Synthesis of all stereoisomers of 3,3′-dimethoxy-7,7′- epoxylignane-4,4′-diol and their plant growth inhibitory activity

Article abstract of DOI:10.1021/jf4046396

All stereoisomers of 3,3′-dimethoxy-7,7′-epoxylignane-4, 4′-diol were synthesized to examine the effect of stereochemistry on their plant growth inhibitory activity using lettuce and Italian ryegrass. The effect of structural modifications such as dehydro

Full text of DOI:10.1021/jf4046396

Article
pubs.acs.org/JAFC
Synthesis of All Stereoisomers of 3,3′-Dimethoxy-7,7′-epoxylignane-
4,4′-diol and Their Plant Growth Inhibitory Activity
Hisashi Nishiwaki, Kumiko Nakayama, Yoshihiro Shuto, and Satoshi Yamauchi*
Faculty of Agriculture, Ehime University, 3-5-7 Tarumi, Matsuyama, Ehime 790-8566, Japan
S
* Supporting Information
ABSTRACT: All stereoisomers of 3,3′-dimethoxy-7,7′-epoxylignane-4,4′-diol were synthesized to examine the effect of stereochemistry
on their plant growth inhibitory activity using lettuce and Italian ryegrass. The effect of structural modifications such as dehydroxylation,
methoxylation and hydroxylation at the 9- and 9′-positions of the lignans on the activity was also studied. Most of the epoxylignanes
showed higher plant growth inhibitory potency against ryegrass than against lettuce, and the inhibitory activity varied depending on the
configurations of each position of the tetrahydrofuran ring (7-, 7′-, 8-, and 8′-positions of the epoxylignanes). Among the 9,9′-position-
modified derivatives, the dehydroxy derivatives showed the highest potency. These results suggested that the plant growth inhibitory
activity should be influenced by the structure of the epoxylignanes.
KEYWORDS: 3,3′-dimethoxy-7,7′-epoxylignane-4,4′-diol, lignan, plant growth inhibitory activity, lettuce, Italian ryegrass
modified to provide the stereoisomers of 3,3′-dimethoxy-7,7′-
epoxylignane-4,4′-diol. This research would contribute to the
collation of stereoisomer libraries of natural products.
INTRODUCTION
■
Lignans widely distributed in plants exert various biological
activities such as anticancer and antioxidant activities.1
Lariciresinol, which is a trisubstituted tetrahydrofuran lignan,
has also interesting biological activities including phytotoxic
activity. Our previous study of the effect of the stereochemistry
of lariciresinol on plant growth regulatory activity against
lettuce (Lactuca sativa L.) and Italian ryegrass (Lolium
multiflorum Lam.) demonstrated that the phytotoxic activity
of lariciresinol depended on its stereochemistry, that is, the
importance of both the 8S absolute configuration and the 7,8′-
trans relative configuration for high activity.2 It is undoubted
that lignans other than lariciresinol should also show potent
phytotoxic activity, as reported for diayangambin and
dihydrodiconiferyl alcohol,3,4 and that the structural modifica-
tion as well as the absolute structure of lignans should influence
their phytotoxicity, but data regarding the phytotoxicity of
lignans, especially in-depth discussion of the relationship
between their stereochemistry and activity, are less available.
Herein we focused on the relationship between the
stereochemistry of 3,3′-dimethoxy-7,7′-epoxylignane-4,4′-diol
compounds, which are tetrasubstituted tetrahydrofuran lignans
(Figure 1), and their plant growth regulatory activity. In
addition, the effect of the structural modifications at the
9- and 9′-positions such as dehydroxylation, methoxylation
and hydroxylation on the activity was also studied. Some of these
lignans have been isolated and named as follows: (−)-verrucosin,
1 (1-H, (−)-odoratisol);5,6 (+)-verrucosin, 4 (2-H);7 (+)-fra-
gransin A2, 7 (3-H);7 (+)-neo-olivil, 9 (3-OH);8 (+)-saucernetin
diol, 13 (5-H);9,10 (−)-neo-olivil, 18 (6-OH);11 (−)-machilin-I,
22 (8-H);12 nectandrin B, 25 (9-H);7 and tetrahydrofuroguaia-
cin B, 28 (10-H).10 The syntheses of 1,13 7,13 and 1314,15 have
been achieved, and the conversion from glucoside to 27 (9-OH)
has been reported.16 The other stereoisomers were synthesized
for the first time in this project. In our previous studies, the
constructions of all stereochemistries of 7,7′-epoxylignane
have been established,17−19 and these synthetic methods were
MATERIALS AND METHODS
■
Chemicals. The synthetic scheme is shown in Figure 2. Reagents
used for the syntheses were purchased from Wako Pure Chemical
Industries, Ltd. (Osaka, Japan), Nacalai Tesque, Inc. (Kyoto, Japan),
Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan), and Aldrich
Chemical Co (Milwaukee, WI, USA). Melting points were
uncorrected. Optical rotations were measured on a SEPA-200
instrument (Horiba Ltd., Kyoto, Japan). NMR data were obtained
using a Bruker AVANCE III 500 spectrometer (Bruker BioSpin K.K.,
Kanagawa, Japan). EIMS data were measured with a JMS-MS700 V
spectrometer (JEOL Ltd., Tokyo, Japan). The silica gel used was
Wakogel C-300 (Wako, 200−300 mesh). The numbering of com-
pounds follows the nomenclature of lignans.20 Information for
compounds 1, 4, 7, 9, 10, 12, 13, 15, 16, 18, 19, 22, 25, 27, and 28
(1-H−10-H, 3-OH, 4-OH, 5-OH, 6-OH, and 9-OH), which has been
published,5−8,10,11,13,14,16,21 was placed in the Supporting Information.
