Synthesis and antibacterial and antiviral activities of myricetin derivatives containing a 1,2,4-triazole Schiff base

Article abstract of DOI:10.1039/c9ra05139b

A series of novel myricetin derivatives containing a 1,2,4-triazole Schiff base were designed and synthesized. Their structures were systematically characterized using ¹H NMR, ¹³C NMR, and HRMS. During antibacterial bioassays, 6f, 6i, and 6q demonstrated a good inhibitory effect against Xanthomonas axonopodis pv. citri (Xac), with half-maximal effective concentration (EC₅₀) values of 10.0, 9.4, and 8.8 μg mL^-1, respectively, which were better than those of bismerthiazol (54.9 μg mL^-1) and thiodiazole copper (61.1 μg mL^-1). Note that 6w demonstrated a good inhibitory effect against Ralstonia solanacearum (Rs) with and EC₅₀ value of 15.5 μg mL^-1, which was better than those of bismerthiazol (55.2 μg mL^-1) and thiodiazole copper (127.9 μg mL^-1). Similarly, 6a, 6d, and 6e demonstrated a good inhibitory effect against Xanthomonas oryzae pv. oryzae (Xoo) with EC₅₀ values of 47.1, 61.2, and 61.0 μg mL^-1, respectively, which were better than those of bismerthiazol (148.2 μg mL^-1) and thiodiazole copper (175.5 μg mL^-1). Furthermore, we used scanning electron microscopy (SEM) to study the possible sterilization process of the target compound 6q against Xac. The results indicated the possibility of destroying the bacterial cell membrane structure, resulting in an incomplete bacterial structure, and thus achieving inhibition. Furthermore, antiviral bioassays revealed that most compounds exhibited excellent antiviral activity against tobacco mosaic virus (TMV) at a concentration of 500 μg mL^-1. The results of the molecular docking studies for 6g with TMV-CP (PDB code: 1EI7) showed that compound 6g had partially interacted with TMV-CP. Therefore, mechanistic studies of the action of compound 6g could be further studied based on that.

Full text of DOI:10.1039/c9ra05139b

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PAPER
Synthesis and antibacterial and antiviral activities of
myricetin derivatives containing a 1,2,4-triazole
Schiff base†
Cite this: RSC Adv., 2019, 9, 23045
a
a
a
a
a
a
a
Ying Chen,‡ Pu Li,‡ Shijun Su, Mei Chen, Jun He, Liwei Liu, Ming He,
b
a
Hua Wang* and Wei Xue
*
A series of novel myricetin derivatives containing a 1,2,4-triazole Schiff base were designed and synthesized.
1
13
Their structures were systematically characterized using H NMR, C NMR, and HRMS. During antibacterial
bioassays, 6f, 6i, and 6q demonstrated a good inhibitory effect against Xanthomonas axonopodis pv. citri
ꢀ1
(
Xac), with half-maximal effective concentration (EC50) values of 10.0, 9.4, and 8.8 mg mL , respectively,
ꢀ1
ꢀ1
which were better than those of bismerthiazol (54.9 mg mL ) and thiodiazole copper (61.1 mg mL ).
Note that 6w demonstrated a good inhibitory effect against Ralstonia solanacearum (Rs) with and EC50
ꢀ
1
ꢀ1
value of 15.5 mg mL , which was better than those of bismerthiazol (55.2 mg mL ) and thiodiazole
ꢀ
1
copper (127.9 mg mL ). Similarly, 6a, 6d, and 6e demonstrated a good inhibitory effect against
ꢀ1
Xanthomonas oryzae pv. oryzae (Xoo) with EC50 values of 47.1, 61.2, and 61.0 mg mL , respectively,
ꢀ1
ꢀ1
which were better than those of bismerthiazol (148.2 mg mL ) and thiodiazole copper (175.5 mg mL ).
Furthermore, we used scanning electron microscopy (SEM) to study the possible sterilization process of
the target compound 6q against Xac. The results indicated the possibility of destroying the bacterial cell
membrane structure, resulting in an incomplete bacterial structure, and thus achieving inhibition.
Furthermore, antiviral bioassays revealed that most compounds exhibited excellent antiviral activity
Received 6th July 2019
Accepted 22nd July 2019
ꢀ1
against tobacco mosaic virus (TMV) at a concentration of 500 mg mL . The results of the molecular
docking studies for 6g with TMV-CP (PDB code: 1EI7) showed that compound 6g had partially interacted
with TMV-CP. Therefore, mechanistic studies of the action of compound 6g could be further studied
based on that.
