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Structural elucidation of two new compounds from Artemisia ordosica and their antioxidative activity

  • Guo-Hua Wu , Qing-Hu Wang EMAIL logo , Xiang He , Wen-Qiang Bao and Bi-Li-Ge-Tu Pa
Published/Copyright: September 13, 2019
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Zeitschrift für Naturforschung B
From the journal Zeitschrift für Naturforschung B Volume 74 Issue 10

Abstract

Two new compounds, namely, arteordosin A (1) and arteordosin B (2), were isolated from the CHCl3 extract of Artemisia ordosica. This is the first report on the structure elucidation of arteordosin A (1) and arteordosin B (2) based on spectroscopic methods including electrospray ionization mass spectrometry, one-dimensional (1D) nuclear magnetic resonance spectroscopy (NMR) and 2D NMR techniques. Antioxidant activities of the compounds were measured for their radical scavenging capacity using 2,2-diphenyl-1-picrylhydrazyl. Compound 1 (IC50 of 1.01 mg mL−1) showed antioxidant activity similar to the standard reference ascorbic acid (IC50 of 0.98 mg mL−1) and is more active than compound 2 (IC50 of 1.87 mg mL−1). In conclusion, arteordosin A (1) and arteordosin B (2) may be used as potential antihyperlipidemic agent in routine clinical practice.

Keywords: antioxidant; Artemisia ordosica; arteordosin A; arteordosin B

1 Introduction

Artemisia ordosica, Asteraceae family, is one of the main arido-active shrubs growing in the arid and semi-arid areas of north China including Inner Mongolia, Ningxia, Gansu and Shanxi [1], [2]. The aerial parts of A. ordosica are utilized as a folk medicine for expelling rheumatism, clearing heat, and dispelling swelling [3]. Sterols [4], coumarins [5], terpenoids [6], flavonoids [7], [8] and acetylenes [3] were isolated from this plant. However, the secondary metabolites from A. ordosica often differ when grown in different ecological environments. In order to continue our research on the bioactive secondary metabolites from A. ordosica collected in Tongliao of Inner Mongolia, China, we now describe the isolation and structure elucidation of the two new compounds (Fig. 1) as well as their antioxidant activity by using 2,2-diphenyl-1-picrylhydrazyl (DPPH) to test on their radical scavenging capacity.

Fig. 1: Structures of compounds 1 and 2.
Fig. 1:

Structures of compounds 1 and 2.

2 Results and discussion

2.1 Structure elucidation of compounds 1 and 2

Compound 1 was obtained as a yellowish powder. The molecular formula was determined as C15H20O5 by high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) at m/z=279.1219 [M−H]− (calcd. 279.1232). The 1H nuclear magnetic resonance spectroscopy (NMR) spectrum of 1 (Table 1) showed two olefinic signals at δH=7.65 ppm (1H, d, J=16.0 Hz) and 6.29 ppm (1H, d, J=16.0 Hz), which suggested the presence of a double bond with (E) geometry. In addition, the signals of three aromatic protons at δH=7.31 (1H, brd, J=8.0 Hz), 6.77 (1H, d, J=8.0 Hz) and 7.39 ppm (1H, brs) indicated the presence of an ABC system, which was confirmed by the HMBC correlations from δH=7.31 ppm to δC=145.0 (C-7), 161.4 (C-4) and 124.5 (C-2) ppm, and δH=7.39 ppm to δC=129.6 (C-6), 144.9 (C-7), 161.4 (C-4) and 33.6 (C-1′) ppm, and δH=6.77 ppm to δC=127.8 (C-1) and 127.4 (C-3) ppm. The 1H NMR spectrum of 1 also exhibited the presence of a methyl group at δH=1.01 ppm (3H, s) and a methoxy group at δH=3.80 ppm (3H, s).

Table 1:

1H and 13C NMR data (500 and 125 MHz, respectively; CDCl3) of arteordosin A (1).