(7S,7′R,8S,8′S)-4,4′-Dibenzyloxy-3,3′-dimethoxy-7,7′-epoxy-
1
lignane-9,9′-diol, 31: colorless oil; [α]20 −18 (c 1.2, CHCl3); H
D
NMR (500 MHz, CDCl3) δ 2.23 (1H, m, H-8′), 2.55 (1H, m, H-8),
2.65−3.00 (1H, br, OH), 3.08 (1H, dd, J = 10.3, 9.9 Hz, H-9a), 3.18−
3.48 (1H, br, OH), 3.30 (1H, dd, J = 10.3, 4.7 Hz, H-9b), 3.55 (1H,
dd, J = 9.6, 9.0 Hz, H-9′a), 3.72 (1H, dd, J = 9.6, 3.4 Hz, H-9′b), 3.84
(3H, s, 3-OCH3), 3.88 (3H, s, 3′-OCH3), 4.47 (1H, d, J = 9.4 Hz, H-
7′), 5.09 (1H, d, J = 8.7 Hz, H-7), 5.11 (2H, s, CH2OPh), 5.14 (2H, s,
CH2OPh), 6.82 (2H, s, H-5, H-6), 6.84 (1H, d, J = 8.3 Hz, H-5′), 6.89
(1H, s, H-2), 6.92 (1H, dd, J = 8.3, 1.9 Hz, H-6′), 7.04 (1H, d, J = 1.9
Hz, H-2′), 7.27−7.30 (2H, m, BnO), 7.33−7.37 (4H, m, BnO), 7.40−
7.43 (4H, m, BnO); 13C NMR (125 MHz, CDCl3) δ 50.9 (C-8), 54.9
(C-8′), 56.0 (C-9′), 56.1 (C-9), 63.0 (OCH3), 63.7 (OCH3), 71.10
(OCH2Ph), 71.13 (OCH2Ph), 81.2 (C-7), 82.5 (C-7′), 110.4 (C-2′),
110.8 (C-2), 113.9 (C-5), 114.0 (C-5′), 118.7 (C-6′), 119.0 (C-6),
Received: October 15, 2013
Revised: December 21, 2013
Accepted: December 22, 2013
Published: December 22, 2013
© 2013 American Chemical Society
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Figure 1. Chemical structures of the epoxylignanes synthesized in the present study.
127.26 (OBn), 127.33 (OBn), 127.86 (OBn), 127.88 (OBn), 128.53
(OBn), 128.55 (OBn), 132.1 (C-1), 133.2 (C-1′), 137.0 (OBn), 137.1
(OBn), 147.7 (C-4), 148.1 (C-4′), 149.5 (C-3), 149.8 (C-3′). Anal.
Found: C, 73.38%; H, 6.60%. Calcd for C34H36O7: C, 73.36%; H,
6.52%.
MS (EI) m/z 376 (M+, 51), 224 (71), 193 (81), 176 (100), 151 (62),
137 (69); HRMS (EI) m/z calcd for C20H24O7 (M+) 376.1522, found
376.1515.
(7R,7′S,8R,8′R)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-diol, 5
(2-OCH3): colorless oil; [α]20D +21 (c 0.2, CHCl3); NMR data agreed
with those of 2.
(7R,7′S,8R,8′R)-3,3′-Dimethoxy-7,7′-epoxylignane-4,4′,9,9′-tetraol,
6 (2-OH): colorless oil; [α]20D +20 (c 0.1, MeOH); NMR data agreed
with those of 3.
(7R,7′S,8R,8′R)-4,4′-Dibenzyloxy-3,3′-dimethoxy-7,7′-epoxy-
lignane-9,9′-diol, 32: colorless oil; [α]20 +18 (c 1.6, CHCl3); NMR
D
data agreed with those of 31.
(7S,7′R,8S,8′S)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-
1
diol, 2 (1-OCH3): colorless oil; [α]20 −21 (c 1.1, CHCl3); H NMR
(7R,7′R,8S,8′S)-4,4′-Dibenzyloxy-3,3′-dimethoxy-7,7′-epoxy-
D
1
lignane-9,9′-diol, 33: colorless oil; [α]20 +46 (c 2.6, CHCl3); H
(500 MHz, CDCl3) δ 2.37 (1H, m, H-8′), 2.63 (1H, m, H-8), 2.97
(1H, dd, J = 9.3, 5.8 Hz, H-9a), 3.07−3.10 (1H, overlapped, H-9b),
3.08 (3H, s, 9-OCH3), 3.36 (3H, s, 9′-OCH3), 3.51 (1H, dd, J = 9.5,
5.2 Hz, H-9′a), 3.55 (1H, dd, J = 9.5, 5.4 Hz, H-9′b), 3.86 (3H, s, 3-
OCH3), 3.90 (3H, s, 3′-OCH3), 4.72 (1H, d, J = 8.0 Hz, H-7′), 5.10
(1H, d, J = 7.3 Hz, H-7), 5.70 (1H, s, ArOH), 5.74 (1H, s, ArOH),
6.89−6.92 (4H, m, H-2, H-5, H-5′, H-6), 6.99 (1H, dd, J = 8.2, 1.9 Hz,
H-6′), 7.01 (1H, d, J = 1.9 Hz, H-2′); 13C NMR (125 MHz, CDCl3) δ
46.7 (C-8), 50.6 (C-8′), 55.85 (9-OCH3), 55.90 (9′-OCH3), 58.6 (3′-
OCH3), 59.0 (3-OCH3), 73.1 (C-9′, C-9), 81.6 (C-7), 82.7 (C-7′),
109.3 (C-2′), 109.5 (C-2), 114.0 (C-5), 114.2 (C-5′), 119.3 (C-6′),
119.5 (C-6), 130.9 (C-1), 133.5 (C-1′), 144.7 (C-4), 145.2 (C-4′),
146.2 (C-3), 146.5 (C-3′); MS (EI) m/z 404 (M+, 34), 175 (100);
HRMS (EI) m/z calcd for C22H28O7 (M+) 404.1835, found 404.1834.
