Morusalbanol a, a neuro-protective Diels-Alder adduct with an unprecedented architecture from Morus alba

Article abstract of DOI:10.1016/j.tet.2012.05.017

Morusalbanol A (1), a neuro-protective Diels-Alder adduct with a new carbon skeleton, was isolated from the bark of Morus alba. Compound 1 showed evidence of interesting astropisomerism, and resulted in the absence of a number of key proton and carbon signals in the NMR spectra. Its structure was thus elucidated by spectroscopic analysis of its peracetylated derivative (2) and its absolute configuration established as 1S,3S,4R,5S via experimental and calculated ECD spectra of 1. In a neuro-protective assay, morusalbanol A (1) significantly attenuated the H₂O₂-induced cell damage in a dose-dependent manner.

Full text of DOI:10.1016/j.tet.2012.05.017

Tetrahedron 68 (2012) 6054e6058
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Morusalbanol A, a neuro-protective DielseAlder adduct with an unprecedented
architecture from Morus alba
Hua-Dong Chen a, Yuan-Qing Ding b, Sheng-Ping Yang a, Xing-Cong Li b, Xu-Jie Wang a, Hai-Yan Zhang a,
,
Daneel Ferreira b, Jian-Min Yue a
*
a State Key Laboratory of Drug Research, Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 555 Zuchongzhi Road, Zhangjiang
Hi-Tech Park, Shanghai 201203, PR China
b National Center for Natural Products Research, Research Institute of Pharmaceutical Sciences, and Department of Pharmacognosy, School of Pharmacy, The University of Mississippi,
University, MS 38677, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Morusalbanol A (1), a neuro-protective DielseAlder adduct with a new carbon skeleton, was isolated
from the bark of Morus alba. Compound 1 showed evidence of interesting astropisomerism, and resulted
in the absence of a number of key proton and carbon signals in the NMR spectra. Its structure was thus
elucidated by spectroscopic analysis of its peracetylated derivative (2) and its absolute configuration
established as 1S,3S,4R,5S via experimental and calculated ECD spectra of 1. In a neuro-protective assay,
morusalbanol A (1) significantly attenuated the H2O2-induced cell damage in a dose-dependent manner.
ꢀ 2012 Elsevier Ltd. All rights reserved.
Received 2 March 2012
Received in revised form 24 April 2012
Accepted 4 May 2012
Available online 12 May 2012
Keywords:
Morus alba
Natural products
Morusalbanol A
Absolute configuration
Neuro-protective activity
1. Introduction
R
17
The plant Morus alba L. (Moraceae) is widely distributed in
China.1 and its bark has been used in Traditional Chinese Medicine
(TCM) to purge lung-fire, relieve dyspnea, promote dieresis, and
lower blood pressure.2 Previous chemical investigations on M. alba
led to the identification of an array of isoprenoid-substituted phe-
nolics,3 organic acids,4 sugars,5 and alkaloids.6 In particular, the
isoprene-substituted flavanone derivatives exhibit a variety of
significant biological activities. These derivatives are presumably
DielseAlder adducts of a chalcone and isoprenylflavanone moie-
ties.7 In the current study, a DielseAlder adduct, morusalbanol A (1)
(Fig. 1), with an unprecedented carbon skeleton, was isolated from
the bark of M. alba. Morusalbanol A (1) showed evidence of
astropisomerism, and resulted in the absence of a number of key
proton and carbon signals in the NMR spectra. Its peracetylated
derivative 2 was thus used for the structural assignment of 1. In the
neuro-protective activity bioassay, morusalbanol A (1) at 2.5, 5, and
19
13
R
6
D
7
15
CH3
1
R
5
A
O
O
2B
21
E
R
8
4
27
11
9
3
O
H
23
O
C
R
R
25
1 R = OH
2 R = OAc
2. Results and discussion
2.1. Structural elucidation
10 mM significantly attenuated the H2O2-induced cell damage in
a dose-dependent manner. We report herein the isolation, struc-
tural elucidation, and neuro-protective activity of compound 1.
