Chemical constituents of equisetum debile

Article abstract of DOI:10.1080/10286020.2011.596829

Three new compounds, debilitriol (1), debilignanoside (2), and equisetumine (3), along with nine known compounds, were isolated from the whole plant of Equisetum debile. Their structures were elucidated by spectral and chemical methods.

Full text of DOI:10.1080/10286020.2011.596829

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Chemical constituents of Equisetum
debile
Jun-Ming Tan a , Yi-Hua Qiu a , Xin-Qi Tan a , Chang-Heng Tan b &
Kai Xiao c
a PLA 98th Hospital , Huzhou, 313000, China
b Department of Natural Medicinal Chemistry , Shanghai Institute
of Materia Medica, Chinese Academy of Sciences , Shanghai,
201203, China
c Laboratory of Toxicology & Pharmacology, Faculty of Naval
Medicine, The Second Military Medical University , Shanghai,
200433, China
Published online: 10 Aug 2011.
To cite this article: Jun-Ming Tan , Yi-Hua Qiu , Xin-Qi Tan , Chang-Heng Tan & Kai Xiao (2011)
Chemical constituents of Equisetum debile , Journal of Asian Natural Products Research, 13:9,
811-816, DOI: 10.1080/10286020.2011.596829
To link to this article: http://dx.doi.org/10.1080/10286020.2011.596829
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Journal of Asian Natural Products Research
Vol. 13, No. 9, September 2011, 811–816
Chemical constituents of Equisetum debile
Jun-Ming Tana, Yi-Hua Qiua, Xin-Qi Tana, Chang-Heng Tanb* and Kai Xiaoc*
b
aPLA 98th Hospital, Huzhou 313000, China; Department of Natural Medicinal Chemistry,
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China;
cLaboratory of Toxicology & Pharmacology, Faculty of Naval Medicine, The Second Military
Medical University, Shanghai 200433, China
(Received 2 April 2011; final version received 6 June 2011)
Three new compounds, debilitriol (1), debilignanoside (2), and equisetumine (3), along
with nine known compounds, were isolated from the whole plant of Equisetum debile.
Their structures were elucidated by spectral and chemical methods.
Keywords: Equisetum debile; debilitriol; debilignanoside; equisetumine
1. Introduction
(rel-2R,4S)-6-(3-hydroxy-4-methoxyphe-
nyl)hexane-1,2,4-triol (1), (7R,8S)-guaia-
glycerol-b-coniferyl ether 9-O-b-D-
glucopyranoside (2), and 2-pentyl-1,5,9-
triazacyclotridecan-4-one (3), respect-
ively, on the basis of spectral evidence.
Equisetum debile Roxb. (Equisetaceae) is
a fern distributed widely in the south of
China, Southeast Asia, and India, which
has a long history as a Chinese folk
medicine for the treatment of acute
hepatitis, urethritis, conjunctivitis, and
diarrhea [1]. Pharmacological studies
disclosed that the alcohol extraction of E.
debile could decrease the level of trigly-
ceride and total cholesterol in rats and
triglyceride in rabbits [2]. A few studies
on E. debile [3–5] reported the existence
of megastigmane glucosides, phenol gly-
cosides, lignan glycosides, and flavonoids
and their glycosides. As a continuous
interest in Chinese folk medicinal plants,
we investigated systematically the chemi-
cal constituents of the title plant, and
obtained 12 compounds, including a new
phenylhexane debilitriol (1), a new 8-O-40
neolignan glucoside debilignanoside (2),
and a new alkaloid equisetumine (3)
(Figure 1). The structures of these
new compounds were determined to be
2. Results and discussion
Debilitriol (1) was obtained as viscous
syrup. Its negative and positive ESI-MS
gave pseudomolecular ion peaks at m/z
255 [M 2 H]2 and 279 [M þ Na]þ,
respectively, in agreement with the mole-
cular formula C13H20O5, which was also
confirmed by the HR-ESI-MS at m/z
279.1205 [M þ H]þ.
