New Pharmacophore from the Stem Bark Fractions of Acacia decurrens (Willd), an Invasive South Africa Tree

Abstract

The tolerance of Acacia decurrens, an invasive species, was exploited pharmacologically in this study. Phytochemical screening revealed important secondary metabolites. Importantly, the assay shows that ethyl acetate and methanol fractions are sources of phytochemicals compared to the hexane and chloroform fractions. A bioassay-guided in vitro assay of the extracts led to the eventual isolation of four bioactive compounds by column chromatography, identification, and characterisation with the aid of GCMS, UV-Vis, FTIR, and NMR. The antimicrobial screening by disc diffusion assay revealed 22.2%, 44.4%, 66.7%, and 77.8% microbial inhibition by 2-methyl-octahydro-indene-4-carboxylic acid (AD1), 6-methyldecahydro-1H-phenanthren-9-one (AD2), 8-hydroxytetradecahydro-chrysene-1-carb aldehyde (AD3), and 8,9-dihydroxy-7-(2-hydroxy-ethyl)-9,9a-hexahydro-1H,3H-2-thia-5a-aza cyclopenta[b]anthracen-6-one (AD4), respectively. Compounds AD3 and AD4 are the most potent antibacterial compounds against Gram-positive bacteria with MIC 12.5–6.25 μg/ml. Antioxidant study of the compounds assayed with DPPH and ABTS^•+ revealed that compound (AD4) is the most efficient DPPH radical scavenger with IC50 30.07 ± 0.31 and ABTS^•+ scavenging activity of 4363.2 ± 452.4 μmol of TE/gDW. This provides scientific information on four pharmacophores with phyto-antioxidants and antimicrobial potential, despite the classification of A. decurrens as a Category 2 invasive plant by the National Water Act.