(7S,7′R,8S,8′S)-3,3′-Dimethoxy-7,7′-epoxylignane-4,4′,9,9′-tetraol,
D
NMR (500 MHz, CDCl3) δ 2.19 (2H, m, H-8, H-8′), 3.44 (2H, dd,
J = 9.1, 8.8 Hz, H-9a, H-9′a), 3.63 (2H, d, J = 9.1 Hz, H-9b, H-9′b),
3.84 (6H, s, OCH3), 4.22 (2H, br s, OH), 4.66 (2H, d, J = 9.0 Hz, H-7,
H-7′), 5.09 (4H, s, OCH2Ph), 6.76 (2H, dd, J = 8.3, 1.9 Hz, H-6,
H-6′), 6.82 (2H, d, J = 8.3 Hz, H-5, H-5′), 6.92 (2H, d, J = 1.9 Hz,
H-2, H-2′), 7.24−7.27 (2H, m, OBn), 7.30−7.33 (4H, m, OBn),
7.38−7.66 (4H, m, Bn); 13C NMR (125 MHz, CDCl3) δ 56.1
(OCH3), 57.0 (C-8, C-8′), 62.6 (C-9, C-9′), 71.1 (OCH2Bn), 83.1 (C-
7, C-7′), 110.0 (C-2, C-2′), 113.9 (C-5, C-5′), 118.7 (C-6, C-6′), 127.3
(OBn), 127.6 (OBn), 127.8 (OBn), 128.5 (OBn), 134.6 (C-1), 134.8 (C-
1′), 137.0 (Bn), 147.9 (C-4, C-4′), 149.8 (C-3, C-3′). Anal. Found: C,
73.40%; H, 6.53%. Calcd. for C34H36O7: C, 73.36%; H, 6.52%.
(7S,7′S,8R,8′R)-4,4′-Dibenzyloxy-3,3′-dimethoxy-7,7′-epoxy-
lignane-9,9′-diol, 34: colorless oil; [α]20 −49 (c 0.9, CHCl3); NMR
D
3 (1-OH): colorless oil; [α]20 −20 (c 1.4, MeOH); 1H NMR
data agreed with those of 33.
D
(500 MHz, CD3OD) δ 1.28 (2H, s, OH), 2.28 (1H, m, H-8′), 2.56
(1H, m, H-8), 3.16 (1H, dd, J = 10.4, 10.0 Hz, H-9a), 3.22 (1H, dd, J =
10.4, 5.1 Hz, H-9b), 3.64 (1H, dd, J = 11.0, 6.1 Hz, H-9′a), 3.71 (1H,
dd, J = 11.0, 4.7 Hz, H-9′b), 3.85 (3H, s, 3-OCH3), 3.89 (3H, s, 3′-
OCH3), 4.65 (1H, d, J = 8.6 Hz, H-7′), 5.10 (1H, d, J = 7.9 Hz, H-7),
6.78 (1H, d, J = 8.1 Hz, H-6), 6.80−6.85 (2H, m, H-2, H-5), 6.95−
6.97 (2H, m, H-5′, H-6′), 7.10 (1H, s, H-2′); 13C NMR (125 MHz,
CDCl3) δ 50.5 (C-8), 54.2 (C-8′), 54.89 (OCH3), 54.91 (OCH3),
60.5 (C-9′), 61.0 (C-9), 76.2 (C-7), 77.1 (C-7′), 98.9 (C-2′), 99.1 (C-
2), 102.5 (C-5), 102.7 (C-5′), 106.1 (C-6′), 106.3 (C-6), 115.2 (C-1),
116.9 (C-1′), 127.4 (C-4), 127.8 (C-4′), 128.8 (C-3), 129.1 (C-3′);
(7R,7′R,8S,8′S)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-
diol, 8 (3-OCH3): colorless crystals; mp 129−130 °C; [α]20 +29 (c
D
0.8, CHCl3); 1H NMR (500 MHz, CDCl3) δ 2.38 (2H, m, H-8, H-8′),
3.33 (6H, s, 9-OCH3, 9′-OCH3), 3.45 (2H, dd, J = 9.5, 4.5 Hz, H-9a,
H-9′a), 3.50 (2H, dd, J = 9.5, 5.0 Hz, H-9b, H-9′b), 3.89 (6H, s,
3-OCH3, 3′-OCH3), 4.96 (2H, d, J = 7.8 Hz, H-7, H-7′), 5.65 (2H, s,
4-OH, 4′OH), 6.87 (2H, d, J = 8.2 Hz, H-5, H-5′), 6.90 (2H, dd, J =
8.2, 1.5 Hz, H-6, H-6′), 7.00 (2H, d, J = 1.5 Hz, H-2, H-2′); 13C NMR
(125 MHz, CDCl3) δ 51.2 (C-8, C-8′), 56.0 (9-OCH3, 9′-OCH3),
59.0 (3-OCH3, 3′-OCH3), 72.4 (C-9, C-9′), 82.8 (C-7, C-7′), 108.8
(C-2, C-2′), 114.1(C-5, C-5′), 119.3(C-6, C-6′), 134.4 (C-1, C-1′),
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Figure 2. Synthetic schemes: (a) (1) MsCl, Et3N, CH2Cl2, rt, 30 min; (2) NaBH4, HMPA, 60 °C, 1.5 h; (3) H2, 5% Pd/C, EtOAc, ambient
temperature, 2 h (3 steps, 1-H, 57%; 2-H, 60%; 3-H, 43%; 4-H, 48%). (b) (1) NaH, MeI, THF, rt, 3 h; (2) H2, 5% Pd/C, ambient temperature, 5 h
(2 steps, 1-OCH3, 65%; 2-OCH3, 62%; 3-OCH3, 51%; 4-OCH3, 48%; 5-OCH3, 50%; 6-OCH3, 51%; 7-OCH3, 44%; 8-OCH3, 46%; 9-OCH3, 35%;
10-OCH3, 32%). (c) H2, 5% Pd/C, EtOAc, ambient temperature, 6 h (1-OH, 59%; 2-OH, 65%; 3-OH, 64%; 4-OH, 70%; 5-OH, 57%; 6-OH, 61%;
7-OH, 73%; 8-OH, 73%; 9-OH, 46%; 10-OH, 58%). (d) (1) MsCl, Et3N, CH2Cl2, rt, 30 min; (2) NaI, DBU, DMF, 80 °C, 30 min; (3) BH3·SMe2,
THF, rt, 1 h, and then saturated aqueous NaHCO3, 30% aqueous H2O2 (3 steps, 35, 13%; 37, 15%; 36, 15%; 38, 16%; 40, 23%). (e) (1) MsCl,
Et3N, CH2Cl2, rt, 30 min; (2) super-H, THF, rt for 5-H−9-H, 60 °C for 10-H, 2.5 h; (3) H2, 5% Pd/C, EtOAc, ambient temperature, 4 h (3 steps,
5-H, 27%; 6-H, 24%; 7-H, 12%; 8-H, 15%; 9-H, 24%; 10-H, 13%).
