A new naphthoquinone and a new neolignan from ligularia vellerea rhizomes

Article abstract of DOI:10.1007/s10600-010-9563-z

In the course of phytochemical investigations of Ligularia vellerea rhizomes, a new naphthoquinone, 2,5-dihydroxy-6,7-dimethylnaphthoquinone (1), and a new neolignan, 4-[(3',4'-dihydroxycinnamoyl)-oxy]-methyl cinnamate (2), have been isolated and characterized on the basis of spectroscopic methods (¹H NMR, ¹³C NMR, 2D NMR, and MS).

Full text of DOI:10.1007/s10600-010-9563-z

Chemistry of Natural Compounds, Vol. 46, No. 2, 2010
A NEW NAPHTHOQUINONE AND A NEW NEOLIGNAN
FROM Ligularia vellerea RHIZOMES
C. F. Wang,1 Y. Zhao, S. Y. Shi, J. P. Li,
,2*
2
2
1
UDC 547.655
1
*
3
Z. Z. Zhang, and Y. Z. Liu
In the course of phytochemical investigations of Ligularia vellerea rhizomes, a new naphthoquinone,
,5-dihydroxy-6,7-dimethylnaphthoquinone (1), and a new neolignan, 4-[(3ꢀ,4ꢀ-dihydroxycinnamoyl)-oxy]-
methyl cinnamate (2), have been isolated and characterized on the basis of spectroscopic methods
2
1
13
(
H NMR, C NMR, 2D NMR, and MS).
Keywords: Ligularia vellerea, naphthoquinone, neolignan, 2,5-dihydroxy-6,7-dimethylnaphthoquinone,
-[(3ꢀ,4ꢀ-dihydroxycinnamoyl)-oxy]-methyl cinnamate.
4
The genus Ligularia Cass (Compositae) is represented in China by over 100 species [1]. A number of Ligularia
species such as L. fischeri, L. sibirica, and L. hodgsoni are commonly used as herbal remedies to treat bronchitis, cough and
asthma, phthisis and so on in southwest China and other areas [2]. Ligularia vellerea has been studied by M. Tori et al [3] and
Y. S. Li [4]. We reinvestigated the plants and isolated two new compounds 1 and 2: 2,5-dihydroxy-6,7-dimethylnaphthoquinone;
1
13
4
-[(3ꢀ,4ꢀ-dihydroxycinnamoyl)-oxy]-methyl cinnamate. The structure elucidation was based on H NMR, C NMR, 2D NMR,
and MS.
Compound 1, yellow powder. Its molecular formula was determined as C H O by NMR data and the
1
2 10 4
+
1
quasi-molecular ion peak at m/z 219.2 [M + H] in its positive APCI-MS. The H NMR spectrum of 1 clearly displayed
singlets for two methyls at ꢁ 2.08 (3H, s) and 2.31 (3H, s) and two olefinic protons at ꢁ 6.76 and 8.25. The C NMR and
1
3
H
H
HSQC spectrums of 1 showed eight quaternary carbons at ꢁ 109.6, 117.0, 131.6, 145.8, 168.9, 169.7, 172.5, and 181.8, two
C
methines at ꢁ 100.0 and 128.6, and two methyls at ꢁ 16.9 and 19.8. The above data revealed that 1 is a naphthoquinone with
C
C
1
two methyls. The very downfield broad singlet at ꢁ 12.08 (br.s, 1H) in the H NMR spectrum showed that the structure of 1
H
has one ꢂ-hydroxyl (because of the deshielding effect from the carbonyl) located at the benzene ring. The downfield proton
singlet at ꢁ 8.25 (s, 1H) is ascribed to one ꢂ proton (because of the deshielding effect from the carbonyl) located at the
H
benzene ring. The cross peaks in HMBC spectrum showed that the two protons at ꢁ 6.76 and 8.25 were respectively located
H
at C-3 and C-8, and the two methyls at C-6 and C-7. Thus compound 1 was identified as 2,5-dihydroxy-6,7-
dimethylnaphthoquinone. The assignments of each signal in the NMR spectra based on HSQC and HMBC are shown in
Table 1.
OH
O
O
O
5
4
1
HO
H
3
C
1
0
2'
5
3
'
6
9'
9
2
HO
O
OMe
7
'
1
7
H C
3
7
9
OH
5
'
3
O
1
2
1
) School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou, P. R. China, 450051, fax: 86 371 67781908,
e-mail: cfwang1040@126.com; zhangzhenzhong@zzu.edu.cn; 2) School of Pharmaceutical Sciences, Zhejiang University,
Hangzhou, P. R. China, 310058; 3) McLean Hospital/Harvard Medical School, 115 Mill Street, Belmont, Massachusetts,
USA, 02478. Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 157–158, March–April, 2010. Original article
submitted November 12, 2008.
0
184
0009-3130/10/4602-0184 2010 Springer Science+Business Media, Inc.

