Phenolic glucosides from dendrobium aurantiacum var. denneanum and their bioactivities

Article abstract of DOI:10.3390/molecules18066153

A new 8,4'-oxyneolignane glucoside 1 has been isolated from the stems of Dendrobium aurantiacum var. denneanum together with six known phenolic glucosides 2-7. The structure of the new compound, including its absolute configuration, was determined by spectroscopic and chemical methods as (-)-(7S,8R,7'E)-4-hydroxy-3,3',5,5'- tetramethoxy-8,4'-oxyneolign-7'-ene-7,9,9'- triol 7,9'-bis-O-β-D-glucopyranoside (1). In the in vitro assays, compound 1 and (-)-syringaresinol-4,4'-bis-O-β-D-glucopyranoside (2) showed evident activity against glutamate-induced neurotoxicity in PC12 cells. Shashenoside I (4) showed a selective cytotoxic activity with the IC50 value of 4.17 μM against the acute myeloid leukemia cell line MV4-11, while it was inactive against 10 other human tumor cell lines.

Full text of DOI:10.3390/molecules18066153

Molecules 2013, 18, 6153-6160; doi:10.3390/molecules18066153
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Phenolic Glucosides from Dendrobium aurantiacum var.
denneanum and Their Bioactivities
1
,2
1,2
1,2,
2
1,2
Liang Xiong , Zhi-Xing Cao , Cheng Peng *, Xiao-Hong Li , Xiao-Fang Xie ,
2
,3
2
2
1,2,
Ting-Mo Zhang , Qin-Mei Zhou , Lian Yang and Li Guo
*
1
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, Sichuan, China; E-Mails: xiling0505@126.com (L.X.);
caozhixing007@163.com (Z-X.C.); xxf14544@163.com (X.-F.X.)
2
Pharmacy College, Chengdu University of Traditional Chinese Medicine, Chengdu 610075,
Sichuan, China; E-Mails: lixiaohong136@126.com (X.-H.L.);
zhangtmchengdu@163.com (T.-M.Z.); zhqmyx@sina.com (Q.-M.Z.);
yanglian080910@163.com (L.Y.)
3
Sichuan Wan’an Dendrobe Industry Development Co., Ltd., Chengdu 610072, Sichuan, China
*
Authors to whom correspondence should be addressed; E-Mails: pengchengchengdu@126.com (C.P.);
gli64@sina.com (L.G.); Tel./Fax: +86-028-6180-0018 (C.P.); +86-028-8739-5072 (L.G.).
Received: 15 April 2013; in revised form: 16 May 2013 / Accepted: 20 May 2013 /
Published: 23 May 2013
Abstract: A new 8,4'-oxyneolignane glucoside 1 has been isolated from the stems of
Dendrobium aurantiacum var. denneanum together with six known phenolic glucosides
2
−7. The structure of the new compound, including its absolute configuration, was
determined by spectroscopic and chemical methods as (−)-(7S,8R,7'E)-4-hydroxy-3,3',5,5'-
tetramethoxy-8,4'-oxyneolign-7'-ene-7,9,9'-triol 7,9'-bis-O-β-D-glucopyranoside (1). In the
in vitro assays, compound 1 and (−)-syringaresinol-4,4'-bis-O-β-D-glucopyranoside (2)
showed evident activity against glutamate-induced neurotoxicity in PC12 cells.
Shashenoside I (4) showed a selective cytotoxic activity with the IC value of 4.17 μM
50
against the acute myeloid leukemia cell line MV4-11, while it was inactive against 10 other
human tumor cell lines.