Morusalbanol A (1), a yellow powder, gave the molecular for-
mula C28H26O10 as determined by HRESIMS at m/z 545.1423
[MþNa]þ (calcd for C28H26O10Na, 545.1424) and 13C NMR data. The
UV maxima at 201, 221, 276, and 312 nm, and IR absorptions at
3384, 1608, 1452, and 1146 cmꢀ1 suggested the presence of similar
* Corresponding author. Tel./fax: þ86 21 50806718; e-mail address: jmyue@
mail.shcnc.ac.cn (J.-M. Yue).
0040-4020/$ e see front matter ꢀ 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.05.017

H.-D. Chen et al. / Tetrahedron 68 (2012) 6054e6058
6055
chromophores and functional groups as those of cathayanon A.7d
However, several proton and carbon resonances were absent in
the 1H and 13C NMR spectra recorded at room temperature in
methanol-d4 (two proton and seven carbon resonances not visible)
and DMSO-d6 (two proton and four carbon resonances not visible).
When the spectra were recorded in DMSO-d6 at 353 K, one proton
and one carbon resonance were still invisible (Table 1). These NMR
phenomena were most likely caused by astropisomerism of 1 in
solution. Thus, compound 1 was acetylated with acetic anhydride
dC 78.2 (C-1) and the downfield shifted olefinic carbon resonance at
dC 157.0 (C-22) suggested their linkage via an ether bond to form
the B-ring. This was confirmed by a weak but key HMBC correlation
4
between H3-7 and C-22 (also a W-type long-range JCH coupling).
The six O-acetyl groups could only be placed at C-10, C-12, C-16, C-
18, C-24, and C-26, respectively. The planar structure of 2 was thus
fully defined and represented an unprecedented carbon skeleton.
The relative configuration of 2 was determined by analysis of the
coupling constants (Table 1) and the NOESY spectrum (Fig. 2). The
large coupling constant (11.8 Hz) between H-4 and H-5 clearly in-
dicated their trans-diaxial arrangement. The small coupling con-
stant (3.0 Hz) between H-3 and H-4 showed their cis-orientation
with H-3 in an equatorial position. In the NOESY spectrum (Fig. 2),
in pyridine to give compound 2 that gave well-resolved 1H and 13
C
NMR spectra. Comparison of the 13C NMR data (Fig. 1) of rings AeE
of compounds 1 and 2 showed high consistency, indicating that the
carbon skeleton and stereochemistry of 1 were kept unchanged in
the acetylation. Further analysis of the spectroscopic data (Table 1)
of compound 2 revealed that it is the peracetylated derivative of 1.
the correlations of H-2
and H-6 indicated that they were cofacial, and randomly assigned
in a -orientation. This analysis also revealed that rings A and B
b/H-4, H-4/H-3, H-4/H-6b, and H3-7/H-2b,
b
b
adopted chair-like and half-chair conformations, respectively. The
relative configuration of 2 is consistent with those of the Diel-
seAlder cisetrans adducts via endo-addition from Moraceous
plants.8
1
2
220
200
180
160
140
120
100
80
Theoretical calculation of the electronic circular dichroism
(ECD) spectrum9 was applied to determine the absolute configu-
ration of compound 1. The arbitrarily assigned 1S,3S,4R,5S absolute
configuration was chosen for a systematic conformational random
search by using the MMFF94 method in Sybyl 8.1. Thirty-one con-
formers were found by molecular mechanics force-field calculation
with an energy cut-off of 15 kcal/mol. The first seven conformers
within the energy cut-off of 5 kcal/mol were included for the full
geometry optimization at the B3LYP/6-31G** level in the gas phase.
Four conformers, 1ae1d (Fig. 3), were relocated with a Boltzman
distribution of 91.8, 3.2, 0, and 4.9%, calculated by relative energy
with zero point energy (ZPE) in the gas phase (Table 2). All four
conformers adopt a chair and half-chair conformations for the A-
and B-rings, respectively (Fig. 3), the only differences being the
orientation of the D-ring and the C-23 methoxycarbonyl group.
Such conformations plausibly explain the experimentally observed
NOE correlations. Next, the ECD spectra of individual conformers
were calculated by using time-dependent density functional theory
(TDDFT) at the B3LYP/6-311þþG**//B3LYP/6-31G** level in the gas
phase. Using the predominant conformer 1a, the experimentally
observed strong positive Cotton effect (CE) in the 280e350 nm
region is attributed to the electronic transitions at 304 and 352 nm
(Fig. 4), the positive CE (shoulder) at 275 nm by the transitions at
264, 260, and 254 nm, and the negative CE at 234 nm by the
transitions at 233 and 228 nm. The overall consistency of the cal-
culated and experimental ECD spectra supports the absolute con-
figuration of 1 as 1S,3S,4R,5S.
