Novel vanillin derivatives containing a 1,3,4-thiadiazole moiety as potential antibacterial agents

Article abstract of DOI:10.1016/j.bmcl.2020.127113

In this study, thirty-four novel vanillin derivatives containing a 1,3,4-thiadiazole structure were obtained and their antibacterial activities were evaluated. The results indicate that most of the title compounds displayed inhibitory effects on Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc). Among them, compound 29 exhibited excellent antibacterial activities against Xoo and Xoc in vitro, with the EC₅₀ values of 3.14 and 8.83 μg/mL, respectively, much superior to thiodiazole copper (87.03 and 108.99 μg/mL) and bismerthiazol (67.64 and 79.26 μg/mL). Under greenhouse condition, the protective efficiency of compound 29 against rice bacterial leaf blight was 49.34%, and curative efficiency was 40.96%. In addition, compound 29 can reduce the exopolysaccharides production of Xoo, increase the permeability of cell membrane and damage cell membrane.

Full text of DOI:10.1016/j.bmcl.2020.127113

Bioorganic&MedicinalChemistryLetters30(2020)127113
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel vanillin derivatives containing a 1,3,4-thiadiazole moiety as potential
antibacterial agents
Qiong Wu, Hui Cai, Ting Yuan, Shaoyuan Li, Xiuhai Gan⁎, Baoan Song⁎
State Key Laboratory Breeding Base of Green Pesticide and Agricultural Bioengineering, Key Laboratory of Green Pesticide and Agricultural Bioengineering, Ministry of
Education, Guizhou University, Huaxi District, Guiyang 550025, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study, thirty-four novel vanillin derivatives containing a 1,3,4-thiadiazole structure were obtained and
their antibacterial activities were evaluated. The results indicate that most of the title compounds displayed
inhibitory effects on Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc). Among
them, compound 29 exhibited excellent antibacterial activities against Xoo and Xoc in vitro, with the EC50 values
of 3.14 and 8.83 μg/mL, respectively, much superior to thiodiazole copper (87.03 and 108.99 μg/mL) and
bismerthiazol (67.64 and 79.26 μg/mL). Under greenhouse condition, the protective efficiency of compound 29
against rice bacterial leaf blight was 49.34%, and curative efficiency was 40.96%. In addition, compound 29 can
reduce the exopolysaccharides production of Xoo, increase the permeability of cell membrane and damage cell
membrane.
Vanillin
1,3,4-Thiadiazole
Antibacterial activity
Rice bacterial diseases
As one of important, indispensable food crops in the world, rice is
vulnerable to large number of pathogenic microorganisms during its
growth. Among them, rice bacterial leaf blight and leaf streak caused by
corresponding pathogenic bacteria Xanthomonas oryzae pv. oryzae (Xoo)
and Xanthomonas oryzae pv. oryzicola (Xoc)1–3 are two destructive
bacterial diseases, which cause serious reduction in production.4–6 At
present, only a handful of agrochemicals, such as thiodiazole copper,
zinc thiazole, bismerthiazol and zhongshengmycin are used to control
these bacterial diseases of rice.7,8 However, long-term use of these
traditional agricultural agents has resulted in increased resistance and
brought environmental pollution.9,10 Therefore, it is still a daunting
challenge in management of rice bacterial diseases to develop new,
highly-effective, low-toxicity, and environmentally-friendly anti-
bacterial agents.
bioactivity, including antimicrobial,25 antifungal,26 insecticidal,27 an-
tiviral,28 anticancer,29 herbicidal.30 Notably, 1,3,4-thiadiazole moiety
is an effective antibacterial group and was used to development for
antibacterial agents, such as thiodiazole copper and bismerthiazol. In
our previous works, we found that 1,3,4-thiadiazole derivatives ex-
hibited outstanding antibacterial activities.8,10,31 Based on these, we
aimed to introduce 1,3,4-thiadiazole moiety into the skeleton of va-
nillin (Fig. 1) to obtain some novel vanillin derivatives (Schemes 1 and
2), and evaluate their antibacterial activities against Xoo and Xoc.
Meanwhile, the preliminary mechanism of action was performed in this
work.
The title compounds were synthesized via the route outlined in
Scheme 1 and 2. As shown in Scheme 1, using different amine com-
pounds as reactant, through substitution, etherification, condensation
and reduction to obtain the title compounds 1–9. As shown in Scheme
2, the title compounds 10–18 were obtained using the vanillin as in-
itiation, through substitution, condensation and reduction reaction, and
further substitution to obtain the title compounds 19–26. Finally, the
target products 27–34, with yield 20.1%–77.6%, were obtained suc-
cessively by oxidation of corresponding compounds 19–26. The
synthesis and characteristic of the title compounds were shown in
Supplementary Data.
Natural products always are important leading source for develop-
ment of pesticide with a wide range of bioactivity and security.11–13
Vanillin is a natural product from the pods of an orchid (Vanilla plani-
folia), as a secure food additive, it is widely used in food, nutraceutical,
beverage and pharmaceutical industry.14,15 Simultaneously, vanillin
and its derivatives possess a wide range of bioactivity, such as anti-
microbial,16 antifungal,17 anti-inflammatory,18 antioxidant,19 anti-alz-
heimer's,20 anticancer,21 antihelminthic,22 antiviral,23 and so on.
Meanwhile, we found that vanillin derivatives exhibited outstanding
antibacterial activities (Fig. 1).24 In addition, 1,3,4-thiadiazoles are
important five-membered heterocyclic compounds with a variety of
The bioassay results indicated that most compounds showed good
antibacterial activities against Xoo and Xoc (Table 1). Of which, com-
pounds 12, 14, 17, 18, 27, 28, and 29 had excellent inhibitory
⁎ Corresponding authors.
E-mail addresses: xhgan3@gzu.edu.cn (X. Gan), basong@gzu.edu.cn (B. Song).
https://doi.org/10.1016/j.bmcl.2020.127113
Received 21 January 2020; Received in revised form 11 March 2020; Accepted 14 March 2020
Availableonline16March2020
0960-894X/©2020ElsevierLtd.Allrightsreserved.

