Three new neolignan glucosides from the stems of Dendrobium aurantiacum var. denneanum

Article abstract of DOI:10.1016/j.phytol.2014.03.013

Three new neolignan glucosides (1-3), together with four known analogs (4-7), have been isolated from the stems of Dendrobium aurantiacum var. denneanum. Structures of the new compounds including the absolute configurations were determined by spectroscopi

Full text of DOI:10.1016/j.phytol.2014.03.013

Phytochemistry Letters 9 (2014) 37–40
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Phytochemistry Letters
journal homepage: www.elsevier.com/locate/phytol
Three new neolignan glucosides from the stems of Dendrobium
aurantiacum var. denneanum
Xiao-hong Li a,b, Li Guo a,b, Lian Yang a,b, Cheng Peng a,b, , Cheng-jun He a,b, Qin-mei Zhou a,b
*
Liang Xiong
,
a,b,**
, Juan Liu a,b, Ting-mo Zhang b,c
a State Key Laboratory Breeding Base of Systematic Research Development and Utilization of Chinese Medicine Resources,
Sichuan Province and Ministry of Science and Technology, Chengdu 610075, PR China
b Pharmacy College, Chengdu University of Traditional Chinese Medicine, Chengdu 610075, PR China
c Sichuan Wan’an Dendrobe Industry Development Co., Ltd, Chengdu 610072, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
Three new neolignan glucosides (1–3), together with four known analogs (4–7), have been isolated from
the stems of Dendrobium aurantiacum var. denneanum. Structures of the new compounds including the
absolute configurations were determined by spectroscopic and chemical methods as (ꢀ)-(8R,70E)-4-
Received 21 December 2013
Received in revised form 5 March 2014
Accepted 25 March 2014
Available online 20 April 2014
hydroxy-3,30,5,50-tetramethoxy-8,40-oxyneolign-70-ene-9,90-diol 4,9-bis-O-
b-D-glucopyranoside (1),
(ꢀ)-(8S,70E)-4-hydroxy-3,30,5,50-tetramethoxy-8,40-oxyneolign-70-ene-9,90-diol 4,9-bis-O-
b-D-gluco-
pyranoside (2), and (ꢀ)-(8R,70E)-4-hydroxy-3,30,5,50,90-pentamethoxy-8,40-oxyneolign-70-ene-9-ol
Keywords:
4,9-bis-O-
b
-D
-glucopyranoside (3), respectively.
Dendrobium aurantiacum var. denneanum
Ochidaceae
ß 2014 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
Neolignan glucosides
1. Introduction
epoxylignan b-D-glucosides. In this paper, we describe the
isolation and structure elucidation of these compounds.
The genus Dendrobium (Orchidaceae) is composed of more than
1100 species (Wood, 2006). The stems of several Dendrobium
species have been used as ‘‘Shihu’’ in traditional Chinese medicine
to reduce fever, improve eyesight, and regulate the immune
function (He et al., 2012; Ng et al., 2012). Our previous study on
Dendrobium aurantiacum Rchb.f. var. denneanum (Kerr.) Z. H. Tsi,
one of the main species in southern China, has led to the isolation
of seven metabolites, some of which showed neuroprotective
activity or cytotoxic activity (Xiong et al., 2013). Continuing
examination of the EtOH extract resulted in the characterization of
three new (1–3) and four known glycosidic metabolites (4–7)
(Fig. 1). Based on IUPAC recommendations for nomenclature of
lignans and neolignans (Moss, 2000), compounds 1–4 were
2. Results and discussion
Compound 1 was obtained as a white gum, and the presence of
OH (3349 cmꢀ1) and aromatic (1589 and 1499 cmꢀ1) groups were