Keywords: Dendrobium aurantiacum var. denneanum; lignan glucosides;
phenylpropanoid glycosides; bioactivities

Molecules 2013, 18
. Introduction
Dendrobium aurantiacum Rchb.f. var. denneanum (Kerr.) Z. H. Tsi (Orchidaceae) is widely
6154
1
distributed and cultivated in southern China, Burma, Laos and South Asia. The stem of the plant,
commonly referred to as “Shihu” or “Huangcao” in Chinese, has been used in traditional Chinese
medicine for its antipyretic, eyesight improving, immunomodulatory, antioxidant and anti-aging
effects [1,2]. Previous chemical investigations on this plant have resulted in more than twenty phenolic
secondary metabolites, including bibenzyls, phenanthrenes, fluorenones, phenylpropanoids, flavones
and coumarins [3–6]. In the course of our search for bioactive natural products, the stems of
D. aurantiacum var. denneanum were shown to afford seven phenolic glucosides, including a new 8,4'-
oxyneolignane 7-O-glucoside 1 and six known phenolic glucosides 2−7. Based on IUPAC
recommendations for the nomenclature of lignans and neolignans [7], 1 was identified as (−)-(7S,8R,7'E)-
4-hydroxy-3,3',5,5'-tetramethoxy-8,4'-oxyneolign-7'-ene-7,9,9'-triol 7,9'-bis-O-β-D-glucopyranoside. All
the compounds were assessed for their neuroprotective activity against glutamate-induced toxicity in
PC12 cells and cytotoxic activity against 11 kinds of human tumor cells. This paper describes the
isolation, structure elucidation, and biological assays of these compounds.
2
. Results and Discussion
The EtOH extract of the stem of D. aurantiacum var. denneanum was suspended in water and
successively partitioned with EtOAc and n-BuOH. Separation of the n-BuOH fraction by column
chromatography provided compounds 1–7 (Figure 1). The known compounds 2–7 were identified as
(
−)-syringaresinol-4,4'-bis-O-β-D-glucopyranoside (2) [8], syringaresinol-4'-O-D-monoglucopyranoside
3) [9], shashenoside I (4) [10], syringin (5) [11], 1-[4-(β-D-glucopyranosyloxy)-3,5-dimethoxyphenyl]-1-
(
propanone (6) [12], and vicenin-2 (7) [13] by comparing their spectroscopic data with those reported in
the corresponding literature.
Figure 1. Structures of compounds 1–7.
OMe
OMe
OH
OH
7
'
9'
OH
OH
OH
1
'''
5'''
MeO 5'
OH
O
O
O
O
HO
1
'
O
O
8'
HO
OH
4
'''
O
O
OMe
OH
O
OMe
9
3'
OMe
H
H
8
H
H
7
MeO
O
MeO
HO
5
O
HO
1''
MeO
O
1
HO
HO
O
O
OHOH
OH
3
5''
O
OH
HO
HO
OMe
OMe
3''
HO
HO
OH
OMe
HO
1
OH
OH
3
HO
HO
HO
2
OH
HO
O
O
O
O
O
MeO
HO
O
O
MeO
O
OH
OH
O
HO
HO
O
HO
HO
HO
O
O
HO
HO
O
OH
HO
HO
OMe
OMe
HO
OH
OH
OH
OMe
HO
OH
HO
7
4
5
6
−1
Compound 1 was obtained as a colorless gum, and the presence of OH (3,374 cm ) and aromatic
−
1
(
48 19
1,588 and 1,502 cm ) groups were indicated by its IR spectrum. The molecular formula of C34H O
+
1
was indicated by a HRESIMS peak at m/z 783.2681 [M+Na] . The H-NMR spectrum of 1 (Table 1)
showed signals attributable to two symmetrically 1,3,4,5-tetrasubstituted aromatic rings at δ 6.77

Molecules 2013, 18
6155
(H-2', 6') and 6.72 (H-2, 6), together with two six-proton aromatic methoxy singlets at δ 3.78 and 3.73.
