Synthesis and biological activity evaluation of novel β-substituted nitromethylene neonicotinoid analogues

Article abstract of DOI:10.3390/molecules170910014

The structure-based design and synthesis of a series of novel neonicotinoid analogues are described. The novel neonicotinoid analogues were designed based upon the reaction of enamine derivatives with electron-withdrawing β-substituents with electrophilic thiocyanogen reagents. These compounds were characterized by spectroscopic methods. Bioassays indicated that some of the synthesized compounds exhibited excellent bioactivity against cowpea aphids (Aphis craccivora). The LC₅₀ values of compounds 7, 9, 12, 13, 15, 17, 19, 20 and commercial imidacloprid were 0.01567, 0.00974, 0.02494, 0.01893, 0.02677, 0.01778, 0.0220, 0.02447 and 0.03502 mmol L^-1, respectively, which suggested that they could be used as leads for future development of new insecticides.

Full text of DOI:10.3390/molecules170910014

Molecules 2012, 17, 10014-10025; doi:10.3390/molecules170910014
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Biological Activity Evaluation of Novel
β-Substituted Nitromethylene Neonicotinoid Analogues
Baozhu Wang, Jiagao Cheng, Zhiping Xu, Xiaoyong Xu, Xusheng Shao and Zhong Li *
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, China
* Author to whom correspondence should be addressed; E-Mail: lizhong@ecust.edu.cn;
Tel.: +86-021-6425-2603; Fax: +86-021-6425-3540.
Received: 25 June 2012; in revised form: 13 August 2012 / Accepted: 14 August 2012 /
Published: 24 August 2012
Abstract: The structure-based design and synthesis of a series of novel neonicotinoid
analogues are described. The novel neonicotinoid analogues were designed based upon the
reaction of enamine derivatives with electron-withdrawing β-substituents with electrophilic
thiocyanogen reagents. These compounds were characterized by spectroscopic methods.
Bioassays indicated that some of the synthesized compounds exhibited excellent
bioactivity against cowpea aphids (Aphis craccivora). The LC50 values of compounds 7, 9,
12, 13, 15, 17, 19, 20 and commercial imidacloprid were 0.01567, 0.00974, 0.02494,
0.01893, 0.02677, 0.01778, 0.0220, 0.02447 and 0.03502 mmol L−1, respectively, which
suggested that they could be used as leads for future development of new insecticides.
Keywords: neonicotinoid analogues; new design strategy; thiocyanogen; insecticidal
activities
1. Introduction
In recent years, neonicotinoid insecticides have been the fastest growing class of insecticides in
modern crop protection, with widespread use against a broad spectrum of sucking and certain chewing
pests [1–5]. Significant progress had been obtained on the chemistry of the insecticidal nicotinic
agonists and the chemical biology of the nicotinic acetylcholine receptors (nAChRs), that is,
chemorational approaches including physicochemical considerations, metabolism, resistance

Molecules 2012, 17
10015
mechanisms, and chemical and structural biology aspects potentially expediting receptor structure-guided
insecticide design [6–12].
Our past endeavors in this field have focused on systematic pharmacophore modifications of
nitromethylene neonicotinoids that appeared to capture the “bioactive” conformation (Figure 1).
Several types of nitromethylene neonicotinoids with the cis-configuration were presented; that is,
neonicotinoids 1 with a tetrahydropyridine fixed cis-configurations; neonicotinoids 2 with bulky group
fixed cis-configurations, neonicotinoids 3 with cis-configuration constructed by aza-Diels-Alder
reactions, and divalent and oxa-bridged neonicotinoids 4 constructed from dialdehydes (Figure 1).
Bioassays indicated that the synthesized cis compounds 1–4 exhibited excellent bioactivity against
cowpea aphids [13–16]. According to our knowledge, the nitro groups in all commercialized
neonicotinoids have a trans configuration, on which three proposals for mode of action are based [17].
The high bioactivity of compounds 1–4 implies that neonicotinoids in the cis configuration might
bind to the receptor in a different way [13]. These efforts accordingly encourage the discovery of
“superneonicotinoids” effective for imidacloprid-resistant pests and lepidoptera species.
Figure 1. Structures of imidacloprid neonicotinoids and structurally related analogues.
R2
NO2
NH
O2N
N
NO2
NH
N
N
N
N
OR1
Cl
N
Cl
N
Cl
N
nitromethylene neonicotinoid
imidacloprid
O2N
1
R
O2N
O2N
N
O
O
CN
N
N
N
N
N
NH2
Cl
Cl
N
N
Cl
N
4
3
2
The structure derivative method through the organic reaction is another important tool for
systematic pharmacophore modifications [18]. It had been theorized that the nitroenamine entities in
these high active compounds play important roles for specific binding to the desired insect nAChRs
site [19–22]. Encouraged by these reports, the modifications of nitroenamine entities to fix its
configuration through organic reactions has attracted our attention. The chemistry of enamines,
including push–pull enamines bearing an additional electron-acceptor group at the β-position, has been
extensively developed, mainly as a result of electrophilic reactions that proceed predominantly at the
β-position [23–25]. Electrophilic modification, followed by a set of transformations, have made
enamines an integral part of synthetic organic chemistry methodology [26]. Additionally, electron-acceptor

