First Discovery of Novel Pyrido[1,2- a]pyrimidinone Mesoionic Compounds as Antibacterial Agents

Article abstract of DOI:10.1021/acs.jafc.9b03606

Plant bacterial diseases cause tremendous decreases in crop yield and quality, and there is a lack of highly effective and low-risk antibacterial agents. A series of novel pyrido[1,2-a]pyrimidinone mesoionic compounds containing vanillin moieties were synthesized, and the application of these mesoionic compounds as plant antibacterial agents was reported here for the first time. The bioassay results revealed that the mesoionic compounds had good antibacterial activity. Of these compounds, compound 11 showed excellent in vitro activity against Xanthomonas oryzae pv. oryzae, with an EC₅₀ value of 1.1 μg/mL, which was substantially better than that of bismerthiazol (92.7 μg/mL) and thiodiazole copper (105.4 μg/mL). Moreover, greenhouse condition trials indicated that the protective and curative activities of compound 11 against rice bacterial leaf blight were 75.12 and 72.04%, respectively, which were better than those of bismerthiazol (62.24 and 50.83%, respectively) and thiodiazole copper (53.35 and 65.04%, respectively). These results provide a basis for the application of mesoionic vanillin moieties as new antibacterial agents.

Full text of DOI:10.1021/acs.jafc.9b03606

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Agricultural and Environmental Chemistry
First Discovery of Novel Pyrido[1,2-a] Pyrimidinone
Mesoionic Compounds as Antibacterial Agents
Dengyue Liu, Jian Zhang, Lei Zhao, WenJing He, ZhengJun Liu, Xiuhai Gan, and Baoan Song
J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.9b03606 • Publication Date (Web): 18 Sep 2019
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Figure 1. Design of target compounds.
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Figure 2. Synthesis route of the target compounds 1−25.
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Figure 3. Curative activity of compounds 11 to rice bacterial leaf blight under greenhouse conditions at 200
μg/mL.
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Figure 4. Protective activity of compounds 11 to rice bacterial leaf blight under greenhouse conditions at 200
μg/mL.
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TOC Graphic
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First Discovery of Novel Pyrido[1,2-a] Pyrimidinone Mesoionic
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Compounds as Antibacterial Agents
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Dengyue Liu, † Jian Zhang, † Lei Zhao, † Wengjing He, † Zhengjun Liu, † 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
9
*Corresponding author (Tel.: 86-851-83620521; Fax: 86-851-83622211; E-mail:
gxh200719@163.com; songbaoan22@yahoo.com)
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ABSTRACT: Plant bacterial diseases cause tremendous decreases in crop yield and
quality, and there is a lack of highly effective and low-risk antibacterial agents. A
series of novel pyrido[1,2-a] pyrimidinone mesoionic compounds containing vanillin
moieties were synthesized, and the application of these mesoionic compounds as plant
antibacterial agents was reported here for the first time. The bioassay results revealed
that the mesoionic compounds had good antibacterial activity. Of these compounds,
compound 11 showed excellent in vitro activity against Xanthomonas oryzae pv.
oryzae, with an EC50 value of 1.1 μg/mL, which was substantially better than that of
bismerthiazol (92.7 μg/mL) and thiodiazole copper (105.4 μg/mL). Moreover,
greenhouse condition trials indicated that the protective and curative activities of
compound 11 against rice bacterial leaf blight were 75.12% and 72.04%, respectively,
which were better than those of bismerthiazol (62.24% and 50.83%, respectively) and
thiodiazole copper (53.35% and 65.04%, respectively). These results provide a basis
for the application of mesoionic vanillin moieties as new antibacterial agents.
KEYWORDS: mesoionic, pyrido[1,2-a] pyrimidinone, vanillin, antibacterial activity,
in vitro, in vivo
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INTRODUCTION
Plant bacterial diseases can cause tremendous decreases in crop yield and quality.
As one of the most destructive plant bacterial diseases, rice bacterial leaf blight
caused by Xanthomonas oryzae pv. oryzae (Xoo) results in rice yield losses ranging
from 74 to 81%.1,2 Additionally, citrus canker caused by Xanthomonas axonopodis pv.
citri (Xac) is probably the of the most detrimental to citrus plants and is extremely
3,4
difficult to control in agricultural production.
