Design, multicomponent synthesis, and bioactivities of novel neonicotinoid analogues with 1,4-dihydropyridine scaffold

Article abstract of DOI:10.1021/jf902034z

Novel neonicotinoid analogues bearing a 1,4-dihydropridine scaffold were designed and synthesized by multicomponent reactions (MCRs) to enhance π-π stacking. The synthesized compounds were identified by ¹H NMR, ¹³C NMR, high-resoluti

Full text of DOI:10.1021/jf902034z

J. Agric. Food Chem. 2010, 58, 2741–2745 2741
DOI:10.1021/jf902034z
Design, Multicomponent Synthesis, and Bioactivities of Novel
Neonicotinoid Analogues with 1,4-Dihydropyridine Scaffold†
§
WENWEN
Z
HANG,§ XIAOBAO
Y
ANG,§ WEIDONG
C
HEN,§ XIAOYONG
,§
X
U
,§ L
U
LI,
HONGBIN
Z
HAI,*,# AND
Z
HONG
LI*
§Shanghai Key Laboratory of Chemistry Biology, Institute of Pesticides and Pharmaceuticals, East China
University of Science and Technology, Shanghai, China 200237, and #Laboratory of Modern Synthetic
Organic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai,
China 200032
Novel neonicotinoid analogues bearing a 1,4-dihydropridine scaffold were designed and synthesized
by multicomponent reactions (MCRs) to enhance π-π stacking. The synthesized compounds were
identified by 1H NMR, 13C NMR, high-resolution mass spectroscopy, and elemental analysis.
Bioassay tests showed that some of them exhibited high insecticidal activities against pea aphid
(Aphis craccivora).
KEYWORDS: 1,4-Dihydropridine; MCRs; biological activity
INTRODUCTION
Acting on nicotinic acetylcholine receptor (nAChR) insect
neuronal systems (1-4), imidacloprid (1a) (Figure 1) started the
era of neonicotinoid insecticides, which have become a major
insecticideclasswith high activitieswidelyused forcrop protection
and veterinary pest control (5). As is well-known, 6-Cl-PMNI ((2-
chloro-5-((2-(nitromethylene)imidazolidin-1-yl)methyl)pyridine,
1b) (Figure 1) was obtained before imidacloprid and had higher
binding affinity and activity than imidacloprid. Although its
application was limited by its photoinstability (6) and inferior
hydrophobicity (7), it is still an attractive molecule as lead
compound for chemists worldwide (8, 9).
In our previous work, numerous 1b derivatives were synthe-
sized. Compounds 2 (Figure 2) were obtained by introducing a
tetrahydropyridine ring. The photostability of 2 was improved as
desired (10). Afterward, compounds 3 (Figure 2) were reported,
which had a bulky group conjugated system introduced by five-
membered heterocycles. Some 3 compounds had higher activities
than imidacloprid (11). The results encouraged us to consider
further structure derivation of 1b.
The research of binding model is always beneficial for molec-
ular design. In the development of neonicotinoid insecticides,
three kinds of action models were proposed by Yamamoto,
Kagabu, and Casida successively (12-14). In 2007, Qian et al.
suggested a new binding model of π-π interaction induced by
the hydrogen bond based on theory calculation (15). Then
two kinds of AChBP-imidacloprid complex crystal structures
were achieved by Casida and Sattelle (16, 17), respectively. After
that, Casida et al. designed compounds with extended N-sub-
stituted imine substituents and presumed the significance of the
π-stacking formed by the amidine plane (18). Also, Kagabu et al.
Figure 1. Structures of imidacloprid (1a) and 1b.
proposed that a water bridge was formed between the neonico-
tinoid and the relevant amino acid at the ligand binding pocket.
Novel compounds with methyl ketone, trifluoromethyl ketone,
and epoxycyclopentylmethyl substituents were obtained and
shown to enhance the binding affinity (19).
On the basis of the theory above, the influence factor of
higher activities of compounds 3 was thought to be over. It
was presumed that π-π stacking was enhanced by the big
conjugated system in compounds 3, which might influence the
binding model and improve the activities. Therefore, we try to
further enhance π-π stacking by introducing an aromatic
bicyclic moiety.
It is well-known that the heteroaromatic moiety and nitro
pharmacophore were very important in the structure of
neonicotinoids, which were also included in 1b (Figure 3).
According to this analysis, reaction sites a and b (Figure 3)
were to be modified, building target compound 6 (Figure 2)
bearing a 1,4-dihydropyridine scaffold. The 1,4-dihydropyr-
idine moiety was frequently used as a subunit of antiathero-
sclerotic, anticancer, and antidiabetic drugs (20-22). It can be
achieved conveniently by multicomponent reactions (MCRs)
using 1b, aryl carbonyl compounds, and malononitrile as
starting materials (23).
