The GC-MS Analysis of the Essential Oil of Cleome austroarabica

Published in Khimiya Prirodnykh Soedinenii, No. 1, January–February, 2021, pp. 146–147.

Cleome (Cleomaceae) is a genus of flowering plants consisting of 206 species, with 12 species in Oman, distributed mainly in tropical and subtropical countries [[1]]. Various species of the genus are used as folk medicine for the treatment of scabies, stomachache, inflammation, and rheumatism; the essential oils from this plant also show cytotoxic and antimicrobial activity [[2]–[6]]. Several secondary metabolites of the genus also show biological activities; these metabolites are terpenes, sterols, flavonoids, glucosinolates, indole alkaloids, and isothiocyanates, and they are found in various Cleome species [[7]–[10]].

Cleome austroarabica D. F. Chamb. & Lamond, endemic to Southern Arabia, including Oman, is a herbaceous sticky plant with unpleasant odor [[11]] and is locally called Muqabil Al Shams in Arabic [[12]]. The plant is traditionally used in Oman for its different medicinal properties. It is used as eyedrops to treat cataract, while the sweet-smelling leaves are crushed and rubbed over the body as a deodorant [[12]]. Previous studies have reported the biological and toxicological evaluation of aerial parts of the extracts of C. austroarabica [[1]]. So far there has been no attempt, to the best of our knowledge, to study the essential oil composition of the selected plant. Therefore, the aim of the current study is to investigate the volatile chemical constituents of the essential oil (EO) of C. austroarabica for the first time.

The hydrodistillation of aerial parts of C. austroarabica gave a light yellowish oil with a yield of 0.3% (v/w). Identification of the compounds was made by comparing their mass spectrum retention indices with those given in the literature and authentic. The chemical profile showed that the EO of C. austroarabica contained 47 chemical compounds, representing 97.11% of the total EO (Table 1). Three constituents, constituting greater than 10% of the total oil, were identified through GC-MS: thunbergol (36.66%), β-eudesmol (13.98%), and α-eudesmol (10.38%). Four compounds, representing greater than 2%, were identified, namely: γ-eudesmol (4.04%), 6-epi-shyobunol (2.88%), β-bisabolene (2.74%), and bicyclo[4.3.0]nonane, 7-methylene-2,4,4-trimethyl-2-vinyl (2.65%) (Table 1). Among the secondary metabolites, the essential oils (EOs) are the most structurally diverse group, with monoterpenes and sesquiterpenes the major volatile compounds released from the plants into the environment [[13]]. The major component of the EO, thunbergol, is a macromonocyclic diterpene alcohol previously reported in Cleome brachycarpa (46.1%) collected from Iran. The second and third major components of the EO, β-eudesmol and α-eudesmol, are sesquiterpenes previously reported in the Cleome droserifolia (β-eudesmol, 7.0%) and C. brachycarpa (12.7%), respectively [[12], [14]–[16]]. This variation in the concentration may be due to climatic and environmental factors such as ecospecies, location, season, soil properties, age of plant, and extraction techniques. The presence of diterpenes and sesquiterpenes in the EO seems to be a characteristic of Cleome species as has been reported for several species of this genus [[14]–[16]].

Table 1 Composition of Essential Oil from C. austroarabica, %

Homologous series of n-alkanes (C8–C30).

The fresh aerial parts of C. austroarabica were collected from Birkat Al Mouz, Nizwa, Oman (November, 2016) and identified by the plant taxonomist Dr. Syed Abdullah Gilani at the Department of Biological Sciences and Chemistry, College of Arts and Sciences, University of Nizwa. A voucher specimen (CA-11/2016) was deposited in the herbarium of Natural and Medical Sciences Research Center, University of Nizwa, Oman. The essential oil was extracted by hydrodistillation for at least 6 h using an 8-quart stove still home distillation unit with a Clevenger apparatus. After drying over anhydrous Na2SO4, the obtained essential oil was kept in the refrigerator prior to further analysis.

The GC-MS analyses were carried out with a Shimadzu GC-MS-QP/5050A apparatus equipped with a quadrupole mass spectrometer and a J&W Scientific DB-5MS (5% phenyl–95% dimethylpolysiloxane) fused-silica capillary column (30 m × 0.25 mm, I.D × 0.25 mm film thickness). The oven temperature was programmed to increase from 31°C to 271°C at 3°C/min. Injector and interface temperatures were kept at 275°C and 300°C, respectively. Helium was used as carrier gas with a linear velocity of 44.6 cm/s, column flow rate of 1.5 mL/min, and total flow rate of 36 mL/min. The split ratio was 1:21. Mass spectra were continuously recorded over the mass range 35 to 501 amu. The MS operating parameters were as follows: ionization voltage 70 eV and scan rate 500 amu/s. Additionally, the mass spectra obtained were compared to those recorded in the computer MS library (Wiley 229,000 database) or with the published data [[16]–[18]].

The authors would like to thank The Oman Research Council (TRC) for generous support through the Project BFP/RGP/CBS/18/011.