Artemyrianosins A–J, cytotoxic germacrane-type sesquiterpene lactones from Artemisia myriantha

Ten new germacrane-type sesquiterpenoids, artemyrianosins A–J (1–10), were isolated from the aerial parts of Artemisia myriantha. Their structures were elucidated by spectral analyses including UV, IR, HRESIMS, 1D and 2D NMR, ECD and the absolute configurations of compounds 1 and 7–9 were characterized using X-ray crystallography. All isolates were tested their cytotoxicity against three human hepatoma cell lines (HepG2, Huh7, and SK-Hep-1), and compounds 1–3, 7, and 10 showed cytotoxicity with IC50 values ranging from 43.7 to 89.3 μM. Among them, the most active compound 3 exhibited activity against three human hepatoma cell lines with IC50 values of 43.7 μM (HepG2), 47.9 μM (Huh7), and 44.9 μM (SK-Hep-1).


Introduction
Hepatocellular carcinoma (HCC) as one of the most serious and common type of liver cancer is mainly caused by HBV or HCV infection, and heavy alcohol intake [1,2]. HCC has resulted in nearly 0.83 million deaths worldwide in the year 2020 [3,4], and suffered more than 1

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Natural Products and Bioprospecting million people will be affected by 2025 [5]. Clinically, four synthetic ones (sorafenib, regorafenib, lenvatinib and cabozantinib) and three monoclonal antibody ones (nivolumab, pembrolizumab and ramucirumab) are used to treat HCC [6,7]. Although these drugs have obtained significant achievements, there are still some inevitable drawbacks, such as the low objective response rate, high incidence of adverse reactions, and drug resistance [8]. Therefore, new drugs with different targets for treating HCC are urgently needed (Fig. 1).
Artemisia, one of the dominant genus within Asteraceae family, contains nearly 380 species globally with 186 species being dispersed in China [9]. Many Artemisia plants, such as A. annua, A. argyi, A. capillaris, and A. scoparia, have been recorded for the treatment of malaria, inflammation, hepatitis, cancer in the traditional Chinese medicine system [9][10][11][12]. Phytochemical investigation revealed that Artemisia genus are rich in sesquiterpenoids with antimalarial, antiinflammatory, antitumor, cytotoxic, antibacterial, and antihelminthic activities [13]. For example, artemisinin, a sesquiterpenoid lactone with an unusual peroxide bridge, which was obtained from A. annua by the Chinese scientist You-You Tu in 1972, showed antimalarial, anticancer and antiinflammatory activities [14]. Dihydroartemisinin, artemether, and artesunate which were chemically modified from artemisinin also exhibited antimalarial, antiviral, antifungal, anticancer, and antiinflammatory properties [15]. Arglabin, a guaiane-type sesquiterpenolide from A. glabella, inhibited of farnesyltransferase and its dimethylamino hydrochloride has been successfully developed into an anticancer drug in Kazakhstan for the treatment of colon, breast, ovarian, lung and liver cancers [16]. Arteminolides A-D from A. argyi were potential inhibitors of farnesyl protein transferase (FPTase) with IC 50 values less than 1.0 μM in vitro, of which arteminolide C could prevent the development of lung tumor and human colon xenograft without causing weight loss in nude mice [17].
The cytotoxicity of all isolates against three human hepatoma cell lines (HepG2, Huh7, and SK-Hep-1) was evaluated at the concentration of 100 μM with sorafenib as the positive control. As shown in Fig. 6,   Fig. 6 Inhibitory ratios of compounds 1-10 at 100 μM Page 9 of 12 Zhang et al. Natural Products and Bioprospecting (2022) 12:16 compounds 1-3, 7, and 10 containing an α-exomethylene γ-butyrolactone group showed activity on HepG2, Huh7, and SK-Hep-1 with inhibitory ratios higher than 50%. The dose-response curves of the active compounds were further investigated to yield their respective IC 50 values. As shown in Table 4

Conclusion
In this study, 10 new germacrane-type sesquiterpenoids (1-10) were isolated and identified from A. myriantha. Their structures were elucidated by extensive analyses of spectral data, X-ray analyses, and ECD spectra.

Materials and methods
General experimental procedures, the ECD calculation, and cytotoxicity assays were provided in Additional file 1.

Extraction and isolation
In connection with our previous paper [25]  Compounds 1 and 7-9 were afforded by recrystallization in a mixture of MeOH-CHCl 3 (95:5). X-ray diffraction analyses were performed on a Bruker D8 QUEST instrument using Cu Kα radiation and the intensity data were collected at 100 (2) K. The crystal structures were solved by using SHELXS-97 and difference Fourier techniques, and refinements were performed through the program and refined by full-matrix least-squares calculations on F 2 . All non-hydrogen atoms were anisotropically refined, and the positions of hydrogens bonded to carbons were initially determined through geometry and refined using a riding model. The crystallographic data for compounds 1 and 7-9 in standard CIF format were deposited in the Cambridge Crystallographic Data Centre. The data can be accessed free of charge at http:// www. ccdc. cam. ac. uk/.