Signals for two olefinic methines and an oxymethylene at δ 6.59 (d, J = 16.0 Hz, H-7'), 6.35 (dt,
J = 16.0, 6.0 Hz, H-8'), 4.43 (dd, J = 13.0, 6.0 Hz, H-9'a), and 4.20 (dd, J = 13.0, 6.0 Hz, H-9'b)
suggested the presence of a trans-arylpropenoxy unit. In addition, an arylpropanediyloxy unit was
indicated by signals of a vicinal coupling system attributed to two oxymethines at δ 5.11 (d, J = 3.5
Hz, H-7) and 4.27 (H-8), and an oxymethylene at δ 3.59 (H-9a) and 3.17 (H-9b). Two diagnostic
doublets attributed to anomeric protons at δ 4.34 (d, J = 7.5 Hz, H-1'') and 4.22 (1H, d, J = 8.0 Hz,
H-1'''), together with partially overlapped signals assigned to oxymethylene and oxymethine protons
13
between δ 3.00 and 3.70, suggested the presence of two β-glycopyranosyl units in 1 [14]. The C-NMR
and DEPT spectra of 1 revealed carbon signals corresponding to the above units and quaternary
aromatic carbons (Table 1). These spectroscopic features suggested that 1 was a syringylglycerol-8-O-
13
4
'-sinapyl alcohol ether (SGSE) β-diglucopyranoside [15]. Comparison of the C-NMR data of 1 with
those of erythro-SGSE showed that the resonances for C-7 and C-9' in 1 were deshielded significantly
by Δδ +6.0 and +6.7 ppm, whereas the C-1, C-8, and C-8' resonances were shielded by Δδ −4.5, −2.6,
and −3.7 ppm, respectively. This revealed that two β-glycopyranosyl units were attached to C-4 and C-9',
which was further confirmed by the HMBC correlations of H-1'' with C-4 and H-1''' with C-9' (Figure 2).
1
13
6
Table 1. H- (500 MHz) and C-NMR (125 MHz) data of 1 (in DMSO-d , δ in ppm, J in Hz).
No.
1
δ
H
δ
C
No.
1''
δ
H
δ
C
–
129.8
106.1
148.2
135.6
148.2
106.1
79.5
4.34 d (7.5)
3.18 m
103.1
75.2
77.8
71.1
78.3
62.1
–
2
6.72 s
2''
3
–
3''
3.06 m
4
–
4''
3.03 m
5
–
5''
3.02 m
6
6.72 s
6''a
3.66 (overlapped)
3.41 (overlapped)
4.22 d (8.0)
3.00 m
7
5.11 d (3.5)
6''b
8
4.27 m
85.0
1'''
103.2
74.5
77.4
70.9
77.9
61.9
9
a
3.59 m
61.2
2'''
9
b
3.17 m
–
3'''
3.13 m
1
'
'
'
'
'
'
'
'
–
133.1
104.8
153.7
136.7
153.7
104.8
132.2
126.8
69.6
4'''
3.12 m
2
6.77 s
5'''
3.23 m
3
4
5
6
7
8
–
–
6'''a
6'''b
3/5-OMe
3'/5'-OMe
3.62 (overlapped)
3.40 (overlapped)
3.73 s
–
57.0
57.0
6.77 s
3.78 s
6.59 d (16.0)
6.35 dt (16.0, 6.0)
4.43 dd (13.0, 6.0)
4.20 dd (13.0, 6.0)
9
'a
'b
9
–
Enzymatic hydrolysis of 1 produced the aglycone 1a and a sugar, which was further identified as
20
D-glucose by the positive optical rotation ([α] +45.5) [16–18] and TLC comparison with an authentic
D
1
sugar sample. Comparison the H-NMR and HREIMS data of 1a with those of known
8
,4'-oxyneolignane led characterization of 1a as erythro-SGSE [15]. The CD spectra of 1 and 1a

Molecules 2013, 18
6156
showed negative Cotton effects at 235 nm (Δε −0.18) and 239 nm (Δε −0.22), respectively, indicating
an 8R configuration for 1 and 1a [18–20]. Thus, compound 1 was determined to be (−)-(7S,8R,7'E)-4-
hydroxy-3,3',5,5'-tetramethoxy-8,4'-oxyneolign-7'-ene-7,9,9'-triol 7,9'-bis-O-β-D-glucopyranoside.
