Elsevier

Phytochemistry

Volume 180, December 2020, 112530
Phytochemistry

Ecdysteroids from the underground parts of Rhaponticum acaule (L.) DC

https://doi.org/10.1016/j.phytochem.2020.112530Get rights and content

Highlights

  • Phytochemical investigation on the roots of Rhaponticum acalue (L.) DC. was performed.

  • Three undescribed stigmastane-type ecdysteroids have been identified.

  • The absolute configurations of some compounds were confirmed crystallographically.

Abstract

In addition to two known ecdysteroids, 20-hydroxyecdysone and turkesterone, three previously undescribed stigmastane-type ecdysteroids were isolated from the underground parts of Rhaponticum acaule (L.) DC. by chromatographic techniques (CC, VLC, MPLC). The structures of the compounds were established by chemical (acetylation) and spectroscopic methods including UV, IR, HRMS, 1D-NMR: 1H-NMR, 13C-NMR, DEPT-135. and 2D-NMR: COSY, NOESY, HSQC, HMBC. Two compounds were isolated as an isomeric mixture and each of them was purified and converted to the corresponding acetylated derivative. Based on all of the evidence, the structures of three undescribed stigmastane-type ecdysteroids were established as 2β,3β,11α,20β,22α,24,28-heptahydroxy-6-oxo-stigmast-7-en-25,29-lactone and the cyclic 22,29-hemiacetals 22R and 22S stigmast-7-en-29-al,2β,3β,11α,20α,22,28-hexahydroxy-6-oxo, and the trivial names acaulesterone and rhapocasterones A and B are suggested, respectively. The structures and absolute configurations of 20-hydroxyecdysone and cyclic-22,29-hemiacetal-22R-stigmast-7-en-29-al,2β,3β,11α,20α,22,28-hexahydroxy-6-oxo were confirmed by X-ray crystal-structure analyses of their acetyl derivatives.

Graphical abstract

Three undescribed stigmastane-type ecdysteroids were isolated from the underground parts of Rhaponticum acaule (L.) DC.

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Introduction

Asteraceae is an important family of flowering plants and considered as the largest of all the families of angiosperms. Genus Rhaponticum, which belongs to the family Asteraceae, includes approximately 25 species worldwide distributed mostly in Eastern and central Asia, the mountains of Siberia, Mongolia, Eastern Australia and one in North Africa (Özbek et al., 2017). The names Rhaponticum Vail (Rhaponticum Ludw, Rhaponticum Hill), Leuzea DC., and Stemmacantha Cass. are used in floristic reports and in publications covering the studies of this genus (Vorobyeva and Gorovoy, 2019).

Literature reports suggest the widespread use of Rhaponticum species in traditional medicine. To name just a few, R. uniflorium, known in China as Qizhou loulu (Guo and Lou, 1992), is used for detoxification, rheumatoid arthritis, fever, lactation and anti-atherosclerosis (Yan et al., 2013). Similarly, R. carthamoides is known as Maral Root in Siberia and Mongolia. It has traditionally been used to enhance physical and sexual energy, improve mood and concentration and as a tonic and anabolic (Skala et al., 2019; Winston and Maimes, 2019).

Reviews of the chemodiversity of some species of Rhaponticum revealed the presence of more than one hundred compounds, including representatives of such classes as sesquiterpenes, diterpenes, triterpenes, sterols, thiophenes, phenolic acids and flavonoids (Zhang et al., 2010). In addition, the Rhaponticum genus has gained attention as a promising source of ecdysteroide compounds. This genus has many species that contain a wide variety of ecdysteroids, which include, but are not limited to, the compounds ecdysone through 20-hydroxyecdysone, as well as Integristerone A and 24 (28)-dehydromaksisterone A (Namuna, 2019). At the present time, there is another species that has captured interest as the only representative of Rhaponticum genus in North Africa (Mosbah et al., 2018). Rhaponticum acaule (L.) DC. is an endemic species, popularly known as Tafgha. In addition to growing in limited geographical areas in North Africa, it is also distributed in the Northwest area of Libya. Rhaponticum acaule is a monocephalic perennial herb and has no stem (acaulescent), which is a characteristic feature that allows it to be distinguished from other species (Alavi et al., 1983). It has been used traditionally to treat disorder associated with inflammation (Rimbau et al., 1996) and also the powdered roots have been used as an aperitif, depurative, digestive, stomachic and tonic (Bendimerad-Mouttas et al., 2018).

