Abstract
Diterpenes are characteristic compounds from the genus Sideritis L., possessing an array of biological activities. Siderol is the main constituent of the ent-kaurene diterpenes in Sideritis species. In order to isolate the specific compound and evaluate for the first time its cytotoxic activity, we explored the dichloromethane extract of cultivated Sideritis euboea Heldr. To track the specific natural bioactive agent, we applied NMR spectroscopy to the crude plant extract, since NMR can serve as a powerful and rapid tool both to navigate the targeted isolation process of bioactive constituents, and to also reveal the identity of bioactive components. Along these lines, from the rapid 1D 1H NMR spectrum of the total crude plant extract, we were able to determine the characteristic proton NMR signals of siderol. Furthermore, with the same NMR spectrum, we were able to categorize several secondary metabolites into chemical groups as a control of the isolation process. Therefore, this non-polar extract was explored, for the first time, revealing eleven compounds—one fatty acid ester; 2-(p-hydroxyphenyl)ethylstearate (1), three phytosterols; β-sitosterol (2), stigmasterol (3), and campesterol (4); one triterpenoid; ursolic acid (5), four diterpenoids; siderol (6), eubol (7), eubotriol (8), 7-epicandicandiol (9) and two flavonoids; xanthomicrol (10) and penduletin (11). The main isolated constituent was siderol. The antiproliferative potential of siderol was evaluated, using the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) assay, on three human cancer cell lines DLD1, HeLa, and A549, where the IC50 values were estimated at 26.4 ± 3.7, 44.7 ± 7.2, and 46.0 ± 4.9 μΜ, respectively. The most potent activity was recorded in the human colon cancer cell line DLD1, where siderol exhibited the lowest IC50. Our study unveiled the beneficial potential of siderol as a remarkable cytotoxic agent and the significant contribution of NMR spectroscopy towards the isolation and identification of this potent anticancer agent.
Highlights
Over the last decades, natural products have been at the forefront as major drug sources in cancer and the explosion of knowledge in this area has brought forward new drug discoveries and Molecules 2020, 25, 2382; doi:10.3390/molecules25102382 www.mdpi.com/journal/moleculesMolecules 2020, 25, 2382 therapeutic developments
In continuation of our phytochemical investigations into cultivated Sideritis species, we report on the isolation and identification of phytochemicals from the non-polar extract from the aerial parts of the specific plant
We examined the effect of isolated siderol against three human cancer cell lines—DLD1, HeLa, and A549
Summary
Natural products have been at the forefront as major drug sources in cancer and the explosion of knowledge in this area has brought forward new drug discoveries and Molecules 2020, 25, 2382; doi:10.3390/molecules25102382 www.mdpi.com/journal/moleculesMolecules 2020, 25, 2382 therapeutic developments. Natural products have been at the forefront as major drug sources in cancer and the explosion of knowledge in this area has brought forward new drug discoveries and Molecules 2020, 25, 2382; doi:10.3390/molecules25102382 www.mdpi.com/journal/molecules. The genus Sideritis is one of the most economically explored in the Lamiaceae family, as its commercial need is continuously on the rise in the global market. In the last few years, there is an effort to cultivate these important medicinal species in order to meet the commercial need and provide high-quality products. Sideritis species are considered as remarkable medicinal plants with great pharmacological activities, attributed to their rich phytochemical profile [4,7]. The European Medicine Agency (EMA) monograph mentions the infusion of Sideritis species
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