Synthesis and insect antifeedant activity of stilbene derivatives against Brontispa longissima Larvae

Article abstract of DOI:10.1007/s00044-012-0212-x

Continuing our search for natural product-based compounds for the control of B. longissima Larvae, 25 stilbene analogs were synthesized and evaluated for insect antifeedant activity against third-instar larvae of B. longissima for the first time. Among all the tested compounds, especially compounds 3a, 3c, and 6 showed pronounced antifeedant activities with AFC₅₀ values of 0.218, 0.327, and 0.226 mg/mL, respectively. The different antifeedant activity ranges of these compounds indicated that variation of chemical structures in the stilbene skeleton markedly affected the activity profiles of this compound class, and some important SAR information has been revealed from it. In addition, to understand the structural requirements for antifeedant activities of the 25 synthesized stilbene analogs, a comparative molecular field analysis (CoMFA) model, which yielded the leave-one-out (LOO) cross-validated correlation coefficient (q ²) of 0.533 and a non-cross-validated correlation coefficient (r ²) of 0.929, was constructed. Together, these preliminary results may be useful in guiding further modification of stilbenes in the development of potential new antifeedants.

Full text of DOI:10.1007/s00044-012-0212-x

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:2196–2206
DOI 10.1007/s00044-012-0212-x
ORIGINAL RESEARCH
Synthesis and insect antifeedant activity of stilbene derivatives
against Brontispa longissima Larvae
•
Ying-Qian Liu Xiao-Jing Li Chun-Yan Zhao
•
•
•
•
•
•
Yan Lu Wen-Qun Li Zhen-Ling Liu Gang Feng
Liu Yang
Received: 9 April 2011 / Accepted: 20 August 2012 / Published online: 6 September 2012
Ó Springer Science+Business Media, LLC 2012
Abstract Continuing our search for natural product-
based compounds for the control of B. longissima Larvae,
25 stilbene analogs were synthesized and evaluated for
insect antifeedant activity against third-instar larvae of
B. longissima for the first time. Among all the tested
compounds, especially compounds 3a, 3c, and 6 showed
pronounced antifeedant activities with AFC50 values of
0.218, 0.327, and 0.226 mg/mL, respectively. The different
antifeedant activity ranges of these compounds indicated
that variation of chemical structures in the stilbene skeleton
markedly affected the activity profiles of this compound
class, and some important SAR information has been
revealed from it. In addition, to understand the structural
requirements for antifeedant activities of the 25 synthe-
sized stilbene analogs, a comparative molecular field
analysis (CoMFA) model, which yielded the leave-one-out
(LOO) cross-validated correlation coefficient (q2) of 0.533
and a non-cross-validated correlation coefficient (r2) of
0.929, was constructed. Together, these preliminary results
may be useful in guiding further modification of stilbenes
in the development of potential new antifeedants.
Keywords Stilbenes ꢀ insect antifeedants ꢀ
Brontispa longissima ꢀ CoMFA ꢀ 3D-QSAR study
Introduction
Brontispa longissima (Gestro) (B. longissima), which is
mainly distributed in Southeast Asia and the Pacific Ocean
islands, is a destructive pest to palm plants (Zhou et al.,
2004; Su et al., 2009). Control of the B. longissima larvae is
frequently dependent on continued applications of conven-
tional pesticides such as organochlorine, organophosphorus,
carbamate, formamidines, and pyrethroid insecticides.
Although effective, their repeated use has produced risks in
the development of insect resistance and residues to humans
and to the environment (Luo et al., 2005; Xie et al., 2007).
These problems have highlighted the need for the devel-
opment of new, more ecologically acceptable methods for
B. longissima larvae control. Accordingly, botanical anti-
feedants, plant-based compounds may represent new alter-
native strategies for selective B. longissima larvae control,
as they are biodegradable, eco-friendly, and safe to the
environment. Especially, the discovery of new antifeeding
leads from plant sources, followed by using them as the
useful prototypes for further modification and structure
optimization, has recently been one of the important ways
for the development of new antifeedants and also offered
considerable promise as components of emerging integrated
pest management (Garcia and Azambuja, 2004; Shaalan
et al., 2005; Scott et al., 2003; Hu et al., 1999).
Y.-Q. Liu (&) ꢀ X.-J. Li ꢀ C.-Y. Zhao ꢀ Y. Lu ꢀ W.-Q. Li
School of Pharmacy, Lanzhou University, Lanzhou 730000,
People’s Republic of China
e-mail: yqliu@lzu.edu.cn
G. Feng
Environment and Plant Protection Institute, Chinese Academy
of Tropical Agricultural Science, Danzhou 571737,
People’s Republic of China
L. Yang
Environmental and Municipal Engineering School,
Lanzhou Jiaotong University, Lanzhou 730000,
People’s Republic of China
Z.-L. Liu
State Key Laboratory of Applied Organic Chemistry,
Lanzhou University, Lanzhou 730000,
People’s Republic of China
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2197
In the course of our screening for novel naturally
occurring antifeedant as pest controlling agents, two nat-
urally occurring compounds resveratrol (1) and combre-
tastatin A-4 (3a) (Fig. 1) based on stilbene structure were
found to display potential antifeedant activity against
B. longissima in laboratory bioassays, which prompted us
to use the stilbene skeletons as useful models for further
optimization as antifeedants. Stilbenes are a class of nat-
urally occurring plant polyphenols and they exhibit a wide-
range of biologic activities, including pharmacological
applications such as antineoplastic, antiinflammatory,
antiviral, and antioxidant activities, as well as agrochemi-
cal applications spanning algicidal, fungicidal, nematicidal,
insecticidal, and antifeedant activities (Shibutani et al.,
2004; Mizuno et al., 2008; Creasy and Coffee, 1988;
Torres et al., 2003; Ioset et al., 2001; Harmatha and Dinan,
2003; Rhoades, 1979; Feeny, 1976).
Experimental
Chemicals
1H and 13C NMR spectra were measured on a Bruker
AM-400 (400 MHz) spectrometer using tetramethylsilane
as an internal standard (Bruker Company, USA). Mass
spectra were recorded on a ZAB-HS and Bruker Daltonics
APEXII49e instrument and the infrared spectra were
recorded on a NIC-5DX spectrophotometer. Melting points
were taken on a Kofler melting point apparatus and were
uncorrected. Elemental analyses were determined on a
Vario El Gmbh elemental analyzer. The synthetic com-
pounds were purified by flash chromatography on Merck
silica gel (70–230 mesh). Thin-layer chromatography
(TLC) involved the use of silica gel plates with a fluores-
cent indicator (Merck Silica Gel 60 F254 0.25 mm thick).
Although few stilbene analogs exhibited promising
antifeeding activity, their antifeeding activity has also been
evaluated against very few insects; to the best of our
knowledge, however, stilbene analogs have not been
previously evaluated for insecticidal activity toward
B. longissima. In addition, systematic structure–activity
relationships (SAR) have not been well determined so the
chemical basis for their insecticidal properties is not yet
known.
