Gymnothelignans A-O: Conformation and absolute configuration analyses of lignans bearing tetrahydrofuran from gymnotheca chinensis

Article abstract of DOI:10.1021/jo301225v

Fifteen new lignans, gymnothelignans A-O (1-15), bearing tetrahydrofuran with variable conformations belonging to three potentially related skeletons were isolated from Gymnotheca chinensis Decne. The structures were elucidated by means of detailed spectroscopic analysis. Absolute configurations were assigned using X-ray single-crystal diffraction and chemical transformations. Moreover, by the homology, compounds 1-11 and eupomatilones were confirmed to have uniform R-configuration at C-5. However, a synthesized congener has long been mistaken as 5-epimer of eupomatilone-6. This work provides guidance for the absolute configuration establishment of the subeupomatilone family with trans-H-4-H-5 configuration.

Full text of DOI:10.1021/jo301225v

Article
pubs.acs.org/joc
Gymnothelignans A−O: Conformation and Absolute Configuration
Analyses of Lignans Bearing Tetrahydrofuran from Gymnotheca
chinensis
Dahai He,† Lisheng Ding,† Hongxi Xu,*,‡ Xinxiang Lei,§ Hongping Xiao,§ and Yan Zhou*,†
†Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization, Chengdu Institute of Biology, Chinese Academy of
Sciences, Chengdu 610041, People’s Republic of China
‡Shanghai University of Traditional Chinese Medicine, Shanghai 201203, People’s Republic of China
§Wenzhou University, Wenzhou 325035, People’s Republic of China
S
* Supporting Information
ABSTRACT: Fifteen new lignans, gymnothelignans A−O
(1−15), bearing tetrahydrofuran with variable conformations
belonging to three potentially related skeletons were isolated
from Gymnotheca chinensis Decne. The structures were
elucidated by means of detailed spectroscopic analysis.
Absolute configurations were assigned using X-ray single-
crystal diffraction and chemical transformations. Moreover, by
the homology, compounds 1−11 and eupomatilones were
confirmed to have uniform R-configuration at C-5. However, a synthesized congener has long been mistaken as 5-epimer of
eupomatilone-6. This work provides guidance for the absolute configuration establishment of the subeupomatilone family with
trans-H-4−H-5 configuration.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
Dried and powdered whole plants of G. chinensis were extracted
with ethanol at room temperature to give an extract, which was
suspended in H2O and extracted with petroleum ether and
ethyl acetate successively. The ethyl acetate extracts were
subjected to silica gel column chromatography followed by
reversed-phase HPLC to yield 15 new lignans and five known
compounds. Structures of these compounds were elucidated by
a combination of detailed spectroscopic analysis. The absolute
configurations were determined by X-ray single-crystal
diffraction and chemical conversions.
Gymnotheca chinensis Decne, as one of the endemic genera of
seed plants in China, is a perennial herb of Saururaceae. The
whole plants of G. chinensis have long been used as traditional
herbal medicine to treat contusions and strains. Little
phytochemical information about this genus is available except
for G. involucrata Pei.1 Our recent investigation on the
constituents of G. chinensis led to the isolation of 15 new
lignans (1−15), together with five known compounds
kaempferol-4′,7-dimethyl-3-O-glucoside (16),1 kaempferol-7-
methyl-3-O-glucoside (17),2,3 blumenol A (18),4 1-bisabolon
(19),5 and β-sitosterol (20).
The 15 new lignans, gymnothelignans A−O (1−15), bearing
tetrahydrofuran (THF) with variable conformations belonged
to three unusual lignan skeletons, namely, dibenzocyclooctene,
eupomatilone, and eupodienone. The latter two rare types were
only previously isolated from the Australian shrub Eupomatia
bennettii6,7 and E. laurina,8,9 respectively. Owing to their
attractive structures, there have been total syntheses of all of
the members of eupomatilones10−20 except eupomatilone-1.
The absolute configuration of eupomatilone-6 has only just
been recently proposed.16 Moreover, it was reported that
eupodienones could be rearranged to form dibenzocyclooctene
derivatives.9,21 Herein, we report the isolation, structural
elucidation, and relative and absolute configuration of these
compounds. We also explored the relationship between
eupomatilones and eupodienones.
Gymnothelignan A (1) was obtained as a colorless crystal. Its
molecular formula, C30H37NO9, was established by HRESIMS,
which requires 13 degrees of unsaturation. The IR (KBr)
spectrum showed absorption bands due to hydroxyl (3437
cm−1) and aromatic groups (1619, 1474 cm−1). The H and
1
13C NMR (Table 1) spectra displayed signals of three methoxy
groups, two secondary methyl groups, one methylenedioxy
group, five methylene groups, five methine groups, four sp2
carbons, and 10 non-hydrogenated carbons (assigned by
DEPT, Table 1).
1
The analyses of H−1H COSY and HMBC spectra (Figure
1) suggested that the gross structure has three subunits (units
A−C), as shown in Figure 2. The connection of C-1′ to C-1″
was deduced from the HMBC correlations of H-2″/6″ to C-1′
(it possesses an unusual doubly attached ring system which
Received: June 15, 2012
Published: September 4, 2012
© 2012 American Chemical Society
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and C was achieved by HMBC correlation of H-2 to C-8‴,
giving rise to the connection of C-2 to C-8‴ through an ether
bond. NOESY cross-peaks of H-2 to H-8‴ also supported the
connection of units B and C (Figure 2).
The stereochemistry of different substituent groups on the
THF (unit B) was designated using a NOESY experiment. The
cross-peaks of H-2/H3-7, H-5/H3-6, and H-4/3′ indicated that
H-2, H-5, H3-6, and H3-7 were cofacial. Likewise, H-3, H-4, and
units A and C were on the opposite face. The assignments were
also buttressed by vicinal coupling constant values of H-2−H-3
(2.1 Hz) and H-4−H-5 (7.7 Hz) when the dihedral angle of H-
2−H-3 took the value close to 90° and that of H-4−H-5 was
close to 180°. In the molecule, the bulky biphenyl group unit A
was in the equatorial position, whereas unit C was in the axial
position (Figure 3). On the basis of single-crystal Cu Kα X-ray
diffraction (Figure S84, Supporting Information), C-7 was
revealed to have α-orientation of the THF moiety. The
absolute stereochemistry of 1 was also determined (Flack
parameter, 0.2(3), calculated using 1217 Friedel pairs).23
Gymnothelignan A (1) was then assigned as (2S,3S,4R,5R)-
3,4-dimethyl-2-hydroxyl-5-(4″-hydroxyl-4′,5′-methylenedioxy-
6′,3″,5″-trimethoxylbiphenyl-2′-yl)tetrahydrofuranyl-8‴-oxo-
1‴-oxa-3‴-azaspiro[4.5]dec-2‴-enyl-2,8‴-ether .
