Synthesis, Nematicidal Activity, and 3D-QSAR of Novel 1,3,4-Oxadiazole/ Thiadiazole Thioether Derivatives

Article abstract of DOI:10.1002/cjoc.201800282

Forty one novel 1,3,4-oxadiazole/thiadiazole thioether derivatives containing phenoxy moiety were designed and synthesized. Bioassay demonstrated that some of them showed remarkable activities against Tylenchulus semipenetrans in vitro and in vivo. Compounds 20, 21, 35 and 39 showed excellent lethal activities after treatment for 48?h in vitro, with LC₅₀ values of 13.4?±?1.8, 11.7?±?2.5, 13.7?±?2.4 and 13.3?±?1.1?mg·L^–1, respectively, which were obviously superior to fosthiazate (49.1?±?2.8?mg·L^–1) and avermectin (26.6?±?2.3?mg·L^–1). Compound 21 can effectively control the citrus nematode disease caused by T. semipenetrans at 200?mg·L^–1 in vivo with (68?±?3)% inhibitory effect, which was even better than that of avermectin ((63?±?2)%). The CoMFA and CoMSIA models of three-dimensional quantitative structure-activity relationships (3D-QSARs) were established. The compound 33 was designed based on the 3D-QSAR models with more vigorous nematicidal activities in vitro (LC₅₀?=?9.8?±?1.4?mg·L^–1) and in vivo ((70?±?5)%). These results demonstrated that compound 33 can be considered as a potential nematicide.

Full text of DOI:10.1002/cjoc.201800282

Synthesis, nematicidal activity, and 3D-QSAR of novel
1,3,4-oxadiazole/thiadiazole thioether derivatives
Jixiang Chen,a Xiuhai Gan,a Chongfen Yi,a Shaobo Wang,a Yuyuan Yang,a Fangcheng He,a Deyu Hu,a and Baoan Song*,a
ABSTRACT Forty one novel 1,3,4-oxadiazole/thiadiazole thioether derivatives containing phenoxy moiety were designed and synthesized. Bioassay
demonstrated that some of them showed remarkable activities against Tylenchulus semipenetrans in vitro and in vivo. Compounds 20, 21, 35 and 39
showed excellent lethal activities after treatment for 48 h in vitro, with LC50 values of 13.4±1.8, 11.7±2.5, 13.7±2.4 and 13.3±1.1 mg L-1, respectively,
which were obviously superior to fosthiazate (49.1±2.8 mg L-1) and avermectin (26.6±2.3 mg L-1). Compound 21 can effectively control the citrus nema-
tode disease caused by T. semipenetrans at 200 mg L-1 in vivo with 68±3% inhibitory effect, which was even better than that of avermectin (63±2%). The
CoMFA and CoMSIA models of three-dimensional quantitative structure activity relationship (3D-QSAR) were established. The compound 33 was de-
signed based on the 3D-QSAR models with more vigorous nematicidal activities in vitro (LC50 = 9.8±1.4 mg L-1) and in vivo (70±5%). These results demon-
strated that compound 33 can be considered as a potential nematicide.
KEYWORDS 1,3,4-Oxadiazole/thiadiazole, Thioether derivatives, Nematicidal activity, Tylenchulus semipenetrans
activity was exhibited against T. semipenetrans. However, we are
eager to find efficient nematicides against T. semipenetrans. So,
Introduction
Plant parasitic nematodes have caused huge economic losses
of more than $ 150 billion per year in the world.[1] As one of the
most important plant parasitic nematodes, citrus nematode (Ty-
lenchulus semipenetrans) distributed in citrus rhizosphere and
can damage to root system, and then the absorption of water and
essential nutrients are hampered.[2] It can cause fearful symptom
to citrus when infected by citrus nematode, such as plant dwarf-
ing, foliage yellowing and wilting. Simultaneously, the citrus with
nematodes attacking is more susceptible to fungi and bacteria.[3,4]
In the past, nematodes are controlled primarily through
chemical nematicides, such as methyl bromid, methomyl, and
triazophos. However, some of them have been banned or re-
stricted not only due to high toxicity and residue, but also harm-
ful environment and human health.[5-7] To date, a few of com-
mercial nematicides are still used to control nematodes with the
rapidly rise resistance, such as fosthiazate and avermectin (Fig.