†Part of the ECUST-Qian Pesticide Cluster.
*Corresponding authors [(Z.L.) telephone þ86-21-64253540, fax
þ86-21-64252603, e-mail lizhong@ecust.edu.cn; (H.Z.) telephone
þ86-21-54925163, fax þ86-21-64166128, e-mail zhaih@mail.sioc.ac.cn].
© 2009 American Chemical Society
Published on Web 12/15/2009
pubs.acs.org/JAFC

2742 J. Agric. Food Chem., Vol. 58, No. 5, 2010
Zhang et al.
Figure 2. Development of novel neonicotinoid analogues in our group.
Figure 3. Pharmacophore and reaction sites at 1b.
MATERIALS AND METHODS
Data for 6d: yield, 41%; mp 224.6-245.8 °C; 1H NMR (400 MHz,
DMSO-d6), δ 4.00-4.13 (m, 4H), 4.73 (dd, J1 = 16.0 Hz, J2 = 20.0 Hz,
2H), 4.75 (s, 1H), 6.67 (s, 2H, NH2), 7.16 (d, J = 8.4 Hz, 1H), 7.24 (d, J =
8.0 Hz, 2H), 7.63 (dd, J1 = 2.4 Hz, J2 = 8.2 Hz, 1H), 7.64 (d, J = 8.4 Hz,
2H), 8.18 (s, 1H); 13C NMR (100 MHz, DMSO-d6), δ 41.8, 43.9, 51.4, 51.7,
58.6, 105.7, 109.9, 119.4, 120.9, 124.3, 127.9, 131.3, 132.7, 139.4, 149.5,
149.9, 149.9, 150.1, 152.3. Anal. Calcd for C21H16ClN7O2: C, 58.14; H,
3.72; N, 22.60. Found: C, 58.00; H, 3.50; N, 22.49.
Data for 6e: yield, 65%; mp 246.4-247.5 °C; 1H NMR (400 MHz,
DMSO-d6), δ 3.99-4.14 (m, 4H), 4.73 (s, 2H), 4.78 (s, 1H), 6.65 (s, 2H,
NH2), 7.24 (d, J = 8.0 Hz, 1H), 7.36 (d, J = 7.2 Hz, 1H), 7.43 (t, J = 7.2
Hz, 1H), 7.50 (s, 1H), 7.62 (s, 2H), 8.22 (s, 1H); 13C NMR (100 MHz,
DMSO-d6), δ 41.6, 43.9, 51.5, 51.6, 58.9, 105.7, 111.8, 119.4, 120.9, 124.2,
129.9, 130.5, 131.0, 131.3, 132.2, 139.4, 146.3, 149.5, 149.8, 149.9, 152.4.
HRMS (ESI) calcd for C21H16ClN7O2 (M þ Na), 456.0952; found,
456.0970.
Data for 6f: yield, 61%; mp 191.5-192.0 °C; 1H NMR (400 MHz,
DMSO-d6), δ 3.97-4.16 (m, 4H), 4.74 (s, 3H), 6.60 (s, 2H, NH2), 7.10 (d,
J = 8.8 Hz, 2H), 7.18 (d, J = 8.0 Hz, 2H), 7.28 (d, J = 8.4 Hz, 1H), 7.65
(dd, J1 = 2.6 Hz, J2 = 8.2 Hz, 1H), 8.26 (d, J = 2.0 Hz, 1H); 13C NMR
(100 MHz, DMSO-d6), δ 41.1, 43.9, 51.4, 51.5, 59.5, 105.9, 119.3, 121.1,
121.2, 121.8, 124.3, 128.6, 131.4, 139.5, 144.1, 147.4, 149.6, 149.7, 149.9,
152.6. HRMS (ESI) calcd for C21H16ClF3N6O3 (M þ Na), 515.0822;
found, 515.0832. Anal. Calcd for C21H16ClF3N6O3: C, 51.18; H, 3.27; N,
17.05. Found: C, 50.43; H, 3.08; N, 16.59.
Data for 6g: yield, 64%; mp 237.7-238.2 °C; 1H NMR (400 MHz,
DMSO-d6), δ 3.91-4.15 (m, 4H), 4.73 (s, 3H), 6.62 (s, 2H, NH2), 6.97 (d,
J = 7.6 Hz, 1H), 7.17 (t, J = 7.8 Hz, 1H), 7.26 (t, J = 1.8 Hz, 1H), 7.28 (d,
J = 8.0 Hz, 1H), 7.37-7.39 (m, 1H), 7.65 (dd, J1 = 2.4 Hz, J2 = 8.4 Hz,
1H), 8.25 (d, J = 2.0 Hz, 1H); 13C NMR (100 MHz, DMSO-d6), δ 41.4,
43.9, 51.1, 51.5, 59.2, 105.8, 121.0, 122.1, 124.3, 126.0, 129.6, 130.0, 131.0,
131.3, 139.4, 147.5, 149.5, 149.8, 149.9, 152.7. Anal. Calcd for
C20H16BrClN6O2: C, 49.25; H, 3.31; N, 17.23. Found: C, 49.19; H, 3.01;
N, 17.05.
