Antinociceptive Diterpenoids from the Leaves and Twigs of Rhododendron decorum

Article abstract of DOI:10.1021/acs.jnatprod.7b00941

Three new leucothane-type (1-3), two new micrathane-type (4, 5), eight new grayanane-type diterpenoids (6-13), and four known compounds were obtained from the ethanol extract of the leaves and twigs of Rhododendron decorum. The structures were determined

Full text of DOI:10.1021/acs.jnatprod.7b00941

Article
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Cite This: J. Nat. Prod. XXXX, XXX, XXX−XXX
Antinociceptive Diterpenoids from the Leaves and Twigs of
Rhododendron decorum
Yu-Xun Zhu, Zhao-Xin Zhang, Hui-Min Yan, Di Lu, Huan-Ping Zhang, Li Li, Yun-Bao Liu,
and Yong Li*
State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of
Medical Sciences & Peking Union Medical College, Beijing 100050, People’s Republic of China
S
* Supporting Information
ABSTRACT: Three new leucothane-type (1−3), two new micrathane-type (4, 5), eight new grayanane-type diterpenoids (6−
13), and four known compounds were obtained from the ethanol extract of the leaves and twigs of Rhododendron decorum. The
structures were determined based on NMR spectra, quantum chemical calculations, and X-ray crystallography. The
antinociceptive activities of compounds 1, 3, 4, 6, 8, 10−13, and 15−17 were evaluated via the acetic acid-induced writhing test.
Compounds 1, 8, 11−13, and 15 exhibited significant antinociceptive activities. In particular, 12 and 15 were found to be
effective at doses of 0.8 and 0.08 mg/kg, respectively.
RESULTS AND DISCUSSION
hododendron decorum (Ericaceae) is an evergreen shrub
■
Rdistributed mainly in southwestern China and northeast-
Compound 1 was obtained as prismatic crystals. Its molecular
formula was defined as C20H32O4 based on high-resolution
electrospray ionization mass spectrometry (HRESIMS) (m/z
359.2208 [M + Na]+, calcd 359.2193), which indicated five
indices of hydrogen deficiency (IHD). The IR spectrum
showed signals typical of hydroxy (3468 cm−1) and olefinic
ern Burma. This plant has been used as a folk remedy for the
treatment of rheumatism and pain in China for centuries.1
However, the components of R. decorum have not been fully
identified.2−5 Previous studies have shown that Ericaceae plants
are rich in di- and triterpenoids.6−15 These compounds exhibit
diverse biological activities, including antinociceptive,16 anti-
viral,17 sodium channel antagonistic,18 and cytotoxic effects.15
Notably, we have reported some grayanane-type diterpenoids
from Rhododendron molle and Pieris formosa that have
significant antinociceptive activities, and several of these
compounds, such as rhodojaponin III, rhodojaponin VI,
pieristoxin N, and pieristoxin P, were shown to be more
potent than morphine in the acetic acid-induced writhing
test.16,19 As a continuation of the studies on structurally unique
and biologically interesting diterpenoids, an ethanol extract of
the leaves and twigs of R. decorum was investigated and afforded
17 diterpenoids, including 13 new analogues (1−13). The
isolation, structural elucidation, and antinociceptive activities of
these compounds are described herein.
1
(1662 cm−1) functionalities. The H NMR (Table 1) data
showed three methyl groups (δH 1.17, 1.47, and 1.60) as well as
two oxygenated methines (δH 3.52 and 4.50). The 13C NMR
data (Table 3) and distortionless enhancement by polarization
transfer (DEPT) (90°, 135°) spectrum of 1 exhibited 20 carbon
resonances, including three methyls, seven methylenes, and five
methines. The correlation spectroscopy (COSY) (Figure 1)
and heteronuclear single-quantum correlation spectroscopy
(HSQC) spectra established two fragments: CH(OH)−CH2−
CH−CH(−CH2)−CH(OH) and CH−CH2−CH2. These
structural features are consistent with leucothane-type
diterpenoids. An exocyclic Δ10(20) double bond was deduced
from the signals at δc 105.4 (C-20) and 154.3 (C-10) and δH
4.96 and 5.10 (H2-20) in conjunction with the heteronuclear
Received: November 10, 2017
© XXXX American Chemical Society and
American Society of Pharmacognosy
A
DOI: 10.1021/acs.jnatprod.7b00941
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multiple-bond correlation spectroscopy (HMBC) correlations
from H2-20 to C-1 (δc 40.7), C-9 (δc 49.1), and C-10 (δc
154.3). The HMBC correlations from H3-18/H3-19/H2-2 to C-
3 (δc 72.8), from H2-7/H3-18/H3-19 to C-5 (δc 80.2), from
H2-14/H3-17 to C-13 (δc 81.6), and from H3-17/H2-14 to C-
16 (δc 77.4) placed the four hydroxy groups at C-3, C-5, C-13,
and C-16, respectively. The relative configuration of 1 was
deduced from its nuclear Overhauser effect spectroscopy
(NOESY) spectrum. The correlations of HO-5/H-3, H-3/H-
1, and H-1/H-9 indicated that HO-5, H-1, H-3, and H-9 are
cofacial (β-face). The β-orientation of CH3-17 was established
via the nuclear Overhauser effect (NOE) correlations of H3-17/
H-11β and H-15β/H-11β. The structure of 1 was confirmed by
a single-crystal X-ray diffraction experiment (data deposited at
the CCDC, no. 1580007). The X-ray crystallography data of 1
(Supporting Information) permitted its absolute configuration
to be assigned as (1S,3R,5R,6R,8R,9R,13S,16R) with a Flack
parameter of 0.08(13) (Figure 2). Thus, the structure of
rhododecorumin I (1) was defined as 3α,5β,13α,16α-
tetrahydroxyleucoth-10(20)-ene.
cofacial. However, the configuration of C-1 remains uncertain
due to the lack of direct NOE evidence. The gauge including
atomic orbitals (GIAO) NMR shifts of the conformers of 2
were calculated at the MPW1PW91/6-311++(2d,p) level,
which has been shown to be an effective method for
determining the configuration of diastereoisomers of natural
products.20,21 From these calculations, the Bayes’s theorem
probability (%) of the A/B trans and A/B cis conformers were
100 and 3.4 × 10−9 (Tables S-1 and S-2, Supporting
Information), respectively, which suggested a trans junction
of the A/B rings in 2. There are four possible structures (2Aa,
2Ab, 2Ba, and 2Bb) with the A/B trans configuration (Figure
4a). Their electronic circular dichroism (ECD) spectra were
calculated at the B3LYP/6-31+G(d,p) level of theory in
methanol. The experimental ECD spectrum of 2 was consistent
with the calculated ECD curves of 2Aa and 2Bb. Ultimately,
the structure of 2 was assumed to be the same as 2Aa since no
natural ent-leucothane derivatives have been found. Thus, the
structure of rhododecorumin II (2) was tentatively defined as
2β,10β,13α,16α-tetrahydroxyleucoth-5-one.
