Synthesis and fungicidal evaluation of novel chalcone-based strobilurin analogues

Article abstract of DOI:10.1021/jf071064x

Strobilurin derivatives have become one of the most important classes of agricultural fungicide due to a novel action mode, wide fungicidal spectrum, lower toxicity toward mammalian cells, and environmentally benign characteristics. To discover new strobilurin analogues with high activity against resistant pathogens, a series of new chalcone-based strobilurin derivatives are designed and synthesized by integrating a chalcone scaffold with a strobilurin pharmacophore. The preliminary bioassay showed that some of the chalcone analogues exhibited good in vivo fungicidal activities against Pseudoperoniospora cubensis and Sphaerotheca fuliginea at the dosage of 200 μg mL^-1. Two compounds, (￡)-methyl 2-[2-({3-[(￡)-3-(2- chlorophenyl)acryloyl]phenoxy}methyl)phenyl]-3-meth-oxyacrylate (1e) and (E)-methyl 2-[2-({3-[(E)-3-(3-bromophenyl)acryloyl]phenoxy}methyl)phenyl]-3- methoxyacrylate (11), were found to display higher fungicidal activities against P. cubensis (EC₉₀ = 118.52 μg ml^-1 for 1e and EC ₉₀ = 113.64 μg mL^-1 for 11) than Kresoxim-methyl (EC₉₀ = 154.92 μg mL^-1) and were identified as the most promising candidates for further study. The present work demonstrated that strobilurin analogues containing chalcone as a side chain could be used as a lead structure for further developing novel fungicides. To our knowledge, this is the first report about the syntheses and fungicidal activities of chalcone-based strobilurin derivatives.

Full text of DOI:10.1021/jf071064x

J. Agric. Food Chem. 2007, 55, 5697−5700 5697
Synthesis and Fungicidal Evaluation of Novel Chalcone-Based
Strobilurin Analogues
PEI-LIANG ZHAO,† CHANG-LING LIU,‡ WEI HUANG,† YA-ZHOU WANG,† AND
GUANG-FU YANG*,†
Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry,
Central China Normal University, Wuhan 430079, People’s Republic of China, and Agrochemical
Discovery Department, Shenyang Research Institute of Chemical Industry,
Shenyang 110021, People’s Republic of China
Strobilurin derivatives have become one of the most important classes of agricultural fungicide due
to a novel action mode, wide fungicidal spectrum, lower toxicity toward mammalian cells, and
environmentally benign characteristics. To discover new strobilurin analogues with high activity against
resistant pathogens, a series of new chalcone-based strobilurin derivatives are designed and
synthesized by integrating a chalcone scaffold with a strobilurin pharmacophore. The preliminary
bioassay showed that some of the chalcone analogues exhibited good in vivo fungicidal activities
against Pseudoperoniospora cubensis and Sphaerotheca fuliginea at the dosage of 200 µg mL-1
.
Two compounds, (E)-methyl 2-[2-({3-[(E)-3-(2-chlorophenyl)acryloyl]phenoxy}methyl)phenyl]-3-meth-
oxyacrylate (1e) and (E)-methyl 2-[2-({3-[(E)-3-(3-bromophenyl)acryloyl]phenoxy}methyl)phenyl]-3-
methoxyacrylate (1l), were found to display higher fungicidal activities against P. cubensis (EC90
)
118.52 µg mL-1 for 1e and EC90 ) 113.64 µg mL-1 for 1l) than Kresoxim-methyl (EC90 ) 154.92 µg
mL-1) and were identified as the most promising candidates for further study. The present work
demonstrated that strobilurin analogues containing chalcone as a side chain could be used as a
lead structure for further developing novel fungicides. To our knowledge, this is the first report about
the syntheses and fungicidal activities of chalcone-based strobilurin derivatives.
KEYWORDS: Strobilurins; fungicide; chalcone; structure-activity relationships
INTRODUCTION
the â-methoxyacrylate group with a structurally diverse side
chain is an effective way to obtain new strobilurin derivatives
with high fungicidal activities (7, 10). We assume that, if the
â-methoxyacrylate pharmacophore was introduced into the
chalcone scaffold, the resulting (E)-methyl 3-methoxy-2-[2-({3-
[(E)-3-substitutedphenylacryloyl]phenoxy}methyl)phenyl]-
acrylate (1) should be an interesting lead structure for fungicide
development (Figure 2), which will be expected to exhibit
interesting features due to the coexistence of two kinds of
fungicidal pharmacophores with different action mechanisms.
