Expanding the Chemical Space of Succinate Dehydrogenase Inhibitors via the Carbon-Silicon Switch Strategy

Article abstract of DOI:10.1021/acs.jafc.0c07322

The carbon-silicon switch strategy has become a key technique for structural optimization of drugs to widen the chemical space, increase drug activity against targeted proteins, and generate novel and patentable lead compounds. Flubeneteram, targeting succinate dehydrogenase (SDH), is a promising fungicide candidate recently developed in China. We describe the synthesis of novel SDH inhibitors with enhanced fungicidal activity to enlarge the chemical space of flubeneteram by employing the C-Si switch strategy. Several of the thus formed flubeneteram-silyl derivatives exhibited improved fungicidal activity against porcine SDH compared with the lead compound flubeneteram and the positive controls. Disease control experiments conducted in a greenhouse showed that trimethyl-silyl-substituted compound W2 showed comparable and even higher fungicidal activities compared to benzovindiflupyr and flubeneteram, respectively, even with a low concentration of 0.19 mg/L for soybean rust control. Furthermore, compound W2 encouragingly performed slightly better control than azoxystrobin and was less active than benzovindiflupyr at the concentration of 100 mg/L against soybean rust in field trials. The computational results showed that the silyl-substituted phenyl moiety in W2 could form strong van der Waals (VDW) interactions with SDH. Our results indicate that the C-Si switch strategy is an effective method for the development of novel SDH inhibitors.

Full text of DOI:10.1021/acs.jafc.0c07322

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Article
Expanding the Chemical Space of Succinate Dehydrogenase
Inhibitors via the Carbon−Silicon Switch Strategy
Ge Wei,§ Ming-Wei Huang,§ Wen-Jie Wang, Yuan Wu, Shu-Fen Mei, Li-Ming Zhou, Long-Can Mei,
Xiao-Lei Zhu,* and Guang-Fu Yang*
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ABSTRACT: The carbon−silicon switch strategy has become a key technique for structural optimization of drugs to widen the
chemical space, increase drug activity against targeted proteins, and generate novel and patentable lead compounds. Flubeneteram,
targeting succinate dehydrogenase (SDH), is a promising fungicide candidate recently developed in China. We describe the
synthesis of novel SDH inhibitors with enhanced fungicidal activity to enlarge the chemical space of flubeneteram by employing the
C−Si switch strategy. Several of the thus formed flubeneteram-silyl derivatives exhibited improved fungicidal activity against porcine
SDH compared with the lead compound flubeneteram and the positive controls. Disease control experiments conducted in a
greenhouse showed that trimethyl-silyl-substituted compound W2 showed comparable and even higher fungicidal activities
compared to benzovindiflupyr and flubeneteram, respectively, even with a low concentration of 0.19 mg/L for soybean rust control.
Furthermore, compound W2 encouragingly performed slightly better control than azoxystrobin and was less active than
benzovindiflupyr at the concentration of 100 mg/L against soybean rust in field trials. The computational results showed that the
silyl-substituted phenyl moiety in W2 could form strong van der Waals (VDW) interactions with SDH. Our results indicate that the
C−Si switch strategy is an effective method for the development of novel SDH inhibitors.
KEYWORDS: succinate dehydrogenase inhibitors, silicon, soybean rust, docking
pyrazole-carboxamide moiety was particularly important for
the fungicidal activity of this novel class of SDH inhibitors
(SDHIs). Recently, we also found that when the diphenyl
ether was connected to the pyrazine-carboxamide, compounds
exhibited a 100% inhibitory rate against Botryotinia fuckeliana
in vitro at a concentration of 20 mg/L and a 95% inhibitory
rate against soybean gray mold in vivo at a concentration of
100 mg/L dosage.20 Indeed, the usefulness of diphenyl ether
substituted compounds is increasingly being recognized, and
recently we have reviewed the medicinal and agrochemical
versatility of the diphenyl ether fragment.21
Herein, novel SDHIs have been developed by employing the
C−Si switch strategy to widen the chemical space of
flubeneteram and thereby increase its fungicidal activity
(Figure 1). We report the design, synthesis, and fungicidal
activity of a series of flubeneteram-silyl compounds with
enhanced fungicidal activity against porcine SDH compared
with the lead compound flubeneteram and positive control.