The 1H, 13C NMR, and HSQC spectra
of 1 showed 1H and 13C signals for a 1,3,4-
trisubstituted aromatic ring at dH 6.79 (1H,
d, J ¼ 8.2 Hz), 6.67 (1H, d, J ¼ 2.0 Hz),
and 6.63 (1H, dd, J ¼ 8.2, 2.0 Hz), as well
as dC 147.9 (s), 147.7 (s), 137.3 (s), 121.0
(d), 117.1 (d), and 113.5 (d), a methoxyl at
dH 3.81 (3H, s) and dC 57.1, four
methylenes at dC 68.4, 42.4, 41.8, and
*Corresponding authors. Email: chtan@mail.shcnc.ac.cn; kaixiaocn@gmail.com
ISSN 1028-6020 print/ISSN 1477-2213 online
q 2011 Taylor & Francis
DOI: 10.1080/10286020.2011.596829
http://www.informaworld.com

812
J.-M. Tan et al.
OH
3
O
OR
OH
9
5
N
H
MeO
MeO
HO
1
3
4
4
7
8
OMe
4
3'
2
12
1
O
1
HN
4'
9
HN
14
17
*
*
9
OH
11
7
1'
15
OH
13
OH
OH
7'
9'
2 R = Glc
5 R = H
1
3
Figure 1. Structures of compounds 1–4.
32.9, and two oxygen-bearing methines at
dC 69.1 and 70.9, indicating a phenylhex-
ane derivative. The aliphatic C6 moiety was
elucidated to be ZCH2CH2CH(OH)CH2
CH(OH)CH2OH based on the 1H–1H
COSY cross-peaks of H2-12/H-11,
H-11/H2-10, H2-10/H-9, H-9/H2-8, and
H2-8/H2-7 (Figure 2). The MeO was
assigned on C-4 of the aromatic ring by
HMBC cross-peaks of MeO/C-4, H-2/C-4,
and H-6/C-4 (Figure 2). The relative
stereochemistry of 1 was determined to be
9,11-trans by the 1H signals of 10-CH2 and
appeared as triplet (d 1.52, t, J ¼ 6.2 Hz)
rather than two sets of multiplets [6]. The
structure of 1 was, therefore, established to
be (rel-2R,4S)-6-(3-hydroxy-4-methoxy-
phenyl)hexane-1,2,4-triol.
In the 1H NMR spectrum of 2, the
aglycone moiety was observed to contain
two 1,3,4-trisubstituted aromatic rings [d
7.06 (d, J ¼ 1.8 Hz), 6.88 (dd, J ¼ 8.1,
1.8 Hz), and 6.74 (d, J ¼ 8.1 Hz); 7.02 (d,
J ¼ 1.7 Hz), 6.98 (d, J ¼ 8.3 Hz), and 6.90
(dd, J ¼ 8.3, 1.7 Hz)], a pair of E-double
bonds (d 6.51 and 6.24, Jgemical ¼ 15.7 Hz),
and two methoxyls (d 3.85 and 3.81, each
3H, s). The 13C NMR spectrum of 2 showed
20 carbon signals (2 £ OCH3, 2 £ OCH2,
2 £ OCH, 8 £ vCH, and 6 £ vC) for the
aglycone, which were almost superposed
with those of guaiacylglycerol-b-coniferyl
ether (4) [7] except for a downfield shift of
C-9 (Dd2–4 ¼ 7.0) due to the glycosidation
effect. The above evidence indicated the
structure of 2 to be a 9-O-b-D-glucopyrano-
side of 4, which was further substantiated
by the HMBC experiment (Figure 2). The
absolute configuration of 2 was determined
to be 7R,8S on the basis of positive CD
curve in the range of 210–250 nm [8] and
the coupling constant of 5.4 Hz between H-
7 and H-8 [9].
Debilignanoside (2) was obtained as a
white amorphous powder. It had the
molecular formula of C26H34O12 as
indicated by the HR-ESI-MS. The acid
hydrolysis and GC analysis, together with
NMR signals at dH 4.27 (d, J ¼ 7.7 Hz)
and dC 105.2 (d), 78.4 (2C, d), 75.7 (d),
72.0 (d), and 63.1(t), revealed a b-D-
glucopyranosyl unit in the molecule of 2.
Equisetumine (3) was obtained as
yellowish oil with positive Dragendorff’s
reaction. Its molecular formula was
OH
O
HO
OH
OH
OH
O
MeO
N
O
H
MeO
OH
OH
OMe
HN
HN
O
OH OH
HO
1
OH
2
3
1H-1H COSY
HMBC (H to C)
1
Figure 2. Selected H–1H COSY and HMBC correlations of 1–3.