Compound 3 was determined to have a molecular formula of
C20H30O4. The NMR data of 3 were similar to those of the
aglycone fragment of pierisformoside F.22 Further structural
analysis via 2D NMR data indicated that 3 has a hydroxy group
at C-13 (δc 81.6). The NOE correlations of HO-3/H-1, H-1/
H-9, and H-6/H3-18 indicated that HO-3, H-1, and H-9 are β-
oriented and that H-6 is α-oriented. Thus, the structure of
rhododecorumin III (3) was defined as 3β,13α,16α-trihydrox-
yleucoth-10(20)-en-5-one.
Compound 2 exhibited a molecular formula of C20H32O5
1
based on its HRESIMS data. The H NMR spectrum showed
resonances at δH 1.13, 1.14, 1.46, and 1.76 attributable to four
methyl groups and a signal of an oxygenated methine at δH
4.70. The 13C NMR as well as the HSQC spectra showed
signals indicative of four methyls, six methylenes, four methines
(one oxygenated at δC 67.5), and a carbonyl group (δC 214.4).
Based on the COSY and HMBC spectra (Figure 3), compound
2 is a leucothane-type diterpenoid. The carbonyl group was
placed at C-5 via the HMBC correlations from H-6/H3-18/H3-
19 to C-5 (δC 214.4). The oxygenated methine was placed at C-
2 via the HMBC correlations from H-2 (δH 4.70) to C-1/C-3/
C-4/C-6/C-10. In addition, the HMBC correlations from H3-
20 to C-1/C-9/C-10 placed a methyl group at C-10.
The molecular formula of 4 was defined as C20H30O5, which
1
indicated an IHD of six. The H NMR data (Table 1) of 4
exhibited signals characteristic of three methyl groups (δH 1.02,
1.59 and 1.74), three oxygenated methine protons (δH 4.17,
4.29, and 4.98), and a pair of terminal olefinic protons at δH
5.32 and 5.55. The COSY and HSQC spectra established three
fragments: CH(OH)−CH(OH)−CH, CH(OH)−CH2, and
CH−CH2−CH2. The 2D structural features of 4 were
The NOE correlations of H3-17/H-12β indicated that CH3-
17 is β-oriented. The NOE correlations of H-2/H-6, H3-20/H-
2, and H3-20/H-6 indicated that H-6, H-2, and CH3-20 are
B
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1
Figure 1. (a) H−1H COSY and key HMBC correlations for 1. (b)
1
Figure 3. (a) H−1H COSY and key HMBC correlations for 2. (b)
Selected NOESY correlations for 1.
Selected NOE correlations for 2.
consistent with a grayanane diterpenoid possessing an exocyclic
Δ10(20) double bond. However, the correlation from H3-17 to
C-12 in the HMBC spectrum and the NOESY correlation of H-
1/H-15 indicated that 4 might have a micranthane skeleton.
The HMBC correlations from H-1/H-3 to C-2 suggested that,
compared to micranthanone A,23 4 has a hydroxy group at C-2.
The NOE correlations of H-3/H-1, H3-18/H-6, H-1/H-6, and
H-2/H3-19 suggested that H-1, H-3, and H-6 are α-oriented
and that H-2 is β-oriented. The NOE correlation of H-7β/H-9
indicated that H-9 is β-oriented. Thus, the structure of
rhododecorumin IV (4) was defined as 2α,3β,5β,6β-tetrahy-
droxymicranthan-10(20)-en-13-one.
Compound 5, a white solid, exhibited a molecular formula of
C20H28O4. The NMR data of 5 (Table 1) resembled those of 4,
except for the signals of C-2 (δC 60.0), C-3 (δC 64.8), H-2 (δH
3.64), and H-3 (δH 3.26), which indicated the presence of an
epoxy moiety in 5. According to the HMBC correlations from
H-1 to C-2 and from H3-19 to C-3, the epoxy group is located
at C-2/C-3. The NOE correlations of H-1/H3-18, H-1/H-3,
and H-2/H-3 indicated that the 2,3-epoxy group is β-oriented
and that H-1 and H-6 are α-oriented. Thus, the structure of
rhododecorumin V (5) was defined as 2β,3β-epoxy-5β,6β-
dihydroxymicranthan-10(20)-en-13-one. Compounds 4 and 5
are the second and third examples of micranthane-type
diterpenoids.
atoms. Therefore, an oxygen bridge must be present between
C-6 and C-10, which was supported by an HMBC correlation
from H-6 to C-10. The NMR data of 6 were similar to those of
principinaol B with two exceptions.24 First, the olefinic carbons
of the Δ15(16) double bond in principinaol B were replaced by
two sp3 carbons in 6, which was supported by their upfield
chemical shifts and the HMBC correlations from H-9 to C-15
and from H3-17 to C-16. Second, in 6, the hydroxy group was
at C-13 instead of C-14 like it is in principinaol B, and this
assignment was supported by the HMBC correlations from H2-
12 to C-14 and from H3-17 to C-13. Thus, the structure of
rhododecorumin VI (6) was defined as 6β,10β-epoxy-
3β,5α,6α,13α,16α-pentahydroxygrayanane.
The molecular formula of 7 was determined to be C20H30O5.
The NMR data of 7 (Tables 1 and 3) resembled those of
craiobiotoxin IX (15).25 The only difference was the
dehydration at C-10 of 15 to form an exocyclic Δ10(20) double
bond in 7; this assignment was made based on the deshielded
chemical shifts of C-10 (15, δC 83.6; 7, δC 151.3) and C-20 (15,
δC 31.3; 7, δC 115.9), and from the HMBC correlations from
H2-20 to C-1/C-9/C-10. Thus, the structure of rhododecor-
umin VII (7) was defined as 2β,3β-epoxy-5β,6β,13α,16α-
tetrahydroxygrayanan-10(20)-ene.
