Secondary metabolites, phytochemical characterization and antioxidant activities of different extracts of Sideritis congesta P.H. Davis et Hub.-Mor.

https://doi.org/10.1016/j.bse.2020.104120Get rights and content

Highlights

  • Seven compounds were isolated from Sideritis congesta.

  • The first report on the isolation of the polar constituent from S. congesta.

  • Compounds 2, 6 and 7 are reported for the first time from the genus Sideritis L.

  • The in vitro antioxidant potential of S. congesta was shown.

  • Quali- and quantitative analyses of phenolics were achieved by LC-MS/MS and HPTLC.

Abstract

Sideritis congesta, an endemic plant to Turkey, is extensively consumed as energizing herbal tea and used as a remedy in folk medicine. This study was designed to comparatively evaluate the phytochemical composition and antioxidant potentials of different extracts (methanol, infusion) and fractions (chloroform, ethyl acetate, and remaining water) of S. congesta. Antioxidant potentials of the samples were evaluated by DPPH radical scavenging, FRAP, CUPRAC, and total antioxidant capacity tests. Total phenolic, phenolic acid, and flavonoid contents were also evaluated spectrophotometrically. Moreover, presence of twenty-two phenolic metabolites were affirmed by using LC-MS/MS in MRM scan mode and then the quantification of verbascoside, martynoside, and leucoseptoside A was performed by using HPTLC densitometry. EtOAc fraction contained the highest phenolic content and the antioxidant activity, as well as the highest verbascoside and martynoside contents followed by R-H2O fraction. Phytochemical studies on R-H2O fraction, yielded seven compounds, including a phenylethanoid glycoside, verbascoside (1), two flavonoids, stachyspinoside (2), isoscutellarein 7-O-(6‴-O-acetyl)-β-allopyranosyl-(1 → 2)-β-glucopyranoside (3), a phenolic acid chlorogenic acid (4), an iridoid glycoside ajugoside (5), and a monoterpenoid glucoside mixture betulalbuside A (6) and 1-hydroxylinaloyl 6-O-β-D-glucopyranoside (7). The molecular structures of the isolated compounds were determined by NMR and MS experiments. This is the first phytochemical study on the polar constituent of S. congesta and the first report of the isolation of compounds 2, 6 and 7 from the genus Sideritis L.

Introduction

As reported by the up to date taxonomical classification, Sideritis genus (Lamiaceae) includes over 150 species spread in the Western Palearctic zone. The name Sideritis evolved from the Greek "σίδερο", which means iron, as it is used for curing wounds caused by metal arms (Aneva et al., 2019). In Turkey, this genus contains 46 species with high rates of endemism (36 of which are endemic). The plant is known as “dağ çayı" (mountain tea) in Turkey. In addition to its utilization as stimulating tea or flavoring agent, infusion has been consumed for healing purposes. Sideritis spp. is utilized against cough, gastrointestinal complaints, and other symptoms of common cold as well as wound healing in traditional medicine (Baytop, 1999). Furthermore, researches proposed that the members of Sideritis genus have a broad range of pharmacological activities such as antimicrobial, antiproliferative, antiinflammatory, antifungal, antiulcerogenic, as well as antidiabetic (Gonzalez-Burgos et al., 2011). Amongst Sideritis spp., Sideritis congesta P.H. Davis et Hub. Mor. is an endemic plant to Southern Anatolia, Turkey. Ethnobotanical studies revealed that S. congesta is used against high blood pressure, cough, and obesity in Turkey (Aneva et al., 2019). Although, there are numerous studies regarding the secondary metabolites of Sideritis spp., only few are related with S. congesta which were particularly concentrated on the essential oil composition and terpenoids. Ent-kaurane diterpenoids were previously reported from the petroleum ether, acetone, and ethyl acetate extracts of the whole plant of S. congesta (Oktemer and Logoglu, 2003; Topcu et al., 2011). Three flavonoids known as chrysoeriol 7-O-gentiobioside, chrysoeriol 7-O-β-D-glucoside and salvigenin were isolated from EtOAc and petroleum ether extracts of S. congesta, respectively by Sezik and Ezer (1984). Furthermore, HPLC-DAD analysis for some free flavonoids and cinnamic acid derivatives of above ground parts of S. congesta showed existence of the high amounts of p-coumaric acid, chlorogenic acid, ferulic acid along with apigenin (Erkan et al., 2011). The essential oil distilled from S. congesta was dominated by β-pinene and α-pinenes (Ezer et al., 1996; Ozcan et al., 2001; Krimer et al., 2001; Ozel et al., 2008; Gumuscu et al., 2011). S. congesta has also been studied for its antioxidant, acetylcholinesterase inhibitory and analgesic activities by Aydin and Ozturk (1996), Erdogan-Orhan et al. (2010), Topcu et al. (2011), and Erkan et al. (2011).

Despite its widely use in Turkish folkloric medicine, S. congesta has not been investigated in terms of its major secondary metabolites through both isolation and analytical (HPTLC and LC-MS/MS) studies. Furthermore, the antioxidant potential of its crude MeOH extract and fractions were not previously investigated comparatively. Accordingly, this study was designed to comparatively assess the antioxidant potentials of crude MeOH extract, fractions (CHCl3, EtOAc, Remaining-H2O) and infusion prepared from the aerial parts of S. congesta by using several in vitro methods as well as to characterize their phenolic compositions by LC–MS/MS and HPTLC techniques. Additionally, main secondary metabolites of the R-H2O fraction were isolated, and their structures were elucidated by NMR and MS experiments.

Section snippets

General procedures

Chromatography: Column chromatography (CC) was achieved on silica gel 60 (0.063–0.200 mm; Merck, Darmstadt, Germany), Sephadex LH-20 (25–100 μm; Sigma-Aldrich, St. Louis, MO, USA) and Polyamide (50–160 μm; Fluka Analytical, Sigma-Aldrich, St. Louis, MO, USA). Medium-pressure liquid chromatography (MPLC) was completed using Sepacore® Flash Systems X10/X50 (Buchi Labortechnik AG, Flawil, Switzerland) on Redisep columns LiChroprep C18 and SiO2 (Teledyne Isco, Lincoln, Nebraska, USA). Thin layer

Isolation and structure elucidation of isolates

The R-H2O fraction was selected to purify the secondary metabolites based on the preliminary TLC analysis of the main fractions which revealed the existence of some different secondary metabolites in R-H2O fraction together with the phenolics that are also present in EtOAc fraction as well as the high amount of aqueous fraction. The successive chromatographic separations on the aqueous fraction afforded seven metabolites belonging to the subclasses of phenylethanoid glycoside [verbascoside (1

Conclusion

In this study the in vitro antioxidant potential of S. congesta as well as its secondary metabolite composition was investigated. The EtOAc and R-H2O fractions exhibited significant antioxidant potential. Phytochemical studies on the polar fraction (R-H2O) yielded seven secondary metabolites three of which (2, 6 and 7) are new for the genus Sideritis. Overall, these findings provided scientific basis for the traditional use of S. congesta which was shown to be potent antioxidant agent and rich

CRediT authorship contribution statement

Hilal Bardakci: Conceptualization, Formal analysis, Writing - original draft. Dicle Cevik: Conceptualization, Formal analysis, Writing - original draft. Timur Hakan Barak: Formal analysis, Writing - original draft. Tuba Gozet: Formal analysis, Writing - original draft. Yuksel Kan: Resources, Supervision. Hasan Kirmizibekmez: Supervision, Conceptualization, Writing - original draft.

Declaration of competing interest

Authors declare there are no conflicts of interest to report.

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