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Diterpenoid alkaloids from Aconitum tanguticum
Shi-Jin Qu
a
, Chang-Heng Tan
a,
*, Zu-Long Liu
b
, Shan-Hao Jiang
a
, Long Yu
b
, Da-Yuan Zhu
a
a
Department of Natural Medicinal Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 ZuChongZhi Road, Shanghai 201203, PR China
b
State Key Laboratory of Genetic Engineering, Institutes of Biomedical Sciences, Fudan University, 220 Handan Road, Shanghai 200433, PR China
1. Introduction
Diterpenoid alkaloids are a class of compounds possessing a C-
skeleton of a diterpenoid with an N-bridge between C-19 and C-20
and are present mainly in Aconitum,Delphinium,Consolida, and
Thalictrum species of the family Ranuculaceae. The important
pharmacological activities and structural complexity of diterpe-
noid alkaloids have attracted scientists’ strong interest in their
phytochemistry, synthesis, and medicinal chemistry (Wang et al.,
2010). Aconitum tanguticum (Maxim.) Stapf is widely distributed in
eastern Qinghai-Tibet Plateau, and has long been used for the
treatment of infectious fever, pneumonia and inflammation as
traditional Tibetan medicine (Delectis Florae Reipublicae Popularis
Sinicae Agendae Academiae Sinicae Edita, 1979). Previous studies
disclosed that the main ingredients of A. tanguticum were mono-
and dimeric diterpenoid alkaloids with hetidine-, hetisine-,
atisine- and aconitine-type skeletons (Chen and Song, 1985; Joshi
et al., 1991, 1993; Wang et al., 2002, 2005; Li et al., 2004). As a
continuous attention on the diterpenoid alkaloids of Aconitum
species (Jiang et al., 1987, 1988, 1989, 2002, 2007; Wu et al., 1996;
Wang et al., 2002; Tan et al., 2006), we undertook a phytochemical
investigation on the title plant, resulting in the isolation of
tanaconitine (1), a rare Aconitum alkaloid with a C
29
skeleton,
together with six known alkaloids.
2. Results and discussion
Compound 1had the molecular formula C
29
H
38
N
2
O
2
as
deduced from the HR-EI-MS (M
+
,m/z446.2932). Its IR absorptions
indicated the presence of hydroxyl (3423 cm
1
) and an
a
,
b
-
unsaturated carbonyl function (1678 and 1643 cm
1
). The
1
H-,
13
C
NMR (Table 1) and HMQC spectra of 1 displayed 29 carbon and 37
carbon-bearing proton signals (2 CH
3
,11CH
2
, 9 CH and 7 C).
Among them, an olefinic proton signal at
d
H
7.42 (d,J= 2.3 Hz)
having HSQC correlation with C-19 (
d
C
169.6 d) displayed obvious
1
H–
1
H COSY correlation with H-20 (
d
H
3.53 br s) and HMBC cross-
peaks with C-20 (
d
C
80.1 d), C-5 (
d
C
72.2 s) and C-4 (
d
C
44.9 s)
(Fig. 1), indicating a
D
19,N
-5-hydroxyhetidine-type diterpenoid
alkaloid. In contrast with the
13
C NMR data of naviculine A (2), a C
20
diterpenoid alkaloid from Aconitum naviculare Stapf (Cao et al.,
2008), the
13
C NMR spectrum of 1contained almost all C-signals of
2except for a methylene (
d
43.4 t)of1instead of the
hydroxymethyl (17-CH
2
OH) of 2and slight differences of those
neighboring carbons (C-12, C-15 and C-16), which demonstrated a
diterpenoid alkaloid moiety characterized with 17-dehydroxyna-
viculine A in the molecule of 1.