Figure 2. Key HMBC correlations of 1.
OH
MeO
OH
O
O
OH
HO
OH
O
OMe
O
MeO
HO
O
HO
OH
OMe
HO
OH
The isolated compounds were assessed for their cytotoxic activity against 11 kinds of human tumor
cells, including the lung cancer cell lines H1975, H358 and A549, hepatocellular carcinoma cell lines
HepG-2 and SMMC7721, colorectal carcinoma cell line HCT116, mammary carcinoma cell lines
MDA-MB-231 and MCF-7, melanoma cell line A2058, pancreatic cancer cell line PANC-1, and acute
myeloid leukemia cell line MV4-11 in in vitro bioassays. Among them, compound 4 showed a selective
cytotoxic activity against acute myeloid leukemia cell line MV4-11, with the IC value of 4.17 μM.
5
0
Other compounds were inactive against the tested human tumor cells at the concentration of 10 μM.
In addition, the protective activity of the compounds against glutamate-induced neurotoxicity in
PC12 cells was evaluated by an MTT assay [18,21]. The results showed that glutamate induced an
inhibition of MTT reduction, while compounds 1 and 2 showed neuroprotective activity at a
concentration of 10 μM, with the relative protection of 25.7 ± 2.2% and 19.3 ± 5.6%, respectively
(
the positive control MK-801, 85.9 ± 3.2%). Thus, lignan glucosides 1 and 2 may be effective in
neurodegenerative disorders.
3. Experimental
3.1. General
NMR spectra were recorded on a INOVA-500 spectrometer. HRESIMS were measured with
Waters Synapt G
obtained on a Shimadzu UV-260 spectrophotometer. Optical rotations were measured with a Perkin-Elmer
41 plus. CD spectra were recorded on a JASCO J-815 CD spectrometer. Column chromatography
2
HDMS. IR were recorded on a Vector 22 FT-IR spectrometer. UV spectra were
3
was performed with silica gel (200–300 mesh, Yantai Institute of Chemical Technology, Yantai,
China) and Sephadex LH-20 (Amersham Pharmacia Biotech AB, Uppsala, Sweden). HPLC separation
was performed on an instrument consisting of a Cometro 6000LDS pump and a Cometro 6000PVW
UV/VIS detector with an Ultimate (250 × 10 mm) preparative column packed with C (5 μm).
1
8
3
.2. Plant Material
The stem of Dendrobium aurantiacum var. denneanum was collected in April of 2011 from a
culture field in Shuangliu, Sichuan Province, China. Plant identity was verified by Prof. Min Li

Molecules 2013, 18
6157
(
Chengdu University of TCM, Sichuan, China). A voucher specimen (SSF-20110410) was deposited
at the School of Pharmacy, Chengdu University of TCM, Chengdu, China.
3.3. Extraction and Isolation
The air-dried stem of D. aurantiacum var. denneanum (10 kg) was 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 H O (2.5 L) and then
2
successively partitioned with EtOAc and n-BuOH (6 × 2.5 L). The n-BuOH extract (110 g) was
applied to a D-101 macroporous adsorbent resin (1.5 Kg) column. Successive elution of the column
with H O, 10% EtOH, 30% EtOH, 50% EtOH, and 95% EtOH (4 L each) yielded five portions. The
2
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 H
2
O to give eight fractions (A-H). Fraction 7
(
185 mg) was precipitated from the fraction D in MeOH. Subsequent separation of fraction F (6.5 g)
over Sephadex LH-20 eluted with MeOH−H O (1:1) gave five subfractions (F −F ). Subfraction F
2
1
5
2
was further fractionated via silica gel CC, eluting with CHCl
3
−MeOH (8:1), to yield six fractions
O) yielded 1 (6.5 mg)
O, 3:7), and then purified
O), to yield 4 (31 mg). Subfraction F was fractioned
by silica gel CC, eluting with a gradient of increasing MeOH (5−50%) in CHCl , to afford seven
fractions (F4-1−F4-7). F4-3 was purified by RP preparative HPLC (35% MeOH in H
(F
2-1−F2-6). Separation of F2-2 with RP semipreparative HPLC (37% MeOH in H
and 2 (38.0 mg). F2-5 was further separated by Sephadex LH−20 (MeOH−H
by RP semipreparative HPLC (34% MeOH in H
2
2
2
4
3
2
O) to afford 3
(
9 mg), 5 (36 mg), and 6 (11 mg).
