Synthesis, insecticidal activity, crystal structure, and molecular docking studies of nitenpyram analogues with an ω-hydroxyalkyl ester arm anchored on the tetrahydropyrimidine ring

Article abstract of DOI:10.1021/jf3024479

On the basis of the research of the proposed modes of action between neonicotinoids and insect nicotinic acetylcholine receptor (nAChR), a new series of nitenpyram analogues with an ω-hydroxyalkyl ester arm anchored on the tetrahydropyrimidine ring was designed and synthesized to further enhance the strength of the hydrogen-bonding action they display in binding with the nAChR. The structures of the target compounds were characterized by ¹H NMR, IR, and elemental analysis, and the cis configuration was confirmed by X-ray diffraction. Preliminary bioassays indicated that all of the nitenpyram analogues exhibited good insecticidal activity against Nilaparvata lugens and Myzus persicae at 100 mg/L, whereas analogues 4d and 6a afforded the best in vitro activity that had ≥95% mortality at 4 mg/L; the LC₅₀ values of the analogues 4d and 6a were 0.170 and 0.154 mg/L, respectively. Structure-activity relationship (SAR) studies suggested that their insecticidal potency was also dual-controlled by the flexibility and size of the molecule. In addition, molecular docking simulations revealed that analogues 4d and 6a displayed stronger hydrogen-bonding action in binding with the nAChR, which explained the SARs observed in vitro and implied that the designed nitenpyram analogues are both practical and feasible.

Full text of DOI:10.1021/jf3024479

Article
pubs.acs.org/JAFC
Synthesis, Insecticidal Activity, Crystal Structure, and Molecular
Docking Studies of Nitenpyram Analogues with an ω‑Hydroxyalkyl
Ester Arm Anchored on the Tetrahydropyrimidine Ring
Chuan-Wen Sun,* Ting Fang, Jing Wang, Zhi-bing Hao, and Shi-bing Nan
College of Life and Environment Sciences, Shanghai Normal University, Shanghai 200234, China
S
* Supporting Information
ABSTRACT: On the basis of the research of the proposed modes of action between neonicotinoids and insect nicotinic
acetylcholine receptor (nAChR), a new series of nitenpyram analogues with an ω-hydroxyalkyl ester arm anchored on the
tetrahydropyrimidine ring was designed and synthesized to further enhance the strength of the hydrogen-bonding action they
display in binding with the nAChR. The structures of the target compounds were characterized by 1H NMR, IR, and elemental
analysis, and the cis configuration was confirmed by X-ray diffraction. Preliminary bioassays indicated that all of the nitenpyram
analogues exhibited good insecticidal activity against Nilaparvata lugens and Myzus persicae at 100 mg/L, whereas analogues 4d
and 6a afforded the best in vitro activity that had ≥95% mortality at 4 mg/L; the LC50 values of the analogues 4d and 6a were
0.170 and 0.154 mg/L, respectively. Structure−activity relationship (SAR) studies suggested that their insecticidal potency was
also dual-controlled by the flexibility and size of the molecule. In addition, molecular docking simulations revealed that analogues
4d and 6a displayed stronger hydrogen-bonding action in binding with the nAChR, which explained the SARs observed in vitro
and implied that the designed nitenpyram analogues are both practical and feasible.
KEYWORDS: neonicotinoid insecticides, nitenpyram analogues, hydrogen-bonding action, ω-hydroxyalkyl ester, insecticidal activities,
structure−activity relationships, molecular docking
of nitenpyam analogues with different amino acid alkyl esters
were synthesized, and the bioassays indicated that analogues 2
and 3 exhibited quite good insecticidal activities against
Nilaparvata lugens. Considering the results of SARs and
molecular docking simulations, we found that the higher
insecticidal potency of compounds 2a (R = iBu), 3a (R = nPr, n
= 2), and 3b (R =iPr, n = 2) (Figure 2) were controlled by the
molecular flexibility and size. However, in the final analysis, we
found that more hydrogen bonds were formed between the
ester groups of compounds 2a, 3a, and 3b and the relevant
amino acid residues at the ligand binding pocket; therefore,
compounds 2a, 3a, and 3b had stronger hydrogen-bonding
actions compared with their binding with the nAChR.
On the basis of the theory above, the core of our work of the
neonicotinoid structural optimization or design is how to
increase the strength of the hydrogen-bonding action of the
neonicotinoid compounds in binding with the nAChR.
We suppose that the main method to control the strength of
the hydrogen-bonding action is the introduction of an organic
segment bearing the electronegative atom into the lead
compounds. Therefore, to enhance the strength of the
hydrogen-bonding action, on the basis of our previous work,
starting from nitenpyram, various amino acid ω-hydroxyalkyl
esters were introduced into the lead compounds (Scheme 1),
and the other novel nitenpyram analogues 4−7 with an ω-
INTRODUCTION
■
Neonicotinoid insecticides (NNSs) selectively act on the insect
nicotinic acetylcholine receptor (nAChR),1−3 which repre-
sented a new generation of synthetic insecticides as they had
some specific properties that allowed them to be the fastest
growing synthetic insecticides on the market. Some of their
properties are no cross-resistance to conventional long-
established insecticide classes, a broad-spectrum insecticidal
activity, low application rate, novel mode of action, and
favorable safety profile.4,5 Emerging as the fourth generation of
pesticides replacing organophosphorus, carbamate, and pyreth-
roid compounds, neonicotinoids are increasingly used in crop
protection and animal health care. However, a significant threat
of resistance was observed after frequent applications of the
NNSs. As a result, development of new neonicotinoids with
novel structures and high insecticidal activities against
resistance is an urgent requirement.6−9 It is well-known that
the structure optimization of commercial neonicotinoids is an
effective resistance management tactic.10−12
In the development of neonicotinoid insecticides, there were
three modes of action of neonicotinoids against nAChR, which
were presumed successively by Yamamoto, Kagabu, and
Casida.13−15 The three modes of action demonstrated that
the interactions between the neonicotinoid compounds and
nAChR were not only due to the electrostatic interaction but
also due to the hydrogen-bonding action. Therefore, the
hydrogen-bonding action had an important effect on the
insecticidal activities of neonicotinoid compounds.
Received: June 7, 2012
Revised: September 2, 2012
Accepted: September 5, 2012
Published: September 5, 2012
A major emphasis in our previous study16,17(Figure 1)
involved the structure optimization of nitenpyram 1; two series
© 2012 American Chemical Society
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Figure 1. Our previous studies of nitenpyam analogues with amino acid alkyl esters.
others. Therefore, the strength of the hydrogen-bonding action
was the influential factor for the bioactivities of our designed
nitenpyram analogues.
MATERIALS AND METHODS
■
Instruments. Melting points were measured using an uncorrected
RK-1 microscopic melting point apparatus. 1H NMR spectra were
recorded on a Bruker AVANCE (400 MHz) spectrometer with
chloroform (CDCl3) as the solvent and tetramethylsilane as the
internal standard. The IR spectra were obtained from KBr disks in the
range of 4000−400 cm−1 on a Nicolet 5DXFT-IR spectrophotometer.
Combustion analyses for elemental composition were conducted on a
Perkin-Elmer 2400 instrument. All microwave experiments were
performed using a YL8023B1 microwave reactor possessing a single-
mode microwave cavity producing controlled irradiation at 2.45 GHz.
Synthetic Procedures. Synthesis procedures for the title
compounds are summarized in Scheme 2. Unless otherwise noted,
reagents and solvents were of analytical reagent grade or were
chemically pure and used as received without further purification.
