Chemical Composition and Preliminary Screening of Anticholinesterase and Antioxidant Activities of the Essential Oil of Ambrosia arborescens Mill. from Southern Ecuador

Ambrosia arborescens Mill., a native medicinal plant traditionally used in the Andean region, has a poorly characterized essential oil (EO), with no prior reports on its anticholinesterase or antioxidant potential. As a first report and preliminary screening study, this work characterizes the chemical composition of the EO and evaluates its acetylcholinesterase (AChE) inhibitory and antioxidant activities. The EO was isolated by hydrodistillation and analyzed using gas chromatography coupled with mass spectrometry (GC–MS) and flame ionization detection (GC-FID). The biological activities were evaluated using the Ellman method to determine AChE inhibition and using ABTS and DPPH assays to determine antioxidant activity. Analysis of the chemical composition revealed 31 compounds, and the major components were γ-curcumene (28.63%), trans-muurola-4(14),5-diene (27.85%), and eucavone (18.46%). The EO showed moderate AChE inhibitory activity, with an IC50 value of 28.04 ± 1.02 µg/mL, and limited antioxidant activity, with ABTS SC50 = 373.75 ± 1.30 µg/mL and DPPH SC50 = 1101.84 ± 1.63 µg/mL. These findings demonstrate that the EO possesses selective anticholinesterase activity and limited antioxidant capacity. Given the structural diversity of its constituents, the observed bioactivity is likely the result of the combined contributions of multiple components; however, the specific active constituents and potential synergistic interactions require further investigation through bioassay-guided fractionation. These findings represent the first preliminary screening of the biological activities of A. arborescens EO and provide a foundation for future bioactivity-guided investigations.