Essential oil composition of Hypericum triquetrifolium Turra growing wild in Iran.

The chemical composition of the volatile oil from aerial parts of Hypericum triquetrifolium Turra was studied by GC-MS. Fifty components (97.1% of the total composition) were detected in the volatile oil. Germacrene-D (21.7%), β-caryophyllene (18.3%), δ-cadinene (6.4%), trans-β-farnesene (4.3%), α-humulene (3.8%), β-selinene (3.7%), γ-cadinene (3.3%) and trans-phytol (3.2%) were found to be the major constituents of the oil. The oil of H. triquetrifolium consisted of five monoterpene hydrocarbons (3.4%), two oxygenated monoterpenes (0.4%), twenty-two sesquiterpene hydrocarbons (77.1%), eight oxygenated sesquiterpenes (7.9%) and one oxygenated diterpene (3.2%). Twelve nonterpenic compounds were also consisted 5.1% of the oil. In conclusion, the oil of H. triquetrifolium was characterized by a high content of sesquiterpenes (85.0%), whereas monoterpenes contained only 3.8% of the essential oil.

INTRODUCTION

The genus Hypericum, belonging to the Hypericaceae family, consists of about 380 species (1). The genus represented in the flora of Iran by seventeen species including three endemics (2). Hypericum perforatum L. (St. John's wort), the most famous species of the genus, is well known as a medicinal plant for the treatment of moderate depression (1).

Previous phytochemical study of Hypericum has led to the isolation naphthodianthrones of hypericin and pseudohypericin (3), phloroglucinol derivatives (4), flavonoids (5), xanthones (6), tannins (7) and essential oils (8).

Hypericum triquetrifolium Turra is an herbaceous perennial plant and one of the Iranian native species of Hypericaceae which is distributed in the south-west of the country. According to the literature, H. triquetrifolium contains hypericin (9), flavonoids, phenolic compounds such as chlorogenic acid (10) and essential oil (11). Volatile oil constituents of H. triquetrifolium from Italy have previously been reported and n-nonane (15%), germacrene-D (13%), caryophyllene oxide (12%), b-caryophyllene (11%), a-pinene (10%), myrcene (5%), b-pinene (4%) and sabinene (3%) were recognized as main components of the oil (12). 1-Hexanal (18.8%), 3-methylnonane (12.5%), α-pinene (12.3%), caryophyllene oxide (4.7%), 2-methyldecane (4.5%) and α-amorphene (4.2%) are predominant constituents of the essential oil of the aerial parts of H. triquetrifolium grown in Turkey (13) and α-humulene, cis-calamenene, δ-cadinene, bi-cyclogermacrene, eremophilene, β-caryo-phyllene, (E)-γ-bisabolene and α-pinene were also found as the major components of the Tunisian H. triquetrifolium oil (14).

There are some reports on the antioxidant (15), antibacterial (16), antiinflammatory (17), antinociceptive (18) and cytotoxic activities (19) of this plant. From ethyl acetate extract of the aerial parts of H. triquetrifolium four compounds including one biflavonoid, one flavonol, one flavonol-glycoside and one phenolic acid, namely, 3,8” biapigenin, quercetin, rutin and chlorogenic acid are reported. Study of the antioxidant activity of isolated compounds indicated that 3,8” biapigenin had an activity similar to α-tocopherol, while rutin, quercetin and chlorogenic acid exhibited a slightly weaker activity than a-tocopherol (20).

In another study, the antioxidant activity of ethanol extract of H. triquetrifolium was investigated. The extract was highly active in the DPPH radical scavenging assay with IC50 value of 39.0 μg/ml. It means that ethanol extracts of the plant is a potential source of natural antioxidants (21). Potential new antioxidant agents are interested for their role in the maintenance of the antioxidant system and prevention of aging, atherosclerotic and inflammatory diseases (22).

Inhibition of mono amino oxidase (MAO) activity of bioactive constituents of hypericin is the most important factor of antidepressive effect of Hypericum extracts (23). Only few species of Hypericum contain hypericin and H. triquetrifolium is one of them (9). Different biological activities of the medicinal plants reported in the literature candidate them as an interesting medicinal source. In this direction and as a part of our research on the aromatic flora of Iran, the constituents of essential oil of H. triquetrifolium growing wild in Iran was investigated.

MATERIALS AND METHODS

Plant material

The aerial parts of H. triquetrifolium were collected during May 2012 from the Fars province in the south-west of Iran at an altitude of ca. 1260 m above the sea level. The plant was identified by Department of Biology, Science and Research Branch, Tehran Islamic Azad University of Iran and a voucher specimen of the plant numbered as 2819 is deposited in the Herbarium of the School of Pharmacy and Pharmaceutical Sciences of Isfahan University of Medical Sciences, Isfahan, Iran.