General Synthetic Procedures for Target Compounds 4a−
7e. Amino acids were converted to the intermediates of amino acid ω-
hydroxyalkyl ester hydrochlorides according to the procedures given in
the literature.18 Starting from 2-chloro-5-chloromethylpyridine, a set of
(E)-N-(6-chloro-3-pyridylmethyl)-N-ethyl-1-chloro-2-nitroethylene-1-
amine and 1 was prepared according to the procedures in the
literature.19,20
Figure 2. Structures of nitenpyram analogues 2a, 3a, and 3b.
hydroxyalkyl ester arm anchored on the tetrahydropyrimidine
ring were designed and synthesized. To confirm the structure of
nitenpyram analogues 4−7 with precise three-dimensional
information, the single-crystal structure of 4g was further
determined by X-ray diffraction (Figure 3). As expected, a
preliminary bioassay against Nilaparvata lugens and Myzus
persicae showed that nitenpyram analogues 4−7 exhibited good
insecticidal activities at 100 mg/L, whereas analogues 4d and 6a
afforded the best in vitro activity that had ≥95% mortality at 4
mg/L; the LC50 values of the analogues 4d and 6a were 0.170
and 0.154 mg/L, respectively. Their SAR studies in this paper
suggested that their insecticidal potencies were also dual-
controlled by the flexibility and size of the molecule. Moreover,
in the rest of this paper, the molecular docking study was
carried out to investigate the interaction between nAChR and
nitenpyram analogues. The results of the molecular docking
study showed that the higher insecticidal potency of analogues
4d and 6a exhibited stronger hydrogen bonding than the
A mixture of compound 1 (2.71 g, 10.0 mmol), amino acid ω-
hydroxyalkyl ester hydrochloride (12.0 mmol), Et3N (1.7 mL), and
formaldehyde (1.95 mL, 37%) in ethanol (20 mL) was heated to 65
Scheme 1. Structures of Novel Nitenpyram 4−7 with Different Amino Acid ω-Hydroxyalkyl Esters
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Figure 3. Crystal structures of compound 4g.
2.15−2.08 (m, 1H), 2.05 (s, 1H, OH), 1.22−1.16 (q, J = 7.4 Hz, 3H,
NCH2CH3), 1.10−1.06 (dd, J = 9.9, 6.7 Hz, 3H, CHCH3), 0.96−0.95
(dd, J = 8.6, 6.1 Hz, 3H, CHCH3); IR (KBr, cm−1) ν 2938, 2871,
1738, 1542, 1243. Anal. Calcd for C20H30ClN5O5: C%, 52.69; H%,
6.63; N%, 15.36. Found: C%, 52.68; H%, 6.65; N%, 15.38.
Scheme 2. General Synthetic Route for the Target
Compounds
a
(+)-2′-Hydroxyethyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl]-3-methyl
25
pentanate (4c): yield 71%; yellow oil; [α]D = +31.740° (c 0.01 g/
mL, CH3COCH3); 1H NMR (CDCl3, 400 MHz) δ 8.33−8.30 (dd, J =
9.6, 1.8 Hz, 1H, Py-H), 7.74−7.64 (m, 1H, Py-H), 7.35−7.33 (d, J =
8.2 Hz, 1H, Py-H), 4.54−4.50 (dd, J = 15.0, 5.1 Hz, 1H, Py-CH2),
4.41−4.36 (dd, J = 6.5, 4.6 Hz, 2H, COOCH2), 4.26−4.14 (dd, J =
14.0, 10.8 Hz, 1H, Py-CH2), 3.85−3.76 (m, 2H, CH2OH), 3.74−3.61
(m, 4H), 3.35−3.27 (m, 1H), 3.25−3.22 (dd, J = 10.1, 2.6 Hz, 1H,
NCHCO), 2.9−2.95 (d, J = 2.3 Hz, 3H, NCH3), 2.94−2.88 (m, 1H),
2.06 (s, 1H, OH), 1.92 (m, 1H, CHCH3), 1.72−1.64 (m, 2H,
CH2CH3), 1.17−1.22 (q, J = 7.0 Hz, 3H, NCH2CH3), 1.00−0.93 (m,
6H); IR (KBr, cm−1) ν 2933, 2875, 1732, 1546, 1245. Anal. Calcd for
C21H32ClN5O5: C%, 53.67; H%, 6.86; N%, 14.90. Found: C%, 53.65;
H%, 6.89; N%, 14.93.
a
Reagents and conditions: (a) ethanamine (41%); (b) 1,1,1-trichloro-
2-nitroethane/CHCl3, 2−7 °C (64%); (c) methanamine, 3−7 °C
(56%); (d) amino acid ω-hydroxyalkyl ester hydrochloride, HCHO,
Et3N/EtOH (59−76%).
(+)-2′-Hydroxyethyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl]-4-methyl
25
pentanate (4d): yield 71%; yellow oil; [α]D = +31.743° (c 0.01 g/
1
mL CH3COCH3); H NMR (CDCl3, 400 MHz) δ 8.34−8.31 (d, J =
°C for 5 min in a microwave reactor and stirred for 20 min at that
temperature. The reaction mixture was concentrated under reduced
pressure and treated with 20 mL of water. Then, the solution was
extracted three times with dichloromethane, and the combined
extracts were dried over MgSO4. The organic phase was evaporated
under reduced pressure, and the residue was subjected to flash
chromatography on silica gel, eluting with ethyl acetate/ethanol
(15:1−20:1) to afford pure products.
11.3 Hz, 1H, Py-H), 7.76−7.68 (dd, J = 8.2, 7.1 Hz, 1H, Py-H), 7.35−
7.33 (d, J = 8.0 Hz, 1H, Py-H), 4.55−4.52 (d, J = 15.3 Hz, 1H, Py-
CH2), 4.33−4.26 (dd, J = 12.0, 4.3 Hz, 1H, Py-CH2), 4.24−4.18 (m,
2H, COOCH2), 3.91−3.82 (t, J = 8.1 Hz, 2H, CH2OH), 3.79−3.68
(m, 4H), 3.61−3.59 (t, J = 7.1 Hz, 1H, NCHCO), 3.32−3.26 (m, 1H),
2.95−2.94 (d, J = 3.4 Hz, 3H, NCH3), 2.91−2.86 (m, 1H), 2.06 (s,
1H, OH), 1.75−1.67 (m, 2H), 1.66−1.61 (m, 1H, CHCH3), 1.19 (dd,
J = 12.9, 6.3 Hz, 3H, NCH2CH3), 1.00−0.95 (dd, J = 12.0, 5.9 Hz, 6H,
CH(CH3)2); IR (KBr, cm−1) ν 2933, 2875, 1732, 1546, 1245. Anal.
Calcd for C21H32ClN5O5: C%, 53.67; H%, 6.86; N%, 14.90. Found: C
%, 53.68; H%, 6.85; N%, 14.88.
(+)-2′-Hydroxyethyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] propa-
nate (4a): yield 75%; yellow oil; [α]D = +21.836° (c 0.01 g/mL,
CH3COCH3); H NMR (CDCl3, 400 MHz) δ 8.32−8.31 (d, J = 2.0
25
1
Hz, 1H, Py-H), 7.77−7.68 (m, 1H, Py-H), 7.34−7.32(d, J = 8.2 Hz,
1H, Py-H), 4.56−4.51 (dd, J = 15.0, 6.4 Hz, 1H, Py-CH2), 4.32−4.23
(m, 2H, COOCH2), 4.21−4.16 (dd, J = 21.2, 6.1 Hz, 1H, Py-CH2),
3.90−3.84 (m, 2H, CH2OH), 3.84−3.68 (m, 4H), 3.67−3.60 (m, 1H,
CHCH3), 3.26 (m, 1H), 2.99−2.97 (d, J = 5.8 Hz, 3H, NCH3), 2.95−
2.86 (m, 1H), 2.04 (s, 1H, OH), 1.45−1.42 (dd, J = 7.1, 3.5 Hz, 3H,
CHCH3), 1.20−1.14 (q, J = 7.3 Hz, 3H, NCH2CH3); IR (KBr, cm−1)
ν 2934, 2875, 1735, 1545, 1243. Anal. Calcd for C18H26ClN5O5: C%,
50.53; H%, 6.12; N%, 16.37. Found: C%, 50.48; H%, 6.15; N%, 16.38.
