Soluble epoxide hydrolase inhibitors from Docynia indica (Wall.) Decne.

Article abstract of DOI:10.1080/14786419.2020.1774759

Nine bioactive compounds, including one new dihydroisocoumarin glycoside, 3S-thunberginol C 6-O-β-D-glucopyranoside (1a/1b), were isolated by chromatographic separation from the fruits of the Vietnamese medicinal plant Docynia indica (Wall.) Decne. 3S-thunberginol C 6-O-β-D-glucopyranoside was determined as a mixture of boat-like conformers based on NMR evidence and density functional theory (DFT) calculations. The in?vitro inhibition of soluble epoxide hydrolase (sEH) by the isolated compounds was comparable to that of AUDA (positive control), yielding IC₅₀ values ranging from 10.0 ± 0.6 to 88.4 ± 0.2 μM. Among isolated compounds, 3-methoxy-4-hydroxy-benzoic acid (7) and 2′,6′-dihydroxy 3′,4′-dimethoxychalcone (9) were identified as a potent inhibitor of sEH, with IC₅₀ values of 19.3 ± 2.2 and 10.0 ± 0.6 mM, respectively. These results suggest that the fruits of D. indica may be useful as daily supplements for the prevention of cardiovascular and other sEH-related diseases. (Figure presented.).

