Essential Oil Composition of Endemic Sideritis leptoclada O . Schwarz & P . H . Davis ( Lamiaceae ) from Turkey by Using Two-Dimensional Gas Chromatography-Time-of-Flight Mass Spectrometry ( GCxGC-TOF / MS )

Abstract: Sideritis genus is present by 46 species in Turkey with high endemism rate (ca. 82%). The chemical composition of essential oil obtained from the aerial parts of endemic Sideritis leptoclada O. Schwarz & P. H. Davis was investigated. The chemical composition of S. leptoclada from the Southern Turkey is reported for the first time by GCxGC-TOF/MS technique. Among the sixteen constituent representing 96.74% of the S. leptoclada oil, major components of S. leptoclada were found as β-pinene (24.84%), trans-β-caryophyllene (22.99%), αpinene (15.14%) and caryophyllene oxide (6.65%). The results were discussed with the genus pattern in means of medicinal purpose and plant essential oils.


Introduction
The genus Sideritis L. (Lamiaceae) with its nearly 150 species distributed in Northern hemisphere, occuring generally in the Mediterranean area [1][2][3].The Sideritis name derives from the Greek word 'sideros' (iron) in reference to these vulnerary plants that heal the wounds [4].Species of this genus, like Sideritis leptoclada O. Schwarz & P. H. Davis possess significant pharmacologic as well as economic values.Local people use this plant as herbal tea.Sideritis species are mainly named as mountain tea (dağ çayı in Turkish) in Turkey and comprises one of the most frequently traded herbs in bazaars.The genus Sideritis representing by 46 species and is an important species among the other Lamiaceae genera because the ratio of endemism (ca.80%) in Turkey [5].Sideritis species are frequently used in folk medicine due to their antiinflammatory, antimicrobial, anti-spasmodic, anti-rheumatic, digestive and diuretic activities [6].Recently, several studies have been reported on the chemical composition of Sideritis oils of different origins [7][8][9][10][11][12].However, there are no studies on the Sideritis oil were conducted by GCxGC-TOF/MS.GCxGC with TOF/MS is highly desirable for identification and increases sensitivity of volatile compounds.Therefore, the purpose of the this study was to investigate the content and composition of essential oil in the leaves of Sideritis leptoclada O. Schwarz & P. H. Davis (Lamiaceae), a local endemic species in Turkey.

Plant Material
The samples of S. leptoclada were collected from different locations from Sandras Mountain-Turkey.Voucher specimens were deposited in the Herbarium of the University of Pamukkale (Denizli, Turkey).Air-dried aerial parts were cut in small pieces (ca.10 mgr) and subjected to GCxGC-TOF/MS.

Direct Thermal Desorption (DTD) and GCxGC-TOF/MS analysis
The volatile compounds in S. leptoclada were analysed using DTD followed by GCXGC-TOF/MS.A GCXGC-TOF/MS system was used with a dual stage commercial thermal desorption injector.This incorporated a thermal desorption unit (TDU) which was connected, using a heated transfer line, to a programmable-temperature vaporisation (PTV) injector, CIS-4 plus (Gerstel, Mulheim an der Ruhr, Germany).The injector was equipped with a Gerstel MPS autosampler.Empty glass thermodesorption tubes were conditioned for 2h before use at a temperature of 400 °C [13].Approximately 10 mg of S. leptoclada was placed into the quartz microfiber filter (QM-A sheets, Whatman, VWR) and loaded into the thermodesorption tubes.To keep the sample in position, glass wool was employed.Initial desorption of the sample was effected by heating the TDU from 40 °C (initial time 0.2 min) to 150 °C at a rate of 120 °C min - 1 with a final hold time of 5 minutes under 1.5 mL min -1 helium flow in splitless mode.Volatile analytes emanating from this were cryo-focused at -40 °C in the CIS which had been cooled by liquid nitrogen prior to injection.The CIS was then heated at a rate of 10 °C s -1 to a final temperature of 150 °C.During this CIS temperature ramp, analytes were transferred to the GC column [13].

Chromatographic Analysis
The GCxGC-TOF/MS system comprised an HP 6890 (Agilent Technologies, Palo Alto, CA, USA) GC and a Pegasus III TOF/MS (Leco, St Joseph, MI, USA).The first column was a non-polar DB5 (30 m x 0.32 mm i.d.x 0.25 µm) and the second column a DB17 (1.9 m x 0.10 mm i.d.x 0.10 µm).Both columns were purchased from J&W Scientific (Folsom, CA, USA).The columns were connected using a press-fit connector [14].The first dimensional separation is based on separation by volatility, whilst the second dimensional separation is based on separation by polarity [15].The modulator secondary oven was operated at +15 °C higher than the GC oven temperature.The modulation time was 5 s and helium was employed as a carrier gas.The initial temperature of the first-dimension column was 60 ºC for 1 min; the temperature was then increased at 5 °C min -1 to 250 ºC, which was held for a 1 min.The initial temperature of the second-dimension column was 75 ºC for 1 min; the temperature was then raised at 5 °C min -1 to 265 ºC and held for a 1 min [16].TOF/MS with electron-impact ionisation was used to identify peaks.Analytes were identified by employing GC-MS software; according to the NIST mass spectral library, and also by comparing their Kovats retention indices.

Results and Discussion
The chemical composition of essential oil from S. leptoclada, an endemic species from the Southwestern Anatolia region of Turkey, was studied for the first time using GCXGC-TOF/MS.Table 1 represents the chemical composition of the essential oil from S. leptoclada.As can be seen from this table, 16 compounds, representing about 96.74% of the essential oil, were characterized.The major components are as follows: β-pinene (24.84%), trans-β-caryophyllene (22.99%), α-pinene (15.14%) and caryophyllene oxide (6.65%).Some of the Sideritis species of Turkey have been collected and their oils have been analysed by 10,12,17,18].Current literatures showed that α-pinene and β-pinene were already proposed as the main constituents of essential oils from certain other Sideritis species such as S. bilgerena P. H. Davis (51.2% and 30.2%, respectively), S. congesta P. H. Davis et Hub.-Mor.(19.5% and 28.8%, respectively), S. argyrea P. H. Davis (16.5% and 23.9%,respectively) and S. lycia Boiss. et Heldr. (21.6% and 32.2%,respectively) [8,11,[18][19][20].Sideritis species classified as 6 groups; monoterpene, oxygenated monoterpene, sesquiterpene, oxygenated sesquiterpene, diterpene and others [21].57% of the Sideritis species existing in Turkey belong to the "monoterpene hydrocarbon-rich" group as shown in Tabanca et al. [22].For our results, Sideritis leptoclada is also included in this group.But Başer [23,24] and Kırımer [20] classified Sideritis essential oils based on their main components, and S. leptoclada was included in the sesquiterpene-rich group, however, its whole essential composition was not presented previously; only the major component was given β-caryophyllene.In fact, Sideritis species are not rich in essential oil, but their smell and aroma are pleasant [25].The percentage of trans-β-caryophyllene was found as 22.99% in the S. leptoclada studied.The result is different from the other Sideritis species.These differences might have been derived both from sampling time and, climatic/seasonal factors particularly genetical features (different chemotype).

Table 1 .
Percentage composition of components identified in the leaves of S. leptoclada.