The HRESIMS data of 8, 9, and 10 suggested they have the
same molecular formula (C20H32O6). The NMR data (Tables 2
and 3) showed that 8, 9, and 10 also share the same 2D
structure, which was similar to that of the known diterpenoid,
pieristoxin S (14).19 The only difference was that 8, 9, and 10
all possess a hydroxy substituent at C-2. For 8 and 9, the NOE
correlations of H-1/H3-18 and H-1/H-6 suggested that H-1
Compound 6 exhibited a molecular formula of C20H32O5
based on its HRESIMS data, indicating an IHD of five.
Resonances attributable to six oxygenated carbons (δC 79.6,
91.1, 77.6, 84.1, 80.6, and 76.8) were observed in the 13C NMR
data (Table 3), but the formula contains only five oxygen
Figure 2. ORTEP drawing of 1.
D
DOI: 10.1021/acs.jnatprod.7b00941
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Figure 4. (a) Structures of isomers 2Aa, 2Ab, 2Ba, and 2Bb. (b) Calculated ECD spectra of 2Aa and 2Ab and the experimental ECD spectrum of 2.
(c) Calculated ECD spectra of 2Ba and 2Bb and the experimental ECD spectrum of 2.
1
Table 2. H NMR Spectroscopic Data of Compounds 8−13 in Pyridine-d5 (δ in ppm, J in Hz)
b
b
b
a
b
b
no.
8
9
10
11
12
13
1
2
3.33, d (7.9)
2.93, d (3.4)
4.68, brs
3.19, d (7.8)
3.25, t (9.2)
2.22, m
2.95, d (8.0)
5.19, brs
2.85, dd (11.3, 7.8)
2.38, m
4.96, dd (7.7, 1.9)
4.98, dd (7.8, 4.4)
2.40, m
2.63, m
3
4
5
6
7
4.16, brs
4.01, d (4.8)
4.00, d (3.9)
4.06, d (3.1)
4.11, brs
4.21, t (6.4)
4.36, d (7.7)
4.25, brs
3.99, d (10.7)
4.02, d (10.1)
4.33, m
4.12, m
1.59, m
2.60, m
1.95, brd (14.1)
2.51, t (11.5)
1.92, d (14.0)
2.62, dd (13.4, 9.3)
1.88, d (13.7)
1.88, d (13.8)
2.28, brd (13.8)
2.65, m
3.23, dd (13.7, 10.4)
3.22, dd (13.8, 10.2)
8
9
2.97, brs
3.06, brs
2.19, d (7.2)
2.18, d (7.8)
1.98, brd (6.8)
2.49, dd (9.0, 5.9)
10
11
1.83, td (11.2, 4.5)
2.19, m
1.85, m
2.05, m
1.95, m
2.22, m
1.83, m
1.88, m
1.95, m
2.21, m
1.84, m
1.94, m
1.98, m
2.20, m
1.81, m
1.46, m
1.59, m
1.46, m
1.92, m
2.43, dd (13.8, 6.4)
1.93, m
12
2.00, m
2.20, m
2.90, m
13
14
2.13, d (10.6)
2.47, d (10.6)
2.16, m
2.04, d (10.3)
2.42, d (10.5)
2.19, d (15.2)
2.34, d (14.5)
2.25, d (10.9)
2.39, d (10.6)
1.78, d (14.4)
2.11, d (14.2)
2.20, d (12.0)
2.39, d (9.7)
1.83, d (13.9)
2.14, d (14.3)
2.57, d (9.9)
2.64, d (9.5)
2.14, brs
1.27, m
1.89, d (13.1)
2.11, d (16.3)
2.35, d (15.3)
15
2.35, d (14.4)
2.14, brs
16
17
1.50, s
1.48, s
1.40, s
1.44, s
1.50, s
4.84, s
4.97, s
18
19
20
1.43, s
1.58, s
5.35, s
5.73, s
1.29, s
1.57, s
5.48, s
5.80, s
1.24, s
1.76, s
5.38, s
5.56, s
1.20, s
1.73, s
5.29, s
5.31, s
1.62, s
1.64, s
1.94, s
1.38, s
1.85, s
5.02, s
5.12, s
1′
2′
3′
4′
5′
6′
5.02, m
4.06, brs
4.28, m
4.28, m
4.44, m
4.44, m
4.60, d (11.4)
a
b
Recorded at 500 MHz. Recorded at 600 MHz.
E
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Table 3. 13C NMR Spectroscopic Data of Compounds 1−13 in Pyridine-d5 (δ in ppm)
a
b
b
a
b
a
a
b
b
b
a
b
b
no.
1
2
3
4
5
6
7
8
9
10
11
12
13
1
40.7
35.6
72.8
41.9
80.2
41.8
43.5
43.4
49.1
154.3
23.4
32.8
81.6
43.1
53.9
77.4
21.9
26.2
19.5
105.4
59.3
67.5
49.3
45.1
214.4
43.3
40.6
40.7
53.4
76.9
20.0
34.4
80.9
43.4
56.3
76.5
22.1
26.3
26.5
21.9
43.1
32.3
77.0
49.9
214.5
48.3
39.3
42.1
48.3
152.0
22.5
31.9
80.9
42.1
53.0
76.6
22.0
24.9
21.0
105.3
52.9
80.8
88.4
48.8
83.8
72.5
45.8
39.6
53.6
149.9
31.6
36.9
49.7
55.6
48.0
219.5
20.5
27.1
21.3
115.8
47.6
60.0
64.8
47.8
80.3
73.5
46.3
39.7
51.0
150.1
32.8
37.1
49.1
55.7
47.6
220.0
20.5
21.2
21.1
115.5
50.2
34.9
79.6
49.1
91.1
77.6
41.3
37.2
55.0
84.1
21.9
33.3
80.6
47.0
62.3
76.8
23.2
23.7
16.9
23.9
49.8
60.1
65.5
48.0
80.6
74.0
48.9
41.1
49.0
151.3
32.2
33.0
81.0
44.5
59.2
77.1
21.7
21.2
21.1
115.9
53.9
84.6
89.3
48.7
84.2
70.6
47.7
41.4
51.3
151.8
27.1
32.9
80.8
43.6
60.9
78.5
20.0
26.1
22.8
113.5
48.1
77.2
81.0
49.3
84.4
70.0
47.5
41.0
48.6
148.5
26.3
32.3
80.3
42.9
58.7
77.4
19.8
27.8
21.6
115.1
68.4
74.5
84.9
49.1
86.9
71.5
49.3
42.5
54.8
152.9
28.5
34.4
81.3
42.4
55.5
77.4
21.6
22.5
22.1
110.5
59.4
37.3
84.1
51.4
87.3
71.5
49.5
42.5
55.0
154.2
28.6
34.4
81.3
42.2
55.6
77.5
21.5
23.3
22.1
111.1
58.3
81.4
87.4
49.6
84.0
73.6
51.0
42.8
52.4
78.7
24.4
34.3
82.2
42.6
59.6
77.3
21.8
26.6
20.8
30.0
43.3
38.2
89.2
51.1
82.8
72.3
45.7
44.1
53.5
151.4
26.3
32.5
41.9
37.4
54.0
158.6
105.1
27.8
21.0
113.6
106.2
76.1
79.1
72.4
79.0
63.4
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1′
2′
3′
4′
5′
6′
a
b
Recorded at 125 MHz. Recorded at 150 MHz.