Then, as a continuation of our research program of the discovery
of novel lead compounds (10), we described herein the synthesis
and fungicidal activity of a series of new chalcone-containing
strobilurin analogues (1). Meanwhile, as a control, we also
synthesized a series of chalcone analogues (E)-methyl 3-meth-
oxy-2-[2-({2-[(E)-3-substitutedphenylacryloyl]phenoxy}methyl)-
phenyl]acrylate (2) and (E)-methyl 3-methoxy-2-[2-({4-[(E)-3-
substituted-phenylacryloyl]phenoxy}methyl)phenyl]acrylate (3).
Strobilurins, an important family of antifungal antibiotics,
have been identified as one of the most promising lead
compounds for the development of a new generation of
industrial fungicides for crop protection (1-6). Since the first
successful landing of Azoxystrobin and Kresoxim-methyl
(Figure 1) in 1996 (2), over 10 strobilurin derivatives are
commercially available. The advantages such as a novel mode
of action, wide spectrum, low toxicity toward mammalian cells,
and favorable profiles to humans (4-6) prompted chemists to
design and synthesize novel strobilurin derivatives (7-10).
As an intermediate in the biosynthetic pathway of flavonoids,
isoflavonoids, and aurone, chalcones have been shown to display
a diverse array of pharmacological activities, among which are
antifungal, antibacterial, antiprotozoal, anti-inflammatory, an-
titumor, antimalarial, and anti-HIV activities (11-15). However,
to the best of our knowledge, there is, to date, no report about
chalcone-based strobilurins analogues.
It has been demonstrated that the â-methoxyacrylate group
is the essential pharmacophore of strobilurin fungicides. Linking
MATERIALS AND METHODS
Unless otherwise noted, all materials were commercially available
and were used directly without further purification. All solvents were
redistilled before use. H NMR spectra were recorded on a Mercury-
† Central China Normal University.
1
‡ Shenyang Research Institute of Chemical Industry.
10.1021/jf071064x CCC: $37.00
© 2007 American Chemical Society
Published on Web 06/19/2007

5698 J. Agric. Food Chem., Vol. 55, No. 14, 2007
Zhao et al.
Figure 1. Structures of strobilurins, azoxystrobin, and Kresoxim-methyl.
Figure 2. Design strategy of the target compounds.
Figure 3. Molecular structure of 3s.
Plus 400 spectrometer in CDCl3 with tetramethylsilane as the internal
reference. MS spectra were determined using a Trace MS 2000 organic
mass spectrometry. Elementary analyses were performed on a Vario
EL III elementary analysis instrument. Melting points were taken on a
Buchi B-545 melting point apparatus and uncorrected. Intermediates 4
and 5 were prepared according to the reported methods (15, 16), and
the detailed procedure can be found in the Supporting Information.
X-ray Diffraction. Colorless blocks of 3s (0.30 mm × 0.20 mm ×
0.20 mm) were counted on a quartz fiber with protection oil. Cell
dimensions and intensities were measured at 299 K on a Bruker
SMART CCD area detector diffractometer with graphite monochro-
mated Mo KR radiation (λ ) 0.71073 Å), θmax ) 26.00, 22804
measured reflections, and 4363 independent reflections
(Rint ) 0.1146) of which 5421 had |Fo| > 2|Fo|. Data were corrected
for Lorentz and polarization effects and for absorption (Tmin ) 0.9741;
Tmax ) 0.9827). The structure was solved by direct methods using
SHELXS-97 (17); all other calculations were performed with Bruker
SAINT System and Bruker SMART programs (18). Full-matrix least-
squares refinement based on F2 using the weight of 1/[σ2(Fo 2) +
(0.1010P)2 + 0.0000P] gave final values of R ) 0.0618, ωR ) 0.1614,
and GOF(F) ) 1.030 for 301 variables and 3201 contributing
reflections. The maximum shift/error ) 0.000(3), and max/min
residual electron density ) 0.265/-0.492 e Å-3. Hydrogen atoms were
observed and refined with a fixed value of their isotropic displacement
parameter.
