medicinal Plants

This study was carried out to compare the in-vitro antioxidant potentials, antidiabetic and phytochemical constituents of methanolic leaf extracts of Anthocleista djalonensis, Chrysophyllum albidium, Bauhinia thonningii, Daniellia oliveri, and Cola nitida. The results of this study show that all the plant extracts have strong antioxidant potentials against various radicals. The extracts scavenged DPPH and ABTS radicals, in a concentration-dependent manner and scavenged nitric oxide radicals with IC50 values of 152.39, 186.36, 213.40, 303.58 and 355.53 µg/ml for C. albidium, D. oliveri, C. nitida, A. djalonensis and B. thonningii, respectively. All the extracts also inhibited the induction of lipid peroxidation and α-amylase activity in a concentration-dependent manner, while the degree of ferric reducing power by the extracts was of the order C. albidium > D. oliveri > B. thonningii > C. nitida > A. djalonensis. Phytochemical and gas chromatography analyses carried out on the extracts revealed the presence of known chemical constituents. The amounts of total phenolics in A. djalonensis, C. albidium, B. thonningii, D. oliveri, and C. nitida were 68.39 mg/g, 95.11 mg/g, 61.03 mg/g, 103.74 mg/g, and 63.31 mg/g, respectively, in gallic acid equivalents. In all cell-free assays, C. albidium and D. oliveri, the two plants with higher amounts of phenolic compounds, were found to be more effective as antioxidants than other plant extracts with lower phenolic contents under the same experimental conditions. Therefore, the effectiveness of the antioxidant and antidiabetic activities of these plant extracts may be related to their phenolic content. The presence of phenolics and various antioxidant compounds in the plants may explain the strong pharmacological potentials of these plants.