Q. Wu, et al.
Bioorganic&MedicinalChemistryLetters30(2020)127113
Fig. 1. Design of title compounds.
Scheme 1. The synthetic route of the title compounds 1–9.
Scheme 2. The synthetic route of the title compounds 10–34.
activities against Xoo, with the EC50 values of 38.74, 33.73, 33.25,
31.78, 16.03, 28.47, and 3.14 μg/mL, respectively, which were much
better than thiodiazole copper (87.03 μg/mL) and bismerthiazol
(67.64 μg/mL). Meanwhile, compounds 17, 18, 27, 28 and 29 had
excellent inhibitory activity against Xoc, with the EC50 values of 35.49,
26.54, 27.69, 36.47 and 8.83 μg/mL, respectively, superior to
2

Q. Wu, et al.
Bioorganic&MedicinalChemistryLetters30(2020)127113
Table 1
The antibacterial activities of the title compounds against Xoo and Xoc in vitro.a
Compound
Xoo
Xoc
50 μg/mL (%)
EC50 (μg/mL)
50 μg/mL (%)
EC50 (μg/mL)
1
49.15
45.15
48.31
57.80
49.17
35.99
54.71
52.79
62.60
46.18
33.82
58.15
59.47
63.40
39.09
32.92
69.08
68.97
31.46
30.90
45.59
13.85
13.51
15.42
22.41
23.64
85.93
72.93
90.05
51.60
60.84
55.79
55.34
44.20
40.61
31.92
5.69
2.99
3.46
2.26
3.93
2.10
1.51
0.64
2.10
1.69
0.67
0.72
0.69
2.06
1.67
2.90
1.13
4.53
3.63
3.30
2.30
1.65
3.16
3.93
4.95
1.64
1.52
2.40
1.63
2.33
2.21
2.16
3.75
1.21
2.49
1.94
51.02
55.9
5.54
4.20
2.05
2.85
53.38
41.22
40.33
56.31
36.68
41.90
45.58
50.55
58.32
40.07
34.56
51.09
53.20
56.23
31.83
42.10
57.40
64.47
24.96
19.40
47.51
14.32
14.07
20.73
24.64
22.84
79.65
65.80
81.42
44.00
51.20
45.80
57.28
49.72
37.19
31.98
3.18
2.37
1.53
3.00
1.71
3.51
2.76
2.52
1.76
1.29
1.13
0.25
1.46
2.23
1.68
1.20
2.94
3.49
1.99
1.84
2.72
1.08
1.44
1.58
1.05
1.26
0.50
3.11
0.96
1.67
2.20
2.29
1.74
1.18
2.05
2.96
51.81
63.50
62.12
42.53
86.29
64.08
72.13
47.62
45.80
60.72
77.23
46.97
48.17
40.23
89.66
65.66
35.49
26.54
107.15
118.91
61.20
163.17
167.98
176.67
140.29
147.33
27.69
36.47
8.83
2.21
2.86
6.22
4.15
4.78
2.09
1.90
2.68
3.11
1.61
1.67
1.96
2.76
1.10
0.76
1.05
1.29
3.30
2
3
54.78
40.6
4
5
47.78
95.37
51.73
48.63
44.45
51.34
78.94
38.74
40.52
33.73
88.08
80.52
33.25
31.78
100.39
107.8
61.66
190.41
182.31
175.29
138.08
143.93
16.03
28.47
3.14
2.10
3.13
0.89
2.17
2.24
2.04
2.24
2.16
2.57
2.16
2.16
3.38
1.14
2.22
6
7
8
9
10
11
12
13
14
15
16
17
18
19
4.57
3.35
1.97
20
4.08
4.72
21
0.47
22
12.21
2.59
2.04
1.38
2.21
3.35
23
3.67
2.97
3.84
3.15
24
25
26
27
1.04
1.30
1.40
28
3.65
0.95
29
1.53
30
51.83
31.13
41.31
44.66
59.56
67.64
87.03
2.98
1.24
1.01
4.35
1.93
2.36
2.88
70.02
44.20
66.12
44.59
61.33
79.26
108.99
2.30
2.25
2.13
0.87
1.66
2.66
31
32
33
34
b
Bismerthiazol
b
Thiodiazole copper
2.80
