Four new prenylflavonol glycosides from the leaves of Cyclocarya paliurus

Article abstract of DOI:10.1080/14786419.2020.1803313

Four new prenylflavonol glycosides (1–4) along with two known analogues (5–6) were isolated from the leaves of Cyclocarya paliurus for the first time. The structures of these compounds were characterized by comprehensive analysis of 1 D, 2 D NMR, HRESIMS,

Full text of DOI:10.1080/14786419.2020.1803313

Natural Product Research
Formerly Natural Product Letters
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gnpl20
Four new prenylflavonol glycosides from the
leaves of Cyclocarya paliurus
Zi-Jun Ye , Hui-Hui Sun , Zu-Hui Chen , Jian-Ping Wu , Jing Li , Hui Zhu , Lu-Lu
Huang , Xi-Wen Chang , Sai-Yu Ou , Wen-Xuan Wang , Xiao-Ai He , Gang-Zhi
Zhu & Kang-Ping Xu
To cite this article: Zi-Jun Ye , Hui-Hui Sun , Zu-Hui Chen , Jian-Ping Wu , Jing Li , Hui Zhu , Lu-
Lu Huang , Xi-Wen Chang , Sai-Yu Ou , Wen-Xuan Wang , Xiao-Ai He , Gang-Zhi Zhu & Kang-
Ping Xu (2020): Four new prenylflavonol glycosides from the leaves of Cyclocaryaꢀpaliurus , Natural
Product Research, DOI: 10.1080/14786419.2020.1803313
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NATURAL PRODUCT RESEARCH
https://doi.org/10.1080/14786419.2020.1803313
Four new prenylflavonol glycosides from the leaves of
Cyclocarya paliurus
Zi-Jun Yea, Hui-Hui Sunb, Zu-Hui Chenc, Jian-Ping Wub, Jing Lib, Hui Zhub, Lu-Lu
Huangb, Xi-Wen Changb, Sai-Yu Oub, Wen-Xuan Wangb, Xiao-Ai Hea, Gang-Zhi
Zhua and Kang-Ping Xub
aDepartment of Pharmacochemistry, Haikou Municipal People’s Hospital and Central South
b
University Xiangya School of Medicine Affiliated Haikou Hospital, Haikou, China; Xiangya School of
c
Pharmaceutical Sciences, Central South University, Changsha, China; Hunan Heran Biotechnology
Development company, Changsha, China
ABSTRACT
ARTICLE HISTORY
Received 5 May 2020
Accepted 20 July 2020
Four new prenylflavonol glycosides (1–4) along with two known
analogues (5–6) were isolated from the leaves of Cyclocarya paliu-
rus for the first time. The structures of these compounds were
characterized by comprehensive analysis of 1 D, 2 D NMR,
HRESIMS, UV data and enzymatic hydrolysis. In bioassays, com-
pounds 1–4 were evaluated for inhibitory effects on xanthine oxi-
dase (XOD) and effects on the inhibition of nitric oxide (NO)
production in lipopolysaccharide (LPS) induced RAW264.7 cells.
Moreover, compounds 1 and 2 showed outstanding XOD inhibi-
tions with IC50 values of 18.16 3.91 and 37.65 5.67 mM, and
exhibited inhibitions against LPS-induced NO production with IC50
values of 80.50 3.09 and 82.28 2.87 mM.
KEYWORDS
Cyclocarya paliurus;
prenylflavonol glycosides;
xanthine oxidase; nitric
oxide; RAW264.7 cells
CONTACT G. Z. Zhu
csdb2012@126.com; K. P. Xu
xukp395@csu.edu.cn
Supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2020.1803313.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
Z.-J. YE ET AL.
1. Introduction
Cyclocarya paliurus (Batal.) Iljinsk is a single species belonging to family Juglandaceae,
widely distributed in south and southeast areas of China (Ramallo et al. 2006). Its
leaves have been consumed as traditional tea in China for a long time due to its palat-
able taste and many curative effects, such as relieving arthrophlogosis, analgesic, anti-
inflammation, hypoglycemic, antioxidant and so on (Xie et al. 2015, Xuan et al. 2019,
Sun et al. 2020). The flavonoids were considered as one of the main active compos-
ition in C. paliurus, such as quercetin and its glycoside derivatives (Fang et al. 2011,
Liu et al. 2016, Li et al. 2020, Lin et al. 2020), while only a few phytochemical investi-
gations about C. paliurus were focused on flavonoids. To explore structurally intriguing
and bioactive flavonoids from C. paliurus, the systematic study on the n-BuOH fraction
of C. paliurus was carried out. Finally, four new prenylflavonol glycosides, Icarisids L-O
(1–4), together with two known analogues (5–6) were isolated and identified (Figure
1). Herein, the isolation, structure elucidation, and biological evaluations
were reported.
2. Results and discussion
2.1. Chemistry
Compound 1 was obtained as yellow, amorphous powder. Its chemical formula:
C33H42O17 was determined by HRESIMS and 13C NMR spectrum. The 1H NMR data
(Supplementry material Table S1) displayed four aromatic protons at dH 8.01 (d,
J ¼ 9.2 Hz, 2H), 7.10 (d, J ¼ 8.8 Hz, 2H) suggested the presence of a p-substituted ben-
zene ring B; an aromatic methine at dH 6.66 (s, 1H) indicated the existence of a penta-
1
substituted ring A; a methoxy group signal at dH 3.86 (s, 3H). Besides, The H NMR
and 13C NMR data (Supplementry material Table S1 and S2) displayed a series of sig-
nals at [dH 3.00, 2.88 (overlapped, 2H), 3.44 (overlapped, 1H), 1.17 (d, J ¼ 3.6 Hz, 6H); dC
24.3 (CH2-11), 77.4 (CH-12), 71.9 (C-13), 26.0 (CH3-14), 25.0 (CH3-15)] ascribed to a 2,3-
Figure 1. Chemical structures of compounds 1–6.