TABLE 1. NMR Spectral Data of 1 in CD COCD (400 MHz, ꢁ, ppm, TMS)
3
3
C atom
ꢁC
ꢁH
HMBC
C atom
ꢁC
ꢁH
HMBC
1
2
3
4
5
6
172.5
169.7
100.0
181.8
168.9
131.6
H-8
H-3, 8
7
8
9
145.8
128.6
117.0
109.6
19.8
CH -6, CH -7
3
3
8.25 s
6.76 s
H-3
H-3
H-8
H-8
CH -6, CH -7
10
CH -6
2.05 s
2.31 s
CH -7
3
3
CH -7
16.9
CH -6, H-3
3
3
3
3
TABLE 2. NMR Spectral Data of 2 in CD COCD (400 MHz, ꢁ, ppm, TMS, J/Hz)
3
3
C atom
1
ꢁC
ꢁH
HMBC
C atom
ꢁC
ꢁH
HMBC
125.9
129.8
115.6
159.4
144.5
114.6
167.2
126.5
114.1
145.2
H-3, 5, 7, 8
H-6, 2, 7
H-5, 3
H-2, 3, 5, 6
H-2, 6
4ꢀ
5ꢀ
147.6
115.2
121.4
144.6
114.2
166.8
H-2ꢀ, 5ꢀ, 6ꢀ
2
3
4
7
8
9
1
2
3
, 6
, 5
7.55 (2H, d, J = 8.0)
6.91 (2H, d, J = 8.0)
6.87 (1H, d, J = 8.0)
6
7
8
9
ꢀ
ꢀ
ꢀ
ꢀ
7.04 (1H, dd, J = 8.0, 2.0)
7.53 (1H, d, J = 16.0)
6.28 (1H, d, J = 16.0)
H-2ꢀ, 5ꢀ, 7ꢀ
H-2ꢀ, 6ꢀ
H-7ꢀ
7.61 (1H, d, J = 16.0)
6.34 (1H, d, J = 16.0)
H-7
H-7ꢀ, 8ꢀ
H-7, 8, -OCH
H-5ꢀ, 7ꢀ, 8ꢀ
H-6ꢀ, 7ꢀ
3
8.89
8.46
3.71 (3H, s)
OH
OH
OCH3
ꢀ
ꢀ
ꢀ
7.16 (1H, d, J = 2.0)
50.4
H-2ꢀ, 5ꢀ
Compound 2, pale yellow powder. Its molecular formula was determined as C H O by NMR data and the quasi-
1
9 16 6
+
1
molecular ion peak at m/z 341.4 [M + H] in its positive APCI-MS. H NMR data (Table 2) showed one methoxyl group
ꢁ 3.71, s, 3H), two hydroxyls (ꢁ 8.89, s, 1H; 8.46, s, 1H), two couples of olefinic protons ꢁ 7.61 (d, J = 16.0 Hz); 7.53 (d,
(
H
H
H
J = 16.0 Hz); 6.34 (d, J = 16.0 Hz); 6.28 (d, J = 16.0 Hz), three aromatic protons ꢁ 7.16 (d, J = 2.0 Hz); 7.04 (dd, J = 8.0 Hz,
H
2
.0 Hz); 6.87 (d, J = 8.0 Hz) in the ABX spin-spin system, and four aromatic protons ꢁ 7.55 (d, J = 8.0 Hz, 2H); 6.89 (d,
J = 8.6 Hz, 2H) in the AAꢀBBꢀ spin-spin system. The C NMR and DEPT data (Table 2) showed one methoxyl group
ꢁ 50.4), seven aromatic quaternary carbons (ꢁ 125.9, 126.5, 145.2, 147.6, 159.4, 166.8, and 167.2), and eleven aromatic
H
1
3
(
C
C
methine carbons (ꢁ 114.1, 114.2, 114.6, 115.3, 115.6 (2C), 121.4, 129.8 (2C), 144.5 and 144.6), which suggested that the
C
structure of 2 includes one p-oxygenated cinnamyl group and one 3,4-dioxygenated cinnamyl group. The assignments of each
signals in the NMR spectra based on HSQC and HMBC. The HMBC spectra are shown in Table 2. The cross peaks (Table 2)
in the HMBC spectrum showed that the two hydroxyls are located at C-3ꢀ and C-4ꢀ, and OCH3 at C-9. Correlations of the
p-oxygenated cinnamoyl group and the 3,4-dioxygenated cinnamoyl group have not been observed in the HMBC spectrum,
so acid hydrolysis was carried out in silica gel thin layer chromatography (TLC), and the spots of 3,4-dihydroxy-
cinnamic acid and 4-hydroxycinnamoyl methyl ester were found by comparision with the authentic compounds. The result
of acid hydrolysis showed that 3ꢀ,4ꢀ-dihydroxycinnamoyl occurred at C-4 through the ester bond. Thus, compound 2 was
identified as 4-[(3ꢀ,4ꢀ-dihydroxycinnamoyl)-oxy]-methyl cinnamate. HSQCand HMBC correlations are shown in Table 2.
EXPERIMENTAL
1
13
General Methods. H (400 MHz) and C (100 MHz) NMR: Bruker DRX-400 spectrometer in acetone-d , values
6
given in ppm; CC: Silica gel and Sephadex LH-20 using the solvent systems (1) petroleum ether–EtOAc–MeOH (3:1:0.1); (2)
MeOH.
Plant Material. The plant material was collected from Lijiang, Guangxi Province, China, in August 2004. A voucher
specimen has been deposited in the School of Pharmaceutical Sciences, Zhejiang University.
185