60
40
20
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Carbon No.
Fig. 1. Comparison of the 13C NMR data of stereogenic centers of 1 and 2.
Compound 2 was obtained as colorless powder, ½a D23
ꢁ þ30 (c 0.03,
MeOH), and its HRESIMS data at m/z 797.2000 [MþNa]þ and 13C
NMR data corresponded to the molecular formula C40H38O16 (calcd
for C40H38O16Na, 797.2058) requiring 22 degrees of unsaturation.
Its 1H and 13C NMR spectra (Table 1) indicated, besides the proton
and carbon resonances attributable to six O-acetyl and an O-
methoxyl groups, the presence of a keto carbonyl and an ester
carbonyl groups, three aromatic rings (two ABX systems and
a pentasubstituted ring), a methyl, two sp3 methylene, three sp3
methine, and an oxygenated sp3 quaternary carbon (dC 78.2 s). Two
ABX systems corresponding to the D- and E-rings were readily
recognized by 1H NMR, 1He1H COSY, and HMBC spectra (Fig. 2). A
proton coupling network from H-2 to H-6 revealed by the 1He1H
COSY spectrum was further supported by the HMBC correlations
from H3-7 to C-1, C-2, and C-6 (Fig. 2), indicating the presence of
a tetrasubstituted methylcyclohexane ring, which was different
from the trisubstituted methylcyclohexene core of cathayanon A.7d
The presence of a 2,3,4,6-tetrasubstituted methyl benzoate moiety
(ring C) was revealed by the NMR data (Table 1) and the HMBC
correlations. The methoxycarbonyl group was attached at C-23 by
the chemical shift at dC 114.0 and a weak HMBC correlation be-
tween H-25 and C-27 (a W-type long-range protonecarbon cou-
pling), which was supported by the well matched NMR data of the
ring C of 1 versus those of the similar 2,3,4,5,6-pentasubstituted
patterns of benzene moieties found in sanggenols L and M,7a and
cathayanons A and B.7d Furthermore, the HMBC correlations of H-
14/C-8, H-4/C-8, and H-4/C-9 connected A- and E-rings via the C-8
keto group; the HMBC correlations from H-5 to C-15 and C-16 at-
tached D-ring to C-5; and the HMBC correlations from both H-3 and
H-4 to C-21 linked A- and C-rings via the C-3eC-21 bond. The A-, C-,
D- and E-rings and the six O-acetyl groups accounted for 21 out of
the 22 degrees of unsaturation in 2; the remaining one required the
presence of an additional ring. The quaternary carbon resonance at
Computationally calculated conformations of compound
1
(Fig. 3) permitted a better understanding of the astropisomerism
observed in the measurement of its NMR spectra. The absence of
a number of proton (H-3 and H-5) and carbon (C-3, C-4, C-5, C-6, C-
15, C-16, and C-20) resonances in methanol-d4 at ambient tem-
perature presumably resulted from interconversions of several
astropisomers due to the rotational hindrance of the D/E-rings
about the C-5eC-15 and C-4eC-8eC-9 bonds. The intramolecular
hydrogen bonding between the C-8 carbonyl group and the C-16
and C-26 hydroxy groups may also significantly contributed to the
rotational restrictions. This hindered rotation was slightly relieved
in DMSO-d6 (resonances of H-3 and H-5 and C-3, C-5, C-15, and C-
20 were absent). At an elevated temperature (353 K), the H-5 and C-
5 were still invisible (Table 1). Principally, there are two methods to
ameliorate the adverse NMR effects of hindered rotation, i.e., to
induce free rotation by temperature elevation, or to completely
inhibit rotation by temperature decrease or to increase the bulk of
substituents close to the axis in order to prevent conformational
exchange. When the NMR spectra of 1 were acquired at 353 K in

6056
H.-D. Chen et al. / Tetrahedron 68 (2012) 6054e6058
Table 1
1H and 13C NMR data of compounds 1 and 2
No.
