8-O-β-D-Glucopyranosyl-2-methylchromone, a new chromone glycoside from the Tibetan medicine plant of Swertia punicea Hemsl

Article abstract of DOI:10.1080/14786419.2020.1777123

A new chromone glycoside, 8-O-β-D-Glucopyranosyl-2-methylchromone (1), together with eight known compounds (2–9) were isolated from the Tibetan medicine plant of Swertia punicea. All compounds of this plant were reported for the first time. The structures of these metabolites were elucidated by analysis of their HR–ESI–MS, 1D and 2D NMR spectroscopic data and comparison with data reported in the literature. In vitro test, all compounds were evaluated for their anti-inflammatory activity through the determination of nitric oxide production. Compounds 1–2 were evaluated for cytotoxic activities against three human cancer cell lines (HeLa, MDA-MB-231 and A375) by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method. Furthermore, the chemotaxonomic significance of these compounds has also been described.

Full text of DOI:10.1080/14786419.2020.1777123

Natural Product Research
Formerly Natural Product Letters
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8-O-β-D-Glucopyranosyl-2-methylchromone, a new
chromone glycoside from the Tibetan medicine
plant of Swertia punicea Hemsl
Lin-Yun Mou, Min Wei, Hai-Yan Wu, Li-Jiao Hu, Jian-Long Li & Gan-Peng Li
To cite this article: Lin-Yun Mou, Min Wei, Hai-Yan Wu, Li-Jiao Hu, Jian-Long Li & Gan-
Peng Li (2020): 8-O-β-D-Glucopyranosyl-2-methylchromone, a new chromone glycoside
from the Tibetan medicine plant of Swertiaꢀpunicea Hemsl, Natural Product Research, DOI:
10.1080/14786419.2020.1777123
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NATURAL PRODUCT RESEARCH
https://doi.org/10.1080/14786419.2020.1777123
8
-O-b-D-Glucopyranosyl-2-methylchromone, a new
chromone glycoside from the Tibetan medicine plant of
Swertia punicea Hemsl
a,b,c
c
c
c
a,b
Lin-Yun Mou , Min Wei , Hai-Yan Wu , Li-Jiao Hu , Jian-Long Li and Gan-
Peng Li
c
a
b
Department of Ecology, School of Life Science, Nanjing University, Nanjing, P.R.China; State Key
Laboratory of Pharmaceutical Biotechnology and Collaborative Innovation Center of Chemistry for
c
Life Sciences, School of Life Sciences, Nanjing University, Nanjing, P.R.China; Key Laboratory of
Chemistry in Ethnic Medicinal Resources, State Ethnic Affairs Commission and Ministry of Education,
Yunnan Minzu University, Kunming, P.R.China
ABSTRACT
ARTICLE HISTORY
A new chromone glycoside, 8-O-b-D-Glucopyranosyl-2-methyl-
chromone (1), together with eight known compounds (2–9) were
isolated from the Tibetan medicine plant of Swertia punicea. All
compounds of this plant were reported for the first time. The
structures of these metabolites were elucidated by analysis of
their HR–ESI–MS, 1D and 2D NMR spectroscopic data and com-
parison with data reported in the literature. In vitro test, all com-
pounds were evaluated for their anti-inflammatory activity
through the determination of nitric oxide production. Compounds
Received 26 March 2020
Accepted 19 May 2020
KEYWORDS
Swertia punicea; chromone
glycoside; anti-inflammatory
activity; cytotoxic effect
1
–2 were evaluated for cytotoxic activities against three human
cancer cell lines (HeLa, MDA-MB-231 and A375) by 3-(4,5-dime-
thylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method.
Furthermore, the chemotaxonomic significance of these com-
pounds has also been described.
1. Introduction
Swertia punicea Hemsl. (Gentianaceae) is a traditional Chinese medicine with the treat-
ment of acute bilious hepatitis, cholecystitis and jaundice (Zheng et al. 2014). It is
CONTACT Gan-Peng Li
ganpeng_li@sina.com; Jian-Long Li
lijianlongnju@163.com
Supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2020.1777123.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
L.-Y. MOU ET AL.