DOI: 10.1039/c9ra05139b
rsc.li/rsc-advances
canker disease that has signicantly impacted production of
citrus worldwide. Moreover, Xanthomonas oryzae pv. oryzae
1
. Introduction
Plant diseases are one of the natural disasters that can seriously (Xoo) is a rod-shaped Gram-negative bacterium causing an
2
threaten agricultural production. According to statistics average annual loss of 10–50% in many rice-growing countries.
released by the Food and Agriculture Organization of the United Therefore, the development of new and highly effective pesti-
Nations (FAO), the annual loss in yield because of plant diseases cide fungicides and antiviral agents is very important. Flavo-
1
is about 10% of the total production. Note that, based on their noids, or bioavonoids, which were previously referred to as the
pathogens, plant diseases can be classied into two categories: basic nucleus structure of 2-phenyl-chromones, and currently
invasive diseases and non-invasive diseases. Infectious patho- referred to as two phenols are a series of compounds in which
gens primarily include bacteria, viruses, actinomycetes, para- benzene rings (A and B) are linked to each other via a central
3,4
sitic plants, fungi, nematodes, viroids, and mycoplasma. For three-carbon chain (Fig. 1a and b).
example, Xanthomonas axonopodis pv. citri (Xac) is a citrus
Aer the initial discovery of avonoid glycosides in the
1930s, they have been extensively studied by researchers. In fact,
in Chinese herbal medicines, avonoids are very important
a
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
b
Institute for Plant Protection and Soil Science, Hubei Academy of Agricultural
Sciences, Wuhan, 430064, China. E-mail: wanghua4@163.com; Fax: +86-851-
8
†
1
‡
8292090; Tel: +86-851-88292090
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra05139b
The rst and the second authors contributed equally to this work.
Fig. 1 Core structures of flavones and isoflavones.
RSC Adv., 2019, 9, 23045–23052 | 23045
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5,6
7,8
active substances. Flavonoids have antibacterial, antiviral, anti- 2.2. General procedure for preparing the intermediates 1, 2,
9
10
0
0
0
tumor, and antioxidant activities. Myricetin (3 ,4 ,5 ,3,5,7-hexahy- 3, 4, and 5
droxyavonol, Myr), similar to bayanone, is an important
ꢁ
Hydrazine hydrate was dissolved in water at 50 C for 0.5 h,
polyphenol avonoid that is widely found in many plants. Modern
pharmacological studies have conrmed that myricetin has anti-
bacterial,
inammatory activities. Furthermore, Ruan et al. reported that
a series of myricetin derivatives could be used to inhibit plant
pathogens. In our previous study, we demonstrated the synthesis
of series of 3-((5-((4-chlorobenzyl)thio)-1,3,4-thiadiazol-2-yl)
methoxy)-5,7-dimethoxy-2-(3,4,5-trimethoxyphenyl)-4H-chromen-4-
one and N-benzyl-2-((5,7-dimethoxy-4-oxo-2-(3,4,5-trimethox-
yphenyl)-4H-chromen-3-yl)oxy) acetamide (Fig. 2a and b), both of
ꢁ
followed by the addition of carbon disulde at 90 C for 1 h. The
solution was then cooled, followed by crystallization to obtain
the intermediate 1. Intermediate 1 and glacial acetic acid were
then reuxed for 4 h, and then cooled to room temperature.
Then, the unreacted acetic acid was distilled off and the
precipitate washed with water to obtain intermediate 2. Subse-
quently, intermediate 2 was heated till it completely dissolved
in ethanol, and then substituted aldehyde was added for 6 h to
obtain intermediate 3. Myricetin and methyl iodide were stirred
at room temperature for 48 h, and then concentrated hydro-
chloric acid deglucoside was added to obtain intermediate 4.
Finally, the intermediate 4 was stirred in DMF at room
temperature for 0.5–1 h and dibromoalkane was added; this
reaction was allowed to continue for 12 h to obtain the inter-
mediate 5.
1
1,12
13,14
15
16
antiviral,
antitumor, antioxidation, and anti-
17
18
a
19,20
which exhibited good antibacterial activities.
Although there have been a number of studies on myr-
icetin, they are primarily focused on myricetin and its
medical applications. Moreover, there have been very few
studies on the derivatives of myricetin and their application
in pesticides.
In recent decades, heterocyclic compounds have played
a critical role for the development of pesticides. In particular, 2.3. General procedure for preparing the target compounds
,2,4-triazole-based heterocyclic derivatives have become very 6a–6w
1
popular because of their high-efficiency and broad-spectrum
biological activity. Similarly, Schiff base compounds have
attracted considerable attention because of their unique bio-
logical activities, e.g., 1,2,4-triazole Schiff base compounds have
both a triazole ring and an imine active fragment of the Schiff
base. Therefore, these compounds have a broad spectrum of
The target compounds 6a–6w were synthesized according to
previously reported methods, although certain modications
were made to the preparation process. Intermediate 3 (1.2
32
mmol), K CO (3 mmol), and DMF (20 mL) were added to
2
3
a 50 mL 3-neck round bottom ask equipped with a magnetic
stirrer. The mixture was stirred at room temperature for 0.5 h,
and then intermediate 5 (1.0 mmol) was added to the reaction
21,22
23
biological activity such as antibacterial,
antitumor, anti-
insecticidal, and weeding. Jin et al. reported that
,2,4-triazole Schiff bases could be used to inhibit plant
24,25
26
27
viral,
1
ꢁ
solution with stirring at 100–105 C for 6 h. The progress of the
reaction was monitored using TLC. Finally, aer cooling the
reaction mixture to room temperature, 100 mL of water was
added, followed by extraction with dichloromethane (3 ꢂ 30
mL). The combined organic phases were washed twice with 5%
NaOH, distilled water, and saturated aqueous NaCl. Finally, the
solvent was dried, evaporated, and puried (petroleum ether-
28
pathogens.
