Microwave assistant one pot synthesis, crystal structure, antifungal activities and 3D-QSAR of novel 1,2,4-triazolo[4,3-a]pyridines

Article abstract of DOI:10.1111/cbdd.12323

A series of novel 1,2,4-triazolo[4,3-a]pyridines were synthesized, and their structures were characterized by ¹H NMR, MS, elemental analysis, and single-crystal X-ray diffraction analysis. The antifungal activities were evaluated. The antifungal activity results indicated that the compound 2b, 2g, 2p, and 2i exhibited good activities. The activity of compound 2b, 2g, 2p, and 2i can compare with the commercial pesticide. The 3D-QSAR model was developed using CoMFA method. Both the steric and electronic field distributions of CoMFA are in good agreement in this work and will be very helpful in designing a new set of analogues. A series of novel 1,2,4-triazolo[4,3-a]pyridines were synthesized. The antifungal activity results indicated that the compounds 2b, 2g, 2p, and 2i exhibited good activities. The activity of compounds 2b, 2g, 2p, and 2i can compare with the commercial pesticide. The 3D-QSAR model was developed using CoMFA method.

Full text of DOI:10.1111/cbdd.12323

Chem Biol Drug Des 2014; 84: 342–347
Research Article
Microwave Assistant One Pot Synthesis, Crystal
Structure, Antifungal Activities and 3D-QSAR of Novel
1
,2,4-Triazolo[4,3-a]pyridines
1
,
1
1
Xing-Hai Liu *, Zhao-Hui Sun , Ming-Yan Yang ,
properties, 1,2,4-triazole fungicides become one of the
focuses in drug research (4).
1
1
Cheng-Xia Tan , Jian-Quan Weng , Yong-Gang
Zhang * and Yi Ma
2
,
3
Furthermore, pyridine derivatives also displayed various
biological activities (5), such as antimalarial activity (6),
anticancer activity (7), anti-inflammatory activity (8), COX-2
inhibitor activity (9), and so on. Meanwhile, many commer-
cial fungicides contain pyridine group, such as fluopico-
lide, boscalid, fluazinam, pyridinitril. Fused heterocyclic
compounds often display two heterocycles’ function. The
incorporation of pyridine ring into triazole ring was proved
to be a good way to produce novel active compounds
(10).
1
College of Chemical Engineering and Materials Science,
Zhejiang University of Technology, Hangzhou 310014,
China
Biology Institute of Shandong Academy of Science, Jinan
50014, China
2
2
3
State-Key Laboratory of Elemento-Organic Chemistry,
National Pesticidal Engineering Centre (Tianjin), Nankai
University, Tianjin 300071, China
*Corresponding authors: Xing-Hai Liu, xhliu@zjut.edu.cn;
Yong-Gang Zhang, zhangyg@sdas.org
A series of novel 1,2,4-triazolo[4,3-a]pyridines were
In our previous work, some interesting 1,2,4-triazole
compounds were synthesized and they exhibited diver-
sity biological activities (11–14).Some compounds
showed good ketol-acid reductoisomerase (KARI) inhibi-
tor activity or fungicidal activities. In view of all these
facts and as continuation of our research on bioactive
heterocycles, herein, a series of novel 1,2,4-triazolo[4,3-
a]pyridine were synthesized and their fungicidal activities
were investigated. The preliminary biological tests
showed that some compounds exhibited significant fun-
gicidal activities.
synthesized, and their structures were characterized
1
by H NMR, MS, elemental analysis, and single-crystal
X-ray diffraction analysis. The antifungal activities
were evaluated. The antifungal activity results indi-
cated that the compound 2b, 2g, 2p, and 2i exhibited
good activities. The activity of compound 2b, 2g, 2p,
and 2i can compare with the commercial pesticide.
The 3D-QSAR model was developed using CoMFA
method. Both the steric and electronic field distribu-
tions of CoMFA are in good agreement in this work
and will be very helpful in designing a new set of ana-
logues.
Experiment
Key words: 1,2,4-triazolo[4,3-a]pyridine, 3D-QSAR, antifungal
activities, Microwave assistant synthesis
General procedure
Preparation of 2a: A CEM designed 10-mL pressure-
rated vial was charged with POCl3 (2 mL), 3-chloro-2-hy-
drazinylpyridine (143 mg, 1 mmol), and 4-isopropylbenzo-
ic acid (1 mmol). The mixture was irradiated in a CEM
Discover Focused Synthesizer (150 W, 140 °C, 200 psi,
15 min). The mixture was cooled to room temperature by
passing compressed air through the microwave cavity for
2 min. It was poured into cold ice (40 mL) and the
formed precipitate filtered. The crude solid was recrystal-
lized from EtOH to give the title compounds 2a. All the
other compounds were synthesized according the same
procedure.
Received 30 December 2013, revised 25 February 2014 and
accepted for publication 4 March 2014
As in recent years, nitrogen heterocyclic compounds
received considerable attention in recent times because of
their medicinal and pesticidal importance (1). Triazole
derivatives often exhibited broad biological activities in
medicine and agriculture (2). Fluconazole, itraconazole,
miconazole, econazole, ketoconazole, diniconazole, tria-
dimefon, triadimenol, flusilazole, etc. have been developed
as commercial fungicides (Figure S1). These fungicides are
one of the important categories of fungicides because of
its excellent protective, curative, and unique of mechanism
of action and broad spectrum (3). Due to their diverse
The physical–chemical data, crystal data, 3D-QSAR
method, and bioassay method were recording in support-
ing information.
3
42
ª 2014 John Wiley & Sons A/S. doi: 10.1111/cbdd.12323