1).[8,9] Recently, some novel and highly effective nematicides (Fig.
1) have been put into the market, such as fluopyram,[10] fluensul-
fone,[11] and tioxazafen.[12] Chemical nematicides play an im-
portant role in the control of plant parasitic nematodes and the
relevant researches have never stopped all along.[13,14] However,
with the growth of human environment protection and health
awareness, the highly toxic nematicides are no longer adapting to
the green development of modern agriculture.[15,16] Therefore,
the development of efficient, low toxicity and environ-
ment-friendly nematicides have become an urgent goal in the
field of plant protection.
on the basis of our previous work, A and B two parts of the parent
structure were derived (Fig. 2). In part A, the rigid chain was re-
placed by introducing the oxygen-containing flexible chain groups
with potent insecticidal activity.[24] Furthermore, the diversified
structures were introduced into part B to instead of the trifluoro-
butenyl to obtain novel 1,3,4-oxadiazole/thiadiazole thioether
derivatives. Their nematicidal activities and three-dimensional
quantitative structure–activity relationship (3D-QSAR) were per-
formed. Compound 33 was designed and synthesized according to
the results of 3D-QSAR models with excellent nematicidal activity
against T. semipenetrans. It is the first reported on the in vitro and
in vivo nematicidal activities of 1,3,4-oxadiazole/thiadiazole thi-
oether derivatives containing oxygen-containing flexible chain
group against T. semipenetrans.
As one of important five-membered heterocyclic chemical
nematicides, fluensulfone has been put on the market successful-
ly with broad spectrum of nematicidal activities, and tioxazafen
has been served as seed treatment and plays a crucial part of the
protection of vegetables and fruits.[17,18] Meanwhile,
1,3,4-oxadiazole/thiadiazole are two known important class of
five-membered heterocyclic active groups, with high efficiency
and broad spectrum of biological activities, such as insecticidal,[19]
antifungal,[20] herbicidal,[21] anticancer activities.[22]
Figure 1 The major commercial nematicides in recent years.
The novel 1,3,4-oxadiazole/thiadiazole thioether derivatives
containing trifluorobuten moiety with good nematicidal activities
have been reported in our previous work,[23] and we found that
some 1,3,4-oxadiazole/thiadiazole derivatives showed good inhib-
itory activities against Caenorhabditis elegans, but the featureless
Figure 2 Design of target compound.
a State Key Laboratory Breeding Base of Green Pesticide and Agricultural Bioen-
gineering, Key Laboratory of Green Pesticide and Agricultural Bioengineering,
Ministry of Education, Center for Research and Development of Fine Chemi-
cals, Guizhou University, Guiyang 550025, China
*E-mail: songbaoan22@yahoo.com;
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been through the copyediting, typesetting, pagination and proofreading process, which
may lead to differences between this version and the Version of Record. Please cite this
article as doi: 10.1002/cjoc.201800282
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Table 1 Nematicidal activities of the target compounds (200 mg L−1)
against T. semipenetrans in vitroa
Results and discussion
Synthesis
24 h mortality 48 h mortality
(LC50/48 h
/mg L−1)b
Compd.
