Phytochemical Profiling and Antioxidant Activity of Justicia thunbergioides (Lindau) Leonard (Acanthaceae): A Promising Source of Therapeutic Metabolites

Background/Objectives: Medicinal plants are widely investigated due to their rich content of biologically active secondary metabolites with potential therapeutic applications. This study aimed to investigate the phytochemical profile and antioxidant activity of extracts with different polarities obtained from Justicia thunbergioides (Lindau) Leonard (Acanthaceae). Methods: Phytochemical screening was initially performed through qualitative analysis, followed by fractionation and characterization of dichloromethane and methanolic extracts using thin-layer chromatography (TLC) and gas chromatography–mass spectrometry (GC–MS). Antioxidant activity was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and electrochemical techniques. Results: GC–MS analysis of the dichloromethane extract revealed a chemically diverse composition, including compounds such as spathulenol, vitamin E, sesamin, squalene, and β-sitosterol, which are widely reported in the literature for their antioxidant and bioactive properties. The methanolic extract exhibited a distinct chemical profile, with a predominance of phenolic and redox-active compounds. DPPH assays demonstrated that the methanolic extract showed the highest radical scavenging capacity in a concentration-dependent manner, whereas the dichloromethane and hexane extracts required higher concentrations to achieve moderate antioxidant effects. Electrochemical analyses indicated that the methanolic extract is rich in electroactive metabolites capable of partially reversible electron transfer, consistent with its enhanced antioxidant performance. Conclusions: Collectively, these findings highlight the antioxidant efficacy of the polar extracts from J. thunbergioides and contribute to a better understanding of the bioactivity of their phytochemical constituents.