Synthesis, antiviral and antibacterial activities and action mechanism of penta-1,4-dien-3-one oxime ether derivatives containing a quinoxaline moiety

Article abstract of DOI:10.1039/c9nj03019k

A series of penta-1,4-dien-3-one oxime ether derivatives containing a quinoxaline moiety were synthesized and their antibacterial and antiviral activities were evaluated. Bioassay activity indicated that some of the compounds displayed significant antibacterial and antiviral activities. In particular, some title compounds were found to show remarkable antiviral activities against tobacco mosaic virus (TMV). Compound 6i showed remarkable curative, protective and inactivation activity against TMV, with a 50% effective concentration (EC₅₀) of 287.1, 157.6 and 133.0 μg mL^-1, respectively. These results were better than or comparable to those of ningnanmycin (356.3, 233.7 and 121.6 μg mL^-1, respectively). Microscale thermophoresis (MST) also showed that the binding of compound 6i to TMV coat protein (TMV-CP) gave a K_d value of 0.115 ± 0.092 μmol L^-1, which was better than that of ningnanmycin (0.523 ± 0.254 μmol L^-1). Meanwhile, the EC₅₀ values of compound 6k against Xanthomonas axonopodis pv. Citri (Xac) and Xanthomonas oryzae pv. oryzae (Xoo) were 16.8 and 33.4 μg mL^-1 respectively, and that of compound 6i against Ralstonia solanacearum (Rs) was 33.9 μg mL^-1. These results were better than those of bismerthiazol (44.3, 42.5 and 62.4 μg mL^-1, respectively). The mechanism of antibacterial action of compound 6k against Xac was analysed through scanning electron microscopy (SEM). This study indicated that the title compounds are valuable in the search for novel agrochemicals.

Full text of DOI:10.1039/c9nj03019k

NJC
View Article Online
View Journal | View Issue
PAPER
Synthesis, antiviral and antibacterial activities and
action mechanism of penta-1,4-dien-3-one oxime
ether derivatives containing a quinoxaline moiety†
Cite this: New J. Chem., 2019,
43, 16461
Rongjiao Xia,‡ Tao Guo,‡ Mei Chen, Shijun Su, Jun He, Xu Tang, Shichun Jiang
and Wei Xue
*
A series of penta-1,4-dien-3-one oxime ether derivatives containing a quinoxaline moiety were synthesized
and their antibacterial and antiviral activities were evaluated. Bioassay activity indicated that some of the
compounds displayed significant antibacterial and antiviral activities. In particular, some title compounds were
found to show remarkable antiviral activities against tobacco mosaic virus (TMV). Compound 6i showed
remarkable curative, protective and inactivation activity against TMV, with a 50% effective concentration (EC50
)
À1
of 287.1, 157.6 and 133.0 mg mL , respectively. These results were better than or comparable to those of
À1
ningnanmycin (356.3, 233.7 and 121.6 mg mL , respectively). Microscale thermophoresis (MST) also showed
that the binding of compound 6i to TMV coat protein (TMV-CP) gave a K
d
value of 0.115 Æ 0.092 mmol LÀ1
,
À1
which was better than that of ningnanmycin (0.523 Æ 0.254 mmol L ). Meanwhile, the EC50 values of
compound 6k against Xanthomonas axonopodis pv. Citri (Xac) and Xanthomonas oryzae pv. oryzae (Xoo)
À1
Received 10th June 2019,
Accepted 25th September 2019
were 16.8 and 33.4 mg mL respectively, and that of compound 6i against Ralstonia solanacearum (Rs)
À1
À1
was 33.9 mg mL . These results were better than those of bismerthiazol (44.3, 42.5 and 62.4 mg mL
,
respectively). The mechanism of antibacterial action of compound 6k against Xac was analysed through
scanning electron microscopy (SEM). This study indicated that the title compounds are valuable in the
search for novel agrochemicals.
DOI: 10.1039/c9nj03019k
rsc.li/njc
Natural products are environmentally friendly and possess
unique bioactivities. Penta-1,4-diene-3-ones are analogs of curcumin
Tobacco mosaic virus (TMV) is a well-studied plant virus world- isolated from the plant Curcuma longa L. As one of the
1
. Introduction
1
5
wide. This virus infects at least 125 species of nine plant families important natural products in medicinal chemistry, penta-1,4-
1
–3
including tobacco, tomato, pepper, and cucumbers. It is very dien-3-ones have been disclosed to exhibit extensive biological
1
6–18
19
difficult to get the plants cured once they are infected and serious activities, such as antimicrobial,
anti-inflammatory,
4–6
20,21
22,23
24,25
26
damage is therefore caused. Controlling plant diseases has long anticancer,
insecticidal,
antiviral
and anti-oxidative
been a challenging task in the agricultural industry. The threats activities. Notably, chemists have reported more and more penta-
caused by Xanthomonas axonopodis pv.citri (Xac), Xanthomonas oryzae 1,4-dien-3-one oxime ether derivatives with good antiviral and
pv oryzae (Xoo) and Ralstonia solanacearum (Rs) have become a antibacterial activities in recent years. In our previous study, we
7–11
serious problem all over the world.