Full text of DOI:10.1080/14786419.2020.1774759

Natural Product Research
Formerly Natural Product Letters
ISSN: 1478-6419 (Print) 1478-6427 (Online) Journal homepage: https://www.tandfonline.com/loi/gnpl20
Soluble epoxide hydrolase inhibitors from Docynia
indica (Wall.) Decne.
Le Xuan Duy, Vinh Le Ba, Dan Gao, Vu Dinh Hoang, Tran Quoc Toan, Seo
Young Yang, Dao Duy Quang, Young Ho Kim & Nguyen Manh Cuong
To cite this article: Le Xuan Duy, Vinh Le Ba, Dan Gao, Vu Dinh Hoang, Tran Quoc Toan, Seo
Young Yang, Dao Duy Quang, Young Ho Kim & Nguyen Manh Cuong (2020): Soluble epoxide
hydrolase inhibitors from Docyniaꢀindica (Wall.) Decne., Natural Product Research
To link to this article: https://doi.org/10.1080/14786419.2020.1774759
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NATURAL PRODUCT RESEARCH
https://doi.org/10.1080/14786419.2020.1774759
SHORT COMMUNICATION
Soluble epoxide hydrolase inhibitors from Docynia indica
(
Wall.) Decne.
a,e
b,c
b
d,e
Le Xuan Duy *, Vinh Le Ba *, Dan Gao , Vu Dinh Hoang , Tran Quoc
a,e
b
f,g
b
Toan , Seo Young Yang
Nguyen Manh Cuong
, Dao Duy Quang , Young Ho Kim
and
a,e
a
Institute of Natural Products Chemistry (INPC), Vietnam Academy of Science and Technology
b
(
VAST), Caugiay, Hanoi, Vietnam; College of Pharmacy, Chungnam National University, Daejeon,
c
Republic of Korea; Institute of Marine Biochemistry (IMBC), Vietnam Academy of Science and
d
Technology (VAST), Caugiay, Hanoi, Vietnam; School of Chemical Engineering, Hanoi University of
Science and Technology, Hanoi, Vietnam; Graduate University of Science and Technology (GUST),
Vietnam Academy of Science and Technology (VAST), Caugiay, Hanoi, Vietnam; Institute of Research
and Development, Duy Tan University, Da Nang, Vietnam; Faculty of Environmental and Chemical
e
f
g
Engineering, Duy Tan University, Da Nang, Vietnam
ABSTRACT
ARTICLE HISTORY
Nine bioactive compounds, including one new dihydroisocoumarin
glycoside, 3S-thunberginol C 6-O-b-D-glucopyranoside (1a/1b), were
isolated by chromatographic separation from the fruits of the
Vietnamese medicinal plant Docynia indica (Wall.) Decne. 3S-thunber-
ginol C 6-O-b-D-glucopyranoside was determined as a mixture of
boat-like conformers based on NMR evidence and density functional
theory (DFT) calculations. The in vitro inhibition of soluble epoxide
hydrolase (sEH) by the isolated compounds was comparable to that
of AUDA (positive control), yielding IC50 values ranging from
Received 28 February 2020
Accepted 10 May 2020
KEYWORDS
Docynia indica; 3S-
thunberginol C 6-O-b-D-
glucopyranoside; soluble
epoxide hydrolase; CD
spectrum; 3-aryl
dihydroisocoumarin; boat-
1
0.0 ± 0.6 to 88.4 ± 0.2 mM. Among isolated compounds, 3-methoxy-4-
like conformer; DFT
0
0
0
0
hydroxy-benzoic acid (7) and 2 ,6 -dihydroxy 3 ,4 -dimethoxychalcone
9) were identified as a potent inhibitor of sEH, with IC50 values of
9.3 ± 2.2 and 10.0 ± 0.6 mM, respectively. These results suggest that
(
1
the fruits of D. indica may be useful as daily supplements for the pre-
vention of cardiovascular and other sEH-related diseases.
CONTACT Young Ho Kim
Nguyen Manh Cuong
yhk@cnu.ac.kr
nmcuong_inpc@yahoo.com.vn
Chungnam National University, Daejeon, 34134 Korea.;CONTACT
Vietnam Academy of Science and Technology, Institute
of Natural Products Chemistry, 18 Hoang Quoc Viet, Caugiay, Hanoi, 10307 Viet Nam.
ꢀ
Le Xuan Duy, and Le Ba Vinh contributed equally to this work
Supplemental data for this article can be accessed online at https://doi.org/10.1080/14786419.2020.1774759.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
L. X. DUY ET AL.
1. Introduction
Cardiovascular diseases are among the leading causes of death worldwide, with an
estimated 17.8 million deaths in 2017 (Jagannathan et al. 2019). Many experimental
studies have shown that certain foods (e.g. garlic, tea, soy, nuts and seeds) are poten-
tially involved in the development or prevention of cardiovascular diseases (Anand
et al. 2015). Furthermore, several potentially severe diseases (e.g. atherosclerosis, dia-
betes, gout and cancer) have been correlated with cardiovascular disease (Low Wang
et al. 2016). Previously, we investigated soluble epoxide hydrolase (sEH) inhibition as a
therapeutic target for cardiovascular disease (Cuong et al. 2017; Kim et al. 2018; Vinh
et al. 2018). The current study explored and identified structurally novel compounds
from fruits of Docynia indica (Wall.) Decne possessing sEH inhibitory activity.sEH
belongs to a large group of epoxide hydrolases that are defined by their ability to
catalyze the conversion of epoxides to their corresponding diols. sEH is a cytosolic
enzyme with C-terminal epoxide hydrolase and terminal lipid phosphatase activities.
Recent studies have reported various relationships of sEH inhibition associated with
neuroprotective (Hashimoto 2019), anti-inflammatory effect (Jones et al. 2019), cardio-
vascular (Huang et al. 2016) and diabetic diseases (Low Wang et al. 2016).
Docynia indica (Wall.) Decne (Rosaceae) is widely distributed in Vietnam, India and
several southern provinces of China (Chi 2012). Docynia indica fruits have been trad-
itionally used as a food and for the treatment of infectious diseases, digestive disor-
ders and hypertension in adults (Chi 2012). Fruit extracts of D. indica exhibit diverse
pharmacological effects, including antimicrobial, anti-inflammatory, cytotoxic and anti-
oxidant activities. Thus far, only docynicasides A ꢁ C, representing new megastigmane
glycosides, have been isolated from the fruits of D. indica (Dung et al. 2016). However,
potential uses of these compounds in the treatment of cardiovascular disease have
not yet been reported. As part of our research on chemical constituents of medicinal
plants that possess sEH inhibitory potential, we report herein the separation and struc-
tural determination of a new dihydroisocoumarin glucoside (1a/1b) and 8 known com-
pounds from the methanolic extract of D. indica, as well as an evaluation of their sEH
inhibitory activities in vitro.
2. Results and discussion
Separation and purification of the ethyl acetate (EtOAc) fraction of the D. indica
extract led to isolation of a new dihydroisocoumarin glycoside, named 3S-thunberginol
C 6-O-b-D-glucopyranoside (1a/1b), as well as 8 other known compounds (2–9, see
0
Figure 1): hyperin (2) phloretin-2 -O-b-D-xylopyranoside (1!6)-O-b-D-glucopyranoside
(
3) chlorogenic acid methyl ester (4) naringenin (5) astilbin (6) 3-methoxy-4-hydroxy-
0
0
0
0
benzoic acid (7) ursolic acid (8) and 2 ,6 -dihydroxy 3 ,4 -dimethoxychalcone (9). The
known compounds were identified by detailed analyses of their spectroscopic data
and comparisons with previously reported data.
Thunberginol C 6-O-b-D-glucopyranoside (1a/1b) was isolated as a white amorph-
ous powder and a mixture of two conformers with the ratio of 11/9. The molecular