Gymnothelignan B (2) had the same molecular formula of
1
C30H37NO9 of 1 by HRESIMS. The H and 13C NMR (Table
1) spectra indicated that it was a diastereoisomer of 1. By
1
comparing the H NMR spectra with those of 1, the signals of
H-6‴−H-10‴ were shifted (Δδ = −0.10 to −0.20), which
indicated that unit C at C-2 (unit B) of 2 should have α-
orientation because the bulk effects from unit A could be
substantially relieved (the alternative explanation that epime-
rization occurred at C-5 was less likely due to the chemical shift
of C-5 and bulk biphenyl group6). Moreover, the 13C NMR
chemical shift of C-2 was shifted (Δδ = −2.6), and the chemical
shift of C-5 was shifted (Δδ = +0.6) instead (it was probably a
result of epimerization occurring at C-2). Similarly, the signals
of C-3 (δC 40.8) and C-7 (δC 9.4) were shifted (Δδ = −3.4 and
−1.8, respectively). This indicated that epimerization(s)
occurred in the molecule.24 Correlation observed in the
NOESY (Figure 2) spectrum of H-2/H3-7 suggested that H-
2 and H3-7 were cofacial. The similar correlation of H-4/H-3′,
which was also observed in the molecule of 1, was indicative of
H-4 being in the β-orientation. Similarly, H-5 and H3-6 were on
the opposite face. Obviously, epimerizations occurred at C-2
and C-3 in comparison to 1. Since the vicinal coupling
constants of H-2−H-3 and H-4−H-5 took moderate value (4−
5 Hz), the conformation of the THF moiety should be a result
of interconversion of two conformational isomers (conformers
1 and 2, Figure 3). In summary, the structure of 2 was
determined to be the 2,3-bisepimer of 1.
Gymnothelignans C (3) and H (8) only differed from unit C
by a methyl group at C-2 based on the HRESIMS and NMR
data analyses (Table 1 for 3, Tables 2 and 3 for 8). The
structure of unit C of 3 was established by comparing its 13C
NMR with that of 2. The main seco-lignan part was assigned as
follows (take 8 for example). Correlations of H-2/H-3, H-3/H-
3′, and H-5/H-4 were observed in the NOESY spectrum
(Figure S36, Supporting Information). This showed that H-2,
H-3, H3-6, and biphenyl were cofacial, whereas H-4, H-5, H3-7,
and 2-OCH3 were on the opposite face. The method
aforementioned was applied for the determination of THF
(Figure 3). Except for 2-OCH3, all of the substituents were in
the equatorial position. The configuration of 8 was finally
exhibits hindered rotation about the biaryl bond6). The
correlations of 3″-OCH3 to C-3″ and 5″-OCH3 to C-5″
positioned the two methoxy groups to C-3″ and C-5″,
respectively. In addition, a hydroxyl group was connected to
C-4″ by analysis of the chemical shift of C-4″, which was shifted
(Δδ = −12.4 and −12.3, respectively) in comparison with those
of C-3″ and C-5″. The presence of a methylenedioxy group was
assigned by the HMBC correlations of OCH2O to C-4′ and C-
5′, as well as H-3′ to C-4′ and C-5′. Similarly, a methoxy group
at C-6′ was also assigned. Thus, the gross structure of unit A
1
was proposed as shown in Figure 1. In unit B, the H−1H
COSY cross-peaks revealed the sequential connections of C-2−
C-7. This was also supported by the HMBC correlations of H-2
to C-7 and H-5 to C-6. The downfield chemical shifts revealed
that C-2 and C-5 were both oxygenated. HMBC correlations of
H-2/C-5 and H-5/C-2 displayed the connection of C-2 to C-5
via an ether bond. The 13C NMR chemical shift of C-2 (δC
108.6) was indicative of a ketal or hemiketal. In unit C, the
sequential connections of C-6‴−C-10‴ were confirmed by the
1H−1H COSY spectrum. HMBC correlations of H-4‴ at δH
2.80 to C-2‴/6‴/10‴ as well as those of H-2‴ at δH 7.12 to C-
4‴/C-5‴ are in association with the relatively downfield 13C
NMR chemical shifts22 of C-2‴ and C-4‴, and HRMS
confirmed that an oxazoline ring fused with a cyclohexanol at
C-5‴.
The connection of C-2′ (unit A) to C-5 (unit B) was
established by the analyses of HMBC correlations of H-5 to C-
1′ and C-3′, and H-3′ to C-5. The connection between units B
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a
Table 1. NMR Data for Compounds 1−3 (CD3COCD3)
1
2
3
no.
δC, mult
δH
δC
δH
δC
δH
2
108.6, CH
44.2, CH
44.1, CH
84.3, CH
12.2, CH3
11.2, CH3
137.1, C
4.86 d (2.1)
106.0
40.8
5.21 d (4.7)
104.1
42.7
5.17 d (3.9)
b
b
b
3
2.15 m
2.38 m
1.82 m*,
b
b
b
4
2.35 m
44.1
2.01 m
47.2
1.79 m*,
5
4.51 d (7.7)
0.71 d (7.0)
0.79 d (7.3)
84.9
4.56 d (4.3)
0.74 d (7.2)
0.90 d (7.2)
79.4
5.07 d (8.1)
0.69 d (6.5)
0.94 d (6.4)
6
15.5
16.5
7
9.4
12.8
2′
3′
4′
5′
6′
1′
1″
2″
3″
4″
5″
6″
137.7
101.6
149.4
137.0
141.8
128.8
127.6
110.0
148.5
135.9
148.3
108.3
102.0
60.1
134.4
103.1
149.0
136.9
141.8
128.8
127.8
109.4
148.5
135.9
148.3
108.1
102.0
60.1
103.0, CH
149.3, C
7.03 s
6.69 s
6.63 s
136.6, C
141.5, C
129.7, C
127.4, C
110.0, CH
148.3, C
6.42 d (1.7)
6.45 d (1.7)
6.44 br s
6.40 br s
135.9, C
148.2, C
108.4, CH
102.1, CH2
60.1, CH3
56.8, CH3
56.7, CH3
146.5, CH
46.2, CH2
84.1, C
6.45 br s
6.43 br s
6.01, 2H, br s
3.75 s
OCH2O
6′-OCH3
3″-OCH3
5″-OCH3
2‴
6.03, 6.01, each 1H, d (1.0)
6.01, 6.00, each 1H, br s
3.74 s
3.74 s
3.82 s
56.8
3.82 s
56.7
3.81 s
3.81 s
56.7
3.82 s
56.7
3.81 s
7.12 t (1.7)
2.80 d (1.7)
146.5
46.5
7.09 br s
146.5
46.4
7.09 br s
2.69 dd (1.7)
4‴
5‴
2.69 d (1.4)
83.8
83.9
6‴
7‴
8‴
9‴
32.9, CH2
28.3, CH2
73.0, CH
30.3, CH2
33.0, CH2
1.62−2.02 m*
1.62−2.02 m*
32.6
1.52−1.82 m*
1.52−1.82 m*
3.70 m
32.7
1.51−1.82 m*
1.51−1.82 m*
3.71 m
28.3
28.6
b
b
b
3.81 m*,
72.6
72.5
1.62−2.02 m*
1.62−2.02 m*
30.3
1.52−1.82 m*
1.52−1.82 m*
30.3
1.51−1.82 m*
1.51−1.82 m*
10‴
32.7
32.8
a
Spectra recorded at 600 MHz for H NMR and 150 MHz for 13C NMR. Chemical shifts (δ) are in ppm and coupling constants (J) in Hz.