1a
1b
1c
2a
dC
dH (pattern, J/Hz)
dC
dH (pattern, J/Hz)
dC
75.5
dH (pattern, J/Hz)
dC
dH (pattern, J/Hz)
1
2
77.8
75.6
78.2
37.2
2.24 (dd, 12.0, 2.7)
35.2
2.27 (brd, 12.0)
35.2
2.26 (dd, 12.8, 2.3)
1.75 (d, 12.8)
4.37 (d, 2.3)
36.3
1.92 (ddd, 13.5, 2.8, 2.6)
2.39 (dd, 13.5, 2.8)
3.68 (dt, 3.0, 2.8)
4.24 (dd, 11.8, 3.0)
3.48 (ddd, 13.0,11.8, 4.2)
2.07 (ddd, 13.5, 4.2, 2.6)
1.77 (dd, 13.5, 13.0)
1.41 (s)
1.74 (d, 12.0)
1.61 (brd, 12.0)
d
d
d
d
d
d
d
d
3
4
5
6
49.8
30.3
33.1
56.8
30.7
47.8
3.63 (2.7)
30.4
49.6
28.3
3.51 (brd)
3.51 (d, 2.4)
d
d
d
d
2.11 (br s)
1.40 (s)
1.98 (br s)
1.29 (s)
45.5
2.05 (brd, 13.0)
1.75 (brd, 13.0)
1.34 (s)
7
29.5
28.1
26.6
197.7
114.8
156.3
120.2
152.9
121.3
133.1
134.4
150.6
118.0
151.0
121.0
129.1
114.8
157.0
114.0
149.8
109.4
151.8
167.2
53.2
8
9
206.7
115.8
166.9
104.1
165.9
109.0
204.2
113.4
164.1
102.3
163.8
107.5
204.0
113.5
164.0
102.3
163.6
107.4
131.7
120.5
155.2
102.7
155.7
105.9
127.9
101.5
157.4
95.9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
CH3O
AcO
6.18 (2.6)
6.14 (d, 2.7)
6.18 (d, 2.4)
6.98 (d, 2.4)
6.39 (dd, 8.9, 2.6)
7.94 (d, 8.9)
6.39 (dd, 8.7, 2.7)
8.06 (br s)
6.41 (dd, 8.9, 2.4)
8.01 (d, 8.9)
7.19 (dd, 8.7, 2.4)
8.16 (d, 8.7)
133.4
131.9
d
d
d
155.3
102.3
155.7
104.6
157.7
6.17 (d, 2.3)
6.12 (d, 2.6)
6.17 (d, 2.4)
6.79 (d, 2.4)
108.2
6.11 (dd, 8.4, 2.3)
6.80 (d, 8.4)
105.8
5.95 (dd, 8.3, 2.6)
6.73 (br s)
6.02 (dd, 8.3, 2.4)
6.74 (d, 8.3)
6.81 (dd, 8.3, 2.4)
7.24 (d, 8.3)
d
d
101.5
160.7
96.1
164.8
95.1
162.7
173.9
52.5
101.4
157.2
96.2
159.4
93.3
159.4
169.8
51.7
159.8
93.4
159.4
169.8
51.2
5.78 (s)
3.85 (s)
5.77 (s)
3.74 (s)
5.81 (s)
3.79 (s)
6.50 (s)
3.86 (s)
2.28 (s)
2.21 (s)
2.20 (s)
2.20 (s)
2.18 (s)
1.51 (s)
171.5
171.4
171.3
170.6
170.6
170.4
21.4
21.3
21.3
21.1
20.8
14.9
a
In methanol-d4.
b
c
In DMSO-d6 at 298 K.
In DMSO-d6 at 353 K.
Signals invisible.
d
DMSO-d6, the H-5 and C-5 resonances were still missing, indicating
that this temperature was not sufficient to overcome the rotational
restrictions. The second strategy was thus pursued by acetylation of
1 to yield the per-O-acetyl derivative 2, which gave well-resolved
1H and 13C NMR spectra (Table 1) at ambient temperature.
Fig. 3. Optimized geometries of predominant conformers of 1 at the B3LYP/6-31G*
level in the gas phase.
Fig. 2. Selected 1He1H COSY (▬), HMBC (H/C) and NOESY correlations (4) of 2.