PositionδH (ppm), (mult., J in Hz)δC (ppm)HMBC
1–127.8
27.39 (brs, 1H)124.5C-4, C-6, C-7, C-1′
3–127.4
4–161.4
56.77 (d, 1H, J=8.0)109.7C-1, C-3
67.31 (brd, 1H, J=8.0)129.6C-2, C-4, C-7
77.65 (d, 1H, J=16.0)144.9C-2, C-6, C-8, C-9
86.29 (d, 1H, J=16.0)114.7C-1, C-9
9–167.9
1′3.33 (dd, 1H, J=13.5, 8.5)33.6C-2, C-4, C-2′, C-3′
3.02 (dd, 1H, J=13.5, 8.5)
2′4.75 (q, 1H, J=8.5)87.7C-3, C-4′, C-5′
3′2.09 (m, 1H)40.9
4′3.78 (d, 1H, J=6.0)66.1
3.75 (dd, 1H, J=8.5, 6.0)
5′1.01 (3H, s)12.7C-2′, C-3′, C-4′
–OCH33.80 (3H, s)51.6C-9

In the HMBC spectrum (Table 1), the methoxy protons (δH=3.80 ppm) correlated with the carbon signals at δc=168.0 ppm (C-9), which revealed that the methoxy group was linked to C-9. Likewise, the methyl proton (δH=1.01 ppm) correlated with the carbon signals at δC=87.7 (C-2′), 40.9 (C-3′) and 66.1 (C-4′) ppm. In addition, the HMBC correlations from δH=7.65 ppm (1H, d, J=16.0 Hz, H-7) to C-2 (δC=124.5 ppm), C-6 (129.6 ppm), C-8 (114.7 ppm) and C-9 (167.9 ppm), and δH=6.29 ppm (1H, d, J=16.0 Hz, H-8) to C-1 (127.8 ppm) and C-9 (167.9 ppm), and δH=4.75 ppm (1H, dd, J=17.5, 9.0 Hz, H-2′) to C-1′ (33.6 ppm), C-4′ (66.1 ppm) and C-5′ (12.7 ppm) further confirmed the structure of 1. The modified Mosher method [9] was applied for the configurational assignment of secondary alcohols. Treatment of two aliquots of 1 with (−)- and (+)-α-methoxy-α-trifluoromethylphenylacetic acid chloride (MTPA), respectively, in dry pyridine gave the corresponding diesters 1a and 1b, respectively. The pattern of ∆δ (S–R) values (Fig. 2) indicated that the absolute configurations of C-2′ and C-3′ are R and S, respectively. Thus, the structure of compound 1 was elucidated and named arteordosin A.

Fig. 2: Results of the modified Mosher method (Δ=δS−δR) for compounds 1 and 2.
Fig. 2:

Results of the modified Mosher method (Δ=δS−δR) for compounds 1 and 2.

Compound 2 was obtained as a yellowish powder. The molecular formula was determined to be C15H20O5 by HR-ESI-MS at m/z=279.1219 [M−H]− (calcd. 279.1232). The spectroscopic data (ultraviolet (UV), infrared (IR), 1H NMR, and 13C NMR) of compound 2 (Table 2) were very similar to those of 1 except for the chemical shift of C-2′ in 2 which moved 2.0 ppm to high field, which suggested that 2 was a diastereomer of 1. Similarly, the modified Mosher method was applied for the assignment of the configurations of the secondary alcohols. The pattern of the ∆δ (S–R) values (Fig. 2) indicated that the absolute configurations of C-2′ and C-3′ are both S. Thus, the structure of compound 2 was elucidated and named arteordosin B.

Table 2:

1H and 13C NMR data (500 and 125 MHz, respectively; CDCl3) of arteordosin B (2).

PositionδH (ppm), (mult., J in Hz)δC (ppm)HMBC
1–126.9
27.39 (brs, 1H)125.2C-4, C-6, C-7, C-1′
3–129.0
4–162.1
56.77 (d, 1H, J=8.5)109.5C-1, C-3
67.43 (brd, 1H, J=8.5)130.4C-2, C-4, C-7
77.57 (d, 1H, J=15.5)145.3C-2, C-6, C-8, C-9
86.42 (d, 1H, J=15.5)114.5C-1, C-9
9–167.5
1′3.17 (dd, 1H, J=13.0, 8.5)31.6C-2, C-4, C-2′, C-3′
2.98 (dd, 1H, J=13.0, 8.5)
2′4.77 (q, 1H, J=8.5)85.7C-3, C-4′, C-5′
3′1.95 (m, 1H)40.7
4′3.51 (dd, 1H, J=10.5, 5.0)62.8C-2, C-4, C-2′, C-3′
3.05 (dd, 1H, J=10.5, 6.5)
5′0.86 (3H, s)12.3C-2′, C-3′, C-4′
–OCH33.69 (3H, s)51.7C-9

2.2 Antioxidant activities

The antioxidant activities of compounds 1 and 2 were evaluated using the DPPH method [10]. Compounds 1 and 2 exhibited the radical scavenging activities at different concentrations (Table 3). This activity could be assigned to the number and position of phenolic hydroxyl groups and conjugated structure of α,β-unsaturated acids. Cinnamic acid derivatives [11] have been reported to have antioxidant activity. Cinnamic acid derivatives with para-hydroxylation had a more strongly antioxidant activity than with ortho-hydroxylation, and the conjugated structure of α,β-unsaturated acids improved the antioxidant activity of the phenolic compounds.

