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. 2022 Oct 14;15(1):151–154. doi: 10.1016/j.chmed.2021.12.007

Chemical constituents from aerial parts of Scoparia dulcis

Yingbo Yang a,b,1, Zhuzhen Han a,1, Tong Tian a, Qi Liao a, Jiaran Geng a, Ying Xiao a,⁎
PMCID: PMC9975620  PMID: 36875433

Abstract

Objective

To study the chemical constituents from the aerial parts of Scoparia dulcis.

Methods

Various chromatographic techniques were used to separate the constituents and their structures were elucidated using spectroscopic methods and by comparing their data to those reported in the literatures. The α-glucosidase inhibitory activity assay was used to identify potential α-glucosidase inhibitors.

Results

Nine compounds were isolated from the aerial parts of S. dulcis. Their structures were identified as Scoparic zolone (1), (2S)-2,7-dihydroxy-2H-1,4-benzoxazin-3(4H)-one (2), (2R)-7-hydroxy-2H-1,4-benzoxazin-3(4H)-one-2-O-β-d-glucopyranoside (3), (2R)-7-methoxy-2H-1,4-benzoxazin-3(4H)-one-2-O-β-d-glucopyranoside (4), (2S)-7-hydroxy-2H-1,4-benzoxazin-3(4H)-one-2-O-β-d-glucopyranoside (5), 6-methoxy-benzoxazolin-2(3H)-one (6), 4-acetonyl-3,5-dimethoxy-p-quinol (7), zizyvoside I (8), and 3,4-dihydroxy benzeneacetic acid (9). Compound 2 showed the potent α-glucosidase inhibitory activity with an IC50 value of (132.8 ± 11.5) μmol/L, which is 28-fold higher than the positive control acarbose.

Conclusion

Compound 1 is a new natural product. Compounds 2 and 9 have not been reported in Scoparia before. Compounds 3, 5, 7, 8 are isolated from Scrophulariaceae for the first time.

Keywords: alkaloids, chemical constituents, α-glucosidase inhibitory activity, Scoparia dulcis L.

1. Introduction

The genus Scoparia contains 10 species, mainly distributed in Mexico and South America, one of which is widespread in the global tropics, and there is only one species in China (Scoparia dulcis L.) (Editorial Committee of Flora Reipublicae Popularis Sinicae). S. dulcis has commonly been used as Chinese folk medicines, had antidiabetic, antigastric ulcer, antiviral, analgesic, anti-inflammatory, sympathomimetic, and diuretic activities (Wu, Chen, Lu, Chen, & Chang, 2012). In previous chemical investigations, alkaloids, saponin, cardiac glycosides, steroids, flavonoids, and terpenoids, have been isolated from S. dulcis. In this study, we isolated and identified nine compounds from the aerial parts of S. dulcis, and examined their α-glucosidase inhibitory activity.

2. Materials and methods

2.1. Apparatus and reagents

Optical rotations were measured on a Krüss-P800-T polarimeter. UV spectra were recorded on a JASCO J-180 spectrometer (JASCO Co., Tokyo, Japan). IR spectra were obtained with a Nicolet-380 spectrometer (Thermo Electron Co., MA, USA). The 1H NMR and 13C NMR spectra were recorded on a Bruker AV 600 Spectrometer (Bruker Co., Karlsruhe, Germany) with tetramethylsilane as an internal standard. HRESIMS were obtained on a Waters UPLC Premior QTOF spectrometer (Waters Co., MA, USA), and UPLC-MS analysis was performed on an Acquity Waters Ultra-Performance liquid chromatographic system equipped with a Waters UPLC column (Acquity UPLC BEH C18 1.7 μm, 2.1 mm × 50 mm) and a Micromass ZQ 2000 ESI mass spectrometer (Waters Co., MA, USA). Thin-layer chromatography was carried out on HSGF254 plates (Yantai Jiangyou Silica Gel Development Co., Ltd., Yantai, China). Column chromatography was performed with silica gel (300–400 mesh, Qingdao Makall Group Co., Ltd., Qingdao, China), MCI gel CHP 20P (70–150 μm, Mitsubishi Chemical Co., Tokyo, Japan), Sephadex LH-20 (GE Healthcare Bio-Sciences AB, Uppsala, Sweden), and YMC gel ODS-A-HG (50 μm, YMC Co., Ltd., Kyoto, Japan). α-d-Glucosidase and acarbose were purchased from Sigma-Aldrich (St. Louis, MO, USA).