Figure 1. The structures of compounds 1–9.
mainly distributed in Southwest China in such provinces as Yunnan, Guizhou, Sichuan
and Hunan (Kang et al. 2011; Mou et al. 2018). The main chemical components of S.
punicea are xanthones and iridoids (Zheng et al. 2014; Zafar and Wang 2018). Previous
investigations indicate that some of the chemical components have antistaphylococcal
activity (Zheng et al. 2019), antibacterial activity (Yoiprommarat et al. 2019), anti-
inflammatory activity (Wei et al. 2013) and neuroprotective effect (Xu et al. 2012).
Accordingly, a variety of bioactivities inspire researchers to explore other novel natural
products in S. punicea.
In the study of the chemical components of S. punicea, our group have isolated
some new compounds from traditional Chinese medicine and tested their anti-inflam-
matory activity (Mou et al. 2018). Further investigations led to the isolation of a new
chromone glycoside (1) and eight known compounds (2–9) from the Tibetan medicine
plant of Swertia punicea. The metabolites’ structures were established based on
detailed spectroscopic analysis and comparison with reported data (Figure 1). In add-
ition, compounds 1–9 were reported from this plant for the first time with anti-inflam-
matory activity as the guide. S. Punicea is used as a traditional Chinese medicine to
eliminate inflammation. So a large number of valuable anti-inflammatory compounds
can be screened from this plant with a clear goal. Coincidentally, tumours are seriously
threatening human health at present. It is an urgent matter to founded new com-
pounds with anti-tumour activity. New compound 1 was selected for anti-tumour

NATURAL PRODUCT RESEARCH
3
activity test to fill the gap in its anti-tumour activity. We checked the changes in activ-
ity due to structural differences between new compound 1 and known compound 2,
which will pave the way for future research on the structure-activity relationship of
such compounds.
2. Results and discussion
Compound 1 was obtained as a brown-yellow powder with the molecular formula of
1
3
þ
C H O , according to its C NMR data and HR-ESI-MS at m/z 361.0893 [M þ Na]
1
6 18 8
(
calcd. 361.0894) with 8 indices of hydrogen deficiency. The IR spectral data indicated
the presence of hydroxyl (3441 cm ), carbonyl (1640 cm ) and an aromatic ring
1444 cm ). The H NMR spectrum displayed the characteristic signals of a methyl
ꢀ
1
ꢀ1
ꢀ
1
1
(
group [d 2.02 (3H, s)], a glycosyl anomeric proton [d 5.79 (1H, d, J ¼ 6.9 Hz)], an ole-
H
H
finic proton [d 6.23 (1H, s)] and three aromatic protons [d 7.24 (1H, t, J ¼ 8.0 Hz),
H
H
1
3
7
1
1
.84 (1H, d, J ¼ 7.9 Hz), 7.99 (1H, d, J ¼ 7.8 Hz)]; Its C NMR and DEPT data exhibited
6 carbon resonances, including a methyl group (d 20.1), four methines (d 125.0,
C
C
19.2, 117.8, and 110.7), four quaternary carbons (d 166.3, 147.4, 147.3 and 125.4), 6
C
carbon signals for a sugar residue (d 102.4, 79.2, 78.6, 74.8, 71.2 and 62.4), as well as
C
a conjugated carbonyl carbon (d 177.4). Based on these data and the structure of the
C
known chromones isolated from the plant, compound 1 was assigned as a chro-
mone glycoside.
After the acid hydrolysis of compound 1, the released sugar was found to be D-glu-
cose by comparison on thin-layer chromatography (TLC) with a standard sample.