indicated by its IR spectrum. The molecular formula of C34H48O18
was indicated by HR-ESI-MS at m/z 767.2738 [M + Na]+. The 1H
NMR spectrum of 1 in CD3OD (Table 1) showed signals attributed
to two symmetrically 1,3,4,5-tetrasubstituted aromatic rings [dH
6.70 (2H, s, H-20, 60) and 6.64 (2H, s, H-2, 6)], a trans-arylpropenoxy
unit [
H-80), and 4.22 (2H, d, J = 5.6 Hz, H2-90)], an arylpropanediyloxy
unit [ H 3.15 (1H, dd, J = 13.6, 6.0 Hz, H-7a), 2.99 (1H, dd, J = 13.6,
d
H 6.54 (1H, d, J = 16.0 Hz, H-70), 6.31 (1H, dt, J = 16.0, 5.6 Hz,
d
categorized as 8,40-oxyneolignan
b-D
-glucosides, 5–7 were 7,90-
6.4 Hz, H-7b), 4.42 (1H, m, H-8), 4.00 (1H, dd, J = 10.4, 3.2 Hz, H-9a),
and 3.62 (1H, dd, J = 10.4, 6.0 Hz, H-9b)], and two six-proton
aromatic methoxy groups [dH 3.82 (6H, s, OMe-3, 5) and 3.80 (6H, s,
*
Corresponding author at: State Key Laboratory Breeding Base of Systematic
OMe-30, 50)]. The 13C NMR and DEPT spectra of 1 revealed carbon
signals (Table 2) corresponding to the above protonated units and
eight aromatic quaternary carbons [dC 134.7 (C-4), 134.8 (C-10),
136.6 (C-1, 40), 153.7 (C-3, 5), and 154.6 (C-30, 50)]. These data
resembled those of the (70E)-3,5,30,50-tetramethoxy-8:40-oxyneo-
lign-70-ene-4,9,90-triol (Wu and Wang, 2011). In addition, two
Research Development and Utilization of Chinese Medicine Resources, Sichuan
Province and Ministry of Science and Technology, Chengdu 610075, PR China.
Tel.: +86 028 61800018; fax: +86 028 61800018.
**
Corresponding author at: State Key Laboratory Breeding Base of Systematic
Research Development and Utilization of Chinese Medicine Resources, Sichuan
Province and Ministry of Science and Technology, Chengdu 610075, PR China.
Tel.: +86 028 62135056.
diagnostic doublets attributed to anomeric protons at
dH 4.78 (1H,
E-mail addresses: pengchengchengdu@hotmail.com,
pengchengchengdu@126.com (C. Peng), xiling0505@126.com (L. Xiong).
d, J = 7.6 Hz, H-100) and 4.30 (1H, d, J = 7.6 Hz, H-1000), together with
http://dx.doi.org/10.1016/j.phytol.2014.03.013
1874-3900/ß 2014 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.

38
X.-h. Li et al. / Phytochemistry Letters 9 (2014) 37–40
HO
HO
HO
6'''
7'
1'
9'
O
MeO 5'
MeO
OH
R
1'''
OH
O
8'
3'''
MeO
OH
O
8
O
9
3'
OMe
OMe
5
MeO
O
7
OH
1
6''
3''
HO
HO
O
HO
HO
O
O
1''
OH
3
OMe
OMe
OH
HO
HO
1
2
3
R = OH; 8R
R = OH; 8S
R = OMe; 8R
4
R
OH
OMe
OMe
OH
OH
O
O
HO
HO
HO
HO
OMe
MeO
O
MeO
HO
HO
HO
O
O
O
R
7
OH
HO
5
R = OMe
R = H
OMe
6
Fig. 1. The structures of compounds 1ꢀ7.
partially overlapped signals assigned to oxymethylene and
oxymethine protons between H 3.16 and 3.86 (Table 1), suggested
the presence of two -glycopyranosyl units in 1. Comparison of the
13C NMR data of 1 with those of (70E)-3,5,30,50-tetramethoxy-8:40-
oxyneolign-70-ene-4,9,90-triol (Wu and Wang, 2011) in DMSO-d6
showed that the resonances for C-3/5 and C-9 of 1 were deshielded
significantly by Dd + 5.1 and +8.0 ppm, respectively. This revealed
Enzymatic hydrolysis of 1 produced 1a and a sugar. The sugar
d
was further identified as D-glucose by the positive optical rotation
b
½
a2D0ꢁ þ 44:8ꢂ (Hudson and Dale, 1917; Zi et al., 2008) and TLC
comparison with the authentic sugar sample. The absolute
configuration for C-8 was elucidated by the CD data analysis.