2.2. Plant materials

The aerial parts of S. dulcis were collected and authenticated by Mr. Yilin Zhu from Guangxi University of Chinese Medicine in Nanning, Guangxi Zhuang Autonomous Region, China, in September 2018. A voucher specimen (No. YGC-Nanning1210) was deposited in the herbarium of the Institute of Chinese Materia Medica, Shanghai University of Traditional Chinese Medicine.

2.3. Extraction and isolation

Aerial parts of dried S. dulcis (3.7 kg) were soaked with 70% aqueous acetone solution at room temperature for three times at an in-terval of 7 d. After filtration and elimination of organic solvent, the extraction was extracted with petroleum ether, ethyl acetate in turn, to acquire 29 g of petroleum ether extracts, 108 g of ethyl acetate extracts, and 194 g of water solution portion, respectively. The ethyl acetate extract was eluted with MeOH-H2O (0:1 to 1:0, volume percent), performed by MCI gel CHP 20P column chromatography, to obtain three fractions (Fr. A–C).

Fr. A was separated by column chromatography via Sephadex LH-20, eluted with MeOH-H2O, (2:8 to 6:4, volume percent) and the YMC-column, eluted with MeOH-H2O (1:9 to 6:4) sequentially to afford compounds 7 (17 mg), 8 (7 mg), 9 (6 mg). Column chromatography through Sephadex LH-20, eluted with MeOH-H2O (0:1 to 8:2, volume percent) and YMC, eluted with MeOH-H2O (1:9 to 6:4, volume percent), acquired 1 (3 mg), 2 (7 mg), 3 (43 mg), 4 (14 mg), 5 (8 mg) from Fr. B. Chromatography of Fr. C on MCI gel CHP 20P eluted with MeOH-H2O (4:6 to 9:1, volume percent) and silica gel eluted with CH2Cl2-MeOH (20:1 to 1:1, volume percent) yielded 6 (67 mg) (Fig. 1).

Fig. 1.

Fig. 1

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Structures of compounds 1–9 isolated from S. dulcis.

Scoparic zolone (1), white amorphous powder; [α] – 42.0 (c 0.03, MeOH); UV (MeOH) λmax (log ε) 208 (4.37), 262 (3.75) nm; IR (KBr) νmax 3365, 2923, 2852, 1711, 1655, 1632, 1469, 1382, 1204, 1075, 620 cm−1; 1H NMR (600 MHz, MeOD): δH 6.30 (1H, d, J = 2.2 Hz, H-4), 6.68 (1H, dd, J = 8.3, 2.2 Hz, H-6), 6.72 (1H, d, J = 8.3 Hz, H-7), 3.30 (1H, d, J = 16.5 Hz, H-8a), 3.13 (1H, d, J = 16.5 Hz, H-8b), 2.10 (3H, s, H-10); 13C NMR (125 MHz, MeOD): δC 181.1 (C-2), 75.3 (C-3), 133.4 (C-3a), 112.9 (C-4), 154.5 (C-5), 116.6 (C-6), 111.8 (C-7), 135.5 (C-7a), 51.1 (C-8), 207.4 (C-9), 30.8 (C-10); HRESIMS 220.0618 [M − H]± (calcd. for 220.0610).