Molecules 2012, 17
10016
groups can participate in chemical transformations. According to this knowledge, a series of prototype
compounds with extended N-substituted (thiocyanogen) substituents were designed in this paper
(Figure 2). The choice of the thiocyanogen was predominantly governed by its traits as electrophilic
reagent, and mainly by its ability to easily cyclize with the NH group in the imidazoline ring to fix the
electron-withdrawing group in the cis position (Figure 2) [27].
Figure 2. Structures of imidacloprid neonicotinoids and its structurally related analogues.
Nucleophilic Reagents
Electrophilic Reagents
highly active
compounds
2, 3, 4
pharmacophore, reaction site
heteroaromatic moiety
O2N
N
H
New design strategy
NH
N
Cl
X
X
SCN
X
S
(SCN)2
Het
N
NH
Het
N
NH
Het
N
N
R1 R2
NH
R1 R2
R1
R2
2. Results and Discussion
2.1. Synthetic Chemistry
The synthetic route of the target compounds is summarized in Scheme 1. The chemical structures of
the novel neonicotinoid analogues under study are depicted in Figure 3. The preparation of the
designed compounds began with the common intermediates 5a–h and 6a–c which were synthesized
according to the method of Kagabu et al. [19]. In the reaction of 5a–h with thiocyanogen at 0 °C for
1.5 h, the corresponding β-thiocyanated products 7–14 were produced in 63%–82% yields. In this
procedure, 5a appears to produce a mixture of 7 and cyclization product 15. Similarly, 5c and 5f also
gave mixtures of aminothiazole and the relevant cyclization product. Compounds 7, 9 and 12 were
synthesized by reducing the reaction time and reaction temperature without forming cyclization
products. Then, these compounds 7–9 and 11–13 were converted quantitatively into the corresponding
cyclization products, 15–20, by stirring at room temperature in dichloromethane solution containing
0.1% piperidine as catalyst. Unexpectedly, 10 and 14 could not be converted into the corresponding
cyclization products. The substrates 6a–c yielded only the corresponding cyclization products 21–23
respectively under the same conditions. Whereas configuration of compounds 7–14 and 21–23 cannot
1
13
be determined easily by standard H- and C-NMR techniques, the compounds 15–20 obtained from
the reaction system are considered to be produced with retention of the configuration of the preformed
enamines with electron-withdrawing β-substituents, followed by catalyzed cyclization. The structures
of the title compounds were well characterized by 1H-NMR, 13C-NMR and HRMS.

Molecules 2012, 17
10017
Scheme 1. Synthetic route for the title compounds 7–23.
X
X
N
SCN
NH
X
S
thiocyanogen
piperidine
R2
N
NH
NH
N
R2
R2
N
r.t. 2h,CH2Cl2
0deg, 1.5h, CH2Cl2
R1
R1
R1
5a-h
15-20
5g
7-14
5h
5a
5f
5c
5e
5b
5d
NO2
NO2
NO2
NO2
NO2
NO2
x
CN
CN
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2-CH2-CH2-
R1 -CH2CH2-
R2
benzo
N
S
Cl
N
S
Cl
Cl
N
Cl
N
F3C
N
Cl
N
Cl
N
NO2
O2N
S
thiocyanogen
r.t. 1.5h,CH2Cl2
N
NH
NH
N
N
R3 R4
R3
R4
Cl
N
Cl
N
6a-c
21-23
6a R3 = CH3CH2- R4 = CH3-
6b R3 = H
6c R3 = H
R4 = CH3-
R4= CH3CH2-
Figure 3. Chemical structures of novel neonicotinoid analogues under study.
X
N
SCN
NH
O2N
N
SCN
NH
X
N
SCN
NH
N
S
Cl
Cl
N
9 X = NO2
10 X = CN
11
7 X = NO2
8 X = CN