Data for 6h: yield, 49%; mp 261.7-262.1 °C; 1H NMR (400 MHz,
DMSO-d6), δ 4.01-4.14 (m, 4H), 4.72 (d, J = 15.6 Hz, 1H), 4.78 (d, J =
16.0 Hz, 1H), 5.14 (s, 1H), 6.53 (s, 2H, NH2), 6.98 (d, J = 8.4 Hz, 1H), 7.20
(dd, J1 = 2.0 Hz, J2 = 8.0 Hz, 1H), 7.42 (d, J = 8.0 Hz, 1H), 7.46 (d, J =
2.0 Hz, 1H), 7.77 (dd, J1 = 2.2 Hz, J2 = 8.2 Hz, 1H), 8.31 (d, J = 1.6 Hz,
1H); 13C NMR (100 MHz, DMSO-d6), δ 39.7, 43.9, 51.3, 51.8, 59.1, 105.5,
120.4, 124.5, 127.9, 129.1, 131.4, 131.6, 132.1, 133.0, 139.8, 141.5, 149.5,
149.7, 150.0, 152.7. Anal. Calcd for C20H15Cl3N6O2: C, 50.28; H, 3.16; N,
17.59. Found: C, 50.36; H, 2.90; N, 17.38.
Data for 6i: yield, 65%; mp 252.1-253.0 °C; 1H NMR (400 MHz,
DMSO-d6), δ 3.96-4.18 (m, 4H), 4.77 (t, J = 17.0 Hz, 2H), 4.89 (s, 1H),
6.56 (s, 2H, NH2), 7.01 (t, J = 8.2 Hz, 1H), 7.09 (d, J = 8.0 Hz, 1H), 7.23
(d, J = 10.4 Hz, 1H), 7.36 (d, J = 8.0 Hz, 1H), 7.72 (d, J = 8.0 Hz, 1H),
8.26 (s, 1H); 13C NMR (100 MHz, DMSO-d6), δ 43.9, 51.4, 51.5, 56.5,
€
Instruments. All melting points (mp) were obtained with a Buchi
Melting Point B540 and are uncorrected. NMR spectra were recorded in
DMSO-d6 (1H at 400 MHz and 13C at 100 MHz) using TMS as the internal
standard on a Bruker WP-400SY (400 MHz) spectrometer. 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. Combustion analyses for elemental
composition were made with an Elementar vario EL III. Analytical thin-
layer chromatography (TLC) was carried out on precoated plates (silica
gel 60 F254), and spots were visualized with ultraviolet (UV) light. All
other solvents and reagents were used as obtained from commercial
sources without further purification.
General Procedure for the Preparation of Compounds 6a-p.
A
solution of malononitrile (15 mmol) in anhydrous alcohol (15 mL) was
added dropwise to a solution of aryl aldehyde (15 mmol) in anhydrous
alcohol (15 mL) at room temperature. After 5 min of stirring at room
temperature, piperidine (0.1 mmol) used as catalyst was added dropwise.
The resulting mixture was stirred for another 2 h, then 1b (10 mmol) was
added to the reaction mixture, refluxed for 15-20 h, and cooled to room
temperature. Solid crystal products was filtered, washed with CH2Cl2, and
dried to give desired products.
Data for 6a: yield, 82%; mp 223.2-223.7 °C; 1H NMR (400 MHz,
DMSO-d6), δ 3.93-4.01 (m, 3H), 4.08-4.17 (m, 1H), 4.72 (s, 1H), 4.74 (s,
2H), 6.54 (s, 2H, NH2), 6.98 (dd, J1 = 1.4 Hz, J2 = 7.8 Hz, 1H), 7.15-7.23
(m, 3H), 7.28 (d, J = 8.0 Hz, 1H), 7.64 (dd, J1 = 2.6 Hz, J2 = 8.2 Hz, 1H),
8.28 (d, J = 2.0 Hz, 1H); 13C NMR (100 MHz, DMSO-d6), δ 41.5, 43.9,
51.1, 51.5, 60.1, 106.2, 121.2, 124.4, 126.7, 127.0, 128.7, 131.4, 139.5, 144.8,
149.5, 149.6, 149.9, 152.9. Anal. Calcd for C20H17ClN6O2: C, 58.75; H,
4.19; N, 20.56. Found: C, 58.77; H, 3.89; N, 20.40.