Bismerthiazol, thiodiazole copper,
zhongshengmycin and zinc thiazole are widely used to prevent plant bacterial diseases.
However, long-term use of traditional bactericides has several apparent shortcomings,
such as the development of resistance in the target pathogens, unsatisfactory field
efficacy, and harm to the environment and plant health. There is still a lack of highly
effective and low-risk antibacterial agents for controlling plant bacterial diseases.
Therefore, the discovery and development of new, highly active, and low-risk
antibacterial drugs with a novel mode of action is urgently needed.
Mesoionic compounds, with distinct regions of positive and negative charge
density associated with a polyheteroatomic system, can cross cellular membranes and
interact strongly with biomolecules, which are beneficial to their development as
potential drugs.5 Additionally, these compounds have desirable biological activities,
such as antifungal,6 antibacterial,7 antitubercular,8 and antihaemostatic9 properties.
Furthermore, mesoionic compounds have high efficiency and low toxicity and are
environmentally friendly.10,11 Therefore, mesoionic compounds have attracted the
attention of medical and pesticidal scientists. Recently, DuPont discovered two
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commercial mesoionic pyrido[1,2-a]pyrimidinone insecticides triflumezopyrim11 and
dicloromezotiaz12 (Figure 1), with novel mechanisms of action.13 Structure-activity
relationship (SAR) studies indicate that the mesoionic pyrido[1,2-a] pyrimidinone is
indispensable for the insecticidal activities of these compounds.14
As a highly efficient pharmacophore, vanillin is widely used in drug design and has
a broad range of biological activities, including antimicrobial,15,16 antifungal,17−19
anti-inflammatory,20 antitumor,21,22 and antioxidant23,24 properties. In recent years,
researchers have increasingly studied the agricultural and biological activities of
vanillin and its derivatives, such as herbicidal,25 pesticidal,26 antibacterial,27 and
antiviral28,29 activities. In our previous study, we synthesized a series of vanillin
derivatives with antiviral30 and plant growth-promoting31 activities and developed the
antiviral agent Xiangcaoliusuobingmi and the plant growth regulator
Fubingliusuoyoumi (Figure 1).
Mesoionic compounds and vanillin derivatives have shown promising medicinal
antibacterial activities. However, studies on the application of mesoionic compounds
as agents against plant bacteria have not been performed. To extend the applications
of mesoionic compounds and our previous study on vanillin derivatives, in this work,
we introduced vanillin moieties into a pyrido[1,2-a] pyrimidinone mesoionic skeleton
to build a series of novel pyrido[1,2-a] pyrimidinone mesoionic compounds
containing vanillin moieties (Figure 1), and the antibacterial activity of these
compounds was systematically studied against Xoo and Xac.
Figure 1
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MATERIALS AND METHODS
Chemicals. All reagents and solvents were purchased and analytically pure.
Instruments. Reactions were monitored by TLC and were visualized under UV
light at 254 nm. The melting points (uncorrected) of compounds were measured using
an X-4B micro melting point instrument (Yidian Physical Optical Instrument Co., Ltd.
1
Shanghai, China). H and 13C NMR spectra were obtained on a 400 MHz
spectrometer (JEOL, Tokyo, Japan) using dimethyl sulfoxide (DMSO-d6) as the
solvent at room temperature. High-resolution mass spectra (ESI TOF (+)) were
recorded on an LTQ Orbitrap XL (Thermo Scientific, MO, USA).
Preparation of intermediate 1a. Using 2-methylmalonic acid and
2,4,6-trichlorophenol as starting materials, intermediate 1a was prepared according to
previously reported methods.32 A solution of 2-methylmalonic acid (50.0 mmol) and
2,4,6-trichlorophenol (100.0 mmol) in phosphorus oxychloride (100 mL) was refluxed
for 3–5 h. After completion of this reaction, the mixture was slowly transferred
dropwise into a beaker containing ice water, and a white solid was collected by
filtration to obtain intermediate 1a.
Bis (2,4,6-trichlorophenyl) 2-methylmalonate (1a). White solid; mp 74–76 °C; yield
1
89.11%; H NMR (400 MHz, DMSO-d6) δ 8.02–7.69 (m, 4H), 4.00–3.73 (m, 1H),
13
1.45 (d, J = 7.2 Hz, 3H); C NMR (100 MHz, DMSO-d6) δ 170.10, 148.99, 129.25,
129.14, 123.53, 45.68, 14.15. HRMS (ESI): calcd for C16H9O4Cl6 ([M+H]+),
474.86265, found, 474.86624.
