Two new neolignan glycosides from Pittosporum glabratum Lindl.

Article abstract of DOI:10.1016/j.phytol.2012.01.003

Two new neolignan glycosides, named pittogoside A (1) and pittogoside B (2) were isolated from the roots of Pittosporum glabratum Lindl. Their structures, including the absolute stereochemistry, were determined on the basis of spectroscopic analysis and chemical evidence, with combination of circular dichroism.

Full text of DOI:10.1016/j.phytol.2012.01.003

Phytochemistry Letters 5 (2012) 240–243
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Phytochemistry Letters
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Two new neolignan glycosides from Pittosporum glabratum Lindl.
1
1
*
Huanxin Zhao , Tiantian Nie , Huanjie Guo, Jun Li, Hong Bai
Institute of Materia Medica, Shandong Academy of Medical Sciences, Jinan 250062, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Two new neolignan glycosides, named pittogoside A (1) and pittogoside B (2) were isolated from the
roots of Pittosporum glabratum Lindl. Their structures, including the absolute stereochemistry, were
determined on the basis of spectroscopic analysis and chemical evidence, with combination of circular
dichroism.
Received 15 November 2011
Received in revised form 19 December 2011
Accepted 5 January 2012
Available online 19 January 2012
ß 2012 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
Keywords:
Pittosporum glabratum Lindl.
Chemical constituents
Neolignan glycosides
1. Introduction
for two aromatic protons at dH 7.59 (2H, s) and a singlet for two
methoxyl groups at dH 3.71 (6H, s), which was supported by the
The roots of Pittosporum glabratum Lindl. (Pittosporaceae),
commonly called ‘‘Shan Zhi Gen’’ in Chinese, have been known for
its analgesic and antidotal activities in the folk medicine (Anon.,
1993). As part of our current interest in biologically active
compounds of folk medicine in China, we investigated the
chemical constituents of the roots of P. glabratum and reported
the isolation of two iridoid glycosides and five lignan glycosides
from its EtOH extract (Nie et al., 2011). Our continuing
phytochemical studies on this extract led to the isolation of two
new benzofuran-type neolignan glycosides, pittogosides A (1) and
B (2). In this paper, we reported the isolation and structural
elucidation of two new neolignan glycosides (Fig. 1).
corresponding carbon signals at dC 166.5, 148.4, 142.5, 120.1, 107.9
and 55.9 in the 13C NMR spectrum (Jung et al., 2004; Yang et al.,
2006). Except for the signals due to a glucopyranose unit and a
syringoyl group, the remaining 21 carbons were assignable to the
aglycone. Taking account of the 15 degree of unsaturation
calculated from the molecular formula of 1, it was suggested that
the aglycone of 1 should have at least two aromatic rings. The 1
NMR data of the aglycone moiety showed a set of characteristic
signals due to dihydrobenzofuran at H 6.04 (1H, d, J = 6.6 Hz) and
H 3.85 (1H, m), a set of signals due to n-propanol group at H 3.89
(1H, t, J = 6.6 Hz), 2.83 (1H, t, J = 7.8 Hz) and 2.05 (1H, m), four
aromatic proton signals at H 7.03 (2H, s), 7.01 (1H, s) and 6.89 (1H,
s), two hydroxymethyl protons at H 4.23 (1H, m) and 4.17 (1H, m),
and three methoxy groups at H 3.62 (6H, s) and 3.80 (3H, s) (Table
H
d
d
d
d
d
d
2. Results and discussion
1). Two partial structures of the aglycone (C-7 to C-9 and C-70 to C-
90) were deduced from the detailed analyses of the 1H–1H COSY
spectrum of 1 (Fig. 2). Interpretation of the HMBC spectral data led
to the connections of the above-described structural units and
quaternary carbons to construct the whole structure of the
aglycone. The HMBC correlations from dH 6.89 (H-20) to dC
Pittogoside A (1) was obtained as a white amorphous powder.
The molecular formula was determined to be C36H44O16 by HRESI-
MS (m/z 755.2528 [M+Na]+, calcd for 755.2522). The IR spectrum
suggested the presence of hydroxyl group (3340 cmꢀ1), carbonyl
group (1705 cmꢀ1) and aromatic ring (1599 and 1515 cmꢀ1).
