Bioactive constituents from Gardenia aqualla (Rubiaceae) stem bark as promising antibacterial agents: In vitro and in silico insights

Continuing phytochemical investigation of the methanolic extract of Gardenia aqualla stem bark led to the isolation of a new fatty acid ester, henpentacontyl acetate (1), together with four known compounds: trans-apo-8'-carotenoic acid (2), ethyl (all-E)-8'-trans-apo-β-caroten-8'-oate (3), D-mannitol (4), and 2,3,4,5,6-pentahydroxyhexyl acetate (5). Acetalation of D-mannitol afforded a new derivative, 1,2:5,6-di-O-isopropylidene-D-mannitol (4a). The structures of all isolated and synthesized compounds were established by spectroscopic and spectrometric analyses and comparison with literature data. The antibacterial potential of compounds 1-5 was assessed in vitro using the microdilution method against Gram-positive and Gram-negative bacteria. Compounds 2 and 3 exhibited significant activity against Staphylococcus aureus ATCC700698 and S. aureus NR46003 (MIC = 8 μg/mL), while other compounds showed low to moderate effects depending on the strain. Molecular docking analysis against S. aureus pyruvate kinase demonstrated that compounds 2 and 3 had higher binding affinities (-11.94 kcal/mol) than ciprofloxacin (-8.54 kcal/mol) and penicillin (-8.16 kcal/mol). ADMET predictions revealed that compound 1 possesses favorable pharmacokinetic and low-toxicity properties, whereas compounds 2 and 3 showed good drug-likeness but limited solubility. Compound 4a exhibited improved pharmacokinetic parameters and an extended half-life, suggesting potential for further development. Collectively, these findings highlight the therapeutic promise of G. aqualla constituents, particularly compounds 2, 3, and 4a, as antibacterial agents for managing oral and ear infections.