Molecules 2012, 17
10018
Figure 3. Cont.
O2N
N
SCN
NH
O2N
N
SCN
NH
O2N
N
SCN
NH
Cl
N
F3C
N
Cl
N
13
12
14
X
O2N
N
O2N
S
S
S
NH
NH
N
N
N
NH
N
N
N
S
Cl
N
Cl
15 X = NO2
16 X = CN
17
18
O2N
O2N
N
S
S
O2N
S
NH
N
N
NH
N
NH
R1
R2
N
N
Cl
N
F3C
N
Cl
N
19
21 R1 = CH3CH2- R2 = CH3-
20
22 R1 = H
23 R1 = H
R2 = CH3-
R2 = CH3CH2-
2.2. Biological Activities
The insecticidal activities of the designed compounds against cowpea aphids are shown in
Table 1. Most of the title compounds showed excellent insecticidal activities against cowpea aphids.
For example, the LC50 values of compounds 7, 9, 12, 13, 15, 17, 19, and 20 were 0.01567, 0.00974,
0.02494, 0.01893, 0.02677, 0.01778, 0.0220 and 0.02447 mmol L−1, respectively, whereas that of
imidacloprid was only 0.03502 mmol L−1 [16]. Activities varied significantly depending upon the
patterns of substituents on the enamine and imidazole ring. It was observed that compounds with NO2
substituents (7, 15, 9 and 17) demonstrated better activities than that with CN substituents (8, 10 and
16). Generally, the imidazolidine substituents appear to be the important factor for insecticidal
activities. A benzene substituent (compound 14) resulted in complete inactivity. Moreover, the cyclic
addition of SCN substituents with the imidazolidine ring is unfavourable for high activities from the
data analysis present of compounds 7, 9, 15 and 17.

Molecules 2012, 17
10019
Table 1. Insecticidal activities of compounds 7–23 against cowpea aphids (Aphis craccivora).
Compounds
Mortality (%, 500mg L−1)
LC50 (mmol L−1)
7
100
34.6
100
0.01567
nt a
8
9
0.00974
nt
10
11
12
13
14
15
16
17
18
19
20
21
22
23
0
23.98
100
nt
0.02494
0.01893
nt
100
87.82
100
0.02677
nt
32.4
100
0.01778
nt
16.19
100
0.02200
0.02447
nt
100
57.6
100
0.11839
nt
50.79
a Not tested.
3. Experimental
3.1. General
Melting points (mp) were recorded on a Büchi B540 apparatus (Büchi Labortechnik AG, Flawil,
Switzerland) and are uncorrected. 1H-NMR and 13C-NMR spectra were recorded on a Bruker AM-400
(400 MHz) spectrometer with CDCl3 or DMSO-d6 as the solvent and TMS as the internal standard.
Chemical shifts are reported in δ (parts per million) values. High-resolution mass spectra were
recorded under electron impact (70 eV) condition using a MicroMass GCT CA 055 instrument.
Analytical thin-layer chromatography (TLC) was carried out on precoated plates (silica gel 60 F254),
and spots were visualized with ultraviolet (UV) light. The compounds 5a–h and 6a–c were synthesized
according to the method of Kagabu et al. [19]. Unless otherwise noted, reagents and solvents were
used as received from commercial suppliers. Yields were not optimized. All reactions were carried out
under a protective atmosphere of drying nitrogen or utilizing a calcium chloride drying tube.
3.1.1. General Synthetic Procedure for 7–14
To a solution of 5a–g (10 mmol) in dichloromethane (100 mL), a thiocyanogen (10 mmol) solution
in dichloromethane (50 mL), which was previously prepared from lead thiocyanate and bromine
at −15 °C, was added dropwise with stirring at −15 °C and then the mixture was stirred for 1.5 h
at 0 °C. The reaction mixture was washed with cold water (3 × 50 mL) and brine (50 mL), and dried
with sodium sulfate. The solvent was removed to give a crude solid, which was recrystallized from a
mixture of dichloromethane/ether (2:1, v/v) to give 7–14.