136.1 (C-10), 144.4 (C-30), 146.9 (C-40) and 117.2 (C-60),
60) to C 146.9 (C-40), 129.5 (C-50) and 54.9 (C-8), and
(H-9) to
C 129.5 (C-50) indicated the connectivity of rings A and B
(Fig. 2). The other aromatic ring, namely ring C and its linkage was
suggested by the HMBC correlations from H 7.03 (H-2 and H-6) to
d
H 7.01 (H-
Enzymatic hydrolysis of 1 afforded
D-glucose, which was identified
d
dH 4.23, 4.17
by HPLC analysis of its 1-[(S)-N-acetyl-
a
-methylbenzylamino]-1-
d
deoxyglucitol acetate derivative (Oshima et al., 1982). The
b-
anomeric configuration for glucose was determined by its large 3JH-
d
coupling constant value (6.6 Hz). Analysis of the 1H NMR
1,H-2
dC 139.0 (C-1), 153.9 (C-3 and C-5), 135.0 (C-4) and 87.7 (C-7).
Three methoxy groups were assigned to be located in C-3, C-5 and
C-30 by the correlations between their protons and chemical shift
assigned carbons of C-3, C-5 and C-30. In addition, a hydroxypropyl
group was attached at C-10 on the basis of the correlation from dH
spectrum showed the presence of a syringoyl group due to a singlet
* Corresponding author. Tel.: +86 531 8291 9971; fax: +86 531 8261 5996.
E-mail address: baihong@gmail.com (H. Bai).
2.83 (H-70) to C 136.1 (C-10). The relative stereochemistry of H-7
d
1
These authors contributed equally to this work.
1874-3900/$ – see front matter ß 2012 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.phytol.2012.01.003

H. Zhao et al. / Phytochemistry Letters 5 (2012) 240–243
241
Fig. 1. Structures of compounds 1 and 2.
Table 1
1H (600 MHz) and 13C NMR (150 MHz) data of 1 in C5D5N and 2 in CD3OD.
Position
1
Position
2
dH
dC
dH
dC
1
2
3
4
5
6
7
8
9
139.0
104.3
153.9
135.0
153.9
104.3
87.7
1
2
3
4
5
6
7
8
9
121.8
110.5
147.8
147.5
115.1
120.6
155.6
131.9
60.3
7.03 (s)
7.53 (d, 1.8)
6.95 (d, 8.0)
7.03 (s)
6.04 (d, 6.6)
3.85 (m)
4.23a
7.45 (dd, 8.0, 1.8)
54.9
64.0
5.10 (d, 12.0)
4.97 (d, 12.0)
4.17a
10
136.1
113.3
144.4
146.9
129.5
117.2
32.4
10
20
30
40
50
60
70
80
90
138.0
107.3
144.7
141.2
110.0
110.8
32.0
20
6.89 (s)
6.78 (s)
30
40
50
60
7.01 (s)
7.22 (s)
70
2.83 (t, 7.8)
2.05 (m)
2.80 (t, 7.2)
1.94 (m)
80
35.8
34.6
90
3.89 (t, 6.6)
61.2
3.63 (t, 6.6)
60.8
100
120.1
107.9
148.4
142.5
166.5
56.2
200, 600
300, 500
400
7.59 (s)
700
3,5-OCH3
30-OCH3
300,500-OCH3
Glc-1
Glc-2
Glc-3
Glc-4
Glc-5
Glc-6
3.62 (s)
3-OCH3
30-OCH3
3.99 (s)
4.02 (s)
55.3
55.0
3.80 (s)
55.8
3.71 (s)
55.9
5.71 (d, 6.6)
4.35a
104.7
75.7
Glc-1
Glc-2
Glc-3
Glc-4
Glc-5
Glc-6
4.50 (d, 7.8)
3.33a
101.3
73.8
76.7
70.3
76.7
61.4
4.35a
77.9
3.33a
4.23a
71.4
3.33a
4.17a
75.5
3.33a
5.14 (br.d, 12.0)
5.00 (dd, 12.0, 6.0)
64.8
3.95 (dd, 11.7, 1.8)
3.77 (dd, 11.7, 6.0)
a
Overlapped.