and H-6 are α-oriented. However, the relative configuration of
C-2 is difficult to determine in grayanoids that lack NOE
correlations between H-2 and H3-18/H3-19 (as for 8 and 9).
To ascertain the relative configuration at C-2, the 13C NMR
chemical shifts of 8 and 9 were calculated with DP4 methods
(Table 4). The chemical shifts of the C-2 carbons bearing the
α-OH moieties were shifted downfield (δcalcd 89.43) relative to
the signals of the C-2 carbons bearing β-OH substituents (δcalcd
76.22). This conclusion is consistent with the data published in
the last 30 years (Table S-3, Supporting Information). The
experimental data of 8 and 9 are consistent with the calculated
values of the 2α-OH- and 2β-OH-derivatives, respectively.
Thus, the structures of rhododecorumins VIII (8) and IX (9)
were defined as 2α,3β,5β,6β,13α,16α-hexahydroxygrayanan-
10(20)-ene and 2β,3β,5β,6β,13α,16α- hexahydroxygrayanan-
10(20)-ene, respectively.
In the NOESY spectrum of 10, the correlations of H-3/H3-
18, H3-18/H-6, H-2/H3-18, and H-1/H-9 suggested that H-2,
H-3, and H-6 are α-oriented and that H-1 and H-9 are β-
oriented, which indicated the A/B cis configuration of 10.
Thus, the structure of rhododecorumin X (10) was defined as
1-epi-2β,3β,5β,6β,13α,16α-hexahydroxygrayanan-10(20)-ene.
The HRESIMS data of 11 indicated that its molecular
formula is C20H32O5. The 2D structure of 11 was established
based on its COSY and HMBC correlations and was found to
be the same as that of pieristoxin S (14). The NOE correlations
of H-6/H-1, H-6/H3-18, and H-1/H-9 suggested that H-6, H-1,
and H-9 are α-oriented, indicating 11 has a B/C trans
configuration. Thus, the structure of rhododecorumin XI (11)
was defined as 9-epi-3β,5β,6β,13α,16α-pentahydroxygrayanan-
10(20)-ene.
The HRESIMS data of 12 suggested a molecular formula of
C20H34O7. The NMR data showed that 12 is structurally similar
to 8, except that the Δ10(20) olefinic carbons in 8 were replaced
by a methyl carbon at δC 30.0 and an oxygenated carbon at δC
78.7 in 12, which was supported by the HMBC correlations
from H3-20 to C-1/C-9/C-10. Thus, the structure of
r h o d o d e c o r u m i n X I I ( 1 2 ) w a s d e fi n e d a s
2α,3β,5β,6β,10α,13α,16α-heptahydroxygrayanane.
Compound 13 exhibited a molecular formula of C26H40O8,
indicating an IHD of seven. Compound 13 is similar to 14-
deoxygrayanotoxin VIII except for the glucose unit at C-3.26
This finding was supported by the HMBC correlation from H-
1′ to C-3. The anomeric proton at H-1′ (δH 5.03) showed a
large coupling constant (7.6 Hz), which indicated the glucose is
in the β-configuration. Acid hydrolysis and GC analysis of the
sugar moiety of 13 confirmed the sugar was D-glucose. Thus,
the structure of rhododeoside I (13) was defined as 3β-[(β-D-
glucopyranosyl)oxy]-5β,6β,13α,16α-tetrahydroxygrayanan-10-
(20),16(17)-diene.
The four known compounds were defined as pieristoxin S
(14),19 craiobiotoxin IX (15),25 pieroside A (16),27 and
paniculoside IV (17)28 by comparison of their experimental
and reported NMR data.
The acetic acid-induced writhing test is usually used as a
sensitive model to measure acute pain.29 In this test,
intraperitoneal (IP) administration was used for all the
compounds. As shown in Figure 5, compounds 12 and 15
showed more potent activities than the other tested
compounds. Compound 15 inhibited 78.0% of the writhes
when administered at a dose of 0.08 mg/kg, while 12 inhibited
68.0% of the writhes when administered at a dose of 0.8 mg/kg.