1
According to the H-NMR signals at d 5.79 (d, J ¼ 6.9 Hz) and d 4.56 (dd, J ¼ 11.6 Hz,
H
H
13
J ¼ 1.2 Hz) together with the C-NMR data (Table S1) assigned to the sugar unit it was
proved a b-D-glucopyranosyl group (Ahmad et al. 2004; Li et al. 2015). Combination
analysis of NMR data of 1 with those of 8-hydroxy-2-methylchromone (2) suggested
that the bicyclic ring was similar (Wang et al. 2011). The only obvious difference was
that the signal for the hydroxy at C-8 in 8-hydroxy-2-methylchromone (2) was replaced
by a b-D-glucopyranosyl group in 1, which can be further confirmed by heteronuclear
0
multiple bond connectivity (HMBC) correlation from H-1 to C-8. Analysis of the HSQC,
H– H COSY and HMBC spectra led to the complete assignments of the proton and
1
1
carbon signals in compound 1 (Table S1). Based on the above data, 8-O-b-D-
Glucopyranosyl-2-methylchromone was characterised as shown (Figure S2).
Through comparing the physical and spectral data with literatures, other eight
known metabolites were identified as 8-hydroxy-2-methylchromone (2) (Wang et al.
2
011), 1,3,5-thihydroxyxanthone (3) (Kuang et al. 2016), 1,7-dihydroxy-2,3-dimethoxyx-
anthone (4) (Pinheiro et al. 1998), decentapicrin C (5) (Van der Sluis and Labadie
981), sweroside (6) (Zhang et al. 2012), Epivogeloside (7) (Kawai et al. 1988), luteolo-
1
side (8) (Shrestha et al. 2012) and Arctigenin (9) (Li et al. 2019), respectively. All com-
pounds were isolated from the S. punicea for the first time.
Compound 1, a new chromone glycoside was isolated and reported from the family
Gentianaceae for the first time. It can be considered as a characteristic component of
S. punicea. Compound 2 was first identified in Halenia elliptica D. Don (Wang et al.
2011). In the same year, compound 2 was found again in this plant (Sun et al. 2012).

4
L.-Y. MOU ET AL.
Interestingly, compound 2 was only found in the family Gentianaceae. Compounds 3
and 4 were previously reported in Kielmeyera species (Gottlieb et al. 1966) and Frasera
speciosa (Dreyer and Bourell 1981) for the first time, respectively. Compounds 5, 6 and
7
were first identified in Centaurium littorale (Van der Sluis and Labadie 1981), Swertia
japonica (Inouye et al. 1966) and Anthocleista vogelii (Chapelle 1976), respectively.
Compound 8 was first reported in Digitalis purpurea L (Nakamura et al. 1936).
Compound 9 was previously reported in Arctium lappa L. (Shinoda 1929) for the first
time. Herein, compound 9 was identified from the family Gentianaceae for the first
time. The present study extends the phytochemical composition of the genus Swertia
and provides new chemotaxonomic markers for S. punicea and the genus Swertia.
Additionally, cell viability was measured by MTT method thereby ruling out the
toxic effects of all compounds on the mouse macrophage cells-RAW 264.7 (Figure S1).
All of the isolated compounds (1–9) were evaluated for their anti-inflammatory activity
through the determination of NO production. As shown in Table S2, the results sug-
gested that secoiridiod glycosides (compounds 5–7) and lignan (compound 9) showed
better anti-inflammatory activity by comparing their activity data. All compounds
exhibited significant to moderate anti-inflammatory activity with IC50 values ranging
3
from 2.373 to 6.687 (10 lM).
The Cervical epithelial adenocarcinoma cells (HeLa), Human breast cancer cells
(MDA-MB-231) and Human malignant melanoma cells (A375) were used to investigate
and evaluated for cytotoxic activity of compounds 1 and 2 in vitro by the MTT assay.
Among them, compound 1 and 2 displayed no activity against cell lines HeLa and
MDA-MB-231 with IC50 > 40 lM. Compound 2 displayed much better cytotoxic activity
against A375 with an IC50 value of 12.959 lM (Table S3), because compound 1 has
one glucose group so it may be due to its bulky nature creating barrier closed to the
active site (Ahmad et al. 2004). This work could provid valuable support for further
research on S. punicea.
