Design and Synthesis of Novel Insecticides Based on the Serotonergic Ligand 1-[(4-Aminophenyl)ethyl]-4-[3-(trifluoromethyl)phenyl]piperazine(PAPP)

Article abstract of DOI:10.1021/jf902640u

1-[(4-Aminophenyl)ethyl]-4-[3-(trifluoromethyl)phenyl]piperazine (PAPP) is a 5-HT_1A agonist and was reported to display high affinity for serotonin (5-HT) receptor from the parasitic nematode Haemonchus contortus. The present investigation explored the possibility of using PAPP as a lead compound of new insecticides with novel mode of action. On the basis of the PAPP scaffold, a series of 1-arylmethyl-4-[(trifluoromethyl)pyridin-2-yl]piperazine derivatives were designed, synthesized, and evaluated for biological activities against the armyworm Pseudaletia separata (Walker). Bioassays showed that most of the target compounds displayed certain growth-inhibiting activities or larvicidal activities against armyworm. The quantitative structure-activity relationship (QSAR) for growth-inhibiting activities was also analyzed and established.

Full text of DOI:10.1021/jf902640u

2624 J. Agric. Food Chem. 2010, 58, 2624–2629
DOI:10.1021/jf902640u
Design and Synthesis of Novel Insecticides Based on the
Serotonergic Ligand 1-[(4-Aminophenyl)ethyl]-4-
[3-(trifluoromethyl)phenyl]piperazine (PAPP)†
MINGYI
C
AI, ZHONG
L
I
,* FENG
F
AN, QINGCHUN
H
UANG, XUSHENG
S
HAO AND
,
G
ONGHUA ONG
S
*
Shanghai Key Laboratory of Chemical Biology, School of Pharmacy, East China University of Science and
Technology, P.O. Box 544, 130 Meilong Road, Shanghai 200237, People’s Republic of China
1-[(4-Aminophenyl)ethyl]-4-[3-(trifluoromethyl)phenyl]piperazine (PAPP) is a 5-HT1A agonist and was
reported to display high affinity for serotonin (5-HT) receptor from the parasitic nematode
Haemonchus contortus. The present investigation explored the possibility of using PAPP as a lead
compound of new insecticides with novel mode of action. On the basis of the PAPP scaffold, a
series of 1-arylmethyl-4-[(trifluoromethyl)pyridin-2-yl]piperazine derivatives were designed, synthe-
sized, and evaluated for biological activities against the armyworm Pseudaletia separata (Walker).
Bioassays showed that most of the target compounds displayed certain growth-inhibiting activities or
larvicidal activities against armyworm. The quantitative structure-activity relationship (QSAR) for
growth-inhibiting activities was also analyzed and established.
KEYWORDS: PAPP; 1-arylmethyl-4-[(trifluoromethyl)pyridin-2-yl]piperazine; larvicidal activity; growth
inhibiting activity; QSAR
INTRODUCTION
according to Smith et al.’s testing results. Thus, it might be
reasonable to regard PAPP as a potential lead compound
for discovering insecticidal candidates with a novel mode of
action.
As one of the main pest management tools, insecticides play a
very important role in modern agriculture. However, the frequent
and wide application of traditional insecticides has brought about
an inevitable problem, namely, the occurrence and development
of resistance of pest species. Therefore, it is critically necessary to
discover new insecticidal candidates with novel modes of action.
In invertebrate species, serotonin [5-hydroxytrytryptamine
(5-HT)] as a significant monoamine neurotransmitter is widely
distributed throughout the central and peripheral nervous sys-
tems and involved in a number of physiological processes such as
feeding, procreation, and development (1-7). Some 5-HT recep-
tors (5-HTRs) have already been cloned from Drosophila, mol-
luscs, and nematodes. It is interesting that most of them show
relatively low affinities with serotonin with the exception of the
5-HT1Hc receptor from the parasitic nematode Haemonchus
contortus. The 5-HT1Hc receptor displayed nanomolar binding
affinity for serotonin and serotonergic ligands. Such a unique
pharmacological profile was distinct from the other known
invertebrate and mammalian 5-HT receptors (8, 9).
To validate the hypothesis, the structural motif of PAPP was
shared involving the introduction of appropriate N1- and N4-
substituent groups for agrochemicals by the following two ways.
First, owing to the successful application in neonicotinoids, aryl-
methyl groups might be adopted as profitable N1-substituent
groups. Second, due to the unique bioactivities in the agrochem-
icals (i.e., herbicides fluazifog-P-butyl and haloxyfog and insecti-
cides fluazuron and chlorfluazuron), the trifluoromethylpyridine
ring might be a good candidate as the N4-substituent group.
Therefore, a series of 1-arylmethyl-4-[(trifluoromethyl)pyridin-2-
yl]piperazine derivatives (Scheme 1) were designed, synthesized
(Scheme 2), and bioassayed. It was found that most of the target
compounds exhibited certain growth-inhibiting activities or lar-
vicidal activities against the armyworm Pseudaletia separata
(Walker). This result verified that PAPP could become a compe-
tent lead compound for the development of new insecticides.