(+)-2′-Hydroxyethyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl]-3-methyl
butanate (4b): yield 74%; yellow oil; [α]D25 = +10.781° (c 0.01 g/mL,
(+)-2′-Hydroxyethyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl]-3-phenyl
25
propanate (4e): yield 70%; yellow oil; [R]D = +13.562° (c 0.01 g/
1
mL CH3COCH3); H NMR (CDCl3, 400 MHz) δ 8.31−8.29 (d, J =
7.4 Hz, 1H, Py-H), 7.73−7.65 (m, 1H, Py-H), 7.35 (s, 1H, Py-H),
7.34−7.19 (m, 5H, Ph-H), 4.54−4.50 (d, J = 14.9 Hz, 1H, Py-CH2),
4.22−4.18 (d, J = 14.7 Hz, 1H, Py-CH2), 4.12−4.17 (dd, J = 8.4, 6.0
Hz, 2H, COOCH2), 3.94−3.90 (m, 2H, CH2OH), 3.84−3.74 (m,
4H), 3.69−3.62 (m, 1H, NCHCO), 3.30−3.21 (m, 1H), 3.13−3.11
(d, J = 7.7 Hz, 2H, CH2-Ph), 2.96−2.88 (m, 1H), 2.83−2.81 (d, J = 6.9
Hz, 3H, NCH3), 2.06 (s, 1H, OH), 1.20−1.15 (q, J = 7.0 Hz, 3H,
NCH2CH3); IR (KBr, cm−1) ν 2931, 2874, 1738, 1546, 1244. Anal.
Calcd for C24H30ClN5O5: C%, 57.20; H%, 6.00; N%, 13.90. Found: C
%, 57.23; H%, 6.05; N%, 13.92.
1
CH3COCH3); H NMR(CDCl3, 400 MHz) δ 8.33−8.30 (d, J = 12.6
Hz, 1H, Py-H), 7.77−7.64 (dd, J = 7.9, 8.1 Hz, 1H, Py-H), 7.35−7.33
(d, J = 8.2 Hz, 1H, Py-H), 4.55−4.50 (dd, J = 14.8, 5.1 Hz, 1H, Py-
CH2), 4.33−4.26 (m, 2H, COOCH2), 4.16−4.12 (dd, J = 40.5, 12.1
Hz, 1H, Py-CH2), 3.87−3.84 (t, J = 4.6 Hz, 2H, CH2OH), 3.82−3.67
(m, 4H), 3.31−3.24 (m, 1H), 3.12−3.08 (dd, J = 10.2, 4.9 Hz, 1H,
NCHCO), 2.97−2.95 (d, J = 1.8 Hz, 3H, NCH3), 2.94−2.87 (m, 1H),
(+)-2′-Hydroxyethyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl]-2-(4-
25
chloro)phenyl acetate (4f): yield 74%; yellow oil; [R]D = +26.541°
1
(c 0.01 g/mLCH3COCH3); mp 95−103 °C; H NMR (CDCl3, 400
MHz) δ 8.33−8.31 (d, J = 7.8 Hz, 1H, Py-H), 7.75−7.66 (dd, J = 8.4
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Hz, 1H, Py-H), 7.43−7.37 (m, 3H, Ph-H), 7.36−7.34 (d, J = 8.0 Hz,
1H, Py-H), 7.28 (t, J = 1.7 Hz, 1H, Ph-H), 4.54−4.46 (dd, J = 12.1, 9.4
Hz, 1H, Py-CH2), 4.35−4.32 (d, J = 10.3 Hz, 1H, Py-CH2), 4.26−4.20
(m, 2H, COOCH2), 3.85−3.82 (m, 2H, CH2OH), 3.80−3.69 (m,
4H), 3.66−3.59 (m, 1H, NCHCO), 3.56−3.49 (dd, J = 16.1, 14.9 Hz,
2H,CH2-Ph), 3.36−3.19 (m, 1H), 3.00−2.93 (dt, J = 14.4, 7.3 Hz,
1H), 2.90−2.86 (d, J = 16.5 Hz, 3H, NCH3), 2.06 (s, 1H, OH), 1.23−
1.17 (q, J = 7.5 Hz, 3H, NCH2CH3); IR (KBr, cm−1) ν 2939, 2877,
1733, 1545, 1249. Anal. Calcd for C24H29Cl2N5O5: C%, 53.54; H%,
5.43; N%, 13.01. Found: C%, 53.53; H%, 5.45; N%, 13.05.
2.98−2.88 (m, 1H), 2.05 (s, 1H, OH), 1.75−1.68 (m, 2H), 1.65−1.58
(m, 2H), 1.47 (m, 2H), 1.21−1.19 (t, J = 7.1 Hz, 3H, NCH2CH3); IR
(KBr, cm−1) ν 2934, 2871, 1733, 1549, 1249. Anal. Calcd for
C20H30ClN5O5: C%, 52.69; H%, 6.63; N%, 15.36. Found: C%, 52.71;
H%, 6.60; N%, 15.38.
6′-Hydroxyhexyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] acetate
1
(5e): yield 59%; yellow oil; H NMR (CDCl3, 400 MHz) δ 8.33 (s,
1H, Py-H), 7.74−7.72 (d, J = 8.2 Hz, 1H, Py-H), 7.35−7.33 (d, J = 8.2
Hz, 1H, Py-H), 4.55−4.52 (d, J = 15.0 Hz, 1H, Py-CH2), 4.19−4.18
(d, J = 6.2 Hz, 1H, Py-CH2), 4.16−4.15 (d, J = 6.5 Hz, 2H,
COOCH2), 3.83−3.69 (m, 4H), 3.67−3.64 (t, J = 6.5 Hz, 2H,
CH2OH), 3.44 (s, 2H, COCH2N), 3.30−3.23 (m, 1H), 3.06 (s, 3H,
NCH3), 2.98−2.88 (m, 1H), 2.05 (s, 1H, OH), 1.70−1.67 (m, 2H),
1.61−1.58 (m, 2H), 1.42−1.41 (d, J = 3.1 Hz, 4H), 1.21−1.17 (t, J =
7.1 Hz, 3H, NCH2CH3); IR (KBr, cm−1) ν 2934, 2878, 1735, 1545,
1249. Anal. Calcd for C21H32ClN5O5: C%, 53.67; H%, 6.86; N%,
14.90. Found: C%, 53.71; H%, 6.89; N%, 14.92.
(+)-2′-Hydroxyethyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl]-3-(4-hy-
25
droxyl) phenyl propanate(4g): yield 72%; yellow solid; [R]D
=
+24.522° (c 0.01 g/mL CH3COCH3); mp 89−91 °C;1H NMR
(CDCl3, 400 MHz) δ 8.30−8.24 (dd, J = 2.1 Hz, 1H, Py-H), 7.68 (m,
1H, Py-H), 7.37−7.28 (t, J = 4.8 Hz, 1H, Py-H), 7.28 (s, 1H, Ph-OH),
7.08−7.04 (t, J = 7.6 Hz, 2H, Ph-H), 6.83−6.80 (dd, J = 8.4, 3.2 Hz,
2H, Ph-H), 4.52−4.48 (dd, J = 13.5, 4.1 Hz, 1H, Py-CH2), 4.22−4.18
(dd, J = 6.8, 2.3 Hz, 1H, Py-CH2), 4.19−4.11 (m, 2H, COOCH2),
3.99−3.85 (m, 2H, CH2OH), 3.84−3.72 (m, 4H), 3.71−3.61 (m, 1H,
NCHCO), 3.32−3.24 (dt, J = 14.2, 6.7 Hz, 1H), 3.07−3.00 (m,
2H,CH2-Ph), 2.92−2.82 (m, 1H), 2.82−2.74 (d, J = 13.4 Hz, 3H,
NCH3), 2.05 (s, 1H, OH), 1.22−1.16 (q, J = 7.0 Hz, 3H, NCH2CH3);
IR (KBr, cm−1) ν 2939, 2877, 1733, 1545, 1249. Anal. Calcd for
C24H30ClN5O6: C%, 55.54; H%, 5.82; N%, 13.47. Found: C%, 55.50;
H%, 5.85; N%, 13.45.