The CD spectra of 1 and 1a showed negative Cotton effects at
235 nm (De ꢀ 0.35) and 234 nm (De ꢀ 0.49), respectively, sug-
gesting the 8R configuration for 1 and 1a (Kim et al., 2011).
that two b-glycopyranosyl units were attached to C-4 and C-9 in 1,
respectively, which was further confirmed by the HMBC correla-
tions of H-100/C-4 and H-1000/C-9.
Table 2
13C NMR data for compounds 1–3.a
No.
1
2
3
Table 1
1H NMR data for compounds 1–3.a
CD3OD
DMSO-d6
CD3OD
DMSO-d6
CD3OD
1
136.6
108.8
153.7
134.7
153.7
108.8
39.0
135.9
108.8
153.1
133.5
153.1
108.8
38.5
136.8
108.6
153.8
134.7
153.8
108.6
38.9
135.8
109.1
153.1
133.5
153.1
109.1
38.6
136.6
108.9
153.7
134.8
153.7
108.9
39.0
No.
1
2
3
2
2
6.64 s
6.59 s
6.64 s
3
6
6.64 s
6.59 s
6.64 s
4
7a
7b
8
3.15 dd (13.6, 6.0)
2.99 dd (13.6, 6.4)
4.42 m
3.12 dd (14.0, 6.0)
2.90 dd (14.0, 6.4)
4.53 m
3.15 dd (14.0, 6.0)
2.99 dd (14.0, 6.5)
4.43 m
5
6
7
9a
9b
20
4.00 dd (10.4, 3.2)
3.62 dd (10.4, 6.0)
6.70 s
4.04 dd (10.4, 4.8)
3.63 dd (10.4, 4.4)
6.69 s
3.99 dd (10.5, 3.0)
3.63 dd (10.5, 6.0)
6.71 s
8
83.6
82.2
83.3
81.6
83.6
9
70.7
70.0
70.6
70.1
70.7
10
134.8
104.6
154.6
136.6
154.6
104.6
131.5
129.8
63.6
133.8
104.5
154.0
135.1
154.0
104.5
131.1
129.6
62.5
134.7
104.8
154.7
136.8
154.7
104.8
131.5
129.7
63.6
133.9
104.5
154.0
134.9
154.0
104.5
131.1
129.6
62.5
134.4
104.7
154.7
136.6
154.7
104.7
133.7
126.5
74.1
60
6.70 s
6.69 s
6.71 s
20
70
80
6.54 d (16.0)
6.31 dt (16.0, 5.6)
4.22 d (5.6)
6.53 d (15.6)
6.30 dt (15.6, 5.6)
4.23 d (5.6)
6.56 d (16.0)
6.26 dt (16.0, 6.0)
4.08 d (6.0)
30
40
90a
90b
100
200
300
400
500
600a
600b
1000
2000
3000
4000
5000
50
60
4.78 d (7.6)
3.46 dd (7.6, 2.8)
3.43 m
4.76 d (7.6)
3.46 dd (7.6, 3.2)
3.42 m
4.78 d (7.5)
3.46 dd (7.5, 2.5)
3.43 m
70
80
90
3.26 m
3.26 m
3.27 m
100
105.7
75.7
104.2
75.2
105.8
75.7
104.5
75.2
105.7
75.7
3.20 m
3.19 m
3.20 m
200
3.68 m
3.68 m
3.68 m
300
77.9
77.6
78.0
77.6
77.9
3.63 m
3.63 m
3.64 m
400
71.7
71.0
71.6
71.0
71.7
4.30 d (7.6)
3.29 m
4.27 d (7.6)
3.28 m
4.30 d (7.5)
3.29 m
500
78.3
78.1
78.4
78.1
78.3
600
62.8
62.0
62.7
61.9
62.8
3.42 m
3.40 m
3.42 m
1000
104.9
75.3
103.9
74.5
104.8
75.1
103.9
74.6
104.9
75.3
4.44 m
4.43 m
4.43 m
2000
3.27 m
3.25 m
3.28 m
3000
77.8
77.5
77.8
77.5
77.8
6000
6000
a
3.85 m
3.85 m
3.85 m
4000
71.3
70.9
71.3
71.0
71.3
b
3.78 m
3.78 m
3.79 m
5000
78.0
77.9
78.0
77.8
78.0
3/5-OMe
30/50-OMe
90-OMe
3.82 s
3.81 s
3.82 s
6000
62.6
61.9
62.6
61.9
62.6
3.80 s
3.79 s
3.80 s
3/5-OMe
30/50-OMe
90-OMe
57.1
57.3
57.0
57.3
57.1
3.37 s
56.5
56.9
56.6
56.9
56.5
58.2
a
Data were measured in CD3OD for 1 and 2 at 400 MHz and for 3 at 500 MHz,
respectively. Proton coupling constants (J) in Hz are given in parentheses. The
assignments were based on 1H–1H COSY, HSQC, and HMBC experiments.
a