It has been found that many N1-substituted N4-arylpiperazine
derivatives, for example, PAPP, BMY7378, and NAN-190
(Table 1), showed high affinities and good selectivity for 5-HTRs
with the incorporation of the appropriate N1- and N4-substituent
groups (9-12). Among those notable serotonergic ligands,
PAPP, a N1-arylated alkyl N4-arylpiperazine derivative, exhibited
the highest affinity with 5-HT1Hc receptor as shown in Table 1 (9)
MATERIALS AND METHODS
Synthesis. All chemicals or reagents were purchased from standard
commercial suppliers. Analytical thin-layer chromatography (TLC) was
carried out on precoated silica gel (SiO2) plates (60 F254). Melting points
€
€
were determined on a Buchi B540 (Buchi Labortechnik AG, Flawil,
Switzerland) and are uncorrected. The infrared spectra were recorded
on a Nicolet 470 IR Fourier transform spectrometer in KBr pellets. H
1
†Part of the ECUST-Qian Pesticide Cluster.
*Authors to whom correspondence should be addressed [e-mail
(Z.L.) lizhong@ecust.edu.cn or (G.S.) ghsong@ecust.edu.cn].
NMR spectra were recorded on a Bruker WP-500SY (500 MHz) spectro-
meter in CDCl3 with TMS as an internal standard. High-resolution mass
spectra were obtained on a MicroMass GCT CA 055 spectrometer.
pubs.acs.org/JAFC
Published on Web 12/10/2009
© 2009 American Chemical Society

Article
J. Agric. Food Chem., Vol. 58, No. 5, 2010 2625
Table 1. Affinities of N1-Substituted N4-Arylpiperazine Derivatives Binding to
the Cloned 5-HT1Hc Receptor of the Parasitic Nematode Haemonchus
contortus Reported by Smith et al. (9)
1-(4-Chlorobenzyl)-4-[5-(trifluoromethyl)pyridin-2-yl]piperazine (B1):
yield, 75%; white solid; mp, 91-92 °C; IR (KBr) υ 2797, 1610, 1507,
1300, 1109, 815 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.52-2.54 (m, 4H,
pip-H), 3.53 (s, 2H, CH2), 3.64-3.66 (m, 4H, pip-H), 6.62 (d, J = 9.01 Hz,
1H, Py-H), 7.30-7.34 (m, 4H, Ar-H), 7.61-7.62 (m, 1H, Py-H), 8.39 (s,
1H, Py-H); EI-MS, m/z (%) 355 (6, Mþ), 209 (4), 193 (16), 180 (34), 175
(37), 168 (8), 125 (100), 56 (10). HRMS (EIþ) calcd for C17H17ClF3N3,
355.1063; found, 355.1064.
1-[(6-Chloropyridin-3-yl)methyl]-4-[5-(trifluoromethyl)pyridin-2-yl]pip-
erazine (B2): yield, 73%; yellow solid; mp, 88-89 °C; IR (KBr) υ 2806,
1606, 1500, 1374, 1118, 817 cm-1 1H NMR (500 MHz, CDCl3) δ
;
2.53-2.55 (m, 4H, pip-H), 3.54 (s, 2H, CH2), 3.65-3.66 (m, 4H, pip-H),
6.64 (d, J = 9.02 Hz, 1H, Py-H), 7.33-7.34 (m, 1H, Py-H), 7.62 (dd, J1 =
2.25 Hz, J2 = 2.24 Hz, 1H, Py-H), 7.70 (dd, J1 = 2.25 Hz, J2 = 2.29 Hz,
1H, Py-H), 8.34 (s, 1H, Py-H), 8.38 (s, 1H, Py-H); EI-MS, m/z (%) 356 (12,
Mþ), 337 (7), 230 (10), 194 (28), 175 (100), 147 (25), 126 (67), 56 (23).
HRMS (EIþ) calcd for C16H16ClF3N4, 356.1016; found, 356.1037.
1-[(2-Chlorothiazol-5-yl)methyl]-4-[5-(trifluoromethyl)pyridin-2-yl]pip-
erazine (B3): yield, 72%; yellow solid; mp, 61-62 °C; IR (KBr) υ 2813,
1613, 1414, 1328, 1119, 811 cm-1 1H NMR (500 MHz, CDCl3) δ
;
2.59-2.61 (m, 4H, pip-H), 3.65-3.67 (m, 4H, pip-H), 371 (s, 2H, CH2),
6.63 (d, J = 9.02 Hz, 1H, Py-H), 7.38 (s, 1H, thiazol-H), 7.63 (dd, J1 =
2.24 Hz, J2 = 2.25 Hz, 1H, Py-H), 8.39 (s, 1H, Py-H); EI-MS, m/z (%) 362
(12, Mþ), 327 (14), 230 (7), 201 (8), 187 (21), 175 (100), 165 (14), 131 (31),
56 (10). HRMS calcd for C14H14ClF3N4S, 362.0580; found, 362.0583.