Forty one 1,3,4-oxadiazole/thiadiazole thioether derivatives
containing oxygen-containing flexible chain moiety were synthe-
sized and the synthetic routes were summarized in Scheme 1. All
target compounds were purified and obtained by crystallization in
ethanol or column chromatographed on a silica gel with yields of
/%
/%
1
58.2±2.1
72.5±1.8
64.6±3.1
52.1±1.2
58.3±1.4
78.2±2.1
62.3±1.7
84.3±3.4
34.5±1.1
39.1±3.4
31.3±1.1
33.5±1.4
79.2±2.6
80.4±2.1
25.6±1.4
22.4±2.2
13.2±1.5
40.3±2.3
15.4±0.5
90.4±1.2
95.6±0.2
71.4±0.8
83.5±3.1
30.3±2.8
33.9±3.7
41.4±1.4
52.3±2.5
25.9±2.9
31.6±2.6
22.3±2.2
31.5±1.7
22.4±1.9
98.2±1.6
86.1±2.3
93.3±1.0
53.1±2.5
21.1±2.7
87.3±1.3
94.7±1.0
44.4±3.7
52.7±3.9
53.3±1.6
71.8±1.2
72.6±2.6
86.6±2.1
74.2±2.8
68.4±1.2
73.8±2.1
86.5±2.5
75.5±1.0
96.5±1.3
60.2±1.6
68.7±2.9
42.2±1.6
46.2±1.9
90.6±0.5
93.2±2.4
51.4±0.5
34.3±2.5
28.3±2.0
62.2±0.1
31.8±1.6
100
42.7±4.6
21.5±3.1
31.8±2.6
60.1±1.5
57.5±1.4
28.1±2.4
37.9±2.6
18.8±3.7
103.1±3.7
53.6±2.9
276.9±3.7
247.2±2.8
21.1±2.3
24.2±1.2
129.9±2.6
370.6±4.1
613.8±3.9
103.8±2.6
426.2±3.9
13.4±1.8
11.7±2.5
26.4±1.7
22.4±1.4
132.4±3.7
101.7±3.1
93.6±3.9
51.9±2.7
238.9±3.5
142.4±3.7
259.0±2.4
175.3±3.5
387.7±4.3
9.8±1.4
2
3
42.3% to 78.6%. Their structures were confirmed by H NMR, 13C
1
4
NMR, IR, and HRMS, which were provided in the Supporting In-
formation.
5
6
Nematicidal activity
7
In vitro nematicidal activity The nematicidal activities of
compounds 1-41 against T. semipenetrans were evaluated. The
nematicidal effects of the target compounds in vitro were re-
vealed in Table 1. Exhilaratingly, some of the title compounds
emerged very excellent nematocidal activities. Compounds 8, 13,
14, 20, 21, 23, 33, 34, 35, 38 and 39 confirmed remarkable ne-
maticidal activities against T. semipenetrans at 200 mg L-1, with
the values of 96.5±1.3%, 90.6±0.5%, 93.2±2.4%, 100%, 100%,
91.3±2.2%, 100%, 95.3±1.8%, 98.4±0.9%, 95.6±1.2%, and 100%,
respectively, which were better than fosthiazate (72.5±1.4%) and
avermectin (87.3±2.2%) after treatment 48 h. The LC50 values of
compounds were tested and the results showed that compounds
2, 8, 13, 20, 21, 23, 33, 34, 35, 38 and 39 exhibited good nemato-
cidal activities against T. semipenetrans, with LC50 values of
21.5±3.1, 18.8±3.7, 21.1±2.3, 13.4±1.8, 11.7±2.5, 22.4±1.4,
9.8±1.4, 18.6±1.2, 13.7±2.4, 20.1±2.9, and 13.3±1.1 mg L-1, re-
spectively, which were better than the fosthiazate (49.1±2.8 mg
L-1) and avermectin (26.6±2.3 mg L-1).
In vivo nematicidal activities In order to determine the con-
trol efficiency of compound against T. semipenetrans in vivo, the
control efficiency of compounds 21 and 33 on the citrus nema-
tode disease caused by T. semipenetrans were carried out in
greenhouse at 200 mg L-1 and the results were concluded in Table
2 and Fig. 3. The results indicated that compounds 21 and 33
possessed potent inhibitory effect on citrus nematode disease at
40 days after pouring root, with the values of 68±3 % and 70±5 %,
respectively, which were superior to avermectin (63±2 %).
8
9
10
11
12
13
14
15
16
17
18
19
20
21
100
22
83.2±1.0
91.3±2.2
59.4±3.3
53.5±2.8
65.9±1.2
73.4±1.2
44.3±3.7
56.3±3.1
43.2±2.4
53.3±2.0
35.7±2.6
100
23
24
25
26
27
Table 2. Control efficacy of compounds 21 and 33 against T. semipene-
trans in vivoa.
