Abstract
In several European countries, especially in Sweden, the seeds of the species Astragalus boeticus L. were widely used as coffee substitutes during the 19th century. Nonetheless, data regarding the phytochemistry and the pharmacological properties of this species are currently extremely limited. Conversely, other species belonging to the Astragalus genus have already been extensively investigated, as they were used for millennia for treating various diseases, including cancer. The current work was addressed to characterize cycloartane glycosides from A. boeticus, and to evaluate their cytotoxicity towards human colorectal cancer (CRC) cell lines. The isolation of the metabolites was performed by using different chromatographic techniques, while their chemical structures were elucidated by nuclear magnetic resonance (NMR) (1D and 2D techniques) and electrospray-ionization quadrupole time-of-flight (ESI-QTOF) mass spectrometry. The cytotoxic assessment was performed in vitro by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays in Caco-2, HT-29 and HCT-116 CRC cells. As a result, the targeted phytochemical study of A. boeticus enabled the isolation of three new cycloartane glycosides, 6-O-acetyl-3-O-(4-O-malonyl)-β-d-xylopyranosylcycloastragenol (1), 3-O-(4-O-malonyl)-β-d-xylopyranosylcycloastragenol (2), 6-O-acetyl-25-O-β-d-glucopyranosyl-3-O-β-d-xylopyranosylcycloastragenol (3) along with two known compounds, 6-O-acetyl-3-O-β-d-xylopyranosylcycloastragenol (4) and 3-O-β-d-xylopyranosylcycloastragenol (5). Importantly, this work demonstrated that the acetylated cycloartane glycosides 1 and 4 might preferentially inhibit cell growth in the CRC cell model resistant to epidermal growth factor receptor (EGFR) inhibitors.
Highlights
Astragalus genus is the largest in the Fabaceae family and it is widely distributed throughout the cool, temperate, semiarid and arid regions of the world [1]
Our group identified compound 4 as a metabolite responsible for the cytotoxicity of the A. boeticus extract. This species underwent a further phytochemical investigation to understand whether analogues of compound 4 exert cytotoxicity as well. As it was already anticipated above, we demonstrated that compounds 1 and 4 were the active cycloartane glycosides isolated from A. boeticus
We focused on the cycloartane derivatives present in A. boeticus, because of its putative cytotoxic activity
Summary
Astragalus genus is the largest in the Fabaceae family and it is widely distributed throughout the cool, temperate, semiarid and arid regions of the world [1]. After the beginning of the 20th century, its cultivation declined, and it was replaced by other substitutes [2] In addition to this information, available literature data describing the phytochemistry and the bioactivities of A. boeticus are currently extremely limited. The Astragalus species were employed as forage for animals, albeit many species were found to be toxic, and responsible for causing locoism in cattle [3,4]. In both folk and modern medicine, several Astragalus spp. were considered medicinal plants of great importance, as these have been successfully used to cure a broad range of ailments [5]. In the Traditional Chinese Medicine “Astragali radix” (dried roots of Astragalus membranaceus Bunge and other Astragalus spp.) was a very well-known drug for its immune stimulant, hepato-protective, anti-diabetic, analgesic, expectorant and sedative properties [6]
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