1-(2-Chlorobenzyl)-4-[3-chloro-5-(trifluoromethyl)pyridin-2-yl]pipera-
zine (B4): yield, 72%; white solid; mp, 7071 °C; IR (KBr) υ 2823, 1606,
1329, 1117, 776 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.67-2.69 (m, 4H,
pip-H), 3.55-3.57 (m, 4H, pip-H), 3.70 (s, 2H, CH2), 7.23-7.25 (m, 2H,
Ar-H), 7.37 (d, J = 7.65 Hz, 1H, Ar-H), 7.50-7.51 (m, 1H, Ar-H), 7.74
(d, J = 1.71 Hz, 1H, Py-H), 8.39 (s, 1H, Py-H); EI-MS, m/z (%) 389 (Mþ),
221 (5), 193 (11), 180 (100), 168 (18), 125 (67), 56 (7). HRMS (EIþ) calcd
for C17H16Cl2F3N3, 389.0673; found, 389.0682.
a Ki values (nM) for [3H]-serotonin binding to Sf9 cell membranes expressing the
Parasitic nematode Haemonchus contortus 5-HT1Hc receptor.
Scheme 1. Structure of Target Compounds
Scheme 2. Synthesis of Target Compounds B
1-(4-Chlorobenzyl)-4-[3-chloro-5-(trifluoromethyl)pyridin-2-yl]pipera-
zine (B5): yield, 72%; yellow oil; IR (KBr) υ 2823, 1606, 1325, 1126, 750
cm-1 1H NMR (500 MHz, CDCl3) δ 2.59-2.61 (m, 4H, pip-H),
;
3.54-3.56 (m, 6H, CH2, pip-H), 7.29-7.32 (m, 4H, Ar-H), 7.74 (d,
J = 1.50 Hz, 1H, Py-H), 8.38 (s, 1H, Py-H); EI-MS, m/z (%) 389 (6, Mþ),
340 (4), 209 (11), 193 (14), 180 (56), 168 (10), 125 (100), 56 (13). HRMS
(EIþ) calcd for C17H16Cl2F3N3, 389.0673; found, 389.0665.
1-(2,6-Difluorobenzyl)-4-[3-chloro-5-(trifluoromethyl)pyridin-2-yl]pip-
erazine (B6): yield, 75%; yellow solid; mp, 43-45 °C; IR (KBr) υ 2844,
1611, 1314, 1134, 785 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.67-2.69 (m,
4H, pip-H), 3.53-3.55 (m, 4H, pip-H), 3.79 (s, 2H, CH2), 6.91-6.93 (m,
2H, Ar-H), 7.26-7.27 (m, 1H, Ar-H),7.72 (d, J = 2.00 Hz, 1H, Py-H),
8.37 (s, 1H, Py-H); EI-MS, m/z (%) 391 (18, Mþ), 372 (12), 221 (12), 195
(33), 182 (100), 170 (25), 127 (74). HRMS (EIþ) calcd for C17H15ClF5N3,
391.0875; found, 391.0861.
General Synthetic Procedure for the Target Compounds. To a
warm (oil bath temperature ca. 50 °C) solution of piperazine
(4.0 mmol) and triethylamine (3.0 mmol) in EtOH (30 mL) was
added dropwise aryl chloromethane (2.0 mmol) in ethanol (15 mL),
and then the reaction mixture was allowed to stir at 55 °C for 12 h.
After the reaction finished, the solvent was removed under vacuum.
The oily residue was treated with water (15 mL) and extracted
with CH2Cl2 (4 ꢀ 15 mL). The combined extracts were washed
with water, dried over anhydrous Na2SO4, and concentrated. The
residue was purified by flash column chromatography on silica gel
with CH2Cl2/EtOH (10:1 v/v) to obtain 1-(arylmethyl)piperazine (A)
in 80-86% yield.
Equimolar amounts (2.0 mmol) of 1-(arylmethyl)piperazine (A), anhy-
drous K2CO3, and 2,3-dichloro-5-(trifluoromethyl)pyridine (or 6-chloro-
3-(trifluoromethyl)pyridine) in MeCN (20 mL) were stirred at 55 °C for
10 h. After cooling, the reaction mixture was treated with water (15 mL)
and extracted with EtOAc (4 ꢀ 15 mL). The combined extracts were
washed with water (10 mL) and brine (10 mL), dried over anhydrous
Na2SO4, and concentrated. The residue was purified by flash column
chromatography on silica gel with petroleum ether/EtOAc (4:1 v/v) to
yield the desired product (B).
1-(Pyridin-3-ylmethyl)-4-[3-chloro-5-(trifluoromethyl)pyridin-2-yl]pip-
erazine (B7): yield, 69%; yellow oil; IR (KBr) υ 2792, 1597, 1324, 1123,
760 cm-1 1H NMR (500 MHz, CDCl3) δ 2.62-2.64 (m, 4H, pip-H),
;
3.54-3.56 (m, 4H, pip-H), 3.60 (s, 2H, CH2), 7.28-7.29 (m, 1H, Py-H),
7.73-7.75 (m, 2H, Py-H), 8.39 (s, 1H, Py-H), 8.54 (d, J = 4.00 Hz, 1H, Py-
H), 8.58 (s, 1H, Py-H), 8.54 (d, J = 4.00 Hz, 1H, Py-H), 8.58 (s, 1H, Py-H).
EI-MS, m/z (%) 356 (4, Mþ), 209 (10), 180 (7), 160 (15), 147 (100), 135
(10), 93 (42), 56 (11);. HRMS (EIþ) calcd for C16H16ClF3N4, 356.1016;
found, 356.1021.