To develop new, highly efficient, environmentally friendly
pesticide compounds, myricetin was used as a lead compound
to introduce triazole Schiff base structure, a series of myricetin
derivatives containing 1,2,4-triazole Schiff base were synthe-
1
13
sized and characterized using H NMR, C NMR, and HRMS.
These compounds were then evaluated for their antibacterial
and antiviral activities.
:
ethyl acetate ¼ 1 : 3, V/V), and the product was obtained with
40–75% yield.
3
. Results and discussion
2
. Experimental
3.1. Spectral properties
1
13
2.1. Methods and materials
H NMR, C NMR and HRMS spectra of all the target
compounds are provided in the ESI.† For example, the analysis
of the spectral data of 6a is given below. In the H NMR spec-
trum, 9H in the d 8.83–7.60 ppm and d 2.44 ppm can be
attributed to the hydrogen on the molecular fragment of the
Scheme 1 shows the synthetic route for developing myricetin
derivatives containing 1,2,4-triazole Schiff bases. The interme-
diates 1, 2, 3, 4, and 5 were prepared according to previously
1
29–31
reported methods.
1
6
,2,4-triazole Schiff base, whereas 4H appearing in the d 7.34–
.48 ppm can be attributed to myricetin. Hydrogens on the
benzene ring, 6H of d 3.99 ppm, d 3.22 ppm, and d 2.08–
.02 ppm, can be attributed to the methylene hydrogen on the
2
carbon chain, whereas 15H of d 3.90–3.74 ppm can be attributed
to the 5 methoxy group of myricetin's benzene ring. In the
HRMS spectrum of the title compound, the characteristic
+
absorption signals of [M + H] ions were obtained, which were
Fig. 2 Compounds previously reported against pathogen.
consistent with their molecular weights.
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Scheme 1 The synthetic route of the target compounds.
3
.2. Antibacterial activity in vitro
good inhibitory effects against Xac with the EC50 values of 10.0,
ꢀ
1
9
.4, and 8.8 mg mL , which were better than those of myricetin
For determining bioactivity, the target compounds were tested
against Xac, Rs, and Xoo using the turbidity method with bis-
merthiazol, thiadiazole copper, and myricetin being used as
control agents. Table 1 lists the antibacterial activities of 6j, 6k,
ꢀ
1
ꢀ1
(107.2 mg mL ), bismerthiazol (54.9 mg mL ), and thiodiazole
ꢀ
1
copper (61.1 mg mL ). Similarly, 6w demonstrated a good
inhibitory effect against Rs with an EC50 value of 15.5 mg mL
which was better than those of myricetin (82.6 mg mL ), bis-
merthiazol (55.2 mg mL ), and thiodiazole copper (127.9 mg
mL ). Moreover, 6a, 6d, and 6e demonstrated good inhibitory
effects against Xoo with EC50 values of 47.1, 61.2, and 61.0 mg
mL , which were better than those of myricetin (222.4 mg
ꢀ1
,
ꢀ
1
ꢀ
1
6l, 6n, 6q, and 6t against Xac at 100 mg mL with the percentage
ꢀ
1
inhibition of 79.6%, 79.8%, 81.2%, 81.8%, 84.5%, and 85.8%,
respectively, which were better than those of myricetin (49.4%),
bismerthiazol (59.5%), and thiadiazole copper (56.9%). Note
that the percentage inhibition of 6l, 6q, and 6t against Xac at 50
mg mL were 74.9%, 75.3%, and 74.9%, respectively, which
were better than those of myricetin (40.4%), bismerthiazol
ꢀ1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
mL ), bismerthiazol (148.2 mg mL ), and thiodiazole copper
ꢀ1
(175.5 mg mL ).
(
49.5%), and thiadiazole copper (47.9%). Furthermore, 6w
ꢀ
1
showed antibacterial activity against Rs at 100 mg mL with the 3.3. Structure–activity relationships (SAR) of antibacterial
percentage inhibition of 83.2%, which was better than those of activities
myricetin (56.4%), bismerthiazol (61.1%), and thiadiazole
According to the results in Tables 2 and 3, combined with the
activity data analysis of the parent structure of myricetin, the
myricetin derivative can be obtained aer introducing the 1,2,4-
triazole Schiff base, which can inhibit biological activity. For
copper (37.1%). Similarly, the percentage inhibition of 6w
ꢀ
1
against Rs at 50 mg mL was 70.3%, which was better than
those of myricetin (43.3%), bismerthiazol (49.5%), and thia-
diazole copper (17.4%). Moreover, 6a, 6e, 6h, and 6w showed
example, 6f (n ¼ 3, R ¼ 3,4-di-CH
3
-Ph), 6i (n ¼ 3, R ¼ 4-t-Bu-Ph),
ꢀ1
antibacterial activities against Xoo at 100 mg mL with the
percentage inhibition of 59.1%, 57.1%, 57.3%, and 56.5%,
respectively, which were better than those of myricetin (41.4%),
bismerthiazol (47.0%), and thiadiazole copper (43.2%). Simi-
larly, the percentage inhibition of compounds 6a, 6h, and 6w
and 6q (n ¼ 4, 3,4-di-CH O-Ph) demonstrated a good inhibitory
3
effect against Xac with the EC values of 10.0, 9.4, and 8.8 mg
5
0
ꢀ1
ꢀ1
mL , which were better than those of myricetin (107.2 mg
mL ), bismerthiazol (54.9 mg mL ), and thiodiazole copper
ꢀ1
ꢀ1
(
61.1 mg mL ). Similarly, 6w (n ¼ 5, R ¼ 3,4-di-CH
3
O-Ph)
ꢀ1
against Xoo at 50 mg mL were 51.6%, 49.5%, and 47.2%,
respectively, which were better than those of myricetin (32.3%),
bismerthiazol (39.6%), and thiadiazole copper (38.2%).
