Diarylheptanoids with inhibitory effects on melanogenesis from the rhizomes of Curcuma comosa in B16 melanoma cells

Article abstract of DOI:10.1016/j.bmcl.2013.07.010

The methanolic extract from the dried rhizomes of Curcuma comosa cultivated in Thailand was found to inhibit melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells. From the methanolic extract, three new diarylheptanoids, diarylcomosols I-III, were isolated together with 12 known diarylheptanoids. Their chemical structures were elucidated on the basis of chemical and physicochemical evidence. The diarylheptanoids inhibited melanogenesis, and several structural requirements of the active constituents for the inhibition were clarified. In particular, (3R)-1,7-bis(4-hydroxyphenyl)- (6E)-6-hepten-3-ol exhibited stronger inhibitory effect [IC₅₀ = 0.36 μM] without inducing cytotoxicity. The biological effect was much stronger than that of a reference compound, arbutin [IC₅₀ = 174 μM]. We conclude that diarylheptanoid analogs are promising therapeutic agents for the treatment of skin disorders.

Full text of DOI:10.1016/j.bmcl.2013.07.010

Bioorganic & Medicinal Chemistry Letters 23 (2013) 5178–5181
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Diarylheptanoids with inhibitory effects on melanogenesis
from the rhizomes of Curcuma comosa in B16 melanoma cells
Takahiro Matsumoto, Seikou Nakamura, Souichi Nakashima, Masayuki Yoshikawa, Katsuyoshi Fujimoto,
⇑
Tomoe Ohta, Azumi Morita, Rie Yasui, Eri Kashiwazaki, Hisashi Matsuda
Department of Pharmacognosy, Kyoto Pharmaceutical University, Misasagi, Yamashina-ku, Kyoto 607-8412, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The methanolic extract from the dried rhizomes of Curcuma comosa cultivated in Thailand was found to
inhibit melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells. From the methanolic
extract, three new diarylheptanoids, diarylcomosols I–III, were isolated together with 12 known diaryl-
heptanoids. Their chemical structures were elucidated on the basis of chemical and physicochemical evi-
dence. The diarylheptanoids inhibited melanogenesis, and several structural requirements of the active
constituents for the inhibition were clarified. In particular, (3R)-1,7-bis(4-hydroxyphenyl)-(6E)-6-hep-
Received 16 April 2013
Revised 5 July 2013
Accepted 9 July 2013
Available online 17 July 2013
Keywords:
Curcuma comosa
Diarylcomosol
Diarylheptanoid
Melanogenesis inhibitor
Thai traditional medicine
ten-3-ol exhibited stronger inhibitory effect [IC50 = 0.36
lM] without inducing cytotoxicity. The biologi-
cal effect was much stronger than that of a reference compound, arbutin [IC50 = 174
lM]. We conclude
that diarylheptanoid analogs are promising therapeutic agents for the treatment of skin disorders.
Ó 2013 Elsevier Ltd. All rights reserved.
A Zingiberaceae plant, Curcuma comosa, is widely distributed in
tropical and subtropical regions of Asia, especially Thailand, Indo-
nesia, and Malaysia. The rhizome of C. comosa has been used as
an aromatic stomachic and anti-inflammatory.1,2 We previously re-
ported the isolation and structure elucidation of monoterpenes and
sesquiterpenes from the air-dried rhizomes of C. comosa cultivated
in Thailand.3–5 On the other hand, we have interested in identifying
inhibitors of melanin production derived from natural medicines.6–
13 In the present study, we found that a methanolic (MeOH) extract
from the thermally-dried rhizomes of C. comosa showed inhibitory
effects on melanogenesis. From the MeOH extract, we have isolated
three new diarylheptanoids, diarylcomosols I (1), II (3), and III (6),
together with 12 known diarylheptanoids. (Fig. 1). In this Letter,
we describe the isolation and structural elucidation of 1, 3, and 6
as well as the inhibitory effects of diarylheptanoids on melanogen-
esis in theophylline-stimulated B16 melanoma 4A5 cells.
