New tetralone derivatives from the leaves of Cyclocarya paliurus

Article abstract of DOI:10.1080/10286020.2017.1409733

Two new tetralone derivatives, named cyclopalosides A (1) and B (2), were isolated from the leaves of Cyclocarya paliurus by column chromatography on silica gel, reversed-phase C₁₈ silica gel and preparative HPLC. Their chemical structures were

Full text of DOI:10.1080/10286020.2017.1409733

Journal of Asian Natural Products Research
ISSN: 1028-6020 (Print) 1477-2213 (Online) Journal homepage: http://www.tandfonline.com/loi/ganp20
New tetralone derivatives from the leaves of
Cyclocarya paliurus
Xian-Li Zhou, Qin Luo, Si-Xin Huang, Peng-Cheng Wang, Qin Xu, Xiao Huang,
Cheng-Qin Liang & Xu Chen
To cite this article: Xian-Li Zhou, Qin Luo, Si-Xin Huang, Peng-Cheng Wang, Qin Xu, Xiao Huang,
Cheng-Qin Liang & Xu Chen (2017): New tetralone derivatives from the leaves of Cyclocarya
paliurus, Journal of Asian Natural Products Research, DOI: 10.1080/10286020.2017.1409733
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Journal of asian natural Products research, 2017
https://doi.org/10.1080/10286020.2017.1409733
New tetralone derivatives from the leaves of Cyclocarya
paliurus
Xian-Li Zhoua§, Qin Luoa§, Si-Xin Huanga, Peng-Cheng Wanga, Qin Xua,b, Xiao Huanga,
Cheng-Qin Lianga and Xu Chena
acollege of Pharmacy, Guilin Medical university, Guilin 541004, china; bGuangxi Key laboratory of Molecular
Medicine in liver injury and repair, Guilin Medical university, Guilin 541001, china
ABSTRACT
ARTICLE HISTORY
received 17 august 2017
accepted 22 november 2017
Two new tetralone derivatives, named cyclopalosides A (1) and B
(2), were isolated from the leaves of Cyclocarya paliurus by column
chromatography on silica gel, reversed-phase C18 silica gel and
preparative HPLC. Their chemical structures were established
on the basis of extensive analyses of spectroscopic data. Their
structural characteristic is tetralone glycoside with a caffeoyl unit.
The antioxidant activities of compound 1 were evaluated by using
hydroxyl, superoxide anion, and DPPH radical scavenging assay.
KEYWORDS
Juglandaceae; Cyclocarya
paliurus; tetralone
derivatives; antioxidant
O
R1
H
O
O
HO
O
R2
OH
O
HO
HO
OH
1 R1 = OH R2 = H
2 R1 = OMe R2 = OH
1. Introduction
Cyclocarya paliurus (Batal.) Ijinskaja (C. paliurus), a native plant from southern provinces
of China belonging to a very distinctive genus of Juglandaceae, is the sole species in its
genus [1–3]. For the special taste and functions of heat clearing and reducing blood pres-
sure and blood glucose, the leaves of C. paliurus have been used as a tea in China [3–5].
Phytochemical and pharmacological studies on leaves revealed that the constituents are
mainly lignans, flavonoids, and triterpenoids that possess various biological activities includ
-
ing antihyperglycemia, antihyperlipidemia, antihypertension, and antioxidant activities
[6–8]. In order to identify new natural compounds with interesting bioactivities, the leaves
of C. paliurus, indigenous to Ziyuan County of Guangxi Zhuang Autonomous Region, were
CONTACT cheng-Qin liang
cqliang@glmc.edu.cn; Xu chen
chenxu@glmc.edu.cn
§these authors contribute to the paper equally.
© 2017 informa uK limited, trading as taylor & francis Group

