Composition and AChE-inhibitory properties of Hypericum calycinum L. essential oil

Abstract

The genus Hypericum (Hypericaceae) is represented by 94 taxa in Turkey. Hypericum species are very well known due to their uses in folk medicine. There is a considerable number of studies done on Hypericum species available in the literature. Previously, the essential-oil composition of Hypericum calycinum L. obtained by microdistillation was reported. According to this report, the main components of the oil were α-pinene (24.2%), β-pinene (14.2%), myrtenal (4.5%), verbenone (4.5%), and trans-pinocarveol (4.2%) [1]. In the current study, the essential-oil composition H. calycinum collected from Şile–İstanbul was determined. The essential oil was obtained by hydrodistillation from aerial parts of the plant with a Clevenger apparatus for 3 h. The essential oil yield was 0.7% (v/w). The oil was dried over anhydrous Na₂SO₄. The essential oil was diluted 1:10 (v/v) in n-hexane and analyzed by GC-MS analysis. 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, afterwards 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. Fifty-four compounds were identified that represented 98.9% of the detected GC-peak areas. The main components of the oil were β-pinene (40.8%), α-pinene (17.7%), limonene (11.9%), and germacrene D (3.3%). The amounts of α- and β-pinene quantified in the oil obtained from Istanbul were found to be different from the previously reported for H. calycinum oil. The essential oil obtained from H. calycinum originating from Istanbul was characterized by a very high amount of β-pinene. The essential oil caused an 86±1% (n=3) AChE activity inhibition at the concentration of 5 mg/mL.