(2S)-2,7-Dihydroxy-2H-1,4-benzoxazin-3(4H)-one (2), white amorphous powder; 1H NMR (400 MHz, MeOD): δH 5.50 (1H, s, H-2), 6.77 (1H, d, J = 8.5 Hz, H-5), 6.46 (1H, dd, J = 8.5, 2.4 Hz, H-6), 6.49 (1H, d, J = 2.4 Hz, H-8); 13C NMR (100 MHz, MeOD): δC 92.2 (C-2), 164.7 (C-3), 119.8 (C-4a), 117.3 (C-5), 110.5 (C-6), 115.4 (C-7), 106.0 (C-8), 143.2 (C-8a).

(2R)-7-Hydroxy-2H-1,4-benzoxazin-3(4H)-one-2-O-β-d-glucopyranoside (3), white amorphous powder; 1H NMR (400 MHz, MeOD): δH 5.77 (1H, s, H-2), 6.95 (1H, m, H-5), 7.03 (1H, m, H-6), 7.03 (1H, m, H-7), 7.11 (1H, m, H-8), 4.70 (1H, d, J = 7.8 Hz, H-Glc-1), 3.21 (1H, t, J = 8.6 Hz, H-Glc-2), 3.30–3.40 (3H, m, H-Glc-3, 4, 5), 3.87 (1H, dd, J = 11.9, 1.7 Hz, H-Glc-6a), 3.70 (1H, dd, J = 11.9, 4.6 Hz, H-Glc-6b); 13C NMR (100 MHz, MeOD): δC 96.5 (C-2), 163.2 (C-3), 127.1 (C-4a), 116.8 (C-5), 125.1 (C-6), 124.2 (C-7), 119.0 (C-8), 142.1 (C-8a), 103.9 (C-Glc-1), 74.9 (C-Glc-2), 78.5 (C-Glc-3), 71.1 (C-Glc-4), 77.9 (C-Glc-5), 62.6 (C-Glc-6).

(2R)-7-Methoxy-2H-1,4-benzoxazin-3(4H)-one-2-O-β-d-glucopyranoside (4), white amorphous powder; 1H NMR (600 MHz, MeOD): δH 5.74 (1H, s, H-2), 6.86 (1H, d, J = 8.7 Hz, H-5), 6.62 (1H, dd, J = 8.7, 2.5 Hz, H-6), 6.75 (1H, d, J = 2.5 Hz, H-8), 4.70 (1H, d, J = 7.9 Hz, H-Glc-1), 3.21 (1H, t, J = 8.6 Hz, H-Glc-2), 3.30–3.40 (3H, m, H-Glc-3, 4, 5), 3.88 (1H, dd, J = 11.9, 1.9 Hz, H-Glc-6a), 3.70 (1H, dd, J = 11.9, 5.1 Hz, H-Glc-6b); 13C NMR (150 MHz, MeOD): δC 96.7 (C-2), 162.7 (C-3), 120.4 (C-4a), 116.2 (C-5), 110.1 (C-6), 158.2 (C-7), 104.9 (C-8), 142.9 (C-8a), 103.1 (C-Glc-1), 74.8 (C-Glc-2), 78.5 (C-Glc-3), 71.1 (C-Glc-4), 77.9 (C-Glc-5), 62.6 (C-Glc-6).

(2S)-7-Hydroxy-2H-1,4-benzoxazin-3(4H)-one-2-O-β-d-glucopyranoside (5), white amorphous powder; 1H NMR (600 MHz, MeOD): δH 5.82 (1H, s, H-2), 6.77 (1H, d, J = 8.5 Hz, H-5), 6.48 (1H, dd, J = 8.5, 1.9 Hz, H-6), 6.56 (1H, d, J = 1.9 Hz, H-8), 4.74 (1H, d, J = 7.9 Hz, H-Glc-1), 3.15 (1H, t, J = 8.6 Hz, H-Glc-2), 3.30–3.39 (3H, m, H-Glc-3, 4, 5), 3.91 (1H, br d, J = 12.0 Hz, H-Glc-6a), 3.70 (1H, dd, J = 11.9, 6.0 Hz, H-Glc-6b); 13C NMR (150 MHz, MeOD): δC 93.3 (C-2), 162.7 (C-3), 119.5 (C-4a), 117.4 (C-5), 111.0 (C-6), 155.7 (C-7), 106.2 (C-8), 142.6 (C-8a), 99.9 (C-Glc-1), 74.5 (C-Glc-2), 78.4 (C-Glc-3), 71.4 (C-Glc-4), 77.8 (C-Glc-5), 62.7 (C-Glc-6).