A MeOH extract of the thermally-dried rhizomes of C. comosa
showed melanogenesis inhibitory activity [inhibition (%): 27.7 6.3 (P
<0.01) at 3 lg/mL]. The MeOH extract was partitioned into an EtOAc–
H2O (1:1, v/v) mixture to furnish an EtOAc-soluble fraction (7.9%) and
an aqueous layer. The aqueous layer was further extracted with 1-buta-
nol to give 1-butanol- (2.8%) and H2O- (15.3%) soluble fractions. The
EtOAc-soluble fraction was found to have significant inhibitory effects
to normal- and reversed-phase silica-gel column chromatography and
repeated HPLC to give three new diarylheptanoids, diarylcomosols I
(1, 0.0033%), II (3, 0.0007%), and III (6, 0.012%), and 12 known diarylhep-
tanoids,
0.01575%),14 (3R)-1,7-bis(4-hydroxyphenyl)-(6E)-6-hepten-3-ol (4,
0.0002%),15
(E)-1,7-bis(4-hydroxyphenyl)-6-hepten-3-one (5,
0.0033%),15(3R0,5S0)-3,5-dihydroxy-1-(40-hydroxy-30,50-dimethoxy-
1,7-bis(4-hydroxyphenyl)hepta-4E,6E-dien-3-one
(2,
phenyl)-7-(400-hydroxy-30-methoxyphenyl)heptane (7, 0.0067%),16
(3R0,5S0)-3,5-dihydroxy-1-(30,40-dihydroxyphenyl)-7-(400-hydroxy-
phenyl)heptane (8, 0.0006%),17 (+)-hannokinol (9, 0.011%),18 (3R,5R)-
3,5-diacetoxy-1-(3,4-dihydroxyphenyl)-7-(4-hydroxyphenyl)heptane
(10, 0.017%),17 (3R,5R)-3-acetoxy-5-hydroxy-1-(3,4-dihydroxyphenyl)-
7-(4-hydroxyphenyl)heptane (11, 0.049%),17 (3R,5R)-3-acetoxy-5-hy-
droxy-1,7-bis(3,4-dihydroxyphenyl)heptane (12, 0.0027%),17 (3R,5R)-
dihydroxy-1-(3,4-dihydroxyphenyl)-7-(4-hydroxyphenyl)heptane (13,
0.0004%),17 platyphyllone (14, 0.0088%),19 and (5R)-5-hydroxy-1-(4-
hydroxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-3-heptanone (15,
0.0039%).20 In this case, monoterpenes 16–194 including comosoxides
A (16)4,21 and B (17),4,21 which were isolated from the air-dried and
clumpy rhizomes of C. comosa, were not detected in the thermally-dried
and sliced rhizomes of C. comosa.
Diarylcomosol I (1) was isolated as a pale yellow powder. The IR
spectrum of 1 suggested the presence of hydroxy (3350 cmꢀ1), car-
bonyl (1708 cmꢀ1), and aromatic ring (1603, 1510 cmꢀ1). In the EI-
MS of 1, a molecular ion peak [M]+ was observed at m/z 310 and
the molecular formula C19H18O4 was determined by HRMS mea-
surement of the molecular ion peak. The 1H NMR (methanol-d4)
and 13C NMR (Table 1) spectra of 1, which were assigned by various
on melanogenesis [inhibition (%): 51.9 2.8 (P <0.01) at 3 lg/mL]. The
EtOAc-soluble fraction, a predominant bioactive portion, was subjected
⇑
Corresponding author. Tel.: +81 75 595 4634; fax: +81 75 595 4768.
E-mail address: myoshika@mb.kyoto-phu.ac.jp (H. Matsuda).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.07.010

T. Matsumoto et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5178–5181
5179
Figure 1. Chemical structures of 1–19.