General procedure for preparation of compounds (3a–s)
A mixture of commercially available phenylacetic acids
(8.84 mmol) and benzaldehydes (4.4 mmol), acetic anhy-
dride (4 mL), and triethylamine (2 mL) were heated under
reflux for 3 h. After acidification with concentrated hydro-
chloric acid (6 mL), the resulting solid was filtered off and
recrystallised from ethanol to give acrylic acid intermediates
2a–s as fine yellow needles. Subsequently, the correspond-
ing acrylic acid intermediates 2a–s (5.56 mmol) was added
to powdered copper (28.8 mmol) in quinoline (20 mL) and
the resulting mixture was heated at 200 °C for 2 h. Upon
cooling, ether was added, and the copper was filtered off
through Celite. The filtrate was washed with 1 M hydro-
chloric acid, and the aqueous layer was separated and
extracted with ether. The combined organic layers were
washed with saturated aqueous sodium carbonate, water,
brine, dried (MgSO4), and concentrated in vacuo. Flash
column chromatography (SiO2 petrol: EtOAc 7:3) and
recrystallization from ethyl acetate and petrol afforded
desired compounds 3a–s in 30–65 % yields.
As a part of our ongoing effort to discover natural
potential leads for B. longissima control funded by Tropical
Agricultural Protection program, in this paper, we first
evaluated antifeedant activities of 25 derivatives of stilb-
enes against B. longissima and studied the preliminary
structure–activity relationships of these compounds. Our
results revealed that the activities of different compounds
varied depending on the substitution of the functional
groups and the side chain attached to the olefin site of
stilbenes. Present study has showed that stilbenes appear to
be promising natural antifeedants and may hold potential
for identification of new lead structures against B. lon-
gissima. In addition, to probe the relationship between the
structure and the activities for the synthesized stilbene
analogs, a comparative molecular field analysis (CoMFA)
was also performed.
(Z)-2-(30-Hydroxy-40-methoxyphenyl)-1-(3,4,5-
trimethoxyphenyl) ethene (3a)
Yield: 65 %; mp 117–118 °C. IR (KBr) (cm-1): 3453,
3006, 1616, 1580, 1327, 1238, 1126, 1010; 1H-NMR
(400 MHz, CDCl3) d: 3.69 (s, 6H), 3.84 (s, 3H), 3.89
(s, 3H), 5.53 (s, 1H), 6.42 (1H, d, J = 12.4 Hz), 6.47 (1H,
d, J = 12.4 Hz), 6.55 (s, 2H), 6.75 (1H, d, J = 8.3 Hz),
6.82 (1H, dd, J = 8.3, 1.9 Hz), 6.92 (1H, d, J = 1.9 Hz);
13C-NMR (100 MHz, CDCl3) d: 153.07, 146.02, 145.45,
137.34, 132.93, 130.81, 129.71, 129.22, 121.32, 115.27,
110.56, 106.28, 61.15, 56.15; MS m/z (%): 316 (M?, 100),
301 (75), 241 (8), 226 (6), 211 (5), 142 (12), 115 (8), 93
OH
MeO
MeO
OH
OMe
OH
HO
OMe
1 (AFC50= 0.816mg/mL)
3a (AFC50= 0.218mg/mL)
Fig. 1 Chemical structures of stilbenes 1 and 3a
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Med Chem Res (2013) 22:2196–2206
(5), 57 (8); Anal.Calc. For C18H20O5: C, 68.40 %, H,
6.38 %. Found: C, 68.37 %, H, 6.30 %.
CDCl3) d: 2.32 (3H, s), 3.88 (3H, s), 3.93 (6H, s), 6.74 (2H,
s), 6.92 (1H, d, J = 12 Hz), 7.09 (2H, d, J = 8.8 Hz), 6.99
(1H, d, J = 12 Hz), 7.51 (2H, d, J = 8.8 Hz); 13C-NMR
(100 MHz, CDCl3) d: 169.46, 153.37, 149.98, 137.97,
134.99, 132.86, 128.84, 127.29, 127.10, 121.79, 103.51,
60.94, 56.09, 21.12; MS m/z (%): 328 (M?, 85), 286 (95),
271 (100), 211 (12), 157 (15), 128 (20), 115 (10); Ana-
l.Calc. For C19H20O5: C, 69.50 %, H, 6.14 %. Found: C,
69.52 %, H, 6.14 %.
(Z)-2-Phenyl-1-(3,4,5-trimethoxyphenyl) ethene (3b)
Yield: 45 %; mp 106–108 °C. IR (KBr) (cm-1): 2997,
2936, 1579, 1327, 1236, 1125, 1006; H-NMR (400 MHz,
1
CDCl3) d: 3.88 (6H, s), 3.93 (3H, s), 6.76 (2H, s), 7.04 (1H,
d, J = 12 Hz), 7.12 (1H, d, J = 12 Hz), 7.28 (1 H, t,
J = 7.2 Hz), 7.38 (2H, dd, J = 7.6, 2.4 Hz), 7.52 (2H, d,
J = 7.6 Hz); 13C-NMR (100 MHz, CDCl3) d: 153.37,
137.90, 137.17, 133.05, 128.68, 128.60, 128.16, 127.58,
126.40, 103.51, 60.96, 56.10; MS m/z (%): 270 (M?, 100),
255 (90), 195 (25), 167 (15), 152 (15), 141 (12), 115 (8), 57
(8); Anal.Calc. For C17H18O3: C, 75.53 %, H, 6.71 %.
Found: C, 75.54 %, H, 6.72 %.
(Z)-2-(40-Nitrophenyl)-1-(3,4,5-trimethoxyphenyl)
ethene (3f)
Yield: 38 %; mp 210–212 °C. IR (KBr) (cm-1): 1610,
1595, 1580, 1530, 1350, 1280, 1220; H-NMR (400 MHz,
1
CDCl3) d: 3.90 (3H, s), 3.94 (6H, s), 6.78 (2H, s), 7.05 (1H,
d, J = 12 Hz), 7.22 (1H, d, J = 12 Hz), 7.63 (2H, d,
J = 8 Hz), 8.22 (2H, d, J = 8 Hz); 13C-NMR (100 MHz,
CDCl3) d: 153.51, 146.68, 143.75, 133.25, 131.82, 126.72,
125.67, 124.17, 104.14, 60.99, 56.17; MS m/z (%): 315
(M?, 85), 300 (85), 285 (5), 211 (12), 168 (20), 152 (25),
139 (30); Anal.Calc. For C17H17NO5: C, 64.75 %, H,
5.43 %.N, 4.44 %. Found: C, 64.75 %, H, 5.42 %, N,
4.44 %.
(Z)-2-(40-Methoxyphenyl)-1-(3,4,5-trimethoxyphenyl)
ethene (3c)
Yield: 71 %; mp 164–165 °C. IR (KBr) (cm-1): 3002,
2938, 2836, 1610, 1579, 1508, 1459, 1419, 1328, 1182,
1
1025, 1004; H-NMR (400 MHz, CDCl3) d: 3.84 (3H, s),
3.88 (3H, s), 3.93 (6H, s), 6.73 (2H, s), 6.31 (1H, d,
J = 13.6 Hz), 6.92 (2H, d, J = 8.8 Hz), 6.96 (1H, d,
J = 13.6 Hz), 7.45 (2H, d, J = 8.8 Hz); 13C-NMR
(100 MHz, CDCl3) d: 159.27, 153.36, 137.59, 133.42,
129.98, 127.73, 127.61, 126.52, 114.13, 103.24, 60.96,
56.09, 55.31; MS m/z (%): 300 (M?, 100), 285 (95), 270
(5), 225 (12), 210 (5), 128 (20), 115 (8); Anal.Calc. For
C18H20O4: C, 71.98 %, H, 6.71 %. Found: C, 71.92 %, H,
6.71 %.