145.0 (C-4, C-4′), 146.6 (C-3, C-3′); MS (EI) m/z 404 (M+, 51), 175
(100); HRMS (EI) m/z calcd for C22H28O7 (M+) 404.1835, found
404.1833.
(c 1.1, CHCl3); 1H NMR (500 MHz, CDCl3) δ 2.70 (2H, m, H-8, H-8′),
2.78 (2H, br s, OH), 3.28 (1H, br d, J = 10.2 Hz, H-9a), 3.60 (1H, dd, J =
10.2, 10.2 Hz, H-9b), 3.72−3.85 (2H, m, H-9′), 3.85 (3H, s, OCH3), 3.88
(3H, s, OCH3), 4.91 (1H, d, J = 9.0 Hz, H-7′), 5.12 (2H, s, OCH2Ph),
5.13 (2H, s, OCH2Ph), 5.43 (1H, d, J = 4.7 Hz, H-7), 6.78 (1H, dd, J =
8.3, 1.6 Hz, H-6), 6.82−6.86 (3H, m, H-5, H-5′, H-6′), 6.90 (1H, d, J =
1.8 Hz. H-2), 6.95 (1H, d, J = 1.6 Hz, H-2′), 7.27−7.30 (2H, m, OBn),
7.33−7.36 (4H, m, OBn), 7.41−7.42 (4H, m, OBn); 13C NMR (125
MHz, CDCl3) δ 48.4 (C-8), 54.3 (C-8′), 56.09 (OCH3), 56.11 (OCH3),
59.8 (C-9′), 59.9 (C-9), 71.18 (OCH2Ph), 71.23 (OCH2Ph), 81.0 (C-7),
83.0 (C-7′), 109.6 (C-2′), 109.7 (C-2), 114.2 (C-5), 114.3 (C-5′), 117.9
(C-6′), 118.4 (C-6), 127.28 (OBn), 127.34 (OBn), 127.8 (OBn), 127.9
(OBn), 128.5 (OBn), 132.4 (C-1), 135.7 (C-1′), 137.15 (OBn), 137.18
(OBn), 147.4 (C-4), 147.9 (C-4′), 149.8 (C-3), 150.0 (C-3′); MS (EI)
m/z 556 (M+, 0.3), 137 (31), 91 (100); HRMS (EI) m/z calcd for
C34H36O7 (M+) 556.2462, found 556.2467.
(7S,7′S,8R,8′R)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-
diol, 11 (4-OCH3): colorless crystals; mp 130−131 °C; [α]20 −29
D
(c 0.4, CHCl3); NMR data agreed with those of 8.
(7R,7′R,8R,8′R)-4,4′-Dibenzyloxy-3,3′-dimethoxy-7,7′-epoxy-
lignane-9,9′-diol, 35, and (7R,7′R,8R,8′S)-4,4′-dibenzyloxy-3,3′-
dimethoxy-7,7′-epoxylignane-9,9′-diol, 37: 35, colorless oil; [α]20
D
+44 (c 1.3, CHCl3); 1H NMR (500 MHz, CDCl3) δ 2.50−2.70 (2H, br,
OH), 2.67 (2H, m, H-8, H-8′), 3.03−3.10 (2H, m, H-9a, H-9′a), 3.46
(2H, br d, J = 8.0 Hz, H-9b, H-9′b), 3.87 (6H, s, OCH3), 5.12 (4H, s,
OCH2Ph), 5.48 (2H, d, J = 6.8 Hz, H-7, H-7′), 6.77 (2H, d, J = 8.4 Hz,
H-5, H-5′), 6.84−6.86 (4H, m, H-2, H-2′, H-6, H-6′), 7.29−7.30 (2H, m,
OBn), 7.34−7.36 (4H, m, OBn), 7.41−7.43 (4H, m, OBn); 13C NMR
(125 MHz, CDCl3) δ 49.1 (C-8, C-8′), 56.1 (OCH3), 62.6 (C-9, C-9′),
71.2 (OCH2Ph), 82.5 (C-7, C-7′), 110.1 (C-2, C-2′), 114.1 (C-5, C-5′),
118.4 (C-6, C-6′), 127.28 (OBn), 127.33 (OBn), 127.9 (OBn), 128.5
(OBn), 133.6 (C-1, C-1′), 137.1 (OBn), 147.7 (C-4, C-4′), 149.7 (C-3,
C-3′); MS (EI) m/z 556 (M+, 1.5), 91 (100); HRMS (EI) m/z calcd for
(7S,7′S,8S,8′S)-4,4′-Dibenzyloxy-3,3′-dimethoxy-7,7′-epoxy-
lignane-9,9′-diol, 36, and (7S,7′S,8S,8′R)-4,4′-dibenzyloxy-3,3′-
C34H36O7 (M+) 556.2462, found 556.2470. 37, colorless oil; [α]20 +66
dimethoxy-7,7′-epoxylignane-9,9′-diol, 38: 36, colorless oil; [α]20 −44
D
D
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Figure 3. Plant growth inhibitory activity (percent from control) of test chemicals against root (A, C, E) and shoot (B, D, F) of lettuce when applied
at the concentration of 1 × 10−3 M. Data are presented as the mean standard error of the mean.