H.-D. Chen et al. / Tetrahedron 68 (2012) 6054e6058
6057
Table 2
CO2CH3
OH
Conformational analysis of compound 1 in the gas phase
HO
oxidative degradation
and methylation
HO
HO
O
OH
a
b
c
c
Ea
PE%b
D
E0
PE
%
D
Ga
PG%b
D
E00
0
00
PE %
Species
D
1a
1b
1c
1d
0.00
1.66
5.05
1.77
90.0
5.5
0.0
0.00
1.98
4.94
1.73
91.8
3.2
0.0
0.00
2.09
4.29
1.51
90.3
2.7
0.1
0.00
1.31
3.88
1.63
85.1
9.3
0.1
OH
ii
OH
OH
i
4.5
4.9
7.0
5.5
HO
a
Relative energy, relative energy with ZPE, and relative Gibbs free energy at the
B3LYP/6-31G** level in the gas phase, respectively (kcal/mol).
OH
OH
HO
HO
b
HO
Conformational distribution calculated by using the respective parameters
above at the B3LYP/6-31G** level in the gas phase.
D-A endo addition
OH
c
Relative energy (kcal/mol) and conformational distribution at the B3LYP/6-
OH
OH
311þþG**//B3LYP/6-31G** level in the gas phase, respectively.
HO
O
O
O
OH
CO2CH3
HO
HO
O iii
ii
OH
iv
+ H+/ −H+
5
60
HO
OH
HO
CH3
0
0
O
O
O
H
HO
O
-60
HO
OH
-5
1
200
240
280
320
360
400
Scheme 1. Plausible biogenetic pathway proposed for morusalbanol A (1).
λ
/ nm
Fig. 4. Experimental (blue, in MeOH) and calculated ECD spectra of compound 1 at the
B3LYP/6-311þþG**//B3LYP/6-31G** level in the gas phase: black, weighted; red, cal-
culated rotatory strengths of predominant conformer 1a; and olive, simulated ECD
curve of predominant conformer 1a.
IR spectra were recorded on a PerkineElmer 577 spectrometer with
KBr disks. NMR spectra were acquired on a Bruker AM-400 spec-
trometer. EIMS (70 eV) were carried out on a Finnigan MAT 95 mass
spectrometer. ESIMS and HRESIMS were obtained on an Esquire
3000plus (Bruker Daltonics) and a Waters-Micromass Q-TOF Ultima
Global electrospray mass spectrometer, respectively. Silica gel
A possible biosynthetic pathway toward the formation of 1 was
postulated in Scheme 1. Oxidative degradation and methylation of
a prenylated chalcone-type compound i would give key precursor
ii. DielseAlder endo-addition of ii with another chalcone-type
compound iii would produce intermediate iv as cisetrans adduct.
This is similar to the mechanism proposed for the formation of
a number of DielseAlder-type adducts isolated from Morus plants
via coupling of a chalcone moiety with a prenylated flavonoid de-
rivative.8 The intermediate iv would be susceptible to acid-
catalyzed regio- and stereo-selective intramolecular cyclization to
form compound 1.10
The cell protecting activityagainst H2O2-induced PC12 cell damage
of 1, was evaluated according to the reported protocol11 with minor
modification. After exposure to 300 mM H2O2, cell viability as de-
termined by MTTreductionwas markedly decreased to67%(##P<0.01
vs control). However, pretreatment with compound 1 at 1, 2.5, 5, and
10
mM significantly attenuated the H2O2-induced cell damage
(**P<0.01 vs H2O2 group) in a dose-dependent manner (Fig. 5).
3. Conclusions
The discovery of a major component morusalbanol A (1) from
the bark of Morus alba, a common traditional Chinese medicine
(TCM), is much important for the TCM standardization and quality
control. Morusalbanol A, a DielseAlder adduct of new carbon
skeleton showed the evidence of astropisomerism and significant
neuro-protective activity, which might be the interesting topics for
both synthetic chemistry and pharmacology in the future.
4. Experimental section
4.1. General experimental procedures
Optical rotations were determined on a PerkineElmer 341 po-
larimeter, and CD spectra were obtained on a Jasco 810 spectrometer.
Fig. 5. Effects of morusalbanol A (1) on cell viability.