Table 3:

Concentration of compounds 1 and 2 reducing 50% of free radical DPPH (IC50).

SamplesIC50 (mg mL−1)
Compound 11.01±0.02
Compound 21.87±0.09
l-Ascorbic acid (reference)0.98±0.01

Compounds 1 and 2 are derivatives of p-coumaric acid. The antioxidant activity of these two new compounds can be assigned to the functional groups mentioned above. Compound 1 (IC50=1.01 mg mL−1) showed antioxidant activity similar to the standard reference ascorbic acid (IC50=0.98 mg mL−1) and is more active than compound 2 (IC50=1.87 mg mL−1). The fact that compound 2 is less active than 1 may be related to the relative configuration of C-2′. Nevertheless, comparing the results to the reference standard ascorbic acid, the antioxidant activities of both compounds 1 and 2 still can be considered as significant.

3 Experimental section

3.1 General experimental procedures

Optical rotations were measured in CHCl3 at T=25°C on a Perkin-Elmer 241 polarimeter (Shanghai, China). The UV spectra were recorded on a Shimadzu UV-2201 spectrometer (Shimadzu, Japan). The IR spectra were recorded in KBr discs on a Thermo Nicolet 200 double beam spectrophotometer (Shimadzu, Japan). The HR-ESI-MS spectra were measured on a Bruker Daltonics MicroTOFQ instrument (Waters, USA). NMR spectra were measured on a Bruker AVAIVCE Ш-500 NMR spectrometer (Bruker, Germany) with tetramethylsilane (TMS) as the internal reference, and chemical shifts are expressed in δ (ppm). Column chromatography was performed by using silica gel (200–300 mesh, Marine Chemical Factory, Qingdao, China). Fractions were monitored by TLC (silica gel GF25410–40 μm, Marine Chemical Factory, Qingdao, China), and spots were visualized by heating silica gel plates sprayed with 10% H2SO4 in EtOH.

3.2 Plant material

The aerial parts of A. ordosica were collected in Tongliao, Inner Mongolia, China, in June 2017, and identified by Prof. Buhebateer (Inner Mongolia University for Nationalities). A voucher (no. 20170612) has been deposited in the School of Traditional Mongolian Medicine of Inner Mongolia University for Nationalities.

3.3 Extraction

Ground-dried aerial parts of A. ordosica (2.0 kg) were extracted with CHCl3 (25 L) under reflux after extraction with 10 L of petroleum ether. The CHCl3 extract (150.0 g) was fractionated by column chromatography on silica gel by elution with a petroleum ether–acetone gradient (60:1–20:1) to give 3 fractions (Fr. 1–3). Fr. 2 (5.0 g) was further eluted on a Sephadex LH-20 column with MeOH and then separated by semi-preparative high-performance liquid chromatography (HPLC) (CH3OH-H2O, 45:55), yielding 1 (61 mg) and 2 (48 mg).

Arteordosin A (1): pale yellow needles. [α]D25=+23.2 (c=0.02, MeOH). – UV/vis (MeOH) λmax (log εmax): 267 nm (3.08). –IR (KBr) ν=3318 (OH), 1697 (C=O), 1661 (C=C), 1601, 1485 and 1207 cm−1. – 1H NMR (500 MHz, CDCl3, 25°C, TMS): δ=7.39 (brs, 1H, 2-H), 6.77 (d, J=8.0 Hz, 1H, 5-H), 7.31 (brd, J=8.0 Hz, 1H, 6-H), 7.65 (d, J=16.0 Hz, 1H, 7-H), 6.29 (d, J=16.0 Hz, 1H, 8-H), 3.33 (dd, J=13.5, 8.5 Hz, 1H, 1′a-H), 3.02 (dd, J=13.5, 8.5 Hz, 1H, 1′b-H), 4.75 (q, J=8.5 Hz, 1H, 2′-H), 2.09 (m, 1H, 3′-H), 3.78 (d, J=6.0 Hz, 1H, 4′a-H), 3.75 (dd, J=8.5, 6.0 Hz, 1H, 4′b-H), 1.01 (s, 3H, 5′-H), 3.80 (s, 3H, OCH3). – 13C NMR (125 MHz, CDCl3, 25°C, TMS): δ=127.8 (C-1), 124.5 (C-2), 127.4 (C-3), 161.4 (C-4), 109.7 (C-5), 129.6 (C-6), 144.9 (C-7), 114.7 (C-8), 167.9 (C-9), 33.6 (C-1′), 87.7 (C-2′), 40.9 (C-3′), 66.1 (C-4′), 12.7 (C-5′), 51.6 (OCH3). – HRMS ((−)-ESI): m/z=279.1219 (calcd. 279.1232 for C15H20O5, [M−H]−).