Journal of Asian Natural Products Research
813
determined to be C15H31N3O by the
HR-EI-MS. The IR bands exhibited
physical and spectroscopic data and/or
with authentic samples.
absorptions of NH (3408 and 3261 cm21
)
and CONH (1651 cm21). The 13C NMR
spectrum displayed 15 carbon signals
(1 £ CH3, 12 £ CH2, 1 £ CH, and
1 £ CON), indicating a monocyclic alka-
loid. The HSQC and 1H–1H COSY
spectra of 3 (Figure 2) revealed three
isolated spin systems: (i) Z5NH6CH27CH28
CH2Z, (ii) Z10CH211CH122CH213CH2Z, and
(iii) Z3CH22CH(NH)(14CH125CH126CH217
CH128CH3)Z. In the HMBC spectrum,
marked correlations were observed at
H2-6/C-4, H2-3/C-4, H-2/C-13, and
H2-8/C-10 (Figure 2), indicating the three
fragments to be connected through two
N-atoms and an amide group to form a
monocyclic structure.
3. Experimental
3.1 General experimental procedures
Optical rotations were determined on a
PerkinElmer 341 polarimeter. The IR
spectra were recorded on a Nicolet-
Magna-750-FT-IR spectrometer. CD anal-
ysis was carried out on a Jasco J-810
spectropolarimeter. The NMR spectra were
recorded on a Bruker AV-400 spectrometer
with TMS as internal standard. ESI-MS and
HR-ESI-MS were obtained on an Esquire
3000plus and a Q-TOF-Ultima mass
spectrometers, respectively. EI-MS and
HR-EI-MS spectra were obtained on a
MAT-95 mass spectrometer. Silica gel
(200–300 mesh, Qingdao Haiyang Chemi-
cal Co. Ltd, Qingdao, China), D-1400
macroporous resin (Yangzhou Pharmaceu-
tical Factory, Yangzhou, China), RP-18
silica gel (150–200 mesh, Fuji Silysia
Chemical Ltd, Aichi, Japan), and Sephadex
LH-20 (Pharmacia Biotech AB, Uppsala,
Sweden) were used for column chroma-
tography (CC). Silica gel HSGF254 (Yantai
Jiangyou Guijiao Kaifa, Co., Yantai,
China) was used for TLC. GC analysis
was carried out on a PerkinElmer Sigma-
115 gas chromatograph.
Equisetumine is a rare macrocyclic
polyamine alkaloid, biogenetically, which
might be derived from spermidine (5) and
g-hydroxycaprylic acid (6) via a conden-
sation reaction (Figure 3). Spermidine
alkaloids were also reported from Equise-
tum palustre L. [10], Clerodendrum
myricoides [11], Meehania fargesii [12],
Dracocephalum tanguticum [13], etc.
These known compounds were ident-
ified to be coumaric acid, p-hydroxyben-
zoic acid, ferulic acid, 5-hydroxymethyl-
2-furfuraldehyde [14], equisetumoside B
[15], guaiacylglycerol-b-coniferyl ether
(4) [7], (þ)-lariciresinol 9-O-b-D-gluco-
pyranoside [16], (þ)-isolariciresinol 3a-
O-b-D-glucopyranoside [17], and thymi-
dine [18] by comparison with published
3.2 Plant material
The whole plants of E. debile were
collected from Anji County, Zhejiang
Province, China, in October 2009. The
H
O
O
HO
HO
N
H
H
HN
HN
HN
–2H2O
HN
N
C5H13
C5H13
H
5
6
3
Figure 3. Possible biogenetic pathway of 3.

814
J.-M. Tan et al.
plant was identified by Dr X.Q. Tan of
PLA 98th Hospital. A voucher sample
(No. 20091013) is deposited in the
Herbarium of Shanghai Institute of
Materia Medica, Chinese Academy of
Sciences.