To the best of our knowledge, very few phytochemical and biological studies were conducted on the R. acaule. In one of the phytochemical reports, the analysis of essential oil from the aerial part and capitula of R. acaule revealed the presence of fifty-seven components. Simultaneously, this study proposed that R. acaule can be used in grain storage against insect pests (Boussaada et al., 2008). The authors observed that the butanol and ethyl acetate extracts of R. acaule showed moderate antibacterial activity against some species of bacteria and concurrently strong inhibition against the fungus Trichophyton rubrum (Abdelkader et al., 2010). In addition, another study concluded that the oil composition of the roots is mainly represented by a variety of aliphatic hydrocarbons and terpenes (Benyelles et al., 2014).

Moreover, there has been an evaluation of the antioxidant, antibacterial and anticoagulant activity of the methanolic extract of the fruits of R. acaule (Benabdesselam et al., 2017). The essential oil of the aerial parts was reported to show strong inhibitory activity against α-glucosidase and xanthine oxidase (Mosbah et al., 2018).

Despite the availability of data in the current literature concerning R. acaule, it has not been investigated so far from a phytochemical point of view and there are to date no available reports on the isolation of specialized metabolites from the roots. The present work aims to provide a detailed report on the chemical composition of compounds isolated from the roots of R. acaule, emphasizing the ecdysteroids. Thus, it will be possible to compare the ecdysteroid profile of this plant with that of R. carthamoides and R. uniflorum used in different countries.

Section snippets

Results and discussion

Compound 1 was obtained as a white amorphous compound. The negative ion HR-MS of 1 gave a quasimolecular ion [M-H]- peak at m/z 479.3037, which corresponds with the molecular formula C27H43O7 with a Mr of 480.31 (calc. 479.30) and six degrees of unsaturation. The positive ion HR-mass spectrum exhibited pseudo-molecular ion peaks [M+H]+ at m/z 481.3157 and [M+Na]+ at m/z 503.2975 (calcd for C27H44O7Na). These results indicate the molecular weight of 1 to be 480.3087 (C27H44O7). The IR spectrum

Conclusion

This study, which was performed on the roots of Rhaponticum acaule (L.) DC., an endemic species limited to the geographical areas in North Africa including Libya, resulted in the isolation and characterizations of five ecdysteroids (15). Two of the isolated compounds, 20-hydroxyecdysone (1) and turkesterone (2) have been reported from Rhaponticum carthamoides (Willd.) Iljin, which is known as a Maral Root or Russian leuzea (Leuzea carthomoides DC.) and used in eastern parts of Russia for its

General experimental procedures

Classical column chromatography and a gradient Medium Pressure Liquid Chromatography (Büchi MPLC equipped by Pump Modules C-601 & C-605 with a pump Controller C-610 and pump manager C-605) and a Büchi Fraction Collector C-615 were used for the isolation process. Silica gel (0.063–200 mm, Merck), LiChroprep C-18 (0.063–200 mm, Merck) and Sephadex LH-20 were used as stationary phases throughout the chromatographical studies. Silica gel alumina plates (Silica Gel 60 F254, Merck) were used for Thin

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors kindly thank Anzarul Haque for 1D and 2D NMR measurements and Ayman Salkini for HRMS (Prince Sattam Bin Abdulaziz University, Saudi Arabia). The authors also thank Dr. Azmi Hanoğlu (Near East University, TRNC) for his kind help during the isolation process and Karar Shukur (Eastern Mediterranean University, TRNC) for UV and FTIR measurements. This study was supported by Near East University Scientific Research Projects (Project Number: SAG-2018-1-029)

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