1-(6-Chloropyridin-3-ylmethyl)-4-[3-chloro-5-(trifluoromethyl)pyridin-
2-yl]piperazine (B8): yield, 76%; yellow oil; IR (KBr) υ 2803, 1597, 1449,
1310, 1128, 749 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.59-2.61 (m, 4H,
pip-H), 3.52-3.54 (m, 4H, pip-H), 3.56 (s, 2H, CH2), 7.32 (d, J = 8.10 Hz,
1H, Py-H), 7.70 (d, J = 7.17 Hz, 1H, Py-H), 7.75 (d, J = 1.84 Hz, 1H, Py-
H), 8.35 (d, J = 1.95 Hz, 1H, Py-H), 8.39 (s, 1H, Py-H); EI-MS, m/z (%)
390 (7, Mþ), 221 (13), 209 (58), 194 (47), 181 (100), 126 (89), 56 (13).
HRMS (EIþ) calcd for C16H15Cl2F3N4, 390.0626; found, 390.0628.
1-[(2-Chlorothiazol-5-yl)methyl]-4-[3-chloro-5-(trifluoromethyl)pyridin-
2-yl]piperazine (B9): yield, 72%; yellow oil; IR (KBr) υ 2823, 1597, 1316,
1126, 750 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.64-2.66 (m, 4H, pip-H),
3.52-3.54 (m, 4H, pip-H), 3.72 (s, 2H, CH2), 7.38 (s, 1H, thiazol-H),
7.74-7.75 (m, 1H, Py-H), 8.39 (s, 1H, Py-H); EI-MS, m/z (%) 396 (7, Mþ),
When 2,6-dichloro-3-(trifluoromethyl)pyridine was used, the reaction
mixture was stirred at 45 °C for 10 h. The 6-substituted products as
the major reaction products were formed along with minor 2-sub-
stituted impurities, which could be removed later by column chroma-
tography.
Compounds C1 and C2 were synthesized in a similar way.

2626 J. Agric. Food Chem., Vol. 58, No. 5, 2010
Cai et al.
361 (24), 223 (29), 209 (76), 187 (53), 165 (33), 145 (16), 131 (100), 56 (21).
HRMS (EIþ) calcd for C14H13Cl2F3N4S, 396.0190; found, 396.0200.
1-(4-Chlorobenzyl)-4-[6-chloro-5-(trifluoromethyl)pyridin-2-yl]pipera-
zine (B10): yield, 46%; yellow oil; IR (KBr) υ 2808, 1601, 1329, 1129,
805 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.51-2.53 (m, 4H, pip-H), 3.54
(s, 2H, CH2), 3.64-3.66 (m, 4H, pip-H), 6.47 (d, J = 8.80 Hz, 1H, Py-H),
7.29-7.32 (m, 4H, Ar-H), 7.67 (d, J = 8.80 Hz, 1H, Py-H); EI-MS, m/z
(%) 389 (54, Mþ), 370 (11), 264 (17), 223 (18), 209 (25), 180 (100), 168 (39),
125 (83). HRMS (EIþ) calcd for C17H16Cl2F3N3, 389.0673; found,
389.0673.
Hz, 1H, Py-H), 7.02 (m, 1H, Ar-H), 7.23-7.25 (m, 2H, Ar-H), 7.65 (d, J
= 8.80 Hz, 1H, Py-H); EI-MS, m/z (%) 407 (18, Mþ), 264 (11), 221 (14),
198 (100), 186 (44), 143 (82), 42 (6). HRMS (EIþ) calcd for
C17H15Cl2F4N3, 407.0579; found, 407.0579.
1-(3-Chlorobenzyl)-4-[6-chloro-5-(trifluoromethyl)pyridin-2-yl]pipera-
zine (B19): yield, 47%; yellow oil; IR (KBr) υ 2823, 1611, 1308, 1134,
780 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.54-2.56 (m, 4H, pip-H), 3.55
(s, 2H, CH2), 3.66-3.68 (m, 4H, pip-H), 6.47 (d, J = 8.80 Hz, 1H, Py-H),
7.26-7.28 (m, 3H, Ar-H), 7.39 (s, 1H, Ar-H), 7.67 (d, J = 8.80 Hz, 1H,
Py-H); EI-MS, m/z (%) 389 (29, Mþ), 264 (13), 221 (16), 209 (22), 180
(100), 168 (34), 125 (63), 42 (6). HRMS (EIþ) calcd for C17H16Cl2F3N3,
389.0673; found, 389.0673.