However, the abuse of demonstrated the synthesis of a series of (E)-3-(3,4-dimethoxy-
traditional antimicrobial agents and plant virucides has caused phenyl)-1-(4-(2-(quinazolin-4-ylthio)ethoxy)phenyl)prop-2-en-1-one,
12,13
resistance in the target pathogens.
Therefore, the search for 3-((1E,3Z,4E)-1-(2-(2,4-dichlorophenoxy)phenyl)-5-(pyridin-2-yl)penta-
new, efficient and safe agricultural chemicals is still of great 1,4-dien-3-ylidene)amino (Fig. 1, a and b) derivatives, which exhib-
14
4,24
significance in pesticide development.
ited excellent antiviral activities.
State Key Laboratory Breeding Base of Green Pesticide and Agricultural
Bioengineering, Key Laboratory of Green Pesticide and Agricultural Bioengineering,
Ministry of Education, Center for Research and Development of Fine Chemicals,
Guizhou University, Guiyang, 550025, China. E-mail: wxue@gzu.edu.cn;
Fax: +86-851-88292090; Tel: +86-851-88292090
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9nj03019k
These authors contributed to this work equally.
Fig. 1 Compounds previously reported against tobacco mosaic virus
(TMV).
‡
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 16461--16467 | 16461

View Article Online
Paper
NJC
d 7.01–8.11 ppm indicating the presence of protons in olefinic
bonds and aromatic nuclei and a singlet at d 5.08–5.25 ppm that
corresponds to a –CH – group; also, a typical chemical shift at
2
1
3
d 63.30–69.70 ppm and d 161.70–158.85 ppm from the C NMR
spectra confirmed the presence of –CH – and –CQN–, respec-
2
+
tively. The strong presence of [M + H] ions indicates that the
Fig. 2 Synthetic route of the title compounds 6a–6o.
title compounds are in a steady state.
Quinoxalines and their derivatives have been regarded as an
important class of nitrogenous heterocycles, and have drawn much
attention due to their wide spectrum of biological activities including
2
.2 Antiviral activity screening of the title compounds against
TMV
27,28
29
30
Using growing N. tobacum L. leaves at the same age as the test
subjects, the antiviral activities of the title compounds 6a–6o
against TMV were evaluated by the halfleaf method.
commercial agent ningnanmycin was used in the control
experiment under the same conditions. It was found that most
of the compounds exhibited good antiviral activities against
TMV in vivo at 500 mg mL and the results are summarized in
Table 1. Compounds 6a and 6i showed remarkable curative
activities against TMV at 500 mg mL , with values of 55.6 and
antimicrobial,
anticancer, and herbicide activities. However,
studies on quinoxaline derivatives as potential bactericidal and
antiviral agents are rarely reported. Thus, studies on the synthesis
and biological activity evaluation and action mechanism of
quinoxaline derivatives have attracted much attention.
Considering the above findings, aiming to search for novel,
ecofriendly and highly efficient lead compounds with better
activities, a series of penta-1,4-diene-3-one oxime ether derivatives
containing a quinoxaline moiety were synthesized (Fig. 2). Their
antibacterial activities against Xac, Rs and Xoo and their antiviral
activities against TMV were evaluated.
3
1–33
The
À1
À1
51.5%, respectively, which were better than that of ningnanmycin
(45.4%). Compounds 6i, 6k and 6l exhibited higher protection
activity (68.3, 67.1 and 62.2%, respectively) than ningnanmycin
À1
(61.4%) at 500 mg mL . Compounds 6c, 6i and 6o showed
À1
remarkable inactivation activity against TMV at 500 mg mL
with values of 74.2, 85.2 and 77.2%, respectively, which were
close to that of ningnanmycin (89.4%). To further confirm the
,
2. Results and discussion
2.1 Spectral properties
The synthetic route to penta-1,4-dien-3-one oxime ether derivatives antiviral activities of our target compounds, the EC50 values
containing a quinoxaline moiety is shown in Scheme 1. The were tested for some compounds, and the results are displayed in
structures of all the target compounds (6a–6o) were characterized Table 2. Compounds 6a and 6i exhibited remarkable curative activity
1
13
À1
by H NMR, C NMR and HRMS. All the spectra are in agree- against TMV, with EC50 values of 304.2 and 287.1 mg mL , which
1
À1
ment with the proposed structure. The H NMR spectra of the were superior compared to ningnanmycin (356.6 mg mL ). Notably,
title compounds using CDCl displayed multiplet signals at compounds 6i, 6j, 6k and 6l exhibited excellent protection
3
Scheme 1 Synthesized route to title compounds 6a–6o.
