Chemical compositions and antioxidant activities of the essential oil from aerial parts of <i>Caryopteris mongolica</i> Bunge grown in Mongolia

The chemical composition of the essential oil from the aerial parts of <i>Caryopteris mongolica</i> Bunge, collected during the flowering period in the mountainous region of Songinokhairhan District, Mongolia, was determined following hydrodistillation and analysis by Gas Chromatography-Mass Spectrometry (GC-MS). A total of 65 compounds were identified, accounting for 95.46% of the total essential oil. The essential oil primarily consisted of monoterpene hydrocarbons (32%), diterpene hydrocarbons (10%), sesquiterpene hydrocarbons (15%), and a high content of oxygenated terpenes (over 36%). The major compounds, identified based on GC-FID peak area, were limonene (22.49%), <i>trans</i>-ferruginol (8.48%), phytol (8.41%), D-cadinene (4.44%), abietatriene (4.23%), caryophyllene oxide (3.84%), and β-pinene (3.26%). The antioxidant activity of the essential oil was evaluated for the first time using various test systems, including 1,1-diphenyl- 2-picrylhydrazyl (DPPH), 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS⁺), and the ferric reducing antioxidant power (FRAP) assays. The essential oil from <i>C. mongolica</i> exhibited moderate antioxidant activity, with IC₅₀ values of 12.73 μg/mL (DPPH), 19.68 μg/mL (ABTS⁺), and FRAP value of 600.12 μmol/L at 25 μg/mL. Molecular docking analysis revealed that the diterpene compounds abietatriene, isopimara-8,15-diene, <i>trans</i>-ferruginol, as well as the sesquiterpene α-calacorene, interact with Keap1, a key protein in the antioxidant pathway. These compounds bind to key amino acids Tyr334, Tyr572 and Phe577, suggesting their potential to inhibit the Keap1-Nrf2 interaction and activate the Nrf2-mediated antioxidant pathway. These findings highlight the promising antioxidant properties of the essential oil from aerial parts of <i>C. mongolica</i> Bunge, warranting further experimental validation.