(Z)-2-(40-Chlorophenyl)-1-(3,4,5-trimethoxyphenyl)
ethene (3g)
Yield: 46 %; mp 153–155 °C. IR (KBr) (cm-1): 3058,
3024, 2926, 2854, 1564, 1494, 1472, 1446, 1473, 1051;
1H-NMR (400 MHz, CDCl3) d: 3.88 (3H, s), 3.93 (6H, s),
6.74 (2H, s), 6.98 (1H, d, J = 12.4 Hz), 7.04 (1H, d,
J = 12.4 Hz), 7.33 (2H, d, J = 8.4 Hz), 7.44 (2H, d,
J = 8.4 Hz); 13C-NMR (100 MHz, CDCl3) d: 153.42,
138.12,135.70, 133.12, 132.70, 129.23, 128.85, 127.54,
126.83, 103.59, 60.96, 56.11; MS m/z (%): 304 (M?, 85),
289 (85), 229 (8), 165 (12), 152 (25), 139 (30); Anal.Calc.
For C17H17ClO3: C 67.00 %, H 5.62 %, Cl, 11.63 %.
Found: C 67.01 %, H 5.62 %, Cl, 11.66 %.
(Z)-2-(40-Hydroxyphenyl)-1-(3,4,5-trimethoxyphenyl)
ethene (3d)
Yield: 38 %; mp 196–198 °C. IR (KBr) (cm-1): 3426,
2937, 2838, 1590, 1459, 1384,1238, 1008; 1H-NMR
(400 MHz, CDCl3) d: 3.88 (3H, s), 3.93 (6H, s), 4.98 (1H,
s), 6.72 (2H, s), 6.92 (1H, d, J = 11.6 Hz), 6.84 (2H, d,
J = 8.8 Hz), 6.95 (1H, d, J = 11.6 Hz), 7.42 (2H, d,
J = 8.8 Hz); 13C-NMR (100 MHz, CDCl3) d: 155.26,
153.35, 137.57, 133.40, 130.16, 127.82, 127.69, 126.57,
115.63, 103.26, 60.97, 56.09; MS m/z (%): 286 (M?, 100),
271 (95), 211 (10), 168 (12), 157 (15), 128 (20), 115 (8);
Anal.Calc. For C17H18O4: C, 71.31 %, H, 6.34 %. Found:
C, 71.31 %, H, 6.32 %.
(Z)-2-(40,60-Dinitrophenyl)-1-(3,4,5-trimethoxyphenyl)
ethene (3h)
Yield: 42 %; mp 180–181 °C. IR (KBr) (cm-1): 3418,
3173, 2912, 1679, 1528, 1351, 1279, 1126; 1H-NMR
(400 MHz, CDCl3) d: 3.92 (3H, s), 3.94 (6H, s), 6.97 (2H,
s), 7.72 (1H, d, J = 12.4 Hz), 7.75 (1H, d, J = 12.4 Hz),
7.33 (2H, d, J = 2 Hz), 8.22 (1H, d, J = 2 Hz), 9.12 (1H,
s); 13C-NMR (100 MHz, CDCl3) d: 159.10, 153.25,
152.74, 148.69, 139.67, 137.02, 131.40, 128.97, 128.55,
124.47, 119.28, 112.14, 106.11, 60.96, 56.33; MS m/z (%):
360 (M?, 100), 342 (30), 314 (30), 197 (12), 182 (25), 126
(Z)-2-(40-Acetoxyphenyl)-1-(3,4,5-trimethoxyphenyl)
ethene (3e)
Yield: 56 %; mp 83–85 °C. IR (KBr) (cm-1): 3006, 1750,
1620, 1580, 1327, 1237, 1126, 1012; H-NMR (400 MHz,
1
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Med Chem Res (2013) 22:2196–2206
2199
(30); Anal.Calc. For C17H16N2O7: C, 56.67 %, H, 4.48 %,
N, 7.77 %, Found: C, 56.65 %, H, 4.48 %, N, 7.78 %.
J = 12.6 Hz), 7.02—7.55 (m, 9H); 13C-NMR (100 MHz,
CDCl3) d: 155.39, 149.93, 137.58, 130.25, 129.89, 128.79,
128.63, 128.13, 127.91, 127.22, 126.85, 126.61, 126.23,
121.17, 115.63; MS m/z (%): 196 (M?, 100), 181 (40), 165
(50), 152 (20), 115 (25); Anal.Calc. For C14H12O: C,
85.68 %, H, 6.16 %. Found: C, 85.68 %, H, 6.16 %.
(Z)-2-(40,60-Dichlorophenyl)-1-(3,4,5-trimethoxyphenyl)
ethene (3i)
Yield: 47 %; mp 117–119 °C. IR (KBr) (cm-1): 3059,
2912, 1681, 1565, 1508, 1278, 1237, 1129; 1H-NMR
(400 MHz, CDCl3) d: 3.89 (3H, s), 3.93 (6H, s), 6.76 (2H,
s), 7.01 (1H, d, J = 12.4 Hz), 7.24 (1H, d, J = 12.4 Hz),
7.26 (2H, d, J = 2 Hz), 7.42 (1H, d, J = 2 Hz), 7.61 (1H,
s); 13C-NMR (100 MHz, CDCl3) d: 153.43, 138.50,
133.94, 133.71, 133.37, 132.44, 131.74, 129.53, 127.29,
127.10, 123.06, 103.95, 60.96, 56.14; MS m/z (%): 338
(M?, 100), 323 (30), 288 (30), 272 (40), 202 (25), 139 (30);
Anal.Calc. For C17H16Cl2O3: C, 60.19, H, 4.75 %, Cl,
20.90 %, Found: C, 60.20 %, H, 4.76 %, Cl, 20.89 %.
(Z)-2-(40-Acetoxyphenyl)-1-(4-methoxyphenyl) ethene (3m)
Yield: 47 %; mp 166–168 °C. IR (KBr) (cm-1): 3006,
1745, 1620, 1585, 1326, 1237, 1126, 1005; 1H-NMR
(400 MHz, CDCl3) d: 2.32 (3H, s), 3.84 (3H, s), 6.91 (2H,
d, J = 8.8 Hz), 6.98 (1H, d, J = 11.2 Hz), 7.01 (1H, d,
J = 11.2 Hz), 7.08 (1H, d, J = 8.4 Hz), 7.45 (2H, d,
J = 8.8 Hz), 7.49 (2H, d, J = 8.4 Hz); 13C-NMR
(100 MHz, CDCl3) d: 149.74, 128.47, 127.72, 127.12,
125.59, 121.73, 114.15, 55.33, 21.15; MS m/z (%): 268
(M?, 20), 226 (100), 311 (40), 165 (30), 113 (25); Ana-
l.Calc. For C17H16O3: C,76.10 %, H, 6.01 %. Found: C,
76.10 %, H, 6.00 %.