16462 | New J. Chem., 2019, 43, 16461--16467 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
NJC
Paper
a
À1
Table 1 Antiviral activities of the title compounds against TMV in vivo at 500 mg mL
a
a
a
Compound
R
1
R
2
O
Curative activity (%)
Protection activity (%)
Inactivation activity (%)
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
2-Cl-Ph
2,4-Di-Cl-Ph
3-Cl-Ph
2-F-Ph
2-Cl-Ph
2,4-Di-Cl-Ph
3-Cl-Ph
2-Cl-Ph
4-Cl-Ph
2,4-Di-Cl-Ph
2-F-Ph
H
H
H
H
Cl
Cl
Cl
H
H
H
2
2
2
2
2
2
2
4
4
4
4
4
4
4
4
—
55.6 Æ 2.8
38.1 Æ 3.6
30.1 Æ 1.4
15.8 Æ 5.0
29.4 Æ 3.5
16.4 Æ 1.2
38.2 Æ 6.9
38.4 Æ 4.2
51.5 Æ 3.4
25.3 Æ 5.5
43.3 Æ 1.2
31.6 Æ 1.0
34.2 Æ 7.3
35.2 Æ 2.8
34.1 Æ 1.4
45.4 Æ 2.3
55.8 Æ 1.4
47.6 Æ 3.2
55.3 Æ 7.7
55.5 Æ 1.2
49.2 Æ 3.1
57.5 Æ 7.4
44.3 Æ 7.2
45.2 Æ 2.8
68.3 Æ 6.6
61.9 Æ 3.2
67.1 Æ 3.5
62.2 Æ 7.0
35.1 Æ 2.6
47.8 Æ 5.2
47.3 Æ 2.4
61.4 Æ 1.7
65.7 Æ 2.1
61.8 Æ 4.8
74.2 Æ 2.4
33.7 Æ 6.0
41.5 Æ 3.1
53.5 Æ 7.4
56.8 Æ 4.8
56.4 Æ 0.6
85.2 Æ 1.7
62.3 Æ 5.8
47.5 Æ 4.3
54.9 Æ 2.8
58.2 Æ 6.2
44.7 Æ 3.6
77.2 Æ 2.4
89.4 Æ 3.9
H
2-Cl-Ph
4-Cl-Ph
2,4-Di-Cl-Ph
2-F-Ph
Cl
Cl
Cl
Cl
—
b
Ningnanmycin
—
a
b
Average of three replicates. The commercial agricultural compound.
À1
activity against TMV, with EC50 values of 157.6, 219.3, 194.2 and 68.3 and 85.2% at 500 mg mL , respectively. This compound was
À1
À1
2
24.6 mg mL , which exceeded that of ningnanmycin (233.7 mg mL ). found to be more active compared to other tested compounds.
The inactivation activities of 6c, 6i and 6o (EC50 values of 177.3,
À1
2.4 Binding sites of 6i, 6g and ningnanmycin to TMV-CP
1
33.0 and 165.4 mg mL ) against TMV were near to that of
À1
ningnanmycin (121.6 mg mL ).
Microscale thermophoresis (MST) analysis is used to analyse
the interactions between two compounds (6i and 6g) and TMV-
3
4–36
CP.
The MST results are shown in Fig. 3 and Table 3, where
2
.3 Structure–activity relationship analysis of the antiviral
the binding of compounds 6g, 6i and ningnanmycin to TMV-CP
activities against TMV
À1
protein yielded K
d
values of 48.486 Æ 32.262 mmol L , 0.115 Æ
À1
À1
Antiviral activities of penta-1,4-dien-3-one oxime ether deriva- 0.092 mmol L and 0.523 Æ 0.254 mmol L , respectively. As
tives containing a quinoxaline moiety were affected by variation indicated in MST, the result indicated that their ability to
1 2
of different substitutes on the R , R and O positions. First, combine in turn was 6i 4 ningnanmycin 4 6g and was basically
when R
1
was 2-Cl-Ph and 4-Cl-Ph groups, the curative activities consistent with their antiviral activity. Meanwhile, when R was
1
À1
of the corresponding compounds 6a and 6i at 500 mg mL were altered to a 4-Cl-Ph group, compound 6i exhibited a stronger
À1
5
5.6 and 51.5%, respectively. 4-Cl-Ph (6i), 2-F-Ph (6k) and 2-Cl- combining capacity, with K values of 0.115 Æ 0.092 mmol L
,
d
À1
Ph (6l) groups at the R
1
position could effectively enhance compared to compound 6g (48.486 Æ 32.262 mmol L ) with a
the protective activities of the title compounds against TMV 2-Cl-Ph group.
