A new megastigmane glycoside, a new organic acid glycoside and other constituents with anticomplementary activity from Artemisia halodendron

Abstract A new megastigmane glycoside, (1R,5R,6S,7E)-megastigman-3,9-dione-7-en-6,11-diol 11-O-β-D-glucopyranoside (1), and a new organic acid glycoside, methyl (4 R)-4-O-β-D-glucopyranosyl-decanoate (2), together with eight known compounds (3–10), were isolated from the aerial parts of Artemisia halodendron Turcz. ex Bess. (Asteraceae). Their chemical structures were elucidated by 1 D and 2 D NMR and HR-ESI-MS spectra and DP4+ probability analysis. Among the identified compounds, compounds 5, 6 and 10 were isolated from the family Asteraceae, and compounds 3, 4 and 7–9 were identified from the genus Artemisia for the first time. All of the compounds were evaluated for their anticomplementary activity against the classical pathway (CP) and the alternative pathway (AP). Compounds 7 and 9 showed anticomplementary activity with the CH50 values of 0.31 ± 0.08 and 0.50 ± 0.09 mM, respectively. Graphic Abstract


Introduction
Artemisia halodendron Turcz.ex Bess., a perennial subshrub specie that belongs to the genus Artemisia and the family Asteraceae, is widely distributed in northern China and has been used as a Chinese folk medicine for the treatment of rheumatoid arthritis, asthma and inflammation (Lou et al. 2018).Previous phytochemical investigations revealed the presence of flavonoids, coumarins, sterols, volatile oils, polyacetylenes and benzofurans isolated from this plant that exhibited hepatoprotection and antiinflammation effects (Wang et al. 2017;Wang et al. 2018;Sun et al. 2019;Jin et al. 2021).
The complement system, a major component of innate immunity, plays an important role in host immune defense against infection.However, it is widely accepted that the complement system is a key trigger for inflammation and its excessive activation leads to chemotaxis of inflammatory cells, vascular permeability, phagocytosis, and release of proinflammatory cytokines and chemokines, possibly triggering pathological tissue damage such as rheumatoid arthritis and asthma (Carroll and Sim 2011;Song et al. 2021).The important role of the complement system in the pathogenesis of inflammatory injury has led to the speculation that small molecule compounds of A. halodendron may be able to treat these diseases by modulating the complement system (Xu et al. 2007).However, the identities of the chemical constituents from the aerial parts of A. halodendron with anticomplementary effects are still unknown.This work reports the isolation and structural identification of one new megastigmane glycoside (1), one new organic acid glycoside (2), two sesquiterpenes (3-4), two diterpenoids (5-6), two polyacetylenes (7-8), one chlorogenic acid (9) and one dihydrochalcone (10) (Figure 1).All of the compounds were evaluated for their anticomplement activity against the classical and alternative pathways.
Compound 2 was obtained as a white amorphous powder.Its molecular formula was determined to be C 17 H 32 O 8 by HR-ESI-MS at m/z 365.2167 365.2170).The 13 C-NMR and DEPT spectra indicated the presence of one glycopyranosyl moiety, one carbonyl group, and the remaining ten carbon signals consisted of one oxymethine, one methoxy, seven methylenes and one methyl group.In the 1 H-NMR spectrum, one anomeric proton signal at d H 4.28 with a coupling constant J ¼ 7.7 Hz indicated the b-configuration of the glycopyranosyl moiety.Acid hydrolysis of 2 yielded a sugar residue that was determined to be D-glucose by the comparison of the retention time and optical rotation value.The 1 H-1 H COSY spectrum revealed the connectivities from H-2 to H-6, and between H-9 and H-10 on the aliphatic chain.In the HMBC spectrum, the locations of the sugar unit and one methoxyl group were identified by the correlations of H-1 0 (d H 4.28) and C-4 (d C 79.2) and 1-OCH 3 (d H 3.66) with C-1 (d C 176.6).Additionally, the specific rotation ½a 25 D À 29.8 (c 0.02, MeOH) of the aglycone from the hydrolysate of Compound 2 suggested that the absolute configuration of 2 was 4 R by comparison of the data ½a 28 D þ 37.7 (c 1.1, MeOH) for (4S)-4hydoxydecanoic acid (Utaka et al. 1990;Wu et al. 2007).Thus, the structure of 2 was proposed to be methyl (4R)-4-O-b-D-glucopyranosyl-decanoate.
The anti-complementary activity of the isolated compounds (1-10) was evaluated on the CP and AP of the complement system in vitro (Wang et al. 2021;Li et al. 2022).The present results provide the first evidence that Compounds 7 and 9 exhibited anticomplementary activity with the CH 50 values of 0.31 ± 0.08 and 0.50 ± 0.09 mM, respectively.The positive control, heparin, showed anticomplementary activity with a CH 50 value of 0.10 ± 0.03 mM (Table S1).To elucidate the anticomplementary mechanism of Compounds 7 and 9 in the classical pathway, their targets in the complement activation cascade were identified using complement-depleted sera.Compound 7 regained the hemolytic capacity of C3-, C4-, C5-and C9-depleted sera, and Compound 9 regained the hemolytic capacity of C3-, C5-and C9-depleted sera.These findings suggested that Compound 7 most likely interacted with the C2 component, while Compound 9 interacted with the C2 and C4 components of the complement (Figure S36).

Conclusion
In this study, a new megastigmane glycoside (1), a new organic acid glycoside (2), together with eight known compounds (3-10) were isolated from A. halodendron.Compounds 5, 6 and 10 were isolated from the family Asteraceae, and 3, 4 and 7-9 were identified from the genus Artemisia for the first time.Moreover, Compounds 7 and 9 were found to affect the classical pathway by selectively blocking the components C2 and C4 in the complement activation cascade and may play a role in eliminating the inflammation effects of A. halodendron.Our results may provide a scientific