Two novel sesquiterpenes and one new monoterpene from the aerial part of Artemisia tournefortiana

Abstract Two novel sesquiterpenes and one new monoterpene, together with eight reported compounds were isolated from dichloromethane–soluble extract of the aerial part of Artemisia tournefortiana Reichb. Their relative and absolute structures were elucidated based on the analysis of 1D and 2D NMR spectra, HRESIMS, and calculated electronic circular dichroism (ECD). Two sesquiterpenes (1 and 2) showed no inhibition effect in anti-inflammatory and cytotoxic activity tests. Three new terpenes (1–3) were tested for antibacterial activity, compounds 2 and 3 showed moderate antibacterial activities with minimum inhibitory concentrations (MICs) between 264 and 556 μg/ml.

To further explore the medicinal value of this plant, we studied the CH 2 Cl 2 -soluble extract of the aboveground part of A. tournefortiana and obtained two novel sesquiterpenes (1 and 2) and one new monoterpene (3), one flavone (4), two ketals (5 and 6), and five aromatic hydrocarbons (7)(8)(9)(10)(11) (Figure 1, Figure S1).Compounds 1-3 were tested for antibacterial activity aimed at Candida albicans, Escherichia coli, and Staphylococcus aureus.Among these, compound 1 had a weak antibacterial effect on C. albicans, compound 2 had a moderate antibacterial effect on C. albicans, compound 3 had moderate effects on C. albicans and S. Aureus.Compounds 1 and 2 were tested for anti-inflammatory and cytotoxic activity and all of the inhibition rates were less than 50%.

Results and discussion
Compound 1 was obtained as a yellow oil.HRESIMS analysis suggested a molecular formula of 13 C-NMR, and HSQC spectra indicated there were three carbonyl groups, two double bonds, one methine group, five methylene groups, two methyl groups, and one methoxy group.According to the 1 H-1 H COSY spectrum, the correlations of H-2/H-3, H-3/H-4, H-7/H-8, and H-8/H-9 indicated the presence of fragments C-2 to C-4 and C-7 to C-9 (Figure 2).According to HMBC spectrum, the correlations from H-15 to C-4/5; from H-4 to C-2/3/5; from H-14 to C-1/2/3/6/10; from H-2 to C-1/10; from H-9 to C-1/6/10 indicated the linkage of C-15/5, C-4/5, C-1/2, C-1/10 and C-6/10.The correlations from H-7/8/9 to C-10, from H-7/8/9 to C-6 indicated the presence of the five-membered ring with a carbonyl group, and the correlations from H-8 to C-11/12/13, from H-13 to C-8/11/12 indicated the a,b-unsaturated ester group linked to C-8.According to the NOESY spectrum, the correlations between H-9 and H-2/3 indicated that the configuration of the double bond (C-1, C-10) was E which was corresponding to the abnormal downfield shift of H-14 (Figure 3).The absolute  would be the same.The absolute configuration of compound 2 was defined as S based on the comparison of experimental and calculated ECD (Figure 4).
Compound 3 was obtained as a yellow oil.HRESIMS analysis suggested a molecular formula of C 15 H 20 O 4 at m/z 265.1432 13 C NMR and HSQC spectra suggested there were three carbonyl groups, one double bond, one quaternary carbon, two methine groups, five methylene groups, and two methyl groups.According to the 1 H-1 H COSY spectrum, the correlations of H-1/H-2, H-2/H-3, H-6/H-7, H-7/H-9, and H-8/H-9 indicated fragments from C-1 to C-3 and C-6 to C-9.According to the HMBC spectrum, the correlations from H-15 to C-4/3 and from H-3 to C-1/2/4 indicated the linkage of C-15/4 and C-4/3; the correlations from H-7 to C-11/12/13, from H-9 to C-12/7 and from H-13 to C-7/11/12 indicated the presence of the lactonic ring with an a-exocyclic double bond; the correlations from H-9 to C-1/5/10/14 and from H-6 to C-5/10 indicated the presence of a six-membered ring with a carbonyl group and the linkage of C-1/10.According to the NOESY spectrum, the NOESY correlations between H 3 -14 and H-9 indicated that H 3 -14 and H-9 were on the same face.The absolute configuration of compound 3 was defined as 7S9R10R based on the comparison of experimental and calculated ECD (Figure 4).

General experimental procedures
The optical rotations were recorded using a Rudolph RS Autopol VI automatic polarimeter (Newburgh, NY).A Chirascan spectropolarimeter (Applied Photophysics, Leatherhead, UK) was used to obtain ECD spectra.FT-IR Spectrometer (Nicolet iS50, Thermo Fisher Scientific, Shanghai, China) was used to measure the IR spectra.The NMR spectra were recorded using a Bruker AVANCE NEO 600 M spectrometer (600 MHz for 1 H and 150 MHz for 13 C NMR) in CD 3 OD, CDCl 3 , or DMSO with TMS as an internal standard.The (þ)-HRESIMS were measured using a Thermo Fisher Q EXACTIVE mass spectrometer (Bremen, Germany).Analytical HPLC was carried out on a Shimadzu LC-2030c 3D instrument (Shimadzu Corp, Japan) with PDA detector, using an Acclaim 120 C 18 (4.6 mm Â 250 mm, 5 lm) column.Semipreparative HPLC was conducted on a Shimadzu LC-20A instrument (Shimadzu Corporation, Kyoto, Japan) with UV detection, using a YMC-Pack Pro C18 RS (250 Â 10 mm, 5 lm) column.The detection wavelengths were set to 210 nm and 254 nm.Flash chromatography separation was carried out on a Sepacore Flash System X50 (Switzerlan, BUCHI) using Cosmosil 75 C 18 -PREP (Nacalai Tesque, Kyoto, Japan) as the packing material.Silica gel (Qingdao Ocean Chemical Factory, China), Sephadex LH-20 (GE Healthcare, Sweden), MCI Gel (CHP20 Mitsubishi Chemical Corporation, Tokyo, Japan) were used for chromatography.All of the solvents used were analytical grade and purchased from Tianjin chemical factory (Tianjin, China).Water for HPLC, semipreparative HPLC from a Milli-Q water purification system (Millipore, Bedford, MA).Fractions were monitored by thin-layer chromatography (TLC, HSGF254, Yantai Jiangyou Silica Gel Development Co., Ltd.Yantai, China) and were visualized by spraying with Vanillin chromogenic agent.

Plant material
The aerial part of Artimisia tournefortiana was collected from abandoned land in Nanshan, Urumqi, Xinjiang in October 2020 and identified by associate Prof. Chunfang Lu (Xinjiang Technical Institute of Physics and Chemistry, CAS, PRC).The specimen was deposited at the Key Laboratory of Plant Resources and Chemistry of Arid Zone, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences (WY01990).

Table 2 .
MICs and MBCs of compounds 2 and 3.