In contrast, in the same assay, morphine inhibited 86% of the
F
DOI: 10.1021/acs.jnatprod.7b00941
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Journal of Natural Products
Article
Table 4. DP4 Analysis of the 13C NMR Data for Compounds 8 and 9
13C expt
13C calcd
scaled shifts
corrected error
probability
position
(8)
2α-OH
2β-OH
2α-OH
2β-OH
2α-OH
2β-OH
2α-OH
0.13
2β-OH
0.20
1
53.9
84.6
89.3
48.7
84.2
70.6
47.7
41.4
51.3
151.8
27.1
32.9
80.8
43.6
60.9
78.5
20
53.89
89.43
88.83
48.85
86.86
67.34
43.01
41.93
42.91
160.49
20.80
28.41
78.76
43.44
55.45
80.68
17.07
18.03
12.64
112.65
48.70
76.22
80.45
50.31
86.25
67.95
42.90
43.97
42.99
156.97
22.59
29.86
79.01
42.39
53.48
79.83
16.58
23.97
14.08
114.26
51.21
85.05
90.23
45.48
84.61
69.62
44.38
37.44
48.35
159.10
21.68
28.07
80.86
39.86
58.93
78.32
13.85
20.58
16.94
116.90
50.69
82.87
87.79
45.24
82.45
68.19
44.19
37.59
47.96
153.30
22.60
28.68
78.88
39.89
58.02
76.47
15.16
21.55
18.09
113.16
2.68
−1.99
−6.65
−7.34
5.07
2
4.39
0.04
0.28
0.09
0.17
0.17
0.28
0.04
0.02
0.28
0.35
0.44
0.19
0.07
0.08
0.16
0.10
0.15
0.04
0.05
7.13 × 10−19
98.7
0.01
0.00
0.03
0.06
0.46
0.29
0.01
0.03
0.07
0.50
0.31
0.48
0.15
0.04
0.09
0.27
0.16
0.05
0.32
3
−1.39
3.36
4
5
2.26
3.80
6
−2.27
−1.37
4.49
−0.25
−1.29
6.38
7
8
9
−5.44
1.39
−4.97
3.67
10
11
12
13
14
15
16
17
18
19
20
−0.88
0.34
−0.01
1.19
−2.10
3.58
0.12
2.50
−3.48
2.35
−4.54
3.36
3.21
1.43
26.1
22.8
113.5
−2.55
−4.30
−4.25
2.42
−4.02
1.11
product of probabilities
9.55 × 10−21
1.3
Bayes’s theorem probability (%)
13C expt
13C calcd
scaled shifts
corrected error
probability
position
(9)
2α-OH
2β-OH
2α-OH
2β-OH
2α-OH
2β-OH
2α-OH
0.00
2β-OH
1
48.1
77.2
81
53.89
89.43
88.83
48.85
86.86
67.34
43.01
41.93
42.91
160.49
20.80
28.41
78.76
43.44
55.45
80.68
17.07
18.03
12.64
112.65
48.70
76.22
80.45
50.31
86.25
67.95
42.90
43.97
42.99
156.97
22.59
29.86
79.01
42.39
53.48
79.83
16.58
23.97
14.08
114.26
46.35
78.98
83.24
47.70
87.06
70.91
45.68
38.39
46.91
158.93
21.91
28.64
82.46
40.52
58.24
79.21
14.62
23.59
16.64
121.48
45.97
77.24
81.32
47.26
84.98
69.50
45.32
38.34
46.51
153.86
22.54
28.99
80.57
40.38
57.36
77.45
15.56
24.16
17.49
117.96
7.54
2.73
0.13
0.33
0.36
0.11
0.30
0.26
0.16
0.02
0.08
0.10
0.49
0.36
0.26
0.20
0.06
0.16
0.33
0.47
0.08
0.07
1.98 × 10−15
100
2
10.45
5.59
−1.02
−0.87
3.05
0.00
3
0.02
4
49.3
84.4
70
1.15
0.31
5
−0.19
−3.56
−2.67
3.53
1.27
0.47
6
−1.56
−2.43
5.63
0.08
7
47.5
41
0.14
8
0.08
9
48.6
148.5
26.3
32.3
80.3
42.9
58.7
77.4
19.8
27.8
21.6
115.1
−4.01
1.56
−3.51
3.11
0.06
10
11
12
13
14
15
16
17
18
19
20
0.26
−1.11
−0.22
−3.70
2.92
0.05
0.32
0.87
0.46
−1.56
2.01
0.07
0.12
−2.79
1.47
−3.88
2.38
0.13
0.27
2.45
1.03
0.16
−5.56
−4.00
−8.83
−0.18
−3.42
−3.70
0.02
0.06
0.00
product of probabilities
1.40 × 10−24
7 × 10−10
Bayes’s theorem probability (%)
writhes when administered at a dose of 0.8 mg/kg. Additionally,
at a dose of 10 mg/kg, 1, 8, 11, and 13 showed significant
antinociceptive activities compared to that of the vehicle (p <
0.01). Compared with our previous studies,16,19 two new
structure−activity relationships (SARs) were elucidated based
on these data. First, when the C-12−C-13 bond shifted to C-16
(micrathane-type compounds such as 4), the antinociceptive
activity was lower. Second, 11 and 8 showed comparable
antinociceptive activities in this study. According to a previous
report,16 the oxidation degree at C-2 does not affect the activity,
which suggested that the change in the configuration of the B/
C rings from cis to trans (as in 11) may have had a small effect
on the antinociceptive activity.
EXPERIMENTAL SECTION
■
General Experimental Procedures. IR spectra were recorded on
a Nicolet 5700 FT-IR spectrometer. Optical rotations were acquired
via a Rudolph automatic polarimeter. HRESIMS data were acquired on
an Agilent 6520 Accurate-Mass Q-TOF LC/MS spectrometer. NMR
spectra were obtained on INOVA-500, Bruker AV600-III, and INOVA
SX-600 spectrometers. A Shimadazu LC-6AD instrument (SPD-20A
and RID-10A detectors) was used for preparative HPLC separations.
Liquid chromatography was conducted via a YMC ODS column (C18,
G
DOI: 10.1021/acs.jnatprod.7b00941
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Journal of Natural Products
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Figure 5. Antinociceptive activities of diterpenoids 1, 3, 4, 6, 8, 10−13, and 15−17 isolated from R. decorum. Data represent the mean SEM *p <
0.05, **p < 0.01, ***p < 0.001, vs vehicle (veh). Control drugs: ibuprofen (ib) and morphine (morph).
250 mm × 20 mm, 5 μm and C18, 250 mm × 10 mm, 5 μm) (Kyoto,
Japan). D101-type macroporous resin, Baoen Corporation (Cangzhou,
China); Sephadex LH-20, GE Chemical Corporation (USA); silica gel
and GF254 TLC plates, Jiangyou Corporation (Yantai, China); and
ODS (50 μm) Merck (Germany) were used for column chromatog-
raphy (CC).