Furthermore, the target compounds were investigated for their
ability to control several important crop diseases in greenhouse
experiments, with most compounds showing particularly high
disease control (>80%) against soybean rust (SBR) at a
INTRODUCTION
■
The incorporation of Si into a drug scaffold and substituting C
at a specific position of the molecular skeleton (known as the
C−Si switch strategy) has become a key approach for widening
the chemical space and optimizing the activity of a compound
against target proteins, which has led to the recent develop-
ment and patenting of a novel lead compound.1−9 Compared
to their all carbon counterparts, organosilicon molecules may
have significantly improved pharmacological properties, such
as improved bioactivity, stability, and pharmacokinetic proper-
ties.10−13 A good example in this regard is silyl-substituted
indomethacin derivatives, which exhibit enhanced anticancer
activity against a human pancreatic cancer cell line and several
human multiple myeloma cell lines compared to the parent
indomethacin.14 In addition, the C−Si switch strategy has also
been successfully applied in the preparation of the fungicide
flusilazole,15 silthiofam,16 and insecticide silafluofen.17 Maien-
fisch et al. recently reported improved pharmacological
properties in the acaracide sila-cyflumetofen compared to
those in cyflumetofen.18
Flubeneteram is a promising fungicide candidate recently
discovered in China in 2017, containing a pyrazole-
carboxamide diphenyl ether moiety, with an IC50 value of
0.19 μM against porcine succinate dehydrogenase (SDH).17
Experiments for determining its biological efficacy showed that
flubeneteram displayed excellent protection against Rhizoctonia
solani and Sphaerotheca fuliginea, even at dosages as low as 6.25
mg/L.17−19 Structure−activity relationships of flubeneteram
determined that the inclusion of a diphenyl ether linked to a
Received: November 19, 2020
Revised: March 10, 2021
Accepted: March 18, 2021
Published: March 29, 2021
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© 2021 American Chemical Society
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Figure 1. Design protocol of flubeneteram-silyl derivatives.
a
Scheme 1. Synthetic Route of Compounds, Reagents, and Conditions
a
(a) triethyl orthoformate, Ac2O, reflux; (b) methylhydrazine, NaOH, toluene/H2O; (c) LiOH, THF/H2O, reflux; (d) SOCl2, reflux; (e)
methylhydrazine, toluene, reflux; (f) phosphorus oxychloride, DMF; (g) KF, tetrabutylazanium, DMF; (h) KMnO4, H2O; (i) SOCl2, reflux; (j) t-
BuLi, chlorosilane, THF, −78 °C; (k) o-fluoronitrobenzene, K2CO3, DMF, reflux; (l) Fe, NH4Cl, EtOH; and (m) pyrazole-4-carbonyl chloride,
Et3N, CH2Cl2.
crystal structure is shown in Figure 1S (SI). The atomic coordinates
of W2 have been deposited with the Cambridge Crystallographic Data
Centre (CCDC-2006730), from where the full crystallographic data
can be obtained.
concentration of 6.25 mg/L. Flubeneteram-silyl analogue W2
exhibited the most potent fungicidal activity against SBR in
both greenhouse and field trials. Further computational
simulations revealed that the distal silyl-substituted phenyl
moiety in W1−W17 occupied the entrance to the SDH
binding site, thereby forming stronger van der Waals (VDW)
interactions compared to those in flubeneteram. This further
clarifies the structural requirements of SDHIs with high
fungicidal activity against SBR.
Molecular Docking. The 3D structures of the newly synthesized
compounds were constructed based on the crystal structure of W2
using SYBYL and then minimized with the steepest descent method
and conjugate gradient method, both with 2000 steps and a
convergence criterion of 0.001 kcal/mol/Å. Molecular docking of
the porcine SDH receptor was performed using its crystal structure
(PDB ID: 3ABV)25 and the modeling was performed with Autodock
4.2.26 In 3ABV, it contains four chains, called A, B, C, and D chains.
The binding site was constructed by B, C, and D chains. And then, the
A chain was deleted in the following molecular docking. The grid
center was set according to the ligand in 3ABV. The grid box was set
as 40 × 40 × 40, and the grid space was set at 0.375 Å. The default
values were used for other parameters. We acquired 256 possible
binding conformations with the conformation search method of the
Lamarckian genetic algorithm (LGA),27 which were then subjected to
further energy minimization and short molecular dynamics simu-
lations following our previously established protocol.28 Finally, the
molecular mechanics/Poisson−Boltzmann surface area (MM/PBSA)
method was used to calculate the binding energy of the minimized
complex structure.29 The final structure was selected based on the
binding energy and binding mode of commercial carboxamide
fungicides obtained from our previous study.30
MATERIALS AND METHODS
■
Chemistry. Melting points were measured on a Bu
̈
CHI B-545
melting point apparatus without correction. H NMR and 13C NMR
spectra were measured on a Varian Mercury-Plus 600 or 400
spectrometer (Varian Inc., Palo Alto, CA) using CDCl3 or DMSO-d6
as the solvent. High-resolution mass spectra (HRMS) were acquired
on a MALDI SYNAPT G2 HDMS (MALDI). Crystal structures were
identified on a Bruker Smart Apex charge-coupled device. All reagents
and solvents were commercially available and used directly without
further purification.