NATURAL PRODUCT RESEARCH
3
dihydroxy-3-methylbutyl moiety; a set of signals at [dH 5.23 (br s)/dC 102.3 (CH-100)]
and [dH 4.92 (d, 1H, J ¼ 6.8 Hz)/101.3 (CH-1000)] indicated the existence of two sugar
moieties. The monosaccharides obtained by enzymatic hydrolysis were identified by
GC-MS analysis with authentic samples as L-rhamnose and D-glucose. And combining
with the coupling constants of terminal protons, the absolute configurations of sugars
were determined as a-L-rhamnopyranosyl and b-D-glucopyranoside. The HMBC correla-
tions (Supplementry material Figure S1) between H-100 (dH 5.23)/C-3 (dC 134.7), H-1000
(dH 4.92)/C-7 (dC 161.5) indicated the a-L-rhamnopyranosyl was linked at C-3 and the
b-D-glucopyranoside was linked at C-7; the correlations between 40-OCH3 (dH 3.86) and
dC C-40 (161.6) suggested C-40 was substituted by a methoxy group. The location of
2,3-dihydroxy-3-methylbutyl moiety to C-8 was proved by the cross-peaks of H-11 (dH
3.00, 2.88) with C-7 (dC 161.5), C-8 (dC 107.8), C-9 (dC 153.5), and C-12 (dC 77.4).
Moreover, the correlations between H-6 (dH 6.66) and C-5 (dC 159.2), C-7 (dC 161.5), C-
8 (dC 107.8), C-10 (dC 105.8) confirmed the proton singlet at dH 6.66 was assignable as
25
D
H-6. Besides, enzymatic hydrolysis of 1 by snailase afforded an aglycone (X1), [a]
ꢀ27.8 (MeOH). The configuration at C-12 was deduced as “S” on the basis of optical
rotation and 13C-NMR chemical shift data comparison with reported analogues
(Yukinori et al. 1994). Therefore, the structure of 1 was established as 8-[(S)-2,3-dihy-
droxy-3-methylbutyl]-5-hydroxy-40-methoxy-3-O-a-L-rhamnopyranosyl-flavonol-7-O-b-D-
glucopyranoside, and named as Icarisid L.
Compound 2 was obtained as yellow, amorphous powder. Its chemical formula:
C33H42O17 was determined by HRESIMS. The 1 D/2D NMR spectra of 2 was almost
same as 1 except for the signals of side-chain. The 13C NMR spectrum of 2 displayed
signals at dC 27.1 (CH3-14) and dC 23.3 (CH3-15) which were significantly different from
that of compound 1 [dC 26.0 (CH3-14) and dC 25.0 (CH3-15)], indicated that the config-
uration at C-12 was different. Besides, enzymatic hydrolysis of 2 afforded an aglycone
25
(X2), [a] 24.6 (MeOH). The configuration at C-12 was deduced as “R” on the basis of
D
optical rotation and 13C-NMR chemical shift data comparison with reported analogues
(Yukinori et al. 1994). Therefore, the structure of 2 was established as 8-[(R)-2,3-dihy-
droxy-3-methylbutyl]-5-hydroxy-40-methoxy-3-O-a-L-rhamnopyranosyl-flavonol-7-O-b-D-
glucopyranoside, and named as Icarisid M.
Compound 3 was obtained as yellow, amorphous powder. Its chemical formula:
C39H52O21 was determined by HRESIMS. The 1 D/2D NMR spectra of 3 were almost
same as 2, except for the existence of another a-rhamnopyranosyl moiety. Further
enzymatic hydrolysis and GC-MS analysis determined the glycosyl moieties were a-L-
rhamnopyranose and b-D-glucupyranose. The HMBC (Supplementry material Figure S1)
correlations between H-10000 (dH 4.91) and C-200 (dC 75.6) suggested that
rhamnopyranosyl0 was linked at C-200. Besides, enzymatic hydrolysis of 3 also afforded
25
D
an aglycone (X3), [a] 26.3 (MeOH), which indicated the configuration at C-12 was
deduced as “R”. Therefore, the structure of 3 was established as 8-[(R)-2,3-dihydroxy-3-
methylbutyl]-5-hydroxy-40-methoxy-3-O-a-L-rhamnopyranosyl-(1!2)-a-L-rhamnopyrano-
syl-flavonol-7-O-b-D-glucopyranoside, and named as Icarisid N.
Compound 4 was obtained as yellow, amorphous powder. Its chemical formula:
C38H48O20 was determined by HRESIMS data. The 1 D/2D NMR spectra of 4 was basic-
ally same as 3, except for the rhamnopyranosyl0 was replaced by a b-xylopyranose