aAverage of three replicates. bCommercial bactericides bismerthiazol and thiodiazole copper were utilized as positive control agents.
Table 2
Curative and protective activities of compound 29 against rice bacterial leaf blight under at 200 μg/mL in vivo (14 days after spraying).
Treatments
Protective effect
Curative effect
Disease index (%)a
Control efficiency (%)b
Disease index (%)a
Control efficiency (%)b
29
40.93
34.81
43.33
81.11
2.41
0.74
1.11
3.33
49.34
56.97
46.43
7.14
3.79
5.05
46.11
40.37
43.70
78.15
0.79
0.52
1.05
3.67
40.96
48.30
43.98
1.76
1.75
3.97
Bismerthiazol
Thiodiazole copper
Negative control
a
b
Disease index, which is a comprehensive indicator of the overall incidence and severity.
Statistical analysis was conducted by the analysis of variance method.
thiodiazole copper (108.99 μg/mL) and bismerthiazol (79.26 μg/mL).
(–CH2CH3). Compared with the same substituent on vanillin and R2, S
was replaced with S(O)2 can significantly enhance the antibacterial
activities, for example compound 27 > 19, 28 > 20, 29 > 21,
which revealed that the activity of sulfone compound is better than that
of the corresponding thioether compound. It maybe that sulfone com-
pounds with privileged structure can react covalently32–34 or form H-
bond35 with the active sites of certain proteins, and show promising
antibacterial active.
Among the target compounds, compound 29 exhibited the best in-
hibitory activities against Xoo and Xoc, and superior to thiodiazole
copper and bismerthiazol.
The structure and activity relationships were explored on the basis
of the inhibitory activity values in Table 1. When title compounds are
thiol derivatives, changing substituent on vanillin (R or R1) did not
cause significant effects on antibacterial activity, such as compounds
1–18. When H was replaced with alkyl at the R2 substituent group
caused significantly reduced their antibacterial activities, that is to say
the antibacterial activity of thiol derivative is better than that of cor-
Compound 29 exhibited the best antibacterial activities in vitro, so,
the in vivo inhibitory effect of the compound 29 on rice leaf blight
caused by Xoo was evaluated under greenhouse condition. The results
showed that compound 29 demonstrated good controlling effect against
rice bacterial leaf blight under greenhouse condition. The protective
and curative efficiency was 49.34% and 40.96% at the concentration of
responding thioether derivative, such as compound 14 (-H)
> 23
(–CH3) and 24 (–CH2CH3); 17 (–H) > 19 (–CH3), 20 (–CH2CH3), 21
(–CH2CHCl) and 22 (4-Cl-Benzyl); 18 (–H) 25 (–CH3) and 26
>
3