3.3.1 Debilitriol (1)
Colorless viscous syrup. ½aꢀD 25.3
(c ¼ 0.417, MeOH). IR (KBr) nmax
3419, 1604, 1452, and 1512 cm21 1H
24
:
;
NMR spectral data (400 MHz, CD3OD):
d 6.79 (d, J ¼ 8.2 Hz, H-5), 6.67 (d,
J ¼ 2.0 Hz, H-2), 6.63 (dd, J ¼ 8.2,
2.0 Hz, H-6), 3.84 (m, H-11), 3.80 (m,
H-9), 3.81 (s, 4-OMe), 3.47 (dd, J ¼ 9.6,
5.0 Hz, Ha-12), 3.43 (dd, J ¼ 9.6, 6.5 Hz,
Hb-12), 2.66 (dt, J ¼ 9.7, 7.7 Hz, Ha-7),
2.52 (dt, J ¼ 9.7, 7.7 Hz, Hb-7), 1.70 (td,
J ¼ 7.7, 6.3 Hz, H2-8), and 1.52 (t,
J ¼ 6.2 Hz, H2-10). 13C NMR spectral
data (100 MHz, CD3OD): d 147.9 (C-3,
s), 147.7 (C-4, s), 137.3 (C-1, s), 121.0
(C-6, d), 117.1 (C-2, d), 113.5 (C-5, d),
70.9 (C-11, d), 69.1 (C-9, d), 68.4 (C-12,
t), 57.1 (OMe, q), 42.4 (C-10, t), 41.8 (C-
8, t), and 32.9 (C-7, t). ESI-MS: m/z 279
[M þ Na]þ, 255 [M 2 H]2. HR-ESI-MS:
m/z 279.1205 [M þ Na]þ (calcd for
C13H20O5Na, 279.1208).
3.3 Extraction and isolation
The dried whole plant of E. debile (5 kg)
was powdered and extracted with 25 liters
95% EtOH for three times. The concen-
trated extract was suspended in water and
partitioned orderly with petroleum ether
(PE), EtOAc, and BuOH. The EtOAc-
soluble fraction (20 g) was subjected to CC
of silica gel with gradient CHCl3–MeOH
(50:1, 25:1, 10:1, and 5:1) as eluents to
give subfractions E1–E4. Fraction E1
offered 3 (40 mg) by repeated silica gel
CC (PE–acetone, 5:1). E2 furnished 5-
hydroxymethyl-2-furfuraldehyde (90 mg)
after purification of repeated silica gel
CC (CHCl3–MeOH, 20:1). Fraction E3
was separated into subfractions E3.1–E3.5
through a silica gel column with gradient
CHCl3–MeOH (15:1 ! 5:1) as eluents.
E3.1 and E3.2 yielded solids, which were
recrystallized to afford coumaric acid
(18 mg) and p-hydroxybenzoic acid
(13 mg), respectively. Compounds 4
(15 mg), 1 (5 mg), and ferulic acid (7 mg)
were obtained from E3.3 after repeated CC
of silica gel (CHCl3–MeOH, 10:1).
3.3.2 Debilignanoside (2)
20
White amorphous powder. ½aꢀD þ5.5
(c ¼ 0.583, MeOH). CD (MeOH):
D1215 nm þ 2.5, D1225 nm þ 4.7, D1240 nm
þ 3.5, D1248 nm þ 4.7. IR (KBr) nmax: 3419
(OH), 1605, 1452, and 1512 (Ar) cm21. 1H
NMR spectral data (400 MHz, CD3OD): d
7.06 (d, J ¼ 1.8 Hz, H-2), 7.02 (d,
J ¼ 1.7 Hz, H-20), 6.98 (d, J ¼ 8.3 Hz, H-
50), 6.90 (dd, J ¼ 8.3, 1.7 Hz, H-60), 6.88
(dd, J ¼ 8.1, 1.8 Hz, H-6), 6.74 (d,
J ¼ 8.1 Hz, H-5), 6.51 (br d, J ¼ 15.7 Hz,
H-70), 6.24 (dt, J ¼ 15.7, 5.6 Hz, H-80),
4.97 (d, J ¼ 5.4 Hz, H-7), 4.49 (td, J ¼ 6.4,
5.4 Hz, H-8), 4.27 (d, 7.7 Hz, H-100), 4.19
(2H, dd, J ¼ 5.6, 1.1 Hz, H2-90), 3.85 (3H,
s, MeO-30), 3.83 (2H, d, J ¼ 6.4, H2-9),
3.81 (3H, s, MeO-3), 3.78 (dd, J ¼ 11.6,
1.9 Hz, Ha-600), 3.64 (dd, J ¼ 11.6, 5.5 Hz,
Hb-600), and 3.40–3.15 (4H, m, H-300, H-400,
H-200, and H-500). 13C NMR spectral data
(CD3OD, 100 MHz): d 152.1 (C-30, s),
149.3 (C-40, s), 149.2 (C-3, s), 147.5
(C-4, s), 134.2 (C-1, s), 133.5 (C-10, s),
BuOH fraction (37 g) was subjected to
macroporous resin CC with gradient
EtOH–H2O (0, 20, 40, 60, and 95%) as
eluents to gain B1–B5. Fraction B3 was
separated into subfractions B3.1–3.5 by
CC of RP-18 (60% MeOH). Fr.B3.2
yielded (þ)-lariciresinol 9-O-b-D-gluco-
pyranoside (25 mg) as solids. Fr.B3.3
offered 2 (18 mg) and equisetumoside B
(11 mg), and Fr.B3.4 afforded (þ)-isolar-
iciresinol
3a-O-b-D-glucopyranoside
(8 mg) after purification of Sephadex
LH-20 CC (75% MeOH), respectively.