1
b
*
Assigned by H−1H COSY. Signals overcharged.
1
1
Figure 1. Key H−1H COSY and HMBC correlations supporting the
structures of units A−C and their final assembly into gymnothelignan
A.
confirmed by single-crystal X-ray diffraction (Figure S85,
Supporting Information). The relative stereochemistry was
thus determined as 2R*,3S*,4S*,5R*.
Gymnothelignan D (4) was found to have the molecular
formula C24H32O8 by HRESIMS. The 1H and 13C NMR
spectra (Table 4) were very similar to those of 1 except for the
OCH3 replacing unit C at C-2. Single-crystal25 X-ray diffraction
(Figure S86, Supporting Information) revealed that 4 had two
conformers (conformers 4a and 4b, Figure 3) on the THF
moiety, but only a single conformer in solution (acetone) was
observed. The chemical shifts values of H-2 and H-5 in
acetone-d6 were distinguishable, and the vicinal coupling
constants of H-4−H-5 (9.9 Hz) and H-2−H-3 (0 Hz) were
Figure 2. Key NOESY spectra of compounds 1 and 2.
in favor of the conformation of THF in 4 (conformer 4b,
Figure 3) when dihedral angle of H-4−H-5 was near 180° and
that of H-2−H-3 was near 90°. Finally, the absolute
configuration was established by single-crystal X-ray diffraction,
as (2S,3S,4R,5R)-3,4-dimethyl-2-methoxyl-5-(4″-hydroxyl-
4′,5′,6′,3″,5″-pentamethoxylbiphenyl-2′-yl)THF.
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Table 3. 13C NMR Data for Compounds 6−9 and 11
a
(Acetone-d6)
no.
6
7
8
9
11
2
111.5
44.0
108.2
40.4
106.2
42.6
104.3
44.1
105.9
44.0
3
4
44.4
44.3
46.6
45.1
44.6
5
84.1
84.9
79.5
83.8
84.3
6
11.8
15.2
16.2
12.2
11.8
7
11.3
9.1
12.5
11.2
11.4
2′
3′
4′
5′
6′
1′
1″
2″
3″
4″
5″
6″
137.2
102.8
149.5
136.3
141.4
130.1
127.4
110.1
148.2
135.9
148.1
108.5
55.0
137.7
101.4
149.3
136.9
141.9
128.5
127.5
110.0
148.5
135.9
148.4
108.3
54.9
134.3
102.9
148.9
136.9
141.7
128.6
127.5
109.3
148.5
135.9
148.2
108.2
54.5
137.0
103.4
149.3
137.1
141.4
129.5
127.6
110.2
148.3
135.9
148.2
108.5
137.3
102.8
149.5
136.1
141.5
130.2
127.4
110.0
148.3
135.9
148.1
108.5
b
b
Figure 3. Conformations of THF in compounds 1−15.
2-OCH3
OCH2O
6′-OCH3
3″-OCH3
102.1
60.1
102.0
60.1
102.0
60.1
102.0
60.1
56.8
56.8
102.1
60.1
56.7
56.7
Gymnothelignan E (5) was assigned as a diastereomer of 4
by comparing its HRESIMS and NMR (Table 4) with those of
4. The 13C NMR chemical shifts of C-2 (δC 108.3) and C-3 (δC
40.3) shifted (Δδ = −3.3 and −3.9, respectively) in comparison
to that of 4, indicating that epimerization(s) had occurred in
the molecule. Characteristic NOESY (Figure S24, Supporting
Information) cross-peaks of H-2/H3-7, H3-7/H-4, 2-OCH3/H-
5, and H-3/5 distinctly confirmed the proposed relative
stereochemistry structure of 5. The vicinal coupling constants
(H-2−H-3 and H-4−H-5) along with the relative configuration
of different substituents on the THF suggested that THF had
two interconvertible conformers (Figure 3). Henceforth, the
structure of 5 was elucidated as the 2,3-bisepimer of 4.
Gymnothelignans F (6) and G (7) had the same molecular
formulas as 8, as shown by HRESIMS. The NMR spectra
(Tables 2 and 3) revealed that 6, 7, and 8 were diastereomers.
Both 6 and 7 demonstrated trans-H-4−H-5 configuration by
comparing their 13C NMR chemical shifts of C-5 with that of 4
(the alternative explanation that the γ-gauche interaction26 had
been substantially relieved by comparing the 13C NMR
56.8
56.7
56.7
5″-OCH3
56.7
56.8
56.7
a
Spectra recorded at 150 MHz. Chemical shifts (δ) are in ppm.
Signals may be exchangeable.
b
chemical shifts of C-2′ with that of 8, in which C-2′ was
shielded by C-6 when it demonstrated cis-H-4−H-5). NOESY
(Figures S28 and S32, diagnostic cross-peaks of H-2/H3-7, H-
4/H-3′, H-5/H3-6, and 2-OCH3/H-3′ for 6, H-2/H3-7/H-4, H-
4/H-3′, and H-5/H3-6 for 7; Supporting Information) and
vicinal coupling constants (H-2−H-3 and H-4−H-5) allowed
the assignment of relative stereochemistry and conformation of
THF (Figure 3). Compounds 6 and 7 were subsequently
established to be the 2,4- and 3,4-bisepimer of 8, respectively.
Gymnothelignans I (9) and J (10) were found to be
demethyl analogues of 6 and 4, respectively, based on the
HRESIMS and NMR data (Tables 2, 3, and 4) analyses, with
major differences in the 13C NMR chemical shifts of C-2.
a
1
Table 2. H NMR Data for Compounds 6−9 and 11 (Acetone-d6)
no.
6
7
8
9
11
2
4.55 s
4.97 d (4.9)
4.91 d (4.4)
5.04 d (1.3)
5.07 br s
b
b
b
b
b
,
c
,
3
2.15 m
2.35 m
1.97 m
1.86 m *
2.02 m *
2.36 m
b
b
b
c
,
4
2.36 m
1.82 m *
5.01 d (8.6)
0.69 d (6.9)
0.91 d (6.6)
6.64 s
2.34 m
2.47 m
5
4.53 d (8.9)
0.72 d (7.0)
0.76 d (7.3)
6.86 s
4.54 d (4.2)
0.64 d (7.2)
0.84 d (7.2)
6.68 s
4.48 d (8.0)
0.69 d (7.0)
0.77 d (7.3)
7.16 s
4.55 d (8.9)
0.79 d (6.9)
0.85 d (7.3)
6.91 s
6
7
3′
2″
6″
2-OCH3
OCH2O
6′-OCH3
6.42 d (1.6)
6.45 d (1.7)
3.38 s
6.42 d (1.7)
6.45 d (1.7)
3.22 s
6.39 br s
6.44 br s
3.21 s
6.42 d (1.6)
6.44 d (1.4)
6.44 br s
6.44 br s
6.02, 6.02 (each 1H, d, 0.9) 5.99, 5.98 (each 1H, d, 0.9) 6.01, 6.00 (each 1H, d, 1.0) 6.00, 6.00 (each 1H, br s) 6.02, 6.01 (each 1H, br s)
3.74 s
3.73 s
3.81 s
3.79 s
3.74 s
3.81 s
3.80 s
3.73 s
3.81 s
3.81 s
3.74 s
3.82 s
3.81 s
3″-OCH3 3.82 s
5″-OCH3 3.80 s
a
b
c
Spectra recorded at 600 MHz. Chemical shifts (δ) are in ppm and coupling constants (J) in Hz. Assigned by NOESY. Assigned by 1H−1H COSY.