2
X.-L. ZHOU ET AL.
phytochemically investigated. As a result, two new tetralone glycosides, cyclopalosides A (1)
and B (2), with caffeoyl unit, were isolated from the leaves of this plant. is paper mainly
reports the isolation and structure elucidation of the new compounds, and the antioxidant
activities of compound 1.
2. Results and discussion
Compound 1 was obtained as a yellow, amorphous solid. Its molecular formula C25H26O11
was deduced from its HR-ESI-MS data ([M + Na]+ m/z 525.1371, calcd 525.1367), with 13
indices of hydrogen deficiency. e IR spectrum showed absorption bands at 3528, 1627,
1647, 1630 and 1264 cm−1, indicating the presence of hydroxy groups, carbonyl functional-
ities, and aromatic ring. e 1H NMR spectrum (Table 1) showed signals for four aromatic
protons (δH 7.43 (2H, d, J = 8.5 Hz, H-2″, 6″) and 6.82 (2H, d, J = 8.5 Hz, H-3″, 5″)), which
constituted a classical AA′BB′ system and defined a para-substituted benzene ring, and
other two aromatic protons (δH 7.44 (1H, d, J = 9.1 Hz, H-6) and 6.78 (1H, d, J = 9.1 Hz,
H-7)), which constituted a classical AB system and defined a 1,2,3,4-tetrasubstituted aro-
1
matic ring. And the H NMR spectrum (Table 1) also showed the presence of a pair of
trans-olefinic protons (δH 7.59 (1H, d, J = 15.9 Hz, H-7″) and 6.32 (1H, d, J = 15.9 Hz,
Table 1. 1h and 13c nMr spectroscopic data for compounds 1 and 2 (cd3od, tMs, δ in ppm, J in hz).
1
2
Position
1Ha
13Cb
1Hc
13Cd
1
206.4
33.5
206.4
33.5
2 a
2 b
3
3.00–3.08 (m)
2.47–2.52 (m)
2.15–2.22 (m)
5.35 (t, 3.0)
2.94–3.04 (m)
2.42–2.48 (m)
2.13–2.18 (m)
5.30 (s)
30.3
61.3
30.3
61.3
4
5
6
7
8
9
10
1′
2′
3′
148.5
128.8
119.0
159.2
116.2
135.3
104.4
75.2
77.8
71.7
75.7
64.5
148.4
128.8
119.0
159.3
116.2
135.3
104.4
75.2
77.8
71.7
75.7
64.4
7.44 (d, 9.1)
6.78 (d, 9.1)
7.40 (d, 9.2)
6.75 (d, 9.2)
4.82 (d, 7.6)
3.55–3.58 (m)
3.49–3.52 (m)
3.42–3.46 (m),
3.63–3.67 (m)
4.53 (dd, 11.9, 1.9)
4.38 (dd, 11.9, 6.6)
4.77 (d, 7.5)
3.48–3.52 (m)
3.41–3.46 (m)
3.35–3.40 (m)
3.57–3.61 (m)
4.46 (dd, 11.9, 1.9)
4.31–4.39 (m)
4′
5′
6′a
6′b
1″
2″
3″
4″
5″
6″
7″
8″
9″
–och3
127.0
131.2
116.9
161.3
116.9
131.2
146.8
114.9
168.9
127.5
111.5
149.4
150.7
116.5
124.3
147.1
115.2
168.8
56.4
7.43(d, 8.5)
6.82 (d, 8.5)
7.12 (d, 1.5)
6.82 (d, 8.5)
7.43 (d, 8.5)
7.59 (d, 15.9)
6.32 (d, 15.9)
6.78 (d, 8.2)
7.01 (dd, 8.2, 1.5)
7.54 (d, 15.9)
6.31 (d, 15.9)
3.86 (s)
arecorded at 600 Mhz.
brecorded at 150 Mhz.
crecorded at 400 Mhz.
drecorded at 100 Mhz.