Data for 6b: yield, 78%; mp 253.5-253.9 °C; 1H NMR (400 MHz,
DMSO-d6), δ 4.02-4.15 (m, 4H), 4.70 (d, J = 15.6 Hz, 1H), 4.77 (d, J =
16.0 Hz, 1H), 4.81 (s, 1H), 6.70 (s, 2H, NH2), 7.21 (d, J = 8.0 Hz, 1H), 7.22
(d, J = 8.8 Hz, 2H), 7.60 (dd, J1 = 1.6 Hz, J2 = 8.0 Hz, 1H), 8.05 (d, J =
8.4 Hz, 2H), 8.17 (s, 1H); 13C NMR (100 MHz, DMSO-d6), δ 41.6, 43.9,
51.3, 51.8, 58.5, 105.6, 120.8, 124.0, 124.3, 128.1, 131.3, 139.5, 146.6, 149.5,
149.9, 150.0, 152.1, 152.2. Anal. Calcd for C20H16ClN7O4: C, 52.93; H,
3.55; N, 21.60. Found: C, 52.90; H, 3.39; N, 21.48.
Data for 6c: yield, 59%; mp 244.3-245.1 °C; 1H NMR (400 MHz,
DMSO-d6), δ 4.01-4.15 (m, 4H), 4.69 (d, J = 16.0 Hz, 1H), 4.74 (d, J =
16.0 Hz, 1H), 4.87 (s, 1H), 6.73 (s, 2H, NH2), 7.17 (d, J = 8.4 Hz, 1H), 7.44
(d, J = 7.6 Hz, 1H), 7.51 (t, J = 7.8 Hz, 1H), 7.60 (dd, J1 = 2.4 Hz, J2 =
8.4 Hz, 1H), 7.88 (t, J = 1.8 Hz, 1H), 8.07 (dd, J1 = 1.2 Hz, J2 = 8.0 Hz,
1H), 8.17 (d, J = 2.4 Hz, 1H); 13C NMR (100 MHz, DMSO-d6), δ 41.3,
44.0, 51.4, 51.5, 58.5, 105.8, 120.9, 121.4, 122.2, 124.1, 130.4, 131.2, 133.7,
139.4, 146.9, 148.1, 149.5, 149.8, 150.2, 152.3. Anal. Calcd for C20H16
-
ClN7O4: C, 52.93; H, 3.55; N, 21.60. Found: C, 52.82; H, 3.22; N, 21.38.

Article
J. Agric. Food Chem., Vol. 58, No. 5, 2010 2743
Scheme 1. Target Compound Synthesis via Aryl Aldehyde-Based Muliticomponet Reactions
58.9, 104.9, 116.3, 116.5, 120.6, 124.4, 124.9, 124.9, 130.6, 130. 8, 131.2,
131.2, 131.3, 132.3, 132.4, 139.6, 149.5, 149.7, 150.1, 152.5, 158.8, 160.3.
HRMS (ESI) calcd for C20H15Cl2FN6O2 (M þ Na), 483.0515; found,
483.0523.
150.1, 152.3. HRMS (ESI) calcd for C21H15Cl2F3N6O2 (M þ H),
511.0664; found, 511.0677.
Data for 6o: yield, 10%; mp 217.1-217.3 °C; 1H NMR (400 MHz,
DMSO-d6), δ 3.73 (s, 3H), 3.89-4.41 (m, 4H), 4.49 (s, 1H), 4.66 (s, 1H),
4.75 (d, J = 2.4 Hz, 1H), 6.51 (s, 2H, NH2), 6.75-6.77 (m, 2H), 6.87-6.90
(m, 1H), 7.30 (d, J = 8.0 Hz, 1H), 7.64 (dd, J1 = 2.8 Hz, J2 = 8.0 Hz, 1H),
8.27 (d, J = 2.4 Hz, 1H); 13C NMR (100 MHz, DMSO-d6), δ 42.9, 43.9,
45.7, 48.4, 51.1, 51.4, 55.5, 60.5, 106.6, 114.1, 124.4, 124.8, 127.7, 131.5,
136.8, 139.5, 139.7, 149.4, 149.6, 149.9, 158.4. HRMS (ESI) calcd for
C21H19ClN6O3 (M þ H), 439.1285; found, 439.1274.
