Abstract
The hydrodistilled essential oil of the roots of Chromolaena odorata (L.) R. M. King & H. Rob. was analysed by gas chromatography equipped with flame ionization detector (GC-FID) and gas chromatography coupled with mass spectrometry (GC/MS). A total of twenty-nine compounds have been identified, accounting 97.6% of the total oil. The main constituents were himachalol (24.2%), 7-isopropyl-1,4-dimethyl-2-azulenol (17.6%), androencecalinol (14.1%), and 2-methoxy-6-(1-methoxy-2-propenyl) naphthalene (5.6%). The essential oil consists mainly of phenyl derivatives (41.6%), followed by oxygenated sesquiterpenes ((26.6%), long-chain hydrocarbons (18.9%), sesquiterpene hydrocarbons (6.8%), oxygenated monoterpenes (2.8%), and monoterpene hydrocarbons (0.9%). This study revealed that the roots of C. odorata produced different chemotypes other than leaves oil. This is the first report on the essential oil composition of the roots of C. odorata.
1. Introduction
Chromolaena odorata (L.) R. M. King & H. Rob. (Syn: Eupatorium odoratum L.) (Asteraceae) is a perennial herb and distributed throughout India, tropical Asia, and Mexico [1, 2]. In traditional medicine this plant is used in the treatment of coughs, colds, and skin diseases [3], wound healing, and as a local antiseptic agent [4]. C. odorata is a medicinal plant having diverse pharmacological properties, namely, anti-inflammatory [5, 6], antimicrobial [7, 8], antigonorrhoeal [9], antipyretic, antispasmodic [6], diuretic [10], analgesic [11], and wound healing [12] activities. The chemical compositions of the essential oils of C. odorata that have been reported from different countries [13–20] are summarized in Table 1. The essential oil constituents of the leaves of C. odorata from Benin reported as α-pinene, pregeijerene, geijerene, β-pinene, and germacrene D [13] as the major compounds. In a report from Cameroon and Congo, α-pinene and p-cymene [14], while, from India, pregeijerene, epi-cubebol, cubebol, cis-sabinene hydrate, 10-epi-γ-eudesmol, germacrene-D-4-ol, δ-cadinene, germacrene D, geijerene, cyperene, 10-epi-γ-eudesmol, α-muurolol and khusimone [15] have been identified as the major constituents. The major compounds such as α-pinene, geijerene, and pregeijerene from Ivory Coast [16, 17] and α-pinene, β-pinene, germacrene D, β-copaen-4α-ol, β-caryophyllene, geijerene, pregeijerene [18], α-pinene, cadinene, camphor, limonene, β-caryophyllene and cadinol isomer [8] from Nigeria have been identified. In another report from Thailand, pregeijerene, germacrene D, α-pinene, β-caryophyllene, vestitenone, β-pinene, δ-cadinene, geijerene, bulnesol, and trans-ocimene [19] have been reported as the major constituents. Review of literature revealed that the essential oil composition of the roots of C. odorata has not been examined. Thus the aim of this work is to present the volatile constituents from the roots of C. odorata. To the best of the author’s knowledge, this is the first report on the essential oil composition of the roots of C. odorata.
2. Experimental
2.1. Plant Material
The roots of C. odorata were collected in June 2011, at a height of 800 m from the district Belgaum (N 15.88668; E 74.52353), Karnataka, India. The plant was identified by Dr. Harsha Hegde, Research Scientist, Regional Medical Research Centre (ICMR), Belgaum (voucher specimen no. RMRC-410).
2.2. Isolation of Essential Oil
The fresh plant material (250 g) was chopped in small pieces and subjected to hydrodistillation using Clevenger-type apparatus for 3 h. The oil was collected and dried over anhydrous sodium sulfate and stored in sealed vials at −4°C until analysis. The oil yield was 0.3% v/w.
2.3. Gas Chromatography
The GC analysis of the oil was carried out on Varian 450 gas chromatograph equipped with FID, using stationary phase CP Sil-8-CB (30 m × 0.25 mm i.d., 0.25 μm film thickness) column under the experimental conditions reported earlier [20]. Nitrogen was a carrier gas at 1.0 mL/min flow rate. Temperature programming was set to 60–220°C at 3°C/min and the injector and detector temperatures were 230 and 250°C, respectively. The injection volume was 1.0 mL of 1% solution diluted in n-hexane; split ratio was 1 : 50.
