A new hexagalloyl compound from Emblica officinalis Gaertn. antioxidant, cytotoxicity, and silver ion reducing activities

Abstract: Plant-derived natural products represent a significant source of green chemical compounds. The fruit extract of Emblica officinalis Gaertn., a traditionally used medicinal plant, was exploited in green synthesis of silver nanoparticles (AgNPs) using AgNO₃ reduction method. Characterization of the synthesized AgNPs was achieved using UV–Vis, FTIR spectroscopy as well as transmission electron microscopy (TEM). The antioxidant and cytotoxic activities of the extract and AgNPs were investigated. The synthesized AgNPs exhibited moderate inhibition of ABTS^•+ (67.2%) compared to the fruit extract (89.9%) and L-ascorbic acid (90.7%). Likewise, the extract exhibited higher cytotoxicity against MCF-7 and HCT-116 (IC₅₀ 25 and 20 µg/mL, respectively) compared to AgNPs (IC₅₀ 75 and 80 µg/mL, respectively). These results indicated that the functional groups of the biomolecules were quenched during the Ag⁺ reduction and surface capping processes. Phytochemical investigation of the active extract led to the isolation of a new hexagalloyl derivative designated as emblifatmin (E4), in addition to four known compounds, namely trans-cinnamic acid (E1), methyl gallate (E2), gallic acid (E3), and quercetin-3-O-α-arabinofuranoside (E5), identified by MS and NMR spectroscopy. The new compound, emblifatmin showed a remarkable AgNPs synthetic capability (minimum active concentration, MAC 0.0019 mg/mL) and considerable ABTS^•+ antioxidant activity (83.9%). Graphic Abstract: [Figure not available: see fulltext.]