2′-Hydroxyethyl-3-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] propa-
1
nate (6a): yield 74%; yellow oil; H NMR (CDCl3, 400 MHz) δ
8.29 (d, J = 2.5 Hz, 1H, Py-H), 7.70−7.67 (dd, J = 8.2, 2.4 Hz, 1H, Py-
H), 7.33−7.30 (d, J = 8.2 Hz, 1H, Py-H), 4.52−4.48 (d, J = 15.0 Hz,
1H, Py-CH2), 4.39−4.35 (t, J = 5.6 Hz, 2H, COOCH2), 4.19−4.15 (d,
J = 15.0 Hz, 1H, Py-CH2), 3.73−3.68 (m, 2H, CH2OH), 3.65−3.62 (t,
J = 5.9 Hz, 4H), 3.30−3.21 (m, 1H), 2.97 (s, 3H, NCH3), 2.95−2.90
(m, 1H), 2.88−2.77 (m, 2H, COCH2CH2), 2.62−2.59 (t, J = 6.7 Hz,
2H, NCH2CH2), 2.03 (s, 1H, OH), 1.19−1.15 (t, J = 7.1 Hz, 3H,
NCH2CH3); IR (KBr, cm−1) ν 2934, 2878, 1735, 1545, 1249. Anal.
Calcd for C18H26ClN5O5: C%, 50.53; H%, 6.12; N%, 16.37. Found: C
%, 50.53; H%, 6.18; N%, 16.35.
2′-Hydroxyethyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] acetate
1
(5a): yield 68%; yellow oil; H NMR (CDCl3, 400 MHz) δ 8.32 (d,
J = 2.4 Hz, 1H, Py-H), 7.73−7.71 (dd, J = 8.2, 2.5 Hz, 1H, Py-H),
7.35−7.33 (d, J = 8.2 Hz, 1H, Py-H), 4.54−4.51 (d, J = 15.0 Hz, 1H,
Py-CH2), 4.32−4.27 (m, 2H, COOCH2), 4.19−4.17 (d, J = 15.0 Hz,
1H, Py-CH2), 3.91−3.84 (m, 2H, CH2OH), 3.83−3.73 (m, 4H), 3.48
(s, 2H, COCH2N), 3.30−3.23 (dt, J = 14.2, 7.1 Hz, 1H), 3.06 (s, 3H,
NCH3), 2.98−2.88 (m, 1H), 2.05 (s, 1H,OH), 1.20−1.17 (t, J = 7.1
Hz, 3H, NCH2CH3); IR (KBr, cm−1) ν 2933, 2875, 1735, 1541, 1249.
Anal. Calcd for C17H24ClN5O5: C%, 49.34; H%, 5.85; N%, 16.92.
Found: C%, 49.30; H%, 5.82; N%, 16.95.
3′-Hydroxypropyl-3-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] propa-
1
nate (6b): yield 76%; yellow oil; H NMR (CDCl3, 400 MHz) δ
8.30 (d, J = 2.3 Hz, 1H, Py-H), 7.72−7.69 (dd, J = 8.2, 2.5 Hz, 1H, Py-
H), 7.33−7.31(d, J = 8.1 Hz, 1H, Py-H), 4.51−4.47 (d, J = 15.0 Hz,
1H, Py-CH2), 4.33−4.28 (m, 1H, COOCH2), 4.26−4.24 (m, 1H,
COOCH2), 4.21−4.17 (d, J = 14.8 Hz, 1H, Py-CH2), 3.70−3.69 (t, J =
5.6 Hz, 2H, CH2OH), 3.68−3.61 (m, 4H), 3.31−3.22 (m, 1H), 2.97
(s, 3H, NCH3), 2.95−2.87 (dd, J = 14.1, 7.1 Hz, 1H), 2.86−2.76 (m,
2H, COCH2), 2.59−2.55 (t, J = 6.7 Hz, 2H, NCH2), 2.04 (s, 1H,
OH), 1.92−1.86 (m, 2H, CH2CH2OH), 1.21−1.18 (t, J = 7.1 Hz, 3H,
NCH2CH3); IR (KBr, cm−1) ν 2930, 2875, 1735, 1545, 1241. Anal.
Calcd for C19H28ClN5O5: C%, 51.64; H%, 6.39; N%, 15.85. Found: C
%, 51.65; H%, 6.36; N%, 15.89.
3′-Hydroxypropyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] acetate
1
(5b): yield 69%; yellow oil; H NMR (CDCl3, 400 MHz) δ 8.33−
8.32 (d, J = 2.3 Hz, 1H, Py-H), 7.74−7.71 (dd, J = 8.2, 2.5 Hz, 1H, Py-
H), 7.35−7.33 (d, J = 8.2 Hz, 1H, Py-H), 4.54−4.51 (d, J = 15.0 Hz,
1H, Py-CH2), 4.33−4.30 (t, J = 6.2 Hz, 2H, COOCH2), 4.20−4.16 (d,
J = 15.0 Hz, 1H, Py-CH2), 3.85−3.78 (m, 2H, CH2OH), 3.76−3.69
(m, 4H), 3.45−3.44 (d, J = 1.4 Hz, 2H, COCH2N), 3.27 (m, 1H), 3.05
(s, 3H, NCH3), 2.98−2.88 (m, 1H), 2.04 (s, 1H, OH), 1.94−1.88 (m,
2H, CH2CH2OH), 1.20−1.17 (t, J = 7.1 Hz, 3H, NCH2CH3); IR
(KBr, cm−1) ν 2933, 2875, 1735, 1541, 1249. Anal. Calcd for
C18H26ClN5O5: C%, 50.53; H%, 6.12; N%, 16.37. Found: C%, 50.55;
H%, 6.16; N%, 16.49.
4′-Hydroxybutyl-3-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] propa-
nate (6c): yield 75%; yellow oil; 1H NMR (CDCl3, 400 MHz) δ
8.30 (d, J = 2.3 Hz, 1H, Py-H), 7.71−7.69 (dd, J = 8.2, 2.5 Hz, 1H, Py-
H), 7.34−7.32 (d, J = 8.2 Hz, 1H, Py-H), 4.52−4.48 (d, J = 15.0 Hz,
1H, Py-CH2), 4.20−4.18 (d, J = 8.6 Hz, 1H, Py-CH2), 4.17−4.12 (m,
2H, COOCH2), 3.69−3.68 (d, J = 6.3 Hz, 2H, CH2OH), 3.65−3.61
(m, 4H), 3.31−3.22 (m, 1H), 2.95 (s, 3H, NCH3), 2.95−2.89 (dd, J =
14.3, 7.2 Hz, 1H), 2.86−2.84 (m, 2H, COCH2), 2.58−2.54 (t, J = 6.8
Hz, 2H, NCH2), 2.05(s,1H, OH), 1.80−1.71 (m, 2H), 1.67−1.60 (m,
2H), 1.21−1.17 (t, J = 7.1 Hz, 3H, NCH2CH3); IR (KBr, cm−1) ν
2930, 2875, 1735, 1545, 1241. Anal. Calcd for C20H30ClN5O5: C%,
52.69; H%, 6.63; N%, 15.36. Found: C%, 52.65; H%, 6.66; N%, 15.39.