demonstrated a good inhibitory effect against Rs with EC50
ꢀ1
value of 15.5 mg mL , which was better than those of myricetin
82.6 mg mL ), bismerthiazol (55.2 mg mL ), and thiodiazole
ꢀ1
ꢀ1
(
Based on these preliminary results of bioassays, EC50 values
of some of the compounds showed good antibacterial activities
against Xac, Rs and Xoo as indicated in Tables 2 and 3. As can be
seen from Tables 2 and 3, compounds 6f, 6i, and 6q showed
ꢀ1
copper (127.9 mg mL ). Moreover, 6a (n ¼ 3, R ¼ Ph), 6d (n ¼ 3,
R ¼ 4-CH O-Ph), and 6e (n ¼ 3, R ¼ 2-CH O-Ph) demonstrated
3
3
good inhibitory effect against Xoo with EC50 values of 47.1, 61.2,
ꢀ1
and 61.0 mg mL , which were better than those of myricetin
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ꢀ
1
ꢀ1
(
222.4 mg mL ), bismerthiazol (148.2 mg mL ), and thiodiazole size, and unbroken in morphology. Aer treatment with 6q
ꢀ
1
ꢀ1
copper (175.5 mg mL ). According to the results in Tables 2 and (12.5 mg mL ), cell wall invagination appeared at both ends of
, together with the activity data analytical of the parent struc- the bacterial cells. Moreover, aer treatment with 6q (25 mg
ture of myricetin, the myricetin derivatives can be obtained aer mL ), the bacterial cell wall showed different degrees of
introducing the 1,2,4-triazole Schiff base, which can inhibit rupture and the cell contents leaked.
3
ꢀ1
biological activity. For example, when n ¼ 3, R is Ph, 4-CH
3
O-Ph,
2
-CH O-Ph, 3,4-di-CH O-Ph, and 2,4-di-CH O-Ph, the activity of
3
3
3
3.5. Antiviral activity of the title compounds against TMV
substituted benzene is higher than that of substituted phenyl-
containing methoxy compounds. When n ¼ 4, R is Ph, 4-
As can be seen in Table 4, at a test concentration of 500 mg
ꢀ1
CH O-Ph, 2-CH O-Ph, and 3,4-di-CH O-Ph, the activity of
3
3
3
mL , the curative, protective, and inactivation activities of the
target compounds against tobacco mosaic virus (TMV) were
tested. The results showed that both 6g and 6j showed a good
therapeutic effect on TMV, whereas the percentage inhibition
were 52.5% and 52.4%, respectively, which exceeded those of
myricetin (31.6%) and ribavirin (39.9%) but close to that of
ningnanmycin (52.7%). Similarly, 6f, 6p, and 6w show a good
protective effect on TMV, and their percentage inhibition were
substituted phenyl is higher than that of substituted benzene
compounds.
To summarize, the derivative obtained by introducing the
1
,2,4-triazole Schiff base into the myricetin structure as
a lead compound has a good inhibitory activity against plant
pathogens and can be used as a potential plant-inhibiting
drug.
58.7%, 57.8%, and 58.0%, respectively, which exceeded those of
myricetin (42.1%) and ribavirin (51.8%) but close to that of
ningnanmycin (65.7%). Furthermore, 6g showed a good
3.4. SEM study
According to the results in Fig. 3A–C, the surface morphology of passivation effect on TMV, and its percentage inhibition was
33,34
Xac was observed by scanning electron microscopy (SEM).
88.6%, which exceeded those of myricetin (50.9%) and ribavirin
Bacterial cells in group (A) were rhabditiform, homogeneous in (73.3%) but close to that of ningnanmycin (90.4%).