NMR experiments,22 showed signals assignable to two methylene
[d 2.70 (t, J = 7.6 Hz H2-1), 2.77 (t, J = 7.6 Hz H2-2)], four olefinic
protons [d 6.10 (d, J = 15.8 Hz, H-4), 6.65 (dd,J = 15.8, 11.0 Hz H-
5), 6.77 (d, J = 15.8 Hz H-7), 7.24 (dd, J = 15.8, 11.0 Hz H-6)], seven
aromatic protons [d 6.56 (d, J = 8.3 Hz, H-30,50), 6.62 (d, J = 8.3 Hz,
H-500), 6.76 (br d, J = 8.3 Hz, H-600), 6.87 (br s, H-200), 6.90 (d,
J = 8.3 Hz, H-20,60)], and a carbonyl carbon [dc 202.3]. As shown in
Figure 2, the DQF COSY experiment of 1 indicated the presence
of certain structures (highlighted by bold lines). The HMBC exper-
iments revealed long-range correlations between the following
protons and carbons: H-1 and C-3, 10, 20, 60; H-2 and C-3, 10; H-4
and C-3, 6; H-7 and C-5, 100, 200, 600; H-2’, 6’ and C-1, 40; H-30, 50
and C-10; H-200 and C-7, 300, 600; H-500 and C-300; H-600 and C-7, 200,
400. On the basis of all this evidence, the chemical structure of
Table 1
13C NMR (125 MHz) data for 1, 3, and 6
Position
1
3
6
1
2
3
4
5
6
30.3
42.6
32.6
40.6
71.1
38.3
30.2
32.8
40.8
70.8
44.8
70.8
40.7
31.8
134.4
106.6
149.1
134.4
149.1
106.6
134.4
130.3
116.1
156.3
116.1
130.3
56.7
202.3
128.2
145.6
122.9
143.5
132.7
129.8
115.6
156.1
115.6
129.8
129.2
114.0
146.2
147.9
115.9
121.3
Figure 2. Important 2D NMR correlations of 1, 3, and 6.
128.2
131.0
135.3
113.2
148.8
145.4
116.1
121.8
131.0
128.1
116.2
157.6
116.2
128.1
56.3
diarylcomosol I (1) was determined to be 1-(40-hydroxyphenyl)-
7-(300,400-dihydroxyphenyl)-hepta-4E,6E-dien-3-one.23
7
10
20
Diarylcomosol II (3) was isolated as a colorless oil with positive
30
optical rotation (½a D25
ꢁ
+12.6 in MeOH). In the EI-MS of 3, a molecular
40
ion peak [M]+ was observed at m/z 328 and the molecular formula
50
60
C20H24O4 was determined by HRMS measurement of the molecular
100
ion peak. The 1H NMR (methanol-d4) and 13C NMR (Table 1) spectra
of 3,22 showed signals assignable to an ABX-type aromatic ring [d
6.61 (dd, J = 8.6, 1.9 Hz, H-60), 6.67 (d, J = 8.6 Hz, H-50), 6.75 (d,
J = 1.9 Hz, H-20)] and an AA0XX0-type aromatic ring [d 6.67 (d,
J = 8.6 H-300,500), 7.13 (d, J = 8.6 Hz H-200,600)] together with a methine
bearing an oxygen function, a methoxy group, and two olefinic
protons. As shown in Figure 2, the HMBC experiments revealed long-
range correlations between the following protons and carbons:
200
300
400
500
600
30-OMe
50-OMe
56.7
Measured in CD3OD.

5180
T. Matsumoto et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5178–5181
H-1 and C-10, 20, 60; H-3 and C-1, 5; H-6 and C-100; H-7 and C-100, 200,
600; H-20 and C-1, 60; H-50 and C-30; H-60 and C-1, 20, 40; H-200, 600 and
C-7, 400; H-300, 500 and C-100. These results supported that the structure
of 3 was diarylhetanoid with a hydroxy group at the 3-position.