6-Methoxy-benzoxazolin-2(3H)-one (6), colorless needle crystal; 1H NMR (600 MHz, Pyridine‑d6): δH 7.01 (1H, d, J = 8.5 Hz, H-4), 6.78 (1H, d, J = 8.5, 2.4 Hz, H-5), 7.03 (1H, d, J = 2.4 Hz, H-7), 3.68 (3H, s, OMe), 12.97 (1H, brs, NH); 13C NMR (125 MHz, Pyridine‑d6): δC 156.1 (C-2), 125.0 (C-3a), 110.0 (C-4), 109.5 (C-5), 156.4 (C-6), 97.5(C-7), 145.4 (C-7a), 55.9 (OMe).

4-Acetonyl-3,5-dimethoxy-p-quinol (7), white amorphous powder; 1H NMR (400 MHz, DMSO): δH 5.32 (2H, s, H-2,6), 3.06 (2H, s, H-7), 2.02 (3H, s, H-9), 3.66 (6H, s, OCH3-2, 6), 6.16 (1H, s, OH-4); 13C NMR (100 MHz, MeOD): δC 186.6 (C-1), 100.1 (C-2,6), 171.5 (C-3,5), 69.4 (C-4), 49.4 (C-7), 204.7 (C-8), 30.8 (C-9), 56.2 (3,5-OMe)。.

Zizyvoside I (8), white amorphous powder; 1H NMR (400 MHz, MeOD): δH 5.90 (1H, s, H-2), 2.54 (1H, d, J = 16.9 Hz, H-6a), 2.16 (1H, d, J = 16.9 Hz, H-6b), 5.87 (1H, d, J = 3.0 Hz, H-7), 5.89 (1H, d, J = 3.0 Hz, H-8), 3.40 (1H, m, H-9), 1.31 (3H, d, J = 6.3 Hz, H-10), 1.94 (3H, s, H-11), 1.06 (3H, s, H-12), 1.06 (3H, s, H-13), 4.43 (1H, d, J = 7.5 Hz, H-1′), 5.26 (1H, d, J = 1.3 Hz, H-1′'); 13C NMR (100 MHz, MeOD): δC 201.2 (C-1), 127.7 (C-2), 167.2 (C-3), 78.0 (C-4), 42.5 (C-5), 50.7 (C-6), 131.6 (C-7), 135.4 (C-8), 77.2 (C-9), 21.2 (C-10), 19.6 (C-11), 24.7 (C-12), 23.4 (C-13), 101.2 (C-1′), 79.5 (C-2′), 77.9 (C-3′), 72.2 (C-4′), 78.7 (C-5′), 62.8 (C-6′), 102.0 (C-1′'), 71.8 (C-2′'), 72.3 (C-3′'), 73.9 (C-4′'), 69.7 (C-5′'), 18.1 (C-6′').

3,4-Dihydroxy benzeneacetic acid (9), white amorphous powder; 1H NMR (400 MHz, MeOD): δH 7.05 (1H, d, J = 2.1 Hz, H-2), 6.80 (1H, d, J = 8.2 Hz, H-5), 6.95 (1H, dd, J = 8.2, 2.1 Hz, H-6), 7.55 (1H, d, J = 15.9 Hz, H-β), 6.24 (1H, d, J = 15.9 Hz, H-α).

2.4. α-Glucosidase inhibitory activity assay

The assay was carried out according to a reported method (Yang, et al. 2015). α-Glucosidase (from Saccharomyces cerevisiae) was dissolved in potassium phosphate buffer (pH 6.8) with a concentration of 0.25 U/mL. Test samples and the positive control, acarbose, were also dissolved in potassium phosphate buffer (pH 6.8).