3. Experimental
3.1. General experimental procedures
IR spectra were recorded on a Nicoiet Is10 (Thermo Fisher Scientific) with KBr pallets.
Optical rotations were measured on an autopol v plus automatic polarimeter (Rudolph
Research Analytical). HR-ESI-MS was performed on a VG Autospec-3000 spectrometer.
The 1D and 2D NMR spectra were acquired in C D N with TMS as internal standard on
5
5
a Bruker AVANCE III-400 NMR spectrometer, all chemical shifts were expressed in d
ppm) referenced to the solvent signals (Bruker BioSpin Group, German). Semi-prepara-
tive HPLC experiments was performed with an instrument consisting of an Agilent
260 (including multi-wavelength detector MWD, binary pump) with Shimadzu shim-
(
1
pack GIS C18 (10 mm ꢁ 250 mm, 5 lm) column (Shimadzu, Japan). Column chromatog-
raphy were performed with silica gel (100–200 mesh and 200–300 mesh, Qing-dao
Marine Chemical, Inc, Qing-dao, People’s Republic of China) and RP-18 gel (MB
1
2
00–40/75 lm, Fuji Silysia Chemical Ltd., Japan). The mouse macrophage cells-RAW
64.7, Cervical epithelial adenocarcinoma cells (HeLa), Human breast cancer cells
(MDA-MB-231) and Human malignant melanomacells (A375) were obtained from

NATURAL PRODUCT RESEARCH
5
Kunming Institute of Zoology, CAS of the Chinese Academy of Sciences (Kunming,
People’s Republic of China). DMEM (Low Glucose) was obtained from HyClone
Laboratories (GE Healthcare Life Sciences, USA). LPS was purchased from the Solarbio.
The nitric oxide (NO) detection kit was purchased from Nanjing Jiancheng
Bioengineering Institute (People’s Republic of China). Indomethacin (positive control),
ethylene diamine tetraacetic acid (EDTA) and dimethyl sulfoxide (DMSO) were pur-
chased from Sigma Life Science.
3.2. Plant material
The whole herb of S. punicea was collected from Liangwang mountain, Kunming city
of the Yunnan Province, People’s Republic of China, in November 2015 and identified
by Ph.D. Li-Pan, Yang at the Yunnan University of Traditional Chinese Medicine. A vou-
cher specimen (No. SP201511) was deposited at the Herbarium of Key Laboratory of
Chemistry in Ethnic Medicinal Resources, State Ethnic Affairs Commission and Ministry
of Education, Yunnan Minzu University.
3.3. Extraction and isolation
The air-dried and powdered whole herb of S. punicea (1.0 kg) was extracted three
ꢂ
times with 95% ethanol (3 ꢁ 2.0 L) at 20 C. The obtained ethanol extracts were com-
bined and concentrated in vacuum to give a crude extract (157.0 g), which was sus-
pended in H O and partitioned with petroleum ether, ethyl acetate, and n-butanol,
2
respectively.
After removal of the solvent in a vacuum, the extract of ethyl acetate fraction
(
87.0 g) was separated through the positive silica gel CC (30 ꢁ 8 cm i.d., 100–200
mesh), and eluted with a gradient of PE–EtOAc (100: 0–0: 100, v/v) to generate twenty
fractions (EA.1–EA.20). The EA.14 (350.3 mg) was subjected to a silica gel CC (200–300
mesh), eluted with PE–EtOAc (1: 1, v/v) to generate six fractions (EA.14a–EA.14f).