*
Signals overcharged.
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1
Table 4. NMR Data for Compounds 4, 5, and 10 (Acetone-
d6)
Table 5. H NMR Data for Compounds 12−15 (Acetone-
a
a
d6)
4
5
10
no.
12
13
14
15
1
6
7
8
9
7.24 s
7.28 s
6.42s
3.43 d (2.4)
6.50 s
no.
H
C
H
C
H
C
5.09 d (1.9)
5.08 d (5.7)
3.41 d (2.7)
2
4.58 s
111.6 5.00 d
(4.9)
108.3 5.07 d
(2.0)
104.4
b
b
b
,
b
2.22 m
1.84 m
2.03 m *
2.76 m
b
b
b
b
b
b
b
b
,
b
,
b
3
4
5
2.15 m
2.40 m
44.2 2.01 m
40.3 2.11 m
44.3 2.40 m
44.3
45.0
83.9
2.33 m
2.08 m *
4.99 d (6.2)
6.36 s
1.97 m *
2.31 m
,
44.5 2.38 m *
84.2 4.62 d
(4.0)
4.48 d (5.5)
4.85 d (5.6)
4.71 s
4.57 d
(9.9)
85.0 4.55 d
(7.7)
11 6.50 s
12
6.20 d (2.3)
6.08 d (2.3)
1.11 d (6.9)
0.85 d (6.8)
6.19 d (2.3)
6.09 d (2.3)
1.02 d (7.4)
1.05 d (7.2)
6
7
0.71 d
(7.0)
11.9 0.65 d
(7.2)
15.3 0.70 d
(7.0)
12.4
11.3
16
17 1.03 d (7.1)
18 1.01 d (7.1)
1.16 d (6.7)
0.59 d (6.8)
0.77 d
(7.3)
11.3 0.85 d
(7.2)
9.1 0.79 d
(7.3)
19 6.02, 5.96 (each 6.06, 5.99 (each 5.97, 5.96 (each 5.96, 5.94 (each
1H, d, 1.0) 1H, d, 0.8) 1H, d, 0.9) 1H, d, 0.9)
2′
3′
4′
5′
6′
1′
1″
2″
137.4
138.7
138.2
110.1
153.7
142.0
151.6
129.7
127.7
108.4
7.08 s
107.5 6.89 s
153.9
106.1 7.41 s
153.6
20 3.68 s 3.68 s 3.65 s 3.65 s
21 3.81 s
22 3.85 s
3.81 s
3.83 s
3.56 s
3.67 s
3.56 s
3.69 s
142.2
142.1
151.6
152.1
a
Spectra recorded at 600 MHz. Chemical shifts (δ) are in ppm and
130.3
129.0
b
*
coupling constants (J) in Hz. Assigned by NOESY. Signals
127.5
127.7
overcharged.
6.44 br s
6.45 br s
110.0 6.45 d
(1.4)
109.9 6.45 br s
Table 6. 13C NMR Data for Compounds 12−15 (Acetone-
3″
4″
5″
6″
148.2
148.4
148.2
135.8
148.2
108.2
a
d6)
135.8
135.9
148.1
148.4
no.
12
13
14
15
108.4 6.48 br s
55.1 3.25 s
61.2 3.87 s
60.8 3.83 s
56.1 3.58 s
56.7 3.81 s
108.2 6.47 br s
54.9
1
2
113.4
146.6
138.8
144.5
130.6
85.2
114.7
146.7
138.5
144.9
132.6
82.2
102.1
148.7
137.7
144.3
49.5
101.1
149.2
137.5
144.0
46.7
2-OCH3 3.44 s
4′-OCH3 3.87 s
5′-OCH3 3.80 s
6′-OCH3 3.58 s
3″-OCH3 3.81 s
5″-OCH3 3.81 s
61.3 3.86 s
60.8 3.82 s
56.3 3.58 s
56.8 3.82 s
56.8 3.82 s
61.2
60.7
56.1
56.8
56.8
3
4
5
6
92.3
92.4
56.7 3.81 s
7
42.6
53.5
42.6
36.7
a
Spectra recorded at 600 MHz for H NMR and 150 MHz for 13C
1
8
49.4
46.1
46.8
45.8
NMR. Chemical shifts (δ) are in ppm and coupling constants (J) in
Hz. Assigned by NOESY. Signals overcharged.
9
90.6
87.9
83.1
85.7
b
*
10
11
12
13
14
15
16
17
18
19
20
21
22
140.6
103.7
147.6
139.4
143.7
124.6
123.7
13.7
133.7
103.9
147.6
139.3
143.4
125.7
124.0
17.5
131.0
120.6
118.8
150.3
175.6
154.0
122.0
19.4
134.5
120.1
118.6
149.7
175.6
154.0
121.7
15.5
NOESY (Figures S40 and S44, Supporting Information)
correlations (H-2/H3-7, H-4/H-3′, and H-5/H3-6 for 9, H-2/
H3-7, H-4/H-3′, and H-5/H3-6 for 10) were similar to those of
corresponding compounds 6 and 4, suggesting the same
relative stereochemistry of different substituents on THF in the
two pairs of compounds. The conformations of THF of 9 and
10 are shown in Figure 3. Their structures were established as
shown.
Gymnothelignan K (11) was shown to have the molecular
formula C44H50O15 by HRESIMS. Its 1H and 13C NMR spectra
(Tables 2 and 3) were in good agreement with those of 9.
Hence, compound 11 was presumed to be a dimer of 9 with a
C2 symmetry axis. Key HMBC (Figure S48, Supporting
Information) correlation from H-2b to C-2a (or H-2a to C-
2b) confirmed the linkage via an oxygen bridge between C-2a
of unit A and C-2b of unit B. NOESY (Figure S49, Supporting
Information) cross-peaks of H-2/H3-7, H-4/H-3′, and H-5/H3-
6 were in agreement with those of 9. Therefore, it was
concluded that the conformations of THF (Figure 3) of both
11 and 9 were identical despite different substituents on the
THF moiety. Thus, the absolute configuration of 11 was
established as 2S,3S,4R,5R.