Table 1 In vitro antibacterial activity of the target compounds against Xac, Rs and Xoo
a
Percentage inhibition /%
Xac
Rs
Xoo
ꢀ1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
Compd
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
6
6
6
6
6
6
6
6
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
78.2 ꢃ 0.2
69.5 ꢃ 4.8
73.6 ꢃ 7.9
74.5 ꢃ 2.9
56.0 ꢃ 0.7
79.2 ꢃ 0.2
76.6 ꢃ 8.3
67.3 ꢃ 6.1
78.3 ꢃ 1.7
79.6 ꢃ 2.0
79.8 ꢃ 3.5
81.2 ꢃ 6.1
73.5 ꢃ 4.4
81.8 ꢃ 5.4
71.3 ꢃ 4.2
78.7 ꢃ 2.0
84.5 ꢃ 2.2
65.3 ꢃ 1.4
73.1 ꢃ 6.2
85.8 ꢃ 3.2
70.8 ꢃ 4.9
69.4 ꢃ 0.2
72.0 ꢃ 7.1
49.4 ꢃ 4.1
59.5 ꢃ 7.7
56.9 ꢃ 1.5
69.7 ꢃ 1.0
65.1 ꢃ 9.2
66.0 ꢃ 6.2
66.9 ꢃ 3.8
50.2 ꢃ 3.9
72.4 ꢃ 1.6
62.9 ꢃ 6.6
56.4 ꢃ 6.0
72.1 ꢃ 5.3
67.7 ꢃ 4.5
63.2 ꢃ 2.7
74.9 ꢃ 6.7
61.1 ꢃ 3.3
68.6 ꢃ 4.5
62.9 ꢃ 2.5
63.1 ꢃ 8.0
75.3 ꢃ 4.8
54.3 ꢃ 2.5
65.6 ꢃ 3.8
74.9 ꢃ 6.8
62.7 ꢃ 5.0
61.0 ꢃ 5.4
64.1 ꢃ 2.8
40.4 ꢃ 0.4
49.5 ꢃ 5.7
47.9 ꢃ 8.5
16.9 ꢃ 3.7
38.1 ꢃ 7.5
25.9 ꢃ 7.2
35.1 ꢃ 5.1
33.2 ꢃ 6.8
41.1 ꢃ 1.5
18.5 ꢃ 7.4
27.2 ꢃ 4.6
29.6 ꢃ 1.2
35.1 ꢃ 1.9
25.4 ꢃ 5.1
36.0 ꢃ 3.6
22.8 ꢃ 0.6
39.7 ꢃ 2.6
43.9 ꢃ 2.9
49.7 ꢃ 6.1
52.1 ꢃ 5.6
43.7 ꢃ 2.4
46.0 ꢃ 0.4
51.2 ꢃ 3.3
17.8 ꢃ 2.7
17.4 ꢃ 4.7
83.2 ꢃ 2.0
56.4 ꢃ 2.0
61.1 ꢃ 6.2
37.1 ꢃ 3.6
6.6 ꢃ 0.2
21.4 ꢃ 7.0
18.7 ꢃ 2.7
24.6 ꢃ 7.7
11.5 ꢃ 1.6
33.9 ꢃ 0.6
13.8 ꢃ 1.4
25.3 ꢃ 4.1
19.7 ꢃ 2.8
31.3 ꢃ 8.9
13.1 ꢃ 7.3
32.7 ꢃ 4.0
11.9 ꢃ 4.6
35.1 ꢃ 9.4
32.0 ꢃ 9.3
45.7 ꢃ 7.7
36.3 ꢃ 7.0
20.8 ꢃ 3.5
26.0 ꢃ 5.8
33.0 ꢃ 0.9
11.0 ꢃ 3.7
6.1 ꢃ 1.0
59.1 ꢃ 8.7
53.1 ꢃ 6.9
45.3 ꢃ 1.5
53.6 ꢃ 3.5
57.1 ꢃ 4.8
43.3 ꢃ 8.2
53.6 ꢃ 4.4
57.3 ꢃ 3.4
54.3 ꢃ 2.9
58.6 ꢃ 5.2
53.5 ꢃ 9.9
53.3 ꢃ 3.0
47.1 ꢃ 4.9
53.7 ꢃ 3.2
49.3 ꢃ 0.8
51.9 ꢃ 4.0
50.7 ꢃ 0.4
48.0 ꢃ 0.9
53.8 ꢃ 3.9
53.4 ꢃ 2.6
48.0 ꢃ 9.6
56.3 ꢃ 1.8
56.5 ꢃ 2.1
41.4 ꢃ 5.9
47.0 ꢃ 3.1
43.2 ꢃ 3.0
51.6 ꢃ 7.8
45.0 ꢃ 5.6
33.9 ꢃ 2.8
46.5 ꢃ 1.2
46.1 ꢃ 6.4
35.6 ꢃ 8.0
47.0 ꢃ 9.6
49.5 ꢃ 3.6
41.3 ꢃ 5.1
44.7 ꢃ 3.7
45.1 ꢃ 6.0
46.3 ꢃ 9.7
40.4 ꢃ 6.7
44.2 ꢃ 5.3
37.7 ꢃ 5.8
45.4 ꢃ 7.6
42.4 ꢃ 9.4
33.8 ꢃ 5.2
38.2 ꢃ 7.3
45.7 ꢃ 8.1
39.7 ꢃ 3.6
45.7 ꢃ 8.5
47.2 ꢃ 3.2
32.3 ꢃ 2.9
39.6 ꢃ 6.1
38.2 ꢃ 6.3
s
t
u
v
w
70.3 ꢃ 3.2
43.3 ꢃ 4.6
49.5 ꢃ 5.3
17.4 ꢃ 6.6
b
Myr
BT
TC
c
c
a
ꢁ
b
c
Average of three replicates (temperature: 28 ꢃ 1 C, time: 24–48 h). Myr (myricetin). BT (commercial fungicides, bismerthiazol) and TC
(thiediazole copper).