General Procedure for the Synthesis of Target Compounds 1,
2, or 3. A mixture of 1.1 mmol of chalcones (8) and 0.16 g (1.2 mmol)
of anhydrous K2CO3 in dry acetone (8 mL) was stirred and refluxed
for 1 h. Then, 0.28 g (1.0 mmol) of (E)-methyl 2-[2-(bromomethyl)-
phenyl]-3-methoxyacrylate (7) was added. The mixture was reacted
for 9-24 h at the refluxing temperature. The resulting mixture was
cooled to room temperature and filtered. The solvent was evaporated
to give the crude product, which was purified by chromatography on
silica using a mixture of petroleum ether and ethyl acetate (8:1) as an
eluant to give the target compounds in yields of 51-84%. The example
data of 1a are shown as follows, while data for 1b-y, 2a-n, and 3a-v
can be found in the Supporting Information.
Evaluation of Fungicidal Activities. The in vivo preventive
activities of compounds 1b-y, 2a-n, and 3a-v against cucumber
Pseudoperoniospora cubensis, Sphaerotheca fuliginea, Botrytis cinerea,
and Rhizoctonia solani were tested according to the procedure described
previously (10, 19). The results are listed in Table 1, in which the
inhibition percentage was expressed as the mean of values obtained in
three independent experiments. Kresoxim-methyl, a commercial fun-
gicide, was used as a control.
1
Data for 1a. Yield, 71%; mp, 101-103 °C. H NMR (400 MHz,
CDCl3): δ: 2.32 (s, 3H, ArCH3), 3.70 (s, 3H, COOCH3), 3.81 (s, 3H,
OCH3), 5.04 (s, 2H, CH2), 7.14-7.23 (m, 2H, ArH), 7.33-7.44 (m,
6H, ArH), 7.51-7.59 (m, 6H, ArH, dCH-CO, dCH-OCH3), 7.78
(d, J ) 15.6 Hz, 1H, dCH-Ar). MS m/z (%): 443 (M+ + 1, 24), 442
(M+, 23), 236 (96), 222 (100), 209 (47), 203 (93), 194 (72), 177 (94),
141(89), 114 (98), 101 (95). Anal. calcd for C28H26O5: C, 76.00; H,
5.92. Found: C, 76.23; H, 5.75.

Chalcone-Based Strobilurin Analogues
J. Agric. Food Chem., Vol. 55, No. 14, 2007 5699
dimethyl sulfate to afford exclusively (E)-methyl 3-methoxy-
2-o-tolylacrylate (6). Then, compound 6 was treated with
N-bromosuccinimide in the presence of a catalytic amount of
2,2′-azobis(isobutyronitrile) to give 7 in a yield of 83%.
Subsequently, compound 7 was reacted with the chalcones 8,
which were prepared by a base-catalyzed Claisen-Schmidt
condensation of o-, m-, or p-hydroxyacetophenone with sub-
stituted benzaldehydes (15), to afford the target compounds 1a-
y, 2a-n, or 3a-v in yields of 51-84%.
The structures of all of the target compounds were character-
ized by 1H NMR, electron impact-mass spectrometry spectra,
and elemental analyses. In addition, the crystal structure of 3s
was determined by X-ray diffraction analyses. As shown in
Figure 3, both the chalcone moiety and the â-methoxyacrylate
group adopt an E-configuration. C25, C24, C25, C26, O4, and O3
are almost coplanar due to the formation of three hydrogen
bonds (C25-HA‚‚‚O3, 2.57 Å; C25-HC‚‚‚O3, 2.61 Å; and C26-
H‚‚‚O3, 2.62 Å). Additionally, the hydrogen bond between O1
and C7-H makes the E-configuration of the chalcone moiety
more stable.
Table 1. Structures and Fungicidal Activities of Compounds 1a−y,
2a
−n, and 3a−v
200 mg/L
P. cubensis S. fuliginea B. cinerea R. solani
no.
