## 3 Discussion
This study was the first report written on the essential oils extracted from Saudi _R. chalepensis_ aerial parts using HS-SPME, and it analyzed its constituent using GC/MS. In recent years, there has been a demand to increase the research and development of new medicines derived from natural products. Essential oils and their constituents are categorized as safe secondary metabolites isolated from natural products. They have been observed with numerous biological activities [8]. The volatile constituents isolated from various genus of _Ruta_ used in folk medicine remedies and the literature have been studied their biological activity. Insecticidal, anti-inflammatory, antioxidant, antiprotozoan, antimicrobial, cytotoxic, herbicidal, larvicidal, and anthelmint are among the important biological activities of _Ruta_ oils [8]. The spread of many modern diseases, as a result of the presence of free radical stimuli these days, requires counteracting agents known scientifically as antioxidants. This is very important, especially with those derived from new, safe, and effective natural products. Various studies confirmed the antioxidant potency of oils [18; 19], and it depends on their constituents. Many essential oils demonstrated significant antioxidant activity and referred to the presence of oxygenated monoterpenes such as alcohols, ketons, aldehydes, and esters. In this work, three in vitro studies were used to evaluate the antioxidant potency of essential oil extracted from the aerial part of _R. chalepensis_ Saudi species. The results of DPPH, nitric oxide scavenging, and FRAP reducing power studies showed a concentration-dependent antiradical potency when compared to a strong natural antioxidant drug, ascorbic acid. An oil dose of 100 \(\upmu\)L gave 86.25 \(\pm\) 1.22, 82.30 \(\pm\) 4.73, and 1.43 \(\pm\) 0.05 compared to ascorbic acid, which gave 91.07 \(\pm\) 2.28, 89.68 \(\pm\) 3.49, and 1.97 \(\pm\) 0.11, respectively (Table 2). Regarding the IC50% inhibition of free radical formation, values were determined as 40.26%, 36.88%, and 19.09% in comparison to the potent antioxidant control drug ascorbic acid, which was 20.94%, 24.75%, and 16.10%, respectively, using DPPH radical inhibition, nitric oxide scavenging, and FRAP reducing power assessment studies, respectively (Table 3). Therefore, it is obvious that the effectiveness of the isolated oil by HS-SPME was proven as a natural and safe source. Further, its antioxidant effect increases with increasing doses, and the oil is considered safe even when high doses are used up to 2000 mg/kg. Recently, there has been an increase in the use of computational methods, such as molecular docking, to assess the interactions between natural products and their biological targets [20; 21]. The ROS are produced in the mitochondria via oxidative phosphorylation and NADPH oxidase. Additionally, NADPH oxidase facilitates abnormal cell proliferation and intracellular signaling processes. This has been detected in numerous modern diseases; thus, when inhibited, it exhibits antioxidant and reactive oxygen scavenging potencies [22]. To understand the ability of the oil to inhibit NADPH oxidase enzymes and to find a correlation between the antioxidant results, all compounds obtained from the GC-MS analysis, along with ascorbic acid (standard), were docked against the NADPH oxidase enzyme. The hydrophobic interactions, such as pi-alkyl and alkyl as well as hydrogen bonds, play a significant role in protein-ligand interactions, and they support its stability. Overall, psoralen, (_E_)-\(\alpha\)-bisabolene, \(\delta\)-cadinene, bergapten, germacrene D, \(\beta\)-eudesmol, and \(\alpha\)-Selinene may have some potential as inhibitors of important oxidative enzyme NADPH and may contribute either singly or in synergistically to achieve the antioxidant properties of the titled plant essential oil.