JOURNAL OF ASIAN NATURAL PRODUCTS RESEARCH
3
H-8″)), an oxygenated methine (δ 5.35 (1H, t, J = 3.0 Hz, H-4)), and an anomeric proton
(δ 4.82 (1H, d, J = 7.6 Hz, H-1′)). e 13C NMR and DEPT spectra (Table 1) exhibited 25
carbon signals, including 3 methylenes (1 oxygenated), 14 methines (6 aromatic, 2 olefinic
and 6 oxygenated), and 8 quaternary carbons (2 carbonyl and 6 aromatic).
1
Careful investigation of the H and 13C NMR spectroscopic data of 1 established that
it was quite similar to those reported for berchemiaside B [9], which was isolated from
Berchemia floribunda. Analysis of HMBC and 1H-1H COSY spectra of 1 showed that two
compounds have same carbon fragments, including a tetralone, a caffeoyl, and a glucosyl
unit (Figure 1). e main difference between 1 and berchemiaside B was that the glucosyl
group connected with a caffeoyl unit at δC 64.5 (t, C-6′) was located at δC 148.5 (s, C-5) in
1, rather than C-4 in berchemiaside B. is was fully confirmed by the HMBC correlation
of δH 4.82 (1H, d, J = 7.6 Hz, H-1′) with δC 148.5 (s, C-5), and the ROESY correlation of δH
4.82 (1H, d, J = 7.6 Hz, H-1′) with δH 7.44 (1H, d, J = 9.1 Hz, H-6).
To determine the absolute configuration of C-4 in 1, the method of the reference [9]
was used. Afer performing the acid hydrolysis of 1, the hydrolysis product of 4,5,8-trihy-
droxy-α-tetralone exhibited a negative optical-rotation value ([ꢀ]2D4 – 34.7 (c 0.13, CHCl ),
3
indicating (R)-configuration at C-4 in comparison with the reported data of the tetralones
from reference [9]. erefore, the structure of 1 was unambiguously determined as shown
in Figure 1 and named cyclopaloside A.
Compound 2 was isolated as an amorphous powder and had the molecular formula of
C26H28O12, which was determined by analysis of 13C and DEPT NMR as well as HR-ESI-MS
data. Careful analysis of 1D and 2D NMR spectroscopic data of 1 and 2 showed that the
structure of 2 was strikingly similar to that of 1, and the main differences between them
only happened on the substituents of the caffeoyl unit. e structure of the caffeoyl unit of
2 was established unambiguously by the HMBC (Figure 2) correlations of δ 7.54 (1H, d,
J = 15.9 Hz, H-7″) with C-1″, C-2″, C-6″, C-8″ and C-9″, δ 6.31 (1H, d, J = 15.9 Hz, H-8″)
with C-1″, C-7″ and C-9″, δ 7.12 (1H, d, J = 1.5 Hz, H-2″) with C-3″ and C-4″, and δ 3.86
(3H, s, -OCH3) with C-4″, together with the spin systems of H-5″/H-6″ and H-7″/H-8″
in the 1H-1H COSY spectrum. Acid hydrolysis of compound 2 also yielded a 4,5,8- trihy-
droxy-α-tetralone. It exhibited a negative optical-rotation value ([ꢀ]2D4 – 33.5 (c 0.20, CHCl ))
which was similar as the value of 1, indicating (R)-configuration at C-4 in 2 [9]. us, t3he
structure of 2 was furnished as showed in Figure 1 and named cyclopaloside B.
Antioxidant activities have been attributed to various reactions and mechanisms, such
as radical scavenging, reductive capacity, prevention of chain initiation, and binding of
5'' 6''
7''
2
3
4
O
R1
1''
4''
1
H
HO
O
2''
3''
9''
8''
O
R2
10
5
9
6'
4'
5'
O
OH
O
8
HO
HO
1'
2'
6
7
3'
OH
1 R1 = OH R2 = H
2 R1 = OMe R2 = OH
Figure 1. structures of compounds 1 and 2.

