Phenolic metabolites, biological activities, and isolated compounds of Terminalia muelleri extract

Terminalia muelleri Benth. (Combretaceae), is rich with phenolics that have antioxidant and cytotoxic activities. No screening studies were published before on T. muelleri.

The study focused on isolation and identification of secondary metabolites from aqueous methanol leaf extract of T. muelleri and evaluation of its biological activities.

The n-butanol extract was chromatographed on polyamide 6, and eluted with H₂O/MeOH mixtures of decreasing polarity, then separated by different chromatographic tools that yielded 10 phenolic compounds. The antioxidant activity of the extract was evaluated by investigating its total phenolic and flavonoid content and DPPH scavenging effectiveness. The extract and the two acylated flavones were evaluated for their anticancer activity towards MCF-7 and PC3 cancer cell lines. Molecular docking study of the acylated flavones was performed against topoisomerase enzyme.

Two acylated flavonoids, apigenin-8-C-(2″-O-galloyl) glucoside 1 and luteolin-8-C-(2″-O-galloyl) glucoside 2, were isolated and identified for the second time in nature, with eight tannins (3-10), from the leaves of T. muelleri. The extract and compound 10 showed the most significant antioxidant activity (IC₅₀ = 3.55 and 6.34 μg/mL), respectively. The total extract and compound 2 demonstrated cytotoxic effect against MCF-7 with IC₅₀ = 29.7 and 45.2 μg/mL respectively, while compound 1 showed cytotoxic effect against PC3 (IC₅₀ = 40.8 μg/mL). The docking study of compounds 1 and 2 confirmed unique binding mode in the active site of human DNA topoisomerase enzyme.

Terminalia muelleri is a promising medicinal plant as it possesses high antioxidant activity and moderate cytotoxic activity against MCF-7.