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Table 2 In vitro antibacterial EC50 activity value of the target compounds against Xac
a
2
ꢀ1
Compd
n
R
Toxic regression equation
r
EC50/(mg mL
)
pEC50/(mM)
6
6
6
6
6
6
6
6
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
p
q
r
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
5
5
5
5
—
—
—
Ph
y ¼ 0.8044x + 4.1554
y ¼ 0.6949x + 4.1397
y ¼ 0.8528x + 3.9474
y ¼ 1.0517x + 3.5664
y ¼ 0.6924x + 3.7991
y ¼ 0.8130x + 4.1875
y ¼ 0.9169x + 3.8298
y ¼ 0.6912x + 3.8298
y ¼ 0.7819x + 4.2398
y ¼ 0.9335x + 3.8960
y ¼ 0.9655x + 3.7731
y ¼ 0.9335x + 4.0630
y ¼ 0.7733x + 4.0122
y ¼ 0.9324x + 3.9636
y ¼ 0.6712x + 4.1730
y ¼ 0.9633x + 3.8184
y ¼ 0.9311x + 4.1191
y ¼ 0.5861x + 4.1558
y ¼ 0.7906x + 4.0584
y ¼ 1.1883x + 3.6956
y ¼ 0.7831x + 3.9652
y ¼ 0.7105x + 4.0749
y ¼ 0.7706x + 4.0642
y ¼ 0.6520x + 3.6763
y ¼ 0.8357x + 3.5466
y ¼ 0.8874x + 3.4149
0.9961
0.9697
0.9972
0.9650
0.9822
0.9977
0.9762
0.9690
0.9917
0.9642
0.9334
0.9877
0.9599
0.9716
0.9624
0.9729
0.9819
0.9706
0.9903
0.9958
0.9780
0.9998
0.9814
0.9838
0.9876
0.9984
11.2 ꢃ 3.4
17.3 ꢃ 2.2
17.2 ꢃ 1.4
23.1 ꢃ 2.8
54.3 ꢃ 2.4
10.0 ꢃ 3.9
18.9 ꢃ 2.6
28.1 ꢃ 1.5
9.4 ꢃ 1.9
4.8
4.6
4.6
4.5
4.1
4.8
4.6
4.4
4.9
4.6
4.6
4.8
4.6
4.7
4.6
4.6
4.9
4.4
4.7
4.7
4.5
4.5
4.7
—
4-CH
3-CH
4-CH
2-CH
3,4-Di-CH
3,4-Di-CH
2,4-Di-CH
4-t-Bu-Ph
2-Thiophene
Ph
4-CH
3-CH
4-CH
2-CH
3,4-Di-CH
3,4-Di-CH
2,4-Di-CH
4-t-Bu-Ph
Ph
4-CH
4-CH
3,4-Di-CH
3
3
3
3
-Ph
-Ph
O-Ph
O-Ph
3
3
3
-Ph
O-Ph
O-Ph
15.2 ꢃ 2.9
18.7 ꢃ 0.8
10.1 ꢃ 1.1
18.9 ꢃ 0.9
12.9 ꢃ 1.9
17.1 ꢃ 2.5
16.9 ꢃ 2.6
8.8 ꢃ 1.9
3
3
3
3
-Ph
-Ph
O-Ph
O-Ph
3
3
3
-Ph
O-Ph
O-Ph
27.6 ꢃ 3.1
15.5 ꢃ 2.0
12.5 ꢃ 2.9
21.0 ꢃ 1.0
20.5 ꢃ 2.7
16.4 ꢃ 1.9
107.2 ꢃ 1.6
54.9 ꢃ 1.4
61.1 ꢃ 3.4
s
t
u
v
w
3
-Ph
O-Ph
3
3
O-Ph
b
Myr
BT
TC
—
—
—
c
—
—
c
a
ꢀ1
b
c
Tested and calculated at the drug test concentrations of 100, 50, 25, 12.5, and 6.25 mg mL
.
Myr (myricetin). BT (commercial fungicides,
bismerthiazol) and TC (thiediazole copper).