4
X.-L. ZHOU ET AL.
5''
7''
2
O
HO
1''
4
9''
1
HO
O
3''
O
10
9
6'
5'
O
OH
O
5
HO
1'
7
HO 3'
OH
Figure 2. selected hMBc correlations of compound 1.
transition metal ion catalysts [10]. In addition, it has been reported that high antioxidant
activity could be attributed to the phenolic hydroxyl groups [11]. So in this experiment, the
in vitro antioxidant capacities of compound 1 were evaluated using different biochemical
methods including DPPH, hydroxyl and superoxide anion radical scavenging assay. As
illustrated in Figure 3(a), the DPPH radical scavenging rate of compound 1 at 80 μmol/L
was 61.94%, with IC50 value of 57.50 μmol/L. In the superoxide test, the scavenging rate of
compound 1 was 44.28% (Figure 3(c)) at 40 μmol/L, and the IC50 value was 61.23 μmol/L.
ese results indicated that compound 1 has potential antioxidant capacity, although the
result of hydroxyl radical scavenging rate at 2–16 μmol/L was weak (Figure 3(b)).
3. Experimental
3.1. General experimental procedures
Optical rotations were recorded on a JASCO P-1020 digital polarimeter (Horiba, Kyoto,
Japan). UV spectra were recorded on a UV-2401PC spectrometer (Shimadzu, Kyoto, Japan).
IR spectra were measured with a Bruker Tensor 27 infrared spectrometer with KBr pel-
lets (Bruker, Karlsruhe, Germany). 1D and 2D NMR spectra were performed on Bruker
AM-400 and AVANCE III-600 MHz spectrometers (Bruker Optics, Ettlingen, Germany).
High-resolution electrospray-ionization mass spectra (HR-ESI-MS) were obtained on an
Agilent 6210 ESI/TOF mass spectrometer (Agilent, Santa Clara, CA, USA). Column chro-
matography (CC) was carried out on silica gel (100–200 and 200–300 mesh, Qingdao Marine
Chemical, Inc., Qingdao, China), MCI gel (75–150 μM, Mitsubishi Chemical Corporation,
Tokyo, Japan), Sephadex LH-20 (Amersham Pharmacia Biotech, Uppsala, Sweden), and
Lichroprep RP-18 gel (40–63 μM, Merck, Merck & Co Inc, Darmstadt, Germany). Semi-
preparative HPLC was carried out on an Agilent 1260 liquid chromatography (LC) with
a Zorbax SB-C18 column (5 μM, 9.4 mm × 25 cm) (Agilent, Santa Clara, CA, U.S.A.).
Absorbance was recorded on an Infinite M200 Pro multifunctional microplate tester (Tecan,
Grodig, Austria). TLC was carried out on silica gel 60 F254 on glass plates (Qingdao Marine
Chemical, Inc., Qingdao, China) using various solvent systems and spots were visualized
by heating the silica gel plates sprayed with 10% H2SO4 in EtOH (V/V = 10:90). Glucose
was obtained from J&K Scientific Ltd. (Beijing, China). Vitamin C, FeSO4, Ethanol, H2O2,
Tris and HCl were obtained from XiLong Scientific Ltd. (Guangdong, China). DPPH and
salicylic acid were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

JOURNAL OF ASIAN NATURAL PRODUCTS RESEARCH
5
3.2. Plant material
e leaves of C. paliurus (50.0 kg) were collected in Ziyuan County of Guangxi Province,
China, in October 2013, and was identified by prof. Ding-Zhong Huang, Guilin Institute
of Botany, Chinese Academy of Science. e voucher specimen (No. 201310001) has been
deposited in the College of Pharmacy, Guilin Medical University, China.
3.3. Extraction and isolation
e air-dried and powdered leaves of C. paliurus (50 kg) were extracted three times with
70% aqueous EtOH (300 L × 3) at room temperature and concentrated in vacuo to yield
a crude extract, which was dissolved in H2O, and then extracted successively with EtOAc
and n-BuOH. e EtOAc-soluble part was chromatographed by using a silica gel column
(100–200 mesh, 20 × 150 cm, 8.0 kg), eluted with a CHCl3–MeOH gradient system (9:1,
8:2, 2:1, 1:1, and 0:1, v/v), to yield four fractions (Fr.A–D). Fr.A (2.985 kg) was further
purified by using silica gel column eluted with petroleum ether-EtOAc (1:2, 1:3, and 0:1,
v/v) and MeOH to give four subfractions (Fr.A1–A4). Afer decolorized on MCI column,
fraction Fr.A1 was chromatographed on Sephadex LH-20 eluted with MeOH to afford three
subfractions (Fr.A1a–A1c). Fr.A1a was purified on silica gel column eluted with petroleum
ether–acetone (5:1, 3:1, 1:1) to afford nine subfractions (Fr.A1a1–A1a9). Fr.A1a6 was sub-
jected to semipreparative HPLC eluted with MeOH (65–75%, gradient system) to afford
compound 1 (tR 25.6 min, 25 mg) and 2 (tR 28.2 min, 33 mg).
3.3.1. Cyclopaloside A (1)
Amorphous powder;[ꢀ]2D4 – 54.5 (c 0.11, MeOH); UV (MeOH) λmax (log ε): 215 (4.19), 265
(3.82), 320 (4.08) nm; IR (KBr) νmax 3528, 1627, 1647, 1630, 1264 cm–1; 1H and 13C NMR
spectral data, see Table 1; ESI-MS: m/z 525 [M + Na]+; HR-ESI-MS: m/z 525.1371 [M + Na]+
(calcd for C25H26O11Na, 525.1367).
3.3.2. Cyclopaloside B (2)
Amorphous powder;[ꢀ]1D8 –37.1 (c 0.40, MeOH); UV (MeOH) λmax (log ε): 203 (3.63), 252
(3.37) nm; IR (KBr) νmax 3432, 2955, 2925, 1697, 1638, 1606, 1515, 1468, 1175, 1075 cm–1; 1H
and 13C NMR spectral data, see Table 1; positive ESI-MS: m/z 555 [M + Na]+; HR-ESI-MS:
m/z 555.1473 [M + Na]+ (calcd for C26H28O12Na, 555.1473).
3.4. Acid hydrolysis of compounds 1 and 2
Compounds 1 (5.0 mg) and 2 (5.0 mg) were each refluxed with 2 N HCl (5 ml) on a boiling
water bath for 2 h. Afer neutralization with NaHCO3 and extraction with ethyl acetate, the
aqueous layer was concentrated, and glucose and aglycone were purified from it. e pres-
ence of glucose was confirmed by comparison with authentic samples by using TLC (silica
gel, BuOH-AcOH-H2O 5:1:5 upperlayer) [9]. And the D-form of glucose was determined
by its positive optical rotation in water.