Arteordosin B (2): pale yellow needles. [α]D25=−21.2 (c=0.02, MeOH). – UV/vis (MeOH) λmax (log εmax): 268 nm (3.04). – IR (KBr) ν=3317 (OH), 1697 (C=O), 1663 (C=C), 1601, 1483 and 1205 cm−1. – 1H NMR (500 MHz, CDCl3, 25°C, TMS): δ=7.39 (brs, 1H, 2-H), 6.77 (d, J=8.5 Hz, 1H, 5-H), 7.43 (brd, J=8.5 Hz, 1H, 6-H), 7.57 (d, J=15.5 Hz, 1H, 7-H), 6.42 (d, J=15.5 Hz, 1H, 8-H), 3.17 (dd, J=13.0, 8.5 Hz, 1H, 1′a-H), 2.98 (dd, J=13.0, 8.5 Hz, 1H, 1′b-H), 4.77 (q, J=8.5 Hz, 1H, 2′-H), 1.95 (m, 1H, 3′-H), 3.51 (dd, J=10.5, 5.0 Hz, 1H, 4′a-H), 3.05 (dd, J=10.5, 6.5 Hz, 1H, 4′b-H), 0.86 (s, 3H, 5′-H), 3.69 (s, 3H, OCH3). – 13C NMR (125 MHz, CDCl3, 25°C, TMS): δ=126.9 (C-1), 125.2 (C-2), 129.0 (C-3), 162.1 (C-4), 109.5 (C-5), 130.4 (C-6), 145.3 (C-7), 114.5 (C-8), 167.5 (C-9), 31.6 (C-1′), 85.7 (C-2′), 40.7 (C-3′), 62.8 (C-4′), 12.3 (C-5′), 51.7 (OCH3). – HRMS ((−)-ESI): m/z=279.1219 (calcd. 279.1232 for C15H20O5, [M−H]−).

Arteordosin A (R)-MTPA ester (1a): amorphous solid. – 1H NMR (500 MHz, CDCl3, 25°C, TMS): δ=8.023 (brs, 1H, 2-H), 3.114 (dd, J=15.5, 9.0 Hz, 1H, 1′a-H), 3.025 (dd, J=15.5, 9.0 Hz, 1H, 1′b-H), 2.076 (m, 1H, 3′-H), 3.772 (d, J=6.0 Hz, 1H, 4′a-H), 3.753 (dd, J=8.5, 6.0 Hz, 1H, 4′b-H), 1.004 (s, 3H, 5′-H), 6.77 (d, J=8.0 Hz, 1H, 5-H), 7.31 (overlapped, 6-H), 7.65 (d, J=16.0 Hz, 1H, 7-H), 6.29 (d, J=16.0 Hz, 1H, 8-H), 7.35 and 7.45 (MTPA phenyl protons).

Arteordosin A (S)-MTPA ester (1b): amorphous solid. – 1H NMR (500 MHz, CDCl3, 25°C, TMS): δ=8.123 (brs, 1H, 2-H), 3.422 (dd, J=15.5, 9.0 Hz, 1H, 1′a-H), 3.234 (dd, J=15.5, 9.0 Hz, 1H, 1′b-H), 2.182 (m, 1H, 3′-H), 3.812 (d, J=6.0 Hz, 1H, 4′a-H), 3.793 (dd, J=8.5, 6.0 Hz, 1H, 4′b-H), 1.065 (s, 3H, 5′-H), 6.77 (d, J=8.5 Hz, 1H, 5-H), 7.31 (overlapped, 6-H), 7.65 (d, J=16.0 Hz, 1H, 7-H), 6.29 (d, J=16.0 Hz, 1H, 8-H), 7.35 and 7.45 (MTPA phenyl protons).