(Z)-2-(40,50-Diacetoxyphenyl)-1-(3,4,5-trimethoxyphenyl)
ethene (3j)
Yield: 47 %; mp 141–143 °C. IR (KBr) (cm-1): 3002,
2954, 1705, 1584, 1510,1421, 1249, 1129, 1037; H-NMR
(Z)-2-(40-Chlorophenyl)-1-(4-hydroxyphenyl) ethene (3n)
1
(400 MHz, CDCl3) d: 2.40 (6H, s), 3.87 (3H, s), 3.92 (6H,
s), 6.71 (2H, s), 6.90 (1H, d, J = 12 Hz), 6.91 (1H, d,
J = 12 Hz), 6.99 (1H, dd, J = 8 Hz), 7.01 (1H, d,
J = 8 Hz), 7.30 (1H, s); 13C-NMR (100 MHz, CDCl3) d:
153.38, 146.36, 138.77, 127.74, 126.93, 125.22, 120.06,
117.95, 103.39, 60.96, 56.10, 21.05; MS m/z (%): 386 (M?,
20), 344 (60), 302 (90), 287 (100), 242 (25), 115 (30);
Anal.Calc. For C21H22O7: C, 65.28 %, H, 5.74 %. Found:
C, 65.30 %, H, 5.74 %.
Yield: 47 %; mp 181–183 °C. IR (KBr) (cm-1): 3400,
1610, 1595, 1580, 1530, 1350, 1280, 1220; 1H-NMR
(400 MHz, CDCl3) d: 4.85 (1H, s), 6.85 (1H, d,
J = 12.6 Hz), 6.89 (1H, d, J = 12.6 Hz), 6.99—7.54
(m, 8H); 13C-NMR (100 MHz, CDCl3) d: 155.37, 136.09,
132.73, 130.03, 128.78, 128.71, 127.98, 127.48, 127.39,
125.35, 115.65; MS m/z (%): 230 (M?, 100), 215 (20), 194
(40), 165 (30), 115 (25); Anal.Calc. For C14H11ClO: C,
72.89 %, H, 4.81 %, Cl, 15.37 %. Found: C, 72.88 %, H,
4.81 %, Cl, 15.37 %.
(Z)-2-(40,50-Methylenedioxyphenyl)-1-(3,4,5-
trimethoxyphenyl)ethene (3k)
(Z)-2-(40-Nitrophenyl)-1-(4-hydroxyphenyl) ethene (3o)
Yield: 36 %; mp 202–204 °C. IR (KBr) (cm-1): 3420, 1610,
1592, 1580, 1530, 1350, 1280, 1220; H-NMR (400 MHz,
Yield: 73 %; mp 79–81 °C. IR (KBr) (cm-1): 3006, 1620,
1582, 1327, 1238, 1126, 1010, 930; H-NMR (400 MHz,
1
1
CDCl3) d: 3.72 (6H, s), 3.85 (3H, s), 5.92 (2H, s), 6.45 (1H,
d, J = 12.4 Hz), 6.50 (1H, d, J = 12.4 Hz), 6.52 (2H, s),
6.74 (1H, d, J = 8 Hz), 6.79 (1H, s), 6.82 (1H, d,
J = 8 Hz); 13C-NMR (100 MHz, CDCl3) d: 152.91,
147.34, 146.59, 137.17, 132.54, 131.16, 129.47, 129.13,
122.91, 109.07, 108.14, 105.98, 100.91, 60.91, 55.92; MS
m/z (%): 314 (M?, 100), 299 (85), 339 (30), 155 (20), 127
(25); Anal.Calc. For C18H18O5: C, 68.78 %, H, 5.77 %.
Found: C, 68.78 %, H, 5.76 %.
CDCl3) d: 5.32 (1H, s), 6.88 (2H, d, J = 8.4 Hz), 6.99 (1H, d,
J = 12.2 Hz), 7.21 (1H, d, J = 12.2 Hz), 7.46 (2H,
d, J = 8.4 Hz), 7.60 (2H, d, J = 8.8 Hz), 8.21 (2H,
d, J = 8.8 Hz); 13C-NMR (400 MHz, CDCl3) d: 147.74,
132.82, 128.64, 126.52, 124.16, 115.88; MS m/z (%): 271
(M?, 100), 256 (20), 194 (30), 165 (25), 152 (20); Anal.Calc.
For C14H11NO3: C, 69.70 %, H, 4.60 %, N, 5.81 %. Found:
C, 69.71 %, H, 4.60 %, N, 5.82 %.
(Z)-2-(40-Methoxy-50-nitrophenyl)-1-(4-hydroxyphenyl)
ethene (3p)
(Z)-2-Phenyl-1-(4-hydroxyphenyl) ethene (3l)
Yield: 42 %; mp 197–199 °C. IR (KBr) (cm-1): 3430, 3002,
1585, 1520, 1510, 1250; 1H-NMR (400 MHz, CDCl3)
d: 5.40 (1H, s), 6.76 (1H, d, J = 12.6 Hz), 7.81 (1H, d,
Yield: 35 %; mp 149–151 °C. IR (KBr) (cm-1): 3453,
3004, 1616, 1586, 1327, 1238, 1123, 1010; 1H-NMR
(400 MHz, CDCl3) d: 3.99 (3H, s), 4.85 (1H, s), 6.88 (2H,
123

2200
Med Chem Res (2013) 22:2196–2206
d, J = 8.4 Hz), 6.91 (1H, d, J = 12.4 Hz), 7.02 (1H, d,
J = 12.4 Hz), 6.85 (2H, d, J = 4.8 Hz), 7.07 (1H, d, J =
8.8 Hz), 7.40 (2H, d, J = 4.8 Hz), 6.82 (1H, dd, J = 8.8,
2.4 Hz), 7.98 (1H, d, J = 2.4 Hz); 13C-NMR (100 MHz,
CDCl3) d: 155.55, 151.89, 131.63, 130.70, 129.68, 129.04,
128.01, 123.68, 122.91, 115.72, 113.76, 56.66; MS
m/z (%): 271 (M?, 100), 256 (20), 194 (30), 165 (25), 152
(20); Anal.Calc. For C15H13NO4: C, 66.41 %, H, 4.83 %,
N, 5.16 %. Found: C, 66.40 %, H, 4.83 %, N, 5.18 %.
100), 181 (40), 152 (40); Anal.Calc. For C15H12O3: C,
74.99 %, H, 5.03 %. Found: C, 74.97 %, H, 5.04 %.
(E)-2-(30-Hydroxy-40-methoxyphenyl)-1-(3,4,5-
trimethoxyphenyl) ethene (4)
To a solution of cis-stilbene 3a (0.63 mmol) in chloroform
(10 mL) iodine (16 mg, 0.06 mmol, 10 mol%) was added.
The resulting solution was stirred at room temperature for
30 min, after which the solution was washed thoroughly
with saturated aqueous sodium metabisulfite to destroy the
remaining iodine. The yellow solution was washed with
water, dried (MgSO4), and concentrated in vacuo to give 4.