6
X.-L. ZHOU ET AL.

JOURNAL OF ASIAN NATURAL PRODUCTS RESEARCH
7
3.5. Evaluation of antioxidant activity
3.5.1. DPPH radical scavenging activity
e radical scavenging activity was evaluated using an improved method of reference [11].
Vitamin C (Vc) was used as a positive control. e reaction mixture contained 100 µl of
0.2 mmol/L DPPH and 100 µl samples with different concentrations, e mixture was kept
for 30 min in dark at room temperature for its reaction before the absorbance was measured
at 517 nm. e antioxidant activity was estimated based on the percentage of DPPH radical
scavenged using the equation: Antioxidant activity (%) = [1 − (A1 − A2)/A0] × 100. Where A0
is the absorbance of DPPH solution without sample, A1 is the absorbance of the test sample
mixed with DPPH solution and A2 is the absorbance of the sample without DPPH solution.
3.5.2. Hydroxyl radical scavenging activity
Hydroxyl radical scavenging assay was performed by mixing the different concentrations
(5, 10, 20, 30, and 40 μmol/L) of compounds and some reaction solutions such as FeSO4,
salicylic acid-ethanol and H2O2 together using the method from reference [12]. e reaction
solutions were incubated at 37 °C for 30 min, and the absorbance was measured at 510 nm
using vitamin C as a positive control. e hydroxyl radical scavenging activity was calculated
by the formula: Hydroxyl radical scavenging rate (%) = [1 − (A1 − A2)/A0] × 100. Where A0
is the absorbance of blank (water instead of sample), A1 is the absorbance of sample, and
A2 is the absorbance of background (water instead of H2O2).
3.5.3. Superoxide radicals scavenging activity
Superoxide radical was generated with the method based on Pu et al. [13]. e reaction
mixture contained 200 µl of Tris–HCl buffer (0.1 mol/L, pH 8.2), which contained 10 µl
pyrogallol solution (0.025 mol/L) and the 10 µl samples with varying concentrations (2.1, 4.2,
8.4, 12.6, 16.8 μmol/L). And afer being incubated at 25 °C for 20 min, the change speed of
absorbance (A/min) of the reactive solution was measured at 320 nm. e superoxide radical
scavenging activity was calculated by the formula: Antioxidant activity (%) = [(ΔA0 – ΔA1)/
ΔA0] × 100. Where ΔA0 is the change speed of absorbance of the control group in the
superoxide radical generation system and ΔA1 is the change speed of absorbance of the
test sample.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
is work was financially supported by the National Natural Science Foundation of China [grant
number 31560100]; and the Science Research and Technology Development Program of Guangxi
[grant number Guikeneng 1598025-18].
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