5′-Hydroxypentyl-3-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] propa-
4′-Hydroxybutyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] acetate
1
(5c): yield 67%; yellow oil; H NMR (CDCl3, 400 MHz) δ 8.32 (s,
1H, Py-H), 7.73−7.71 (d, J = 8.2 Hz, 1H, Py-H), 7.35−7.33 (d, J = 8.2
Hz, 1H, Py-H), 4.55−4.51 (d, J = 15.0 Hz, 1H, Py-CH2), 4.22−4.18 (t,
J = 6.4 Hz, 2H, COOCH2), 4.17−4.10 (m, 1H, Py-CH2), 3.83−3.79
(t, J = 8.6 Hz, 2H, CH2OH), 3.79−3.67 (m, 4H), 3.43 (s, 2H,
COCH2N), 3.31−3.23 (m, 1H), 3.05 (s, 3H, NCH3), 2.98−2.89 (m,
1H), 2.05 (s, 1H, OH), 1.81−1.74 (m, 2H), 1.69−1.60 (m, 2H),
1.20−1.17 (t, J = 7.1 Hz, 3H, NCH2CH3); IR (KBr, cm−1) ν 2938,
2871, 1733, 1541, 1249. Anal. Calcd for C19H28ClN5O5: C%, 51.64; H
%, 6.39; N%, 15.85. Found: C%, 51.65; H%, 6.36; N%, 15.89.
5′-Hydroxypentyl-2-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] acetate
1
nate (6d): yield 64%; yellow oil; H NMR (CDCl3, 400 MHz) δ
8.31−8.30 (d, J = 2.2 Hz, 1H, Py-H), 7.72−7.69 (dd, J = 8.2, 2.5 Hz,
1H, Py-H), 7.35−7.33 (d, J = 8.3 Hz, 1H, Py-H), 4.53−4.49 (d, J =
15.0 Hz, 1H, Py-CH2), 4.20−4.16 (d, J = 15.0 Hz, 1H, Py-CH2),
4.15−4.11 (t, J = 6.6 Hz, 2H, COOCH2), 3.76−3.70 (m, 2H,
CH2OH), 3.68−3.63 (dd, J = 9.3, 5.8 Hz, 4H), 3.32−3.23 (m, 1H),
2.98 (s, 3H, NCH3), 2.96−2.88 (m, 1H), 2.85−2.77 (m, 2H,
COCH2), 2.58−2.55 (t, J = 6.8 Hz, 2H, NCH2), 2.05 (s, 1H,
OH),1.72−1.67 (m, 2H), 1.64−1.57 (m, 2H), 1.51−1.42 (m, 2H),
1.21−1.18 (t, J = 7.2 Hz, 3H, NCH2CH3); IR (KBr, cm−1) ν 2933,
1
(5d): yield 63%; yellow oil; H NMR (CDCl3, 400 MHz) δ 8.33 (d,
J = 2.3 Hz, 1H, Py-H), 7.74−7.71 (dd, J = 8.2, 2.4 Hz, 1H, Py-H),
7.36−7.33 (d, J = 8.2 Hz, 1H, Py-H), 4.55−4.51 (d, J = 15.0 Hz, 1H,
Py-CH2), 4.19 (s, 1H, Py-CH2), 4.18−4.16 (d, J = 6.5 Hz, 2H,
COOCH2), 3.86−3.70 (m, 4H), 3.69−3.66(t, J = 6.4 Hz, 2H,
CH2OH), 3.44 (s, 2H, COCH2N), 3.32−3.23(m, 1H), 3.06 (s, 3H),
9556
dx.doi.org/10.1021/jf3024479 | J. Agric. Food Chem. 2012, 60, 9553−9561

Journal of Agricultural and Food Chemistry
Article
Table 1. Insecticidal Activities of Nitenpyram Analogues 4a−4g against Myzus persicae and Nilaparvata lugens
mortality (%) at different concentrations
Myzus persicae
Nilaparvata lugens
compd
R
n
100 mg/L
20 mg/L
4 mg/L
100 mg/L
20 mg/L
4 mg/L
a
4a
4b
4c
4d
4e
4f
Me
iPr
sBu
2
2
2
2
2
2
2
100
100
100
100
90
40
58
NT
95
95
45
65
NT
NT
35
NT
30
95
100
100
80
95
b
iBu
100
15
100
NT
NT
NT
100
20
95
benzyl
NT
NT
NT
4-Cl-ph
95
25
95
25
4g
2a
4-OH-benzyl
85
10
80
15
c
100
100
100
100
50
d
nitenpyram
100
100
100
100
a
b
c
d
NT, not tested. LC50 = 0.170 mg/L. LC50 = 0.216 mg/L. LC50 = 0.129 mg/L.
2877, 1735, 1545, 1246. Anal. Calcd for C21H32ClN5O5: C%, 53.67; H
%, 6.86; N%, 14.90. Found: C%, 53.69; H%, 6.83; N%, 14.86.
6′-Hydroxyhexyl-3-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] propa-
(t, J = 7.2 Hz, 2H, NCH2), 2.05 (s, 1H, OH), 1.91−1.84 (m, 2H),
1.78−1.75 (m, 2H), 1.67−1.60 (m, 2H), 1.22−1.18 (t, J = 7.1 Hz, 3H,
NCH2CH3); IR (KBr, cm−1) ν 2937, 2872, 1735, 1547, 1242. Anal.
Calcd for C21H32ClN5O5: C%, 53.67; H%, 6.86; N%, 14.90. Found: C
%, 53.65; H%, 6.89; N%, 14.93.
1
nate (6e): yield 62%; yellow oil; H NMR (CDCl3, 400 MHz) δ
8.31 (d, J = 2.4 Hz, 1H, Py-H), 7.72−7.69 (dd, J = 8.2, 2.5 Hz, 1H, Py-
H), 7.35−7.33 (d, J = 8.2 Hz, 1H, Py-H), 4.54−4.50 (d, J = 14.5 Hz,
1H, Py-CH2), 4.20−4.16 (d, J = 15.0 Hz, 1H, Py-CH2), 4.14−4.10 (t, J
= 6.6 Hz, 2H, COOCH2), 3.76−3.71 (q, J = 7.0 Hz, 2H, CH2OH),
3.67−3.64 (m, 4H), 3.32−3.23 (m, 1H), 2.99 (s, 3H, NCH3), 2.97−
2.87 (m, 1H), 2.86−2.77 (m, 2H, COCH2), 2.58−2.55 (t, J = 6.8 Hz,
2H, NCH2), 2.05 (s, 1H, OH), 1.68−1.65 (m, 2H), 1.60−1.57 (m,
2H), 1.42−1.40 (m, 4H), 1.21−1.18 (t, J = 7.1 Hz, 3H, NCH2CH3);
IR (KBr, cm−1) ν 2933, 2877, 1735, 1545, 1246. Anal. Calcd for
C22H34ClN5O5: C%, 54.60; H%, 7.08; N%, 14.47. Found: C%, 54.65;
H%, 7.09; N% 14.43.