Preparation of intermediates 2d–2y. Intermediates 2d–2y were prepared
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according to the literature.22 A solution of vanillin (5.0 mmol), potassium carbonate
(6.0 mmol) and substituted benzyl chloride (6.0 mmol) in MeCN (30 mL) was heated
under reflux for 4–6 h. After completion of the reaction, the solvent was removed in
vacuo, followed by the addition of 20 mL of water, and extracted with 20 mL of
dichloromethane. The organic layer was dried over anhydrous Na2SO4. Finally,
dichloromethane was removed using a rotary evaporator to obtain intermediates
2d–2y. Representative data for 2i is shown below.
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3-Ethyl-4-(2-methylphenethyl)benzaldehyde (2i). White solid; mp 74–76 °C; yield
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86.0%; H NMR (400 MHz, DMSO-d6) δ 9.84 (s, 1H, -CHO), 7.55–7.52 (m, 1H,
Ar-H), 7.41 (d, J=19 Hz, 1H, Ar-H), 7.37–7.32 (m, 2H, Ar -H), 7.26–7.20 (m, 3H,
Ar-H), 5.16 (s, 2H, -CH2-), 3.83 (s, 3H, -OCH3), 2.31 (s, 3H, Ar-CH3); 13C NMR (100
MHz, DMSO-d6) δ 191.80, 153.68, 149.87, 137.86, 133.73, 130.21, 129.49, 128.54,
126.35, 113.08, 110.18, 70.41, 56.02, 21.25. HRMS (ESI): calcd for C16H17O3
([M+H]+), 257.11722, found, 257.11691.
Preparation of intermediates 3a–3y. Intermediates 3a–3y were prepared
according to previously reported methods.33 A solution of intermediate 2a–2y (4.6
mmol) and 2-aminopyridine (3.0 mmol) in 1,2-dichloroethane (30 mL) was heated
under reflux for 3–5 h. Then, sodium borohydride (6.0 mmol) was added into the
reaction system in batches, followed by heating under reflux for 2–3 h. After the
reaction was complete, the solvent was removed by distillation under reduced pressure.
Then, 20 mL of water was added, and the mixture was extracted using 20 mL of
dichloromethane to obtain the respective intermediates 3a–3y. Representative data for
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3i is shown below.
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N-(3-methoxy-4-((2-methylbenzyl)oxy)benzyl)pyridin-2-amine (3i). White solid; mp
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85–87 °C; yield 68.1%; H NMR (400 MHz, DMSO-d6) δ 7.31 (d, J = 7.8 Hz, 2H,
Ar-H), 7.21–7.16 (m, 3H, Ar-H), 6.96–6.91 (m, 2H, Ar-H), 6.79–6.77 (m, 1H, Ar-H),
5.09–4.97 (s, 3H, O-CH3), 4.41 (s, 2H, -N-CH2), 3.74 (s, 2H, O-CH2), 2.30 (s, 3H,
Ar-CH3); 13C NMR (100 MHz, DMSO-d6) δ 149.49, 147.01, 137.41, 135.98, 134.74,
129.36, 128.26, 118.94, 114.05, 111.29, 70.38, 63.24, 55.92, 21.24. HRMS (ESI):
calcd for C21H23O2N2 ([M+H]+), 335.17540, found, 335.17490.
General method for the synthesis of title compounds 1–25. A solution of
intermediate 1a (1.5 mmol) and 3a–3y (1.0 mmol) in toluene (15 mL) was heated to
reflux for 4–6 h. After completion of the reaction, the solvent was removed in vacuo,
and the crude product was purified by column chromatography using ethyl acetate as
the eluent. Representative data for 9 is shown below.