at 500 mg mL , with inhibition rates of 68.3, 67.1 and 62.2%,
respectively. Furthermore, when R1 was a 4-Cl-Ph group, the
inactivation activity of the compound 6i at 500 mg mL was To identify the 6i and 6g recognition sites in TMV-CP (Protein
À1
2.5 Molecular docking of 6i and 6g with TMV-CP
À1
8
R
5.2%. Second, when R
1
was substituted with a 4-Cl-Ph group and Data Bank code: 1EI7), the Gold method with 200 cycles was
3
7
2
= H, the compound 6i displayed better curative, protection and performed in the molecular docking strategy (Fig. 4). After
inactivation activities against TMV with inhibition rates of 51.5, optimization we found that the two compounds (6i and 6g)
a
Table 2 EC50 values of the title compounds against TMV in vivo
À1
Tested bacterial
Curative activity
Compd
Toxic regression equation
r
EC50/(mg mL
)
6a
y = 0.5414x + 3.6556
y = 0.4197x + 3.9683
y = 0.3956x + 3.9683
y = 1.0140x + 2.7716
y = 1.1078x + 2.4066
y = 1.2465x + 2.1475
y = 0.8124x + 3.0897
y = 0.6853x + 3.3767
y = 0.9272x + 2.9905
y = 1.3074x + 2.2232
y = 1.2609x + 2.2025
y = 1.8667x + 1.1080
0.9976
0.9493
0.9729
0.9824
0.9799
0.9722
0.9871
0.9908
0.9849
0.9667
0.9593
0.9739
304.2
287.1
356.3
157.6
219.3
194.2
224.6
233.7
177.3
133.0
165.4
121.6
6i
b
Ningnanmycin
6i
Protection activity
6
6
6
j
k
l
b
Ningnanmycin
6c
Inactivation activity
6
6
i
o
b
Ningnanmycin
a
b
Average of three replicates. The commercial agricultural.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 16461--16467 | 16463

View Article Online
Paper
NJC
Fig. 3 Microscale thermophoresis (MST) of 6i, 6g and ningnanmycin.
Table 3 The dissociation constant of 6i, 6g and ningnanmycin with
TMV-CP
2
.6 Antibacterial activity screening of the title compounds
against Xac, Xoo and Rs in vitro
À1
Compounds
K
d
(mmol L
)
The bacteriostatic activities of the compounds were evaluated
by the turbidimetry method.
exhibited considerable antibacterial activities against Xac, Xoo
and Rs in vitro at 50 and 100 mg mL and the observed results
3
8–40
6
6
i
g
0.115 Æ 0.092
48.486 Æ 32.262
0.523 Æ 0.254
Some of the title compounds
Ningnanmycin
À1
are shown in Table 4. For instance, the inhibitory rates of
were inserted in the pocket (including residues of ARG-90, compounds 6d, 6i, 6j and 6k indicated against Xac were
À1
THR-42, ARG-46 and GLN-38) between the two subunits of respectively, 73.6, 90.4, 72.0 and 99.3% at 100 mg mL , which
TMV-CP. Such as 2-bit N on the pyrazole ring in compound 6i were superior to that of bismerthiazol (54.3%). Meanwhile, the
forms a hydrogen bond with the ARG-46 residue (N–H = inhibition rates of compounds 6d, 6i, 6j and 6k against Xac at
À1
2
.059 Å). Quinoxaline has been demonstrated to have a strong 50 mg mL were 63.5, 55.9, 62.1 and 84.3%, respectively, which
hydrogen bond with ARG-90 (2.298 Å) and ARG-90 forming two were better than that of bismerthiazol (32.6%). The bioassay
hydrogen bonds with the O on the oxime ether (O–H = 2.307 Å and results indicated that the antibacterial activities of compounds
À1
1
.944 Å). At the same time, THR-46 forms two hydrogen bonds with 6i and 6k against Xoo at 100 mg mL were 75.5 and 97.5%,
the O and N on the oxime ether (O–H = 2.156 Å and N–H = 2.379 Å). respectively, which were much better than that of bismerthiazol
Moreover, GLN-38 showed hydrogen bonds with 6g (2.066 Å). (70.5%). Compounds 6i and 6k have fine antibacterial activity
À1
Therefore, the antiviral activity (protection activity) of the against Xoo at 50 mg mL , with the inhibition rates of 71.1 and
corresponding compounds was consistent with their ability to 79.4%, respectively, which were superior to that of bismerthiazol
combine with TMV-CP and the results of the molecular docking (45.3%). The bioassay results indicated that the antibacterial
À1
studies. These displayed that penta-1,4-dien-3-one oxime ether activities of compounds 6i and 6o against Rs at 100 mg mL
derivatives may be a potential lead structure for developing were 83.6 and 50.7%, respectively, which were preferable to that
novel anti-TMV agents.
of bismerthiazol (49.3%). Compounds 6i and 6o have fine
Fig. 4 Molecular docking studies of compounds 6i (A and B) and 6g (C and D).