Finally, the absolute configuration of the 3-position in 3 was char-
acterized by the application of the modified Mosher’s method. Namely,
1-(30,40-dimethoxyphenyl)-7-(400-methoxyphenyl)-(6E)-6-hepten-
3-ol (3a), which was derived from 3 upon reaction with trimethyl-
silyldiazomethane (TMSCHN2) in MeOH, gave the (S)-MTPA ester
(3b) by treatment with (ꢀ)-2-methoxy-2-trifluoromethylpheny-
lacetyl choloride [(ꢀ)-MTPACl] in pyridine. In addition, the (R)-
MTPA ester (3c) was obtained from 3a using (+)-MTPACl in
pyridine. As shown in Figure 3, the signals due to protons attached
to the 1, 2, 20, 50, and 60-positions in 3b were observed at lower fields
the molecular ion peak. The 1H NMR (methanol-d4) and 13C NMR
(Table 1) spectra of 6 indicated the presence of two aromatic rings,
two methines bearing an oxygen function, and two methoxy groups.
The proton and carbon signals in the 1H and 13C NMR spectra of 6
were superimposable on those of (3R0,5S0)-3,5-dihydroxy-1-(40-hy-
droxy-30,50-dimethoxyphenyl)-7-(400-hydroxy-30-methoxy-
phenyl)heptane (7),16 except for the signals around the 300-postion of
6. The structure of 6 was characterized by means of DQF COSY and
HMBC experiments (Fig. 2). Next, since compound 6 was optically
inactive as well as known diarylhetanoids, 716 and (3R0,5S0)-3,5-
dihydroxy-1-(30,40-dihydroxyphenyl)-7-(400-hydroxyphenyl)hep-
tane (8),17 the relative configuration at C-3 and C-5 was suggested to
be syn type. On the basis of all this evidence, the chemical structure
of diarylcomosol III (6) was determined to be (3R0,5S0)-3,5-dihy-
droxy-1-(40-hydroxy-30,50-dimethoxyphenyl)-7-(400-
compared with those of 3c [Dd: positive], while the signals due to
protons attached to the 4, 5, 6, 7, 200, and 300-positions in the (S)-
MTPA ester (3b) were observed at higher field compared with those
hydroxyphenyl)heptane.25
Melanin production, which is principally responsible for skin
color, is a major defense mechanism against the harmful ultraviolet
rays in sunlight. However, excess production of melanin after long
periods of exposure to the sun can cause dermatological disorders
such as melasma, freckles, postinflammatory melanoderma, and so-
lar lentigines. We have reported that several constituents from nat-
ural medicines and medicinal foods inhibited the melanogenesis in
theophylline-stimulated B16 melanoma 4A5 cells.6–13 We also
reported that four diaryheptanoids [5-hydroxy-1,7-diphenyl-3-
of the (R)-MTPA ester (3c) [Dd: negative]. Thus, the absolute config-
uration at the 3-position in 3 was determined to be S. On the basis of
all this evidence, the chemical structure of diarylcomosol II (3) was
determined to be (3S)-1-(30-methoxy-40-hydroxyphenyl)-7-(400-
hydroxyphenyl)-(6E)-6-hepten-3-ol.24
Diarylcomosol III (6) was isolated as a colorless oil. In the EI-MS of
6, a molecular ion peak [M]+ was observed at m/z 376 and the molec-
ular formula C21H28O6was determined by HRMS measurement of
Figure 3. Determination of the absolute configurations of 3-position in 3.