(c 1.1, CHCl3). 38, colorless oil; [α]20D −66 (c 1.2, CHCl3). NMR data of
36 and 38 agreed with those of 35 and 37, respectively.
5.8 Hz, H-9′a), 3.62 (1H, dd, J = 9.3, 8.5 Hz, H-9′b), 3.895 (3H, s, 3-
OCH3), 3.899 (3H, s, 3′-OCH3), 4.98 (1H, d, J = 8.5 Hz, H-7′), 5.44
(1H, d, J = 6.2 Hz, H-7), 5.56 (1H, s, ArOH), 5.57 (1H, s, ArOH),
6.83 (1H, dd, J = 8.1, 1.5 Hz, H-6), 6.85−6.91 (3H, m, H-5, H-5′, H-
6′), 6.95 (1H, d, J = 1.5 Hz, H-2), 7.03 (1H, d, J = 1.5 Hz, H-2′); 13C
NMR (125 MHz, CDCl3) δ 46.2 (C-8), 51.7 (C-8′), 56.0 (9-OCH3,
9′-OCH3), 58.5 (3-OCH3), 58.8 (3′-OCH3), 69.3 (C-9), 70.5 (C-9′),
82.7 (C-7′), 83.6 (C-7), 108.5 (C-2′), 109.1 (C-2), 113.8 (C-5), 114.1
(C-5′), 119.20 (C-6′), 119.23 (C-6), 131.8 (C-1), 135.4 (C-1′), 145.1
(C-4, C-4′), 146.3 (C-3), 146.7 (C-3′); MS (EI) m/z 404 (M+, 28),
210 (51), 207 (63), 175 (100); HRMS (EI) m/z calcd for C22H28O7
(M+) 404.1835, found 404.1836.
(7R,7′R,8R,8′R)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-
diol, 14 (5-OCH3): colorless oil; [α]20D +21 (c 0.2, CHCl3); 1H NMR
(500 MHz, CDCl3) δ 2.73 (2H, m, H-8, H-8′), 2.85 (2H, dd, J = 9.4,
6.7 Hz, H-9a, H-9′a), 3.13 (2H, dd, J = 9.4, 2.6 Hz, H-9b, H-9′b), 3.16
(6H, s, 9-OCH3, 9′-OCH3), 3.90 (6H, s, 3-OCH3, 3′-OCH3), 5.54
(2H, d, J = 6.6 Hz, H-7, H-7′), 5.57 (2H, s, ArOH), 6.84 (2H, dd, J =
8.2, 1.5 Hz, H-6, H-6′), 6.89−6.90 (4H, m, H-2, H-2′, H-5, H-5′); 13C
NMR (125 MHz, CDCl3) δ 45.4 (C-8, C-8′), 56.0 (9-OCH3, 9′-
OCH3), 58.7 (3-OCH3, 3′-OCH3), 71.9 (C-9, C-9′), 82.4 (C-7, C-7′),
109.0 ((C-2, C-2′), 114.0 (C-5, C-5′), 119.3 (C-6, C-6′), 132.3 (C-1,
C-1′), 144.7 (C-4, C-4′), 146.3 (C-3, C-3′); MS (EI) m/z 404 (M+,
14), 210 (100), 194 (53), 175 (94); HRMS (EI) m/z calcd for
C22H28O7 (M+) 404.1835, found 404.1831.
(7R,7′R,8R,8′S)-3,3′-Dimethoxy-7,7′-epoxylignane-4,4′,9,9′-tetraol,
21 (7-OH): colorless oil; [α]20 +56 (c 0.1, MeOH); 1H NMR
D
(500 MHz, CD3OD) δ 2.71 (2H, m, H-8, H-8′), 3.53 (1H, dd, J =
11.5, 8.8 Hz, H-9), 3.68 (1H, dd, J = 11.5, 4.5 Hz, H-9), 3.80−3.92
(2H, overlapped, H-9′, H-9′), 3.85 (3H, s, 3-OCH3), 3.88 (3H, s, 3′-
OCH3), 4.98 (1H, d, J = 8.5 Hz, H-7′), 5.47 (1H, d, J = 5.4 Hz, H-7),
6.77−6.83 (3H, m, H-5, H-5′, H-6), 6.86 (1H, dd, J = 8.3, 1.8 Hz, H-
6′), 6.97 (1H, d, J = 1.4 Hz, H-2), 7.01 (1H, d, J = 1.8 Hz, H-2′); 13C
NMR (125 MHz, CD3OD) δ 55.4 (C-8, C-8′), 56.46 (3-OCH3),
56.51 (3′-OCH3), 60.0 (C-9), 60.5 (C-9′), 83.1 (C-7′), 84.7 (C-7),
110.88 (C-2′), 110.94 (C-2), 116.0 (C-5), 116.2 (C-5′), 119.8 (C-6′),
(7S,7′S,8S,8′S)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-diol,
17 (6-OCH3): colorless oil; [α]20 −20 (c 0.1, CHCl3); NMR data
D
agreed with those for 14.
(7R,7′R,8R,8′S)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-diol,
20 (7-OCH3): colorless oil; [α]20 +39 (c 0.2, CHCl3); 1H NMR
D
(500 MHz, CDCl3) δ 2.67 (1H, m, H-8′), 2.74 (1H, m, H-8), 3.09
(1H, dd, J = 9.8, 5.3 Hz, H-9a), 3.12 (3H, s, 9-OCH3), 3.21 (1H, dd,
J = 9.8, 4.1 Hz, H-9b), 3.30 (3H, s, 9′-OCH3), 3.44 (1H, dd, J = 9.3,
654
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Figure 4. Plant growth inhibitory activity (percent from control) of 1-H−10-H against root (A) and shoot (B) of lettuce when applied at
concentrations from 1 × 10−3 to 1 × 10−8 M (from left to right for each compound). The plant growth activity of the commercial herbicide, diuron,
was as follows: for root (1 × 10−3−1 × 10−8 M), −48.5 1.78%, −37.6 1.48%, −9.9 3.05%, −2.8 5.09%, −8.2 4.04%, and 0.0 7.85%; for
shoot (1 × 10−3−1 × 10−8 M), −29.9 5.09%, −23.7 1.06%, +7.8 6.67%, +13.9 6.24,% +8.1 6.24%, and +9.0 1.55%. Data are presented
as the mean standard error of the mean.