(
−)-(7S,8R,7'E)-4-hydroxy-3,3',5,5'-tetramethoxy-8,4'-oxyneolign-7'-ene-7,9,9'-triol
7,9'-bis-O-β-D
2
0
glucopyranoside (1): White gum, [α] = −12.2 (c = 0.20, MeOH); IR (KBr) νmax: 3374, 2920, 1588,
D
−1
1
502, 1462, 1420, 1331, 1226, 1124, 1071, 1023, 835, 706, 615 cm ; UV (MeOH) λmax (log ε): 204
(
4.35), 226 (4.03, sh), 271 (3.67) nm; CD (MeOH): 222 (Δε +0.16), 235 (Δε −0.18), 251 (Δε +0.03),
+
+
2
66 (Δε −0.12), 290 (Δε +0.23) nm; ESI-MS m/z 783 [M+Na] ; HRESI-MS: m/z 783.2681 [M+Na]
1
13
(
calcd for C34
H
48
O
19Na, 783.2687); H- and C-NMR data see Table 1.
3
.4. Enzymatic Hydrolysis of 1
A solution of compound 1 (2 mg) in H O (10 mL) was hydrolyzed with β-glucosidase (15 mg) at
2
3
7 °C for 96 h. The reaction mixture was extracted with EtOAc (3 × 10 mL) to yield the individual
EtOAc extract and H
preparative TLC eluted with MeCN−H
D-glucose by the sign of its positive optical rotation. The EtOAc extracts were purified by preparative
2
O phase after removing the solvents. The aqueous phases were subjected to
2
O (8:1) to yield the sole sugar, which could be identified as
2
D
0
TLC using CHCl
3
-MeOH (12:1) to afford 1a (0.2 mg): [α] = +13.2 (c = 0.02, MeOH); CD (MeOH)
1
2
21 (Δε +1.25), 239 (Δε −0.22), 270 (Δε +0.43) nm; H-NMR (CD
3
OD, 500 MHz) δ: 6.76 (2H, s,
H-2', 6'), 6.68 (2H, s, H-2, 6), 6.55 (1H, d, J = 16.0 Hz, H-7'), 6.38 (1H, dt, J = 16.0, 6.0 Hz, H-8'),
4
.99 (1H, d, J = 3.5 Hz, H-7), 4.27 (2H, d, J = 6.0 Hz, H
2
-9'), 4.19 (1H, m, H-8), 3.88 and 3.83
+
(
each 6H, s, OMe-3, 5, 3', 5'), 3.87 (1H, m, H-9a), 3.48 (1H, m, H-9b); ESI-MS m/z: 459 [M+Na] ;
+
HR-ESI-MS m/z: 459.1624 [M+Na] (calcd for C22
H
28
O
9
Na, 459.1631).

Molecules 2013, 18
.5. Cell Culture and Assessment of Cytotoxic Activity against Human Tumor Cells
The human lung cancer cell lines H1975, H358 and A549, human hepatocellular carcinoma cell
6158
3
lines HepG-2 and SMMC7721, human colorectal carcinoma cell line HCT116, human mammary
carcinoma cell lines MDA-MB-231 and MCF-7, human melanoma cell line A2058, human pancreatic
cancer cell line PANC-1, human acute myeloid leukemia cell line MV4-11 were obtained from the
American Type Culture Collection (ATCC) and grown in RPMI1640, DMEM or IMDM containing
3
3
1
0% fetal bovine serum (v/v) in 5% CO at 37 °C. Cells (2 × 10 –10 × 10 ) were seeded in 96-well
2
plates and cultured for 24 h, followed by the test compounds treatment at concentrations of 0.625–20 µM
for 72 h. After the culture period, 20 µL of MTT (5 mg/mL) was added per well and incubated for 4 h
at 37 °C, then 50 μL of 20% acidified SDS was used to lyse the cells. Finally, absorbance was
measured at 570 nm using a microplate reader. Each assay was replicated three times. The effect of the
compounds on tumor cells viability was calculated and expressed by IC of each cell line.