13.9
13.8
14.0
15.1
102.2
56.4
102.3
56.7
102.4
59.7
102.1
59.7
60.2
60.4
55.2
55.2
60.4
61.5
55.5
55.5
a
Spectra recorded at 150 MHz. Chemical shifts (δ) are in ppm.
tions of H-6/C-9 and H-9/C-6 presented the 6,9-epoxide. The
correlations of H-1 to C-2, C-3, C-5, C-15, and C-16
corroborated the proton δH 7.24 at C-1, differing from that
of a congener reported in the literature.27 In addition, a strong
correlation of H3-22/H-6 was observed in the NOESY
spectrum (Figure 4, excluding the possibility of δH 7.24 at C-
4). The correlations of H-6 to H3-17 and H-9 to H3-18
suggested H-6/H3-17 and H-9/H3-18 to be cofacial. The vicinal
coupling constants (H-6 and H-9), along with assigned relative
stereochemistry of H3-17 and H3-18, allowed the conformation
assignment of THF, as shown in Figure 3. Compound 12 was
established as 6S*,7S*,8R*,9R* and R*-biphenyl.28
Gymnothelignan L (12) was found to have molecular
formula C22H24O7 by HRESIMS. The 1H and 13C NMR
spectra (Tables 5 and 6) indicated that it had a
dibenzocyclooctene skeleton. The HMBC (Figure 4) correla-
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a
Scheme 1. Possible Mechanism of 14 to 8
Figure 4. Selected NOESY and HMBC spectra of compounds 12 and
14.
Gymnothelignan M (13) was assigned as a diastereomer of
12 by comparison of the HRMS and NMR (Tables 5 and 6)
data with that of 12. Diagnostic cross-peaks in the NOESY
(Figure S57, Supporting Information) of H-11/H-9, H-11/H3-
18, H-7/H3-18, H-7/H3-17, and H-6/H3-17 supported that H3-
17 and H3-18 were in the α- and β-orientation, respectively.
Consequently, compound 13 was proposed to be an epimer of
12 at C-8. The vicinal coupling constants of H-6 and H-9 along
with substituents on the THF allowed the conformation
assignment of THF as shown in Figure 3. The structure of 13
was therefore elucidated as the 8-epimer of 12.
a
The major product could arise from either inside attack on the
diequatorial oxocarbenium ion 1 or outside attack on the diaxial cation
2.29 Actually, the minor product was also elucidated by comparison of
the NMR spectra with those of 8.
hindrance). The structure of 15 was thus determined to be the
8-epimer of 14.
Scheme 2. Chemical Transformation of 15 to 15a
Gymnothelignan N (14) was assigned to have molecular
1
formula C22H24O7 on the basis of HRESIMS. The H and 13C
NMR spectrum (Tables 5 and 6) showed that it probably
belonged to the eupodienone8 family. The HMBC (Figure 4)
correlations of H-6/C-9 and H-9/C-6 confirmed an epoxide at
C-6 and C-9. The stereochemistry of epoxide at C-6 and C-9
was proposed to be in α-orientation due to the α-orientation of
a substituent at C-9 of eupodienone (it was favorable for
cyclization occurring at C-6 and C-9 without epimerizing). Two
trans-methyl groups (H3-17 and H3-18) were determined by
NOESY (Figure 4, cross-peaks of H-9/H-8 and H-6/H3-17).
The conformation of THF (Figure 3) favored the proposed
relative configuration. Finally, the absolute configuration was
established by single-crystal X-ray diffraction (Figure S85,
Supporting Information) as (6S,7S,8S,9R)-6,9-epoxy-7,8-di-
methyl-2,3-methylenedioxy-4,13,15-trimethoxy-10,11-
benzospiro[5.6]dodec-13,15-dien-14-one.
The chemical transformation of 14 to yield 8 allowed us to
establish the absolute configuration of the eupomatilone
family,32 which was consistent with that of eupomatilone-6
assigned previously.12,16 It was reported that eupomatilone was
derived from eupodienone (Scheme 3).6 Chemical trans-
formation in vitro buttressed the plausible biosynthetic
pathways of eupodienone to eupomatilone mentioned above.
The absolute configuration of eupomatilone-3 was therefore
proposed as 3S,4S,5R. Considering that compounds 1−11
Gymnothelignan O (15) was found to have molecular
1
formula C22H24O7 by HRESIMS. Its H and 13C NMR spectra
Scheme 3. Plausible Biosynthetic Pathways of
Eupomatilone-36
(Tables 5 and 6) were quite close to those of 14. Detailed
analysis of 1H and 13C NMR spectra suggested that compounds
14 and 15 were diastereomeric at C-8. The vicinal coupling
constants (H-9/H-8) value was 5.6 Hz for 14, whereas that of
15 was 0 Hz, indicating an epimerization at C-8. NOESY
(Figure S65, Supporting Information) correlations of H-6/H3-
17 and H-9/H3-18 supported that H-6, H-9, H3-17, and H3-18
existed in the same orientation. The conformation of THF is
shown in Figure 3.
In order to determine the absolute configurations of
compounds 3 and 8, compound 14 underwent nucleophilic
substitution reactions29,30 to afford 8/14a and 14b.31 The
possible mechanism of the conversion of 14 to 8 is shown in
Scheme 1.29 Therefore, a total of four chiral centers of 3/8 were
undoubtedly determined to be 2R,3S,4S,5R.
Similarly, treatment 15 afforded 15a (Scheme 2; a possibly
minor product could not be detected probably due to the steric
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Scheme 4. Plausible Biosynthetic Pathways of 1, 9, 12, and 15
μm, 19 × 250 mm). Column chromatography was carried out on silica
gel (160−200 mesh), MCI CHP-20 gel (75−150 μm), ODS (40−63
μm), and Sephadex LH-20. TLC was performed on precoated plates
(GF254), and spots were detected on TLC under UV and by heating
after spraying with color reagents: vanillic aldehyde (15 g) + ethanol
(250 mL) + H2SO4 (2.5 mL). X-ray crystallographic analyses were
carried out using Cu Kα radiation (λ = 1.54178 Å) at 298 K and Mo
Kα radiation (λ = 0.71073 Å) at 153 K. The structures were solved by
direct methods using the SHELXS-97 program.
Plant Material. The plant was collected from Jinfoshan in
Chongqing City, People’s Republic of China, in July 2010 and
identified as G. chinensis by Prof. S. R. Yi. A voucher specimen (T57)
has been deposited at the herbarium of Chengdu Institute of Biology,
Chinese Academy of Science.
Extraction and Isolation. Dried and powdered whole plants of G.
chinensis (1.4 kg) were extracted with ethanol at room temperature (3
× 7 days) to give an extract (146 g), which was suspended in H2O and
extracted with petroleum ether and ethyl acetate (3 × 0.5 L, 3 h each)
successively. The ethyl acetate extract (16 g) was separated by column
chromatography on MCI CHP-20 (6 × 30 cm) with a gradient system
of aqueous methanol (7:3, 1 L, 8:2, 2 L, 9:1, 1 L, and 10:0, 1 L) to
yield three fractions (A−C). Fraction B (8 g) was subjected to silica
gel chromatography (4 × 60 cm) with chloroform/methanol mixtures
of increasing polarity (35:1 to 1:1) to give fractions (BA−BH) and 20.