NATURAL PRODUCT RESEARCH
3
Figure 1. The structures of compounds 1–9.
formula (C H O ) of 1a/1b was determined by HR-ESI-MS with molecular ion peaks
2
1 22 10
at m/z 469.0890 [M þ Cl]\bar (calculated for C H ClO \bar, 469.0896) and m/z
21
22
10
4
33.1119 [M - H]\bar (calculated for C H O \bar, 433.1129).
21
21 10
13
1
The H-NMR (DMSO-d , 500 MHz) and C-NMR (125 MHz) spectra of 1a/1b were
6
1
indicative of dihydroisocoumarin glycosides (Liu et al. 2013). The H-NMR spectrum
0
0
0
0
contained a doublet at dH 6.80 (d, J ¼ 8.5 Hz, H-3 , 5 ) and 7.32 (d, J ¼ 8 Hz, H-2 , 6 ),
corresponding to a disubstituted benzene ring; it also contained peaks at d 6.55 (br
H
s, H-5), 6.52 (d, J ¼ 2 Hz, H-7, in 1a), and 6.51 (d, J ¼ 2 Hz, H-7, in 1b), corresponding to
a tetrasubstituted benzene ring. The presence of a chelated d-lactone was evidenced
by peaks at dH 5.61 (t, J ¼ 2.5; H-3eq, in 1a), 5.59 (t, J ¼ 2.5; H-3eq, in 1b), 3.11 (t,
J ¼ 2.5 Hz, H-4a, in 1a), 3.07 (t, J ¼ 2.5 Hz, H-4a, in 1b) and 3.35 (m, H-4b). Based on
13
these data and comparisons of the C-NMR spectrum (see Experimental section) with
reference data, the aglycone of 1a/1b was confirmed to be thunberginol C. Acid
hydrolysis of 1 with 1 M HCl liberated D-glucose, as confirmed by TLC and HPLC analy-
ses and comparisons with authentic samples (Supplementary material). The attach-
ment of a glycoside chain at C-6 of 1 was confirmed by an HMBC correlation between
0
0
the anomeric proton H-1 (d 4.99 in 1a/4.97 in 1b) and C-6 (d 163.28). Another evi-
H
C
dence is that the chemical shift of carbonyl carbon C-1 in 1a/1b is similar to those of
thunberginol-like compounds containing hydroxyl group at C-8 (Toshikawa et al.
1
992), and different to those of some thunberginol 8-O-b-D-glucopyranosides (Liu
22
et al. 2013). Compound 1a/1b had a negative value of the specific rotation ([a] D
¼
ꢁ
69 (c 0.1, MeOH), similar to that of (-)-florahydroside II, a 3S-thunberginol 8-O-b-D-
glucopyranoside derivative (Liu et al. 2013). 1a/1b showed a weak negative Cotton