Plant Material. Twigs and leaves of R. decorum were collected in
Chuxiong, Yunnan Province in April 2014. The plant was
authenticated by Prof. Lin Ma of PUMC. A voucher specimen (ID-
s-2603) was deposited in the herbarium of our institute.
the macroporous resin column was also loaded on a silica gel column
and eluted with a step gradient of CH2Cl2−MeOH (100:1, 40:1, 20:1,
10:1, and 5:1, v/v). Fractions G1-G8 were collected based on the
results of TLC analysis. Fraction E60G6 was purified via Sephadex LH-
20 column to yield two fractions, E60G6L1 and E60G6L2. Then, E60G6L1
was purified via preparative HPLC to afford eight fractions, E60G6L1-1
to E60G6L1-8. E60G6L1-2 was purified via HPLC (MeCN−H2O, 20:80,
v/v) to afford 15 (1.5 mg, tR = 22.2 min). Compound 3 (3.6 mg, tR =
26.2 min) was isolated from E60G6L1-6 using preparative HPLC
(MeCN−H2O, 23:77, v/v). Fraction E60G7 was purified on a Sephadex
LH-20 column to yield two fractions, E60G7L1 and E60G7L2. Fraction
E60G7L1 was separated via ODS into two fractions, E60G7L1M1 and
E60G7L1M2. Compounds 13 (5.5 mg, tR = 35.6 min) and 17 (1.5 mg,
tR = 13.6 min) were isolated from E60G7L1M2 via preparative HPLC
with MeCN−H2O (30:70, v/v, 3.5 mL/min).
Extraction and Isolation. Twigs and leaves of R. decorum (100
kg) were air-dried and extracted twice (2 h each time) with EtOH at
reflux. The crude extract (not completely dry, 16 kg) was loaded into a
Soxhlet extractor and extracted successively with petroleum ether,
CH2Cl2, EtOAc, and MeOH. The EtOAc extract (1.4 kg) was
separated on a macroporous resin column eluted sequentially with
70:30, 40:60, and 5:95 (v/v) H2O−EtOH solutions. Silica gel CC was
used to separate the 30% EtOH fraction (376 g). The column was
eluted with a step gradient of CH2Cl2−MeOH (20:1, 10:1, 5:1, and
1:1, v/v). Fractions E30G1−E30G6 were collected based on the TLC
results. Fraction E30G3 was separated via a Sephadex LH-20 column
eluted with MeOH−H2O (60:40, v/v) and yielded six fractions
(E30G3L1−E30G3L6). Fraction E30G3L1 (12.1 g) was separated via ODS
column and eluted with a step gradient of MeOH/H2O (10:90, 20:80,
30:70, 50:50, 30:70, and 100:0, v/v) to yield seven fractions,
E30G3L1M1 to E30G3L1M7. Fraction E30G3L1M6 was separated via
preparative HPLC (MeOH−H2O, 42:58, v/v, 5 mL/min) and yielded
eight fractions, E30G3L1M6-1 to E30G3L1M6-8. Fraction M6-3 was
purified via semipreparative HPLC (MeCN−H2O, 14:86, v/v, 3.5 mL/
min) to afford 4 (73.9 mg, tR = 28.8 min). Fraction M6-4 was purified
with MeCN−H2O (13:87, v/v, 3.5 mL/min) to afford 2 (1.2 mg, tR =
47.9 min) and 6 (5.2 mg, tR = 36.9 min). Fraction M6-5 was purified
with MeCN−H2O (13:87, v/v, 3.5 mL/min) to yield 1 (11.3 mg, tR =
26.6 min) and 14 (303.1 mg, tR = 37.9 min). Compound 11 (11.9 mg,
tR = 17.6 min) was isolated from fraction M6-8 using MeCN−H2O
(15:85, v/v, 3.5 mL/min). Compound 7 (4.9 mg, tR = 23.0 min) was
obtained from E30G3L1M7 with MeCN−H2O (14:86, v/v, 3.5 mL/
min). Fraction E30G4 was separated via Sephadex LH-20 column and
yielded two fractions (E30G4L1 and E30G4L2). Fraction E30G4L1 (24.1
g) was separated via an ODS column and eluted with a gradient of
MeOH−H2O (30:70, 50:50, 40:60, 30:70, 20:80, and 100:0, v/v) to
yield 6 fractions, E30G4L1M1 to E30G4L1M6. Compounds 8 (7.0 mg, tR
= 7.6 min), 9 (3.2 mg, tR = 3.2 mg, tR = 17.3 min), and 12 (1.2 mg, tR
= 12.3 min) were isolated from E30G4L1M3 using HPLC with MeCN−
H2O (14:86, v/v, 3.5 mL/min). Compound 10 (6.5 mg, tR = 8.6 min)
was isolated from E30G4L1M2 via HPLC (MeCN−H2O, 14:86, v/v, 3.5
mL/min). Compounds 5 (1.9 mg, tR = 64.8 min) and 16 (9.2 mg, tR =
52.5 min) were obtained from E30G4L1M6 via preparative HPLC
(MeCN−H2O, 37:63, v/v, 3.5 mL/min). The 60% EtOH fraction of
Rhododecorumin I (1). [α]20D −27 (c 0.03, MeOH); IR vmax 3468,
1
3244, 2935, 1662, 1446, 1408, 1087, 1040, 899 cm−1; H and 13C
NMR data, see Tables 1 and 3; HRESIMS m/z 359.2208 [M + Na]+
(calcd for C20H32NaO4, 359.2193).
Rhododecorumin II (2). [α]20D −40 (c 0.03, MeOH); IR vma1x 3384,
2927, 1702, 1659, 1452, 1374, 1090, 1056, 1032, 858 cm−1; H and
13C NMR data, see Tables 1 and 3; HRESIMS m/z 375.2156 [M +
Na]+ (calcd for C20H32NaO5, 375.2142).
Rhododecorumin III (3). [α]20D −29 (c 0.1, MeOH); IR vmax 3472,
2938, 1699, 1644, 1445, 1391, 1065, 1039, 938, 912 cm−1; 1H and 13
C
NMR data, see Tables 1 and 3; HRESIMS m/z 357.2038 [M + Na]+
(calcd for C20H30NaO4, 357.2036).
Rhododecorumin IV (4). [α]20D −44 (c 0.2, MeOH); IR vmax 3410,
1
2928, 1731, 1630, 1455, 1404, 1075, 1042, 805 cm−1; H and 13C
NMR data, see Tables 1 and 3; HRESIMS m/z 373.1988 [M + Na]+
(calcd for C20H30NaO5, 373.1985).
Rhododecorumin V (5). [α]20D −73 (c 0.03, MeOH); IR vmax 3416,
1
2930, 1732, 1598, 1465, 1379, 1363, 1205, 1123, 1088, 851 cm−1; H
and 13C NMR data, see Tables 1 and 3; HRESIMS m/z 355.1884 [M
+ Na]+ (calcd for C20H28NaO4, 355.1880).