Data for 6j: yield, 72%; mp 265.4-265.8 °C; 1H NMR (400 MHz,
DMSO-d6), δ 3.98-4.05 (m, 3H), 4.09-4.12 (m, 1H), 4.71 (d, J = 15.6 Hz,
1H), 4.76 (d, J = 15.6 Hz, 1H), 5.12 (s, 1H), 6.53 (s, 2H, NH2), 6.89 (d, J =
8.4 Hz, 1H), 7.31 (dd, J1 = 2.0 Hz, J2 = 8.0 Hz, 1H), 7.42 (d, J = 8.0 Hz,
1H), 7.56 (d, J = 2.0 Hz, 1H), 7.76 (dd, J1 = 2.4 Hz, J2 = 8.4 Hz, 1H), 8.30
(d, J = 2.0 Hz, 1H); 13C NMR (100 MHz, DMSO-d6), δ 40.1, 43.9, 51.3,
51.8, 59.0, 105.5, 120.3, 120.4, 124.5, 130.8, 131.4, 131.8, 131.9, 133.2,
139.8, 141.9, 149.5, 149.7, 150.0, 152.7. HRMS (ESI) calcd for
C20H15BrCl2N6O2 (M þ Na), 542.9715; found, 542.9741.
Data for 6p: yield, 19%; mp 225.1-226.2 °C; 1H NMR (400 MHz,
DMSO-d6), δ 2.32 (d, J = 1.6 Hz, 3H), 3.98-4.15 (m, 4H), 4.76 (s, 2H),
5.02 (s, 1H), 6.48 (s, 2H, NH2), 6.59 (d, J = 7.6 Hz, 1H), 6.95-6.99 (m,
1H), 7.01-7.04 (m, 1H), 7.40 (d, J = 8.4 Hz, 1H), 7.76 (dd, J1 = 2.4 Hz,
J2 = 8.0 Hz, 1H), 8.32 (d, J = 2 Hz, 1H); 13C NMR (100 MHz, DMSO-
d6), δ 10.1, 10.2, 37.7, 43.9, 51.2, 51.8, 60.7, 106.8, 112.9, 113.2, 120.9,
121.7, 121.8, 123.3, 124.5, 127.6, 127.6, 131.5, 139.7, 148.9, 149.7, 149.9,
152.8, 159.2, 161.6. HRMS (ESI) calcd for C21H18ClFN6O2 (M þ H),
441.1242; found, 441.1227.
Data for 6k: yield, 40%; mp 202.6-203.2 °C; 1H NMR (400 MHz,
DMSO-d6), δ 2.23 (s, 3H), 3.90-4.01 (m, 3H), 4.14-4.20 (m, 1H), 4.73 (d,
J = 16.0 Hz, 1H), 4.78 (d, J = 15.6 Hz, 1H), 4.84 (s, 1H), 6.49 (s, 2H,
NH2), 6.82 (dd, J1 = 2.0 Hz, J2 = 7.6 Hz, 1H), 6.90 (dd, J1 = 8.6 Hz, J2 =
10.6 Hz, 1H), 6.99-7.02 (m, 1H), 7.35 (d, J = 8.4 Hz, 1H), 7.70 (dd, J1 =
2.2 Hz, J2 = 8.2 Hz, 1H), 8.29 (d, J = 2.4 Hz, 1H); 13C NMR (100 MHz,
DMSO-d6), δ 20.7, 37.6, 44.0, 50.8, 51.5, 59.7, 105.0, 115.5, 115.7, 120.7,
124.4, 129.2, 129.3, 130.0, 130.1, 131.0, 131.1, 131.3, 133.6, 133.6, 139.6,
149.3, 149.7, 149.9, 152.9, 157.5, 159.9. Anal. Calcd for C21H18ClFN6O2:
C, 57.21; H, 4.12; N, 19.06. Found: C, 56.98; H, 3.78; N, 18.79.
Data for 6l: yield, 32%; mp 257.4-258.4 °C; 1H NMR (400 MHz,
DMSO-d6), δ 2.39 (s, 3H), 3.97-4.09 (m, 4H), 4.72 (d, J = 16.0 Hz, 1H),
4.76 (d, J = 16.8 Hz, 1H), 4.93 (d, J = 1.6 Hz, 1H), 6.51 (s, 2H, NH2), 6.75
(d, J = 9.6 Hz, 1H), 7.37 (d, J = 8.0 Hz, 1H), 7.41 (d, J = 7.2 Hz, 1H), 7.81
(dd, J1 = 2.6 Hz, J2 = 8.2 Hz, 1H), 8.27 (d, J = 2.0 Hz, 1H); 13C NMR
(100 MHz, DMSO-d6), δ 18.3, 38.1, 43.9, 51.4, 52.0, 59.9, 105.5, 105.7,
106.4, 115.4, 115.6, 120.8, 124.3, 131.5, 132.9, 133.0, 134.3, 139.7, 146.4,
Biological Assay. All compounds were dissolved in acetone and
diluted with water containing Triton X-100 (0.1 mg/L) to obtain series
concentrations of 500.0, 50.0, and 25.0 mg/L and others for bioassays.