16464 | New J. Chem., 2019, 43, 16461--16467 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
NJC
Table 4 Antibacterial activities (inhibition rate/%) of target compounds 6a–6o
Paper
a
Xac
Xoo
Rs
À1
À1
À1
À1
À1
À1
Compound
100 mg mL
50 mg mL
100 mg mL
50 mg mL
100 mg mL
50 mg mL
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
58.9 Æ 1.3
56.5 Æ 3.2
57.5 Æ 4.5
73.6 Æ 3.0
59.0 Æ 2.3
52.1 Æ 3.7
58.7 Æ 1.5
51.2 Æ 2.8
90.4 Æ 2.2
72.0 Æ 2.6
99.3 Æ 0.8
58.1 Æ 3.6
61.0 Æ 1.5
55.6 Æ 3.8
45.7 Æ 1.8
54.3 Æ 4.2
55.6 Æ 3.4
40.5 Æ 2.9
52.2 Æ 0.4
63.5 Æ 4.4
54.4 Æ 1.0
38.1 Æ 6.9
55.2 Æ 3.9
40.6 Æ 5.4
55.9 Æ 3.5
62.1 Æ 4.0
84.3 Æ 4.9
55.9 Æ 1.2
54.4 Æ 0.9
53.2 Æ 0.4
40.9 Æ 1.7
32.6 Æ 2.1
35.8 Æ 1.8
34.7 Æ 4.6
38.6 Æ 1.2
65.5 Æ 2.0
63.7 Æ 4.7
55.1 Æ 1.6
64.9 Æ 2.3
56.9 Æ 4.1
75.5 Æ 6.4
52.5 Æ 2.7
97.5 Æ 4.9
45.6 Æ 3.8
65.1 Æ 2.2
60.4 Æ 1.4
26.7 Æ 1.8
70.5 Æ 3.0
32.7 Æ 4.8
32.4 Æ 3.9
32.9 Æ 4.0
39.5 Æ 5.1
39.3 Æ 1.4
23.0 Æ 2.2
21.9 Æ 4.5
48.7 Æ 2.8
71.1 Æ 1.6
46.2 Æ 5.1
79.4 Æ 1.4
39.3 Æ 3.4
59.4 Æ 3.7
55.5 Æ 3.1
29.3 Æ 2.5
45.3 Æ 3.7
46.9 Æ 0.4
36.1 Æ 5.7
31.1 Æ 4.2
6.5 Æ 3.7
22.7 Æ 4.7
25.0 Æ 7.9
18.1 Æ 6.5
3.4 Æ 1.8
39.8 Æ 3.6
37.1 Æ 2.7
31.5 Æ 1.1
49.7 Æ 8.9
83.6 Æ 1.6
47.9 Æ 4.4
46.9 Æ 0.4
49.4 Æ 1.4
43.9 Æ 2.6
44.7 Æ 3.7
50.7 Æ 2.5
49.3 Æ 2.5
36.6 Æ 2.2
36.8 Æ 6.1
28.2 Æ 2.2
30.7 Æ 3.6
42.9 Æ 5.5
21.2 Æ 2.1
22.7 Æ 4.7
40.5 Æ 2.6
37.4 Æ 7.4
40.4 Æ 3.5
45.2 Æ 7.1
30.4 Æ 0.8
b
BT
a
b
Average of three replicates. BT: Bismerthiazol.
Table 5 EC50 values of the title compounds against Xac, Xoo and Rs 2.7 Structure–activity relationship analysis of the
a
in vitro
antibacterial activities against Xac, Xoo and Rs
Tested
bacterial
Toxic regression
equation
EC50
(mg mL )
/
As indicated in Tables 4 and 5, most of the title compounds exhibited
better antibacterial activities against Xac, Xoo and Rs that were greatly
À1
Compound
r
Xac
6d
y = 0.1839x + 4.6724
y = 0.3020x + 4.5020
y = 0.7923x + 3.848
y = 1.3866x + 3.3012
y = 0.4767x + 4.2151
y = 0.7576x + 3.7937
y = 0.8912x + 3.6413
y = 0.8284x + 3.6514
y = 1.0110x + 3.4536
y = 1.2984x + 2.9743
y = 0.6689x + 3.7994
0.9960
0.9985
0.9756
0.9837
0.9837
0.9844
0.9721
0.9708
0.9985
0.9807
0.9839
33.5
44.6
28.4
16.8
44.3
39.1
33.4
42.5
33.9
35.7
62.4
1 2
affected by variation of different substituents on the R , R and O
positions. The inhibitory rates of most of the compounds against Xac
were superior to those of the compounds against Xoo and Rs.
6
6
6
i
j
k
b
b
b
BT
6i
With the presence of a 2-F-Ph group at the R position, the
1
Xoo
Rs
corresponding compounds presented better in vitro bioactivity
6k
against Xac, following the order of 6k (R
6d (R = 2-F-Ph, R = H, O = 2) 4 6o (R
1
= 2-F-Ph, R = H, O = 4) 4
2
= 2-F-Ph, R = Cl, O = 4).
2
BT
6i
1
2
1
6o
Compounds 6k, 6d and 6o have antibacterial activity against Xac at
BT
À1
1
00 mg mL , with the inhibition rates of 99.3, 73.6 and 45.7%,
a
b
Average of three replicates. BT: Bismerthiazol.
respectively. Meanwhile, compounds 6a, 6b, 6c and 6d had the
same R = H and O = 2, and the inhibition rates of compounds 6a,
1
6
b, 6c and 6d exhibited antibacterial activities against Xac at
À1
antibacterial activity against Rs at 50 mg mL , with the inhibi-
tion rates of 42.9 and 45.2%, respectively, which were better
than that of bismerthiazol (30.4%).
À1
100 mg mL following the order of 6d (R1 = 2-F-Ph) 4 6a
(R
1
1 1
= 2-Cl-Ph) 4 6c (R = 3-Cl-Ph) 4 6b (R = 2,4-di-Cl-Ph).