Table 2
Inhibitory effects of diarylheptanoids, 1–15 from the dried rhizomes of Curcuma comosa on melanogenesis in B16 melanoma 4A5 cells
(
l
M)
Inhibition (%)
1
IC50 (lM)
Control
0.1
0.3
37.8 1.7⁄⁄
3
10
16.3 4.8⁄⁄
1a
2a
3b
4a
5c
6a
7a
8c
9a
0.0 2.9
0.0 9.1
0.0 5.0
0.0 2.0
0.0 1.2
0.0 4.2
0.0 5.5
0.0 3.9
0.0 1.6
0.0 4.5
0.0 3.1
0.0 3.3
0.0 2.2
0.0 7.8
0.0 6.4
27.8 1.9⁄⁄
25.4 4.7
13.7 2.1
27.7 2.6
21.2 3.5⁄
11.5 4.4
35.4 1.9⁄⁄
ꢀ0.7 8.9
22.0 1.4⁄⁄
3.6 3.8
15.4 2.1
ꢀ1.6 3.6
7.0 7.0
13.1 7.4
4.0 4.3
30.5 3.9⁄⁄
23.4 5.3⁄⁄
41.9 3.6⁄⁄
27.2 3.8⁄⁄
79.3 2.2⁄⁄
61.4 2.4⁄⁄
25.0 5.8⁄⁄
50.3 3.0⁄⁄
—
31.7 3.1⁄⁄
8.9 3.4⁄⁄
47.5 1.7
29.9 4.2⁄⁄
23.2 3.7⁄⁄
43.2 5.7⁄⁄
ꢀ3.7 8.2
20.3 4.5⁄⁄
6.3 2.7
53.4 2.4⁄⁄
28.9 4.5⁄⁄
67.3 2.6⁄⁄
44.9 5.0⁄⁄
23.1 5.4⁄⁄
38.4 4.3⁄⁄
ꢀ10.9 8.1
15.7 4.8⁄
8.1 3.4
68.4 3.6⁄⁄
37.8 3.6⁄⁄
90.5 1.1⁄⁄
57.1 6.5⁄⁄
7.2 4.8
1.99
>10
0.36
1.24
—
ca. 3
—
>10
>10
4.91
—
34.4 2.7
ꢀ23.7 9.1
23.1 3.7⁄⁄
7.3 1.3
—
21.9 2.1⁄⁄
27.3 6.4⁄⁄
59.9 6.1⁄⁄
5.5 2.2
10a
11a
12a
13a
14a
15a
15.1 3.8
–9.9 9.0
8.9 8.8
16.8 7.2
ꢀ11.9 3.7
27.3 7.1⁄⁄
ꢀ5.7 4.5
ꢀ22.7 4.2
12.5 3.8
21.8 2.3⁄
4.5 3.4
0.1 10.2
19.9 5.2
4.4 3.8
–18.9 6.2
31.5 1.7⁄⁄
ꢀ24.9 2.3
—
>10
—
16.6 3.3
(
l
M)
Control
0.0 1.4
10
30
100
300
1000
(
l
M)
Arbutind
10.6 0.6⁄⁄
20.4 0.5⁄⁄
38.1 0.9⁄⁄
61.5 0.6⁄⁄
61.5 0.6⁄⁄
174
Each value represents the mean SEM, (n = 4).
Significantly different from the control group, ⁄P <0.05, ⁄⁄P <0.01.
a
The cell viabilities at 3 and 10
The cell viabilities for 3 at 3 and 10 M are 84.6% and 76.0%, respectively.
l
M are more than 95.2% and 92.3%, respectively.
b
c
l
The cell viabilities for 5 and 8 at 3 and 10 lM are more than 91.9% and 71.6%, respectively.
d
Reference compound.6–13

T. Matsumoto et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5178–5181
5181
heptanone (IC50 = 48
phenylhept-4-en-3-one (IC50 = 10
300-methoxyphenyl)-1-phenyl-3-heptanone (IC50 = 30
3,5-dihydroxy-1,7-diphenylheptane (IC50 = ca. 33 M)] exhibited
l
M), 7-(400-hydroxy-300-methoxyphenyl)-1-
M), 5-hydroxy-7-(400-hydroxy-
M), and
References and notes
l
1. Sodsai, A.; Piyachaturawat, P.; Sophasan, S.; Suksamrarn, A.; Vongsakul, M. Int.
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8. Nakamura, S.; Chen, G.; Nakashima, S.; Matsuda, H.; Pei, Y.; Yoshikawa, M.
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l
l
moderate inhibitory effects.6 However, there have been only a
few reports on diaryheptanoids with melanogenesis inhibitory ef-
fects before, and those effects were moderate or weak.26–29 There-
fore, the inhibitory effects of diaryheptanoids from the dried
rhizomes of Curcuma comosa on melanogenesis were examined (Ta-
ble 2). Among the isolates, diaryheptanoids (1–5, 7, and 11) inhib-
ited melanogenesis [inhibition: 27.3ꢀ67.3% (P <0.01) at 1
paricular, (3R)-1,7-bis(4-hydroxyphenyl)-(6E)-6-hepten-3-ol (4,
IC50 = 0.36 M) exhibited a potent inhibitory effect on melanogen-
esis without inducing cytotoxicity [cell viability 93.0% at 10 M].
lM]. In
l
l
Indeed, 4 displayed greatest potency for inhibiting melanogenesis
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Matsuda, H.; Yoshikawa, M. Chem. Pharm. Bull. 2012, 60, 752.