Rhododecorumin VI (6). [α]20D −60 (c 0.01, MeOH); IR vmax 3372,
2940, 1730, 1645, 1587, 1453, 1379, 1121, 1066, 1041, 951, 855 cm−1;
1H and 13C NMR data, see Tables 1 and 3; HRESIMS m/z 375.2140
[M + Na]+ (calcd for C20H32NaO5, 375.2142).
Rhododecorumin VII (7). [α]20 −90 (c 0.01, MeOH); IR vmax
D
1
3362, 2927, 1595, 1415, 1122, 1088, 1044, 857 cm−1; H and 13C
NMR data, see Tables 1 and 3; HRESIMS m/z 373.1986 [M + Na]+
(calcd for C20H30NaO5, 373.1985).
Rhododecorumin VIII (8). [α]20 −53 (c 0.02, MeOH); IR vmax
D
3383, 2943, 1630, 1601, 1451, 1382, 1334, 1081, 1056, 965, 815 cm−1;
1H and 13C NMR data, see Tables 2 and 3; HRESIMS m/z 369.2277
[M + H]+ (calcd for C20H33O6, 369.2272).
Rhododecorumin IX (9). [α]20D −90 (c 0.01, MeOH); IR vmax 3364,
2942, 1677, 1450, 1384, 1336, 1082, 915, 836 cm−1; 1H and 13C NMR
H
DOI: 10.1021/acs.jnatprod.7b00941
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Article
data, see Tables 2 and 3; HRESIMS m/z 369.2274 [M + H]+ (calcd
AUTHOR INFORMATION
■
for C20H33O6, 369.2272).
Rhododecorumin X (10). [α]20 −2 (c 0.1, MeOH); IR vmax 3415,
Corresponding Author
*Phone: 86-10-63165324. Fax: 86-10-83162679. E-mail:
liyong@imm.ac.cn.
D
1
2942, 1675, 1637, 1450, 1385, 1336, 1078, 1040, 894 cm−1; H and
13C NMR data, see Tables 2 and 3; HRESIMS m/z 391.2093 [M +
Na]+ (calcd for C20H32NaO6, 391.2091).
ORCID
Rhododecorumin XI (11). [α]20D +7 (c 0.1, MeOH); IR vmax 3388,
Yun-Bao Liu: 0000-0002-1338-0271
Yong Li: 0000-0003-1672-6589
2939, 1675, 1637, 1450, 1063, 1040, 1012, 892, 857 cm−1; 1H and 13
C
NMR data, see Tables 2 and 3; HRESIMS m/z 375.2147 [M + Na]+
(calcd for C20H32NaO5, 375.2142).
Notes
Rhododecorumin XII (12). [α]20 −50 (c 0.01, MeOH); IR vmax
D
The authors declare no competing financial interest.
3370, 2968, 1675, 1450, 1381, 1337, 1080, 1057, 913, 848 cm−1; H
1
and 13C NMR data, see Tables 2 and 3; HRESIMS m/z 409.2201 [M
ACKNOWLEDGMENTS
+ Na]+ (calcd for C20H34NaO7, 409.2197).
■
Rhododeoside I (13). [α]20 −38 (c 0.1, MeOH); IR vmax 3382,
This work was supported by grants from the National Natural
Science Foundation of China (Grant Nos. 21572274 and
81630094) and the CAMS Innovation Fund for Medical
Sciences (Grant No. 2016-I2M-3-012).
D
2932, 1655, 1448, 1367, 1079, 1042, 878 cm−1; 1H and 13C NMR data,
see Tables 2 and 3; HRESIMS m/z 503.2630 [M + Na]+ (calcd for
C26H40NaO8, 503.2615).
Acid Hydrolysis and GC Analysis of the Sugar Moiety of
Compound 13. The configuration of the sugar moiety was
established according to the published method.30,31 Compound 13
(1.0 mg) was dissolved in MeOH (2 mL), and the solution was added
to 2 N HCl (3 mL). The solution was heated at 90 °C for 13 h. The
reaction mixture was evaporated and partitioned with EtOAc and H2O.
The aqueous layer was concentrated to furnish the sugar mixture,
which was dissolved in dry pyridine and reacted with L-cysteine methyl
ester hydrochloride (2 mg) at 60 °C for 2 h. After removal of the
solvent, N-trimethylsilylimidazole (0.5 mL) was added, and the
mixture was heated at 60 °C for 2 h. The mixture was evaporated to
dryness, and the residue partitioned into n-hexane and H2O.
Anhydrous Na2SO4 was added to the organic layer to remove residual
water. The sample was analyzed on a GC system equipped with an
FID (detector temperature, 300 °C). Chromatography conditions:
injection temperature, 280 °C; column, HP-5 (60 m × 0.32 mm ×
0.25 μm); initial column temperature, 200 °C; column temperature
increased to 280 °C (10 °C/min) and kept at 280 °C for 35 min under
N2 carrier gas.
REFERENCES
■
(1) Chinese Materia Medica Compilation Commission. Chinese
Materia Medica; Shanghai Scientific & Technical Publishers: Shanghai,
China, 1999; Vol. 16, p 5260.
(2) Zhang, H. P.; Wang, H. B.; Wang, L. Q.; Bao, G. H.; Qin, G. W. J.
Asian Nat. Prod. Res. 2005, 7, 87−90.
(3) Zhang, W. D.; Jin, H. Z.; Chen, G.; Li, X. F.; Yan, S. K.; Zhang,
L.; Shen, Y. H.; Yang, M. Fitoterapia 2008, 79, 602−604.
(4) Rateb, M. E.; Hassan, H. M.; Arafa, el-SA.; Jaspars, M.; Ebel, R.
Nat. Prod. Commun. 2014, 9, 473−476.
(5) Jin, H. Z.; Chen, G.; Li, X. F.; Shen, Y. H.; Yan, S. K.; Zhang, L.;
Yang, M.; Zhang, W. D. Chem. Nat. Compd. 2009, 45, 85−86.
(6) El-Naggar, S. F.; Doskotch, R. J. Nat. Prod. 1980, 43, 617−631.
(7) Klocke, J. A.; Hu, M. Y.; Chiu, S. F.; Kubo, I. Phytochemistry
1991, 30, 1797−1800.
(8) Li, C. J.; Wang, L. Q.; Chen, S. C.; Qin, G. W. J. Nat. Prod. 2000,
63, 1214−1217.
(9) Chen, S. N.; Zhang, H. P.; Wang, L. Q.; Bao, G. H.; Qin, G. W. J.
Nat. Prod. 2004, 67, 1903−1906.