Yield: 92 %; mp 102–104 °C. IR (KBr) (cm-1): 3446,
3000, 1620, 1580, 1327, 1238, 1126, 1010; 1H-NMR
(400 MHz, CDCl3) d: 3.87 (s, 3H), 3.92 (s, 9H), 5.63
(s, 1H), 6.73 (s, 2H), 6.86 (1H, d, J = 8.3 Hz), 6.89 (1H, d,
J = 16.2 Hz), 6.95 (1H, d, J = 16.2 Hz), 6.99 (1H, dd,
J = 8.3, 1.9 Hz), 7.16 (1H, d, J = 1.9 Hz); 13C-NMR
(100 MHz, CDCl3) d: 153.34, 146.38, 145.77, 137.64,
133.29, 130.96, 127.79, 127.03, 119.17, 111.71, 111.66,
110.62, 103.34, 103.28, 60.98, 60.90, 56.13, 56.04, 55.93;
MS m/z (%): 316 (M ? , 100), 301 (75), 241 (8), 226 (6),
211 (5), 115 (8), 93 (15), 57 (20); Anal.Calc. For
C18H20O5: C, 68.34 %, H, 6.37 %. Found: C, 68.35 %, H,
6.37 %.
(Z)-2-(40-Methoxy-50-acetoxyphenyl)-1-(4-acetoxyphenyl)
ethene (3q)
Yield: 58 %; mp 151–153 °C. IR (KBr) (cm-1): 3006, 1734,
1616, 1578, 1327, 1236, 1126, 1010; H-NMR (400 MHz,
1
CDCl3) d: 2.32 (3H, s), 2.34 (3H, s), 3.92 (3H, s), 6.83 (1H, d,
J = 12.4 Hz), 6.86 (1H, d, J = 8.8 Hz), 6.96 (1H, d,
J = 12.4 Hz), 6.99 (1H, dd, J = 8.8, 2 Hz), 7.15 (2H,
d, J = 2 Hz), 7.24 (1H, d, J = 2 Hz), 7.31 (2H, d,
J = 2 Hz); 13C-NMR (100 MHz, CDCl3) d: 169.05, 156.30,
138.70, 130.70, 128.53, 127.69, 127.24, 127.20, 126.12,
125.46, 121.77, 121.72, 120.37, 119.29, 112.41, 111.79,
110.65, 56.01, 21.15; MS m/z (%): 326 (M?, 20), 284 (50),
242 (100), 227 (30), 181 (20); Anal.Calc. For C19H18O5: C,
69.93 %, H, 5.56 %. Found: C, 69.92 %, H, 5.54 %.
(Z)-2-(40,50-Diacetoxyphenyl)-1-(4-acetoxyphenyl) ethene
(3r)
(E)-Methyl-3-(30-hydroxy-40-methoxyphenyl)-2-(3,4,5-
Trimethoxyphenyl) prop-2-enoate (5)
Yield: 47 %; mp 163–165 °C. IR (KBr) (cm-1): 3012,
1750, 1625, 1580, 1327, 1238, 1126, 1010; 1H-NMR
(400 MHz, CDCl3) d: 2.31–2.33 (9H, s), 7.01 (1H, d,
J = 12.4 Hz), 7.12 (1H, dd, J = 8.4, 2 Hz), 7.17 (1H, d,
J = 12.4 Hz), 7.34 (1H, d, J = 2 Hz), 7.37 (1H, s), 7.18
(2H, d, J = 8.4 Hz), 7.31 (2H, d, J = 8.4 Hz); 13C-NMR
(100 MHz, CDCl3) d: 169.43, 168.31, 150.26, 142.29,
136.27, 134.67, 127.54, 127.16, 124.75, 121.86, 20.64; MS
m/z (%): 354 (M?, 30), 312 (50), 283 (15), 270 (100), 228
(50); Anal.Calc. For C20H18O6: C, 67.79 %, H, 5.12 %.
Found: C, 67.80 %, H, 5.14 %.
Concentrated H2SO4 (2 mL) was added to a stirred solution
of propenoic acid 2a (5.35 mmol) in methanol (20 mL) and
the mixture was heated under reflux overnight. Upon
cooling, the solid was filtered off and recrystallised from
methanol to give the ester 5. Yield: 68 %; m.p.
177–179 °C. IR (KBr) (cm-1): 3450, 3006, 1752, 1628,
1580, 1327, 1238, 1126, 1010; 1H-NMR (400 MHz,
CDCl3) d: 3.68 (6H, s), 3.69 (3H, s), 3.72 (3H, s), 3.74 (3H,
s), 6.47 (2H, s), 6.54 (1H, d, J = 1.9 Hz), 6.63 (1H, dd,
J = 8.3, 1.9 Hz), 6.82 (1H, d, J = 8.3 Hz), 7.61 (1H, s),
8.98 (1H, s); 13C-NMR (100 MHz, CDCl3) d: 168.43,
153.55, 147.50, 145.07, 140.28, 137.69, 131.39, 130.24,
127.84, 123.75, 116.66, 110.13, 106.68, 56.15, 56.08,
55.89; MS m/z (%): 374 (M?, 100), 359 (40), 315
(40),241(20), 115 (8), 59 (40); Anal.Calc. For C20H22O7:
C, 64.16 %, H, 5.92 %. Found: C, 63.98 %, H, 6.00 %.
(Z)-2-(40,50-Methylenedioxyphenyl)-1-(4-hydroxyphenyl)
ethene (3s)
Yield: 62 %; mp 185–188 °C. IR (KBr) (cm-1): 3453,
3000, 1620, 1580, 1327, 1242, 1126, 1010, 932; H-NMR
1
(400 MHz, CDCl3) d: 4.82 (1H, s), 5.98 (2H, s), 6.78 (1H,
d, J = 12.2 Hz), 6.91 (2H, d, J = 8.4 Hz), 6.93 (1H, d,
J = 12.2 Hz), 7.38 (2H, d, J = 8.4 Hz), 7.05 (1H, dd,
J = 8, 2 Hz), 6.83 (1H, d, J = 2 Hz), 6.90 (1H, s);
13C-NMR (100 MHz, CDCl3) d: 154.97, 148.09, 147.0,
132.14, 130.46, 127.69, 126.46, 126.40, 121.05, 115.55,
108.39, 105.38, 105.33, 101.06; MS m/z (%): 240 (M?,
(E)-3-(30-Hydroxy-40-methoxyphenyl)-2-(3,4,5-
Trimethoxyphenyl)prop-2-en-1-ol (6)
To a solution of lithium aluminum hydride (39.5 mmol) in
dry THF (30 mL) at –15 °C under Ar a warm saturated
THF solution of ester 5 (10.7 mmol) was added dropwise.