1-(2,3-Dichlorobenzyl)-4-[6-chloro-5-(trifluoromethyl)pyridin-2-yl]pip-
erazine (B11): yield, 47%; yellow oil; IR (KBr) υ 2823, 1617, 1319, 1113,
769 cm-1 1H NMR (500 MHz, CDCl3) δ 2.61-2.63 (m, 4H, pip-H),
;
1-(2-Chlorobenzyl)-4-[6-chloro-5-(trifluoromethyl)pyridin-2-yl]pipera-
zine (B20): yield, 51%; yellow oil; IR (KBr) υ 2806, 1593, 1113, 750
3.65-3.69 (m, 6H, CH2, pip-H), 6.48 (d, J = 8.40 Hz, 1H, Py-H), 7.22 (m,
1H, Ar-H), 7.41-7.42 (m, 2H, Ar-H), 7.68 (d, J = 8.00 Hz, 1H, Py-H);
EI-MS, m/z (%) 423 (22, Mþ), 404 (21), 388 (19), 264 (14), 243 (29), 214
(100), 158 (79), 123 (8). HRMS (EIþ) calcd for C17H15Cl3F3N3. 423.0284;
found. 423.0288.
cm-1 1H NMR (500 MHz, CDCl3) δ 2.59-2.61 (m, 4H, pip-H),
;
3.65-3.67 (m, 6H, CH2, pip-H), 6.46 (d, J = 8.78 Hz, 1H, Py-H),
7.23-7.25 (m, 2H, Ar-H), 7.36-7.37 (m, 1H, Ar-H), 7.50 (d, J =
7.23 Hz, 1H, Ar-H), 7.66 (d, J = 8.81 Hz, 1H, Py-H); EI-MS, m/z (%)
389 (Mþ), 209 (12), 180 (86), 168 (28), 125 (100), 69 (10), 56 (19). HRMS
(EIþ) calcd for C17H16Cl2F3N3, 389.0673; found, 389.0700.
1-[(6-Chloropyridin-3-yl)methyl]-4-[6-chloro-5-(trifluoromethyl)pyridin-
2-yl]piperazine (B12): yield, 46%; yellow solid; mp, 98-99 °C; IR (KBr) υ
2810, 1611, 1315, 1123, 750 cm-1 1H NMR (500 MHz, CDCl3) δ
;
1-(2,4-Dichlorobenzyl)-4-[6-chloro-5-(trifluoromethyl)pyridin-2-yl]pip-
erazine (B21): yield, 56%; yellow oil; IR (KBr) υ 2833, 1606, 1328, 1135,
2.52-2.54 (m, 4H, pip-H), 3.54 (s, 2H, CH2), 3.64-3.65 (m, 4H, pip-H),
6.50 (d, J = 8.79 Hz, 1H, Py-H), 7.33 (d, J = 8.08 Hz, 1H, Py-H),
7.66-7.68 (m, 2H, Py-H), 8.34 (d, J = 2.17 Hz, 1H, Py-H); EI-MS, m/z
(%) 390 (14, Mþ), 221 (10), 209 (41), 194 (11), 181 (100), 169 (12), 126 (72),
56 (10). HRMS (EIþ) calcd for C16H15Cl2F3N4, 390.0626; found,
390.0633.
804 cm-1 1H NMR (500 MHz, CDCl3) δ 2.58-2.60 (m, 4H, pip-H),
;
3.64-3.68 (m, 6H, CH2, pip-H), 6.48 (d, J = 8.80 Hz, 1H, Py-H), 7.26 (m,
1H, Ar-H), 7.41-7.43 (m, 2H, Ar-H), 7.68 (d, J = 8.80 Hz, 1H, Py-H);
EI-MS, m/z (%) 423 (18, Mþ), 264 (31), 214 (98), 202 (36), 158 (100), 123
(6), 56 (5). HRMS calcd for C17H15Cl3F3N3, 423.0284; found, 423.0285.
1-[(6-Chloropyridin-3-yl)methyl]-4-phenylpiperazine (C1): yield, 87%;
white solid; mp, 135-136 °C; 1H NMR (500 MHz, CDCl3) δ 2.63-2.65
(m, 4H, pip-H), 3.43-3.45 (m, 4H, pip-H), 3.69 (s, 2H, CH2), 6.88 (d, J =
7.98 Hz, 1H, Py-H), 7.21-7.23 (m, 2H, Ar-H), 7.34-7.36 (m, 2H,
Ar-H), 7.53 (m, 1H, Ar-H), 7.74 (d, J = 8.07 Hz, 1H, Py-H); EI-MS,
m/z (%) 287 (100, Mþ), 181 (16), 161 (52), 154 (42), 126 (64), 106 (68), 77
(44), 56 (52). HRMS (EIþ) calcd for C17H16Cl2F3N3, 287.1189; found,
287.1189.
1-[(2-Chlorothiazol-5-yl)methyl]-4-[6-chloro-5-(trifluoromethyl)pyridin-
2-yl]piperazine (B13): yield, 46%; yellow oil; IR (KBr) υ 2806, 1593, 1316,
1126, 778 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.57-2.59 (m, 4H, pip-H),
3.63-3.65 (m, 4H, pip-H), 3.70 (s, 2H, CH2), 6.47 (d, J = 8.66 Hz, 1H,
Py-H), 7.38 (s, 1H, thiazol-H), 7.68 (d, J = 8.66 Hz, 1H, Py-H); EI-MS,
m/z (%) 396 (12, Mþ), 361 (37), 223 (40), 209 (82), 187 (61), 175 (24), 165
(11), 153 (15), 145 (15), 131 (100), 56 (37). HRMS (EIþ) calcd for
C14H13Cl2F3N4S, 396.0190; found, 396.0196.