3
and H-8 was established as trans relationship based on the JH-7,
H-8 coupling constant (6.6 Hz) (Yuan and Li, 2003; Matsuda et al.,
1996). Thus, the structure of the aglycone of 1 was concluded as
5-methoxy-dihydrodehydrodiconiferyl alcohol (1a) (Chin et al.,
2008), which was obtained by enzymatic hydrolysis. It was worth
mentioning that enzymatic hydrolysis of 1 with cellulase gave
2010) and a desyringoyl derivative of 1 (5-methoxy-dihydrode-
hydrodiconiferyl alcohol-4-O- -glucopyranoside, 1c) (Wang
b
-D
et al., 2010) (Scheme 1), which were identified by the 1H NMR
and ESI-MS data. To determine the absolute configuration of the
aglycone, circular dichroic method was applied. As a negative
cotton effect at 244 nm (De = ꢀ0.61) was observed, 7R and 8S
configurations were indicated (Matsuda et al., 1996; Iida et al.,
not only 1a and D-glucose, but also syringic acid (1b) (Xu et al.,
2010; Lemiere et al., 1995). The
C-4 of the aglycone by the HMBC correlation from
1) to C 135.0 (C-4) and the location of syringoyl group at C-6 of
-glucopyranose was deduced by the correlation from H 5.14,
5.00 (Glc-H-6) to dC 166.5 (C-700). Based on the above evidences,
b
-
D
-glucopyranose was linked to
d
H 5.71 (Glc-H-
d
b
-
D
d
the structure of
1 was established as (7R,8S)-5-methoxy-
dihydrodehydrodiconiferyl alcohol-4-O-(600-O-syringoyl)-
b-D-
glucopyranoside.
Pittogoside B (2) was obtained as a yellow amorphous power. It
exhibited [M+Na]+ ion peak at m/z 543.1839 (calcd for 543.1837) in
HRESI-MS, corresponding to the molecular formula C26H32O11. The
IR spectrum suggested the presence of hydroxyl group (3340 cmꢀ1),
Fig. 2. 1H–1H COSY and key HMBC correlations of compound 1.

242
H. Zhao et al. / Phytochemistry Letters 5 (2012) 240–243
Scheme 1. Enzymatic hydrolysis of compound 1.
carbonyl group (1705 cmꢀ1
)
and aromatic ring (1604 and
-glucose as a
b-anomeric configuration for glucose was
100 mM. In this experiment, the results indicated that antioxidant
1514 cmꢀ1). On enzymatic hydrolysis, 2 afforded
D
activities were closely related with the structural type of the lignans:
aryltetralin lignans (3–6) showed antioxidant activities whereas
neolignans (1 and 2) and furofuran lignan (7) showed no activities.
component sugar. The
3
determined by its large JH-1,H-2 coupling constant (7.8 Hz). In
comparison of the NMR data of the aglycone of 2 with those of 1, the
signals due to ring A were superimposable, while some differences
were observed for rings B and C. The absence of two methenyl
3. Experimental
carbons at
olefinic carbons at
benzofuran lignan instead of dihydrobenzofuran lignan. In addition,
the proton signals observed at 7.53 (1H, d, J = 1.8 Hz), 7.45 (1H, dd,
J = 8.0, 1.8 Hz) and 6.95 (1H, d, J = 8.0 Hz) indicated the ABX
substitution type of ring C. The placement of two methoxy groups
was confirmed by the HMBC correlations from d
H 4.02 (30-OCH3) to
dC 144.7 (C-30) and dH 3.99 (3-OCH3) to dC 147.8 (C-3). Thus, the
structure of the aglycone of 2 was determined to be 7-en-
dihydrodehydrodiconiferyl alcohol (2a), which was obtained by
enzymatic hydrolysis. The NMR data of 2a was in accord with that of
a known compound, 4-[3-(hydroxymethyl)-5-(3-hydroxypropyl)-
7-methoxy-1-benzofuran-2-yl]-2-methoxyphenol, isolated from
the bark of Abies sachalinensis (Wada et al., 2009). The connection
d
87.7 and 54.9, coupled with the appearance of two
3.1. General
d
155.6 and 131.9, suggested that 2 was a
The UV spectra were obtained with a Hitachi U-3000 spectropho-
tometer, whereas the IR spectra were measured with a Thermo
Nicolet 670 FT-IR (by a KBr disk method) spectrometer. Specific
rotation was measured on high-precision digital automatic polarim-
eter (Kerncher, Germany), while the CD spectra were recorded on an
d
Applied Photophysics Chirascan spectropolarimeter. The 1H and 13
C
NMR spectra were recorded on Bruker Avance-600 spectrometer
with TMS as the internal standard. The ESI-MS were taken on an
Agilent Trap VL mass analyzer and the HRESI-MS were taken on a
Thermo Scientific LTQ Orbitrap XL mass spectrometer. Preparative
HPLC was performed on Agilent 1100 apparatus, equipped with a
G1314A Variable Wavelength Detector and YMC-Pack RP-C18
column (150 mm ꢂ 20 mm, i.d.). Column chromatography was
carried out using silica gel (200–300 mesh, Qingdao Marine Chemical
Factory, Qingdao, China), Sephadex LH-20 (Amersham Biosciences,
Sweden), Diaion HP-20 (20–60 mesh, Mitsubishi Chemical Holdings
of
HMBC correlation from
the above evidences, the structure of 2 was established as 7-en-
dihydrodehydrodiconiferyl alcohol-9-O- -glucopyranoside.
b-D-glucopyranose at C-9 of the aglycone was deduced by the
d
H 4.50 (Glc-H-1) to C 60.3 (C-9). Based on
d
b-D
Recent studies showed that lignan glycosides exhibited antioxi-
dant activity (Yang et al., 2009; Sadhu et al., 2007; Zhang et al., 2008).