123

Med Chem Res (2013) 22:2196–2206
2201
After stirring at room temperature for 2 h, aqueous THF
(5–50 % water) was added carefully until excess lithium
aluminum hydride had reacted. The lithium salts were fil-
tered off and the filtrate concentrated in vacuo. The aque-
ous layer was separated and extracted with EtOAc
(3 9 50 mL). The combined organic layers were washed
with water (2 9 50 mL), brine (50 mL), dried (MgSO4),
and concentrated in vacuo. Recrystallisation from EtOAc
gave the alcohol 6. Yield: 80 %; m.p. 119–120 °C. IR
(KBr) (cm-1): 3452, 3068, 2942, 1676, 1584, 1510, 1411,
1257, 1238, 1222, 1126, 1035; 1H-NMR (400 MHz,
CDCl3) d: 3.78 (6H, s), 3.85 (3H, s), 3.89 (3H, s), 4.35 (1H,
d, J = 5.7 Hz), 5.47 (1H, s), 6.49 (2 H, s), 6.55 (1H, dd,
J = 8.3, 1.9 Hz), 6.56 (1H, s), 6.65 (1H, d, J = 8.3 Hz),
6.98 (1H, d, J = 1.9 Hz), 7.28 (1H, s); 13C-NMR
(100 MHz, CDCl3) d: 153.56, 145.65, 144.95, 139.66,
137.42, 133.99, 129.75, 126.58, 126.52, 121.36, 115.32,
115.25, 110.11, 105.73, 105.66, 68.85, 56.14, 56.04; MS
m/z (%): 346 (M?, 20), 317 (5), 287 (40), 217 (20), 149
(50), 129 (60); Anal.Calc. For C19H22O6: C, 65.88 %;
H, 6.40 %. Found: C, 65.55 %, H, 6.44 %.
(EtOAc/hexane) to give 8. Yield: 52 %; m.p. 194–196 °C.
IR (KBr) (cm-1): 3346, 3186, 2934, 1661, 1581, 1508, 1459,
1410, 1275, 1237, 1125, 1024; 1H-NMR (400 MHz, CDCl3)
d: 3.97 (3H, s), 3.88 (3H, s), 3.78 (6H, s), 5.56 (1H, s), 6.62
(2H, s), 6.78 (1H, d, J = 8.7 Hz), 6.83 (1H, s), 7.29 (1H, dd,
J = 2.4, 8.7 Hz), 7.49 (1H, d, J = 2.4 Hz); 13C-NMR
(100 MHz, CDCl3) d: 153.64, 148.02, 145.30, 143.58,
138.74, 128.01, 126.85, 123.27, 120.51, 115.62, 111.95,
110.22, 105.96, 103.22, 61.00, 56.30, 56.19, 55.94; MS
m/z (%): 341 (M?, 100), 326 (75), 149 (40); Anal.Calc. For
C19H19NO5: C, 66.85 %, H, 5.61 %, N, 4.10 %. Found: C,
66.88 %, H, 5.65 %, N, 4.12 %.
Insects
First- or second-instar larvae of B. longissima were col-
lected from suburban vegetable fields of Danzhou, Hainan
Povince, China, and reared in our laboratory under con-
trolled photoperiod (12:12 h light:dark) and temperature
(25 ( 1) °C) and fed daily with cabbage until they
reached the earlier stage of the third-instar larvae when
they were used for testing.
(E)-3-(30-Hydroxy-40-methoxyphenyl)-2-(3,4,5-
trimethoxyphenyl)acrylamide (7)
Insect antifeedant assay
To a solution of 2a (1.82 mmol) in CH2Cl2 (9 mL) SOCl2
(0.70 mL) was added in DMF (1 mL). The solution was
stirred at room temperature for 1 h and then the mixture was
evaporated to dryness. The residue was dissolved with
CH2Cl2 (5 mL) and the solution was added to well-stirred
28 % aqueous NH3 (30 mL) at room temperature. After
30 min, the reaction mixture was extracted with CH2Cl2 and
dried over Na2SO4. After concentration, the residue was
purified by preparative TLC (EtOAc/hexane) to give 7.
Yield: 38 %; m.p. 183–185 °C. IR (KBr): 3471, 3347, 3179,
2935, 1663, 1582, 1514, 1463, 1412, 1280, 1237, 1126, 1030,
Antifeedant activities of synthesized compounds were
evaluated against third-instar larvae of B. longissima accord-
ing to previously reported method (Liu et al., 2008). Briefly,
a leaf-dipping method was used to evaluate the activity of the
test samples. Cabbage leaves were washed with 70 % double
distilled alcohol and air dried for 15 min before dipping into
the required amount of compounds in acetone. The leaf disk
(6.5 cm) of cabbage was used for evaluating antifeedant
activity of the samples against B. longissima. Ten leaf disks
per dose were separately dipped in each test solution for 30 s.
Solvents were evaporated, and the larvae were transferred
individually on treated and controlled (disks treated with
solvent and emulsified water only) leaf disks placed in Petri
plates. Treated leaves were fed to third-instar larvae of B.
longissima. Five replications were used per dose for the test.
Experiments were maintained at 28 1 °C and 65 5 %
relative humidity. The antifeedant activities of synthesized
compounds were determined at different concentrations
(0.050, 0.125, 0.250, 0.500, and 1.000 mg/mL) after 48 h of
treatment. If a whole disk was consumed, food consumption
was recorded as 1. If only part of a disk was consumed, the
food consumption was assessed by estimating the percentage
of the surface of the leaf wafer consumed. The antifeedant
rate (AR) was calculated as
1
1104; H-NMR (400 MHz, CDCl3) d: 3.82 (s, 6H), 3.86
(s, 3H), 3.93 (s, 3H), 5.50 (s, 1H), 5.54 (bs, 2H), 6.51 (s, 2H),
6.64 (bs, 1H), 6.65 (1H, dd, J = 2, 8 Hz), 6.69 (1H, d,
J = 8 Hz), 7.75 (s, 1H); 13C-NMR (100 MHz, CDCl3)
d: 154.26, 147.39, 145.12, 137.83, 131.90, 127.98, 123.78,
116.32, 110.18, 106.34, 61.09, 56.25, 55.84; MS m/z (%):
269 (M?, 40), 241 (25), 165 (40); Anal.Calc. For
C19H21NO6: C, 63.50, H, 5.89, N, 3.90 %. Found: C, 56.28,
H, 5.70, N, 3.45 %.
(E)-3-(‘4-Methoxy-30-hydroxyphenyl)-2-(3,4,5-
trimethoxyphenyl)acrylonitrile (8)
To a solution of 7 (0.3 mmol) in pyridine (5 mL) SOCl2
(0.10 mL) was added. The reaction mixture was stirred at
room temperature for 6 h. The mixture was concentrated to
dryness and the residue was purified by preparative TLC
AR ¼ ðC ꢁ TÞ ꢂ 100=C
where C is the average consumption by one larva in the
control and T in the treatment. The concentration for 50 %
123

2202
Med Chem Res (2013) 22:2196–2206
antifeedant effect (AFC50) was determined by log-probit
analysis. All data were treated by log-probit analysis and
95 % fiducial limits were calculated.
structures of 25 molecules were aligned on the template
molecule ‘3a’ which had the highest activity by the
database alignment method.