28
29
Compd.
21
Concentration
200 mg L−1
200 mg L−1
200 mg L−1
Inhibitory%
68±3
30
31
33
70±5
32
33d
Avermectin
63±2
a Average of three replicates.
34
95.3±1.8
98.4±0.9
82.4±2.8
32.4±3.1
95.6±1.2
100
18.6±1.2
13.7±2.4
31.5±2.0
425.0±4.1
20.1±2.9
13.3±1.1
108.3±3.2
37.5±3.5
49.1±2.8
26.6±2.3
35
36
37
38
39
40
60.2±2.2
76.1±3.1
72.5±1.4
87.3±2.2
41
Fosthiazatec
Avermectinc
c
a Average of three replicates. b half-maximal effective concentration.
Figure 3 Nematicidal activities of compounds 21 and 33 under
greenhouse conditions at 200 mg L−1. A, B, C, and D were the negative
control, positive control (avermectin), compound 21, and compound 33
groups, respectively.
positive control. d The compound was designed based on the CoMFA and
CoMSIA models.
Table 3 Experimental and predicted results of pLC50 for CoMFA and
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CoMSIA
Compd.
ness and predictive ability of the models and the value of criteria
are q2 > 0.5 and r2 > 0.8.
Exp.b
3.750
4.073
3.984
3.726
3.621
3.956
3.769
4.098
3.449
3.754
3.070
3.138
4.078
4.042
3.260
2.876
2.691
3.463
2.902
4.281
4.364
4.041
4.132
3.330
3.391
3.456
3.784
3.120
3.330
3.151
3.359
2.961
4.462
4.139
4.297
4.029
2.911
4.133
4.334
3.474
3.990
Pred.c
3.808
4.013
3.580
3.785
3.692
3.897
3.738
3.931
3.488
3.702
3.010
3.223
4.060
4.260
3.278
2.564
2.666
3.405
2.879
4.207
4.381
4.038
4.140
3.440
3.487
3.341
3.612
3.148
3.355
3.363
3.363
2.982
4.415
4.189
4.413
4.002
2.945
4.044
4.226
3.814
3.975
Res.d
0.057
-0.059
-0.404
0.058
0.071
-0.059
-0.031
-0.168
0.038
-0.052
-0.060
0.085
-0.018
0.218
0.018
-0.311
-0.024
-0.057
-0.023
-0.074
0.017
-0.003
0.008
0.109
0.096
-0.115
-0.171
0.028
0.026
0.112
0.004
0.021
-0.047
0.050
0.117
-0.027
0.034
-0.089
-0.108
0.341
-0.015
Pred.e
3.797
4.027
3.480
3.714
3.666
3.905
3.708
3.938
3.496
3.732
2.970
3.198
4.033
4.269
3.242
2.478
2.651
3.498
2.908
4.155
4.367
4.060
4.160
3.405
3.479
3.452
3.735
3.089
3.323
3.277
3.399
2.975
4.457
4.198
4.369
4.063
2.958
4.057
4.205
3.908
3.915
Res. d
0.047
-0.046
-0.504
-0.012
0.045
-0.051
-0.061
-0.160
0.047
-0.022
-0.101
0.060
-0.045
0.227
-0.018
-0.398
-0.040
0.036
0.006
-0.126
0.003
0.019
0.028
0.074
0.088
-0.004
-0.049
-0.031
-0.007
0.127
0.039
0.013
-0.005
0.059
0.072
0.034
0.047
-0.077
-0.129
0.434
-0.075
As shown in Table 4, the q2, r2 and standard error of estimate
(SEE) of the CoMFA model were 0.722, 0.985 and 0.070, respec-
tively. The q2, r2 and SEE of the CoMSIA model were 0.634, 0.988,
and 0.065, respectively. These parameters indicate that the mod-
els have good predictive ability. The contributions of the steric
and electrostatic fields of the CoMFA model are 60.4% and 39.6%,
which suggest that steric distribution of the groups is a main fac-
tor on the nematicidal activity. While the steric, electrostatic,
hydrophobic, hydrogen bond donor and hydrogen bond acceptor
contribution of the CoMSIA model are 20.4%, 28.6%, 43.5%, 0.0%
and 7.6% respectively, which indicate that hydrophobic plays an
important role on nematicidal activity.