Therefore, pittogosides A and B (1 and 2), and five lignan glycosides
isolated previously from P. glabratum Lindl (Nie et al., 2011), (+)-
CO., Kyoto, Japan) and ODS (50 mm, YMC Co. Ltd., Kyoto, Japan).
3.2. Plant material
lyoniresinol-3a-O-(600-3-methoxy-4-hydroxybenzoyl)-
pyranoside (3), lyoniresinol-3a-O- -glucopyranoside (4), (+)-
lyoniresinol-3a-O-(600-3,5-dimethoxy-4-hydroxybenzoyl)-
-glu-
copyranoside (5), (ꢀ)-4-epi-lyoniresinol-3a-O- -glucopyranoside
(6) and syringaresinol-4,40-bis-O-
-glucopyranoside (7), were
evaluated for their antioxidant activities by 1,1-diphenyl-2-picryl-
hydrazyl (DPPH) radical scavenging assay. Compounds 3–6 showed
antioxidant activities with IC50 values of 35.3 ꢁ 2.3, 35.7 ꢁ 0.5,
47.4 ꢁ 4.3 and 75.1 ꢁ 7.7 mM, as compared to the activity of edaravone,
which was used as a positive control (32.8 ꢁ 2.8 mM). Two new
compounds (1 and 2) and a known lignan glycoside (7) were inactive at
b-D
-gluco-
The roots of P. glabratum Lindl. were collected from Sichuan
Province, People’s Republic of China, in September 2009, and
identified by one of the authors B. H. A voucher specimen (No.
PG200909) has been deposited at the Department of Natural
Products Chemistry, Institute of Materia Medica, Shandong Acade-
my of Medical Sciences, Jinan, China.
b
-D
b-D
b-D
b-D
3.3. Extraction and isolation
The air-dried roots of P. glabratum (12 kg) were extracted with
75% EtOH three times. Evaporation of the aqueous alcohol solution

H. Zhao et al. / Phytochemistry Letters 5 (2012) 240–243
243
under reduced pressure gave the EtOH extract (1065 g). The extract
3.5. Absolute configuration of sugars in compounds 1 and 2
was suspended in H2O and partitioned successively with EtOAc
and n-BuOH. The EtOAc extract (91 g) was subjected to silica gel
column chromatography (CC) and eluted with a gradient of CHCl3–
MeOH to give 7 fractions (Fr.A–Fr.G). Further isolation of Fr.D (28 g)
was achieved by repeated silica gel CC, Sephadex LH-20 CC and
preparative HPLC to give compound 1 (9 mg). The n-BuOH extract
(198 g) was loaded on Diaion HP-20 column and eluted with 0%,
30%, 60% and 90% EtOH to obtain four fractions. The 30% EtOH
eluate (39 g) was separated by silica gel CC with a gradient of
CHCl3–MeOH to give 10 fractions (Fr.I–Fr.X). Fr.VII (5 g) was
fractionated by repeated silica gel, Sephadex LH-20, ODS CC and
preparative HPLC to give compound 2 (5 mg).
The sugar fraction obtained by enzymatic hydrolysis was
dissolved in 1 ml H2O, to which (S)-(ꢀ)- -methylbenzylamine
(17 l) and NaBH3CN (8 mg) in EtOH (1 ml) was added. After being
stirred at 40 8C for 4 h followed by addition of glacial acetic acid
(0.2 ml) and evaporated to dryness, the resulting solid was
acetylated with acetic anhydride (0.3 ml) in pyridine (0.3 ml) for
24 h at room temperature. After evaporation, H2O (1 ml) was added
a
m
to the residue and the solution was passed through a Cleanert C18
SPE column(Agela)withH2O, 20% and 50% CH3CN(15, 15and 10 ml)
as solvents. The 50% CH3CN eluate, the 1-[(S)-N-acetyl- -methyl-
-
a
benzylamino]-1-deoxyglucitol acetate derivative, was then ana-
lyzed by HPLC under the following conditions: Column, Agilent SB-
Pittogoside A (1): White amorphous power. [
MeOH:H2O 4:6). IR (KBr):
lmax (MeOH:H2O 4:6) nm (log
(3.44). HRESI-MS (positive) m/z: 755.2528 [M+Na]+ (calcd for
36H44O16Na 755.2522). 1H NMR (600 MHz, C5D5N) and 13C NMR
a
]
20 = ꢀ9.0 (c 0.9,
D
n
max: 3340, 1705, 1599, 1515 cmꢀ1. UV
C18 (4.6 mm ꢂ 250 mm, 5
0.8 ml/min; detection, DAD detection, 230 nm. The identification of
-glucose or -glucose present in the sugar faction was carried outby
a comparison of retention times of their derivatives with those of the
authenticsamples:tR (min)22.36(derivativeof -glucose)and20.67
(derivative of -glucose). -Glucose was detected from 1 and 2.