Molecules 2012, 17
10020
2-Chloro-5-((2-(nitro(thiocyanato)methylene)imidazolidin-1-yl)methyl)pyridine (7). Yield: 92%, m.p.:
1
130.6–132.1 °C; H-NMR (DMSO-d6): δ 3.76 (br.s, 4H), 4.77 (s, 2H), 7.55 (d, J = 8.4 Hz, 1H), 7.86
(dd, J1 = 2.6 Hz, J2 = 8.4 Hz, 1H), 8.42 (d, J = 2.0 Hz, 1H), 9.43 (s, 1H) ppm; 13C-NMR (DMSO-d6):
δ 162.6, 149.9, 149.1, 139.1, 131.8, 124.7, 112.3, 87.5, 50.7, 50.2, 42.7; HRMS (ES+) calcd for
C11H1035ClN5O2S (M+H)+: 312.0244. Found: 312.0330. Calcd for C11H1037ClN5O2S (M+H)+: 314.0214
Found: 314.0284.
2-(1-((6-Chloropyridin-3-yl)methyl)imidazolidin-2-ylidene)-2-thiocyanatoacetonitrile (8). Yield: 63%,
1
m.p.: 118.2–119.7 °C; H-NMR (DMSO-d6): δ 3.51–3.56 (m, 2H), 3.66–3.70 (m, 2H), 4.79 (s, 2H),
13
7.54 (d, J = 8.4 Hz, 1H), 7.78–7.80 (m, 1H), 8.11 (s, 1H), 8.36 (d, J = 2.4 Hz, 1H) ppm; C-NMR
(DMSO-d6): δ 164.9, 150.0, 149.2, 139.2, 132.1, 124.8, 122.1, 113.8, 51.6, 47.4, 41.5, 31.2; HRMS
(EI+) calcd for C12H1035ClN5S (M+): 291.0345. Found: 291.0344. Calcd for C12H1037ClN5S (M+):
293.0316 Found: 293.0318.
1-((2-Chlorothiazol-5-yl)methyl)-2-(nitro(thiocyanato)methylene)imidazolidine (9). Yield: 75%, m.p.:
85.1–86.3 °C; 1H-NMR (DMSO-d6): δ 3.69–3.78 (m, 4H), 4.84 (s, 2H), 7.73 (s, 1H), 9.40 (s, 1H) ppm;
13C-NMR (DMSO-d6): δ 162.2, 151.6, 141.8, 135.9, 112.1, 87.3, 50.1, 46.3, 42.6; HRMS (ES+) calcd
35
37
for C9H8 ClN5O2S2 (M+H)+: 317.9808. Found: 317.9890. Calcd for C9H8 ClN5O2S2 (M+H)+:
319.9778 Found: 319.9860.
2-(1-((2-Chlorothiazol-5-yl)methyl)imidazolidin-2-ylidene)-2-thiocyanatoacetonitrile (10). Yield: 52%,
1
m.p.: 120.3–122.2 °C; H-NMR (DMSO-d6): δ 3.30–3.70 (m, 4H), 4.93 (s, 2H), 7.70 (s, 1H), 8.17
(s, 1H) ppm; 13C-NMR (DMSO-d6): δ 164.5, 151.3, 141.6, 135.8, 122.0, 113.5, 51.0, 43.0, 41.5, 31.8;
35
37
HRMS (ES−) calcd for C10H8 ClN5S (M−H)+: 295.9910. Found: 295.9829. Calcd for C10H8 ClN5S
(M−H)+: 297.9880 Found: 297.9803.
1-Benzyl-2-(nitro(thiocyanato)methylene)imidazolidine (11). Yield: 82%, m.p.: 102.3–104.2 °C;
13
1H-NMR (DMSO-d6): δ 3.72 (s, 4H), 4.75 (s, 2H), 7.32–7.42 (m, 5H), 9.40 (s, 1H) ppm; C-NMR
(DMSO-d6): δ 162.3, 136.1, 129.2, 128.1, 127.6, 112.3, 86.9, 52.7, 50.3, 42.6; HRMS (ES+) calcd for
C12H12N4O2S (M+H)+: 277.0681. Found: 277.0750.
1-((6-Chloropyridin-3-yl)methyl)-2-(nitro(thiocyanato)methylene)-hexahydropyrimidine (12). Yield:
1
70%, m.p.: 158.1–160.3 °C; H-NMR (DMSO-d6): δ 2.14 (t, J = 5.2, 2H), 3.38 (t, J = 5.6 Hz, 2H),
3.85 (t, J = 5.6 Hz, 2H), 4.06 (s, 2H), 7.57 (d, J = 8.0 Hz, 1H), 7.91 (dd, J1 = 8.4 Hz, J2 = 2.8 Hz, 1H),
8.45 (d, J = 2.4 Hz, 1H) ppm; 13C-NMR (DMSO-d6): δ 164.7, 158.9, 150.2, 146.2, 140.1, 131.0, 124.5,
106.5, 56.8, 47.2, 45.1, 19.1; HRMS (ES+) calcd for C12H1235ClN5O2S (M+H)+: 326.0400. Found:
326.0477. Calcd for C12H1237ClN5 O2S (M+H)+: 328.0371 Found: 328.0465.
5-((2-(Nitro(thiocyanato)methylene)imidazolidin-1-yl)methyl)-2-(trifluoromethyl)pyridine (13). Yield:
1
82%, m.p.: 140.1–142.3 °C; H-NMR (DMSO-d6): δ 3.76 (s, 4H), 3.38 (t, J = 5.6 Hz, 2H), 4.85
(s, 2H), 7.91 (d, J = 8.0 Hz, 1H), 8.04 (s, 1H), 8.75 (s, 1H), 9.45 (s, 1H) ppm; 13C-NMR (DMSO-d6):
δ 162.7, 149.3, 137.2, 136.6, 121.1, 112.3, 87.7, 50.9, 50.8, 42.8; HRMS (ES+) calcd for C12H10F3N5O2S
(M+H)+: 345.0507. Found: 345.0617.