The remaining moiety, composed of C
9
H
12
NO, displayed
1
H and
13
C signals (Table 1) for an
a
,
b
-unsaturated ketone group (
d
H
6.61
and 5.89, J
gem
= 9.9 Hz;
d
C
197.5 s, 156.0 d, and 125.7 d), three N-
bearing groups: methine (
d
H
2.42 br s;
d
C
69.8 d), methylene (
d
H
2.23 and 3.10, J
gem
= 9.3 Hz;
d
C
54.5 t) and methyl (
d
H
2.27 s;
d
C
40.0), as well as two methylenes (
d
C
35.9 and 37.2) and one
quaternary carbon (
d
C
46.9). This fragment was established to be
cis-1-methyl-3,3a,7,7a-tetrahydro-1H-indol-6(2H)-one on the ba-
sis of following evidences: (i) EIMS fragment ion peak at m/z149
Phytochemistry Letters 4 (2011) 144–146
ARTICLE INFO
Article history:
Received 14 September 2010
Received in revised form 14 February 2011
Accepted 17 February 2011
Available online 2 March 2011
Keywords:
Aconitum tanguticum
Ranuculaceae
Aconitum alkaloid
Diterpene alkaloid
Tanaconitine
ABSTRACT
Tanaconitine (1), a novel Aconitum alkaloid with a C
29
skeleton, together with six known diterpenoid
alkaloids, was isolated from the roots of Aconitum tanguticum. The structure of 1was elucidated to be 17-
dehydroxyl-3
0
a(cis-1
0
-methyl-3
0
,3
0
a,7
0
,7
0
a-tetrahydro-1H-indol-6
0
(2H)-one)-naviculine A by spectro-
scopic analysis.
ß2011 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
* Corresponding author. Tel.: +86 21 50806728; fax: +86 21 50807088.
E-mail address: chtan@mail.shcnc.ac.cn (C.-H. Tan).
Contents lists available at ScienceDirect
Phytochemistry Letters
journal homepage: www.elsevier.com/locate/phytol
1874-3900/$ – see front matter ß2011 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.phytol.2011.02.003
for [C
9
H
12
NO
+
–H
+
]; (ii) nearly superimposed
13
C NMR data with
the same unit of coryphine (Yusupova et al., 1991); (iii) HMBC
cross-peaks shown in Fig. 1; and (iv) a weak W-type coupling
between H-4
0
and H-7
0
a in the
1
H–
1
H COSY spectrum.
The linkage position C
17
–C
3
0
a
of the above two moieties was
elucidated by HMBC cross-peaks of H
2
-17 with C-3
0
a, C-4
0
and C-
7
0
a(Fig. 1). The relative configuration of 1was concluded to be the
same as the corresponding fragments of 2(C
20
unit) and coryphine
(C
9
unit) based on the similarity of the
13
C NMR data. Thus,
tanaconitine (1) was established to be 17-dehydroxyl-3
0
a(cis-1
0
-
methyl-3
0
,3
0
a,7
0
,7
0
a-tetrahydro-1H-indol-6
0
(2H)-one)-naviculine
A.
Tanaconitine is a rare Aconitum alkaloid with a C
29
skeleton,
which might be a C
20
diterpenoid alkaloid derivative in terms of
biogenesis. A possible predecessor 1a might be formed through an
etherification reaction of 2with hordeine (3)(Wang et al., 2002),
which would be transformed to 1by two Claisen rearrangements
and electron shifts (Fig. 2).
The known alkaloids were identified to be tangutimine,
hetisinone, 9-hydroxynominine, atisine, hetisine and 11-acetylhe-
tisine by comparison with published physical and spectroscopic
data (Wang et al., 2002; Gonza
´lez et al., 1986; Bai et al., 1994). They
had been reported from the title plant.
3. Experimental
3.1. General experimental procedures
Optical rotations were determined on a Perkin-Elmer 341
polarimeter. IR spectra were recorded on a Nicolet Magna-750-
FTIR spectrometer with KBr tablet.
1
H (400 MHz) and
13
C NMR
(100 MHz) spectra were acquired on a Bruker AM-400 spectrome-
ter with TMS as internal standard. EI-MS and HR-EI-MS data were
acquired on Finnigan LCQ-Deca and Q-Tof-Ultima mass spectro-
meters, respectively. Silica gel (200–300 meshes) and Sephadex
LH-20 (Pharmacia Biotech AB, Uppsala, Sweden) were used for
column chromatography (CC), and precoated plates of silica gel
(HSGF254; Qingdao Haiyang Chemical Group Co., Qingdao, China)
were used for TLC.
Table 1
1
H- and
13
C NMR data of 1(CDCl
3
,Jin Hz,
d
in ppm).