Fraction BG was separated on a semipreparative column (2−13 min,
40−95%, 13−16 min, 95−100%) to afford 17 (13 mg, tR 9.4 min) and
16 (18 mg, tR 11.7 min). Fraction BD was purified on a
semipreparative column (2−15 min, 40−95%, 15−18 min, 100%) to
afford 18 (21 mg, tR 9.1 min). Fraction BB (1.2−1.5 L, 3 g) was
subjected to repeated silica gel chromatography with petroleum ether/
acetone mixtures of increasing polarity to give a fraction, which was
separated on a semipreparative column (2−16 min, 60−95% aqueous
methanol, flow rate, tR 14.3 min) to afford 1 (15 mg), as well as a
mixture (2−8 min, 70−80%, 8−16 min, 80%, 16−18 min, 95%
aqueous methanol) which afforded 2 (6 mg, tR 13.2 min) and 3 (2 mg,
tR 12.8 min). Thereafter, fraction BBD was separated on a
semipreparative column (2−8 min, 20−85%, 8−12 min, 85−95%,
12−18 min, 95% aqueous methanol, flow rate, 16 mL/min) to afford
14 (25 mg, tR 11.5 min), 15 (30 mg, tR 11.8 min), and 12 (8 mg, tR
uniformly demonstrated R-configuration at C-5 regardless of
whether its 13C NMR chemical shift was near δ 79 ppm, the
revised structure of synthesized 5-epi-eupomatilone-619,20 to
3,5-bis-epi-eupomatilone-618 should again be 4-epi-eupomati-
lone-615 by our establishment of the absolute configuration.
The discovery of the three arrays of new lignans is an
example of chemical diversity, extending the lignan family by
derivatives formed by ring cleavage, oxidation, and esterifica-
tion. Compounds 1, 9, 12, and 15 were considered to be
derived from the same parent compound (Scheme 4).
Compound 1 may biogenetically be derived from precursor A
via intermediates 9 and 15 (two pathways, paths 1a and 1b).8,33
Compound 12 was probably derived from precursor A via
intermediates B or 15 (paths 12a and 12b) by dehydoxyl
reaction and rearrangement.8 These compounds were tested for
cytotoxic activity on HepG2 and Bcl7404 cell lines using
MTT34 methods, while 3 exhibited moderate cytotoxicity
against HepG2 and Bcl7404 cells, with IC50 values of 15 and
17.5 μg/mL, respectively (Table S1, Supporting Information).
The seco-lignans 1−11 are rare natural products. Compounds
1−11, except 3 and 8, demonstrate trans-H-4−H-5, which were
isolated as natural products for the first time and were mistaken
as enantiomers of eupomatilones according to previous
studies.19,20 From now on, it is feasible to determine the
absolute configuration for C-5 of the eupomatilone family with
trans-H-4−H-5. In summary, the three skeletons of lignans are
proposed to be derived from the same parent compound.
EXPERIMENTAL SECTION
■
General Experimental Procedures. NMR spectra were recorded
at 300 K (600 MHz for 1H and 150 MHz for 13C) with the
CD3COCD3 (δ 2.05/29.8) solvent as internal standard. The 1D and
2D NMR spectra were performed using standard software. The
HRESIMS was performed on a Q-TOF mass spectrometer.
Preparative HPLC was performed on a liquid chromatograph
equipped with an UV detector and semipreparative column (C18, 5
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12.6 min), as well as a mixture, which was further purified on a
semipreparative column (2−15 min, 85−95%) to afford 19 (15 mg, tR
9.7 min). Fraction BBE was then subjected to silica gel
chromatography (3 × 60 cm) eluted with gradient polarity of
petroleum ester/acetone (8:1 to 1:1) to give fraction BBEC and was
further separated on a semipreparative column (2−15 min, 63−82%,
15−19 min, 82%, 19−23 min, 82−90%) to afford 9 (5 mg, tR 6.4 min),
10 (3 mg, tR 10.0 min), 14 (13 mg, tR 11.3 min), 15 (9 mg, tR 12.5
min), 6 (8 mg, tR 13.4 min), 8 (8 mg, tR 15.2 min), 7 (8 mg, tR 15.5
min), and 12 (2 mg, tR 16.1 min). Fraction BBF was subjected to silica
gel chromatography (3 × 60 cm) eluted with 80/20 petroleum ether/
ethyl acetate (5% i-PrOH) to give 8 and a mixture, which was further
separated on a semipreparative column (2−15 min, 60−95%, 15−18
min, 95−100%) to afford 4 (8 mg, tR 11.4 min) and 5 (7 mg, tR 12.1
min). Fraction BBG was separated by silica gel chromatography with
petroleum ether/ethyl acetate mixtures of increasing polarity to give
three fractions (BBGA−BBGC). Compound 13 (6 mg, tR 13.6 min)
was obtained from fraction BBGB (2−15 min, 60−95%, 15−18 min,
95%), whereas 11 (4 mg, tR 15.6 min) was obtained from fraction
BBGA (2−6 min, 30−60%, 6−6.2 min, 60−80%, 6.2−18 min, 80−
95%). Semipreparative column chromatography solvent, aqueous
MeOH; flow rate, 16 mL/min.
Crystal Structure Determination of 14. Diffraction data (φ and
ω scans) were collected using Cu Kα radiation (λ = 1.54178 Å).
Compound 14, C24H24O7, MW = 400.41, was monoclinic and space
group P21 with a = 10.068(3) Å, b = 9.308(2) Å, c = 11.584(3) Å, α =
γ = 90°, β = 108.829(10)°, V = 1027.5(5) Å3, Z = 2, d = 1.294 g/cm3,
F(000) = 424; crystal size 0.28 × 0.22 × 0.19 mm; 4103 reflections
measured, 3642 independent reflections (Rint = 0.0266). The final R1
values were 0.0714 (I > 2σ(I)). The final wR(F2) values were 0.2309 (I
> 2σ(I)). The final R1 values were 0.1246 (all data). The final wR(F2)
values were 0.2943 (all data). The goodness of fit on F2 was 1.156.
Flack parameter = −0.3(6). The structure was solved by direct
methods (SHELXS-97) and expanded using SHELXL-97. Crystallo-
graphic data for gymnothelignan N (14) have been deposited at the
Cambridge Crystallographic Data Center (deposition number CCDC
870520). These data can be obtained free of charge from the
Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/
data_request/cif.
Gymnothelignan A (1): colorless crystals; [α]2D0 −9 (c 0.09,
CH3OH); mp 171−172 °C; UV λmax (CH3OH) 284 nm; IR (KBr)
1
νmax 3437, 1619 cm−1; H and 13C NMR data (Table 1); HRESIMS
m/z 578.2368 [M + Na]+ (calcd for C30H37NO9Na 578.2361).
Gymnothelignan B (2): off-white powder; [α]2D0 −65 (c 0.04,
CH3OH); UV λmax (CH3OH) 281 nm; IR (KBr) νmax 3436, 1615
cm−1; 1H and 13C NMR data (Table 1); HRESIMS m/z 578.2382 [M
+ Na]+ (calcd for C30H37NO9Na 578.2361).