3.6. Structure–activity relationship (SAR) of the title
against the plant virus. According to the anti-TMV activity data
compounds against TMV
of 1,2,4-triazole Schiff base myricetin derivatives, when R ¼ Ph,
3
,4-di-CH -Ph, 3,4-di-CH O-Ph, and 2-thiophene, the
3 3
In summary, the introduction of the 1,2,4-triazole Schiff base
into the myricetin structure showed a good inhibitory activity
compounds have good curative and protective activities. For
Table 3 In vitro antibacterial EC50 activity value of the target compounds against Rs and Xoo
a
2
ꢀ1
Bacteria
Compd
n
R
Toxic regression equation
r
EC50/(mg mL
)
pEC50/(mM)
Rs
6w
5
3,4-Di-CH
3
O-Ph
y ¼ 1.0988x + 3.6922
y ¼ 0.8815x + 3.3101
y ¼ 0.9991x + 3.2599
y ¼ 1.3627x + 2.1291
y ¼ 0.8103x + 3.6447
y ¼ 0.7806x + 3.5304
y ¼ 0.7023x + 3.7451
y ¼ 0.8457x + 3.4899
y ¼ 0.8448x + 3.4411
y ¼ 0.6866x + 3.7132
y ¼ 0.8236x + 3.4626
y ¼ 0.9248x + 3.1185
y ¼ 0.9574x + 3.2088
y ¼ 0.1077x + 2.8916
y ¼ 0.7280x + 3.6251
y ¼ 0.7541x + 3.4240
y ¼ 0.6512x + 3.4715
y ¼ 0.5525x + 3.8806
y ¼ 0.5876x + 3.6813
0.9829
0.9399
0.9930
0.9184
0.9958
0.9988
0.9841
0.9871
0.9947
0.9990
0.9798
0.9728
0.9960
0.9494
0.9920
0.9929
0.9862
0.9947
0.9950
15.5 ꢃ 1.3
82.6 ꢃ 1.0
55.2 ꢃ 3.5
127.9 ꢃ 2.5
47.1 ꢃ 2.6
76.3 ꢃ 1.0
61.2 ꢃ 2.1
61.0 ꢃ 2.9
70.0 ꢃ 3.1
74.8 ꢃ 2.6
73.6 ꢃ 3.9
108.3 ꢃ 2.0
74.3 ꢃ 2.5
90.8 ꢃ 1.8
77.4 ꢃ 3.3
123.0 ꢃ 3.0
222.4 ꢃ 2.4
148.2 ꢃ 2.4
175.5 ꢃ 2.1
4.7
—
—
—
4.1
3.9
b
Myr
—
—
—
3
3
3
3
3
4
4
—
—
—
Ph
c
BT
c
TC
6a
Xoo
6
6
6
6
6
6
6
6
6
6
6
b
d
e
g
k
l
m
n
p
t
4-CH
4-CH
2-CH
3
3
3
-Ph
O-Ph
O-Ph
4.0
4.0
3.9
4.0
3.8
4.0
3.9
3.9
3.7
—
3,4-Di-CH
Ph
3
O-Ph
4-CH
3-CH
4-CH
3
3
3
-Ph
-Ph
O-Ph
4
4
4
5
3,4-Di-CH
Ph
3
-Ph
u
5
3
4-CH -Ph
b
Myr
—
—
—
—
—
—
c
BT
—
—
c
TC
a
ꢀ1
b
c
Tested and calculated at the drug test concentrations of 100, 50, 25, 12.5, and 6.25 mg mL
.
Myr (myricetin). BT (commercial fungicides,
bismerthiazol) and TC (thiediazole copper).
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ꢀ1
ꢀ1
ꢀ1
Fig. 3 SEM images for Xac after incubated in different concentration of compound 6q. (A) 0 mg mL , (B) 12.5 mg mL , and (C) 25 mg mL . Scale
bar for (A, B, and C) are 2 mm.
example, 6a, 6g, 6j, 6t, and 6w have a good therapeutic effect on R group is Ph, 3,4-di-CH -Ph, 3,4-di-CH O-Ph, and 2-thiophene,
3
3
TMV with percentage inhibition of 51.5%, 52.5%, 52.4%, 51.3%, the therapeutic and protective activity of the compounds
and 51.1%, respectively, which are higher than those of myr- against tobacco ower leaf virus is superior to the R group being
icetin (31.6%) and ribavirin (39.9%) but close to that of ning- the other substituent. When n ¼ 3, and n ¼ 4, and the R group is
3
nanmycin (52.7%). Similarly, 6f, 6g, 6k, 6p, 6t, and 6w have 3,4-di-CH O-Ph, the compounds has a relatively good passiv-
a good protective effect on TMV with percentage inhibition of ating activity against tobacco mosaic virus.
