LC–ESI–MS/MS Profiling and In Vitro Evaluation of Antioxidant, Enzymatic Inhibitory, and Cytotoxic Activities, Along With Complementary In Vitro and In Silico Assessment of the Antibacterial Potential of <i>Centaurea papposa</i> Leaf Extracts

The main objective of this study was to characterize the phenolic composition of the hydromethanolic extract and its fractions from Centaurea papposa leaves, and to evaluate their antioxidant, enzymatic inhibitory, cytotoxic, and antibacterial activities. In addition, molecular docking analysis was performed using dihydropteroate synthase as the bacterial target enzyme to explore the interactions with major phenolic compounds. LC-MS/MS analysis identified shikimic acid and chlorogenic acid as predominant in the hydromethanolic extract. In the ethyl acetate fraction, vanillic acid, protocatechuic acid, chlorogenic acid, and shikimic acid were the major constituents. Meanwhile, the chloroform fraction was rich in salicylic acid and luteolin. Furthermore, the antioxidant assays, including 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS⁺), ferric reducing power (FRAP), and phenanthroline, revealed that the ethyl acetate fraction had significant activity, varying between 5.20 and 65.02 µg/mL. With regard to enzyme inhibition, all extracts were found to be ineffective. Based on the cytotoxicity results, the ethyl acetate fraction exhibited significant inhibitory effects against HEp-2 and HCT-116, with an IC₅₀ value below 40 µg/mL. Concerning the antibacterial activity, the chloroform fraction was found to be the most effective against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli (MIC = 62.5 µg/mL). Whereas the ethyl acetate fraction showed excellent activity against Proteus mirabilis, with an inhibition zone of 22 mm. The results of molecular docking indicated that most of the compounds exhibited good stability within the DHPS active site. Among them, salicylic acid emerged as the most stable compound, demonstrating a remarkable affinity as reflected by its docking score of -6.901 kcal/mol. Overall, this plant could have therapeutic potential against oxidative stress, bacterial infections, and cancer.