1-(2,6-Difluorobenzyl)-4-[6-chloro-5-(trifluoromethyl)pyridin-2-yl]pip-
erazine (B14): yield, 44%; white solid; mp, 65.0-65.9 °C; IR (KBr) υ
1-[(6-Chloropyridin-3-yl)methyl]-4-[2,6-dinitro-4-(trifluoromethyl)phe-
nyl]piperazine (C2): yield, 79%; yellow solid; mp, 162-164 °C; IR (KBr)
υ (cm-1) 1540, 1321, 1156 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.54-2.56
(m, 4H, pip-H), 3.14-3.16 (m, 4H, pip-H), 3.55 (s, 2H, CH2), 7.34 (d,
J = 8.07 Hz, 1H, Py-H), 7.68 (s, 1H, Py-H), 8.03 (s, 2H, Ar-H), 8.32 (s,
1H, Py-H); EI-MS, m/z (%) 445 (1, Mþ), 291 (5), 231 (7), 126 (100), 90 (8),
42 (11). HRMS (EIþ) calcd for C17H15ClF3N5O4, 445.0765; found,
445.0746.
2886, 1613, 1314, 1122, 791 cm-1 1H NMR (500 MHz, CDCl3) δ
;
2.62-2.64 (m, 4H, pip-H), 3.67-3.69 (m, 4H, pip-H), 3.83 (s, 2H, CH2),
6.45 (d, J = 8.80 Hz, 1H, Py-H), 6.94-6.95 (m, 2H, Ar-H), 7.29 (m, 1H,
Ar-H), 7.66 (d, J = 8.80 Hz, 1H, Py-H); EI-MS, m/z (%) 391 (19, Mþ),
264 (13), 221 (10), 182 (100), 127 (76), 56 (2). HRMS (EIþ) calcd for
C17H15ClF5N3, 391.0875; found, 391.0870.
Biological Assay. Larvae of the armyworm, P. separata (Walker),
were reared continuously on freshly cut maize seedling under standard
laboratory conditions (25 °C, 60% relative humidity, and a 16:8 h light/
dark photoperiod). All compounds were dissolved in acetone and diluted
with water containing Triton X-100 (0.1 mg L-1) to 500 and 250 mg L-1 in
concentration for bioassay. Fresh leaves were dipped in diluted solutions
of the chemicals for 5 s, and excess fluid was removed. Water containing
Triton X-100 (0.1 mg L-1) and acetone was used as control.
Effects on larval growth were assessed using second-instar larvae of the
armyworm. After weighing, each batch of second-instar larvae of the
armyworm (n = 10) was released on leaves. Controls were treated
similarly. Each treatment was replicated three times. Larvae were re-
weighed after 120 h for every batch to count the growth inhibition.
Mortality was assessed 72 h after treatment.
1-(4-Iodobenzyl)-4-[6-chloro-5-(trifluoromethyl)pyridin-2-yl]piperazine
(B15): yield, 45%; white solid; mp, 78.8-79.7 °C; IR (KBr) υ 2813,
1593, 1321, 1129, 791 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.52-2.54 (m,
4H, pip-H), 3.52 (s, 2H, CH2), 3.64-3.66 (m, 4H, pip-H), 6.47 (d, J = 8.80
Hz, 1H, Py-H), 7.11-7.13 (m, 2H, Ar-H), 7.69 (m, 3H, Ar-H, Py-H); EI-
MS, m/z (%) 481 (23, Mþ), 285 (11), 272 (87), 260 (31), 216 (100), 209 (8).
HRMS (EIþ) calcd for C17H16ClF3IN3, 481.0030; found, 481.0031.
1-(4-tert-Butylbenzyl)-4-[6-chloro-5-(trifluoromethyl)pyridin-2-yl]pip-
erazine (B16): yield, 45%; white solid; mp, 111.5-112.1 °C; IR (KBr) υ
2806, 1600, 1321, 1113, 797 cm-1; 1H NMR (500 MHz, CDCl3) δ 1.34 (s,
9H, C(CH3)3), 2.55-2.57 (m, 4H, pip-H), 3.57 (s, 2H, CH2), 3.66-3.68 (m,
4H, pip-H), 6.46 (d, J = 9.20 Hz, 1H, Py-H), 7.28-7.29 (m, 2H, Ar-H),
7.37-7.38 (m, 2H, Ar-H), 7.66 (d, J = 9.20 Hz, 1H, Py-H); EI-MS,
m/z (%) 411 (27, Mþ), 264 (30), 202 (50), 190 (19), 147 (100), 117 (13), 56
(4). HRMS (EIþ) calcd for C21H25ClF3N3, 411.1689; found, 411.1689.
1-(2-Chlorobenzyl)-4-[6-chloro-3-(trifluoromethyl)pyridin-2-yl]pipera-
zine (B17): yield, 24%; yellow oil; IR (KBr) υ 2826, 1587, 1302, 1103,
RESULTS AND DISCUSSION
Biological Activity. The biological activities against army-
worm, P. separata (Walker), of the target compounds are
summarized in Table 2. Most of the compounds B1-B17 showed
certain growth-inhibiting activities. Through careful observation,
the treated larvae were found to decrease feeding compared to the
control ones. It was also found that the bodies of the treated
larvae were thinner and shorter than those of control ones, and
the growth development of treated larvae lagged behind that of
the control larvae. Generally, the symptoms induced by the target
compounds were similar to those described for typical insect
759 cm-1 1H NMR (500 MHz, CDCl3) δ 2.64-2.66 (m, 4H, pip-H),
;
3.44-3.46 (m, 4H, pip-H), 3.69 (s, 2H, CH2), 6.88 (d, J = 7.98 Hz, 1H, Py-
H), 7.22-7.23 (m, 2H, Ar-H), 7.36 (m, 1H, Ar-H), 7.53 (m, 1H, Ar-H),
7.74 (d, J = 8.07 Hz, 1H, Py-H); EI-MS, m/z (%) 389 (12, Mþ), 209 (12),
180 (86), 168 (28), 125 (100), 56 (19). HRMS (EIþ) calcd for
C17H16Cl2F3N3, 389.0673; found, 389.0700.