1
2
3a
4
5
6
7
8a
9
Table 4 Statistical parameters for the CoMFA and CoMSIA models
10
11
12
13
14a
15
16a
17
18
19
20a
21
22
23
24a
25
26
27a
28
29
30a
31
32
33f
34
35
36
37
38
39
40a
41a
CoMFA
model
CoMSIA
model
Validation
criterion
Statistical parameter
q2 a
ONC b
r2 c
SEE d
0.722
8
0.634
10
>0.5
>0.8
>100
0.985
0.070
171.087
0.988
0.065
157.050
F-value
Fraction of field contributions e
Steric
0.604
0.396
0.204
0.286
0.435
0.076
Electrostatic
Hydrophobic
H-bond acceptor
a
b
c
Cross-validated correlation.
Optimum number of components.
Non-cross-validated correlation. d Standard error of estimate. e Field con-
tributions: Steric, Electrostatic, Hydrophobic, H-bond acceptor.
a Sample of the testing set. b Experimental pLC50. c Predicted by CoMFA.
d
Relative error of (experimental predicted). e Predicted by CoMSIA. f The
compound was designed based on the CoMFA and CoMSIA models.
Figure 4 Plot of experimental and predicted pLC50 for the CoMFA and
CoMSIA models
Analysis of 3D-QSAR models
3D-QSAR models generation The CoMFA and CoMSIA models
of 3D-QSAR were generated based on bioactivities. The experi-
mental pLC50 values of the compounds in both the training and
testing sets were presented in Table 3 and the relevant results of
the models are listed in Table 4. The cross-validation coefficient q2
and the non-cross-validation coefficient r2 represent the robust-
The predicted activities of compounds were calculated using
CoMFA and CoMSIA models and the residuals of the actual values
and the predicted values were listed in Table 3 and the linearity of
them is illuminated in Fig. 4. As shown in Fig. 4, the correlation
coefficients R2 of the CoMFA and CoMSIA models are 0.9849 and
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0.9881, respectively, which indicate that the models have a good
correlation and further confirm that the CoMFA and CoMSIA
models have an excellent predictive ability.
Analysis of CoMFA and CoMSIA contour maps The CoMFA
and CoMSIA contour maps with the template molecule 21 were
generated. Green contours in the CoMFA steric field (Fig. 5A)
indicate that bulky groups would increase activities; On the con-
trary, yellow polyhedras illustrate regions where bulky groups
would decrease activities. The red polyhedras in the CoMFA elec-
trostatic field (Fig. 5B) demonstrate regions where electronega-
tive groups would increase activities, while blue polyhedras indi-
cate regions where electropositive groups would increase activi-
ties. It can be clearly seen in Fig. 5A that there is a yellow polyhe-
dra at the para position of benzene ring, indicating that it is suita-
ble to introduce a small substitution group at this position. There
is a big green polyhedra near R2 depicts that bulky groups are
favorable for activities in those regions, meanwhile there are
long-chain alkanes at R2 would increase the activities, which can
Figure
6
CoMSIA contour maps of steric (A), electrostatic (B),
hydrophobic (C), and H-bond acceptor fields (D)
Conclusions
Forty one 1,3,4-oxadiazole/thiadiazole thioether derivatives
containing oxygen-containing flexible chain moiety were synthe-
sized and their nematicidal activities against T. semipenetrans
were evaluated. Some compounds exhibited excellent nemati-
cidal activities. The CoMFA and CoMSIA models were constructed
by partial least-squares and compound 33 with good nematicidal
activity was designed and synthesized based on these models.
