Bioactive metabolites of Bulbine natalensis (Baker): Isolation, characterization, and antioxidant properties

Background: Medicinal plants continue to play a key role in disease management and modern drug development. Bulbine natalensis is one of several South Africa’s indigenous succulent medicinal species. B. natalensis’ high medicinal profile has made it a commercially-available herb within the South African market and beyond. However, there is a limited scientific report on its bioactive metabolites. Objectives: This study’s objective was to isolate and identify bioactive compounds from B. natalensis leaves and evaluate the compounds and crude extracts for antioxidant activity. Materials and Methods: Fractionation and purification of B. natalensis dichloromethane extract were done using chromatographic techniques. Whole extract profiling was carried out on dichloromethane and methanol extracts using gas chromatography-mass spectrometry (GC-MS). The isolated compounds and extracts were evaluated for antioxidant activity. Results: The dichloromethane extract yielded two pentacyclic triterpenes (glutinol and taraxerol), one tetracyclic triterpene (β-sitosterol), a phytylated porphyrin pigment, pheophytin a and knipholone, and a phenyl anthraquinone. GC-MS analysis and 1H nuclear magnetic resonance (1HNMR) fingerprinting of the leaf extracts identified additional bioactive metabolites as α- and β-tocopherol, campesterol, p-hydroxyphenylacetic acid, and long-chain alcohols. The antioxidant assays revealed the methanol extract to have good ferric reducing antioxidant power while dichloromethane extract displayed stronger Mo(IV) reducing power compared to α-tocopherol and isolated compounds. Conclusion: This study revealed previously unreported compounds from B. natalensis and GC-MS profiling supported by 1H NMR fingerprints provide comprehensive detail of the plant’s bioactive metabolites in addition to the isolated compounds. The antioxidant potential of B. natalensis may be partly responsible for its use in the management of some oxidative-stress induced diseases