Several literature reports show that reduction in oxidative damage to DNA, proteins, and lipids enhances longevity and health span [ 11 , 12 ]. Phytochemical analysis of the crude precipitate, fractions, and compound from the methanol root-bark extract of A. boonei showed the presence of phytochemicals which have been demonstrated to possess antioxidant properties such as alkaloids [ 13 ], steroids [ 14 ], saponins [ 15 ], triterpenes [ 16 ], flavonoids [ 17 ], tannins [ 18 ], and glycosides [ 19 ]. The presence of these phytocompounds may have contributed to the antioxidant activity exhibited by the fractions, precipitate, and isolated compound. DPPH method for evaluation of antioxidant properties of compounds and plant extracts is quick, reliable, and highly reproducible [ 20 ]. The inhibition of DPPH radical exhibited by the ethyl acetate, acetone, and methanol fractions could be explained by the presence of phenolic compounds in these fractions. The best-described property of most phenolic compounds is their capacity to act as antioxidants [ 21 ]. The antioxidant activity of phenolic compounds has been attributed to their high content of hydroxyl groups and their reducing potentials through electron −/H-donation. Phenolic compounds are known to concentrate in ethyl acetate fractions [ 22 ] and might have accounted for the high antioxidant activity exhibited by this fraction compared with other fractions, precipitate, and isolated compound. Also significant inhibition of DPPH radical by ethyl acetate fraction of A. scholaris belonging to the same family with A. boonei (Apocynaceae) has been documented and activity attributed to presence of phenolic compounds [ 23 ]. Steroids have good antioxidant activity acting mainly through membrane stabilization [ 24 ]; however, their poor solubility in polar reaction medium may hinder free interaction with DPPH radical in methanol solution. This may have contributed to the decreased DPPH inhibition exhibited by the crude precipitate and isolated compound.