The results demonstrated this work offered an important struc-
tural insight for design of the nematicides in the future.
be explained with the activities order of compound 25 (R2
=
CH2CH3) > 15 (R2 = CH3), 10 (R2 = CH2CH3) > 9 (R2 = CH3), 29 (R2 =
CH2CH3) > 28 (R2 = CH3), and 39 (R2 = CH2CH3) > 38 (R2 = CH3). In
Fig. 5B, there are some blue polyhedras near R1 of benzene ring,
which reveal that the regions with electron-withdrawing groups
are beneficial to improve activity. For example, compounds 1 (R1 =
4-F), 20 (R1 = 4-Cl), and 18 (R1 = 4-Br) are more active than com-
pound 15 (R1 = 4-CH3), meanwhile compounds 2 (R1 = 4-F), 21 (R1
= 4-Cl), and 27 (R1 = 4-Br) are more active than compound 25 (R1 =
4-CH3).
Experimental
Chemicals and instruments
All reagents of analytical reagent grade were purchased from
commercial suppliers and without further purification in before
used. The progress of the reaction was monitored by thin layer
chromatography (TLC) on glass plates (silica gel GF254). Melting
points were determined by the WRX-4 microscopic melting point
apparatus (Shanghai Yice Appdraous ＆ Equipment Co., Ltd.
1
China) and uncorrected. H and 13C NMR (nuclear magnetic reso-
nance) spectras were measured on the JEOL-ECX-500 spectrome-
ter (JEOL, Tokyo, Japan) in CD3OD, CDCl3 or DMSO-d6 solvent with
TMS as internal standard. The IR spectras were recorded by using
KBr disks on the Bruker VECTOR 22 spectrometer (Bruker, Karls-
ruhe, Germany). High-resolution mass spectrometer (HRMS) data
were measured on the Thermo Scientific Q Exactive (Thermo,
USA).
Figure 5 CoMFA contour maps of steric (A) and electrostatic (B) fields
The steric, electrostatic, hydrophobic, and hydrogen bond ac-
ceptor contour maps of the CoMSIA model are demonstrated in
Fig. 6. Similarly, it is known that based on the steric field (Fig. 6A)
and electrostatic field (Fig. 6B) contour maps of CoMSIA model
with small electronegative groups at the para position of the
benzene ring and large groups on the R2 position are favorable for
biological activity. In the CoMSIA hydrophobic field (Fig. 6C), yel-
low polyhedras show that the regions with hydrophobic groups
are beneficial for activity, white polyhedra means with hydrophilic
groups is favorable for activity. There are yellow polyhedras at the
para position of benzene ring and R2 indicate that the activity of
compound with hydrophobic group is superior to that of the
compound with hydrophilic group. For example, 20 (R1 = 4-Cl) >
13 (R1 = 4-OCH3) and 21 (R1 = 4-Cl) > 14 (R1 = 4-OCH3). Fig. 6D is a
contour map of the hydrogen acceptor field, purple polyhedras
indicate hydrogen bond acceptors favor activity. There are hydro-
gen bond acceptors near to the para position of benzene ring and
R2 can increase biological activity. For example, compounds 3 and
4 with 4-OCF3 at R1 are more active than that of compounds 28
and 29 with 4-CF3.
Exhilaratingly, compound 33 was designed based on the
CoMFA and CoMSIA models by introducing the 4-Cl at R1 and the
propyl group at R2 and the activity was predicted by the 3D-QSAR
model, we found that the nematicidal activity of compound 33
was higher than other compounds. Then the compound 33 was
synthesized and its nematicidal bioactivity was evaluated. The
result showed that 33 had a good nematicidal activity in vitro and
in vivo.
General synthetic procedure
As shown in Scheme 1. Substituted phenols, ethyl chloroace-
tate (23.3 mmol), and potassium carbonate (35.0 mmol) in ace-
tonitrile (30 mL) at reflux temperature gave various ethyl
2-phenoxyacetates (1a −1p).[25,26] Ethyl 2-phenoxyacetates (12.0
mmol) was reacted with 80% hydrazine hydrate (13.2 mmol) in
ethanol
(30
mL)
to
afford
pure
substituted
2-phenoxyacetohydrazide (2a−2p).[27,28] Carbon disulfide (11.2
mmol) was dropwise added into the mixture of various
2-phenoxyacetohydrazide (7.5 mmol) and KOH (11.2 mmol) in
ethanol (20 mL), and refluxed for 8 h to 10 h. After the reaction
was completed and removed the solvent under reduced pressure.
