Chemical Composition, Biological Activities, and Docking Studies of Essential Oil from Eupatorium odoratum L. Collected in Dak Lak, Vietnam

Eupatorium odoratum L. (Asteraceae), also known as Siam weed, is widely used to stop bleeding and treat diarrhea. However, studies on the chemical composition and biological properties of essential oil from individuals of this species collected in Dak Lak, Vietnam have not been investigated. The chemical composition of E. odoratum essential oil was analyzed using gas chromatography-mass spectrometry (GC–MS), while the antioxidant and antibacterial capacity of E. odoratum essential oil were evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the agar disc diffusion methods, respectively. Molecular docking was used to study the binding energy between major constituents of the essential oil and Escherichia coli DNA (deoxyribonucleic) gyrase subunit B (GyrB). An essential oil yield of 0.61% was obtained, with 51 compounds identified. Among them, the major constituents were germacrene D (20.59%), caryophyllene oxide (12.10%), estragole (11.01%), caryophyllene (9.52%), geijerene (8.21%), cadinene (5.96%), guaia-6,9-diene (4.49%), 3-ethenylcyclopentene (3.54%), and copaen (3.08%). The antioxidant efficiency of the essential oil was determined, with an IC50 of 5.8 ± 0.3 μg/mL. In the antibacterial test, E. odoratum essential oil demonstrated strong antibacterial activity against E. coli (ATCC 25922), with an inhibition zone of 16.4 ± 0.4 mm and a lowest minimum inhibitory concentration (MIC) value of 4.2 ± 0.5 mg/mL. Molecular docking studies revealed binding energy between the essential oil’s major constituents and GyrB ranges of −5.0 to −6.5 kcal/mol, predominantly involving hydrophobic interactions with active site residues. These findings indicate that E. odoratum collected in Dak Lak, Vietnam, possesses a high natural potential for pharmaceutical applications.