120.2 (C-6), 132.3 (C-1), 135.6 (C-1′), 146.8 (C-4), 147.3 (C-4′),
148.9 (C-3), 149.2 (C-3′); MS (EI) m/z 376 (M+, 49), 193 (79), 175
(86), 151 (100), 137 (84); HRMS (EI) m/z calcd for C20H24O7 (M+)
376.1522, found 376.1519.
3.7 Hz, H-9a, H-9′a), 3.43 (2H, dd, J = 11.2, 9.9 Hz, H-9b, H-9′b),
3.88 (6H, s, OCH3), 5.11 (2H, d, J = 6.9 Hz, H-7, H-7′), 5.14 (4H, s,
OCH2Ph), 6.87 (4H, s, H-5, H-5′, H-6, H-6′), 6.95 (2H, s, H-2, H-2′),
7.28−7.31 (2H, m, OBn), 7.34−7.37 (4H, m, OBn), 7.42−7.44 (4H,
m, OBn); 13C NMR (125 MHz, CDCl3) δ 48.0 (C-8, C-8′), 56.0
(OCH3), 60.9 (C-9, C-9′), 71.2 (OCH2Ph), 80.9 (C-7, C-7′), 109.9
(C-2, C-2′), 114.1 (C-5, C-5′), 118.2 (C-6, C-6′), 127.3 (OBn), 127.9
(OBn), 128.6 (OBn), 132.1 (C-1, C-1′), 137.1 (OBn), 147.5 (C-4,
C-4′), 149.6 (C-3, C-3′); MS (EI) m/z 556 (M+, 0.4), 91 (100); HRMS
(EI) m/z calcd for C34H36O7 (M+) 556.2462, found 556.2464.
(7S,7′S,8S,8′R)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-diol,
23 (8-OCH3): colorless oil; [α]20 −39 (c 0.2, CHCl3); NMR data
D
agreed with those of 20.
(7S,7′S,8S,8′R)-3,3′-Dimethoxy-7,7′-epoxylignane-4,4′,9,9′-tetraol,
24 (8-OH): colorless oil; [α]20D −56 (c 0.1, MeOH); NMR data agreed
with those of 21.
(7R,7′S,8S,8′R)-4,4′-Dibenzyloxy-3,3′-dimethoxy-7,7′-epoxy-
(7R,7′S,8R,8′S)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-diol,
29 (10-OCH3): colorless oil; 1H NMR (500 MHz, CDCl3) δ 2.85 (2H,
m, H-8, H-8′), 3.03 (2H, dd, J = 9.6, 6.1 Hz, H-9a, H-9′a), 3.05 (6H, s,
9-OCH3, 9′-OCH3), 3.26 (2H, dd, J = 9.6, 6.2 Hz, H-9b, H-9′b), 3.91
(6H, s, 3-OCH3, 3′-OCH3), 5.17 (2H, d, J = 7.0 Hz, H-7, H-7′), 5.59
(2H, s, 4-OH, 4′-OH), 6.91 (2H, d, J = 8.1 Hz, H-5, H-5′), 6.97 (2H, dd,
J = 8.1, 1.4 Hz, H-6, H-6′), 7.07 (2H, d, J = 1.4 Hz, H-2, H-2′); 13C NMR
(125 MHz, CDCl3) δ 46.5 (C-8, C-8′), 55.9 (9-OCH3, 9′-OCH3), 58.4
(3-OCH3, 3′-OCH3), 70.2 (C-9, C-9′), 81.5 (C-7, C-7′), 109.5 (C-2,
C-2′), 113.9 (C-5, C-5′), 119.5 (C-6, C-6′), 131.2 (C-1, C-1′), 144.6
(C-4, C-4′), 146.1 (C-3, C-3′); MS (EI) m/z 404 (M+, 32), 175 (100);
HRMS (EI) m/z calcd for C22H28O7 (M+) 404.1835, found 404.1831.
(7R,7′S,8R,8′S)-3,3′-Dimethoxy-7,7′-epoxylignane-4,4′,9,9′-tetraol,
30 (10-OH): colorless oil; 1H NMR (500 MHz, CD3OD) δ 2.91 (2H,
m, H-8, H-8′), 3.29 (2H, dd, J = 11.2, 4.2 Hz, H-9a, H-9′a), 3.44 (2H,
dd, J = 11.2, 10.2 Hz, H-9b, H-9′b), 4.84 (6H, s, OCH3), 5.13 (2H, d,
J = 6.9 Hz, H-7, H-7′), 6.82 (2H, d, J = 8.1 Hz, H-5, H-5′), 6.89 (2H,
dd, J = 8.1, 1.7 Hz, H-6, H-6′), 7.02 (2H, d, J = 1.7 Hz, H-2, H-2′); 13C
NMR (125 MHz, CD3OD) δ 49.4 (C-8, C-8′), 56.4 (OCH3), 61.4 (C-9,
C-9′), 82.6 (C-7, C-7′), 111.1 (C-2, C-2′), 116.1 (C-5, C-5′), 120.0 (C-6,
C-6′), 131.9 (C-1, C-1′), 146.9 (C-4, C-4′), 148.9 (C-3, C-3′); MS (EI)
m/z 376 (M+, 43), 224 (54), 193 (81), 175 (100), 151 (66), 137 (69);
HRMS (EI) m/z calcd for C20H24O7 (M+) 376.1522, found 376.1523.