Then, water was added and removed the precipitate by filtration
to afford yellowish transparent liquid. A variety of halide were
dropwise added into the liquid and kept the pH 8−9 by weak solu-
tion of NaOH. The reaction was stirred at room temperature for
1−5 h to gain the title compounds 1−33 by filtration or extraction.
Before to bear precipitate through filtration, the carbon disulfide
(11.2 mmol), substituted 2-phenoxyacetohydrazide (7.5 mmol)
and KOH (11.2 mmol) in ethanol (11.2 mmol) were stirred at
room temperature for 4 h, then precipitate was added into H2SO4
and stirred at 0−5 ℃ for 4−6 h. Upon completed of the reaction,
water was added in order to received residue, and the residue
was dissolved in weak solution of NaOH for keeping the pH 8−9 to
acquired yellowish transparent liquid. Then the target com-
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pounds 34−41 were received by the same way. The physical
nematodes were recorded by a stereoscopic binocular microscope,
and the nematicidal activities were evaluated according to the
death rates of tested nematodes. The nematodes were considered
as dead when their bodies were in a straight or prodded with a
needle. The LC50 values of target compounds were calculated by
using the probit method.[32]
1
characteristics of title compounds were determined by H NMR,
13C NMR, IR, and HRMS. The data of representative compound 33
was shown as below and the data for all compounds are shown in
Supporting Information.
2-((4-chlorophenoxy)methyl)-5-(propylthio)-1,3,4-oxadiazole
(33), White solid, yield, 70.1%; m.p. 31–32 °C; 1H NMR (500 MHz,
CD3OD) δ: 7.30–7.24 (m, 2H, Ph-H), 7.04–6.96 (m, 2H, Ph-H), 5.28
(s, 2H, -O-CH2-), 3.23–3.18 (t, 2H, J = 12.5 Hz, -S-CH2CH2CH3),
1.84–1.72 (m, 2H, -S-CH2CH2CH3), 1.03 (t, J = 7.3 Hz, 3H,
-S-CH2CH2CH3). 13C NMR (125 MHz, CD3OD) δ: 166.54, 163.79,
156.48, 129.23, 126.79, 116.25, 59.75, 33.91, 22.58, 11.90; IR (KBr)
ν: 3077, 2918, 1538, 1494, 1085, 1038, 823 cm-1; HRMS (ESI) calcd
for C12H14O2N2ClS [M+H]+ 285.04590, found 285.04538.
In vivo nematicidal activity Compounds 21 and 33 were dis-
solved with N,N-dimethylformamide (DMF) and diluted with
Tween 80 (1%) to obtain 200 mg L-1 concentration for bioassays.
The final concentration of DMF in each treatment never exceeded
1% (v/v). The 1-year-aged citrus trees saplings were replanted in
flowerpots (aseptic organic soil: aseptic sand = 1: 2, one sapling
per flowerpot; flowerpot size, 20×250 mm) and cultivated for 40
days in a greenhouse. Subsequently, the roots of each sapling
were treated with 100 mL of test solution. Avermectin as a posi-
tive control, and the test solution of lacking compound was used
as negative control. Then, approximately 2000 nematodes of ju-
venile were inoculated into the rhizosphere soil of each sapling.
Each treatment was replicated 3 times. All test flowerpots were
cultivated in the greenhouse again and kept consistent with
management of water and fertilizer. The T. semipenetrans galling
index was determined by digging the roots of plants and evaluat-
ing root damage using a 0−20 scale where 0 = no knots and 20 =
100% knots. The inhibition rates were calculated by comparison
to the negative control group.[33]
Inhibition rate (%) = [(score of negative control - score of
treatment) / (score of negative control)] ×100
Scoring criteria: 0, 0−5 knots; 5, 6−10 knots; 10, 11−20 knots;
and 20, more than 20 knots.