Fraction EA.14e (19.5 mg) was subjected to semi-preparative HPLC on Shimadzu shim-
pack GIS C18 column (10 mm ꢁ 250 mm, 5 lm) with MeOH–H O (2.0 mL/min, MeOH:
2
H O ¼ 83: 17, v/v) to obtain 4 (10.0 mg). Fraction EA.16e (33.5 mg) was subjected to
2
semi-preparative HPLC on Shimadzu shim-pack GIS C18 column (10 mm ꢁ 250 mm,
5
lm) with MeOH–H O (2.0 mL/min, MeOH: H O ¼ 78: 22, v/v) to obtain 3 (10.0 mg).
2
2
The extract of the n-butanol fraction (16.0 g) was separated through RP-18 column
(
(
40–75lm, 80 ꢁ 6 cm i.d.) with MeOH–H O (1: 1–4: 1, v/v) to give fifteen fractions
2
NBA1–NBA15). Fraction NBA12 (150.9 mg) was subjected to semi-preparative HPLC on
Shimadzu shim-pack GIS C18 column (10 mm ꢁ 250 mm, 5 lm) with MeOH–H O
2
(
2.0 mL/min, MeOH: H O ¼ 68: 32, v/v) to obtain 9 (3.0 mg).
2
The extract of aqueous fraction (17.0 g) was separated through RP-18 column
(
(
40–75lm, 80 ꢁ 6 cm i.d.) with MeOH–H O (1: 9–0: 10, v/v) to give eighteen fractions
2
W1–W18). Fraction W3 (60.8 mg) was subjected to semi-preparative HPLC on
Shimadzu shim-pack GIS C18 column (10 mm ꢁ 250 mm, 5 lm) with MeOH–H O
2
(
2.0 mL/min, MeOH: H O ¼ 68: 32, v/v) to obtain 1 (12.3 mg). Fraction W4 (65.6 mg)
2
was subjected to semi-preparative HPLC on Shimadzu shim-pack GIS C1 column
8

6
L.-Y. MOU ET AL.
(
10 mm ꢁ 250 mm, 5 lm) with MeOH–H O (2.0 mL/min, MeOH: H O ¼ 68: 32, v/v) to
2
2
obtain 2 (10.1 mg). Fraction W7 (188.9 mg) was subjected to semi-preparative HPLC on
Shimadzu shim-pack GIS C18 column (10 mm ꢁ 250 mm, 5 lm) with MeOH–H O
2
(
2.0 mL/min, MeOH: H O ¼ 60: 40, v/v) to obtain 8 (50.2 mg). Fraction W8 (70.3 mg)
2
was subjected to semi-preparative HPLC on Shimadzu shim-pack GIS C1 column
8
(
10 mm ꢁ 250 mm, 5 lm) with MeOH–H O (2.0 mL/min, MeOH: H O ¼ 60: 40, v/v) to
2
2
obtain 7 (3.5 mg). Fraction W13 (60.8 mg) was subjected to semi-preparative HPLC on
Shimadzu shim-pack GIS C18 column (10 mm ꢁ 250 mm, 5 lm) with MeOH–H O
2
(
2.0 mL/min, MeOH: H O ¼ 59: 41, v/v) to obtain 6 (13.5 mg). Fraction W15 (83.5 mg)
2
was subjected to semi-preparative HPLC on Shimadzu shim-pack GIS C18 column
(
10 mm ꢁ 250 mm, 5 lm) with MeOH–H O (2.0 mL/min, MeOH: H O ¼ 58: 42, v/v) to
2
2
obtain 5 (30.6 mg).
3
.3.1. 8-O-b-D-Glucopyranosyl-2-methylchromone
17:4
Brown yellow powder; ½aꢃ
¼ ꢀ98:8(c ¼ 0.03, MeOH); IR (KBr): m
3441, 1640, 1444,
D
ꢀ
max
1
1
13
1269, 1069, 863, 569 cm ; H NMR and C NMR spectral data (C D N, 400 and
5 5
1
00 MHz, respectively), see Table S1. HR-ESI-MS (positive mode): m/z 361.0893
þ
[M þ Na] (calcd for C H O Na, 361.0894).