Data were measured for 1 and 2 at 100 MHz, and for 3 at 125 MHz. The
assignments were based on 1H–1H COSY, HSQC, and HMBC experiments.

X.-h. Li et al. / Phytochemistry Letters 9 (2014) 37–40
39
Therefore, compound
1
was determined as (ꢀ)-(8R,70E)-4-
Biotech AB, Uppsala, Sweden). HPLC separation was performed on
an instrument consisting of a CoMetro 6000 LDS pump and a
CoMetro 6000 PVW UV/VIS detector with an Ultimate
hydroxy-3,30,5,50-tetramethoxy-8,40-oxyneolign-70-ene-9,90-diol
4,9-bis-O-b-D-glucopyranoside.
Compound 2 was also obtained as a white gum. The NMR, HR-
ESI-MS, IR, and UV spectra of 2 were almost identical to those of 1.
However, 1 and 2 were separable by reversed-phase HPLC with
MeOH–H2O (32:68, v/v). Detailed comparison of the 1H NMR data
between 2 and 1 displayed that the resonance for H-8 of 2 was
deshielded by Dd + 0.11 ppm, and the H-7b resonance was
shielded by Dd ꢀ 0.09 ppm. This implied that 2 was an 8S-isomer
of 1, which was further verified by 2D NMR experiments and
enzymatic hydrolysis of 2. The 2D NMR data analysis confirmed the
planar structure of 2 and furnished the assignments of resonances
(250 mm ꢄ 10 mm) preparative column packed with C18 (5
mm).
3.2. Plant material
The stems of Dendrobium aurantiacum var. denneanum were
collected in April of 2011 from the culture field in Shuangliu,
Sichuan Province, China. Plant identity was verified by Prof. Min Li
(Chengdu University of TCM, Sichuan, China). A voucher specimen
(SSF-20110410) was deposited at the School of Pharmacy,
Chengdu University of TCM, Chengdu, China.
in the NMR spectra. The enzymatic hydrolysis of 2 gave 2a and b-D-
glucose. The optical rotation (½a2D0ꢁ ꢀ46.68) and CD data (233 nm,
De + 0.32) of 2a were opposite those of 1a, indicating the 8S
configuration for 2. Accordingly, compound 2 was determined to
3.3. Extraction, isolation and characterization of compounds
The air-dried stems of D. aurantiacum var. denneanum (10 kg)
were powdered and extracted three times with 95% EtOH (30 L) for
3 h under reflux. The EtOH extract was evaporated under reduced
pressure to yield a dark brown residue (530 g), which was
suspended in H2O (2.5 L) and then successively partitioned with
EtOAc (6ꢄ 2.5 L) and n-BuOH (6ꢄ 2.5 L). The n-BuOH extract
(110 g) was chromatographed over a D-101 macroporous adsor-
bent resin (1.5 kg) column. Successive elution of the column with
H2O, 10% EtOH, 30% EtOH, 50% EtOH, and 95% EtOH (4 L each)
yielded five portions. The portion (48 g) eluted by 30% EtOH was
separated by MPLC over reversed-phase silica gel eluting with a
gradient of increasing MeOH (5–90%) in H2O to give eight fractions
(A–H). Fraction G (7.3 g) was separated over Sephadex LH-20
eluted with MeOH–H2O (1:1) to give five subfractions (G1–G6).