Q. Wu, et al.
Bioorganic&MedicinalChemistryLetters30(2020)127113
Fig. 2. Protective effect of compound 29 against rice bacterial leaf blight at 200 μg/mL.
Fig. 3. Curative effect of compound 29 against rice bacterial leaf blight at 200 μg/mL.
200 μg/mL, respectively (Table 2, Fig. 2 and Fig. 3), as well as com-
mercial agents thiodiazole copper (46.43% and 43.98%), and bis-
merthiazol (56.97% and 48.30%).
inhibited the production of exopolysaccharides at the concentration of
50, 25, and 5 μg/mL, with rates of 85.7%, 54.6% and 24.4%, respec-
tively, which can weaken the pathogenicity of Xoo.
Exopolysaccharides are not only a barrier to resist adverse external
conditions, but also one of the vital virulence factors of Xoo.36 The ef-
fect of compound 29 on the exopolysaccharides of Xoo was tested and
the result was shown in Fig. 4A. The results showed that compound 29
The effect of compound 29 on the cell membrane permeability of
Xoo was shown in Fig. 4B. After treatment with compound 29, the re-
lative permeability of Xoo’s cell membrane increased following time
and concentration. Especially, the relative permeability increases
4

Q. Wu, et al.
Bioorganic&MedicinalChemistryLetters30(2020)127113
Fig. 4. A: changes in the exopolysaccharides production, B: cell membrane permeability.
Fig. 5. Scanning electron microscopy images for Xoo after treatment with the compound 29 at the concentrations of 5, 25, and 50 μg/mL.
quickly within the first 120 min after treatment, and increases slowly
from 150 to 300 min. After treatment for 300 min at concentrations of
50, 25, and 5 μg/mL, the corresponding relative permeability was
21.32%, 20.59%, and 15.94%, respectively, which were higher than
that of negative control (12.38%). This result indicated that compound
29 may damage the cell membrane of Xoo, cause electrolyte leakage of
intracellular, thereby causing cell weakness or apoptosis.
Acknowledgements
The authors are grateful to the National Key Research Development
Program of China (2018YFD0200100) and the National Natural Science
Foundation of China (21672044) and Program of Introducing Talents of
Discipline to Universities of China (111 Program, D20023) for the fi-
nancial support.
The surface morphology of Xoo treated with compound 29 was
observed by scanning electron microscope (Fig. 5). The cells of the
negative control were intact and had no wrinkles on the surface. After
treatment with compound 29, the cell surface was wrinkled. With the
increase of the concentration of the compound, the cells deform, even
shrivel and rupture. So, compound 29 may damage Xoo's cell mem-
brane, causing Xoo to be unhealthy or apoptotic, which is the primary
reason of this compound exhibited excellent antibacterial activity in
vitro.
Appendix A. Supplementary data
Materials and Methods, 1H and 13C NMR spectra, and HRMS can be
found in the Supplementary Data. Supplementary data to this article
can be found online at https://doi.org/10.1016/j.bmcl.2020.127113.
References
In summary, thirty-four novel vanillin derivatives containing a
1,3,4-thiadiazole moiety were constructed, and their antibacterial ac-
tivities were systematically evaluated. Compound 29 demonstrated the
best inhibitory to Xoo and Xoc in vitro, much better than that of com-
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Meanwhile compound 29 exhibited good protective and curative effects
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