Phytochemical analysis of Saponaria officinalis L. shoots and flowers essential oils

Abstract Phytochemical analysis by GC and GC/MS of the essential oil samples obtained from fresh shoots and flowers of Saponaria officinalis L. allowed the identification of 96 components in total, comprising 94.7% and 86.0% of the total oils compositions, respectively. Regarding the shoots essential oil, the major of 87 identified volatile compounds were phytol (14.1%), tricosane-6,8-dione (13.4%), patchouli alcohol (7.9%) and tricosane (7.2%), whereas patchouli alcohol (20.0%), heneicosane (11.5%) and tricosane (8.4%) were dominant among the 66 volatiles in the flower oil. Nonterpenoid compounds had the highest contribution in S. officinalis shoots essential oil (53.7%), while in the flower oil, constituents were almost evenly distributed between the oxygenated sesquiterpenoid (41.2%) and nonterpenoid compounds (39.5%).


Introduction
Saponaria species (Caryophyllaceae) are perennial, flowering plants, native to Europe and Asia and commonly known as soapworts. According to the Plant list database the genus comprises 18 species altogether (The Plant List 2013;internet within the genus is Saponaria officinalis L. (common soapwort), which is native to Eurasia but is known in much of the world as an introduced species, often a weed, and sometimes as cultivated ornamental plant. It is also known by many other common names including bouncing-bet, crow soap, wild sweet William and soapweed. As its common name implies, due to the well documented high content of triterpene saponins, it can be used as a very gentle liquid soap, produced by boiling the leaves or roots in water (Jia et al. 1998;Vincken et al. 2007). In addition to saponins, soapwart also contains quillaic acid, flavonoids, different phenolic compounds and fatty acids (Cisowski et al. 1995;Lu et al. 2015). The biological activity of S. officinalis (including anti-inflammatory, cytotoxic, haemolytic, antiproliferative, antifungal or antibacterial effects) has been also widely described in the literature, which justified plant use in traditional medicine (Sparg et al. 2004;Wood 2008;Sengul et al. 2011). However, there are no previously published data about the essential oil chemical composition of any Saponaria species.
So, this study aims to determine the chemical compositions of the S. officinalis shoots and flowers essential oils. To the best of our knowledge this is the first report on the S. officinalis essential oil.

Results and discussion
The fresh shoots and flowers of the S. officinalis were chopped and separately hydrodistillated once per sample for 3 h, using a Clevenger type apparatus, to give essential oils with a yield of less than 0.01% (w/w). Chemical composition of the essential oils was determined by GC and GC/MS analyses, and it is presented in Table S1.
The composition of the essential oils of the shoots and the oil obtained from flowers was found to be quite different. The shoot essential oil has a lower content of sesquiterpenes compared to the flower oil, 22.1 and 42.5%, respectively. The distribution between sesquiterpene hydrocarbons and oxygenated sesquiterpenes appeared to be different too. In both essential oils the oxygenated sesquiterpenes predominated over the sesquiterpene hydrocarbons. A reverse distribution was observed for the diterpenes which are prevalent in shoots essential oil over the flowers oil (15.7 vs. 1.4%, respectively). Only the nonterpenoid compounds (mostly alkanes) were present in comparable amounts in both investigated essential oils.
In total, 87 components were identified in the oil isolated from the shoots, which accounting 94.7% of the essential oil composition. Nonterpenoid compounds were the main class (53.7%) with tricosane-6,8-dione (13.4%) and tricosane (7.2%) as the components with the highest content. Among the sesquiterpenoids, the second most abundant class of the oil, patchouli alcohol (7.9%) was found to be a main component. But, separately observed, the major component of the oil was the oxygenated diterpene phytol (14.1%). In the oil isolated from the flowers, 66 components were identified which makes 86% of total. Oxygenated sesquiterpenes and nonterpenoid compounds were present with similar contents (41.2 and 39.5%, respectively) with patchouli alcohol (20.0%) and heneicosane (11.5%) as the main representatives within classes. However, particularly in the flower oil, a high content of unidentified compounds was found (9.0%), for which there is no literature data and according to the characteristic ions in their mass spectra they could be some derivatives of alkaloid arecaidine.
Since there are no previously published investigations of the Saponaria species essential oils, the nearest reasonable comparison of their chemical composition might be done by taking into account volatiles composition of phylogenetically closely related Caryophyllaceae genera, Lychnis L. and Silene L., being distinguished from these by having only two styles in the flower. As reported, Silene morganae Freyn essential oil contained terpenoid compounds (43.5%) particularly monoterpene hydrocarbons (24.2%) as main constituents (Azadi & Sohrabi 2015). The most dominant compounds detected in the Silene armeria L. essential oil (Bajpai et al. 2008) were small mass nonterpenoid compounds: 1-butene (39.2%), methylcyclopropane (21.5%) and 2-butene (18.0%). On the contrary, in the essential oil of S. officinalis these constituents were not detected at all. Moreover, it was consisted mainly of high mass nonterpenoid and sesquiterpenoid compounds.

Conclusions
According to the obtained results, the essential oils of S. officinalis are consisted mainly of nonterpenoid and sesquiterpenoid compounds, implying that there are great differences in composition of the investigated essential oils and chemical profiles of volatiles isolated from the other representatives of the Caryophyllaceae family. It has already been suggested that essential oils may, despite their small yield, contribute to the plant medicinal properties of the plant and could be potentially used as a tool which gives a quick insight to the (dis) similarity of the compared species on a molecular level.
Considering the fact that volatiles of genus Saponaria are not investigated at all, more studies are needed regarding essential oil constituents of its species, which may be used as valuable chemotaxonomic markers for revealing infrageneric evolutionary relationships throughout this genus.

Supplementary material
Experimental details relating to this paper, alongside Table S1 (chemical compositions of the S. officinalis essential oils) are available online.

Disclosure statement
No potential conflict of interest was reported by the authors.

Funding
This work was supported by the Ministry of Education, Science and Technological Development of Serbia under Grant 172 047.