A multidirectional investigation of stem bark extracts of four African plants: HPLC-MS/MS profiling and biological potentials

The practice of traditional medicine, especially herbal medicine, is still prevalent across the African continent. Yet, their in-depth pharmacological and chemical exploitation by the scientific community remain a necessity. The aim of the present study was to investigate into the phenolic components, antioxidant, and enzyme-inhibitory activities of three solvent extracts (ethyl acetate, methanol, and water) of the stem bark of four African plant species (Senna siamea, Distemonanthus benthamianus, Harrisonia abyssinica, and Pycnanthus angolensis). It was found that D. benthamianus followed by P. angolensis, displayed the highest DPPH and ABTS scavenging, ferric and cupric reducing, and total antioxidant capacity in the phosphomolybdenum assay. A similar result was observed for ACNE, BChE, and tyrosinase inhibition. The two plants also showed comparable alpha-amylase inhibitory effect. On the other hand, H. abyssinica showed high metal chelating and alpha-glucosidase inhibition. Among the solvents used, the methanol extract seemed to be the most bioactive. In addition, TPC was highest in D. benthamianus (135.33-192.29 mg GAE/g) while P. angolensis was richest in TFC (7.68-12.48 mg RE/g). A range of bioactive compounds were identified in the extracts, with variations observed among the plants. Senna siamea stem bark showed the presence of nine compounds; where flavonoids (e.g. naringenin, kaempferol, dihydroquercetin) were recorded. Genistein (m/z 271.06), procyanidin B (m/z 577.13) and C (m/z 865.19) isomers were common in stem barks extracts of D. benthamianus and P. Angolensis. To conclude, D. benthamianus and P. angolensis can be considered as potential pharmaceutical agents or functional food components that could reduce the risks of oxidative stress-related disorders. (C) 2019 Elsevier B.V. All rights reserved.