Subfraction G2 was further fractionated via silica gel CC, eluting
with a gradient of CHCl3–MeOH (10:1, 6:1, 4:1, 2:1, 0:1), to yield
eight fractions (G2–1–G2–8). Separation of G2–2 with Sephadex LH-
20 (CHCl3–MeOH, 1:1) and RP semipreparative HPLC (37% MeOH in
H2O) yielded 4 (14.7 mg), 5 (6.9 mg), 6 (11.3 mg), and 7 (9.4 mg).
Fraction G2–6 was further separated by Sephadex LH-20 (CHCl3–
MeOH, 1:1) and then purified by RP semipreparative HPLC (32%
MeOH in H2O) to yield 1 (7.9 mg), 2 (6.1 mg), and 3 (3.4 mg).
be
(ꢀ)-(8S,70E)-4-hydroxy-3,30,5,50-tetramethoxy-8,40-oxyneo-
lign-70-ene-9,90-diol 4,9-bis-O-
b-D-glucopyranoside.
Compound 3 had the molecular formula C35H50O18 (HR-ESI-MS)
with one more CH2 than 1 and 2. The IR, UV and NMR data were
very similar to those of 1 except for the presence of an additional
methoxy in 3 (dH 3.37 and dC 58.2). In addition, the resonance for
H2-90 of 3 was shielded by DdH ꢀ0.14 ppm, whereas the C-90
resonance was deshielded by DdC + 10.5 ppm, as compared with
those of 1 (Tables 1 and 2). Thus, the above data implied that OH-90
in 1 was substituted by OMe-90 in 3, which was confirmed by a
correlation for OMe-90/C-90 in the HMBC spectrum of 3. In the CD
spectrum, the negative Cotton effect at 240 nm of 3 was consistent
with that of 1, but opposite that of 2, indicating the 8R
configuration for 3. Thus, compound 3 was assigned to be (ꢀ)-
(8R,70E)-4-hydroxy-3,30,5,50,90-pentamethoxy-8,40-oxyneolign-70-
ene-9-ol 4,9-bis-O-b-D-glucopyranoside.
By comparison of spectroscopic data with those reported in the
literature, the known compounds were identified as picraquassio-
side C (4) (Yoshikawa et al., 1995), (ꢃ)-5,50-dimethoxylariciresinol
40-O-b-D-glucopyranoside (5) (Ida et al., 1993), lariciresion-40-O-b-D-
glucoside (6) (Sugiyama and Kikuchi, 1993), and mangliesides E (7)
(Kiem et al., 2008). All of the known compounds were first reported
from the genus.
It is worth mentioning that plants of the genus Dendrobium are
known to contain bibenzyls, phenanthrenes, fluorenes, coumarins,
sesquiterpenes, flavanones, and alkaloids (Chang et al., 2010), but
the 8,40-oxyneolignans were only found previously from Dendro-
bium chrysanthum in this genus (Ye et al., 2004). Thus, the results of
this study suggest that there may be a genetic relationship
between D. aurantiacum var. denneanum and D. chrysanthum, and
the 8,40-oxyneolignan glucosides may be potential chemotaxo-
nomic markers to differentiate the two species from others of
Dendrobium.