4
Z.-J. YE ET AL.
1
and the change of side-chain. The H and 13C NMR data (Supplementry material Table
S1 and S2) displayed a set of signals at [dH 2.99, 2.87 (overlapped, 2H), 4.17 (m, 1H),
4.86, 4.72 (s, each 1H), 1.75 (s, 3H); dC 29.2 (CH2-11), 73.7 (CH-12), 148.4 (C-13), 109.6
(CH2-14), 17.8 (CH3-15)] indicated the side chain at C-8 was a 2-hydroxy-3-methylbut
unit. The HMBC (Supplementry material Figure S1) correlations between H-10000 (dH
4.12) and C-200 (dC 80.8) suggested that b-xylopyranose was linked at C-200. Further
enzymatic hydrolysis and GC-MS analysis determined the glycosyl moieties were a-L-
rhamnopyranose, b-D-glucupyranose and b-D-xylopyranose. Enzymatic hydrolysis of 4
25
also afforded an aglycone (X4), [a]
ꢀ19.6 (MeOH). Moreover, because of the 2-
D
hydroxy-3-methylbut group did not contribute much to Electronic circular dichroism
(ECD), the rotation of X4 was finally deduced as “-” by its specific rotation (-19.6,
MeOH). Therefore, the structure of compound 4 was established as 8-[(-)-2-hydroxy-3-
methylbut]-5-hydroxyl-40-methoxy-3-O-b-D-xylopyranose-(1!2)-a-L-rhamnopyranosyl-
flavonol-7-O-b-D-glucopyranoside, and named as Icarisid O.
Together with two known analogues (5-6) were identified by comparison of their
reported spectroscopic data as diphylloside B (5) (Liang et al. 1993) and epimedoside
E (6) (Su et al. 2018).
2.2. Bioassay
The xanthine oxidase (XOD) inhibitory effects of 1-4 and allopurinol (positive control)
have been evaluated by measuring the production of superoxide ion and uric acid,
and the results (see Supplementry material Table S3) indicated that compounds 1 and
2 showed outstanding inhibitions on XOD with the IC50 values of 18.16 3.91 and
37.65 5.67 mM. Besides, the anti-inflammation activities of 1-4 and indometacin (posi-
tive control) were evaluated in the RAW 264.7 cells, and the results were listed in
Supplementry material Table S4. Compounds 1 and 2 exhibited inhibitory activities on
lipopolysaccharide (LPS) induced NO production with IC50 values of 80.50 3.09
and 82.28 2.87 mM.
3. Experimental
3.1. General experimental procedures
Optical rotations were measured on a JASCO model 1020 polarimeter (Horiba, Tokyo,
Japan) at room temperature. NMR spectra were measured on Bruker AVANCE 400
spectrometer (Bruker, Karlsruhe, Germany) using dimethyl sulfoxide (DMSO-d6) as solv-
ent and tetra methylsilane (TMS) as an internal standard. High resolution electrospray
ionization mass spectroscopy (HRESIMS) was recorded with an Agilent Technologies
liquid chromatograph connected to Q-TOF mass spectra. Gas Chromatography-Mass
Spectrometer (GC-MS) was measured on GCMS-QP2010 Ultra (Shimadzu Corporation).
Analytical HPLC experiments was carried out on an Agilent 1200 with YMC-Pack ODS-
C18 column (250 ꢁ 4.6 mm, 5 lm, YMC Co. Ltd., Kyoto, Japan). Column chromato-
graphic (CC) separations were carried out on Macroporous resin HPD-100 (Zhengzhou
Qinshi Technology Co., Ltd), polyamide (80-100 or 30-60 mesh, Taizhou Luqiao Sijia
Biochemical Plastics Factory, Taizhou, China), HW-40C (TOYOPEARL, TOSOH, Japan) and