2.4. Gas Chromatography-Mass Spectrometry
The GC-MS analysis of the oil was carried out on Thermo Scientific Trace Ultra GC (Thermo Fisher Scientific Austria, Vienna, Austria) interfaced with a Thermo Scientific ITQ 1100 Mass Spectrometer (Thermo Fisher Scientific Austria) fitted with TG-5 (30 m × 0.25 mm i.d., 0.25 μm film thickness) column. The oven temperature was programmed from 60 to 220°C at 3°C/min using helium as a carrier gas at 1.0 mL/min. The injector temperature was 230°C, injection volume was 0.1 mL of 1% solution prepared in n-hexane; split ratio was 1 : 50. MS were taken at 70 eV with mass scan range of 40–450 amu.
2.5. Identification of the Components
Identification of the constituents was done on the basis of retention index (RI, determined with reference to homologous series of n-alkanes C8–C25, under identical experimental conditions), MS library search (NIST 08 MS Library Version 2.0 f; Thermo Fisher Scientific Austria), and WILEY MS 9th Edition (Thermo Fisher Scientific Austria) and by comparing with the MS literature data [21]. The relative amounts of individual components were calculated based on the GC peak area (FID response) without using a correction factor.
3. Results and Discussion
Twenty-nine compounds were characterized and identified by GC-MS, comprising 97.6% of the total oil. The identified compounds are listed in Table 1 in elution order from the TG-5 MS column, along with the percentage composition of each component and its retention index. The main constituents were himachalol (24.2%), 7-isopropyl-1,4-dimethyl-2-azulenol (17.6%), androencecalinol (14.1%), and 2-methoxy-6-(1-methoxy-2-propenyl) naphthalene (5.6%). The essential oil consists mainly of 5 phenyl derivatives (41.6%), followed by 5 oxygenated sesquiterpenes (26.6%), 6 long-chain hydrocarbons (18.9%), 6 sesquiterpene hydrocarbons (6.8%), 4 oxygenated monoterpenes (2.8%), and 3 monoterpene hydrocarbons (0.9%). It is interesting that constituents identified in the essential oil of the roots of C. odorata were found contrary (see Table 2). The signature compounds from the leaves oil of this plant reported from different countries were almost the same with quantitative differences. The major constituents, pregeijerene, epi-cubebol, cubebol, cis-sabinene hydrate, germacrene-D-4-ol, germacrene D, geijerene, cyperene, α-muurolol, khusimone, β-copaen-4α-ol, camphor, limonene, vestitenone, bulnesol, and trans-ocimene (Table 1) were reported from the leaves oil of C. odorata, which could not identified even in trace amount from the roots oil of this plant. Moreover, the majority of the oil composition from other plant parts, namely, aerial parts and flowers of C. odorata were dominated by monoterpene and sesquiterpene hydrocarbons [13–20]. In this report, it is found that long-chain hydrocarbons and high contents of phenyl derivative compounds are present. The composition of the essential oil often changes between different plant parts [22]. The difference in the complex composition of essential oils of one kind may sometimes be difficult to assign to specific chemotypes. The formation of essential oils depends on the tissue differentiation (secretory cells and excretion cavities, etc.) and on ontogenetic phase of the respective plant [23]. The conclusion of this study revealed that the roots of C. odorata produced different chemotypes, namely, himachalol, 7-isopropyl-1,4-dimethyl-2-azulenol, androencecalinol, and 2-methoxy-6-(1-methoxy-2-propenyl) naphthalene, other than reported from the leaves oil.
Conflict of Interests
The author reports no conflict of interests. The author alone is responsible for the content and writing of this paper.
Acknowledgments
The author is thankful to the Dr. S. D. Kholkute, Director in Charge, Regional Medical Research Centre (ICMR), Belgaum, Karnataka, India, for providing necessary facilities and also thankful to Mr. Manjunath Patil, Laboratory Attendant, Department of Phytochemistry, RMRC, Belgaum, for the collection of the plant materials and extraction of the essential oils.