1,2,4-Triazolo[4,3-a]pyridines with Antifungal Activities
Scheme 1: The synthetic route of title compounds.
Results and Discussion
Synthesis
The synthesis procedures for compound 2 are shown in
Scheme 1. In the literature (15–17), these methods often
contain two steps: first, intermediates (hydrazide or hydraz-
one) were synthesized; then, fused 1,2,4-triazoleheterocy-
cles were prepared via catalyst or catalyst free. The one pot
cyclization reaction of hydrazide with substituted acid in
POCl under microwave irradiation led to novel 1,2,4-triazolo
3
[4,3-a]pyridines. After the reaction was completed, the purifi-
cation of these compounds is easy. Also, the conventional
method had been employed in this experiment. From the
Table 1, the yield of microwave synthesis is higher than that
of conventional method, and the reaction time is shorter.
1
Compound 2 was identified by H NMR, FTIR, and EI-MS
Figure 1: The single crystal of compound 2i.
1
spectra. In the H NMR spectra of title compounds, the
CH proton signals of pyridine structure of title compounds
were obvious. The mass spectra of 1,2,4-triazolo[4,3-a]
pyridines 2 showed molecular ion peak. The measured
elemental analyses were also consistent with the corre-
sponding calculated ones.
Table 2: Antifungal activity of some target compounds
Compounds
PP
66
SS
26
RS
2a
37
56
67
49
57
25
62
64
42
37
57
72
49
2
2
2
2
2
2
2
b
d
f
24
19
31
59
100
54
19
22
43
51
5
0
0
33
33
100
30
0
16
23
23
0
Crystal structure
g
i
The structure of compound 2i was further confirmed by
single-crystal X-ray diffraction analysis (Figure 1). In the
molecular structure of title compound, the two rings (ben-
zene ring and heterocyclic ring) are of h angle of 40.8°.
The molecular structure is stabilized by C3-H3. . .Cl1 inter-
action into a one-dimensional chain in the bc plane. Mean-
while, intermolecular edge-to-face p–p stacking appears
between the t-Bu group of phenyl ring and the heterocy-
clic ring in another adjacent molecule, in which the
j
l
2m
2n
2o
2
2
p
s
14
62
PP, Physalospora piricola; SS, Sclerotinia sclerotiorum; RS, Rhi-
zoctonia solanii.
distance of H14C and the centroid of heterocyclic ring is
ꢀ
3
.715 A. The average bond lengths and bond angles of
the phenyl ring (18,19), the triazole ring (20), and pyridine
ring (21) are normal.
Antifungal activities
Antifungal Activity for Phyllosticta Pirina.,
Sclerotinia sclerotiorum, Rhizoctonia solanii
The fungicidal results of 1,2,4-triazolo[4,3-a]pyridines 2a–
2u at 50 lg/mL against Phyllosticta Pirina., Sclerotinia
sclerotiorum, Rhizoctonia solanii are listed in Table 2. The
EC50 value of compound 2i was estimated and the result
is given in Table 3.
Table 1: Comparison of yields of 2a through methods with or
without microwave irradiation
No.
Method
Time/h
Temperature/°C
Yield/%
2
2
a
a
Heat
MW
6
0.25
Reflux
140
85
92
Chem Biol Drug Des 2014; 84: 342–347
343