NATURAL PRODUCT RESEARCH
5
ODS-AA (50 lm, YMC). Semi-preparative HPLC separations were conducted by using
Agilent 1260 system with an ODS-C18 column (250 ꢁ 10 mm, 5 lm, YMC). All the ana-
lytic reagents were analytical grade.
3.2. Plant material
The leaves of Cyclocarya paliurus (Batal.) Iljinsk were collected from Xinning, Shaoyang,
Hunan Province. A voucher specimen (No. 20160820) was identified by Prof. Kangping
Xu from Xiangya School of Pharmaceutical Sciences, Central South University, and
deposited in Xiangya School of Pharmaceutical Sciences, Central South University.
3.3. Extraction and isolation
Air-dried leaves of C. paliurus (10 Kg) were powdered and extracted with 70% EtOH-
H2O (100 L ꢁ 2h ꢁ 2) under reflux conditions, and were dried under reduced pressure
to get crude extract then suspended in water and successively partitioned with
CH2Cl2, EtOAc and n-BuOH. The n-BuOH extraction (445 g) was subjected to column
chromatography on Macroporous resin HPD-100 with EtOH-H2O to obtain five frac-
tions Fr.A-E (0-95%, stepwise). Fr.C (107 g) was separated by a polyamide column using
EtOH-H2O to afforded six sub-fractions Fr.C1-C6 (0-95%, stepwise). Fr.C1 (22.9 g) was
separated to twelve fractions Fr.C1-C12 by HW-40C eluted with MeOH-H2O (from 0:100
to 70:30). Fr.C1.2 was purified by ODS column with MeOH-H2O (10-75%, stepwise) and
obtained 45 sub-fractions (Fr.C1.2.1-Fr.C1.2.45). Fr.C1.2.29 was separated by Semi-
preparative HPLC (ACN-H2O 24%, v/v, 220 nm, 3 mL/min) to give compound 1 (9.7 mg).
Fr.C1.3 was purified by the ODS column with MeOH-H2O (10-75%, stepwise) and
obtained 28 sub-fractions (Fr.C1.3.1-Fr.C1.3.28). Fr.C1.3.12 was separated by Semi-pre-
parative HPLC (ACN-H2O 18%, v/v, 220 nm, 3 mL/min) to give compounds 2 (7.8 mg)
and 3 (4.9 mg). Fr.C1.3.15 was separated by Semi-preparative HPLC (ACN-H2O 21%, v/
v, 220 nm, 3 mL/min) to give compounds 5 (13.1 mg) and 6 (21.4 mg). Fr.C1.3.17 was
separated by Semi-preparative HPLC (ACN-H2O 24%, v/v, 0.1% CH3COOH, 220 nm,
3 mL/min) to give compound 4 (6.4 mg).
3.3.1. Icarisid L (1)
25
D
Yellow amorphous powder; [a] ꢀ127.0 (c 0.07, MeOH); UV (MeOH) kmax (log e) nm:
204 (4.10), 271 (2.30), 316 (1.29), and 350 (1.05) nm; H and 13C NMR data (400 and
1
100 MHz in DMSO-d6) see Supplementry material Tables S1 and S2; HRESIMS, m/z
711.2500 [M þ H]þ (calcd for C33H43O17, 711.2500).
3.3.2. Icarisid M (2)
25
D
Yellow amorphous powder; [a] ꢀ111.3 (c 0.09, MeOH); UV (MeOH) kmax (log e) nm:
200 (3.70), 271 (1.05), 316 (0.59), and 350 (0.48) nm; H and 13C NMR data (400 and
1
100 MHz in DMSO-d6) see Supplementry material Tables S1 and S2; HRESIMS, m/z
711.2505 [M þ H]þ (calcd for C33H43O17 711.2500).