1-(2-Chloro-6-fluorobenzyl)-4-[6-chloro-5-(trifluoromethyl)pyridin-
2-yl]piperazine (B18):yield, 46%; yellow oil; IR (KBr) υ 2849, 1596,
1324, 1124, 780 cm-1 1H NMR (500 MHz, CDCl3) δ 2.65-2.67 (m,
;
4H, pip-H), 3.66-3.69 (m, 4H, pip-H), 3.79 (s, 2H, CH2), 6.45 (d, J = 8.80

Article
J. Agric. Food Chem., Vol. 58, No. 5, 2010 2627
I (%)
Table 2. Biological Activities I (%) of Compounds B1-B21 against Armyworm
compd
R1
R2
B1
4-chlorobenzyl
5-(trifluoromethyl)pyridin-2-yl
5-(trifluoromethyl)pyridin-2-yl
5-(trifluoromethyl)pyridin-2-yl
76.9a
73.7a
48.4a
78.6a
55.5a
36.6a
78.6a
83.5a
88.6a
84.1a
51.2a
25.4a
89.5a
22.2a
13.7a
30.0a
74.8a
27.5b
B2
(6-chloropyridin-3-yl)methyl
(2-chlorothiazol-5-yl)methyl
2-chlorobenzyl
B3
B4
3-chloro-5-(trifluoromethyl)pyridin-2-yl
3-chloro-5-(trifluoromethyl)pyridin-2-yl
3-chloro-5-(trifluoromethyl)pyridin-2-yl
3-chloro-5-(trifluoromethyl)pyridin-2-yl
3-chloro-5-(trifluoromethyl)pyridin-2-yl
3-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-3-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
6-chloro-5-(trifluoromethyl)pyridin-2-yl
phenyl
B5
4-chlorobenzyl
2,6-difluorobenzyl
B6
B7
(pyridin-3-yl)methyl
(6-chloropyridin-3-yl)methyl
(2-chlorothiazol-5-yl)methyl
4-chlorobenzyl
B8
B9
B10
B11
B12
B13
B14
B15
B16
B17
B18
B19
B20
B21
C1
2,3-dichlorobenzyl
(6-chloropyridin-3-yl)methyl
(2-chlorothiazol-5-yl)methyl
2,6-difluorobenzyl
4-iodobenzyl
4-tert-butylbenzyl
2-chlorobenzyl
2-chloro-6-fluorobenzyl
3-chlorobenzyl
2-chlorobenzyl
100b
93.3b
100b
0a
71.3c
76.6c
76.6c
2,4-dichlorobenzyl
(6-chloropyridin-3-yl)methyl
(6-chloropyridin-3-yl)methyl
C2
2,6-dinitro-4-(trifluoromethyl)phenyl
14.9a
a Growth inhibiting activities at 500 mg L-1, I% = 1 - T/D (D = the increased weight of the control larvae during 120 h; T = the increased weight of the treated larvae during
120 h). b Mortalities of the armyworm at 500 mg L-1 (I%) during 72 h. c Mortalities of the armyworm at 250 mg L-1 (I%) during 72 h.
Figure 2. Crystal structure of compound B2.
Workbench (DDW) module of Cerius2 (version 4.8). The
structures were minimized on the basis of the crystal structure
of B2 (Figure 2; the crystallographic data have been deposited
at the Cambridge Crystallographic Data Centre in supple-
mentary publication CCDC-658617. Copies of the data can
Figure 1. Symptoms of poisoned armyworm induced by B21 at
500 mg L-1
.
be obtained, free of charge, at http://www.ccdc.cam.ac.uk/
data_request/cif.
growth regulators. Interestingly, compounds B18-B21 exhibited
distinctly different bioactivities from compounds B1-B17. They
The data matrix was analyzed by the partial least-squares
(PLS) method. The quality of each of the regression models was
evaluated using the square of the correlation coefficient (r2),
cross-validation squared correlation coefficient (XVr2), and pre-
dicted sum of squares (PRESS). The cross-validation squared
correlation coefficient XVr2 was used to measure the predictive
ability of the equation (13, 14).
To find out which parameters are more important to activity,
several equations were obtained according to the different com-
binations of the parameters. The most significant combination of
physicochemical parameters affecting activity were log P(o/w),
PEOE_VSA-1, and vsa_hyd, which were calculated by
MOE (15,16) presented in Table 3. The growth inhibiting activity
data (% I) at 500 mg L-1 were converted to log{I/[(100 - I) ꢀ
MW]} (17) as a dependent parameter, X.
caused the armyworm’s death within 72 h at 500 and 250 mg L-1
.