CoMFA steric and electrostatic interaction fields were
calculated at each lattice intersection on a regularly spaced
˚
grid of 2.0 A. The grid pattern was generated automatically
Molecular modeling and CoMFA analysis
˚
by the Sybyl/CoMFA routine and extended 4.0 A units in
All molecular modeling and calculation studies were
performed by means of the Sybyl 6.9 programs running on
an SGI Origin server. The structures were built and opti-
mized by means of Tripos force field with a distance-
dependent dielectric function until a root mean square
(RMS) deviation of 0.005 kcal/mol. Next, the structures
were extracted and optimized by the PM3 method. The
conformational search was performed by multisearch
method with the following settings: maximum cycles
(400), maximum conformers (400), energy cutoff (70 kcal/
mol), maximum RMS gradient (3.0) tolerance (0.40), and
number of hit (12). The derived minimum energy con-
formation thus was used in the analysis. Alignment criteria
play an important role in CoMFA studies and it is pref-
erable to choose an alignment which maintains the bio-
active conformation. In the present study, the optimized
the X, Y, and Z directions beyond the dimensions of each
molecule. A sp3-hybridized carbon atom with a van der
˚
Waals of 1.52 A and a ?1.0 charge was used as the probe
to calculate the steric field energies and electrostatic fields
with a distance-dependent dielectric at each lattice point.
Values of the steric and electrostatic fields were truncated
to 30 kcal/mol.
Partial least squares (PLS) analysis was used to correlate
the molecular fields and the activities with magnitude of
steric, electrostatic, and other potentials. The optimal num-
ber of components was determined by SAMPLS (Samples-
distance Partial Least Square) and cross-validation was
carried out by the leave-one-out method. The final CoMFA
model with an optimal number of components obtained by
means of LOO cross-validation and with the highest (q2) and
with the lowest standard error considered.
CO2CH3
CH2OH
H3CO
H3CO
LiAlH4
H3CO
H3CO
OCH3
OH
OCH3
OCH3
OH
OCH3
5
6
MeOH/H2SO4
reflux
2a
COOH
H
HO2C
O
R1
R2
R1
R2
Cu/quinoline
NEt3/Ac2O
reflux
+
reflux
R3
R4
R6
R3
R3
R1
R6
R4
R6
R4
R5
R2
R5
2a-s
R5
3a-s
2a
SOCl2 / NH3
I2/CHCl3
3a
CONH2
CN
OCH3
OH
H3CO
H3CO
SOCl2/pyridine
H3CO
H3CO
H3CO
H3CO
OCH3
OH
OCH3
OH
4
OCH3
OCH3
OCH3
7
8
Fig. 2 Synthesis of compounds 3a–s and 4–8
123

Med Chem Res (2013) 22:2196–2206
Results and discussion
Synthesis
2203
iodine-catalyzed isomerization of the representative cis-
stilbene 3a resulted in complete conversion to the corre-
sponding trans-stilbene 4. The cis and trans configurations
of these compounds were confirmed by measuring the
characteristic coupling constants of the olefinic protons in
the NMR spectra. The cinnamic acid 2a was first converted
to the methyl ester 5 which was reduced with LiAlH4 to
afford alcohol 6. The acid 2a was converted to amide 7 by
treatment with SOCl2 followed by aqueous NH3 treatment.
The acrylamide 7 was then reacted with SOCl2 to give
acrylonitrile 8.
As shown in Fig. 2, a series of desired compounds 3a–s were
obtained via the Perkin condensation of commercially
available phenylacetic acids and benzaldehydes followed by
decarboxylation of the acrylic acid intermediates 2a–s using
copper and quinoline. In this reaction, only pure cis-isomers
were obtained in moderate yields (30–65 %) after purifica-
tion of the crude precipitate by fractional crystallization. The
Table 1 Antifeedant activities of stilbene derivatives against third-instar larvae of B. longissima
R'
R1
R2
R3
R6
R4
R5
Compd.
A-ring
R1
B-ring
R4
AFC50 (mg/mL)
(95 % fiducial limits)
R2
R3
R5
R6
3a
3b
3c
3d
3e
3f
3g
3h
3i
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
H
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OH
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
H
H
H
H
H
H
H
H
NO2
Cl
H
H
H
H
H
H
H
H
H
H
OCH3
H
OH
H
0.218 (0.137–0.274)
0.529 (0.372–0.663)
0.327 (0.243–0.410)
1.261 (0.864–1.580)
0.843 (0.629–1.057)
0.982 (0.585–1.231)
1.634 (1.018–2.048)
1.05 (0.698–1.316)
2.234 (1.567–2.799)
1.918 (1.334–2.404)
0.731 (0.533–0.916)
1.161 (0.494–1.455)
0.732 (0.464–0.917)
0.412 (0.269–0.516)
1.185 (0.892–1.485)
1.301 (0.905–1.630)
2.501 (1.528–3.134)
0.64 (0.450–0.803)
1.005 (0.471–1.259)
0.357 (0.260–0.447)
1.453 (0.890–1.821)
0.226 (0.108–0.284)
0.736 (0.518–0.923)
0.431 (0.302–0.540)
1.461 (0.994–1.830)
OCH3
OH
H
H
OAc
NO2
Cl
H
H
H
H
NO2
Cl
OAc
H
3j
3k
3l
OAc
–OCH2O–
H
H
3m
3n
3o
3p
3q
3r
3s
4
H
OAc
H
OCH3
Cl
H
H
OH
H
H
H
OH
H
NO2
OCH3
OCH3
OAc
–OCH2O–
H
H
OH
H
NO2
OAc
OAc
H
OAc
H
H
OAc
H
H
OH
H
5
6
7
8
2a
123

2204
Med Chem Res (2013) 22:2196–2206
Biologic activity
Strikingly, acrylamide 7 was significantly more potent than
2a. Introduction of a hydroxymethyl group resulted in a
compound (6, AFC50, 0.226 mg/mL) which had compara-
ble antifeedant activity than the parent compound 3a. Also,
nitrile 8 showed slightly decreased antifeedant activity
(AFC50, 0.431 mg/mL) comparable to 3a. These results
demonstrated that the insertion of different substituents
onto the olefin site adjacent to the A-ring resulted in
weaker activity and a nitrile group was about the maximum
tolerable size. Furthermore, the difference between cis- and
trans-isomers 3a and 4 in antifeedant activity was signifi-
cant and indicated the relative importance of the spatial
arrangement of the molecule in the activity displayed.
With the 25 stilbene derivatives in hand, we next examined
their antifeedant effects against third-instar larvae of
B. longissima. The results were summarized in Table 1. In
view of our goal to contribute to robust SAR studies and
develop potential insect antifeedants, many modifications,
related to chemical features of the molecule (i.e., double
bond geometry and substitution pattern of both rings), were
evaluated in detail. First, for the compounds with 3,4,5-
trimethoxy group on the A-ring, these analogs with dif-
ferent substituents on the B-ring seemed to be preferred for
antifeedant activities. Among the test compounds, 3a–3c
possessed the highest overall antifeedant potency with
AFC50 values of 0.218, 0.529, and 0.327 mg/mL against
third-instar larvae of B. longissima, respectively.