Fraction B4 yielded thymidine (42 mg) as
needles.

Journal of Asian Natural Products Research
815
131.9 (C-70, d), 129.0 (C-80, d), 121.2
(C-6, d), 121.1 (C-60, d), 118.9 (C-50, d),
116.3 (C-5, d), 112.4 (C-2, d), 111.7 (C-20,
d), 105.2 (C-100, d), 85.2 (C-8, d), 78.4
(C-300 and C-500, each d), 75.7 (C-200, d), 74.1
(C-7, d), 72.0 (C-400, d), 69.5 (C-9, t), 64.2
(C-90, t), 63.1 (C-600, t), 57.0 (MeO-30, q),
and 56.9 (MeO-3, q). ESI-MS: m/z 561
[M þ Na]þ, 537 [M 2 H]2. HR-ESI-MS:
m/z 561.1949 [M þ Na]þ (calcd for C26H34
O12Na, 561.1948).
by CC of Sephadex LH-20 (MeOH–H2O
1:1, v/v) to give the sugar moiety.
The purified sugar and standard D-glucose
(Sigma-Aldrich, St Louis, MO, USA)
were treated with L-cysteine methyl
ester hydrochloride (2 mg) in pyridine
(1 ml) at 608C for 1 h. Then, the solution
was treated with N,O-bis(trimethylsilyl)-
trifluoroacetamide (0.02 ml) at 608C for
1 h. The supernatant was subjected to GC
analysis to identify the sugars. Conditions
for GC were capillary column, DB5-MS
(30 m £ 0.25 mm £ 0.25 mm), oven tem-
perature program, 180–3008C at 68C/min;
injection temperature 3508C; carrier gas,
He at 1 ml/min. D-Glucose was detected by
comparing its retention time with that of
the authentic sample (tR ¼ 12.30 min).
3.3.3 Equisetumine (3)
20
Yellowish oil. ½aꢀD þ18 (c ¼ 0.7,
CHCl3). IR (KBr) nmax: 3408, 3261,
3076, 2929, 2658, 1651, 1556, 1441,
1367, 1178, 1066, and 629 cm21 1H
.
NMR spectral data (CDCl3, 400 MHz): d
8.39 (1H, t, J ¼ 5.7 Hz, NH-5), 3.73
(1H, m, Ha-6), 3.20–3.10 (4H, m, H-2,
Hb-6, and H2-8), 2.96 (1H, m, Ha-13), 2.92
(1H, m, Ha-10), 2.82 (1H, m, Hb-10), 2.62
(1H, m, Hb-13), 2.42 (1H, m, Ha-3), 2.38
(1H, m, Hb-3), 2.20–1.90 (3H, m, H2-7
and Ha-11), 1.90–1.75 (4H, m, Hb-11,
H2-12, and Ha-14), 1.50–1.20 (7H, Hb-14,
H2-17, H2-16, and H2-15), and 0.87 (3H, t,
J ¼ 6.8 Hz, Me-18). 13C NMR spectral
data (CDCl3, 100 MHz): d 173.0 (s, C-4),
55.3 (d, C-2), 49.3 (t, C-10), 48.9 (t, C-8),
44.2 (t, C-13), 41.6 (t, C-3), 38.4 (t, C-6),
31.94 (t, C-16), 31.90 (t, C-14), 26.7 (t, C-
7), 26.1 (t, C-11), 26.0 (t, C-12), 24.7 (t, C-
15), 22.6 (t, C-17), and 14.0 (q, C-18). EI-
MS: m/z 269 (Mþ, 11), 252 (19), 226 (28),
198 (100), 155 (43), 140 (37), 126 (37),
100 (44), and 84 (70). HR-EI-MS: m/z
269.2455 [M]þ (calcd for C15H31N3O,
269.2467).
Acknowledgements
This study was financially supported by grants
from the National Science & Technology Major
Project ‘Key New Drug Creation and Manu-
facturing Program’ (Nos 2009ZX09301-001
and 2008ZXJ09002-011), and the National
Science Natural Foundation of China (Nos
81072545 and 20872179).
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