Evaluation of Plant Growth Inhibitory Activity. For all of the
synthesized epoxylignane derivatives, their plant growth inhibitory
activities were evaluated using lettuce (L. sativa L., green-wave (Takii
Seed Co. Ltd., Kyoto, Japan)) and Italian ryegrass (L. multiflorum
Lam., wase-fudo (Takii Seed Co. Ltd., Kyoto, Japan)), according to
our earlier paper.2 Briefly, 30 seeds of each plant were placed on a filter
paper (in a 90 mm Petri dish) moisturized with 3 mL of water
1
lignane-9,9′-diol, 39: colorless crystals; mp 79−80 °C (MeOH); H
NMR (500 MHz, CDCl3) δ 2.57 (2H, m, H-8, H-8′), 3.19 (2H, br s,
OH), 3.75 (2H, dd, J = 11.4, 2.6 Hz, H-9, H-9′), 3.87 (6H, s, OCH3),
3.89 (2H, dd, J = 11.4, 3.9 Hz, H-9, H-9′), 4.62 (2H, d, J = 7.3 Hz, H-
7, H-7′), 5.14 (4H, s, OCH2Ph), 6.85 (2H, d, J = 8.3 Hz, H-5, H-5′),
6.89 (2H, dd, J = 8.3, 1.8 Hz, H-6, H-6′), 6.99 (2H, d, J = 1.8 Hz),
7.28−7.30 (2H, m, OBn), 7.34−7.37 (4H, m, OBn), 7.42−7.43 (4H,
m, OBn); 13C NMR (125 MHz, CDCl3) δ 51.6 (C-8, C-8′), 56.0
(OCH3), 60.4 (C-9, C-9′), 71.1 (OCH2Ph), 82.1 (C-7, C-7′), 110.4
(C-2, C-2′), 114.0 (C-5, C-5′), 118.8 (C-6, C-6′), 127.3 (OBn), 127.8
(OBn), 128.5 (OBn), 134.3 (C-1, C-1′), 137.1 (OBn), 148.0 (C-4, C-
4′), 149.8 (C-3, C-3′). Anal. Found: C, 73.40%; H, 6.34%. Calcd for
C34H36O7: C, 73.36%; H, 6.52%.
(7R,7′S,8S,8′R)-3,3′,9,9′-Tetramethoxy-7,7′-epoxylignane-4,4′-diol,
1
26 (9-OCH3): colorless oil; H NMR (500 MHz, CDCl3) δ 2.61 (2H,
m, H-8, H-8′), 3.34 (6H, s, 9-OCH3, 9′-OCH3), 3.50 (2H, dd, J = 9.5,
5.0 Hz, H-9a, H-9′s), 3.57 (2H, dd, J = 9.5, 6.3 Hz, H-9b, H-9′b), 3.84
(6H, s, 3-OCH3, 3′-OCH3), 4.82 (2H, d, J = 6.6 Hz, H-7, H-7′), 5.71
(2H, s, 4-OH, 4′-OH), 6.87 (2H, d, J = 8.0 Hz, H-5, H-5′), 6.92 (2H,
dd, J = 8.0, 1.8 Hz, H-6, H-6′), 6.96 (2H, d, J = 1.8 Hz, H-2, H-2′);
13C NMR (125 MHz, CDCl3) δ 49.0 (C-8, C-8′), 55.8 (9-OCH3, 9′-
OCH3), 58.9 (3-OCH3, 3′-OCH3), 70.6 (C-9, C-9′), 82.9 (C-7, C-7′),
109.3 (C-2, C-2′), 114.2 (C-5, C-5′), 119.4 (C-6, C-6′), 134.0 (C-1,
C-1′), 145.1 (C-4, C-4′), 146.5 (C-3, C-3′); MS (EI) m/z 404 (M+,
30), 210 (73), 194 (54), 175 (100), 151 (52); HRMS (EI) m/z calcd
for C22H28O7 (M+) 404.1835, found 404.1835.
(7R,7′S,8R,8′S)-4,4′-Dibenzyloxy-3,3′-dimethoxy-7,7′-epoxy-
1
lignane-9,9′-diol, 40: colorless oil; H NMR (500 MHz, CDCl3) δ
2.75 (2H, br s, OH), 2.90 (2H, m, H-8, H-8′), 3.35 (2H, dd, J = 11.2,
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Figure 5. Plant growth inhibitory activity (percent from control) of test chemicals against root (A, C, E) and shoot (B, D, F) of ryegrass when
applied at the concentration of 1 × 10−3 M. Data are presented as the mean standard error of the mean.
containing each sample at the concentration of 1.0 mM. After they
were incubated in the dark at 20 °C for 3 and 5 days for lettuce and
grass, respectively, the lengths of their roots and shoots were measured
using a ruler. Experiments were performed in triplicate, and statistical
analyses were conducted by one-way ANOVA followed by Tukey’s
multiple-comparison test using PRISM software (Graphpad Software,
San Diego, CA, USA).
38 were obtained from diol 34. The intermediate 40 was obtained
by the isomerization of 39 using elimination followed by
hydroboration. The intermediates 35−38 and 40 were subjected
to mesylations followed by superhydride reductions, giving 5-H,
6-H, 7-H, 8-H, and 10-H, respectively.
Among 10 stereoisomers of H-type epoxylignane (1-H−10-
H), the compounds with the configurations of 7S,7′R,8R,8′R
(1-H) and 7R,7′S,8R,8′S (9-H) suppressed the growth of
lettuce root to −94 and −69%, respectively, whereas the other
stereoisomers showed less activity (from −25 to +7.5%)
(Figure 3A). Against the lettuce shoot (Figure 3B), −60 and
−52% inhibitions relative to the control were observed for 1-H
and 2-H, respectively. On the other hand, 5-H, 6-H, 7-H, 8-H,
and 9-H suppressed the shoot growth moderately (from −20
to −40%), but statistically insignificant relative to the control.
The application of 3-H, 4-H, and 10-H did not influence the
lettuce shoot growth. With these results taken together, 1-H
showed the highest potency against lettuce. Introduction of the
methoxy and hydroxyl groups to the 9 and 9′ carbon atoms (1-
OCH3−10-OCH3 and 1-OH−10-OH) induced the absolute
values of the growth rate below 25% (Figure 3C−F),
demonstrating that the modification of the 9 and 9′ carbon
atoms with the methoxy and hydroxyl groups influences the
For compounds 1-H and 2-H, the germination rates of lettuce and
grass seeds were recorded 3 days after seeding.