Crystal Structure Determination of 1. Diffraction data (φ and ω
scans) were collected using Cu Kα radiation (λ = 1.54178 Å).
C30H37NO9, MW = 555.61, orthorhombic, a = 10.3937(13) Å, b =
10.5073(13) Å, c = 25.914(3) Å, α = β = γ = 90.00°, V = 2830.0(6) Å3,
T = 298(2) K, space group P212121, Z = 4, d = 1.304 g/cm3, F(000) =
Gymnothelignan C (3): off-white powder; [α]2D0 −30 (c 0.03,
CH3OH); UV λmax (CH3OH) 280 nm; IR (KBr) νmax 3401, 1635
cm−1; 1H and 13C NMR data (Table 1); HRESIMS m/z 578.2385 [M
+ Na]+ (calcd for C30H37NO9Na 578.2361).
1184, 6996 reflections measured, 4123 independent reflections (Rint
=
0.1332). The final R1 values were 0.0603 (I > 2σ(I)). The final wR(F2)
values were 0.1795 (I > 2σ(I)). The final R1 values were 0.1954 (all
data). The final wR(F2) values were 0.2478 (all data). The goodness of
fit on F2 was 1.175. Flack parameter = 0.2(3). Crystallographic data for
gymnothelignan A (1) have been deposited at the Cambridge
Crystallographic Data Center (deposition number CCDC 857186).
These data can be obtained free of charge from the Cambridge
Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/
cif.
Gymnothelignan D (4): colorless crystals; [α]2D0 −12 (c 0.03,
CH3OH); mp 133−134 °C; UV λmax (CH3OH) 276 nm; IR (KBr)
1
νmax 3392, 2960, 2933, 1607, 1490, 1461, 1097 cm−1; H and 13C
NMR data (Table 4); HRESIMS m/z 471.1978 [M + Na]+ (calcd for
C24H32O8Na 471.1989).
Gymnothelignan E (5): white powder; [α]2D0 −7 (c 0.35, Me2CO);
UV λmax (CH3OH) 277 nm; IR (KBr) νmax 3429, 2935, 1608, 1488,
1
1463, 1102 cm−1; H and 13C NMR data (Table 4); HRESIMS m/z
Crystal Structure Determination of 4. Diffraction data (φ and ω
scans) were collected using Cu Kα radiation (λ = 1.54178 Å).
Compound 4, C24H32O8, MW = 448.50, was monoclinic and space
group P21 with a = 10.8975(4) Å, b = 18.7065(8) Å, c = 11.7408(5) Å,
α = γ = 90°, β = 92.968(3)°, V = 2390.20(17) Å3, Z = 4, d = 1.246 g/
cm3, F(000) = 960; crystal size 0.22 × 0.15 × 0.13 mm; 14 004
reflections measured, 6996 reflections unique, θmax = 67.49°. The final
R1 values were 0.0482 (I > 2σ(I)). The final wR(F2) values were
0.1253 (I > 2σ(I)). The final R1 values were 0.0960 (all data). The
final wR(F2) values were 0.1870 (all data). The goodness of fit on F2
was 0.990. Flack parameter = 0.1(3). The structure was solved by
direct methods (SHELXS-97) and expanded using SHELXL-97.
Crystallographic data for gymnothelignan D (4) have been deposited
at the Cambridge Crystallographic Data Center (deposition number
CCDC 857185). These data can be obtained free of charge from the
Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/
data_request/cif.
Crystal Structure Determination of 8. Diffraction data (φ and ω
scans) were collected using Mo Kα radiation (λ = 0.71073 Å).
Compound 8, C23H28O8, MW = 432.45, was orthorhombic and space
group P212121 with a = 6.9969(17) Å, b = 11.484(3) Å, c = 27.382(7)
Å, α = β = γ = 90°, V = 2200.1(9) Å3, Z = 4, d = 1.306 g/cm3, F(000)
= 920; crystal size 0.48 × 0.35 × 0.08 mm; 19 484 reflections
measured, 3370 reflections unique (Rint = 0.0477). The final R1 values
were 0.0438 (I > 2σ(I)). The final wR(F2) values were 0.0906 (I >
2σ(I)). The final R1 values were 0.0511 (all data). The final wR(F2)
values were 0.0944 (all data), θmax = 29.12°, goodness of fit was 0.999.
The structure was solved by direct methods (SHELXS-97) and
expanded using SHELXL-97. Crystallographic data for gymnotheli-
gnan H (8) have been deposited at the Cambridge Crystallographic
Data Center (deposition number CCDC 870519). These data can be
obtained free of charge from the Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/data_request/cif.
471.1976 [M + Na]+ (calcd for C24H32O8Na 471.1989).
Gymnothelignan F (6): yellowish powder; [α]2D0 −2 (c 0.20,
Me2CO); UV λmax (CH3OH) 287 nm; IR (KBr) νmax 3430, 2962,
2936, 1614, 1519, 1476, 1112 cm−1; 1H and 13C NMR data (Tables 2
and 3); HRESIMS m/z 455.1690 [M + Na]+ (calcd for C23H28O8Na
455.1676).
Gymnothelignan G (7): off-white powder; [α]2D0 −10 (c 0.25,
Me2CO); UV λmax (CH3OH) 296 nm; IR (KBr) νmax 3442, 2928,
1
1606, 1469, 1115 cm−1; H and 13C NMR data (Tables 2 and 3);
HRESIMS m/z 455.1673 [M + Na]+ (calcd for C23H28O8Na
455.1676).
Gymnothelignan H (8): colorless crystals; [α]2D0 −80 (c 0.03,
Me2CO); mp 184−185 °C; UV λmax (CH3OH) 301 nm; IR (KBr)
νmax 3393, 2958, 2934, 1607, 1475, 1465, 1115, 1026 cm−1; 1H and 13
C
NMR data (Tables 2 and 3); HRESIMS m/z 455.1675 [M + Na]+
(calcd for C23H28O8Na 455.1676).
Gymnothelignan I (9): yellowish powder; [α]2D0 −8 (c 0.10,
Me2CO); UV λmax (CH3OH) 302 nm; IR (KBr) νmax 3436, 2964,
1
2937, 1614, 1476, 1113 cm−1; H and 13C NMR data (Tables 2 and
3); HRESIMS m/z 441.1522 [M + Na]+ (calcd for C22H26O8Na
441.1520).
Gymnothelignan J (10): yellowish powder; [α]2D0 −4 (c 0.10,
Me2CO); UV λmax (CH3OH) 298 nm; IR (KBr) νmax 3426, 2962,
2936, 1608, 1460, 1100 cm−1; 1H and 13C NMR data (Table 4);
HRESIMS m/z 457.1852 [M + Na]+ (calcd for C23H30O8Na
457.1833).
Gymnothelignan K (11): white powder; [α]2D0 −10 (c 0.09,
CH3OH); UV λmax (CH3OH) 280 nm; IR (KBr) νmax 3435, 2935,
1
1615, 1476, 1114 cm−1; H and 13C NMR data (Tables 2 and 3);
HRESIMS m/z 841.3069 [M + Na]+ (calcd for C44H50O15Na
841.3043).