16 18 8
3.4. Cell viability assay
Mouse macrophage cells-RAW 264.7 were pre-treated with compounds 1–9 whose the
ꢂ
final concentration is 200 mM and cultured for 24 hours at 37 C in 5% CO in 96 well
2
plates, and then the cell viability was measured by MTT [3-(4,5-dimethylthiazol-2-yl)-
2,5-diphenyl tetrazolium bromide] assay (Hou et al. 2015).
3.5. Measurement of NO production
The strength of the anti-inflammatory activity was determined by measurement of NO
production (Viet Cuong et al. 2019). Mouse macrophage cells-RAW 264.7 were sus-
pended to a concentration of 3 ꢁ 105 cells/mL and incubated in 96-well tissue culture
ꢂ
plates (150 lL/well) at 37 C, 5% CO for 2 h. The plates were pre-treated with various
2
concentrations (final concentration: 200 lM, 20 lM and 2 lM) of test samples for
30 min. These cells were randomly divided into blank group (DMEM), model group
(
DMEM þ LPS), positive control group (DEME þ LPS þ Indomethacin) and sample test
group (DMEM þ LPS þ compounds) after the cells were stimulated by 2 lg/mL of LPS.
ꢂ
Cells were further incubated for 20 h at 37 C with saturated humidity 5% CO .
2
Repeated for three times. Then, the cell culture supernatants were treated with NO kit.
Absorbance at 550 nm was recorded in each well using a Multiskan Go (ThermoFisher)
microplate reader.
3
.6. Cytotoxicity assay
Cervical epithelial adenocarcinoma (HeLa) cells, Human breast cancer cells (MDA-MB-
31) and Human malignant melanoma (A375) cells were used for the cytotoxic assay.
2

NATURAL PRODUCT RESEARCH
7
The MTT assay was used to evaluate the cytotoxicity activity of compounds 1 and 2
(
Chokchaisiri et al. 2019; Wang et al. 2020). For the cytotoxicity assay, the cells were
ꢂ
seeded up to 1 ꢁ 104 cells/well in a 96-well plate. After incubating at 37 C under a
humidified 5% CO incubator for 24 h, the cells were treated with various concentra-
2
tions of compounds 1 and 2 (40, 8, 1.6, 0.32, and 0.064 lM) for 48 h. Then, the MTT
ꢂ
solution was added to each well and incubated for 4 h in dark at 37 C, 5% CO . The
2
supernatant was removed and 100 lL of DMSO was added before the absorption at
570 nm was determined spectrophotometrically.
3.7. Acid hydrolysis
ꢂ
Compound 1 (2 mg) was refluxed with 3.0 mL HCl (2.5 N) at 90 C for 12 h. After cool-
ing, water (3.0 mL) was added into the reaction mixture and then extracted with ethyl
acetate (6.0 mL ꢁ 3). Then the aqueous layer residue was compared with standard
sugar through TLC (n-butanol: EtOAc: 2-propanol: HOAc: H O ¼ 7: 20: 12: 7: 6, v/v).
2
The sugar was identified as D-glucose (R ¼ 0.47) (Sun et al. 2018, Huang et al. 2019).
f
4
. Conclusions
In conclusion, a new chromone glycoside, together with eight known compounds
2–9) were isolated from the Tibetan medicine plant of Swertia punicea. All com-
(
pounds were isolated from this plant for the first time. The present study extends the
phytochemical composition of the genus Swertia and provides new chemotaxonomic
markers for S. punicea and the genus Swertia. All compounds were evaluated for their
anti-inflammatory activity, the results suggested that all compounds exhibited signifi-
cant to moderate anti-inflammatory activity. Additionally, compounds 1–2 were eval-
uated for cytotoxic activities against three human cancer cell lines (HeLa, MDA-MB-231
and A375) by MTT method, compound 2 displayed much better cytotoxic activity
against A375.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This research was supported by the National Natural Science Foundation of China
(No. 21262048).
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