CoMFA analysis
The small differences in activities observed between 3a
and 3c could only be attributed to the extra OH in the
structure of 3a, which seemed slightly to increase the
antifeedant activity. In comparing the antifeedant effects at
the 40-position of the B-phenyl ring, compounds with
electron-donating methoxy group were generally more
potent than those with the electron-withdrawing nitro or
chloro moieties. For example, replacement of 4-OMe of the
B-ring with a 4-NO2 group (3f) or 4-OAc group (3e)
resulted in approximately threefold decrease in antifeedant
potency. A further dramatic loss of activity was observed
by replacement of 4-OMe of the B-ring with a 4-chloro
group (3g), as Table 1 showed. In comparison with 3c,
introduction of a hydroxy group (3d) on the B-ring
severely weakened the antifeedant potency. Similarly,
those bearing two chloro or nitro groups on the 30,
40-position of the B-ring (3h and 3i) also showed a five- to
tenfold decreased antifeedant effects. The results also
clearly underlined the antifeedant differences could be
ascribed to a combination of factors, like the nature of the
substitutes (which may depend on the size of substitutes,
electronic characteristics of substitutes, or other factors) or
a different interaction at the site. Next, we turned our
attention to variations in other parts of the hydroxy or
acetyl groups at the 4-position of the A-ring (3l–s); a
similar trend could be observed for variations of the 3,4,5-
trimethoxy group on the A-ring where only few minor
structural changes were tolerated. Unexpectedly, com-
pound 3n was found to be the most active (AFC50,
0.412 mg/mL) and it was 4-times more potent than 3g
(AFC50, 1.634 mg/mL).
In this study, CoMFA analysis was applied based on the 25
compounds which were divided into a training set with 20
compounds (unasterisked molecule in Table 2) for model
construction and a test set with the remaining 5 compounds
(asterisked molecules in Table 2) for model validation.
Table 2 Predicted activities from CoMFA models compared with the
experimental activities and the residues
Compounds Experimental pAFC50 Predicted pAFC50 Residual
2a
3a
3b
3c
3d
3e
3f
-0.17
0.66
-0.29
0.67
0.12
-0.01
0.00
0.28
0.28
0.48
0.47
0.01
-0.10
0.07
-0.18
0.02
0.08
0.05
0.01
0.02
-0.01
-0.03
0.06
3g
3h
3i
-0.21
-0.02
-0.35
-0.28
0.14
-0.19
-0.08
0.08
-0.43
-0.03
0.05
3j
-0.25
0.08
3k
3l
-0.06
0.14
-0.05
0.22
-0.02
-0.09
0.16
3m
3n
3o
3p
3q
3r
3s
0.39
0.23
-0.07
-0.11
-0.40
0.19
-0.03
-0.12
-0.37
0.18
-0.04
0.00
-0.03
0.01
0.00
0.09
-0.09
-0.12
-0.11
0.15
4
0.45
0.57
Subsequently, in an effort to better understand the
structure–activity relationships of this class of derivatives,
we examined small substituents on the olefin site (2a and
5–8). As shown in Table 1, compounds 2a and 5 displayed
approximately sevenfold decreased activity comparable to
natural 3a although they still remained antifeedant activity.
5
-0.16
0.65
-0.05
0.50
6
7
0.13
0.04
0.09
8
0.36
0.38
-0.02
Test set
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Med Chem Res (2013) 22:2196–2206
2205
and test set were listed together with the residue. Figure 3
depicts a good correlation between the predicted activities
and the experimental ones of the training and test set,
which indicated that the developed CoMFA model was
reliable.
Table 3 Summary of CoMFA analysis
CoMFA
Result
R2 cross-validated (q2)
Number of components
Non cross-validated r2
Standard error of estimate
Fish test
0.533
3
0.929
0.085
70.309
0.415
0.585
For the CoMFA model, the contributions of steric and
electrostatic field were 41.5 % and 58.5 %, respectively.
The CoMFA contour map of steric field was shown in
Fig. 4a. Considering the R2 position, there was a large
green contour below it. However, there was also yellow
field close to it which indicated careful substituent group
selection for this region.
Steric contribution
Electrostatic contribution
With respect of R0 substitute, a moderate yellow contour
around the R’ position indicated that the sterically bulky
group was disfavored for activity in these areas. It may
be the reason why compound 6 (R0 = CH2OH) was
more active than compound 5 (R0 = CO2CH3). Figure 4b
showed electrostatic contour map. Considering the R2
position; there was a large blue contour below it, but close
to it there was also a moderate red contour near it, indi-
cating careful substituent group selection for this region.
There were two moderate red contours close to the R6
position, suggesting that any negative charge or electron
sufficient substitute would enhance the activity. It could
well explain that the activity of compound 3h (R6 = NO2)
was higher than that of the corresponding compound 3i
(R6 = Cl). A moderate blue contour was observed beside
the R5 position, revealing that positive charge was favored.
For example, the activity of compound 3g (R5 = Cl) was
lower than that of 3b (R5 = H).
Fig. 3 Plot of observed versus predicted activity based on the
CoMFA model
The activity values expressed as negative log unit of
antifeedant activity (pAFC50) were used as dependent
variables. As summarized in Table 3, CoMFA analysis was
carried out and the obtained PLS models yielded cross-
validated q2 value of 0.533 with 3 components. Subse-
quently, a non-cross validated PLS model for training set
was also developed with a regression coefficients r2 of
0.929, Fish test value of 70.309, and a standard error of
estimated (SEE) of 0.107. In addition, to evaluate the
predictive ability of this model, the test set was applied to
verify if the development model can predict the activity of
compounds that were structurally distinct from those
included in the training set. As it can be seen in Table 2,
the predicted activities of compounds from both training
Further investigation on the SAR was carried out by
CoMFA analysis. The results demonstrated that the estab-
lished 3D QSAR model was statistically reliable with good
predictive power (r2 = 0.929 and q2 = 0.533). In addition,
based on the CoMFA contours, details on the relationship
between structure and the activities, as well as clues for
structural modifications, were also explained. The results
not only lead to a better understanding of structural
requirements of antifeedant activities but also can help in
the design of novel compounds with enhanced activity.
Fig. 4 Steric and electrostatic
A
B
CoMFA maps of the compound 3a
(a). The green colored contour
favors steric bulk while sites where
steric bulk is disfavored are shown
in yellow. b The red contour shows
regions where electronegative
substituents are favored, while the
blue contour is associated with
positions where electropositive
substituents improve activity
(Color figure online)
MeO
MeO
OMe
OH
OMe
3a
123

2206
Med Chem Res (2013) 22:2196–2206
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Conclusion
In summary, the antifeedant activities of 25 new synthetic
stilbene analogs were first investigated in relation to their
chemical structures. Among these analogs, compounds 3a,
3c, and 6 showed pronounced antifeedant activities with
AFC50 values of 0.218, 0.327, and 0.226 mg/mL, respec-
tively. The different antifeedant activity ranges of these
compounds indicated that variation of chemical structures
in the stilbene skeleton markedly affected the activity
profiles of this compound class and some important SAR
information was also revealed. This research has provided
a new class of compounds for further investigation toward
the discovery of environment-friendly antifeedants.
Acknowledgments This work was financially supported by the
National Natural Science Foundation of China (30800720, 20972061);
the Post-Doctor Research Foundation (20090450142); the Fundamen-
tal Research Funds for the Central Universities (lzujbky-2009-98); Key
Scientific Research Programme of EPPI (2010hzsZDZX003) of Chi-
nese Academy of Tropical Agricultural Science from the Ministry of
agriculture; the Fundamental Research Funds for the Central Univer-
sities (zujbky-2010-134) and Natural Science Foundation of Gansu
Province (0916RJZA033).
`
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of Picea glehnii (Sieb. et Zucc) and their related compounds
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Conflict of interest The authors report no conflict of interest. The
authors alone are responsible for the content and writing of the article.
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