Liu et al.
As shown in Table 2, compounds 2a, 2g, 2i, 2j, and 2o
exhibited moderate inhibition effect against Phyllosticta
Pirina. Specifically, compound 2i showed excellent inhibi-
tion (100%) against Phyllosticta Pirina. Surprisingly, com-
pound 2i possessed excellent inhibition rates 100%
against Sclerotinia sclerotiorum, while all of other com-
pounds were less effective against Sclerotinia sclerotio-
rumat 50 lg/mL. Compound 2s displayed 62.5%
inhibitory against Sclerotinia sclerotiorumat 50 lg/mL.
Compounds 2b, 2d, 2f, 2g, 2o, 2p, and 2s held 49–71%
inhibitory rates against Rhizoctonia solanii at 50 lg/mL.
Antifungal Activity for Fusarium oxysporum,
Fusarium nivale, Aspergillus fumigatus and
Candida albicans
The antifungal activity results of 1,2,4-triazolo[4,3-a]pyridines
2a–2s at 20 lg/mL against Fusarium oxysporum, Fusarium
nivale, Aspergillus fumigatus (FGSCA1100), and Candida
albicans (ATCC 10231) are listed in Table 4. The IC50 values
of compounds 2b, 2g, and 2p are presented in Table 5.
From the Table 5, all the compounds exhibited low inhibi-
tion effect against Fusarium oxysporum, Fusarium nivale,
Aspergillus fumigatus, and Candida albicans. Surprisingly,
compound 2b displayed moderate inhibition rate (49.8%)
against Fusarium nivaleat 20 lg/mL. For Aspergillus fumig-
atus, it was found that compound 2g and 2p also exhibited
moderate activity and held 57.97% and 66.76% inhibitory
rates at 20 lg/mL, respectively. Therefore, the IC50 values
of compound 2b, 2g, and 2p were determined and the
commercial product ketoconazole and tricyclazole were
used as control. It was found that the IC50 values of com-
pound 2b, 2g, and 2p against Aspergillus fumigates are
On the basis of the preliminary bioassays, the compound
2
i was selected for further bioassay at lower dose (EC50).
The subsequent results in Table 3 showed that the tested
compounds had good antifungal activity against Alternaria
solani, Sclerotinia sclerotiorum, Botrytis cinerea, with EC50
values of 2.41, 11.45, and 25.49 lg/mL, respectively. The
EC50 results showed that it was compared with the com-
mercial drug tricyclazole.
3
7.46 Æ 2.91, 14.58 Æ 0.79, and 11.86 Æ 1.04 lg/mL,
respectively, while the IC50 values of ketoconazole against
Aspergillus fumigates are 3.03 lg/mL. These results indi-
cated that compound 2b, 2g, and 2p displayed compara-
ble antifungal activity with ketoconazole against Aspergillus
fumigatus. However, the results in Table 5 indicate that the
fungicidal activities against Fusarium oxysporum, Fusarium
nivale of the compound 2b, 2g, and 2p were significantly
low compared with that of the corresponding commercial
products and ketoconazole from the values of IC50, but it is
comparable with the tricyclazole.
Table 3: Antifungal activity as EC50 (lg/mL) of the target com-
pound 2i
EC50 (lg/mL)
Compound
AS
SS
BC
2
i
2.41
–
11.13
11.45
6.91
25.49
Tricyclazole
AS, Alternaria solani; SS, Sclerotinia sclerotiorum; BC, Botrytis
cinerea.
CoMFA analysis
CoMFA method is widely used in drug design, because it
allows for rapid prediction of QSAR of newly designed
molecules (22). The results of these computations are
summarized in Table 6.
Table 4: The antifungal activity of title compounds at 20 lg/mL
No.
FO
FN
AF A1100
CA
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
a
b
c
d
e
f
10.64
22.53
34.19
10.54
4.61
10.12
À1.78
6.54
25.11
49.80
0.00
7.23
0.00
4.08
0.00
0.00
18.96
0.00
À2.54
20.38
6.63
22.02
47.80
11.70
17.92
25.40
13.53
19.68
8.05
31.30
7.17
12.57
28.77
7.73
16.35
43.10
14.69
3.46
14.34
5.50
The CoMFA contour models are very similar, suggesting that
for this training set, using four components is acceptable.
Experimental and predicted activities by CoMFA for all com-
pounds are listed in Table 7 in supporting information. As
shown in Table 6, a predictive CoMFA model was estab-
0.00
21.42
26.14
57.97
7.87
14.34
24.30
12.30
13.81
6.37
25.22
66.76
11.42
3.81
g
h
i
2
lished with the conventional correlation coefficient r = 0.875
7.69
2
and the cross-validated coefficient q = 0.58. It is shown in
j
15.93
13.56
10.80
11.70
34.87
8.88
Figure S3 that the contributions of steric and electrostatic
fields (‘stdev*coeff’) are 67.6% and 32.4%, respectively.
k
l
0.00
39.75
11.13
2.39
38.64
À2.98
0.00
m
n
o
p
q
r
With the CoMFA analysis, we obtained the isocontour dia-
grams of the steric and electrostatic field contributions
8.36
(‘stdev*coeff’), which is displayed in Figure 2. The plots of
11.68
22.10
9.20
the predicted versus the actual activity values for all the com-
pounds are shown in Figure S2. In Figure 2A, the steric field
contours are represented with different colors: the green
color at 3- or 4-position means a bulky group here would be
favorable for higher antifungal activity, while the yellow color
0.00
29.79
4.55
À1.35
s
FO, Fusarium oxysporum; FN, Fusarium nivale; AF, Aspergillus
fumigates; CA, Candida albicans.
3
44
Chem Biol Drug Des 2014; 84: 342–347