1-(3-methoxy-4-((2-methylbenzyl)oxy)benzyl)-3-methyl-2-oxo-1,2-dihydropyrido[1,
1
2-a]pyrimidin-5-ium-4-olate (9). Yellow solid; mp 71–73 °C; yield 21.6%; H NMR
(400 MHz, CDCl3) δ: 9.47–9.45 (m, 1H, Ar-H), 7.93–7.88 (m, 1H, Ar-H), 7.61 (d, J =
8.1 Hz, 1H, Ar-H), 7.52 (d, J = 8.1 Hz, 1H, Ar-H), 7.43–7.34 (m, 2H, Ar-H), 7.27 (d,
J = 6.2 Hz, 1H, Ar-H), 7.23–7.16 (m, 2H, Ar-H), 6.91–6.63 (m, 3H, Ar-H), 5.52 (s,
2H, -OCH2-), 5.06 (s, 1H, -CH2-), 3.84 (s, 3H, -OCH3), 2.36 (s, 2H, Py-CH3), 2.21 (s,
3H, Ar-CH3); 13C NMR (100 MHz, CDCl3) δ: 159.96, 154.02, 150.54, 148.15, 145.59,
141.16, 136.38, 134.64, 131.74, 130.34, 128.30, 128.12, 127.23, 125.97, 118.85,
115.28, 114.32, 113.39, 110.55, 91.20, 69.68, 56.19, 45.97, 18.88, 10.54. HRMS (ESI)
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for C25H24O4N2Na ([M+Na]+), calcd. 439.16283; found. 439.16211.
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Antibacterial activity
Antibacterial activity in vitro. The antibacterial activity against Xoo and Xac in
vitro were evaluated using turbidimeter tests.34 All compounds were dissolved in
DMSO and diluted with 0.1% Tween-20 to obtain the test solution.
Thiodiazole-copper (20% water dispersible granules) and bismerthlazol (20%
wettable powder) solutions served as the positive controls, while DMSO in sterile
deionized water served as the negative control. Cultures (40 μL) in the logarithmic
growth phase were added to the test tubes, which were loaded with 5 mL of nutrient
broth and test solution. The tubes were then shaken continuously for 36–48 h at 28 °C
and 180 rpm until the growth of the negative control culture reached the logarithmic
growth phase according to measurements of the optical density at 595 nm (OD595) on
a model 680 Microplate reader (Bio-Rad, Hercules, CA, USA). All experiments were
repeated three times, and each treatment was replicated four times. The inhibition rate
was calculated using the following equation, where the corrected turbidity value of
the negative control group is expressed as N, and the turbidity value of the treated
group is expressed as T.
Inhibition rate (%) = (N − T) ∕N × 100
Antibacterial activity in vivo. The protective and curative activities of compound 11
against rice bacterial leaf blight caused by Xoo were evaluated by a potting
experiment in a greenhouse according to previously reported methods.35 Thiodiazole
copper and bismerthlazol solutions were used as the positive controls, while DMSO in
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sterile deionized water was used as the blank control. Compound 11 was dissolved in
DMSO and diluted with 0.1% Tween-20 to obtain a test solution of 200 μg/mL. In the
curative activity experiment, 5-week-old rice leaves of the variety Fengyouxiangzhan
were inoculated with Xoo culture during the logarithmic growth phase by using the
leaf-cutting method. The test solution was sprinkled onto the rice leaves one day after
inoculation until the solution dripped down. Similarly, in the protective activity
experiment, rice leaves were treated with the test solution one day prior to inoculation
with the Xoo culture. Subsequently, the inoculated rice was placed in the greenhouse.
The lesion lengths were measured after two weeks.
The control effects (%) of the curative and protective activities were calculated
using the following equation, where the disease index of the negative control group is
expressed as D, and the treatment group disease index is expressed as T.
Control effect (%) = (D - T) / D × 100
RESULTS AND DISCUSSION
Chemistry. As shown in Figure 2, 2-methylmalonic acid was treated with
2,4,6-trichlorophenol using phosphorus oxychloride as the solvent under reflux for
3–5 h to produce intermediate 1a. Substitution of vanillin with different substituted
benzyl chlorides produced intermediates 2d–2y. The reductive amination of
intermediates 2a–2y with 2-aminopyridine using 1,2-dichloroethane as the solvent
under reflux produced intermediates 3a–3y. Finally, intermediate 1a was treated with
intermediates 3a–3y using toluene as the solvent under reflux for 4–6 h to produce the
corresponding target compounds 1–25. The structures of the target compounds were
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characterized by 1H NMR, 13C NMR and HRMS.