As previously tested (10), cowpea aphids (Aphis craccivora) were dipped
according to a slightly modified FAO dip test (24). 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) 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; the
control mortality was 4.3%. Each treatment had three repetitions, and the
data were corrected and subjected to probit analysis using SPSS software.
146.5, 149.0, 149.6, 150.0, 152.6, 156.4, 158.8. Anal. Calcd for C21H17
-
BrFN6O2: C, 48.53; H, 3.30; N, 16.17. Found: C, 48.28; H, 2.98; N,
16.02.
RESULTS AND DISCUSSION
1
Data for 6m: yield, 63%; mp 236.2-236.9 °C; H NMR (400 MHz,
Synthesis. The neonicotinoid analogues bearing a 1,4-dihydro-
pyridine scaffold (6a-p) were synthesized as shown in Scheme 1.
The assembly of 6 can be explained via the initial Michael
addition of 7 to the ylidenic bond in 1b, leading to the formation
of anacyclic intermediate 8, which cyclized into the intermediate9
via nucleophilic attack of an NH group on a cyano carbon,
followedby tautomerization tothe final product 6. The formation
of 7 is via Knoevenagel condensation reaction of malononitrile 4
and appropriate aromatic aldehyde 5.
The search for one-pot condensation reaction parameters
started with nitromethylene (1b), malononitrile (4), and p-nitro-
benzaldehyde (5a) in molar ratios from 1:1:1 to 1:2:2 in boiling
ethanolic piperidine from 2 to 17 h; desirable product could be
obtained up to 78% yield. However, no substantial gain in the
DMSO-d6), δ 2.41 (s, 3H), 3.96-4.14 (m, 4H), 4.74 (d, J = 16.0 Hz, 1H),
4.79 (d, J = 15.6 Hz, 1H), 4.99 (d, J = 2.0 Hz, 1H), 6.48 (s, 2H, NH2), 6.59
(dd, J1 = 2.4 Hz, J2 = 10.0 Hz, 1H), 6.85-6.90 (m, 1H), 7.09-7.12 (m,
1H), 7.39 (d, J = 8.4 Hz, 1H), 7.82 (dd, J1 = 2.4 Hz, J2 = 8.0 Hz, 1H), 8.31
(d, J = 2.0 Hz, 1H); 13C NMR (100 MHz, DMSO-d6), δ 18.7, 38.3, 43.9,
51.1, 52.0, 60.6, 106.6, 113.4, 113.7, 113.8, 114.0, 120.9, 124.4, 130.7, 130.7,
131.5, 131.7, 131.8, 139.6, 146.5, 146.6, 149.0, 149.6, 149.9, 152.9, 160.4,
162.8. HRMS (ESI) calcd for C21H18ClFN6O2 (M þ Na), 463.1061;
found, 463.1056.
Data for 6n: yield, 26%; mp 236.1-236.8 °C; 1H NMR (400 MHz,
DMSO-d6), δ 4.07 (m, 4H), 4.75 (s, 2H), 5.03 (s, 1H), 6.54 (s, 2H, NH2),
7.03 (d, J = 6.0 Hz, 1H), 7.42-7.46 (m, 2H), 7.62 (d, J = 1.6 Hz, 1H), 7.77
(dd, J1 = 2.4 Hz, J2 = 8.0 Hz, 1H), 8.30 (d, J = 1.6 Hz, 1H); 13C NMR
(100 MHz, DMSO-d6), δ 37.9, 43.9, 51.7, 51.8, 60.3, 106.7, 120.1, 122.5,
124.5, 125.5, 125.6, 131.5, 131.9, 132.2, 133.2, 139.8, 144.4, 149.7, 149.7,

2744 J. Agric. Food Chem., Vol. 58, No. 5, 2010
Zhang et al.
Table 1. Insecticidal Activities of Neonicotinoid Analogues 6a-p Bearing a 1,4-Dihydropyridine Scaffold against Pea Aphid (Aphis craccivora)
compd
R
mortality (%) in vivo at 1 day (500 mg L-1
)
LC50 (mmol L-1
)
6a
6b
6c
6d
6e
6f
Ph
4-NO2-C6H4
3-NO2-C6H4
4-CN-C6H4
3-CN-C6H4
83.1
77
nta
nt
91.9
93.7
80
0.07903
0.1746
nt
4-CF3O-C6H4
3-Br-C6H4
100
91.8
93.4
88
0.09797
0.19702
0.1326
nt
6g
6h
6i
2,4-DiCl-C6H3
2-F-4-Cl-C6H3
2-Cl-4-Br-C6H3
2-F-4-Me-C6H3
2-Br-4-F-5-Me-C6H2
2-CH3-5-F-C6H3
2-CF3-4-Cl-C6H3
4-OCH3-C6H4
2-CH3-3-F-C6H3
6j
85
nt
6k
6l
72.9
75.9
100
100
100
100
100b
nt
nt
6m
6n
0.09614
0.06159
0.00975
0.00345
0.03502b
6o
6p
imidacloprid
a Not tested. b Data from Shao et al. (11).