4
L. X. DUY ET AL.
effect at 227 nm (De227 – 2.29) and a characteristic strong negative at 255 nm (De255
.85 and also at 305 nm (De305 – 1.21), which are indicative of 3S-configuration of 3-
aryl dihydroisocoumarin (Liu et al. 2013).
–
4
In order to elucidate the preponderant conformer of 1a/1b, we have employed the
density functional theory (DFT) calculations using Gaussian 16 A.03 package at the
M05-2X/6-311þþG(d,p) level of theory (Frisch et al. 2016). Table S2 (Supplementary
material) resume the five most stable boat-like conformers and the four most stable
chair-like conformers of the studied compound. As a result, the boat-like conformer
(boat conformer C3) is seen as the more stable structure with a relative enthalpy of
2
.7 kcal/mol lower than that of the chair-like one (chair conformer C2). Figure S11 dis-
plays the two most stable boat-like conformers 1a and 1b of 3S-thunberginol C 6-O-
b-D-glucopyranoside with the relative enthalpy difference of only 0.2 kcal/mol. In the
boat-like conformation, proton H-3 of 1a and 1b is equatorial, in agreement with a
small coupling constant J ¼ 2.5 Hz. Consequently, compound 1a/1b was identified as a
mixture of two boat-like conformers of 3S-thunberginol C 6-O-b-D-glucopyranoside.
The inhibitory activities of isolated compounds 1–9 from D. indica were evaluated
against sEH in vitro, in accordance with previously reported protocols with some minor
modifications (Sun et al. 2015) as described in the Supplementary Materials. The sEH
inhibitory activities were determined using recombinant human sEH incubated with
PHOME, an artificial substrate for fluorescence detection. Specifically, the quantity of
6-methoxy-2-naphthaldehyde produced from the substrate (PHOME) was quantified in
the presence or absence of compounds 1–9 using a fluorescence photometer at wave-
lengths of 330 and 465 nm. AUDA was used as positive control (IC50 ¼ 16.8 ± 0.5 nM).
Table S1 (Supplementary Materials) shows that compounds 2, 3, 4, 5, 6, 7, 8, and 9
exhibited sEH inhibitory activity comparable to that of the positive control AUDA; with
IC50 values were of 30.5 ± 0.2, 88.4 ± 0.2, 41.9 ± 1.1, 24.7 ± 2.5, 22.9 ± 0.2, 19.3 ± 2.2,
3
6.1 ± 0.6, and 10.0 ± 0.6 mM, respectively. To the best of our knowledge, this is the
0
first report of sEH inhibitory activity of phloretin-2 -O-b-D-xylopyranoside (1!6)-O-b-D-
0
0
0
0
glucopyranoside (3), astilbin (6), and 2 ,6 -dihydroxy 3 ,4 -dimethoxychalcone (9). Most
of the compounds from D. indica fruits showed moderate to high sEH inhibitory activ-
ities, in comparison to other natural compounds, such as flavonoids (Thao et al. 2016),
alkaloids (Thao et al. 2017), anthocyanin (Kim et al. 2018) and phenolic compounds
(
Khanh et al. 2016). Based on the results obtained and compared with the references
0
0
mentioned above, compounds 3-methoxy-4-hydroxy-benzoic acid (7) and 2 ,6 -dihy-
0
0
droxy 3 ,4 -dimethoxychalcone (9) may be potential compounds which can be used in
the development of sEH inhibitors. These results indicate that D. indica fruits may
serve as a dietary supplement for the treatment of cardiovascular diseases and other
related ailments.
Supplementary material
General experimental procedures, acid hydrolysis and sugar identification, enzymatic assay,
HR-ESI, MS, and 1D-2D-NMR spectra of 1a/1b, conformer search by DFT approach.

NATURAL PRODUCT RESEARCH
5
Disclosure statement
The authors have declared that there is no conflict of interest.
ORCID
Seo Young Yang
Young Ho Kim
http://orcid.org/0000-0002-5248-1374
http://orcid.org/0000-0002-7441-9459
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