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Antibacterial activity. Antibacterial activity in vitro. The in vitro antibacterial
activity of target compounds 1–25 against Xoo and Xac are summarized in Tables 1
and 2. The results of the preliminary antibacterial activity assay showed that
compounds 4, 8, 9, 10 and 11 exhibited significant inhibitory activity against Xoo at a
concentration of 100 μg/mL, and the inhibition rates were 81%, 82%, 84%, 81%, and
97.1%, respectively, which are superior to the rates of the commercial agents
bismerthiazol (45%) and thiodiazole copper (61%). Moreover, compounds 11 and 14
showed excellent inhibitory activity against Xac at a concentration of 100 μg/mL, and
the inhibition rates were 92% and 82%, respectively, which are better than those of
bismerthiazol (69%) and thiodiazole copper (46%).
To further confirm the antibacterial activity and to study the SAR of the target
compounds, their EC50 values were tested against Xoo and Xac. Compounds 4, 10 and
11 exhibited excellent inhibitory activity to Xoo, with EC50 values of 7.4 μg/mL, 9.1
μg/mL, and 1.1 μg/mL, respectively, which are better than the values of bismerthiazol
(92.7 μg/mL) and thiodiazole copper (105.4 μg/mL). Furthermore, compounds 11 and
14 also showed excellent inhibitory activity against Xac, with EC50 values of 12.4
μg/mL and 22.1 μg/mL, respectively, which are better than those of bismerthiazol
(89.0 μg/mL) and thiodiazole copper (138.3 μg/mL).
Antibacterial activity in vivo. The antibacterial activity of compound 11 under
greenhouse conditions against rice bacterial leaf blight is shown in Tables 3 and 4.
The results showed that compound 11 had excellent curative activity against rice
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bacterial leaf blight at 200 μg/mL, with a control effect of 72.04%, which is superior
to that of bismerthiazol (50.83%) and thiodiazole copper (65.04%) (Figure 3).
Moreover, compound 11 exhibited outstanding protection activity against rice
bacterial leaf blight at 200 μg/mL, with a control effect of 75.12%, which is better
than that of bismerthiazol (62.24%) and thiodiazole copper (53.35%) (Figure 4).
SAR Analysis. According to the antibacterial activity data in Tables 1 and 2, SAR
analysis indicated that introducing different 4-hydroxybenzaldehyde substituents into
a pyrido[1,2-a] pyrimidinone mesoionic skeleton could affect the antibacterial activity,
and electron-donating substituents had more favorable activity than
electron-withdrawing substituents (1 > 2, 3). Methoxy groups (vanillin) were the most
suitable groups for activity. Furthermore, different substitutions at the hydroxy
position could influence the antibacterial activity. Among compounds 4−25,
methyl-substituted benzyl ether-containing compounds exhibited better antibacterial
activity (9−11). In addition, the position of the substituent on the benzyl group could
influence antibacterial activity, and 4-substituted benzyl ether-containing compounds
exhibited higher activity (11 > 9, 10).
In summary, for the first time, twenty-five novel pyrido [1,2-a] pyrimidinone
mesoionic compounds containing vanillin moieties were synthesized, and their
antibacterial activities against Xoo and Xac were systematically evaluated. Compound
11 showed prominent antibacterial activity against Xoo and Xac. These results
demonstrated that these novel pyrido[1,2-a] pyrimidinone mesoionic compounds can
be considered new antibacterial agents. This work has laid a solid foundation for the
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application of mesoionic compounds and their derivatives in the control of plant
bacterial diseases.
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ASSOCIATED CONTENT
Supporting information
Characterization data, 1H and 13C NMR spectra and HRMS for intermediates and title
compounds are provided. The Supporting Information is available free of charge on
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: gxh200719@163.com; songbaoan22@yahoo.com.
*Phone: 86-851-83620521; Fax: 86-851-83622211.
ORCID
Baoan Song: 0000-0002-4237-6167
Funding
The authors are grateful to the National Key Research Development Program of
China (2018YFD0200100) and the National Natural Science Foundation of China
(21672044, 31972290).
Notes
The authors declare no competing financial interest.
ABRREVIATIONS
Xoo, Xanthomonas oryzae pv. oryzae; Xac, Xanthomonas axonopodis pv. citri; 1,
NMR, nuclear magnetic resonance; DMSO, dimethylsulfoxide; SARs,
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structure-activity relationships; HRMS, high resolution mass spectrum.