2.8 Scanning electron microscopy (SEM) studies
Based on the preliminary bioassays, the EC50 values of
selected compounds that exhibited good activities against Based on the antibacterial activity of compound 6k, the mechanism
Xac, Xoo and Rs were calculated and summarized in Table 5. of antibacterial action of the compound against Xac was analyzed by
The results indicated that compounds 6d, 6i, 6j and 6k SEM. The results showed that the change of concentration would
effectively inhibited Xac in vitro, with the EC values of lead to the deepening of cell membrane damage. The cell membrane
5
0
À1
3
3.5, 44.6, 28.4 and 16.8 mg mL , respectively, which were of the untreated bacteria remains intact (Fig. 5A). Meanwhile, when
superior to that of bismerthiazol (44.3 mg mL ). Mean- the concentration was 50 mg mL , the cell membranes began to
while, Table 5 indicated that compounds 6i and 6k effectively appear wrinkled. Thereafter, as the concentration of cells increased,
À1
À1
À1
À1
inhibited Xoo, with the EC50 values of 39.1 and 33.4 mg mL
,
the degree of folding was severe at 100 mg mL . Therefore, the
respectively, which were preferable to that of bismer- results of SEM showed that compound 6k destroyed the cell
À1
thiazol (42.5 mg mL ). Compounds 6i and 6o have fine membrane structure leading to an incomplete cell structure, to
antibacterial activity against Rs with the EC50 values of achieve the purpose of antibacterial mechanism.
À1
3
3.9 and 35.7 mg mL , respectively, which were better than
À1
that of bismerthiazol (62.4 mg mL ). Strickingly, the EC50
values of the title compound 6i against Xac, Xoo and Rs were
respectively 44.6, 39.1 and 33.9 mg mL , which were better
3
. Experimental
À1
3.1 Methods and materials
À1
than those of bismerthiazol (44.3, 42.5 and 62.4 mg mL
,
The melting points were determined on an XT-4 binocular
microscopic melting point apparatus (Beijing Tech Instrument
respectively).
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 16461--16467 | 16465

View Article Online
Paper
NJC
À1
À1
Fig. 5 SEM images for Xanthomonas axonopodis pv. Citri (Xac) after incubation in different concentrations of compound 6k: (A) 0 mg mL , (B) 50 mg mL
and (C) 100 mg mL . Scale bars for (A, B and C) are 2 mm.
À1
1
13
19
Co, Beijing. China). H, C and F NMR spectra were obtained 3.5 General procedure for the synthesis of title compounds
on a Bruker Ascend-400 spectrometer (Bruker Optics, Germany) 6a–6o
and CDCl3 was used as a solvent and TMS was used as an
Potassium carbonate as a base, acetonitrile as a solvent and
intermediates 4 and 5 as the starting materials were mixed and
stirred for 30 min and refluxed at 80 1C for 4 h. After the completion
of the reaction, the mixture was filtered and the residue was
recrystallized with acetonitrile and dichloromethane, and com-
pound 6a was obtained. By following the same procedure, the title
compounds 6b–6o were then obtained. The H NMR, C NMR and
HMRS spectra of the designated title compounds 6a–6o are also
provided in the ESI.†
internal standard. Mass spectral studies were performed on a
quadrupole electrostatic field orbitrap mass spectrograph. The
MST of the compounds to check the interaction with TMV-CP
was determined using a micro thermophoresis instrument
(NanoTemper Technologies GmbH, Germany). The molecular
docking was obtained by using DS-CDocker implemented in
Discovery Studio (version 4.5, San Diego, CA, USA). The
chemical reaction was monitored by thin-layer chromatography
under ultraviolet light of 254 nm. Thin-layer chromatography
purifications were carried out on 200–300 mesh silica gel. All
the reagents and solutions used were analytically pure. Inter-
mediates 1 and 2 were respectively synthesized by the proce-
1
13
4. Conclusions
4
1,42
In summary, we have designed and synthesized a series of
penta-1,4-dien-3-one oxime derivatives containing quinoxaline
fragments in order to obtain novel and efficient agents with
better biological activities. Their biological activities against
TMV, Xac, Xoo and Rs were evaluated. The action mechanism of
the title compounds against plant bacteria and virus has been
studied. Compound 6i showed remarkable curative, protective
and inactivation activity against TMV, with EC values of 287.1,
dures described in the literature.
3
.2 General procedure for the synthesis of intermediates 3
A mixture of intermediates 2 (4 mmol), 2-chlorobenzyl chloride
4.78 mmol), KI (1.99 mmol), K CO (5.97 mmol) and 20 mL of
(
2
3
acetone was heated under reflux. After the reaction was com-
pleted, the mixture was filtered, and the solvent was removed
under vacuum. On silica gel (200–300 mesh), chromatography
from a mixture of petroleum ether and ethyl acetate (v : v = 2 : 1)
gave a yellow solid of the intermediates 3.
5
0
À1
1
57.6 and 133.0 mg mL , respectively, which were superior to
those of ningnanmycin (356.3, 233.7 and 121.6 mg mL
À1
,
respectively). MST also showed that the binding of compound
À1
6
i to TMV-CP gave K
d
values of 0.115 Æ 0.092 mmol L , which
3.3 General procedure for the synthesis of intermediates 4
À1
was better than that of ningnanmycin (0.523 Æ 0.254 mmol L ).