Molecules 2012, 17
10021
(E-1-((6-Chloropyridin-3-yl)methyl)-2-(nitro(thiocyanato)methylene)-2,3-dihydro-1H-enzo[d]imid-azole
(14). Yield: 74%, m.p.: 125.6–127.2 °C; 1H-NMR (DMSO-d6): δ 4.79 (s, 2H), 7.39–7.7 (m, 6H), 8.35
13
(d, J = 2.4 Hz, 1H) ppm; C-NMR (DMSO-d6): δ 150.1, 148.7, 148.6, 138.5, 132.5, 131.3, 130.4,
35
126.0, 125.4, 124.8, 113.8, 112.2, 112.0, 86.0, 55.4, 47.2; HRMS (ES−) calcd for C10H8 ClN5S
37
(M−H)+: 358.0244. Found: 358.0130. Calcd for C10H8 ClN5S (M−H)+: 360.0214. Found: 297.0166.
3.1.2. General Synthetic Procedure for 15–20
The solution of 7–9 and 11–13 (10 mmol) in dichloromethane (50 mL) containing 0.1% piperidine
was stirred for 2 h at room temperature. After removal of the solvent, the residue was recrystallized
from dichloromethane to give 15–20 in quantitative yields.
1-((6-Chloropyridin-3-yl)methyl)-7-nitro-2,3-dihydroimidazo[1,2-c]thiazol-5(1H)-imine (15). Yield:
93%, m.p.: 136.4–138.5 °C; 1H-NMR (DMSO-d6): δ 3.85 (s, 2H), 4.08 (s, 2H), 5.27 (s, 2H), 7.58 (br.s,
13
1H), 7.91–7.92 (m, 1H), 8.47 (s, 1H), 8.91 (br.s, 1H) ppm; C-NMR (DMSO-d6): δ 150.6, 150.1,
149.7, 139.8, 132.0, 124.8, 99.7, 55.7, 49.4, 41.8; HRMS (ES+) calcd for C11H1035ClN5O2S (M+H)+:
312.0244. Found: 312.0321. Calcd for C11H1037ClN5O2S (M+H)+: 314.0279. Found: 314.0284.
1-((6-Chloropyridin-3-yl)methyl)-5-imino-1,2,3,5-tetrahydroimidazo[1,2-c]thiazole-7-carbonitrile (16).
Yield: 82%, m.p.: 201.5–202.3 °C; 1H-NMR (DMSO-d6): δ 3.87 (s, 4H), 4.61 (s, 2H), 7.41 (d, J = 8.0 Hz,
13
1H), 7.73–7.76 (m, 1H), 8.38 (d, J = 2.0 Hz, 1H) ppm; C-NMR (DMSO-d6): δ 155.2, 153.0, 152.0,
149.3, 138.9, 129.1, 125.0, 114.7, 53.2, 47.8, 47.2, 41.0; HRMS (ES+) calcd for C12H1035ClN5S
(M+H)+: 292.0345. Found: 292.0430. Calcd for C12H1037ClN5S (M+H)+: 294.0316. Found: 294.0410.
1-((2-Chlorothiazol-5-yl)methyl)-7-nitro-2,3-dihydroimidazo[1,2-c]thiazol-5(1H)-imine (17). Yield:
1
78%, m.p.: 150.3–151.4 °C; H-NMR (DMSO-d6): δ 3.81–4.16 (m, 4H), 5.34 (s, 2H), 7.77 (s, 1H),
13
8.96 (s, 1H) ppm; C-NMR (DMSO-d6): δ 152.3, 150.0, 142.0, 136.0, 99.9, 55.5, 45.2, 41.7; HRMS
(EI+) calcd for C9H8ClN5O2S2 (M+): 316.9808. Found: 316.9807.
1-Benzyl-7-nitro-2,3-dihydroimidazo[1,2-c]thiazol-5(1H)-imine (18). Yield: 74%, m.p.: 82.3–84.4 °C;
1H-NMR (DMSO-d6): δ 3.81–4.06 (m, 4H), 5.26 (s, 2H), 7.32–7.43 (s, 1H), 8.96 (s, 1H) ppm;
13C-NMR (DMSO-d6): δ 150.2, 136.4, 129.2, 128.3, 55.5, 52.3, 41.6; HRMS (ES+) calcd for calcd for
C12H12N4O2S (M+H)+: 277.0681. Found: 277.0746.
1-((6-Chloropyridin-3-yl)methyl)-8-nitro-1,2,3,4-tetrahydrothiazolo[3,4-a]pyrimidin-6-imine
(19).
Yield: 65%, m.p.: 165.3–167.4 °C; 1H-NMR (DMSO-d6): δ 2.01 (t, J = 5.2 Hz, 2H), 3.30 (t, J = 5.6 Hz,
2H), 3.73 (t, J = 5.6 Hz, 2H), 4.90 (s, 2H), 7.53 (d, J = 8.4 Hz, 1H), 7.92 (dd, J1 = 8.4 Hz, J2 = 2.4 Hz,
13
1H), 8.43 (d, J = 2.0, 1H), 9.19 (s, 1H) ppm; C-NMR (DMSO-d6): δ 153.5, 150.5, 150.0, 149.8,
139.9, 131.9, 124.4, 103.2, 56.5, 47.3, 41.6, 19.3; HRMS (ES+) calcd for C12H1235ClN5O2S (M+H)+:
326.0400. Found: 326.0476. Calcd for C12H1237ClN5O2S (M+H)+: 328.0371. Found: 328.0473.
7-Nitro-1-((6-(trifluoromethyl)pyridin-3-yl)methyl)-2,3-dihydroimidazo[1,2-c]thiazol-5(1H)-imine (20).
Yield: 88%, m.p.: 148.2–149.3 °C; 1H-NMR (DMSO-d6): δ 3.85 (t, J = 8.2 Hz, 2H), 4.10 (t, J = 9.2 Hz,
2H), 5.36 (s, 2H), 7.94 (d, J = 8.4 Hz, 1H), 8.13 (d, J = 8.4 Hz, 1H), 8.81(s, 1H), 8.94 (s, 1H) ppm;