3. Results and discussion

Compound 1 was obtained as a white amorphous powder, with the molecular formula C11H11NO4 deduced by HR-ESI-MS at m/z 220.0618 ([M−H]−, calcd for 220.0610), 1H and 13C NMR spectra. 1H NMR spectroscopic characteristics demonstrated that the structure of this compound contains a set of aromatic protons attributed to a 1,3,4-trisubstituted benzene ring [δH 6.30 (1H, d, J = 2.2 Hz, H-4), 6.72 (1H, d, J = 8.3 Hz, H-7), 6.68 (1H, dd, J = 8.3, 2.2 Hz, H-6)] and one methyl [δH 2.10 (3H, s, H-10)]. Removed the signals of benzene ring from 13C NMR data, other carbon signal were observed, including two carbonyl groups [δC 207.4 (C-9), 181.1 (C-2)], one oxygenated carbon [δC 75.3 (C-3)], and two saturated alkane carbons [δC 51.1 (C-8), 30.8 (C-10)]. Conjectured from the degrees of unsaturation, compound 1 should contain an extra ring structure apart from a benzene ring. Compared with literature (Luppi, et al. 2005), the above spectral characteristics are very similar to 3-(2-oxopropyl)-3-hydroxyindolin-2-one, except for an additional hydroxyl group in compound 1. HMBC correlations of H-4 (δH 6.30) with C-3 (δC 75.3), H-8 (δH 3.30, 3.13) with C-2 (δC 181.1), C-3 (δC 75.3), C-3a (δC 133.4) and C-9 (δC 207.4) further confirmed the above inference, assigning that the hydroxyl at the C-5 position. In addition, the CD spectrum of this compound displayed a positive Cotton effect between 220 and 260 nm, indicating that the configuration of C-3 was determined to be S, by comparison with the CD spectrum of 3-(2-oxopropyl)-3-hydroxyindolin-2-one (Luppi, et al. 2005). Thus, the structure of compound 1 was established, named Scoparic zolone.

Compound 2 was isolated as a white amorphous powder. Analysis of its 1H NMR spectrum, there displayed a 1,3,4-trisubstituted benzene ring signal [δH 6.77 (1H, d, J = 8.5 Hz, H-5), 6.49 (1H, d, J = 2.4 Hz, H-8), 6.46 (1H, dd, J = 8.5, 2.4 Hz, H-6)] and a dioxymethine proton [δH 5.50 (1H, s H-2)]. Also, 13C NMR spectrum exhibited eight carbon signals totally. The above spectroscopic data was identical to those of (2S)-2,7-dihydroxy-2H-1,4-benzoxazin-3(4H)-one (Kluge, Hartenstein, Hantschmann, & Sicker, 1995). Accordingly, the structure of compound 2 was elucidated as (2S)-2,7-dihydroxy-2H-1,4-benzoxazin-3(4H)-one.

Compound 3 was isolated as a white amorphous powder. 1H NMR data displayed one disubstituted benzene ring signal [δH 7.11 (1H, m, H-8), δH 7.03 (2H, m, H-6, 7), δH 6.95 (1H, m, H-5)] and one β-glucosyl anomeric proton signal [δH 4.70 (1H, d, J = 7.8 Hz, Glc-1)]. After comparing with the spectral data of the literature (Yin, Zhang, Luo, & Liu, 2008), the structure of this compound was established as (2R)-7-hydroxy-2H-1,4-benzoxazin-3(4H)-one-2-O-β-d-glucopyranoside.

Compound 4 was isolated as a white amorphous powder. Similar to compound 3, compound 4 has a benzene ring signal and a group of β-glucosyl signals in the 1H NMR spectrum. The only difference between compound 3 and compound 4 was an extra methoxy signal (δH 3.78, 3H, s) in compound 4. The spectral data of compound 4 were consistent with those reported in the literature (Baumeler, Hesse, & Werner, 2000) for (2R)-7-methoxy-2H-1,4-benzoxazin-3(4H)-one-2-O-β-d-glucopyranoside.