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Matsuda, H.; Yoshikawa, M. J. Nat. Prod. 2012, 75, 1425.
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H.; Muraoka, O.; Yoshikawa, M. Bioorg. Med. Chem. 2013, 21, 779.
13. Nakamura, S.; Nakashima, S.; Oda, Y.; Yokota, N.; Fujimoto, K.; Matsumoto, T.;
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14. Ali, M. S.; Tezuka, Y.; Awale, S.; Banskota, A. H.; Kadota, S. J. Nat. Prod. 2001, 64,
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15. Li, J.; Zhao, F.; Li, M. Z.; Chen, L. X.; Qiu, F. J. Nat. Prod. 2010, 73, 1667.
16. Ma, J.; Jin, X.; Yang, L.; Liu, Z. L. Phytochemistry 2004, 65, 1137.
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of all active compounds (diaryheptanoid,6 flavonoids,6,7 sterol
derivatives,8 acylated triterpene glycosides,9–11 and alkaloids12,13
)
previously reported by us, and was much more effective than a ref-
erence compound, arbutin (IC50 = 174 M). The structural require-
l
ments of the active constituents were examined. Compounds 1–5
with double bond on the side chain part showed stronger inhibitory
effects than compounds 8–15 with saturated side chain. Com-
pounds 2, 4, and 5 with two 4-hydroxyphenyl parts also showed
stronger inhibitory effects than compounds 1 and 3 with a 3,4-dihy-
droxyphenyl or a 4-hydroxy-3-methoxyphenyl part. These findings
indicate that the existence of the 1,7-bis(4-hydroxyphenyl)heptane
skeleton and the double bond on the side chain is essential for the
activity.
Next, the effects of diaryheptanoids (1–15) on tyrosinase were
examined. Mushroom tyrosinase has conventionally been used
for the development of tyrosinase inhibitors. Among the isolates,
2 and 4 with melanogenesis inhibitory effects showed weak tyros-
inase inhibitory effects [inhibition (%): 34.3 1.0 and 25.5 0.9 (P
18. Veith, M.; Dettner, K.; Boland, W. Tetrahedron 1996, 52, 6601.
19. Smite, E.; Lundgren, L. N.; Andersson, R. Phytochemistry 1993, 32, 365.
20. Shin, D.; Kinoshita, K.; Koyama, K.; Takahashi, K. J. Nat. Prod. 2002, 65, 1315.
21. The structure of 16 and 17 was revised as shown Figure 1. The knowledge and
data will be presented in a full paper.
22. The 1H and 13C NMR spectra was assigned with the aid of distortionless
enhancement by polarization transfer (DEPT), double quantum filter
correlation spectroscopy (DQF COSY), heteronuclear multiple quantum
coherence spectroscopy (HMQC), and heteronuclear multiple bond
connectivity spectroscopy (HMBC) experiments.
<0.01) at 10
no detectable activity against tyrosinase [inhibition (%): <17.0 at
10 M]. This finding suggests that the inhibition of tyrosinase
lM, respectively]. Other diaryheptanoids also showed
l
23. Diarylcomosol I (1): A pale yellow powder; IR (KBr) vmax 3350, 2948, 1708,
1647, 1603, 1510 cmꢀ1; UV [MeOH, nm, (log )]: 365 (4.10); 1H NMR (MeOH-
e
activity is unimportant with regard to the inhibition of melanogen-
esis by the diaryheptanoids from the dried rhizomes of C. comosa.
