Chemical Composition and Biological Activities of Essential Oils from the Oleogum Resins of Three Endemic Soqotraen Boswellia Species

The chemical composition, antioxidant and anticholinesterase activity of three essential oils (EOs) obtained from the oleogum resin of three endemic Sqotraen Boswellia species, Boswellia socotrana Balf. f, Boswellia ameero Balf. f, and Boswellia elongata Balf. f were determined. GC-MS technique was used for the analysis of the oils. Oils of B. socotrana and B. ameero were characterized by a high content of monoterpenes. The main constituens of B. socotrana and B. ameero were (E)-2,3-epoxycarene (51.8%), 1,5-isopropyl-2methylbicyclo[3.1.0]hex-3-en-2-ol (31.3%), and α-cymene (7.1%); (3E,5E)-2,6-dimethyl-1,3,5,7-octatetraene (34.9%), 1-(2,4-Dimethylphenyl)ethanol (20.3%), 3,4-dimethylstyrene (17.3%), α-campholenal (13.4%) and αterpineol (12.4%) respectively. The composition of B. elongata oil was dominated by the diterpene verticiol (52.4%), the sesquiterpene caryophellene (39.1%) and methylcycloundecanecarboxylate (7.8%). The oils were screened for their antioxidant activity by using the DPPH free radical scavenger assay and their anticholinesterase activity on acetylcholinesterase enzyme by using in vitro Ellman method. The antioxidant activity of EOs from B. socotrana (IC50 =121.4 μg/mL) appeared to be more potent than that of B. elongata (IC50 =211.2 μg/mL) and B. ameero (IC50 =175.2 μg/mL). EO of B. socotrana showed the higher AChE inhibitory activity with 59.3% at concentration of 200 μg/mL in comparison to EOs of B. elongata and B. ameero (29.6, 41.6 enzyme inhibition) respectively.