Antioxidant, antimicrobial and antityrosinase activities of phytochemicals from the leaves of Globimetula braunii (Engler) Van Tiegh (Loranthaceae)

ABSTRACT. Herbal preparations of Globimetula braunii leaves are used in tropical African countries for the treatment of several illnesses. A preliminary study of the leaf extracts of Globimetula braunii has confirmed the antioxidant, antibacterial, biochemical and toxicological potency of the plant. The leaf extracts were subjected to bioactivity guided fractionation that led to the isolation of the active compounds. Antioxidant, antityrosinase and antimicrobial inhibitory activities of the isolated compounds were evaluated. Structural elucidations of the isolated compounds were carried out spectroscopically, including the use of 1D/2D nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopies and mass spectrometry. Results indicated that quercetin (15) isolated from ethyl acetate fraction exhibited the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) scavenging capacity and also showed the highest ferric reducing antioxidant potential (FRAP) equivalent value. Quercetin (15) and dodoneine (14) displayed the highest tyrosinase inhibition activity with IC50 value of 0.12±0.32 mM and 0.19±0.20 mM, respectively. All the isolated compounds showed weak to not active in the antimicrobial inhibition assay. The findings in this report have revealed the antioxidant and antityrosinase potential of Globimetula braunii and thus supporting their traditional uses.   KEY WORDS: Globimetula braunii, Antioxidant, Antityrosinase, Antimicrobial, Triterpenoid esters, Dodoneine   Bull. Chem. Soc. Ethiop. 2022, 36(2), 387-397.                                                                DOI: https://dx.doi.org/10.4314/bcse.v36i2.12