The dried roots (20 kg) were extracted with 95% EtOH at room temperature. The EtOH extract was evaporated at
4
5ꢃC to yield a black residue (1.75 kg). The residue was suspended in H O and extracted with petroleum ether, EtOAc, and
2
n-butanol. The EtOAc extract was subjected to silica gel column chromatography with CHCl –MeOH (gradiently) as eluent to
3
give fractions I–VI. Fraction IV was purified by silica gel column chromatography (eluted with petroleum ether–EtOAc–
MeOH 1:1:0.05, v/v/v) and then by Sephadex LH-20 column chromatography (eluted with MeOH) repeatedly to afford
compound 1 (5 mg) and compound 2 (8 mg).
2
,5-Dihydroxy-6,7-dimethylnaphthoquinone (1). Yellow powder; molecular weight C H O ; positiveAPCI-MS
12 10 4
+
1
13
m/z 219.2 [M + H] ; H NMR, C NMR data and HMBC, see Table 1.
-[(3ꢀ,4ꢀ-Dihydroxycinnamoyl)-oxy]-methyl cinnamate (2). Pale yellow powder; molecular weight C H O ;
4
1
9 16 6
+
1
13
positive APCI-MS m/z 341.4 [M + H] ; H NMR, C NMR data and HMBC, see Table 2.
Acid Hydrolysis. Compound 2 was placed on a silica gel plate and acid hydrolysis carried out for 10 min using 12 N
HCl in a sealed container. The plate was taken out and dried, then examined by chromatography using the solvent system
CHCl –MeOH–HCOOH 10:1:0.02 and the results compared with authentic samples 3,4-dihydroxycinnamic acid and
3
p-hydroxycinnamyl methyl ester.
REFERENCES
1
2
3
.
.
.
B. Z. Ding and S. Y. Wang, in: Flora of Henan, Henan Science and Technology Publishing House, 3, 1996, p. 668.
Chinese Herbal Medicine Assembly of the Whole Country, Peopleꢀs Health Publishing House, 1975, p. 850.
M. Tori, H. Nakamizo, K. Mihara, M. Sato, Y. Okamoto, K. Nakashima, M. Tanaka, Y. Saito, M. Sono, X. Gong,
Y. M. Shen, R. Hanai, and C. Kuroda, Phytochemistry, 69, 1158 (2008).
4
.
Y. S. Li, Studies on Sesquiterpenes of Four Ligularia Herbs and Their Bioactivities, Ph.D. Dissertation,
Chinese Pharmaceutical University, 2002, p. 23.
186