It was found that the larvae could hardly move after eating the
leaves containing the test substances (B18-B21), and the bodies
remainedspasmodic until the testlarvaediedasshown inFigure1.
The causation of the bioactivity difference between B18-B21 and
B1-B17 is still under investigation.
Effect of N4-Aryl Group on Activities. To verify the effect of an
N4-aryl group on activities, compounds C1 and C2 were prepared
by replacing the trifluoromethylpyridinyl group on N4-substitu-
tents of B2 with substituted phenyl groups. The bioassays showed
that such replacement did weaken the growth-inhibiting activity,
which demonstrated that a suitable N4-substitutent, such as the
trifluoromethylpyridinyl group, was significant for a compound
to remain effective against the insect.
Quantitative Structure-Activity Relationship (QSAR). The
relationship between growth-inhibiting activities and the
structures of compounds B1-B17 was analyzed by a QSAR
(Hansch) approach against physicochemical parameters. The
computational work was accessed from the Drug Discovery
X ¼ logfI=½ð100 -IÞ ꢀ MWꢁg
The physical parameters log P(o/w), PEOE_VSA-1, and
vsa_hyd are the independent variables of the regression, and

2628 J. Agric. Food Chem., Vol. 58, No. 5, 2010
Cai et al.
Table 3. Experimental Activities, Calculated Activities, and Physicochemical
Parameters of Compounds B1-B17
values could result in better bioactivities. In addition, log P(o/w)
was found to be the most important factor for the activities.
Lower log P(o/w) suggested that the decrease of lipophilic
property would strengthen the growth-inhibiting activity. This
result suggested the introduction of a hydrophilic factor, such as
the use of heterocyclic rings including oxygen and/or nitrogen
might benefit the bioactivity of compounds. In agreement with the
lower log P(o/w), lower vsa_hyd values meant the decrease of
surface area of hydrophobic atoms in the molecule. A higher
PEOE_VSA-1 value was associated with the increase of electro-
negative atoms in the molecule. Thus, the application of an
electronegative atom or group (i.e., chlorine, fluorine, and triflu-
oromethyl group) would be encouraged for better bioactivity.
In conclusion, a series of 1-arylmethyl-4-[(trifluoromethyl)-
pyridin-2-yl]piperazine compounds derived from PAPP were
synthesized, and their biological activities against armyworm
were evaluated. By the preliminary bioassay, most of the target
compounds exhibited certain growth-inhibiting activities or lar-
vicidal activities against armyworm, P. separata (Walker). The
results indicated that PAPP could become a lead compound for
insecticides with novel modes of action. QSAR demonstrated that
log P(o/w), PEOE_VSA-1, and vsa_hyd were the critical para-
meters for growth-inhibiting activities of target compounds.
Further structural modification and biological evaluation are
currently under investigation and will be reported in due course.
compd I%
Xa
calcdb
log P(o/w)c PEOE_VSA-1d vsa_hyde
B1
76.9 -2.027 -2.4145
73.7 -2.104 -2.02767
48.4 -2.587 -1.87392
78.6 -2.025 -2.16922
55.5 -2.494 -2.41951
36.6 -2.894 -2.99858
78.6 -1.986 -2.06364
83.5 -1.887 -2.03269
88.6 -1.707 -1.87893
84.1 -1.868 -1.99634
51.2 -2.607 -2.37305
25.4 -1.992 -2.02729
89.5 -1.667 -1.84258
22.2 -3.137 -2.96223
13.7 -3.481 -3.53444
30.0 -2.982 -2.81454
74.8 -2.117 -2.13287
3.83276
3.00476
2.69176
4.45776
4.45976
4.16976
2.63476
3.63176
3.31876
4.00076
5.41676
3.00376
3.68776
4.53876
5.42676
5.73576
4.82676
54.091755
41.836849
33.766548
95.928604
83.673698
41.836849
41.836849
71.4188
299.9382
284.101
B2
B3
274.2206
318.2314
318.2314
310.1802
293.1117
302.3942
292.5139
293.3834
327.5138
284.101
B4
B5
B6
B7
B8
B9
63.348495
71.4188
B10
B11
B12
B13
B14
B15
B16
B17
113.25565
41.836849
63.348495
41.836849
54.091755
134.84459
95.928604
283.5031
301.1694
325.1491
365.5528
309.2206
a X = log{I/[(100 - I) ꢀ MW]} (I% = growth-inhibiting activities at 500 mg L-1
;
MW = molecular weight). b The calculated activities. c Log P(o/w) = octanol/water
partition coefficient. d PEOE_VSA-1 = van der Waals surface area of atomic partial
charge -0.10 e q e -0.05. e vsa_hyd = approximate van der Waals surface area
of hydrophobic atoms.
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Received for review July 29, 2009. Revised manuscript received October
20, 2009. Accepted November 19, 2009. Financial support from the
National Key Project for Basic Research (Grant 2003CB114400),
National Natural Science Foundation of China (Grant 20972052),
Science and Technology Commission of Shanghai Municipality
(Grant 08391911600), and Shanghai Leading Academic Discipline
Project (Project B507) is gratefully acknowledged.