Molecules 2012, 17
10022
13C-NMR (DMSO-d6): δ 151.0, 149.8, 137.8, 136.8, 121.1, 56.0, 50.0, 41.8; HRMS (ES+) calcd for
C12H10F3N5O2S (M+H)+: 346.0507. Found: 346.0634.
3.1.3. General Synthetic Procedure for 21–23
To a solution of 6a–c (10 mmol) in dichloromethane (50 mL) was added with stirring at −15 °C a
dichloromethane solution of thiocyanogen (10 mmol) which had previously prepared from lead
thiocyanate and bromine at −15 °C, and then the mixture was stirred for 1.5 h at room temperature.
The reaction mixture was washed with cold water (3 × 50 mL) and brine (50 mL) and then dried with
sodium sulfate. The solvent was evaporated in vacuo, and fractional precipitation of the residue from
dichloromethane afforded 21–23.
N-((6-Chloropyridin-3-yl)methyl)-N-ethyl-2-imino-3-methyl-5-nitro-2,3-dihydrothiazol-4-amine (21).
Yield: 84%, m.p.: 120.3–121.4 °C; 1H-NMR (DMSO-d6): δ 1.14 (t, J = 7.2 Hz, 3H), 3.17 (d, J = 7.2 Hz,
2H), 3.40 (s, 3H), 4.57 (s, 2H), 7.54 (d, J = 8.0 Hz, 1H), 7.92–7.95 (m, 1H), 8.49 (d, J = 2.0 Hz, 1H)
13
ppm; C-NMR (DMSO-d6): δ 165.1, 150.7, 150.5, 140.9, 131.8, 124.8, 118.2, 51.9, 46.8, 36.1, 13.9;
HRMS (EI+) calcd for C12H14ClN5O2S (M+): 327.0557. Found: 327.0559.
N-((6-Chloropyridin-3-yl)methyl)-2-imino-3-methyl-5-nitro-2,3-dihydrothiazol-4-amine (22). Yield:
1
82%, m.p.: 116.4–118.4 °C; H-NMR (DMSO-d6): δ 3.28 (s, 3H), 5.37 (s, 2H), 7.80 (s, 1H) ppm;
35
13C-NMR (DMSO-d6): δ 152.1, 142.5, 141.2, 42.5, 34.6, 33.3; HRMS (ES−) calcd for C8H8 ClN5O2S2
37
(M−H)+: 303.9808. Found: 303.9716. calcd for C8H8 ClN5O2S2 (M−H)+: 305.9778. Found: 305.9703.
N-((6-Chloropyridin-3-yl)methyl)-3-ethyl-2-imino-5-nitro-2,3-dihydrothiazol-4-amine (23). Yield: 78%,
m.p.: 115.4–117.2 °C; 1H-NMR (DMSO-d6): δ 1.23 (t, J = 7.2 Hz, 3H), 3.66 (q, J = 7.2 Hz, 2H), 5.34
13
(s, 2H), 7.81 (s, 1H); C-NMR (DMSO-d6): δ 152.1, 141.2, 134.7, 42.7, 42.1, 15.7; HRMS (ES−)
calcd for C9H1035ClN5O2S2 (M-H)+: 317.9964. Found: 317.9870. calcd for C9H1037ClN5O2S2 (M−H)+:
319.9935. Found: 319.9836.
3.2. Biological Assay
All compounds were dissolved in acetone and diluted with water containing Triton X-100 (0.1 mg L−1)
to obtain series concentrations of 500.0, 250.0, 125.0 mg L−1 and others for bioassays. Pea aphids
(Aphis craccivora) were dipped according to our previously reported procedure [13,23]. Tender shoots
of soybean with 40-60 healthy apterous adults were dipped in diluted solutions of the chemicals
containing Triton X-100 (0.1 mg L−1) for 5 s, the superfluous fluid was removed, and the shoots were
placed in the conditioned room (25 ± 1 °C, 50% RH). Water containing Triton X-100 (0.1 mg L−1) was
used as control. Mortality was assessed after 24 h. Each treatment had three repetitions, and the data
were adjusted and subjected to probit analysis as before.
4. Conclusions
In conclusion, a series of a novel class of neonicotinoids, in which the common nitromethylene
pharmacophore was substituted by electrophilic thiocyanogen reagents, were designed and synthesized.