RESULTS AND DISCUSSION
■
The intermediates 31−34 and 39 were synthesized according
to the previously described method with modification.17−19
The mesylation of the two hydroxyl groups, followed by
reduction, gave dimethyl compounds. To obtain 1-H, 2-H, 3-H,
and 4-H, NaBH4 in hexamethylphosphoramide (HMPA) was
employed for the corresponding mesylates. On the other hand,
lithium triethylborohydride (superhydride) was used for
reduction of mesylate from the intermediate 39, giving 9-H. To
prepare the intermediates 35 and 37, compound 33 was selected
as a starting compound. After conversion of 33 to the correspond-
ing conjugated diene by elimination, hydroboration was tried to
give two stereoisomers 35 and 37. By the same procedure, 36 and
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Figure 6. Plant growth inhibitory activity (precent from control) of 1-H−10-H against root (A) and shoot (B) of ryegrass when applied at
concentrations from 1 × 10−3 to 1 × 10−8 M (from left to right for each compound). The plant growth activity of the commercial herbicide, diuron,
was as follows: for root (1 × 10−3−1 × 10−8 M), −78.2 3.79%, −49.8 2.47%, −21.8 8.69%, −4.83 1.29%, −0.02 6.1%3, and −9.70
8.83%; for shoot (1 × 10−3−1 × 10−8 M), −66.7 8.15%, −32.9 6.29%, −24.1 8.59%, −21.9 3.19%, −15.8 5.54%, and −25.4 5.52%.
Data are presented as the mean standard error of the mean.
activity adversely. At the dose-dependent assay for evaluating
the influence on the lettuce growth of the H-type epoxylignane
compounds, the compounds did not influence the root growth
at the diluted concentrations (Figure 4A). The inhibitory
activity of 2-H against the lettuce shoot decreased depending
on the dilution of the concentration, but no significant activity
was observed for the other compounds at the tested concentra-
tions (Figure 4B).
The phytotoxicity of all stereoisomers of lariciresinol has
been evaluated in our previous paper,2 in which (−)-lariciresinol
and its 7S,8S,8′R stereoisomer have been found to inhibit the
growth of Italian ryegrass as well as suppress the germination of
the ryegrass seed to some extent. The most potent compound in
the present study, 2-H, inhibited the root growth of ryegrass
almost completely, demonstrating that lariciresinol, which
suppressed the growth of ryegrass root to around 50%, was
less potent than 2-H. Lariciresinol has the hydroxyl group at the
9-position, and all of the OH-type epoxylignanes in the present
study were slightly potent, suggesting that hydrophilic features of
the compounds having a hydroxyl group at the 9-position should
be adverse to the root growth of ryegrass. Because the
substitution patterns on the epoxylignanes synthesized in this
study are basically different from that of lariciresinol, the effects
of the conformations of each compound on the phytotoxicity
were not compared.
The germination rate of the lettuce seed applied by 1-H,
which showed the highest inhibitory activity against the lettuce
root (Figure 3), was 92.5 1.12% (mean SEM, n = 3), which
was almost the same as the control (95.7 2.15%, n =3). Also,
the germination rate of the ryegrass seed applied by 2-H, which
almost completely suppressed the growth of the ryegrass root
(Figure 5), was 87.3 2.07% (n = 3), which was a little smaller
than that of the control (94.7 2.78%, n = 3), suggesting that
these potent epoxylignanes should not suppress the germination
process of the seed, unlike lariciresinol,2 but influence the
development and growth process other than germination. Because
the inhibitory effects of the compounds on the shoot of both
lettuce and grass were similar (in Figures 3B and 5B, 3-H and 4-H
were ineffective, but the others suppressed the growth to some
degree), the target sites would be the same in both species,
although the mode of action of these compounds remains
unknown.
Ryegrass root was found to be more sensitive to the
epoxylignanes than lettuce root (Figure 5). Among the H-type
epoxylignanes, not only the compounds 1-H and 9H, which
were active to the lettuce root, but also 2-H, 5-H, 6-H, 7-H,
and 8-H suppressed the growth of the grass root below −50%,
whereas 3-H and its enantiomer 4-H, which have the
configuration of all R and all S, respectively, did not show
any inhibitory activity (Figure 5A). Among these epoxy-
lignanes, compound 2-H with the 7R,7′S,8S,8′S configuration
was the most potent compound, which could suppress the
growth of the root almost completely at 1 × 10−3 M. The order
of the sensitivity of the grass shoot to the H-type epoxylignanes
was likely to be similar to that of the sensitivity of the grass
root, although the sensitivity of the shoot was relatively less
than that of the root (Figure 5A vs 5B). Introduction of the
methoxy group induced less activity except the compounds
with the configuration of all R and all S; especially the
inhibitory activity of the all R configuration compound 3-H,
which showed no activity to the grass shoot, was strengthened
up to −76% from control by attaching the methoxy group
(3-OCH3, Figure 5C). The inhibitory activity against the grass
shoot of the compounds having the methoxy group was weak
(Figure 5D). The compounds having the hydroxyl group did not
influence the growth of grass root as well as shoot (Figure 5E,F).
At the dose-dependent assay for evaluating the influence on the
grass of the H-type epoxylignane compounds, compounds 1-H,
8-H, and 9-H showed a promotive effect on the growth of grass
root at diluted concentrations (Figure 6).
Among the epoxylignanes that have been isolated in the
previous studies, the antifungal activity5 and disruption of ion
homeostasis of (−)-verrucosin (1-H)22 have been reported.
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ASSOCIATED CONTENT
* Supporting Information
Additional experimental details. This material is available free of
charge via the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*(S.Y.) Phone: +81-89-946-9846. Fax: +81-89-977-4364.
E-mail: syamauch@agr.ehime-u.ac.jp.
Funding
Part of this study was performed at the INCS (Johoku station)
of Ehime University. We are grateful to Marutomo Co. for
financial support.
■
Notes
The authors declare no competing financial interest.
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