2′-Hydroxyethyl-4-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] butanate
(7a): yield 69%; yellow oil; 1H NMR (CDCl3, 400 MHz) δ 8.32−8.31
(d, J = 2.4 Hz, 1H, Py-H), 7.72−7.69 (dd, J = 8.2, 2.5 Hz, 1H, Py-H),
7.34−7.32 (d, J = 8.2 Hz, 1H, Py-H), 4.53−4.49 (d, J = 14.9 Hz, 1H,
Py-CH2), 4.36−4.34 (t, J = 6.2 Hz, 2H, COOCH2), 4.21−4.17 (d, J =
15.0 Hz, 1H, Py-CH2), 3.72−3.69 (t, J = 6.8 Hz, 2H, CH2OH), 3.64−
3.55 (m, 4H), 3.33−3.16 (m, 1H), 3.00 (s, 3H, NCH3), 2.98−2.89 (m,
1H), 2.60−2.52 (m, 2H, COCH2CH2), 2.50−2.46 (t, J = 7.2 Hz, 2H,
NCH2), 2.05 (s, 1H, OH), 1.89 (m, 2H), 1.22−1.18 (t, J = 7.1 Hz, 3H,
NCH2CH3); IR (KBr, cm−1) ν 2937, 2875, 1735, 1545, 1246. Anal.
Calcd for C19H28ClN5O5: C%, 51.64; H%, 6.39; N%, 15.85. Found: C
%, 51.63; H%, 6.38; N%, 15.87.
3′-Hydroxypropyl-4-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] butanate
(7b): yield 73%; yellow oil; 1H NMR (CDCl3, 400 MHz) δ 8.30 (d, J =
2.2 Hz, 1H, Py-H), 7.71−7.68 (dd, J = 8.2, 2.5 Hz, 1H, Py-H), 7.33−
7.31 (d, J = 8.2 Hz, 1H, Py-H), 4.50−4.47 (d, J = 15.0 Hz, 1H, Py-
CH2), 4.23−4.20 (dd, J = 7.4, 4.2 Hz, 2H, COOCH2), 4.17−4.16 (d, J
= 5.3 Hz, 1H, Py-CH2), 3.71−3.68 (t, J = 6.1 Hz, 2H, CH2OH), 3.67−
3.53 (m, 4H), 3.29−3.20 (m, 1H), 3.00 (s, 3H, NCH3), 2.97−2.90 (dt,
J = 14.1, 7.1 Hz, 1H), 2.56−2.44 (m, 2H, COCH2), 2.42−2.38 (t, J =
7.1 Hz, 2H, NCH2), 2.03 (s, 1H, OH), 1.90−1.87 (dd, J = 7.4, 4.9 Hz,
2H, CH2CH2OH), 1.85−1.80 (dd, J = 14.4, 7.1 Hz, 2H), 1.20−1.17 (t,
J = 7.1 Hz, 3H, NCH2CH3); IR (KBr, cm−1) ν 2937, 2875, 1735,
1545, 1246. Anal. Calcd for C20H30ClN5O5: C%, 52.69; H%, 6.63; N%,
15.36. Found: C%, 52.65; H%, 6.66; N%, 15.39.
5′-Hydroxypentyl-4-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] butanate
(7d): yield 67%; yellow oil; 1H NMR (CDCl3, 400 MHz) δ 8.32 (d, J =
2.2 Hz, 1H, Py-H), 7.72−7.69 (dd, J = 8.2, 2.5 Hz, 1H, Py-H), 7.35−
7.33 (d, J = 8.3 Hz, 1H, Py-H), 4.53−4.49 (d, J = 15.0 Hz, 1H, Py-
CH2), 4.21−4.17 (d, J = 15.0 Hz, 1H, Py-CH2), 4.11−4.08 (t, J = 6.6
Hz, 2H, COOCH2), 3.69−3.64 (t, J = 6.4 Hz, 2H, CH2OH), 3.61−
3.56 (m, 4H), 3.32−3.23 (m, 1H), 3.00 (s, 3H, NCH3), 2.99−2.89 (m,
1H), 2.57−2.46 (m, 2H, COCH2), 2.43−2.40 (t, J = 7.2 Hz, 2H,
NCH2), 2.05 (s, 1H, OH), 1.91−1.84 (m, 2H), 1.70−1.65 (dd, J =
14.8, 6.8 Hz, 2H), 1.63−1.57 (m, 2H), 1.50−1.42 (m, 2H), 1.22−1.18
(t, J = 7.2 Hz, 3H, NCH2CH3); IR (KBr, cm−1) ν 2933, 2872, 1735,
1541, 1247. Anal. Calcd for C22H34ClN5O5: C%, 54.60; H%, 7.08; N%,
14.47. Found: C%, 54.65; H%, 7.09; N%, 14.43.
6′-Hydroxyhexyl-4-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl] butanate
1
(7e): yield 63%; yellow oil; H NMR (CDCl3, 400 MHz) δ 8.32 (s,
1H, Py-H), 7.71−7.69 (dd, J = 8.0, 2.1 Hz, 1H, Py-H), 7.35−7.33 (d, J
= 8.3 Hz, 1H, Py-H), 4.54−4.49 (d, J = 15.0 Hz, 1H, Py-CH2), 4.21−
4.17 (d, J = 15.0 Hz, 1H, Py-CH2), 4.13−4.10 (t, J = 6.8 Hz, 2H,
COOCH2), 3.70−3.63 (t, J = 6.8 Hz, 2H, CH2OH), 3.60−3.54 (m,
4H), 3.34−3.23 (m, 1H), 3.05 (s, 3H, NCH3), 2.98−2.88 (m, 1H),
2.57−2.49 (m, 2H, COCH2), 2.20−2.12 (m, 2H, NCH2), 2.05 (s, 1H,
OH), 1.90−1.84 (m, 2H), 1.69−1.64 (m, 2H), 1.61−1.58 (m, 2H),
1.44−1.39 (m, 4H), 1.22−1.18 (t, J = 7.2 Hz, 3H, NCH2CH3); IR
(KBr, cm−1) ν 2939, 2872, 1737, 1543, 1247. Anal. Calcd for
C23H36ClN5O5: C%, 55.47; H%, 7.29; N%, 14.06. Found: C%, 55.45;
H%, 7.25; N%, 14.03.
X-ray Crystallography. The yellow crystal of the title compound 4g
(grown from a mixed solution of petroleum ether/ethyl acetate) was
mounted on a glass fiber in a random orientation, with approximate
dimensions of 0.20 mm × 0.13 mm × 0.10 mm. The data were
collected by a Bruker Smart Apex CCD diffractometer with a graphite-
́
monochromated Mo Kα radiation (k = 0.71073 Å), using a φ−ω scan
mode in the range of 2.47° ≤ θ ≤ 26.49° at 298(2) K. Empirical
absorption correction was applied, and a total of 13121 reflections
including 4511 unique ones (Rint = 0.1048) were measured. The
structure was solved by direct methods and refined by full-matrix least-
squares techniques on F2 using the SHELXTL program package.21 All
of the non-hydrogen atoms were refined anisotropically, and hydrogen
atoms were located at their idealized positions. The final R = 0.0746
4′-Hydroxybutyl-4-[4-[N-(6-chloro-3-pyridyl)methyl-N-ethyl]-
amino-3-methyl-5-nitro-1,2,3,6-tetrahydropyrimidin-1-yl]
1
butanate(7c): yield 70%; yellow oil; H NMR (CDCl3, 400 MHz) δ
2
and wR = 0.1586 {w = 1/[σ2(Fo ) + (0.0749P)2 + 0.0000P], where P =
8.31 (d, J = 2.3 Hz, 1H, Py-H), 7.72−7.69 (dd, J = 8.2, 2.5 Hz, 1H, Py-
H), 7.35−7.33 (d, J = 8.2 Hz, 1H, Py-H), 4.53−4.49 (d, J = 15.0 Hz,
1H, Py-CH2), 4.21−4.17 (d, J = 15.0 Hz, 2H, COOCH2), 4.15−4.13
(dd, J = 6.8, 4.7 Hz, 1H, Py-CH2), 3.71−3.67 (dd, J = 10.4, 6.4 Hz, 2H,
CH2OH), 3.66−3.55 (m, 4H), 3.32−3.23 (m, 1H), 3.00 (s, 3H,
NCH3), 2.98−2.91 (m, 1H), 2.56 − 2.46 (m, 2H, COCH2), 2.43−2.40
2
(Fo + 2Fc2)/3, S = 1.097, (Δ/σ)max = 0.004, (Δρ)max = 0.385, and
3
́
(Δρ)min = −0.227 e/Å }. The structural plots were drawn with the
SHELXTL-97 software package. Other details of the structure have
been deposited with the Cambridge Crystallographic Data Centre,
CCDC740000 (see also the Supporting Information).