Isolation of the oil

The essential oil of the aerial parts of H. triquetrifolium was obtained by hydro-distillation using a Clevenger-type apparatus for 3h according to the method recommended in the British Pharmacopoeia (24). The volatile oil was dried over anhydrous sodium sulfate and stored in a sealed vial at 4 °C until analysis.

Analysis of the oil

Gas chromatography combined with mass spectrometry was used for identification of the oil components. The analysis was performed on an Agilent 5975C mass selective detector coupled with an Agilent 7890A GC, equipped with an HP-5MS capillary column (30 m × 0.25 mm; film thickness 0.25 μm). The oven temperature was programmed from 60-280 °C at the rate of 4 °C per min.

Helium was used as the carrier gas at a flow rate of 2 mL/min. Injector and detector temperatures were set at 280 °C. The MS operating parameters were as follows: ionization voltage, 70 eV; ion source temperature, 230 °C (25). The MSD ChemStation was used as operating software.

Retention indices were calculated by using retention times (RT) of n-alkanes (C8-C24) that were injected following oil injection under the same conditions. Components of the oil were identified by comparison of their retention indices (RI) with those reported in the literature (26) and computer matching with NIST and Wiley275.L libraries. The fragmentation patterns of the mass spectra were also compared with those reported in the literature(2627).

RESULTS

The aerial parts of H. triquetrifolium yielded 0.1% (v/w) of a pale yellowish essential oil. Fifty components were detected in the volatile oil. The identified components and their percentage are given in Table 1, where the components are listed in order of their elution on the HP-5MS column. Germacrene-D (21.7%), β-caryophyllene (18.3%), δ-cadinene (6.4%), trans-β-farnesene (4.3%), α-humulene (3.8%), β-selinene (3.7%), γ-cadinene (3.3%) and trans-phytol (3.2%) were found to be the major constituents of the oil.

Table 1

Percentage composition of the essential oil of Hypericum triquetrifolium Turra.

The structure of major constituents of essential oil of H. triquetrifolium could be seen in Fig. 1.

Fig. 1

Structure of major components of essential oil of H. triquetrifolium

The oil of H. triquetrifolium consisted of five monoterpene hydrocarbons (3.4%), two oxygenated monoterpenes (0.4%), twenty-two sesquiterpene hydrocarbons (77.1%), eight oxygenated sesquiterpenes (7.9%) and one oxygenated diterpene (3.2%). Twelve nonterpenic compounds were also consisted 5.1% of the oil. In conclusion, the oil of H. triquetrifolium was characterized by a high content of sesquiterpenes (85.0%), whereas monoterpenes contained only 3.8% of the essential oil.

DISCUSSION

Volatile oil of the leaf of H. triquetrifolium from Calabria (Italy) have previously been reported to contain n-nonane (15%), germacrene-D (13%), caryophyllene oxide (12%), β-caryophyllene (11%), α-pinene (10%), myrcene (5%), β-pinene (4%) and sabinene (3%)(12). Evidently nonane, caryophyllene oxide and α-pinene are the major components of the oil of the leaf of H. triquetrifolium from Calabria (Italy), while these components was found to be present in trace amounts in the volatile oil examined in the present study.

While sesquiterpenes are the dominant fractions of essential oil of the aerial parts of Tunisian H. triquetrifolium, α-humulene, cis-calamenene, δ-cadinene, bicyclogermacrene, eremophilene, β-caryophyllene and (E)-γ-bisabolene were found as the main sesquiterpenes components presented in this oil. α-Pinene was also reported as the main monoterpene of the oil (14).

In contrast to Iranian and also Tunisian sample of H. triquetrifolium, study of volatile oil constituents of aerial parts of H. triquetrifolium grown in Turkey showed that monoterpene concentrations were higher than sesquiterpene levels. 1-Hexanal (18.8%), 3-methylnonane (12.5%), α-pinene (12.3%), caryophyllene oxide (4.7%), 2-methyldecane (4.5%) and α-amorphene (4.2%) are three predominant constituents of the oil of H. triquetrifolium samples grown in Iran and Tunisia (13). Essential oils composition of the plants could be affected by many parameters such as seasonal variation (28), phonological cycle (29) and geographic distribution. Study of volatile constituents of five populations of Tunisian H. triquetrifolium indicates that the essential oil compositions are variable and four chemotype groups could be recognized (30).

CONCLUSION

It is concluded from this study that in spite of some similaritIes in essential oil composition of H. triquetrifolium growing in Iran to one growing in Italy, the effect of geographic distribution in variety of components and their percentages could completely be observed.