Gymnothelignan L (12): yellow powder; [α]2D0 −2 (c 0.20,
Me2CO); UV λmax (CH3OH) 307 nm; IR (KBr) νmax 3429, 2961,
8442
dx.doi.org/10.1021/jo301225v | J. Org. Chem. 2012, 77, 8435−8443

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1
2934, 1616, 1479, 1101 cm−1; H and 13C NMR data (Tables 5 and
(2) Alberto Marco, J; Barbera,
Phytochemistry 1985, 24, 2471.
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Gupta, M. P. J. Nat. Prod. 1994, 57, 400.
́
O.; Sanz, J. F.; Sanchez-Parareda, J.
6); HRESIMS m/z 401.1595 [M + H]+ (calcd for C22H25O7
401.1594).
Gymnothelignan M (13): yellow powder; [α]2D0 +8 (c 0.03,
CH3OH); UV λmax (CH3OH) 300 nm; IR (KBr) νmax 3428, 2957,
́
1
2928, 1617, 1451, 1079 cm−1; H and 13C NMR data (Tables 5 and
(5) Bohlmann, F.; Zdero, C.; Schoneweiss, S. Chem. Ber. 1976, 109,
̈
6); HRESIMS m/z 401.1597 [M + H]+ (calcd for C22H25O7
401.1594).
3366.
(6) Carroll, A.; Taylor, W. Aust. J. Chem. 1991, 44, 1705.
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Ed. 2005, 44, 6177.
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70, 9658.
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Avery, V. M. J. Org. Chem. 2011, 77, 680.
Gymnothelignan N (14): colorless crystals; [α]2D0 +13 (c 0.04,
CH3OH); mp 201−202 °C; UV λmax (CH3OH) 290 nm; IR (KBr)
νmax 2958, 2936, 1668, 1614, 1475, 1112 cm−1; 1H and 13C NMR data
(Tables 5 and 6); HRESIMS m/z 423.1423 [M + Na]+ (calcd for
C22H24O7Na 423.1414).
Gymnothelignan O (15): white powder; [α]2D0 +15 (c 0.04,
CH3OH); UV λmax (CH3OH) 283 nm; IR (KBr) νmax 2936, 1668,
1615, 1477, 1113 cm−1; H and 13C NMR data (Tables 5 and 6);
1
HRESIMS m/z 423.1435 [M + Na]+ (calcd for C22H24O7Na
423.1414).
Treatment of 14 and 15 with H2SO4. Gymnothelignan N (14,
11 mg) was dissolved in methanol (2 mL) and then added 5 mL of 2
M H2SO4 and heated at 80 °C under reflux for 1 h. After cooling to
room temperature, the solution was neutralized with excess NaHCO3
and filtered, and the filtrate was extracted three times each with 7 mL
of ethyl acetate. The combined organic layer was evaporated to
dryness and then separated by HPLC with a C18 column, using a
mixed solvent of methanol/water (0−2 min, 70%, 2−16 min, 70−95%,
16−18 min, 95%) to yield the corresponding 14a (1.7 mg, tR 10.8 min,
15% yield) and 14b (0.5 mg, tR 9.7 min, 5% yield). 14a: white powder,
[α]2D0 −80 (c 0.03, Me2CO); 1H NMR (600 MHz, acetone-d6, δH 2.05,
Figure S66) was in good agreement with that of 8. 14b: yellowish
powder, [α]2D0 +100 (c 0.02, Me2CO); H NMR (600 MHz, acetone-
1
d6, δH 2.05, Figure S67) δH 6.90 (s, H-3′), 6.45, 6.36 (br s, each 1H, H-
6″, and 2″), 6.01, 6.00 (br s, each 1H, OCH2O), 5.11 (d, J = 7.1 Hz,
H-5), 4.54 (d, J = 2.6 Hz, H-2), 3.82, 3.80, 3.74, 3.43 (s, each 3H, 3″,
5″, 6′, and 2-OCH3), 1.69, 1.67 (m, 2H, H-4, and H-3), 0.90 (d, J =
7.1 Hz, H3-7), 0.71 (d, J = 7.2 Hz, H3-6). Treatment of 15 (17 mg) as
described for 14 afforded corresponding 15a (2.8 mg, tR 16.2 min,
16% yield, solvent, 60−95% aqueous MeOH, flow rate, 16 mL/min).
(25) Crystals were crystallized from the sample that was previously
used for NMR spectra.
(26) Hamed, W.; Brajeul, S.; Mahuteau-Betzer, F.; Thoison, O.;
Mons, S.; Delpech, B.; Hung, N. V.; Sev
Prod. 2006, 69, 774.
́
enet, T.; Marazano, C. J. Nat.
1
15a: white powder, H NMR (600 MHz, acetone-d6, δH 2.05, Figure
S68) was in good agreement with that of 6.
(27) Spencer, G. F.; Flippen-Anderson, J. L. Phytochemistry 1981, 20,
2757.
(28) Liu, J.-S.; Li, L. Phytochemistry 1995, 38, 241.
(29) Smith, D. M.; Tran, M. B.; Woerpel, K. A. J. Am. Chem. Soc.
2003, 125, 14149.
ASSOCIATED CONTENT
* Supporting Information
IR, 1D, and 2D NMR spectra of compounds 1−15, H NMR
spectra of 14a, 14b, and 15a, NMR free induction decay (FID)
files of compounds 1, 4, and 8, CIFs of compounds 1, 4, 8, and
14, cytotoxic activity of these compounds on HepG2 and
Bcl7404 cell lines. This material is available free of charge via
the Internet at http://pubs.acs.org.
■
S
1
(30) Larsen, C. H.; Ridgway, B. H.; Shaw, J. T.; Woerpel, K. A. J. Am.
Chem. Soc. 1999, 121, 12208.
(31) The diastereoselectivity of the nucleophilic substitution
confirmed the inherent stereoelectronic preference for inside versus
outside attack. However, rearrangement products were not isolated.
(32) Compound 14 had the same absolute configuration of
eupodienone which was isolated from the genus Eupomatia. It was
therefore supposed that compound 14 and eupodienone were derived
from the same parent compound. See ref 6.
(33) Pelter, A.; Satchwell, P.; Ward, R. S.; Blake, K. J. Chem. Soc.,
Perkin Trans. 1 1995, 2201.
(34) Wang, X.; Chen, Y.; Han, Q.-b.; Chan, C.-y.; Wang, H.; Liu, Z.;
Cheng, C. H.-k.; Yew, D. T.; Lin, M. C. M.; He, M.-l.; Xu, H.-x.; Sung,
J. J. Y.; Kung, H.-f. Proteomics 2009, 9, 242.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: xuhongxi88@gmail.com, zhouyan@cib.ac.cn.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by grants from the 2010
technological talents program of the Chinese Academy of
Sciences granted to Y. Zhou and the National Natural Sciences
Foundation (Nos. 30973634, 30900129 and 81130069) of
China.
REFERENCES
■
(1) Yang, W.-L.; Tian, J.; Ding, L.-S. Chin. J. Chin. Mater. Med. 2001,
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