9557
dx.doi.org/10.1021/jf3024479 | J. Agric. Food Chem. 2012, 60, 9553−9561

Journal of Agricultural and Food Chemistry
Article
Table 2. Insecticidal Activities of Nitenpyram Analogues 5a−7e against Myzus persicae and Nilaparvata lugens
mortality (%) at different concentrations
Myzus persicae
Nilaparvata lugens
compd
5a
n
n1
100 mg/L
20 mg/L
4 mg/L
100 mg/L
20 mg/L
4 mg/L
a
2
3
4
5
6
2
3
4
5
6
2
3
4
5
6
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
100
100
100
100
95
58
50
NT
100
100
95
50
45
NT
NT
NT
NT
NT
5b
NT
NT
NT
NT
100
55
5c
33
30
5d
25
90
23
5e
10
90
15
b
6a
100
100
100
98
100
100
83
100
100
100
100
90
100
98
100
6b
70
6c
NT
NT
NT
10
80
NT
NT
NT
NT
NT
NT
NT
NT
6d
50
40
6e
95
33
25
7a
100
100
95
100
92
100
100
100
98
90
7b
NT
NT
NT
NT
80
7c
70
78
7d
95
25
15
7e
88
10
90
10
c
3a
100
100
100
100
100
100
75
d
3b
70
e
e
nitenpyram
100
100
100
100
a
b
c
d
e
NT, not tested. LC50 = 0.154 mg/L. LC50 = 0.194 mg/L. LC50 = 0.162 mg/L. LC50 = 0.129 mg/L.
Biology Assay. The bioassay was measured according to the
delocalization of the electrons, which extend to the strong
electron-withdrawing group NO2, a coplanar olefin−amine π-
electron network is formed. In addition, the bond lengths of
standard test22 with a slight modification, and all analogues were tested
against N. lugens to evaluate their insecticidal activities. The
compounds were dissolved in dimethylformamide (DMF) and serially
diluted with water containing Triton X-80 (0.1 mg/L) to get the
required test concentrations. All experiments were carried out in three
replicates for the purpose of statistical requirements. The insects were
reared at 25( )1 °C, 25( 2)% relative humidity, and 12 h light
photoperiod. Groups of 12 were transferred to glass Petri dishes and
sprayed with the aforementioned solutions using a Potter sprayer.
After they were air-dried, they were kept in a special room for normal
cultivation. Assessments were made after 72 h by the number of killed
and size of live insects relative to that in the negative control, and
evaluations were based on a percentage scale of 0−100, in which 100
was total kill and 0 was no activity. The mortality rates were subjected
to probit analysis.23 All results are shown in Tables 1 and 2. The
reference compound was nitenpyram, and water containing DMF (0.5
mg/L) and Triton X-80 (0.1 mg/L) was used as a negative control.
́
C(9)C(10) and C(10)N(6) are 1.42 and 1.37 Å, which
́
are longer than the pure CC(1.34 Å) and shorter than the
́
typical CN in CNO2 (1.49 Å). Besides, as compared with
the trans configuration of nitro in the crystal structure of
nitenpyram, the nitro group in 4g is obviously in the cis
configuration.
SARs. The insecticidal activities of the nitenpyam analogues
4−7 against N. lugens and M. persicae are listed in Tables 1 and
2. Most of them showed good insecticidal activities at 100 mg/
L, and analogues 4d and 6a afforded the best in vitro inhibitory
activities and had ≥95% mortality at 4 mg/L. The LC50 values
of analogues 4d and 6a were 0.170 and 0.154 mg/L,
respectively.
As for analogues 4a−4g, based on the nitenpyram analogue
2, they were derived from the chiral amino acid hydroxyethyl (n
= 2) esters with different side chains R. As indicated in Table 1,
all of the analogues 4a−4g (n = 2) exhibited good activities at
high dose (100 mg/L), but when the dose was reduced to 20
and 4 mg/L, analogue 4d(R = iBu, n = 2, LC50 = 0.170 mg/L)
showed the best average insecticidal potency. Analogues 4a−4g
(n = 2) with different side chains R showed insecticidal
activities increasing in the order 4g (R = 4-OH-benzyl) < 4e (R
= benzyl) < 4f (R = 4-Cl-ph) < 4a(R = Me) < 4b (R = iPr) <
4c (R = sBu) < 4d (R = iBu). In addition, analogue 4d(R = iBu)
exhibited about 10-fold more potency than analogue 4g (R = 4-
OH-benzyl), and also analogue 4a (R = Me) exhibited about 3-
fold more potency than analogue 4g (R = 4-OH-benzyl).
Therefore, these results clearly suggest that the insecticidal
activities of analogues 4a−4g were dual-controlled by the
flexibility of side chain R and the size of the molecule.
Analogues 5a−7e with a flexible hydroxyalkyl ester arm (n1 =
1, 2, 3), based on the nitenpyram analogue 3, were derived
from three different length straight chain amino acid ω-
hydroxyalkyl esters. As shown in Table 2, analogues 5a−7e
RESULTS AND DISCUSSION
■
Synthesis. The reaction of nitenpyam 1, amino acid ω-
hydroxyalkyl ester hydrochlorides, formaldehyde, and triethyl-
amine could proceed readily in ethanol at 65 °C by Mannich
reaction under microwave irradiation (Scheme 2), which was a
highly efficient way that gave good yields (59−76%) and had
easy post-treatments. The structures of the target compounds
were well characterized by 1H NMR, IR, and elemental analysis.
Crystal Structure Analysis. The structure of compound 4g
was confirmed on the basis of spectral data and finally by X-ray
crystallographic data analysis. The crystal structure showed that
the tetrahydropyrimidine cycle of the molecule 4g adopts a sofa
conformation (Figure 3). According to the single-crystal data,
we found that five atoms of C(9)−N(4)−C(12)−C(11) and
C(10) define a plane, with the biggest deviation from the plane
́
being 0.9 Å for the N(3) atom. Also, because of the lone-pair
electrons transferring on the N(2) and N(4) to C(9)C(10),
the C(9)N(2) and C(9)N(4) bond lengths are 1.35 and
́
1.36 Å, remarkably shorter than the typical CN single bond
14
́
́
(1.47 Å) but close to CN (imine) (1.33 Å). Due to the
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Figure 4. Binding site interactions of analogues 4d, 6a, and 7c with the extracellular domain of nAChR (Protein Data Bank code 2zju). (a)
Compound 6a is bound into the subunit interfacial binding pocket between two faces of adjacent subunits. For clarity, only two of five subunits are
extracted and shown from the pentameric nAChRs structure, and the corresponding interfacial binding pocket of interest is displayed. (b) Zoomed-
in view of the interactions between compound 4d and amino acids from the active site of the receptor. (c) Zoomed-in view of the interactions
between compound 6a and amino acids from the active site of the receptor. (d) The predicted binding mode of compound 7c with relatively low
activity. Key H-bonds are indicated by green dotted lines.
exhibited good activities at high dose (100 mg/L); however, the
insecticidal activities showed significant differences when the
doses were reduced to 20 and 4 mg/L. Clearly, analogues 6a−
6e (n1 = 2) displayed better insecticidal potencies than
analogues 5a−5e (n1 = 1) and analogues 7a−7e (n1 = 3).