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Information of FIGURE
Figure 1. Design of target compounds.
378
379
380
381
382
383
Figure 2. Synthesis route of the target compounds 1−25.
Figure 3. Curative activity of compounds 11 to rice bacterial leaf blight under
greenhouse conditions at 200 μg/mL.
Figure 4. Protective activity of compounds 11 to rice bacterial leaf blight under
greenhouse conditions at 200 μg/mL.
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Table 1. In Vitro Antibacterial Activities of the Target Compounds Against Xoo
O
Inhibition rate (%)
N
a
EC50
Compounds
N
O
R1
O
(µg/mL)
100 µg/mL 50 µg/mL
R2
1
R1=-OCH3 R2=-H
73.4±3.7
66.9±1.2
57.1±3.3
81.3±2.1
69.9±1.7
61.7±1.2
64.4±2.0
82.5±1.6
84.1±2.3
81.1±1.0
97.1±1.1
61.1±4.1
48.7±1.9
61.4±1.1
69.7±2.7
79.8±3.4
65.6±2.0
53.1±1.8
72.5±2.2
74.6±1.9
70.9±1.1
48.4±2.0
49.4±1.1
66.9±2.8
75.8±2.0
45.5±3.1
61.8±1.9
54.5±2.2 28.9±2.1
40.4±2.4 45.7±1.3
32.9±1.5 69.9±3.1
64.7±3.1 7.4±3.5
52.5±1.2 31.1±1.5
45.0±1.9 41.3±2.2
51.1±2.1 32.8±2.0
63.6±2.1 12.8±1.9
52.1±1.0 11.1±2.0
69.1±1.4 9.1±3.7
80.7±1.9 1.1±2.1
28.9±3.1 72.8±1.9
33.7±2.0 282.9±4.2
39.2±1.3 55.3±1.3
57.8±3.1 17.4±3.1
63.9±1.2 14.5±3.1
43.9±2.6 65.9±3.0
50.3±3.2 33.0±2.3
67.5±1.1 12.7±3.0
58.4±3.2 34.2±1.6
53.6±2.0 44.2±4.8
23.5±1.1 114.9±2.9
30.4±2.6 93.0±2.4
27.7±2.2 83.3±1.9
55.9±0.6 13.2±3.8
28.9±2.2 92.7±4.5
13.9±2.8 105.4±1.4
2
R1=-Cl
R1=-Br
R2=-H
R2=-H
3
4
R1=-OCH3 R2=-Et
R1=-OCH3 R2=n-Pr
R1=-OCH3 R2=i-Bu
R1=-OCH3 R2=-CH2CH2Cl
R1=-OCH3 R2=Benzyl
5
6
7
8
9
R1=-OCH3 R2=2-CH3-Benzyl
R1=-OCH3 R2=3-CH3-Benzyl
R1=-OCH3 R2=4-CH3-Benzyl
R1=-OCH3 R2=2-OCH3-Benzyl
R1=-OCH3 R2=3-OCH3-Benzyl
R1=-OCH3 R2=4-OCH3-Benzyl
R1=-OCH3 R2=2-F-Benzyl
R1=-OCH3 R2=4-F-Benzyl
R1=-OCH3 R2=2-Cl-Benzyl
R1=-OCH3 R2=3-Cl-Benzyl
R1=-OCH3 R2=2,4-diCl-Benzyl
R1=-OCH3 R2=4-Br-Benzyl
R1=-OCH3 R2=4-CF3-Benzyl
R1=-OCH3 R2=2- CN-Benzyl
R1=-OCH3 R2=4-CN-Benzyl
R1=-OCH3 R2=2-Cl-Thiazole-5-CH2
R1=-OCH3 R2=2-Cl- Pyridyl-5-CH2
Bismerthiazol
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Thiodiazole copper
386
a Average of three replicates.