5
0
3
.6. Cell Culture and Assessment of Neuroprotective Activity
3
PC12 cells at a density of 5 × 10 cells per well in 96-well plates were suspended in Dulbecco’s
Modified Eagle’s Medium (DMEM, Gibco) media supplemented with 5% fetal bovine serum (FBS,
Hyclone) and 5% horse serum, penicillin (100 IU/mL), streptomycin (100 μg/mL), and L-glutamine
(
2 μM) and incubated in a CO incubator (5%) at 37 °C for 24 h. The cells were pre-treated with test
2
compounds and MK-801 for 1 h, respectively, and then exposed to glutamate (50 μM). After
incubation for an additional 24 h, MTT (0.5 mg/mL) was added to the medium and incubated for 4 h.
Absorbance was measured at 570 nm using a microplate reader, the cell viability was evaluated by
relative protection, which was calculated as 100 × [optical density (OD) of test compound +
glutamate-treated culture − OD of glutamate-treated culture]/[OD of control culture − OD of
glutamate-treated culture].
4
. Conclusions
Several Dendrobium species are not only ornamental plants, but are also used as Traditional
Chinese Medicines. To search for bioactive natural products from the botanical drugs, we carried out
an examination of the n-BuOH soluble portion of the ethanolic extract of the stems of D. aurantiacum
var. denneanum. A new 8,4'-oxyneolignane 7-O-glucoside, (−)-(7S,8R,7'E)-4-hydroxy-3,3',5,5'-
tetramethoxy-8,4'-oxyneolign-7'-ene-7,9,9'-triol 7,9'-bis-O-β-D-glucopyranoside (1) was isolated,
together with two 7,9':7',9-diepoxylignan glucosides 2−3, four phenylpropanoid glycosides 4−6 and a
flavone C-glycoside 7. The results showed that the types of compounds of D. aurantiacum var.
denneanum were similar to other species of Dendrobium, including D. chrysanthum, D. loddigesii,
D. nobile, D. moniliforme, D. trigonopus, and D. aphyllum. Previous phytochemical studies of these
species have also led to the isolation of lignans [22–27], phenylpropanoids [28], and flavonoids [26,27].
However, to fully elucidate the systematic correlation of these Dendrobium plants, further
phytochemical investigations are necessary. In addition, it deserves to be mentioned that most of the
lignans from Dendrobium plants were 7,9':7',9-diepoxylignans, while 8,4'-oxyneolignans were rarely
reported. To the best of our knowledge, in Dendrobium 8,4'-oxyneolignans have been only reported

Molecules 2013, 18
6159
from D. chrysanthum so far, which implied chemotaxonomic significance between D. aurantiacum
var. denneanum and D. chrysanthum. In the in vitro assays, compounds 1 [(−)-(7S,8R,7'E)-4-hydroxy-
3
,3',5,5'-tetramethoxy-8,4'-oxyneolign-7'-ene-7,9,9'-triol 7,9'-bis-O-β-D-glucopyranoside] and
(−)-syringaresinol-4,4'-bis-O-β-D-glucopyranoside] showed neuroprotective activity in PC12 cells, while
(shashenoside I) had selective cytotoxic activity against the acute myeloid leukemia cell line MV4-11.
2
[
4
Acknowledgments
Financial support from the National Technology R&D Program for the “Twelfth Five-Year” Plan of
China (grant No. 2011BAI13B02-8) is acknowledged.
Conflict of Interest
The authors declare no conflict of interest.
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