mm); solvent, 40% CH3CN; flow rate,
e
): 206 (4.28), 243 (sh, 3.39), 279
D
L
C
(150 MHz, C5D5N) data see Table 1.
Pittogoside B (2): Yellow amorphous powder, [a D
0.5, MeOH). IR(KBr):
(MeOH) nm (log
D
]
20 = ꢀ22.1 (c
L
D
n
max: 3340, 1705, 1604, 1514 cmꢀ1. UV lmax
e
): 216 (4.21), 306 (4.04). HRESI-MS (positive) m/z:
Acknowledgement
543.1839 [M+Na]+ (calcd for C26H32O11Na 543.1837). 1H NMR
(600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD) data see Table 1.
This project was supported by Key Laboratory for Rare and
Uncommon Diseases of Shandong Province.
3.4. Enzymatic hydrolysis of compounds 1 and 2
Appendix A. Supplementary data
A solution of 1 (4.8 mg) and 2 (3.1 mg) in 1 ml H2O was treated
with cellulase (Sigma Chemical Co., 20 mg and 15 mg) and then the
mixture was stirred at 40 8C for 112 h and 96 h. The reaction
mixture was suspended in H2O, then extracted successively with
CHCl3, EtOAc and BuOH for 1 and extracted with EtOAc for 2. The
organic layers were evaporated or purified by pre-HPLC to give 1a
(1.0 mg), 1b (0.3 mg), 1c (0.2 mg) and 2a (0.1 mg), respectively.
The aqueous layers of 1 and 2 were concentrated under reduced
pressure to give the sugar fractions.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.phytol.2012.01.003.
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lignans from Dryopteris fragrans (L.) Schott. Chin. Tradit. Herbal Drugs 39, 343–
346.
(sh, 3.38), 282 (2.75). CD (c = 2.41 ꢂ 10ꢀ4 mol/l, MeOH) De ꢀ0.21
(248 nm). ESI-MS (positive) m/z: 575 [M+Na]+. 1H NMR (600 MHz,
CD3OD) d
: 6.76 (2H, s, H-2, 6), 6.77 (1H, s, H-60), 6.73 (1H, s, H-20),
5.59 (1H, d, J = 6.0 Hz, H-7), 3.47 (1H, m, H-8), 3.89 (1H, dd, J = 11.0,
4.8 Hz, H-9a), 3.78 (1H, dd, J = 11.0, 7.8 Hz, H-9b), 3.90 (3H, s,
30-OCH3), 3.84 (6H, s, 3, 5-OCH3), 2.64 (2H, t, J = 7.2 Hz, H-70), 1.83
(2H, m, H-80), 3.58 (2H, t, J = 6.6 Hz, H-90), 4.90 (1H, overlapped,
Glc-H-1), 3.78 (1H, dd, J = 12.0, 2.4 Hz, Glc-H-6a), 3.67 (1H, dd,
J = 12.0, 5.4 Hz, Glc-H-6b), 3.30–3.35 (4H, overlapped, Glc-H-2,
3, 4, 5).
7-en-Dihydrodehydrodiconiferyl alcohol (2a): ESI-MS (posi-
tive) m/z: 381 [M+Na]+. 1H NMR (600 MHz, CD3OD)
d: 7.49 (1H, d,
J = 1.8 Hz, H-2), 7.36 (1H, dd, J = 8.0, 1.8 Hz, H-6), 6.94 (1H, d,
J = 8.0 Hz, H-5), 7.14 (1H, s, H-60), 6.77 (1H, s, H-20), 4.85 (2H, s, H-
9), 4.03 (3H, s, 30-OCH3), 3.97 (3H, s, 3-OCH3), 3.63 (2H, t, J = 6.6 Hz,
H-90), 2.80 (2H, t, J = 7.8 Hz, H-70), 1.93 (2H, m, H-80).