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Z.-J. YE ET AL.
3.3.3. Icarisid N (3)
25
D
Yellow amorphous powder; [a] ꢀ141.7 (c 0.07, MeOH); UV (MeOH) kmax (log e) nm:
199 (3.75), 271 (1.13), 316 (0.63), and 350 (0.52) nm; H and 13C NMR data (400 and
1
100 MHz in DMSO-d6) see Supplementry material Tables S1 and S2; HRESIMS, m/z
857.3083 [M þ H]þ (calcd for C39H53O21, 857.3079).
3.3.4. Icarisid O (4)
25
D
Yellow amorphous powder; [a] ꢀ165.3 (c 0.1, MeOH); UV (MeOH) kmax (log e) nm:
203 (3.88), 270 (1.42), 320 (0.77), and 349 (0.71) nm; H and 13C NMR data (400 and
1
100 MHz in DMSO-d6) see Supplementry material Tables S1 and S2; HRESIMS, m/z
825.2822 [M þ H]þ (calcd for C38H49O20, 825.2817).
3.4. Enzymatic hydrolysis
The sugar units of compounds were identified by enzymatic hydrolysis and followed
by GC-MS analysis. This part was conducted according to published method with
some modifications (Jia et al. 2010).
3.5. XOD activity bioassay
The production of superoxide ion was detected by the nitrite method in 96-well plates
(Shang et al. 2006). The mixture was consisted of 10 lL compound solution (100,
33.33, 11.11, 3.70, 1.23 and 0.41 mM), 10 lL Nitrotetrazolium Blue chloride (NBT) solu-
tion (50 lM) and 40 lL XOD (20 U/L) as the substrate, incubated at 37 ꢂC for 10 min.
The reaction was initiated by adding 40 mL xanthine (120 mM), and incubated at 37 ꢂC
for another 30 min. Finally, the reaction was stopped with adding 50 mL HCl (2 M), the
absorbance value was detected at 560 nm. The uric acid content was measured
according to published method with some modifications (Liu et al. 2017). The method
was similar to the method above, excepted for the NBT solution was replaced by
phosphate buffer and final absorbance value was detected at 295 nm. Allopurinol was
used as the positive control.
3.6. NO production bioassay
According to the published method with some modifications (Yang et al. 2011), RAW
264.7 cells were cultured in RPMI-1640 medium, and were plated at 8000 cells per
well in a 96-well plate and incubated for 24 h under 5% CO2 atmosphere at 37 ꢂC.
After incubated for 24 h, the cells were pre-treated with different compounds (100,
33.33, 11.11, 3.70, 1.23 and 0.41 mM) for 1 h, and then stimulated with LPS (1 mg/mL)
for 23 h. The final concentration of DMSO should not exceed 0.1% in the culture
medium. The supernatant (50 mL) was harvested and measured by Griess reagent.
Subsequently, nitrite content was measured at 540 nm. Indometacin was used as a
positive control.

NATURAL PRODUCT RESEARCH
7
4. Conclusion
The research reported four new and two known prenylflavonol glycosides from
Cyclocarya paliurus for the first time. The bioassays suggested that compounds 1 and
2 exhibited outstanding inhibitory activities on XOD and moderate inhibitions on LPS-
induced NO production. The discovery of these compounds enriched the chemical
constituents of flavonoids in C. paliurus. And the bioassay results proposed new
insights for the usage of C. paliurus.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the Central South University postgraduate independent exploration
and innovation project under Grant [No. 2019zzts751; No. 2018zzts239], Central South University
College Students Innovation and Entrepreneurship Project under Grant [No. GS201910533126X;
No. GS201910533022X; No. XCX20190632], Hunan Province Ordinary Higher Education Teaching
Reform Research Project, Central South University Deepening Innovation and Entrepreneurship
Education Reform Research Project under Grant [No. 2019CG006], and Hunan Graduate Research
and Innovation Project under Grant [No. CX20190247].
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