product yield was observed with increasing 4 and 5a loading from
150 to 200 mol %. Therefore, the optimum usage was fixed at
1:1.5:1.5 (1b/2/3a) for all subsequent experiments. To evaluate the
novel analogues, compounds 6b-p (Table 1) were achieved from 15
additional aryl aldehydes (5b-p) using the optimized reaction
conditions. Unfortunately, no desirable product could be obtained
from alkyl aldehydes such as butyl aldehyde or heterocyclic
aldehydes such as pyridine aldehyde, furaldehyde, and thienyl
aldehyde. The structures of the title compounds were well char-
acterized by 1H NMR, 13C NMR, HRMS, and elemental analysis.
Biological Activities. Compounds 6c, 6d, 6f, 6g, 6h, 6m, 6n, 6o,
and 6p exhibited good insecticidal activity against pea aphid
(Table 1) and had >90% mortality at 500 mg L-1. The LC50
values of those compounds were 0.07903, 0.1746, 0.09797,
0.19702, 0.1326, 0.09614, 0.06159, 0.00975, and 0.00345 mmol
(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) Kagabu, S. Chloronicotinyl insecticides-discovery, application and
future perspective. Rev. Toxicol. 1997, 1, 75–129.
(6) Okazawa, A.; Akamatsu, M.; Ohoka, A.; Nishiwaki, H.; Cho, W. J.;
Nakagawa, Y.; Nishimura, K.; Ueno1, T. Prediction of the binding
mode of imidacloprid and related compounds to housefly head
acetylcholine receptors using three-dimensional QSAR analysis.
Pestic. Sci. 1998, 54, 134–144.
(7) Nishiwaki, H.; Nakagawa, Y.; Ueno, T.; Kagabu, S.; Nishimura, K.
Insecticidal and binding activities of N3-substituted imidacloprid
derivatives against the housefly Musca domestica and the R-bungaro-
toxin binding sites of nicotinic acetylcholine receptors. Pest Manage.
Sci. 2001, 57, 810–814.
(8) Kagabu, S.; Medej, S. Chloronicotinyl insecticides. Part VI. Stability
comparison of imidacloprid and related compounds under simulated
sunlight, hydrolysis conditions, and to oxygen. Biosci., Biotechnol.,
Biochem. 1995, 59, 980–985.
(9) Yamamoto, I.; Tomizawa, M.; Satio, T.; Miyamoto, T.; Walcott,
E. C.; Sumikawa, W. Structural factors contributing to insecticidal
and selective actions of neonicotinoids. Arch. Insect. Biochem.
Physiol. 1998, 37, 24–32.
L
L
-1, respectively, whereasthat of imidacloprid was 0.03502 mmol
-1. It was concluded that compounds 6o and 6p showed 3.6- and
10.2-fold potency compared with imidacloprid. For the effect of
substituents at the phenyl group, it was observed that compounds
demonstrated good activities with either electron-withdrawing or
electron-donating groups. Nevertheless, an electron-donating
group is favorable for high activities from the data analysis
present. Further study is underway.
(10) Tian, Z. Z.; Shao, X. S.; Li, Z.; Qian, X. H.; Huang, Q. C. Synthesis,
insecticidal activity and QSAR of novel nitromethylene neonicoti-
noids with tetrahydropyridine fixed cis configuration and exo-ring
ether modification. J. Agric. Food Chem. 2007, 55, 2288–2292.
(11) Shao, X. S.; Li, Z.; Qian, X. H.; Xu, X. Y. Design, synthesis, and
insecticidal activities of novel analogues of neonicotinoids: replace-
ment of nitromethylene with nitroconjugated system. J. Agric. Food
Chem. 2009, 57, 951–957.
In conclusion, various neonicotinoid analogues bearing a 1,4-
dihydropridine scaffold were synthesized successfully via multi-
component reactions. Most of compounds showed good insecti-
cidal activities at 500 mg L-1, which implied a new method of
molecular design, which is to obtain highly active compounds by
enhancing π-π stacking.
Supporting Information Available: 1H NMR and 13C NMR
spectra of compounds 6. This material is available free of charge
via the Internet at http://pubs.acs.org.
(12) Tomizawa, M.; Yamamoto, I. Structure-activity relationships of
nicotinoids and imidacloprid analogs. Nihon Noyaku Gakkaishi
1993, 18, 91–98.
(13) Kagabu, S.; Matsuno, H. Chloronicotinyl insecticides. 8. Crystal and
molecular structures of imidacloprid and analogous compounds.