Molecules 2012, 17
10023
Most of the compounds exhibited excellent insecticidal activities against cowpea aphids (A. craccivora),
which implied that reaction of nitromethylene with the electrophilic system to obtain novel
neonicotinoids analogues with high activities was feasible.
Acknowledgments
The work was financial supported by National Basic Research Program of China (973 Program,
2010CB126100), National High Technology Research Development Program of China (863 Program,
2011AA10A207), Key Projects in the National Science & Technology Pillar Program during the
Twelfth Five-Year Plan Period (2011BAE06B05). National Natural Science Foundation of China
(21002030), Natural Science Foundation of Shanghai (10ZR1407300), Shanghai Education Committee
(12ZZ057) and the Fundamental Research Funds for the Central Universities. This work was also
partly supported Shanghai Leading Academic Discipline Project, Project Number: B507 and Australia
DC Foundation.
References
1. Ohno, I.; Tomizawa, M.; Aoshima, A.; Kumazawa, S.; Kagabu, S. Trifluoroacetyl neonicotinoid
insecticides with enhanced hydrophobicity and effectiveness. J. Agric. Food Chem. 2010, 58,
4999–5003.
2. Tomizawa, M.; Casida, J.E. Selective toxicity of neonicotinoids attributable to specificity of insect
and mammalian nicotinic receptors. Annu. Rev. Entomol. 2003, 48, 339–364.
3. Tomizawa, M.; Casida, J.E. Neonicotinoid insecticide toxicology: Mechanisms of selective
action. Annu. Rev. Pharmacol. Toxicol. 2005, 45, 247–268.
4. Matsuda, K.; Shimomura, M.; Ihara, M.; Akamatsu, M.; Sattelle, D.B. Neonicotinoids show
selective and diverse actions on their nicotinic receptor targets: Electrophysiology, molecular
biology, and receptor modeling studies. Biosci. Biotechnol. Biochem. 2005, 69, 1442–1452.
5. Jeschke, P.; Nauen, R. Neonicotinoids—From zero to hero in insecticide chemistry. Pest Manag. Sci.
2008, 64, 1084–1098.
6. Yu, H.; Qin, Z.; Fang, J. Synthesis and insecticidal activity of N-substituted (1,3-thiazole)alkyl
sulfoximine derivatives. J. Agric. Food Chem. 2008, 56, 11356–11360.
7. Unruh, T.; Willett, L. Survey for resistance to four insecticides in Myzus persicae clones from
peach trees and weeds in south-central Washington. J. Econ. Entomol. 2008, 101, 1919–1926.
8. Soderlund, D.M. Pyrethroids, knockdown resistance and sodium channels. Pest Manag. Sci. 2008,
64, 610–616.
9. Sayyed, A.H.; Ahmad, M.; Saleem, M.A. Cross-resistance and genetics of resistance to
indoxacarb in Spodoptera litura (Lepidoptera: Noctuidae). J. Econ. Entomol. 2008, 101, 472–479.
10. Elbert, A.; Nauen, R. Resistance of Bemisia tabaci (Homoptera: Aleyrodidae) to insecticides in
southern Spain with special reference to neonicotinoids. Pest Manag. Sci. 2000, 56, 60–64.
11. Rauch, N.; Nauen, R. Identification of biochemical markers linked to neonicotinoid cross
resistance in Bemisia tabaci (Hemiptera: Aleyrodidae). Arch. Insect Biochem. Physiol. 2003, 54,
165–176.