A mixture of intermediates 3 (2.66 mmol), hydroxylamine Among them, the EC50 values of compound 6k against Xac and
hydrochloride (7.98 mmol), and pyridine (10 mL) in ethanol Xoo were 16.8 and 33.4 mg mL respectively. The EC50 value of
À1
À1
(
20 mL) was stirred for 20 h at room temperature. A white solid compound 6i against Rs was 33.9 mg mL . These results were
À1
began to appear in the solvent. After the reaction was com- better than those of bismerthiazol (44.3, 42.5 and 62.4 mg mL
,
pleted, the mixture was filtered, and the residue was washed respectively). SEM analyses proved that the bacterial cell
with ethanol to yield the intermediates 4.
membrane could be damaged by the title compounds. There-
fore, penta-1,4-dien-3-one oxime ether derivatives containing
quinoxaline moieties will be valuable in future studies as potential
replacement templates in the search for novel agricultural
agents.
3
.4 General procedure for the synthesis of intermediates 5
In waterless conditions, 2-hydroxyquinoxaline (6.84 mmol) and
-hydroxy-6-chloroquinoxaline (5.54 mmol) were dissolved in
2
phosphorus oxychloride (12 mL) and DMF (0.5 mL), stirred and
refluxed at 90 1C for 1 h until the completion of the reaction.
Following this, it was poured into ice water, and filtered to
obtain intermediates 5.
Conflicts of interest
The authors declare that they have no competing interests.
16466 | New J. Chem., 2019, 43, 16461--16467 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
NJC
Paper
Acknowledgements
20 K. Yuan, B. A. Song, L. H. Jin, S. Xu, D. Y. Hu, X. Q. Xu and
S. Yang, Med. Chem. Commun., 2011, 2, 585–589.
The authors gratefully acknowledge the financial support of
the National Key Research and Development Program of China
2
2
2
2
1 J. Q. Wang, X. B. Wang, Y. Wang, W. J. Tang, J. B. Shi and
X. H. Liu, Eur. J. Med. Chem., 2018, 156, 493–509.
(No. 2017YFD0200506) and Science and Technology Project of
2 L. J. Xia, L. J. Chen, X. B. Wang, X. J. Du, Z. Y. Zheng and
W. Xue, Fine Chem., 2017, 34, 834–840.
3 Y. G. Zheng, Z. Deng, S. Song, C. Zhou, M. Z. Luo, Y. Ning
and Q. Q. Guo, Chin. J. Appl. Chem., 2015, 32, 405–411.
4 L. J. Chen, X. B. Wang, X. Tang, R. J. Xia, T. Guo, C. Zhang,
X. Y. Li and W. Xue, BMC Chem., 2019, 13, 34.
Guizhou Province (No. 20185781, 20191105).
References
1
2
L. Bos, Trends Microbiol., 2000, 8, 82–87.
L. Yu, X. H. Gan, D. G. Zhou, F. C. He, S. Zeng and D. Y. Hu, 25 J. Ma, P. Li, X. Y. Li, Q. C. Shi, Z. C. Wan, D. Y. Hu and
Molecules, 2017, 22, 658. B. A. Song, J. Agric. Food Chem., 2014, 62, 8928–8934.
M. H. Chen, D. Y. Hu, X. Y. Li, S. Yang, W. Y. Zhang, P. Li 26 M. A. Al-Omara, K. M. Youssefa, M. A. El-Sherbenya, S. A. A.
3
and B. A. Song, Bioorg. Med. Chem. Lett., 2015, 25,
840–3844.
Awadallab and H. I. El-Subbagh, Arch. Pharm. Chem. Life
Sci., 2015, 338, 175–180.
3
4
5
X. B. Wang, M. H. Chen, Q. Li, J. P. Zhang, X. H. Ruan, Y. Xie 27 Y. Zhao, G. Y. Cheng, H. H. Hao, Y. H. Pan, Z. L. Liu,
and W. Xue, Chem. Pap., 2017, 71, 1225–1233. M. H. Dai and Z. H. Yuan, BMC Vet. Res., 2016, 12, 186.
J. Wu, Y. Y. Zhu, Y. H. Zhao, W. L. Shan, D. Y. Hu, J. X. Chen, 28 D. L. Zhang, J. P. Liang, Y. Liu, X. H. Wang and L. Y. Hua,
D. Y. Liu, X. Y. Li and S. Yang, Chin. Chem. Lett., 2016, 27,
48–952.
G. Han, L. Chen and Q. Wang, J. Agric. Food Chem., 2018, 66,
80–788.
W. M. Xu, F. F. Han, M. He, D. Y. Hu, J. He, S. Yang and
B. A. Song, J. Agric. Food Chem., 2012, 60, 1036–1041.
P. Y. Wang, L. Zhou, J. Zhou, Z. B. Wu, W. Xue, B. A. Song 30 J. Z. Ma, H. B. Wang and H. Jiang, Fine Chem., 2004, 21,
and S. Yang, Bioorg. Med. Chem. Lett., 2016, 26, 1214–1217. 309–312.