Furthermore, when various ω-hydroxyalkyl esters were
introduced into the nitenpyram analogues, the flexibility of
the molecule increased; the size also increased at the same time.
Typical for analogues 6, when the dose was reduced to 20 and 4
mg/L, analogues 6a (n = 2, n1 = 2, LC50 = 0.154 mg/L) showed
higher insecticidal potency than 6b−6e (n = 3, 4, 5, 6; n1 = 2),
and their insecticidal activities increased in the order 6e (n = 6)
< 6d (n = 5) < 6c (n = 4) < 6b (n = 3) < 6a (n = 2). Therefore,
the analogues bearing the smaller ester groups had better
insecticidal potency in the respective series. These differences
clearly suggest that the insecticidal activities of analogues 5a−
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7e were dual-controlled by the flexibility of the ester arm and
the size of the molecule.
analogues. On these bases, further target inhibitory tests and
advanced insecticide design are underway.
Considering the discussion above, we found the insecticidal
potencies of our designed nitenpyram analogues in this paper
were also dual-controlled by the flexibility and the size of the
molecule. Only when a molecule can keep a good balance
between flexibility and size will it have the best insecticidal
activity, such as analogues 4d and 6a. Also, as compared with
our previous analogues 2 and 3, analogues 4d and 6a had a
broader pesticidal spectrum, and the insecticidal activities were
better than those of 2a (LC50 = 0.216 mg/L), 3a (LC50 = 0.194
mg/L), and 3b (LC50 = 0.162 mg/L) when the doses were
reduced to 4 mg/L. The LC50 values of analogues 4d and 6a are
0.170 and 0.154 mg/L, which is close to that of nitenpyram.
These good results implied that the nitenpyram analogues
designed in this paper are both practical and feasible.
Molecular Docking Study. To further explore the
structural features for better activities, models of these new
compound−receptor complexes were investigated by docking
studies with CDOCK.24 Because the amino acids formed at the
active sites are both structurally and functionally consistent in
the diverse nAChRs and AchBPs, the published crystal
structure of a Lymnaea stagnalis−AChBP (Ls-AChBP)
cocrystallized with imidacloprid (PDB ID: 2zju)25 was used
as the template of the receptor. The docking study was
performed by using the program CDOCK (Discovery Studio
3.1); the only modification was the number of Top Hits, which
was set to 30 (previously 10) for greater accuracy.
As a result, the scoring function of the docking program
ranked the compounds in the same general order observed
experimentally (data not shown), and all active analogues
exhibited hydrogen-bonding interactions with the nAChR
target. As illustrated in Figure 4, analogues 4d, 6a, and 7c
were chosen to understand the ligand protein interactions in
detail, and analogues 4d and 6a had stronger hydrogen-bonding
action in binding with the nAChR. Analogue 6a exhibits two
important hydrogen bonds via its nitro O(2) with NH of
Gln155, respectively, and the Cl(1) of its chloropyridine
interacts with NH of Arg104. Besides, its binding conformation
exhibited three important hydrogen bonds: O(4) of the
carbonyl and O(6) of the hydroxyl with NH of Gln155 and
H of the hydroxyl with O of Gln155. These observations also
explain why analogue 6a attained the highest score.
Furthermore, most of the other active analogues shared a
quite similar binding mode with analogue 6a, and many of
them exhibited more than two hydrogen bonds with different
amino acids of the active pocket between the nAChR subunits.
However, not all nitro O(2), carbonyl O(4), hydroxyl O(6),
and hydroxyl H of analogues 4−7 can form hydrogen bonds
within the same hydrogen bond distance, such as the binding
mode of analogue 7c (Figure 4d), nitro O(2), hydroxyl O(6),
and the hydroxyl H cannot interact with amino acid residues
from the Ls−AChBP.
In conclusion, to further enhance the strength of the
hydrogen-bonding action of the neonicotinoid compounds
binding with the nAChR, a series of novel nitenpyram
analogues 4−7 was synthesized by introducing different
amino acid ω-hydroxyalkyl esters into nitenpyram. The target
compounds were characterized by 1H NMR, IR, and elemental
analysis, and the cis configuration was confirmed by X-ray
diffraction. All of the analogues exhibited good insecticidal
activities at 100 mg/L against N. lugens and M. persicae, and
analogues 4d and 6a afforded the best in vitro activity and had
≥95% mortality at 4 mg/L. The LC50 values of analogues 4d
and 6a were 0.170 and 0.154 mg/L, respectively. SARs
suggested that the insecticidal activities of our designed
nitenpyram analogues were also dual-controlled by the
flexibility and size of the molecule. In addition, molecular
docking studies were also carried out to model the ligand−
nAChR complexes. The docking results revealed that analogues
4−7 with various ω-hydroxyalkyl esters on the tetrahydropyr-
imidine ring showed different binding affinities to the insect
nAChR, which explained the SARs observed in vitro. Moreover,
carbonyl O(4) and hydroxyl H of analogue 4d and carbonyl
O(4), hydroxyl O(6), and hydroxyl H of analogue 6a can
exhibit hydrogen bonding with amino acid residues of the
receptor. These differences suggested that analogues 4d and 6a
exhibited stronger hydrogen bonding than the others, which
had a crucial effect on their high insecticidal activities.
Therefore, the docking study revealed that the strength of the
hydrogen-bonding action was the influential factor for the
bioactivities of our designed nitenpyram analogues, and further
research on many more test objects of nitenpyram are
underway.
ASSOCIATED CONTENT
■
S
* Supporting Information
Crystal structure data of compound 4g. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Phone/fax: +86021-64321926. E-mail: willin112@163.com.
Funding
The bioassay was supported by bioassay department, Branch of
National Pesticide R&D South Center. This work was
supported by the National Natural Science Foundation of
China (21102092, 21042010, and 30870560), the Key
Scientific “Twelfth Five-Year” National Technology Support
Program (2011BAE06B01-17), the Key Project of of Science and
Technology Commission of Shanghai (105405503400), the
Innovation Project of Shanghai Education Commission
(12YZ078), the Leading Academic Discipline Project of
Shanghai Normal University (DZL808), Shanghai Key
Laboratory of Rare Earth Functional Materials, and Shanghai
Normal University (07dz22303). We are also grateful for the
support from Branch of National Pesticide R&D South Center.
Moreover, we found that analogues 4d and 6a offered the
highest experimental activities when nitro O(2), carbonyl O(4),
hydroxyl O(6), and the hydroxyl H can exhibit hydrogen bonds
with different amino acid residues (Figure 4b,c). These
observations also explain the structure−activity relationships
observed in vitro. The newly introduced moiety of our designed
analogues presumably played an important role in ligand
recognition and binding interactions, which may further explain
the strength of the hydrogen-bonding action as the influential
factor for the bioactivities of our designed nitenpyram
Notes
The authors declare no competing financial interest.
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