Molecules 2012, 17
10024
12. Nauen, R.; Denholm, I. Resistance of insect pests to neonicotinoid insecticides: Current status and
future prospects. Arch. Insect Biochem. Physiol. 2005, 58, 200–215.
13. Tian, Z.; Shao, X.; Li, Z.; Qian, X.; Huang, Q. Synthesis, insecticidal activity, and QSAR of novel
nitromethylene neonicotinoids with tetrahydropyridine fixed cis configuration and exo-ring ether
modification. J. Agric. Food Chem. 2007, 55, 2288–2292.
14. Shao, X.; Li, Z.; Qian, X.; Xu, X. Design, synthesis, and insecticidal activities of novel analogues
of neonicotinoids: Replacement of nitromethylene with nitroconjugated system. J. Agric. Food
Chem. 2009, 57, 951–957.
15. Zhang, W.; Yang, X.; Chen, W.; Xu, X.; Li, L.; Zhai, H.; Li, Z. Design, multicomponent
synthesis, and bioactivities of novel neonicotinoidanalogues with 1,4-dihydropyridine scaffold.
J. Agric. Food Chem. 2010, 58, 2741–2745.
16. Shao, X.; Fu, H.; Liu, Z.; Xu, X.; Li, Z. Divalent and oxabridged neonicotinoids constructed by
dialdehydes and nitromethylene analogues of imidacloprid: Design, synthesis, crystal structure,
and insecticidal activities. J. Agric. Food Chem. 2010, 58, 2696–2702.
17. Tomizawa, M.; Zhang, N.J.; Durkin, K.A.; Olmstead, M.M.; Casida, J.E. The eonicotinoid
electronegative pharmacophore plays the crucial role in the high affinity and selectivity for the
drosophila nicotinic receptor: An anomaly for the nicotinoid cation-π interaction model.
Biochemistry 2003, 42, 7819–7827.
18. Babine, R.E.; Bender, S.L. Molecular recognition of protein-ligand complexes: Applications to
drug design. Chem. Rev. 1997, 97, 1359–1472.
19. Kagabu, S.; Matsuno, H. Chloronicotinyl insecticides. 8. Crystal and molecular structures of
imidacloprid and analogous compounds. J. Agric. Food Chem. 1997, 45, 276–281.
20. Tomizawa, M.; Lee, D.L.; Casida, J.E. Neonicotinoid insecticides: Molecular features conferring
selectivity for insect versus mammalian nicotinic receptors. J. Agric. Food Chem. 2000, 48,
6016–6024.
21. Tokumitsu, T.; Hayashi, T. Reaction of .beta.-nitroenamines with electrophilic reagents. Synthesis of
.beta.-substituted .beta.-nitroenamines and 2-imino-5-nitro-4-thiazolines. J. Org. Chem. 1985, 50,
1547–1550.
22. Tian, Z.Z.; Jiang, Z.X.; Li, Z.; Song, G.H.; Huang, Q.C. Syntheses and biological activities of
octahydro-1H-cyclopenta[d]pyrimidine derivatives. J. Agric. Food Chem. 2007, 55, 143–147.
23. Srinwasachari, R. Nitroenmines: Preparation, structure and synthetic potential. Tetrahedron 1981,
37, 1453–1480.
24. Mattson, A.E.; Zuhl, A.M.; Reynolds, T.E.; Schiedt, K.A. Direct nucleophilic acylation of
nitroalkenes promoted by a fluoride anion/thiourea combination. J. Am. Chem. Soc. 2006, 128,
4932–4933.
25. Coustard, J.M.; Soro, Y.; Siaka, S.; Bamba, F.; Cousson, A. Synthesis of 6- to 10-membered
ring (E)-hydroxyiminohydroazaazoniabenzocycloalkenes derivative from cyclization of
2-nitromethylene-1-(ω-phenylalkyl)imidazolidine
or
2-nitromethylene-1-(ω-phenylalkyl)
hexahydropyrimidine in trifluoromethanesulfonic acid. Tetrahedron 2006, 62, 3320–3328.
26. Zhang, N.J.; Tomizawa, M.; Casida, J.E. α-Nitro Ketone as an electrophile and nucleophile:
Synthesis of 3-Substituted 2-nitromethylenetetrahydrothiophene and-tetrahydrofuran as Drosophila
nicotinic receptor probes. J. Org. Chem. 2004, 69, 876–881.

Molecules 2012, 17
10025
27. Foks, H.; Pancechowska-Ksepko, D.; Janowiec, M.; Zwolska, Z.; Augustynowicz-Kopeé, E.
Synthesis and tuberculostatic activity of some 1,1-bis-methylthio-2-nitro-ethene derivatives.
Phosphorus Sulfur Silicon Relat. Elem. 2005, 180, 2291–2297.
Sample Availability: Samples of the title compounds are available from the authors.
© 2012 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).