Three new tetrahydrobenzofuran derivatives from Ferula sinkiangensis K.M.Shen and their cytotoxic activities

Abstract Phytochemical investigation the resins of Ferula sinkiangensis K.M.Shen yielded three new tetrahydrobenzofuran derivatives named as Sinkiangensis A-C (1–3). The structures of the new compounds were elucidated by analysis of their NMR, HRMS, and ECD spectra, and the absolute configurations were established through the comparison of experimental and calculated ECD spectra. Compound 3 exhibited moderate antitumor activities against AGS cancer cell with IC50 values of 15.6 µM. Moreover, assays demonstrated that compound 3 could induce AGS cancer cell apoptosis. Graphical abstract


Introduction
The genus Ferula is the third largest and a well-known genus of the Apiaceae family. It is categorized in the Peucedaneae tribe and Ferulinae subtribe of the Apiaceae family. At present, about 180 Ferula species have been reported. The genus is mainly distributed throughout central and South-West Asia (especially Iran and Afghanistan), the far-East, North India and the Mediterranean (Priyankaraj and Mukesh 2021). The main photochemical components present in the genus Ferula are as follows: coumarin, coumarin esters, sesquiterpenes, sesquiterpene lactones, monoterpene, monoterpene coumarins, prenylated coumarins, sulfur-containing compounds, phytoestrogen, flavonoids and carbohydrates (Iranshahi et al. 2018;Mohammadhosseini et al. 2019;Salehi et al. 2019). In vivo and in vitro studies showed hypotensive, neuroprotective, memoryenhancing, anti-oxidant, hepatoprotective, antimicrobial, anticarcinogenic, anticytotoxic, antiobesity and anthelmintic effects for various species of Ferula and their constituents (Zahra et al. 2021). Ferula sinkiangensis K. M. Shen is the well-known species of the genus Ferula. The gum resin of the genus Ferula is commonly referred to as 'Xinjiang A wei' in China. The Xinjiang A wei from F. sinkiangensis is recorded as a traditional folk medicine with a long history of application in the treatment of stomach diseases and rheumatoid arthritis . As a traditional folk medicine used for the treatment of stomach disorders in Xinjiang District of China for thousands of years, the potential value of this herb for treating gastric cancer could not be ignored. Previous phytochemical investigations of F. sinkiangensis led to the isolation of sesquiterpene coumarins (Li et al. , 2016Xing et al. 2017;Wang et al. 2020), organic acid glycosides, steroidal esters (Li et al. 2014), lignans (Wang et al. 2018) and sulfur-containing compounds (Ye et al. 2011). Pharmacological and biological studies have shown that F. sinkiangensis has antitumor , anti-inflammatory (Ghorbani et al. 2016;Mi et al. 2021), antibacterial (Shahverdi et al. 2007), antifungal (Liu et al. 2020), antivirus (Li et al. 2016), and antiparasitic (Bashir et al. 2014) effects, which have attracted more attention of scientists.
However, the tetrahydrobenzofuran derivative of the F. sinkiangensis has been little researched. As a result, the phytochemical investigation of the F. sinkiangensis was performed and obtained three new tetrahydrobenzofuran derivatives sinkiangensis A-C ( Figure 1). Extensive spectroscopic and spectrometric analyses, including 2D NMR and ECD spectra, were described. In this paper, we report the isolation and structural elucidation of the new compounds, as well as the cytotoxic activity in vitro of the isolates against AGS, K562 and Hela human cancer cell lines.
Compound 2 was obtained as an amorphous white powder, and its molecular formula was established as C 17 H 24 O 6 from the molecular ion peak at m/z 347.1465 [M þ Na] þ in the HRESMS. The 1 H and 13 C NMR pectroscopic data (Supplementary material, Table S1) were closely related to those of 1 except for one hydroxyl group at C-15 in 1 was replaced by an acetoxyl group in 2. In the HMBC spectrum, the signals of d H 5.28 (1H, d, J ¼ 13.2 Hz, H-15a), 5.21 (1H, d, J ¼ 13.2 Hz, H-15b) had long-range correlations with d C 126.4 (C-3), 147.6 (C-2), 121.6 (C-9) and 170.1 (C-17), which demonstrated the attachment of the methylacetate group to C-3. Its NOESY correlations and ECD spectrum were almost the same as those of 1. Hence, the absolute configuration of 2 was determined to be 6S,7S, and its structure was determined to be (6S,7S)-6,7-dihydroxy-3-methylacetate-6-methyl-2-isopentene-4,5,6,7-tetrahydrobenzofuran, and it was named sinkiangensis B.
Compound 3, which was isolated as a white acicular crystal. In the HRESMS analysis revealed the molecular formula of 3 to be C 12 H 16 O 5 . An examination of the 1 H and 13 C NMR data (Supplementary material, Table S1) showed the structure of 3 to be similar to that of 1 except for the isovaleroyl group at C-2 in 1 was replaced by an acetyl group in 3. In the HMBC spectrum, the signals of d H 2.21 (3H, s, H-11) had long-range correlations with d C 126.4 (C-3), 147.6 (C-2) and 189.9 (C-10), which demonstrated the attachment of the acetyl group to C-2. Taken along with 1 H-1 H COSY, HSQC, HMBC, NOE and ECD spectra, the absolute configuration of 3 was assigned as 6S,7S, the structure of compound 3 was determined to be (6S,7S)-6,7-dihydroxy-3methylol-6-methyl-2-acetyl-4,5,6,7-tetrahydrobenzofuran, and named as sinkiangensis C (Figure 1).
In this study, the isolated compounds 1-3 were evaluated for their cytotoxic activity in vitro against AGS, K562 and Hela human cancer cell lines using the MTT method with Taxol as the positive control. The data in Table S2 (Supplementary material) suggested that the isolated compound 3 exhibited significant cytotoxic activity against AGS cancer cell lines with IC 50 value of 15.6 lM. Compounds 1,2 showed weak cytotoxicity against AGS cancer cells with IC 50 value between 87.1 and 72.7 lM. No significant cytotoxic activity against HeLa and K562 cancer cells were observed for compounds 1 À 3.

Conclusion
In summary, Phytochemical investigation of the resins of Ferula sinkiangensis K.M.Shen yielded three new tetrahydrobenzofuran derivatives named as sinkiangensis A-C (1-3). The structures were established by extensive analyses of spectroscopic data (1D and 2D NMR, HRESIMS) and ECD spectra (Supplementary Materials). Their absolute configurations were established through the comparison of experimental and calculated ECD spectra. Compound 3 exhibited moderate antitumor activities against AGS cancer cell with IC 50 values of 15.6 mM. Moreover, assays demonstrated that compound 3 could induce AGS cancer cell apoptosis.

Disclosure statement
No potential conflict of interest was reported by the authors.

Funding
This study was financially supported by the 2019 Youth Fund Project in Xinyang Agricultural and Forestry University (No. 2019LG015), the Training Project of Young Leading Teachers in Xinyang Agriculture and Forestry University, the Science and Technology Innovation Team in Xinyang Agriculture and Forestry University (No. kjcxtd-202005).