Chemical Composition and Biological Activity of Vietnamese Vernonia amygdalina Essential Oil: In Vitro and In Silico Studies

Vernonia amygdalina Del. (Asteraceae) is widely used to treat intestinal diseases, abdominal pain, helminth infections, dysentery, gastritis, and pinkeye. However, the chemical composition and biological properties of the essential oil of V. amygdalina collected in Dak Lak, Vietnam, have not been investigated. Gas chromatography-mass spectrometry (GC-MS) was used to identify the chemical composition of V. amygdalina essential oil. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and the agar disc diffusion method were used to evaluate the antioxidant and antibacterial activities of the essential oil, respectively. The binding energy between essential oil major constituents and Escherichia coli DNA gyrase subunit B (GyrB) was studied by molecular docking. The essential oil content was 0.67% by weight, and 40 constituents were identified, the major ones being 4-methylheptane (3.19%), 2-fluoromesitylene (26.61%), 4-(1,1-dimethylethyl) benzenethiol (10.99%), butylated hydroxytoluene (16.22%), 3-ethyl-4-heptanone (6.73%), and 3,5-dihydroxy-N,N-diethylbenzamide (13.91%). The strong antioxidant and antibacterial effects of V. amygdalina essential oil were demonstrated with an IC50 value of 6.4 ± 0.2 μg/mL and a lowest minimum inhibitory concentration (MIC) value of 4.6 ± 0.3 mg/mL, respectively. In molecular docking studies, the binding energy between the essential oil's major constituents and GyrB ranges from -6.0 to -4.5 kcal/mol. All major constituents were classified as “Caution” using the DL-AOT prediction server. Our results indicate that the essential oil of V. amygdalina collected in Dak Lak, Vietnam, has great potential in the pharmaceutical industry.