6058
H.-D. Chen et al. / Tetrahedron 68 (2012) 6054e6058
(200e300 mesh) (Qingdao Haiyang Chemical Co. Ltd.), C18 reverse-
phased silica gel (150e200 mesh, Merck), MCI gel (CHP20P,
where
s is the width of the band at 1/e height and DEi and Ri are the
excitation energies and rotatory strengths for transition i, re-
75e150
m
M, Mitsubishi Chemical Industries Ltd.) were used for col-
spectively. In this work,
s¼0.15 eV was used.
umn chromatography. All solvents used were of analytical grade
(Shanghai Chemical Plant, Shanghai, PR China).
4.5. Bioassay
Cells were incubated with 300 mM H2O2, and the cultures were
4.2. Plant material
developed for another 24 h in fresh medium. Compounds were
added to the cultures 2 h prior to H2O2 addition. Three independent
experiments were carried out in triplicate. All data were expressed
as percentage of the control value. Statistical comparison was made
by using one way ANOVA followed by Duncan’s test. The data are
expressed as meansþSEM; ##P<0.01 versus control; **P<0.01
versus H2O2 group.
The M. alba L. plant material was collected from Hunan Province
of the People’s Republic of China, and was authenticated by Pro-
fessor Zheng-Tao Wang of Shanghai University of Traditional Chi-
nese Medicine. A voucher specimen (accession number MAL-2004-
3Y) has been deposited in the Shanghai Institute of Materia Medica.
4.3. Extraction and isolation
Acknowledgements
The powder of the root bark of M. alba (2.5 kg) was extracted
with 95% EtOH at ambient temperature to give a dark crude extract
(300 g), which was partitioned between EtOAc and H2O. The EtOAc-
soluble portion (113 g) was subjected to column chromatography
on silica gel using petroleum ethereacetone mixtures of increasing
polarity. The fraction that eluted with petroleum ethereacetone
(3:1) was subjected to CC on MCI gel (MeOH/H2O, 4:6e9:1) to
obtain a major fraction (5.1 g), which was first separated over
a column of silica gel eluted with CHCl3/MeOH (20:1), and then the
major component (0.6 g) was purified by CC on RP-18 silica gel (50%
MeOH in H2O) to afford 1 (81 mg).
Financial support of the National Natural Science Foundation
(Grant No. 81021062; 20932007) of the People’s Republic of China
is gratefully acknowledged. This work was also supported in part by
the USDA Agricultural Research Service Specific Cooperative
Agreement No. 58-6408-2-0009. We thank Professor Z.-T. Wang,
Shanghai University of Traditional Chinese Medicine, for the iden-
tification of the plant material. We thank the Mississippi Center for
Supercomputing Research (MCSR) for computational facilities.
Supplementary data
4.3.1. Morusalbanol A (1). Yellow powder; ½a D23
ꢁ þ163 (c 0.12, MeOH);
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2012.05.017.
UV (MeOH) lmax (log ) 201 (4.59), 221 (4.55), 276 (4.42), 312
3
(3.99) nm; CD (MeOH)
275þ0.74, 281þ0.47,
D
3
ꢀ4.27,
D
3
225ꢀ0.86,
D
3
234ꢀ3.70,
206
D
3
D
3
D 3
309þ2.43; IR (KBr) nmax 3385, 2972, 1608,
References and notes
1510, 1443, 1321, 1242, 1157, 1095, 975, 806, 624 cmꢀ1; for 1H and 13
C
NMR data, see Table 1; positive ESIMS m/z 545.2 [MþNa]þ, 1067.3
[2MþNa]þ, negative ESIMS m/z 521.2 [MꢀH]ꢀ, 1043.4 [2MꢀH]ꢀ;
HRESIMS m/z 545.1423 [MþNa]þ (calcd for C28H26O10Na 545.1424).
1. Zhang, X. S.; Wu, Z. Y. Flora of China (Zhongguo Zhiwu Zhi); Science: Beijing,
1998; vol. 23, pp 6e9.
2. State Administration of Traditional Chinese Medicine. Chinese Herb (Zhong-
hua Bencao); Shanghai Science and Technology: Shanghai, 1999; vol. 2;
525e528.
3. (a) Nomura, T. Pure Appl. Chem. 1999, 71, 1115; (b) Nomura, T. Yakugak Zasshi
2001, 121, 535; (c) Du, J.; He, Z. D.; Jiang, R. W.; Ye, W. C.; Xu, H. X.; Paul, P. H.