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Table 2. In Vitro Antibacterial Activities of the Target Compounds Against Xac
O
Inhibition rate (%)
N
a
EC50
Compounds
N
O
R1
O
(µg/mL)
100 µg/mL 50 µg/mL
R2
1
R1=-OCH3 R2=-H
53.5±2.1
55.6±2.1
48.8±1.2
58.7±2.4
52.2±2.1
50.4±3.0
49.1±1.2
59.4±2.8
56.6±1.3
75.6±2.4
91.8±1. 5
72.5±1.6
46.6±2.8
82.2±2.2
70.6±2.1
70.5±2.1
42.9±3.0
62.6±3.5
35.4±1.1
40.5±2.0
45.7±1.9
49.5±3.6
39.8±4.1
62.9±3.7
41.0±2.4
69.0±2.2
46.6±3.0
35.6±2.1 64.3±2.5
24.9±5.9 97.4±1.6
25.3±2.5 106.1±1.7
42.0±2.7 56.7±1.7
33.9±1.8 72.0±1.7
30.8±2.5 71.8±2.4
27.8±2.1 91.4±3.6
40.4±2.1 58.7±3.3
38.6±2.6 60.9±4.5
58.5±4.1 33.6±2.0
69.1±2.6 12.4±2.3
45.5±1.2 83.3±2.0
28.1±3.3 114.0±3.7
59.7±3.3 22.1±1.9
47.8±1.6 52.0±1.4
53.5±2.8 44.9±2.6
29.6±2.3 106.8±1.3
41.8±2.1 52.6±4.8
2
R1=-Cl
R1=-Br
R2=-H
R2=-H
3
4
R1=-OCH3 R2=-Et
R1=-OCH3 R2=n-Pr
R1=-OCH3 R2=i-Bu
R1=-OCH3 R2=-CH2CH2Cl
R1=-OCH3 R2=Benzyl
5
6
7
8
9
R1=-OCH3 R2=2-CH3-Benzyl
R1=-OCH3 R2=3-CH3-Benzyl
R1=-OCH3 R2=4-CH3-Benzyl
R1=-OCH3 R2=2-OCH3-Benzyl
R1=-OCH3 R2=3-OCH3-Benzyl
R1=-OCH3 R2=4-OCH3-Benzyl
R1=-OCH3 R2=2-F-Benzyl
R1=-OCH3 R2=4-F-Benzyl
R1=-OCH3 R2=2-Cl-Benzyl
R1=-OCH3 R2=3-Cl-Benzyl
R1=-OCH3 R2=2,4-diCl-Benzyl
R1=-OCH3 R2=4-Br-Benzyl
R1=-OCH3 R2=4-CF3-Benzyl
R1=-OCH3 R2=2- CN-Benzyl
R1=-OCH3 R2=4-CN-Benzyl
R1=-OCH3 R2=2-Cl-Thiazole-5-CH2
R1=-OCH3 R2=2-Cl- Pyridyl-5-CH2
Bismerthiazol
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
8.9±1.6
385.5±1.9
21.1±5.5 206.1±4.6
19.8±1.6 170.2±4.0
26.0±2.5 123.8±2.4
15.9±4.0 219.4±4.8
38.1±1.7 69.4±2.0
15.8±1.5 207.9±4.7
46.2±3.3 89.0±2.6
28.0±3.4 138.3±3.2
Thiodiazole copper
389
a Average of three replicates.
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392
Table 3. Curative Activity of Compound 11 to Rice Bacterial Leaf Blight Under
Greenhouse Conditions at 200 μg/mL
14 days after inoculation
treatment
morbidity(%)
disease index (%)
16.82
control efficiency (%)b
11
100
100
100
100
72.04A
50.83B
65.04B
/
Bismerthiazol
Thiodiazole copper
CKa
28.66
20.38
58.29
b
aNegative control. Statistical analysis was conducted via the ANOVA method under a
condition of equal variances assumed (P > 0.05) and equal variances not assumed (P < 0.05).
Different uppercase letters indicate the values of curative activity with significant difference
among different treatment groups at P < 0.05.
393
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396
Table 4. Protective Activity of Compound 11 to Rice Bacterial Leaf Blight Under
Greenhouse Conditions at 200 μg/mL
14 days after inoculation
treatment
morbidity(%)
disease index (%)
14.50
control efficiency (%)b
11
100
100
100
100
75.12A
62.24B
53.35B
/
Bismerthiazol
Thiodiazole copper
CKa
22.01
27.19
58.29
b
aNegative control. Statistical analysis was conducted via the ANOVA method under a
condition of equal variances assumed (P > 0.05) and equal variances not assumed (P < 0.05).
Different uppercase letters indicate the values of protective activity with significant difference
among different treatment groups at P < 0.05.
397
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