(10) Zhong, G. H.; Hu, M. Y.; Wei, X. Y.; Weng, Q. F.; Xie, J. J.; Liu,
J. X.; Wang, W. X. J. Nat. Prod. 2005, 68, 924−926.
(11) Huang, X. Z.; Wang, Y. H.; Yu, S. S.; Fu, G. M.; Hu, Y. C.; Liu,
Y.; Fan, L. H. J. Nat. Prod. 2005, 68, 1646−1650.
(12) Li, C. H.; Niu, X. M.; Luo, Q.; Xie, M. J.; Luo, S. H.; Zhou, Y. Y.
Org. Lett. 2010, 12, 2426−2429.
(13) Li, Y.; Liu, Y. B.; Yu, S. S. Phytochem. Rev. 2013, 12, 305−325.
(14) Niu, C. S.; Li, Y.; Liu, Y. B.; Ma, S. G.; Liu, F.; Li, C.; Yu, H. B.;
Wang, X. J.; Qu, J.; Yu, S. S. Tetrahedron 2018, 74, 375−382.
(15) Lv, X. J.; Li, Y.; Ma, S. G.; Qu, J.; Liu, Y. B.; Li, Y. H.; Zhang, D.;
Li, L.; Yu, S. S. J. Nat. Prod. 2016, 79, 2824−2837.
(16) Li, Y.; Liu, Y. B.; Zhang, J. J.; Liu, Y.; Ma, S. G.; Qu, J.; Lv, H.
N.; Yu, S. S. J. Nat. Prod. 2015, 78, 2887−2895.
In the GC chromatogram, the derivatives of the acid hydrolysate of
13 and the D-glucose standard showed approximate retention times of
20.31 and 20.45 min, respectively.
Animals. Male Kunming mice (16−20 g) were housed for 3 days
before use. Food and water were freely available. Animal experiments
were conducted following the guidelines of the NIH, and experimental
procedures were approved by the Ethics Committee of our institute.
The doses administered in each test were based on preliminary
experiments. The mice used to test each compound were removed
from the cages at random. The behavior reaction of each mouse was
independently counted by three observers to minimize subjective bias.
Acetic Acid-Induced Writhing Tests. Kunming mice (eight per
group) were used in the tests. Control mice received 0.9% NaCl by
intraperitoneal injection (10 mL/kg), and the test mice received
aqueous solutions of the different compounds (hydrotropic agent,
Tween 80) by intraperitoneal injection (10 mg/kg). 15 minutes later,
0.8% v/v HOAc solution (0.1 mL/10 g) was administered to the mice
by intraperitoneal injection. The number of writhing events for each
mouse was counted for 30 min.
(17) Li, Y.; Liu, Y. B.; Zhang, J. J.; Li, Y. H.; Jiang, J. D.; Yu, S. S.; Ma,
S. G.; Qu, J.; Lv, H. N. Org. Lett. 2013, 15, 3074−3077.
(18) Li, C. J.; Liu, H.; Wang, L. Q.; Jin, M. W.; Chen, S. N.; Bao, G.
H.; Qin, G. W. Acta. Chim. Sin. 2003, 61, 1153−1156.
(19) Niu, C. S.; Li, Y.; Liu, Y. B.; Ma, S. G.; Li, L.; Qu, J.; Yu, S. S.
Tetrahedron 2016, 72, 44−49.
(20) Smith, S. G.; Goodman, J. M. J. Am. Chem. Soc. 2010, 132,
12946−12959.
ASSOCIATED CONTENT
■
S
(21) Tuan, N. Q.; Oh, J.; Park, H. B.; Ferreira, D.; Choe, S.
Phytochemistry 2017, 133, 45−50.
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jnat-
prod.7b00941.
(22) Wang, L. Q.; Chen, S. N.; Cheng, K. F.; Li, C. J.; Qin, G. W.
Phytochemistry 2000, 54, 847−852.
(23) Zhang, M. K.; Zhu, Y.; Zhan, G. Q.; Shu, P. H.; Sa, R. J.; Lei, L.;
Xiang, M.; Xue, Y. B.; Luo, Z. W.; Wan, Q.; Yao, G. M.; Zhang, Y. H.
Org. Lett. 2013, 15, 3094−3097.
1
IR, HRESIMS, H and 13C NMR, HSQC, HMBC, and
NOESY spectra of compounds 1−13 (PDF)
Crystallographic data for compound 1 (CIF)
(24) Liu, C. C.; Lei, C.; Zhong, Y.; Gao, L. X.; Li, J. Y.; Yu, M. H.; Li,
J.; Hou, A. J. Tetrahedron 2014, 70, 4317−4322.
I
DOI: 10.1021/acs.jnatprod.7b00941
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Article
(25) Zhang, W. D.; Jin, H. Z.; Chen, G.; Li, X. F.; Yan, S. K.; Zhang,
L.; Shen, Y. H.; Yang, M. Fitoterapia 2008, 79, 602−604.
(26) Zhang, M. K.; Xie, Y. Y.; Zhan, G. Q.; Lei, L.; Shu, P. H.; Chen,
Y. L.; Xue, Y. B.; Luo, Z. W.; Wan, Q.; Yao, G. M.; Zhang, Y. H.
Phytochemistry 2015, 117, 107−115.
(27) Wang, L. Q.; Li, C. J.; Chen, S. N.; Qin, G. W. Chinese
Traditional and Herbal Drugs 2000, 31, 407−409.
(28) Yamasaki, K.; Kohda, H.; Kobayashi, T.; Kaneda, N.; Kasai, R.;
Tanaka, O.; Nishi, K. Chem. Pharm. Bull. 1977, 25, 2895−2899.
(29) Niu, C. S.; Li, Y.; Liu, Y. B.; Ma, S. G.; Liu, F.; Li, L.; Xu, S.;
Wang, X. J.; Liu, S.; Wang, R. B.; Qu, J.; Yu, S. S. RSC Adv. 2017, 7,
43921−43932.
(30) Hara, S.; Okabe, H.; Mihashi, K. Chem. Pharm. Bull. 1987, 35,
501−506.
(31) Feng, Z. M.; Song, S.; He, J.; Yang, Y. N.; Jiang, J. S.; Zhang, P.
C. Carbohydr. Res. 2013, 380, 59−63.
J
DOI: 10.1021/acs.jnatprod.7b00941
J. Nat. Prod. XXXX, XXX, XXX−XXX