R1
R2
1a 4-MeC6H4
100
95
100
0
97
0
96
0
94
30
31
0
45
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
16
24
10
0
0
0
0
0
0
0
0
0
0
0
21
0
0
0
11
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1b 4-OMeC6H4
1c 4-ClC6H4
1d 3,4-Cl2C6H3
1e 2-ClC6H4
98
33
97
96
94
81
72
99
100
97
0
1f
3-ClC6H4
1g 4-FC6H4
1h C6H5
1i
1j
4-BrC6H4
3-MeC6H4
1k 3,4-(OMe)2C6H3
1l 3-BrC6H4
0
99
92
13
0
0
0
0
0
0
0
1m 3,4-(Me)2C6H4
1n 2-F-6-ClC6H3
1o 4-N(Me)2C6H4
1p 3,4-OCH2OC6H4
1q 4-EtOC6H4
0
32
29
0
30
0
0
33
54
0
0
0
1r
1s 2-C4H3O
1t 2-C4H3S
2,4-Cl2C6H4
Fungicidal Activity and Structure-Activity Relationship.
The in vivo fungicidal results of all of the compounds against
P. cubensis, S. fuliginea, B. cinerea, and R. solani were listed
in Table 1. For the convenience of structure-activity relation-
ship analysis, compounds 1a-y, 2a-n, and 3a-v were defined
as m-chalcone derivatives, o-chalcone derivatives, and p-
chalcone derivatives, respectively. Although it seems impossible
to extract an obvious structure-activity relationship from the
data shown in Table 1, we can conclude clearly that all
compounds did not exhibit good fungicidal activity against B.
cinerea and R. solani at the concentration of 200 µg mL-1, and
overall, the sequence of fungicidal activity against P. cubensis
and S. fuliginea is m-chalcone derivatives > p-chalcone deriva-
tives > o-chalcone derivatives. For example, m-chalcone
derivative 1m (R1 ) 3,4-dimethylphenyl, 100 and 92%)
displayed a much higher fungicidal activity against P. cubensis
and S. fuliginea than the corresponding p-chalcone derivative
3f (67 and 30%), while the o-chalcone derivative 2m did not
show any fungicidal activity. However, compounds 1u and 3q
are two exceptions: Compound 1u did not exhibit fungicidal
activity against P. cubensis and S. fuliginea, while compound
3q showed excellent fungicidal activity (97%) against P.
cubensis. Within the series of m-chalcone derivatives, com-
pounds 1a (R1 ) 4-methylphenyl), 1c (R1 ) 4-chlorophenyl),
1e (R1 ) 2-chlorophenyl), 1l (R1 ) 3-bromophenyl), and 1m
(R1 ) 3,4-dimethylphenyl) displayed excellent fungicidal activ-
ity (>90%) against both P. cubensis and S. fuliginea at the
concentration of 200 µg mL-1, while compounds 1b (R1 )
4-methoxylphenyl), 1g (R1 ) 4-fluorophenyl), 1h (R1 ) phenyl),
1i (R1 ) 4-bromophenyl), 1n (R1 ) 2-fluoro-6-chlorophenyl),
1w (R1 ) 2-bromophenyl), and 1x (R1 ) 4-ethylphenyl)
exhibited excellent fungicidal activity (>90%) against S. fuligi-
nea. However, only three compounds among 22 p-chalcone
derivatives were found to display over 90% preventive effect
0
1u 3-FC6H4
1v 2-FC6H4
1w 2-BrC6H4
1x 4-EtC6H4
1y 4-t-BuC6H4
2a 4-MeC6H4
2b 4-MeOC6H4
2c C6H5
36
38
31
0
0
0
100
100
28
0
0
0
39
78
89
0
0
0
0
0
61
0
0
56
56
62
47
75
67
11
86
33
100
0
59
78
78
0
0
0
0
0
0
0
86
0
0
0
0
0
0
0
0
0
0
0
30
0
0
67
0
0
0
0
78
0
0
0
67
0
56
67
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4-Cl
4-Cl
4-Cl
2d 3-ClC6H4
2e 3-BrC6H4
2f
4-ClC6H4
4-Me
4-Cl
4-Cl
2g 2-ClC6H4
2h 4-ClC6H4
2i
2j
4-BrC6H4
4-MeOC6H4
2k 4-ClC6H4
2l 3-MeOC6H4
2m 3,4-(Me)2C6H3
2n 3,4-(OMe)2C6H3
3a 4-BrC6H4
3b 3-BrC6H4
0
0
0
3c 4-MeOC6H4
3d 3-MeC6H4
3e 4-MeC6H4
38
0
3f
3,4-(Me)2C6H4
3g 3,4-(OMe)2C6H4
3h 3-MeOC6H4
0
20
37
0
3i
3j
3,4-Cl2C6H4
2-ClC6H4
3k 3,4-OCH2OC6H3
3l 4-FC6H4
0
100
59
67
0
23
0
27
0
3m 4-EtOC6H4
3n 2,4-Cl2C6H4
3o 2-C4H3O
3p 2-C4H3S
3q 3-FC6H4
0
0
0
97
83
0
15
22
67
100
3r
2-BrC6H4
21
0
69
0
3s C6H5
3t
4-EtC6H4
3u 4-t-BuC6H4
3v 2-F-6-ClC6H3
Kresoxim-methyl (200 mg/L)
0
against P. cubensis at the concentration of 200 µg mL-1
.