Compound 5 was a white amorphous powder. Its 1H spectrum was very similar to that of compound 4 (Baumeler, Hesse, & Werner, 2000), except for the lack of one methoxyl group singal. However, 13C NMR showed that the chemical shift value of C-2 position (δC 93.3) was 3.4 × 10-6 lower than compound 4, suggesting that C-2 configuration should be S. Further comparison of the two spectral data, compound 5 was identified as (2S)-7-hydroxy-2H-1,4-benzoxazin-3(4H)-one-2-O-β-d-glucopyranoside.

Compound 6 was isolated as a colorless needle crystal (CHCl2-MeOH 1:1). 13C NMR spectroscopic data exhibited seven carbon resonances totally, representing the feature of benzoxazolone alkaloids. With reference to the spectra data which displayed in literature (Nagao, Otsuka, Kohda, Sato, & Yamasaki, 1985), the structure of compound 6 was established as 6-methoxy-benzoxazolin-2(3H)-one, accordingly.

Compound 7 was obtained as a white amorphous powder. The 1H NMR spectroscopic data exhibited two methoxy signals [δH 3.66 (6H, s)] and two alkene hydrogen signals overlapped, respectively [δH 5.32 (2H, s)], suggesting that compound 7 beared symmetrical groups. Besides, the 13C and DEPT NMR spectra revealed total eleven carbon signals, classified as three methyls, one methylenes, two methines, and five quaternary carbons. These spectral data match those of 4-acetonyl-3,5-dimethoxy-p-quinol reported in the literature completely (Wu, Yang, Wu, & Liu, 1995). Therefore, its structure was confirmed as 4-acetonyl-3,5-dimethoxy-p-quinol.

Compound 8 was obtained as a white amorphous powder. The 1H NMR spectrum displayed two anomeric protons at δH 4.43 (1H, d, J = 7.5 Hz, Glc-1) and δH 5.26 (1H, d, J = 1.3 Hz, Rha-1). Apart from two group of sugar signals, the remaining signals in 13C NMR data could be sorted into four methyls, a pair of olefinic carbons, one ketone group, one methylene group and one oxylated quaternary carbon. Based on 1H NMR, 13C NMR and DEPT spectra data, the above spectroscopic characteristics closely resembled those of zizyvoside I (Yagi, et al., 1981), moreover, HMBC spectra also verified the identity of these two compounds. Thus, compound 8 was identified as zizyvoside I.

Compound 9 was isolated as a white amorphous powder. The 1H NMR spectrum indicated an isolated methylene signal [δH 3.48 (2H, s, H-7)] and a group of 1,3,4-trisubstituted benzene ring signals. Combined with the literature (Ma, Yang, Zhang, Wang, & Wang, 2008), it was identified as 3,4-dihydroxy benzeneacetic acid.

All isolated compounds were evaluated for their inhibitory effect against α-glucosidase. Compound 2 was found to exhibit a strong inhibitory effect against α-glucosidase with an IC50 value of (132.8 ± 11.5) μmol/L, 28-fold higher than the positive control, acarbose, for which the IC50 value was (3760 ± 157.2) μmol/L. Other compounds failed to enhance the inhibitory activity relative to acarbose. Therefore, compound 2 is expected to be a promising lead compound for the treatment of diabetes.

4. Conclusion

The present study reports led to the isolation and identification of nine compounds from the aerial parts of S. dulcis, including six alkaloids (compounds 1–6), 4-acetonyl-3,5-dimethoxy-p-quinol (compound 7), zizyvoside I (compound 8) and 3,4-dihydroxy benzeneacetic acid (compound 9). By comparison of the existing literature, compounds 2 and 9 have not been reported in Scoparia. Compounds 3, 5, 7, 8 are isolated from Scrophulariaceae for the first time.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We are thankful for financial supports from the National Natural Science Foundation of China (32170402, 81703682, 81874335).

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