The essential-oil composition of Inula helenium L. subsp. turcoracemosa Grierson from Turkey

Abstract

Inula helenium L. (Asteraceae) lipophilic root extracts were previously reported to contain antiproliferative eudesmane (alantolactone derivatives), germacrane and elemane-type sesquiterpene lactones [1]. Additionally, according to a previous report, the essential oil of I. helenium roots contained predominantly alantolactone (52.4%), and isoalantolactone (33.0%), while the oil displayed fungistatic and bacteriostatic properties [2]. In the current study, the essential oil composition of the aerial parts of I. helenium subsp. turcoracemosa collected in Trabzon was determined. The essential oil was obtained by hydrodistillation (3 h) using a Clevenger apparatus. The essential-oil yield was below 0.01% (v/w). The essential oil was trapped in n-hexane and dried over anhydrous Na₂SO₄. The essential oil was analyzed by GC-MS without further dilution. The essential oil was analyzed with an Agilent 5977 MSD GC-MS system operating in EI mode; injector and MS transfer line temperatures were set at 250 °C. Splitless injection was used in the analysis. Innowax FSC column (60 m x 0.25 mm, 0.25 µm film thickness) and helium as the carrier gas (1 mL/min) were used in GC-MS analyses. The oven temperature program was: 60 °C for 10 min and then raised to 220 °C at a rate of 4 °C/min, afterward the temperature was kept constant at 220 °C for 10 min and then raised to 240 °C at a rate of 1 °C/min. Mass spectra were recorded at 70 eV with the mass range m/z 35-425. Relative amounts of the separated compounds were calculated from the integration of the peaks in MS chromatograms. Identification of essential-oil components was carried out by comparison of their retention indices (RI), relative to a series of n-alkanes (C₅ to C₃₀), with the literature values, as well as by mass spectral comparison. Ninety-one compounds were identified representing 82.4% of the detected oil constituents. The main components of the oil were caryophyllene oxide (14.7%), eudesma-5,11(13)-dien-8,12-olide (alantolactone, 6.7%), isoalantalactone (3.8%), and aromadendrene oxide (3.3%). The aerial parts oil of I. helenium subsp. turcoracemosa also contained high amounts of eudesmane sesquiterpenes in accordance with the previous reports on I. helenium root essential oil. Our results indicate that eudesmanolides are also present in the aerial parts essential oil.