Site
1
H
13
C
1 1.52 (m),
a
1.64 (m)
a
28.2 t
2 1.27 (m),
a
1.54 (m)
a
20.5 t
3 1.26 (m),
a
1.73 (m)
a
30.5 t
4 – 44.9 s
5 – 72.2 s
6 1.57 (m),
a
1.65 (m)
a
31.6 t
7 1.76 (m),
a
1.96 (dd,J= 13.3, 6.1) 31.0 t
8 – 43.8 s
9 1.61 (m)
a
46.4 d
10 – 45.3 s
11 1.36 (br t,J= 13.6), 1.55 (m)
a
27.5 t
12 2.35 (br s) 35.5 d
13 1.52 (m),
a
1.84 (m)
a
43.4 t
14 1.61 (m)
a
43.6 d
15 5.44 (s) 132.6 d
16 – 146.3 s
17 2.41 (d,J= 13.6), 2.47 (d,J= 13.6) 44.2 t
18 1.05 (s) 18.9 q
19 7.42 (d,J= 2.3) 169.6 d
20 3.53 (s) 80.1 d
1
0
-Me 2.27 (s) 40.0 q
2
0
2.23 (br t,J= 9.3), 3.10 (td,J= 9.3, 3.1) 54.5 t
3
0
1.83 (m),
a
1.94 (m)
a
35.9 t
3
0
a – 46.9 s
4
0
6.61 (br d,J= 9.9) 156.0 d
5
0
5.89 (d,J= 9.9) 125.7 d
6
0
– 197.5 s
7
0
2.57 (dd,J= 16.7, 3.8), 2.61 (d,J= 16.7, 2.3) 37.2 t
7
0
a 2.42 (br s) 69.8 d
a
Overlapping signals.
[()TD$FIG]
Fig. 1. Selected HMBC correlations (H to C) of 1.
[()TD$FIG]
Fig. 2. Possible biogenetic pathway of 1.
S.-J. Qu et al. / Phytochemistry Letters 4 (2011) 144–146
145
3.2. Plant material
The roots of A. tanguticum were collected on Guide County,
Qinghai Province, PR China, in July 2008, and identified by Prof.
Shan-Hao Jiang. A voucher specimen (No. 2008-17) was deposited
in the Herbarium of Shanghai Institute of Materia Medica.
3.3. Extraction and isolation
Dried and powdered roots of A. tanguticum (500 g) were
refluxed in MeOH for 1 h. The MeOH extract (ca. 50 g) gave crude
alkaloids (ca. 20 g) after treatment with a general separation
procedure as previous described (Wu et al., 1996). A part (ca. 2.0 g)
of crude alkaloids was subjected to silica gel column chromatog-
raphy (CC) and eluted with a gradient of petroleum ether (PE)/
EtOAc (10:1, 8:1, 5:1, 3:1, 1:1) to afford fractions A–F. Fr. B
(316 mg) was further isolated into subfractions B1–B5 by silica gel
CC and eluted with PE/acetone (10:1, 8:1, 5:1, 3:1, 1:1). Frs. B3
(64 mg) and B4 (75 mg) gave 1 (22 mg) and tangutimine (51 mg),
respectively, after purification by Sephadex LH-20 CC (CHCl
3
/
MeOH 5:1). By the same procedures as treated Fr. B, Fr. C (350 mg)
offered 9-hydroxynominine (50 mg) and hetisinone (32 mg). Fr. D
(412 mg) was separated into Frs. D1–D5 by silica gel CC (PE/
acetone 8:1, 5:1, 3:1, 2:1, 1:1). Atisine (44 mg) was obtained from
Fr. D2 (82 mg), and hetisine (40 mg) and 11-acetylhetisine (43 mg)
from Fr. D3 (125 mg), after further purification by silica gel CC
(CHCl
3
/MeOH 15:1).
3.4. Tanaconitine A (1)
White amorphous powder; [
a
]
D14
+90 (ca. 0.06, CHCl
3
); IR(KBr)
n
max
(cm
1
): 3423, 2933, 2864, 2787 1678, 1643, 1450, 1244, 1182,
1045, 771; CD (ca. 0.08, MeOH)
l
max
,nm(
De
): 208 (138.6), 247
(+50.0), 334 (10.6);
1
H- and
13
C NMR data see Table 1; EI-MS m/z
(rel. int.): 446 (4, M
+
), 418 (10), 403 (3), 377 (5), 298 (6), 282 (1),
149 (100), 121 (10); HR-EI-MS m/z: 446.2932 ([M]
+
, calcd. for
C
29
H
38
N
2
O
2
: 446.2933).
Acknowledgments
This study was supported by grant ‘‘Key New Drug Creation and
Manufacturing Program (2009ZX09301-001)’’ of the National
Science & Technology Major Project from the Ministry of Science
& Technology of China.
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