1,2,4-Triazolo[4,3-a]pyridines with Antifungal Activities
Table 5: The IC50 of compound 2b, 2p, 2g (lg/mL)
No.
CA
AF
FO
FN
2
2
2
b
g
p
26.12 Æ 1.18
–
37.46 Æ 2.91
14.58 Æ 0.79
11.86 Æ 1.04
3.03
48.46 Æ 1.65
–
42.58 Æ 1.02
–
26.12 Æ 1.98
35.30 Æ 0.58
43.28 Æ 1.33
Ketoconazole
Tricyclazole
4.19 Æ 0.01
9.91
16.00
38.17 Æ 0.08
19.18 Æ 0.46
Table 6: Summary of CoMFA Analysis
Contributor (%)
Steric
2
2
q
r
S
F
No.
Electrostatic
32.4
CoMFA
0.58
0.875
0.301
101.691
2a
67.6
A
the antifungal activity. This is in agreement with the actual
experimental data: for example, compounds 2a, 2b, 2e, 2i,
and 2o all have higher antifungal activity with a bulky group in
this position. In the same Figure 2B, the electrostatic con-
tours are displayed in distinguishable colors: blue means an
increase in the positive charge will lead to an increase in the
activity, while the red contour defines in the opposite. So, the
target compounds bearing an electron-withdrawing group at
the 2-position or 3-position of the benzene ring and an elec-
tron-donating group at the other positions displayed higher
activity. These results provided useful information for further
optimization of the compounds.
Conclusion
The 1,2,4-Triazolo[4,3-a]pyridines were synthesized under
microwave irradiation. And these compounds have exhib-
ited promising antifungal activity. The 3D-QSAR model
developed using CoMFA exhibits good statistical signifi-
cance with all values in an acceptable range. The results
indicate that the steric bulky substitution at the para posi-
tion of phenyl ring or the electron-withdrawing group at
the 2-position or 3-position of the benzene ring is required
for good antifungal activity. The 3D-QSAR experiment has
provided us crucial information, which will be very helpful
in designing a new set of analogues.
B
Acknowledgment
This research was supported in part by National Natural
Science Foundation of China (No. 21002090, 31000008),
The Key Innovation Team of Science and Technology in
Zhejiang Province (2010R50018-06) and the National Key
Technologies R&D Program (2011BAE06B03-01).
Figure 2: Steric and Electrostatic contribution contour maps of
CoMFA.
means oppositely. As shown in Figure 2A, there is a green
region located around the 4-position of the benzene ring,
indicating that the bulky groups at this position will increase
Conflict of Interest
The authors declare no competing financial interest.
Chem Biol Drug Des 2014; 84: 342–347
345

Liu et al.
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Chem Biol Drug Des 2014; 84: 342–347

1,2,4-Triazolo[4,3-a]pyridines with Antifungal Activities
Figure S4 Superposition modes of compounds.
Figure S2 CoMFA predicted as experimental pED values.
Figure S3 The asterisk skeleton of title compounds.
Table S1 The structures, activities, and total score of
compounds.
Chem Biol Drug Des 2014; 84: 342–347
347