Study of 3D-QSAR models
Datasets for 3D-QSAR analysis In this study, thirty title com-
pounds were selected randomly as the training set, while the
remaining ten compounds as the testing set (labeled with foot-
note in Table 2). The biological activities of all compounds were
expressed as pLC50.
Molecular modelling and alignment SYBYL-X 2.1 (Tripos Inc.,
St. Louis, MO, USA) software was used to construct the 3D struc-
tures of all molecules, energy minimizations were performed us-
ing the Gasteiger–Huckelincrease charge, tripos force field and
Powell conjugate gradient algorithm with convergence criterion
and max iterations were 0.005 kcal mol-1 Å-1 and 10000, respec-
tively, the other parameters were used default settings.[34] Com-
pound 21 with the best nematicidal activity against T. semipene-
trans was used as common template molecule for CoMFA and
CoMSIA models study. The alignment result is shown in Fig. 7.
Scheme 1 Synthesis route of the target compounds
Nematicidal activity
Extraction and isolation of Nematodes According to the re-
ported method,[29,30] the soil samples were collected in a citrus
orchard of Guangxi Special Crop Research Institute in Guangxi
Province, China. The nematodes (mixture of juvenile and adult
nematodes) were obtained by a modified Baerman funnel meth-
od, and then, the juvenile suspensions of nematodes were pre-
pared by washing the sieve (325 mesh/inch) inversely to remove
adult nematodes to obtain a suspension.
In vitro nematicidal activities The nematicidal activity was
evaluated according to a modified method,[31] all pure title com-
pounds were dissolved with N,N-dimethylformamide (DMF) and
diluted with Tween 80 (1%) to obtain 200 mg L−1 concentration for
bioassays. The final concentration of DMF in each treatment nev-
er exceeded 1% (v/v). The test solution (500 μL) was added to
wells of 48-well plates. Subsequently, the suspension containing
approximately 200 nematodes of juvenile were introduced into
the wells, and these lids were covered to avoid evaporation or
pollution. Fosthiazate and avermectin were used as positive con-
trols, and the test solution of lacking compound was used as neg-
ative control. All test plates were incubated at 25 °C. Each treat-
ment and the entire experiment were repeated 3 times. The dead
Figure 7 The molecular alignment result of the target compounds
Partial least-squares (PLS) analysis The biological activities
and the structural characteristics of all molecules were associated
by using partial least-squares (PLS) analysis. Steric, electrostatic,
hydrophobic, hydrogen bond donor and hydrogen bond acceptor
potential fields were calculated by using a volume-dependent
lattice with a 2.0 Å grid spacing. Firstly, the Leave-One-Out meth-
od was applied to cross-validate the training set compounds to
determine the best principal component (ONC) and the predictive
ability of the model. Then the non-cross-validated regression was
calculated by using ONC. Lastly, the biological activities of all
compounds were predicted based on the CoMFA and CoMSIA
models.
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Supporting Information
The supporting information for this article is available on the
WWW under https://doi.org/10.1002/cjoc.2018xxxxx.
[19] Tok, F.; Kocyigit-Kaymakcioglu, B.; Tabanca, N.; Estep, A. S.; Gross,
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[20] Xu, W. M.; Han, F. F.; He, M.; Hu, D. Y.; He, J.; Yang, S.; Song, B. A. J.
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This work was financially supported by the National Key Re-
search Development Program of China (2018YFD0200100) and
the National Natural Science Foundation of China (No. 21672044)
and Subsidy Project for Outstanding Key Laboratory of Guizhou
Province in China (20154004).
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Entry for the Table of Contents
Page No.
Synthesis, nematicidal activity, and
3D-QSAR of novel 1,3,4-oxadiazole/ thiadi-
azole thioether derivatives
Jixiang Chen, Xiuhai Gan, Chongfen Yi,
Shaobo Wang, Yuyuan Yang, Fangcheng
He, Deyu Hu, and Baoan Song*
Compound 33 was designed based on the CoMFA and CoMSIA models, which exhibited
excellent nematicidal acivity against Tylenchulus semipenetrans better than avermectin
and fosthiazate.
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