Essential Oil from the Aerial Part of Saponaria griffithiana and S. officinalis

Translated from Khimiya Prirodnykh Soedinenii, No. 5, September–October, 2021, pp. 828–830.

Species of the family Caryophyllaceae are perennial flowering plants growing in Europe and Asia and commonly known as soapwort [[1]].

The genus Saponaria is a member of the subfamily Caryophylloideae and numbers about 40 species inhabiting temperate Eurasia, mainly the Mediterranean region [[2]]. Six species grow in Uzbekistan.

According to the literature, essential oils from the aerial part (runners and flowers) of S. officinalis were studied only in the Flora of Serbia [[3]]. The main compounds in essential oil of runners were phytol (14.1%), tricosan-6,8-dione (13.4%), pachouli alcohol (7.9%), and tricosane (7.2%) while the dominant compounds in oil from flowers were pachouli alcohol (20.0%), heneicosane (11.5%), and tricosane (8.4%).

The chemical compositions and antimicrobial activities of essential oils obtained from the aerial parts of S. officinalis L. and S. griffithiana Boiss. were studied. The plants were collected during flowering in 2020 in the vicinity of Tashkent. The species was identified by Cand. O. M. Nigmatullaev in the Laboratory of Medicinal and Technical Plants, S. Yu. Yunusov Institute of the Chemistry of Plant Substances, AS RUz (herbarium No. 40.236431).

Essential oil was obtained from the aerial part of the air-dried plant by steam distillation in a Clevenger apparatus for 3 h using CH2Cl2 as a trap [[4]]. The obtained distillate was extracted by CH2Cl2. The extract of essential oil was dried over anhydrous Na2SO4. The yield of essential oil from S. officinalis was 0.7%; from S. griffithiana, 0.6% of the air-dried raw material. The compositions of the isolated volatile compounds were determined by GC-MS and NMR spectroscopy. Table 1 presents the results.

TABLE 1. Constituent Composition of Essential Oil from S. officinalis and S. griffithiana, %

*Missing in Wiley Registry of Mass Spectral Data, 9th Ed.; NIST Mass Spectral Library, 2011.

GC-MS analysis used an Agilent 5975C inert MSD/7890A GC chromatograph–mass-spectrometer. Essential oil constituents were separated over an Agilent HP-INNOWax quartz capillary column (30 m × 250 μm × 0.25 μm) using temperature regime 50°C (1 min), 4°C/min to 220°C (6 min), and 15°C/min to 250°C (15 min). The injected sample volume was 1.0 μL; mobile phase (H2) flow rate 1.1 mL/min; vaporizer temperature, 220°C; ion source, 230°C. Electron-impact ionization (70 eV) was used. EI-MS spectra were obtained in the range m/z 10–550 amu. Constituents were identified by comparing mass spectra with electronic libraries (Wiley Registry of Mass Spectral Data, 9th Ed.; NIST Mass Spectral Library, 2011) of the chromatograph–mass-spectrometer, the retention indices (RI) of the compounds determined from the ratio to the retention times of a mixture of n-alkanes (C9–C28), and their mass spectral fragmentations as compared to those in the literature [[5]]. The quantitative contents of essential oil constituents were calculated from chromatographic peak areas.

The volatile compounds of S. officinalis contained 38 identified constituents making up 92.5% of the total oil constituents. Alcohols (67.0%) and aldehydes and ketones (19.2%) dominated the essential oil. The contents of sesquiterpenes and oxidized sesquiterpenes were only 1.1 and 0.7%, respectively. The main constituents of the essential oil were decanal (1.1%), 2-furanmethanol (1.3%), benzyl alcohol (1.5%), nonanal (2.4%), phenylacetonitrile (2.5%), phenylacetaldehyde (10.1%), and an unidentified compound (62.3%) (Table 1).

Table 1 shows that the essential oil composition of S. griffithiana included 32 identified constituents making up 97.2% of all volatile constituents. Essential oil of this species was also dominated considerably by alcohols (86.4%) and aldehydes and ketones (7.7%). The main constituents were 1-hexanol (1.1%), 2-hexenol (1.1%), (E)-3-hexenyl acetate (2.0%), (Z)-3-hexen-1-ol (14.6%), phenylacetaldehyde (3.9%), and an unidentified compound (67.9%).

Considering the contents of the unidentified constituent (62.3 and 67.9%) in both samples, it was decided to establish its chemical structure using NMR spectroscopy. 1D (1H and 13C) and 2D (HSQC, HMBC, COSY) NMR spectra of the essential oils were recorded in CDCl3 with TMS internal standard on a JNM-ECZ600R spectrometer (JEOL, Japan) at operating frequency 600 MHz. The internal standard for 13C NMR spectra was CDCl3 (77.16 ppm vs. TMS). An analysis of the NMR spectral data established the structure of the unidentified constituent as 1-(2-furyl)ethanol. This compound was not included in the electronic library of the chromatograph–mass-spectrometer and its RI was not found in the literature. Thus, the RI (1570) of 1-(2-furyl)ethanol was reported for the first time for a polar column.

1-(2-Furyl)ethanol. C6H8O2. EI-MS, 70 eV, m/z (%): 112 (44), 97 (100), 95 (32), 94 (63), 69 (23), 66 (24), 65 (36), 43 (22), 41 (34), 39 (38). 1H NMR (600 MHz, CDCl3, δ, ppm, J/Hz): 1.54 (3H, d, J = 6.6, CH3), 4.88 (1H, qd, J = 6.6, 0.7, H-1), 6.23 (1H, dt, J = 3.2, 0.8, H-3′), 6.32 (1H, dd, J = 3.2, 1.8, H-4′), 7.37 (1H, dd, J = 1.8, 0.8, H-5′). 13C NMR (150 MHz, CDCl3, δ, ppm): 63.76 (C-1), 21.40 (CH3), 157.76 (C-2′), 105.22 (C-3′), 110.25 (C-4′), 142.03 (C-5′) [[7]].

Antimicrobial and antifungal activity were determined using a modified agar-diffusion method [[8]]. The results of the antimicrobial tests showed that bacteria test strains Bacillus subtilis, Staphylococcus aureus, and Escherichia coli were sensitive to the action of S. officinalis essential oil with an inhibition zone diameter between 8.08 ± 0.12 and 10.04 ± 0.10 mm. Essential oil from the aerial part of S. griffithiana exhibited antibacterial activity against all tested bacteria test cultures with the greatest antibacterial activity (17.08 ± 0.12 mm) against S. aureus. The studied essential oils did not possess antifungal activity against the conditionally pathogenic fungus Candida albicans.

Thus, essential oils from S. officinalis and S. griffithiana growing in Uzbekistan were considerably dominated by alcohols with 1-(2-furyl)ethanol having the greatest content.