Radical scavenging dihydroxycinnamic natural compounds from Trianthema pentandra

Background Trianthema pentandra is a promising plant with numerous medical applications. Previous studies have confirmed that the plant is strongly cytotoxic in brine shrimp lethality tests and has antibacterial effects. However, the compounds responsible for these biological activities have not been identified. This study aimed to screen plants in an antiradical assay using 1,1-diphenyl-2-picrylhydrazyl (DPPH). This assay was used to guide the isolation of active compounds, which were identified at the molecular structural level by spectroscopic methods. Methods The plant was extracted using ethanol, labelled F1 and fractionated by solvents of different polarities (F2 chloroform, F4 ethyl acetate, F5 aqueous methanol, and F6 n-hexane). The ethyl acetate and aqueous methanol (F4 and F5) fractions were selected for further purification based on their yields and activities. They were run on chloroform-methanol and n-hexane-ethyl acetate gradients, respectively. Fractions resulting from column chromatography were further screened for DPPH antioxidant activity, upon which fraction F5-1-077 had unusually high activity (IC50 = 3.57 µg/ml). Further purification of these fractions through recrystallization and high-performance liquid chromatography (HPLC) led to the isolation of three compounds. Results: Among these compounds, two were identified and characterized using FT-IR, LC-MS, and complete nuclear magnetic resonance (NMR) data, and 2,3-dihydroxycinnamic acid ethyl ester and its analog acid were isolated from the ethyl acetate fraction (F4). The former compound has been proven to have good activity in comparison with standards, ascorbic acid, and butylated hydroxytoluene (BHT), even at a low concentration of 5 µg/ml with an IC50 value of 0.13 µg/ml in the DPPH assay. The molecular docking data supported the potent activity of the compound with binding affinity, ∆G = -6.4 kcal/mol compared to the ascorbic acid (∆G = -5.0 kcal/mol) used as standard. Conclusion This study serves as a groundbreaking foundation for the investigation of the natural dihydroxycinnamic compounds present in this plant.