In conclution, 15 diarylheptanoids including three new constit-
uents, diarylcomosols I (1), II (3), and III (6), were isolated from the
dried rhizomes of Curcuma comosa cultivated in Thailand and sev-
eral structural requirements of the active constituents with mela-
nogenesis inhibitory effects were clarified. In addition, (3R)-1,7-
bis(4-hydroxyphenyl)-(6E)-6-hepten-3-ol (4) exhibited stronger
inhibitory effect on melanogenesis without inducing cytotoxicity.
Therefore, 4 is promising therapeutic agents for the treatment of
skin disorders. Further structure activity relationship studies and
elucidation of the inhibitory mechanism are warranted.
d4, 500 MHz) d 2.70 (t, J = 7.6 Hz H2-1), 2.77 (t, J = 7.6 Hz H2-2), 6.10 (d,
J = 15.8 Hz, H-4), 6.56 (d, J = 8.3 Hz, H-30,50), 6.62 (d, J = 8.3 Hz, H-500), 6.65 (dd,
J = 15.8, 11.0 Hz H-5), 6.76 (br d, J = 8.3 Hz, H-600), 6.77 (d, J = 15.8 Hz H-7), 6.87
(br s, H-200), 6.90 (d, J = 8.3 Hz, H-20,60), 7.24 (dd, J = 15.8, 11.0 Hz H-6); 13C
NMR: given in Table 1; EIMS m/z 310 [M]+; HREIMS m/z 310.1207 (calcd for
C
19H18O4 [M]+, m/z 310.1205).
24. Diarylcomosol II (3): A colorless oil; ½a D25
ꢁ
+12.6 (c 0.50, MeOH); IR (film) vmax
)]: 261 (4.11), 288 (3.45);
3400, 2945, 1615, 1510 cmꢀ1; UV [MeOH, nm, (log
e
1H NMR (methanol-d4, 500 MHz) 1.59 (m, H2-4), 2.20 (m, H-5a), 2.28 (m, H-
5b), 2.57 (m, H-1a), 2.68 (m, H-1b), 1.69 (m, H-2a), 1.74 (m, H-2b), 3.58 (m, H-
3), 3.79 (s, 30-OCH3), 5.98 (ddd, J = 15.9, 6.9, 6.9 Hz, H-6), 6.26 (d, J = 15.9 Hz H-
7), 6.61 (dd, J = 8.6, 1.9 Hz, H-60), 6.67 (d, J = 8.6 Hz, H-50), 6.67 (d,J = 8.6 H-
300,500), 6.75 (d, J = 1.9 Hz, H-20), 7.13 (d, J = 8.6 Hz H-200,600); 13C NMR: given in
Table 1; EIMS: m/z 328 [M]+; HREIMS m/z 328.1676 (calcd for C20H24O4 [M]+,
m/z 328.1674).
25. Diarylcomosol III (6): A colorless oil; ½a D25
ꢁ
ꢀ0.10 (c 0.50, MeOH); IR (film) vmax
3400, 2942, 1615, 1516 cmꢀ1; UV [MeOH, nm, (log
e
)]: 279 (3.39); 1H NMR
Acknowledgments
(methanol-d4, 500 MHz) 1.57 (m, H2-4), 1.62 (m, H2-6), 1.70 (m, H2-2), 2.48 (m,
H-7a), 2.51 (m, H-1b), 2.59 (m, H-7b), 2.61 (m, H-1b), 3.70 (m, H-3, 5), 3.74 (s,
30, 50-OCH3), 6.41 (s, H-20, 60), 6.62 (d, J = 8.3 Hz, H-300, 500), 6.93 (d, J = 8.3 Hz, H-
200, 600); 13C NMR: given in Table 1; EIMS: m/z 376 [M]+; HREIMS m/z 376.1888
(calcd for C21H28O6 [M]+, m/z 376.1886.
This research was supported in part by a Ministry of Education,
Culture, Sports, Science and Technology (MEXT)-Supported Pro-
gram for the Strategic Research Foundation at Private Universities,
by a Grant-in-Aid for Young Scientists (B) from theJapan Society for
the Promotion of Science (JSPS).
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Supplementary data
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.07.
010.