Phytochemistry 2003, 62, 1235; (d) Deshpande, V. H.; Parthasarathy, P. C.;
Venkataramn, K. Tetrahedron Lett. 1968, 9, 1715.
4. Hatanaka, S. I.; Kaneko, S. Phytochemistry 1977, 16, 1041.
5. Asano, N.; Oseki, K.; Tomioka, E.; Kizu, H.; Matsui, K. Carbohydrate Res. 1994,
4.3.2. Preparation of compound 2. To a solution of pyridine (3 mL)
containing 8.0 mg of compound 1, 0.5 mL of acetic anhydride was
added. The mixture was stirred for 8 h at room temperature. After
removal of the solvents under reduced pressure, the residue was
purified by a silica gel column eluted with petroleum/EtOAc (4:1) to
259, 243.
give compound 2 (8.5 mg). Compound 2: white powder; ½a D23
ꢁ þ30 (c
6. Asano, N.; Yamashita, T.; Yasuda, K.; Ikeda, K.; Kizu, H.; Kameda, Y.; Kato, A.;
Nash, R. J.; Lee, H. S.; Ryu, K. S. J. Agric. Food Chem. 2001, 49, 4208.
7. (a) Shi, Y. Q.; Fukai, T.; Sakagami, H.; Chang, W. J.; Yang, P. Q.; Wang, F. P.;
Nomura, T. J. Nat. Prod. 2001, 64, 181; (b) Nomura, T.; Fukai, T.; Hano, Y.; Uzawa,
J. Heterocycles 1982, 17, 381; (c) Nomura, T.; Fukai, T.; Hano, Y.; Uzawa, J. Het-
erocycles 1981, 16, 2141; (d) Shen, R. C.; Lin, M. Phytochemistry 2001, 57, 1231.
8. Nomura, T.; Hano, Y. Nat. Prod. Rep. 1994, 11, 205.
9. (a) Diedrich, C.; Grimme, S. J. Phys. Chem. A 2003, 107, 2524; (b) Ding, Y.; Li, X.-
C.; Ferreira, D. J. Org. Chem. 2007, 72, 9010; (c) Ding, Y.; Li, X.-C.; Ferreira, D. J.
Nat. Prod. 2009, 72, 327; (d) Ding, Y.; Li, X.-C.; Ferreira, D. J. Nat. Prod. 2010, 73,
435.
0.03, MeOH); UV (MeOH) lmax (log ) 198 (4.74), 240 (4.03), 250
3
(4.06), 304 (3.83) nm; CD (MeOH)
D
3
204ꢀ0.42,
D
3
216ꢀ1.47,
D
3
285þ0.48; IR (KBr) nmax 3423, 2920, 1772, 1606, 1201, 1093 cmꢀ1
;
for 1H and 13C NMR data, see Table 1; positive ESIMS m/z 797.3
[MþNa]þ; HRESIMS m/z 797.2000 [MþNa]þ (calcd for C40H38O16Na
797.2058).
4.4. Methods of computational calculations
10. Dewick, P. M. Medicinal Natural Products: A Biosynthetic Approach, 2nd ed.; John
Wiley: Chichester, 2004, pp 175.
The theoretical calculations were performed by the SYBYL 8.1
program (Tripos International, St. Louis, MO) and the Gaussian03
program package.12 MMFF94 molecular mechanics force-field was
employed to search the possible conformations. All ground-state
geometries were optimized at the B3LYP/6-31G** level at 298 K, and
harmonic frequency analysis was computed to confirm the minima.
TDDFT at the B3LYP/6-311þþG**//B3LYP/6-31G** level in the gas
phase was employed to calculate excitation energy (in nm) and ro-
tatory strength R (velocity form Rvel and length form Rlen in 10ꢀ40 erg-
esu-cm/Gauss) between different states. The ECD spectra were sim-
ulated by overlapping Gaussian functions for each transition accord-
A
11. Wang, R.; Xiao, X. Q.; Tang, X. C. Neuroreport 2001, 12, 2629.
12. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.;
Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.;
Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J.
V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-
Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03,
Revision B. 02; Gaussian: Pittsburgh PA, 2003.
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