100
In addition, as shown in Table 1, compounds 1a,c,e,l,m were
found to display broad spectrum fungicidal activities. Then, these
five compounds were selected for further tests, and Kresoxim-
methyl was used as a control to make a judgment on the
fungicidal potency of these compounds. As shown in Table 2,
the fungicidal activities against S. fuliginea of compounds
1a,c,e,l,m were much lower than that of Kresoxim-methyl.
Fortunately, compounds 1e (EC90 ) 118.52 µg mL-1, P.
cubensis) and 1l (EC90 ) 113.64 µg mL-1, P. cubensis) were
RESULTS AND DISCUSSION
Synthetic Chemistry. The synthetic route for the target
compounds is outlined in Scheme 1. Methyl 2-o-tolylacetate
(4), which was prepared in a good yield (94%) according to
the reported method (9), reacted with methyl formate in the
presence of sodium hydride to give the intermediate 5.
Fortunately, compound 5 was reacted stereoselectively with

5700 J. Agric. Food Chem., Vol. 55, No. 14, 2007
Zhao et al.
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concentration
EC90
g mL
EC90
g mL
-1
-
1
-1
(µ
g mL
)
100
50
25
3
(
µ
)
100 50 25
(
µ
)
1a
1c
1e
1l
47
4
22
22
77
7
52
26
85
87
69
80
11
77 69
37
44
118.52
113.64
3
14
4
1m
139.47
7.30
Kresoxim-methyl 100 100 98
56 27
154.92
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found to display higher fungicidal activity against P. cubensis
than Kresoxim-methyl (EC90 ) 154.92 µg mL-1, P. cubensis).
However, compound 1l displayed a lower activity against P.
cubensis than Kresoxim-methyl at low concentration (50 and
25 µg mL-1). On the basis of these results, it can be concluded
that 3-chalcone is the best side chain among 2-, 3-, and
4-chalcone.
In conclusion, we have demonstrated the molecular designs,
syntheses, and fungicidal activities of a series of chalcone
analogues of strobilurin derivatives. The preliminary bioassay
showed that some of the chalcone analogues exhibited good in
vivo fungicidal activities against P. cubensis and S. fuliginea
at the dosage of 200 mg/L. Two compounds, 1e and 1l, were
found to display higher fungicidal activities against P. cubensis
(EC90 ) 118.52 µg mL-1 for 1e and EC90 ) 113.64 µg mL-1
for 1l) than Kresoxim-methyl (EC90 ) 154.92 µg mL-1) and
were identified as the most promising candidate for further
study. To our knowledge, this is the first report about the
syntheses and fungicidal activities of chalcone-based strobilurin
derivatives. Further structural optimization and fungicidal activi-
ties about the chalcone analogues are well under way.
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ACKNOWLEDGMENT
We thank Dr. Jie Chen for the test of biological activity.
Supporting Information Available: 1H NMR, MS, melting
point, and element analysis data for the intermediates and the
target compounds. This material is available free of charge via
the Internet at http://pubs.acs.org.
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Received for review April 11, 2007. Revised manuscript received May
17, 2007. Accepted May 17, 2007. The present work was supported by
National “973” Project (2003CB114400), National NSFC (20572030,
20528201, and 20432010), the Cultivation Fund of the Key Scientific
and Technical Innovation Project, Ministry of Education of China
(705039), and Program for Excellent Research Group of Hubei Province
(2004ABC002).
JF071064X