S. Perumalsamy, M. Bharani, M. Sudha, P. Nagarajan, L. Arul, 31 C. W. Long, P. Li, M. H. Chen, L. R. Dong, D. Y. Hu and
Chin. J. Pharm., 2008, 39, 410–412.
9
29 A. Monge, J. A. Palop, A. L. D. Cer ´a in, V. Senador,
F. J. Mart ´ı nez-Crespo, Y. Sainz, S. Narro, E. Garc ´ı a,
C. D. Miguel, M. Gonz ´a lez, E. Hamilton, A. J. Barker,
E. D. Clarke and D. T. Greenhow, J. Med. Chem., 1995, 38,
1786–1792.
6
7
8
9
7
R. Saraswathi, P. Balasubramanian and J. Ramalingam, Plant
Breeding, 2010, 129, 400–406.
0 T. Q. Yu, B. Liang, C. R. Ye, F. R. Xu, C. F. Tang, X. Q. Mao
and L. Y. Dai, Agric. Sci. China, 2006, 5, 299–306.
1 P. Y. Wang, L. Zhou, J. Zhou, H. S. Fang, Z. B. Wu, W. Xue,
B. A. Song and S. Yang, Chem. Pap., 2016, 71, 1–6.
B. A. Song, Eur. J. Med. Chem., 2015, 102, 639–647.
32 D. G. Zhou, D. D. Xie, F. C. He, B. A. Song and D. Y. Hu,
Bioorg. Med. Chem. Lett., 2018, 28, 2091–2097.
33 Y. J. Wang, D. G. Zhou, F. C. He, J. X. Chen, Y. Z. Chen,
X. H. Gan, D. Y. Hu and B. A. Song, Chin. Chem. Lett., 2018,
28, 127–130.
1
1
1
1
1
1
1
2 X. Wang, P. Li, Z. Li, J. Yin, M. He, W. Xue, Z. Chen and 34 X. Y. Li, J. Liu, X. Yang, Y. Ding, J. Wu, D. Y. Hu and
B. A. Song, J. Agric. Food Chem., 2013, 61, 9575–9582. B. A. Song, Bioorg. Med. Chem., 2015, 23, 3629–3637.
3 X. M. Zhong, X. B. Wang, L. J. Chen and W. Xue, Chem. Cent. J., 35 C. J. Wienken, P. Baaske, U. Rothbauer, D. Braun and
017, 11, 106. S. Duhr, Nat. Commun., 2010, 1, 100.
4 X. Tang, S. J. Su, M. Chem, J. He, R. J. Xia, T. Guo, Y. Chen 36 B. Bhyravbhatla, S. J. Watowich and D. L. Caspar, Biophys. J.,
and W. Xue, RSC Adv., 2019, 9, 6011–6020. 1998, 74, 604–615.
5 H. Luo, J. J. Liu, L. H. Jin, D. Y. Hu, Z. Chen, S. Yang, J. Wu 37 Y. Y. Wang, F. Z. Xua, Y. Y. Zhu, B. A. Song, D. X. Luo, G. Yu,
2
and B. A. Song, Eur. J. Med. Chem., 2013, 63, 662–669.
S. H. Chen, W. Xue and J. Wu, Bioorg. Med. Chem. Lett.,
2018, 28, 2979–2984.
6 J. P. Zhang, P. Li, Y. H. Wang, C. Zhang, L. J. Chen, X. Tang,
M. He and W. Xue, Chem. J. Chinese Univ., 2018, 36, 38 P. Li, J. Yin, W. M. Xu, J. Wu, M. He, D. Y. Hu, S. Yang and
455–1461. B. A. Song, Chem. Biol. Drug Des., 2013, 82, 546–556.
7 J. P. Zhang, Q. Li, C. Zhang, P. Li, L. J. Chen, Y. H. Wang, 39 P. Li, P. Tian, Y. Chen, Y. Z. Chen, S. Yang and B. A. Song,
1
1
X. H. Ruan, W. Xiao and W. Xue, Chem. Pap., 2018, 72,
193–2202.
8 J. Zhou, Q. Q. Tao, P. Y. Wang, W. B. Shao, Z. B. Wu, Z. Li
and S. Yang, Bioorg. Med. Chem. Lett., 2018, 28, 1742–1746. 41 X. H. Gan, D. Y. Hu, P. Li, J. Wu, X. W. Chen, W. Xue and
9 Z. G. Liu, L. G. Tang, P. Zou, Y. L. Zhang, Z. Wang, B. A. Song, Pest Manage. Sci., 2015, 72, 534–543.
Q. L. Fang, L. L. Jiang, G. Z. Chen, Z. Xu, H. J. Zhang and 42 L. J. Chen, T. Guo, R. J. Xia, X. Tang, Y. Chen, C. Zhang and
G. Liang, Eur. J. Med. Chem., 2014, 74, 671–682. W. Xue, Molecules, 2019, 24, 925.
Pest Manage. Sci., 2017, 11, 106.
40 X. B. Wang, Z. J. Ren, M. Q. Wang and M. Chen, Chem. Cent. J.,
2018, 12, 83.
2
1
1
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 16461--16467 | 16467