3.3.1. (ꢀ)-(8R,70E)-4-hydroxy-3,30,5,50-tetramethoxy-8,40-
oxyneolign-70-ene-9,90-diol 4,9-bis-O-
b-D-glucopyranoside (1)
White gum; ½a2D0ꢁ ꢀ 7:7ꢂ (c 0.15, MeOH); UV (MeOH)
): 202 (4.39), 226 sh (4.07), 270 (3.66) nm; CD (MeOH): 213
De + 0.70), 235 (De ꢀ 0.35), 269 (De + 0.51), 293 (De + 0.26) nm;
IR (KBr) max: 3349, 2921, 1589, 1499, 1463, 1420, 1327, 1297,
lmax (log
e
(
n
1250, 1122, 1071, 1033, 833, 673 cmꢀ1; 1H and 13C NMR data see
Tables 1 and 2; ESI-MS m/z: 767 [M + Na]+; HR-ESI-MS m/z:
767.2734 [M + Na]+ (calcd. for C34H48O18Na, 767.2738).
3.3.2. (ꢀ)-(8S,70E)-4-hydroxy-3,30,5,50-tetramethoxy-8,40-
oxyneolign-70-ene-9,90-diol 4,9-bis-O-
b-D-glucopyranoside (2)
3. Experimental
White gum; ½a2D0ꢁ ꢀ 34:4ꢂ (c 0.10, MeOH); UV (MeOH)
): 203 (4.38), 227 sh (4.05), 270 (3.65) nm; CD (MeOH): 217
lmax (log
e
(
3.1. General experimental procedures
De + 1.94), 237 (De + 0.44), 278 (De ꢀ 0.62) nm; IR (KBr) nmax
:
3346, 2921, 1588, 1498, 1465, 1424, 1329, 1223, 1123, 1072, 1022,
832, 674 cmꢀ1; 1H and 13C NMR data see Tables 1 and 2; ESI-MS m/
z: 767 [M + Na]+; HR-ESI-MS m/z: 767.2740 [M + Na]+ (calcd. for
IR spectra were recorded on a Vector 22 FT-IR spectrometer. UV
spectra were obtained on a Shimadzu UV-260 spectrophotometer.
Optical rotations were measured with a Perkin-Elmer 341 plus. CD
spectra were recorded on a JASCO J-815 CD spectrometer. NMR
spectra were obtained at 400 or 500 MHz for 1H, and 100 or
125 MHz for 13C, respectively, on Bruker-AV-400 MHz or INOVA
500 MHz spectrometers with solvent peaks being used as
references. HR-ESI-MS were measured with Waters Synapt G2
HDMS. Column chromatography was performed with silica gel
(200–300 mesh, Jiangyou Silical Gel Development Co., Yantai,
C34H48O18Na, 767.2738).
3.3.3. (ꢀ)-(8R,70E)-4-hydroxy-3,30,5,50,90-pentamethoxy-8,40-
oxyneolign-70-ene-9-ol 4,9-bis-O-
b-D-glucopyranoside (3)
White gum; ½a2D0ꢁ ꢀ 12:0ꢂ (c 0.10, MeOH); UV (MeOH)
): 202 (4.39), 226 sh (4.04), 273 (3.59) nm; CD (MeOH): 214
lmax (log
e
(
De + 0.29), 240 (De ꢀ 0.01), 274 (De + 0.39) nm; IR (KBr) nmax
:
3367, 2919, 1587, 1502, 1464, 1420, 1330, 1225, 1123, 1072, 1018,
China) and Sephadex LH-20 (40–70
m
m, Amersham Pharmacia
833, 675 cmꢀ1; 1H and 13C NMR data see Tables 1 and 2; ESI-MS m/

40
X.-h. Li et al. / Phytochemistry Letters 9 (2014) 37–40
z: 781 [M + Na]+; HR-ESI-MS m/z: 781.2902 [M + Na]+ (calcd. for
35H50O18Na, 781.2895).
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Acknowledgment
Support from the National Technology R&D Program for the
‘‘Twelfth Five-Year’’ Plan of China (Grant No. 2011BAI13B02-8) is
acknowledged.