J. Agric. Food Chem. 1997, 45, 276–281.
LITERATURE CITED
(1) Liu, M.; Casida, J. E. High affinity binding of [3H] imidacloprid in
the insect acetylcholine receptor. Pestic. Biochem. Physiol. 1993, 46,
40–46.
(2) Mori, K.; Okumoto, T.; Kawahara, N.; Ozoe, Y. Interaction of
dinotefuran and its analogues with nicotinic acetylcholine receptors
of cockroach nerve cords. Pest Manage. Sci. 2001, 58, 190–196.
(3) Tomizawa, M.; Casida, J. E. Neonicotinoid insecticide toxicology:
mechanisms of selective action. Annu. Rev. Pharmacol. Toxicol.
2005, 45, 247–268.
(14) Tomizawa, M.; Lee, D. L.; Casida, J. E. Neonicotinoid insecticides:
molecular features conferring selectivity for insect versus mamma-
lian nicotinic receptors. J. Agric. Food Chem. 2000, 48, 6016–6024.
(15) Wang, Y. L.; Cheng, J. G.; Qian, X. H.; Li, Z. Actions between
neonicotinoids and key residues of insect nAChR based on an ab
initio quantum chemistry study: hydrogen bonding and cooperative
π-π interaction. Bioorg. Med. Chem. 2007, 15, 2624–2630.
(16) Tomizawa, M.;Talley, T. T.;Maltby, D.;Durkin, K. A.;Medzihradszky,
K. F.; Burlingame, A. L.; Taylor, P.; Casida, J. E. Mapping the

Article
J. Agric. Food Chem., Vol. 58, No. 5, 2010 2745
elusive neonicotinoid binding site. Proc. Natl. Acad. Sci. U.S.A.
2007, 104, 9075–9080.
derivatives: a comparison of structure-activity relationships. Eur. J.
Med. Chem. 1992, 27, 229–235.
(17) Ihara, M.; Okajima, T.; Yamashita, A.; Oda, T.; Hirata, K.;
Nishiwaki, H.; Morimoto, T.; Akamatsu, M.; Ashikawa, Y.;
Kuroda, S.; Mega, R.; Kuramitsu, S.; Sattelle, D. B.; Matsuda, K.
Crystal structures of Lymnaea stagnalis AChBP in complex with
neonicotinoid insecticides imidacloprid and clothianidin. Invert.
Neurosci. 2008, 8, 71–81.
(18) Tomizawa, M.; Kagabu, S.; Ohno, I.; Durkin, K. A.; Casida, J. E.
Potency and selectivity of trifluoroacetylimino and pyrazinoylimino
nicotinic insecticides and their fit at a unique binding site niche.
J. Med. Chem. 2008, 51, 4213–4218.
(19) Ohno, I.; Tomizawa, M.; Durkin, K. A.; Casida, J. E.; Kagabu, S.
Neonicotinoid substituents forming a water bridge at the nicotinic
acetylcholine receptor. J. Agric. Food Chem. 2009, 57, 2436–2440.
(20) Sausins, A.; Duburs, G. Synthesis of 1,4-dihydropyridines by cyclo-
condensation reactions. Heterocycles 1988, 27, 269–289.
(21) Mager, P. P.; Coburn, R. A.; Solo, A. J.; Triggle, D. J.; Rothe, H.
QSAR, diagnostic statistics and molecular modeling of 1,4-dihydro-
pyridine calcium antagonists: a difficult road ahead. Drug Design
Discov. 1992, 8, 273–289.
(23) Sharanin, Y. A.; Baskakov, Y. A.; Abramenko, Y. T.; Putsykin,
Y. G.; Vasil’ev, A. F.; Nazarova, E. B. Cyclization of nitriles. III.
Synthesis of o-cyanoanilines using the Thorpe reaction. Zh. Org.
Khim. 1980, 16, 2192–2204.
(24) FAO. Recommended methods for the detection and measurement of
resistance of agricultural pests to pesticides: method for adult aphids;
FAO method 17. FAO Plant Prot. Bull. 1979, 18, 6-9.
Received for review June 15, 2009. Revised manuscript received August
28, 2009. Accepted November 19, 2009. This work was financially
supported by National Key Project for Basic Research
(2003CB114405), National Natural Science Foundation of China
(2087203), Program for New Century Excellent Talents in University
(NCET070284), and National High Technology Research and
Development Program of China (863 Program, 2006AA10A201). We
also appreciate partial support from the Shanghai Foundation of Science
and Technology (064319022, 08391911600), Shanghai Leading
Academic Discipline Project, Project B507 and 111 Project (No.
B07023).
(22) Manhold, R.; Jablonka, B.; Voigdt, W.; Schoenfinger, K. F.;
Schravan, K. Calcium- and calmodulin-antagonism of elnadipine