8.7%, 55.4%, 57.2%, 57.8%, 56.0%, and 58.0%, respectively,
which are higher than those of myricetin (42.1%) and ribavirin
5
3
.7. Molecular docking of 6g and TMV-CP
(
3
51.8%) but close to that of ningnanmycin (65.7%). When R ¼
,4-di-CH O-Ph, the compound showed better passivation Molecular docking studies for 6g with TMV-CP (PDB code:
activity, e.g., 6g had a good passivation effect on TMV with an 1EI7)
3
35,36
indicated that the compound was well embedded in
percentage inhibition of 88.6%, which exceeded those of myr- the pocket (including residues of TYR139, PRO254, LYS268,
icetin (50.9%) and ribavirin (73.3%) but was close to that of ARG134, ASN140, VAL75, etc.) between the two subunits of TMV-
ningnanmycin (90.4%). In summary, when n ¼ 3, and n ¼ 4, the CP (Fig. 4). It has been reported that these residues played
ꢀ1
Table 4 Antiviral activities of the target compounds against TMV in vivo at 500 mg mL
a
Percentage inhibition /%
Compd
n
R
Curative
Protection
Inactivation
6
6
6
6
6
6
6
6
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
p
q
r
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
5
5
5
5
—
—
—
Ph
51.5 ꢃ 3.1
41.6 ꢃ 2.9
40.8 ꢃ 5.3
47.5 ꢃ 4.8
45.6 ꢃ 7.0
50.4 ꢃ 7.6
52.5 ꢃ 1.9
46.1 ꢃ 5.4
44.3 ꢃ 3.7
52.4 ꢃ 6.8
50.8 ꢃ 3.3
42.0 ꢃ 4.5
39.5 ꢃ 7.0
50.2 ꢃ 4.7
39.0 ꢃ 7.3
49.9 ꢃ 3.4
50.4 ꢃ 7.3
45.1 ꢃ 0.2
44.8 ꢃ 2.6
51.3 ꢃ 5.5
49.6 ꢃ 6.9
46.2 ꢃ 0.8
51.1 ꢃ 7.4
31.6 ꢃ 7.2
39.9 ꢃ 3.7
52.7 ꢃ 1.3
52.6 ꢃ 5.2
48.9 ꢃ 2.8
42.9 ꢃ 3.7
50.0 ꢃ 1.2
27.8 ꢃ 4.9
58.7 ꢃ 5.9
55.4 ꢃ 6.5
50.7 ꢃ 6.2
49.3 ꢃ 7.4
54.6 ꢃ 7.5
57.2 ꢃ 7.2
45.8 ꢃ 2.4
46.1 ꢃ 5.6
48.0 ꢃ 3.6
53.6 ꢃ 6.5
57.8 ꢃ 8.5
52.6 ꢃ 5.8
36.8 ꢃ 4.3
45.5 ꢃ 3.0
56.0 ꢃ 7.1
50.8 ꢃ 4.5
45.3 ꢃ 6.4
58.0 ꢃ 3.1
42.1 ꢃ 6.4
51.8 ꢃ 6.0
65.7 ꢃ 1.9
67.5 ꢃ 8.1
70.4 ꢃ 4.4
47.6 ꢃ 8.5
57.3 ꢃ 9.2
44.5 ꢃ 6.6
41.4 ꢃ 2.8
88.6 ꢃ 4.5
73.2 ꢃ 5.7
77.5 ꢃ 8.9
67.5 ꢃ 8.5
58.9 ꢃ 8.3
60.9 ꢃ 5.3
49.5 ꢃ 2.9
71.4 ꢃ 1.0
67.5 ꢃ 7.1
52.3 ꢃ 2.4
68.9 ꢃ 5.7
55.4 ꢃ 3.5
37.3 ꢃ 7.1
56.4 ꢃ 2.8
51.7 ꢃ 4.6
74.6 ꢃ 8.3
42.8 ꢃ 2.0
50.9 ꢃ 6.3
73.3 ꢃ 2.9
90.4 ꢃ 3.1
4-CH
3-CH
4-CH
2-CH
3,4-Di-CH
3,4-Di-CH
2,4-Di-CH
4-t-Bu-Ph
2-Thiophene
Ph
4-CH
3-CH
4-CH
2-CH
3,4-Di-CH
3,4-Di-CH
2,4-Di-CH
4-t-Bu-Ph
Ph
4-CH
4-CH
3,4-Di-CH
3
3
3
3
-Ph
-Ph
O-Ph
O-Ph
3
3
3
-Ph
O-Ph
O-Ph
3
3
3
3
-Ph
-Ph
O-Ph
O-Ph
3
3
3
-Ph
O-Ph
O-Ph
s
t
u
v
w
3
-Ph
O-Ph
3
3
O-Ph
b
Myr
Ribavirin
Ningnanmycin
—
—
—
c
c
a
b
c
Average of three replicates. Lead compound myricetin. Commercial antiviral agents ribavirin and ningnanmycin.
23050 | RSC Adv., 2019, 9, 23045–23052
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Fig. 4 The binding mode of compound 6g docked with TMV-CP.
33,35,36
important roles in the self-assembly of TMV particles.
For
Conflicts of interest
example, LYS268 and TYR139 play continuous hydrophobic
35
interactions in the ring. In addition, VAL75, VAL260, LYS253, The authors declare that they have no competing interests.
33,35
GLY135, ASN140, ASP266 and other subunits of TMV-CP.
Moreover, there are also p-alkyl, alkyl, amide-p stacking effects,
carbon hydrogen bond between the molecules and the above
residues in TMV-CP as depicted in Fig. 4. For example, TYR139,
PRO254, LYS268, and ARG134 had strong hydrogen bonds with
Acknowledgements
The authors gratefully acknowledge the nancial support of the
National Nature Science Foundation of China (No. 21867003)
and Science Foundation of Guizhou Province (No. 20185781,
˚
˚
˚
˚
6
g (2.40 A, 2.47 A, 2.11 A, and 2.41 A). These interactions
between small molecules and TMV-CP are likely to inhibit the
interaction of two subunit of TMV-CP, thereby preventing the
self-assembly of TMV particle. The results showed that
compound 6g had partially interacted with TMV-CP, and
20191105).
mechanistic studies of the action of compound 6g could be References
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