Arteordosin B (R)-MTPA ester (2a): amorphous solid. – 1H NMR (500 MHz, CDCl3, 25°C, TMS): δ=8.005 (brs, 1H, 2-H), 3.211 (dd, J=15.5, 9.0 Hz, 1H, 1′a-H), 3.190 (dd, J=15.5, 9.0 Hz, 1H, 1′b-H), 2.109 (m, 1H, 3′-H), 3.592 (d, J=6.0 Hz, 1H, 4′a-H), 3.101 (dd, J=8.5, 6.0 Hz, 1H, 4′b-H), 0.963 (s, 3H, 5′-H), 6.77 (d, J=8.0 Hz, 1H, 5-H), 7.43 (overlapped, 6-H), 7.57 (d, J=16.0 Hz, 1H, 7-H), 6.42 (d, J=16.0 Hz, 1H, 8-H), 7.35 and 7.45 (MTPA phenyl protons).

Arteordosin B (S)-MTPA ester (2a): amorphous solid. – 1H NMR (500 MHz, CDCl3, 25°C, TMS): δ=7.923 (brs, 1H, 2-H), 3.008 (dd, J=15.5, 9.0 Hz, 1H, 1′a-H), 2.987 (dd, J=15.5, 9.0 Hz, 1H, 1′b-H), 2.218 (m, 1H, 3′-H), 3.625 (d, J=6.0 Hz, 1H, 4′a-H), 3.134 (dd, J=8.5, 6.0 Hz, 1H, 4′b-H), 1.010 (s, 3H, 5′-H), 6.77 (d, J=8.0 Hz, 1H, 5-H), 7.43 (overlapped, 6-H), 7.57 (d, J=16.0 Hz, 1H, 7-H), 6.42 (d, J=16.0 Hz, 1H, 8-H), 7.35 and 7.45 (MTPA phenyl protons).

3.4 Antioxidant activities

DPPH with a concentration of 37 mg L−1 was prepared by methanol (HPLC grade). l-ascorbic acid was utilized as standard reference. The antioxidant activity was performed using the methods given in reference [10].

4 Supporting information

Copies of the spectra of compounds 1 and 2 are given as supplementary material available online.

Acknowledgment

This work was supported by the international cooperative scientific and technological innovation project for Mongolian medicine standardization (no. MDKBZH2018017).

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Supplementary Material

The online version of this article offers supplementary material (https://doi.org/10.1515/znb-2019-0047).

Received: 2019-02-19
Accepted: 2019-08-22
Published Online: 2019-09-13
Published in Print: 2019-10-25

©2019 Walter de Gruyter GmbH, Berlin/Boston

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https://doi.org/10.1515/znb-2019-0047
Keywords for this article
antioxidant; Artemisia ordosica; arteordosin A; arteordosin B

Articles in the same Issue

  1. Frontmatter
  2. In this Issue
  3. Research Articles
  4. Structural elucidation of two new compounds from Artemisia ordosica and their antioxidative activity
  5. Chemical constituents from Penianthus camerounensis Dekker (Menispermaceae)
  6. Zur Formylierung von Hydroxy- und Alkoxyaromaten mit Ameisensäure
  7. Chitosan-attached nano-Fe3O4 as a superior and retrievable heterogeneous catalyst for the synthesis of benzopyranophenazines using chitosan-attached nano-Fe3O4
  8. Syntheses, structures, and properties of zinc(II) and copper(II) coordination polymers with imidazole-containing ligands
  9. Synthesis, crystal structure and antimicrobial activities of a dinuclear silver(I) complex of bis(diphenylphosphano)methane and thiourea
  10. [Nb6Cl12(HIm)6](OAc)2·3MeOH – a hydrogen-bonded network of niobium cluster cations, acetate anions and methanol molecules
  11. Synthesis of the first nickel borate nitrate K7Ni[B18O24(OH)9](NO3)6· (H3BO3)
  12. Polymorphs and derivates of Sr2LiAlO4:Eu2+
  13. Investigation of mesitylene-solvated group 13 mixed-metal halides: syntheses and crystal structures of bis(1,3,5-trimethylbenzene)gallium(I) tetrachlorido- and tetrabromidoaluminate(III) and (1,3,5-trimethylbenzene)gallium(I) tetraiodidoaluminate(III). Variation of the gallium-π-arene bond strength
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