1
Synthetic Chemistry. Intermediates 5a, 10a, and 12a−12q were
synthesized according to the previously published methods.22−24
Detailed synthetic procedures and characterization data for all of the
newly synthesized compounds are given in the Supporting
Information (SI).
X-ray Diffraction. We used X-ray diffraction to verify the
structure of W2 on Bruker Smart Apex DUO. The crystal data and
refinement parameters of W2 are listed in Table 1S (SI), and the
Enzymatic Activity. SDH from the porcine heart was prepared
following our previously established procedure.31,32 The enzymatic
activities of SDH were analyzed as reported previously.31,32 The
inhibition rates of target compounds were determined at concen-
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trations of 1 μM, while IC50 values were determined by varying
inhibitor concentrations. The commercial fungicide pydiflumetofen
and benzovindiflupyr were chosen as the positive controls.
Fungicidal Activity in Greenhouse. The protective activities of
the target compounds in a greenhouse against soybean rust (SBR:
Phakopsora pachyrhizi Sydow), wheat powdery mildew (WPM:
Erysiphe graminis), rice blast (RB: Pyricularia grisea), cucumber
downy mildew (CDM: Pseudoperonospora cubensis), and soybean gray
mold (SGM: Botritis cinerea) were determined following the pesticide
bioassay developed by Shenyang Sinochem Agrochemicals R&D
Company Ltd. (Shenyang, China);33,34 the results are summarized in
Tables 3, 2S, and 3S (SI).
Table 1. Inhibition Activities of Compounds W1−W17
a
against Porcine SDH
Field Trials. Field trials were conducted in the experimental base
of Shenyang (Liaoning province) in a plot with an area of 25 m2, and
with soybean plants at the five-leaf stage using the standard method
(see SI for full details).
RESULTS AND DISCUSSION
■
Synthetic Chemistry. A series of novel flubeneteram-silyl
derivatives were synthesized, and the general synthetic route is
outlined in Scheme 1. The key electrophilic intermediates 5a
and 10a are the classic pyrazole-4-carbonyl chloride in
succinate dehydrogenase inhibitors (SDHIs), and the synthetic
routes from our previously published methods were followed.35
Silyl-substituted phenols 12a−12q were obtained by the
reaction of substituted phenols and chlorosilane in the
presence of n-BuLi. The intermediate then reacts with 2-
fluoronitrobenzene in DMF and potassium carbonate affording
diphenyl ethers 13a−13q, which were subsequently reduced to
generate silyl-substituted 2-aminodiphenyl ethers 14a−14q.
The final coupling step involved the reaction of acyl chlorides
5a and 10a with the silyl-substituted amino analogues 14a−
14q to generate the corresponding target compounds W1−
W17 in yields generally exceeding 60%.
a
I = inhibition rate tested at 1 μM concentration.
With this in mind, we investigated the effect of varying the
steric bulk of the groups R1−R3 at C-2 of the distal phenyl
group on the compound activity. We found that increasing the
steric bulk of R1−R3 (R4 = 5-methyl) increased the activity of
the target compounds against porcine SDH, as observed by
comparing W2 (R1−R3 = methyl, IC50 = 0.23 μM), W7 (R1−
R3 = ethyl, IC50 = 0.19 μM), and W12 (R1−R3 = n-Pr, IC50
=
0.034 μM). However, an excessively large alkyl-substituted silyl
moiety was deleterious for the activity, and when R1−R3 was
increased to n-butyl as in W14, the inhibitory rate decreased to
41% compared with W2 (IC50 = 0.23 μM). In addition, the
same steric effect was also observed by single substitution on
the silyl moiety, such as in W8, which has a greater inhibition
(R1, R2 = methyl, R3 = ethyl; IC50 = 0.083 μM), than W2 (R1−
R3 = methyl). The inhibition with W8 was comparable to that
with W10 (R1, R2 = methyl, R3 = trifluoropropyl; IC50 = 0.086
μM) but, in any case, considerably greater than W2, which
confirms our finding of greater inhibition as the steric bulk in
R1−R3 increases. However, the similar inhibitory rate in W13
(R1, R2 = methyl, R3 = allyl, IC50 = 0.27 μM) compared to W2
despite the increased steric bulk in W13 suggests that the
interaction between SDH and inhibitor is intricate.
The structure of the target compounds was confirmed by 1H
NMR, 13C NMR, and HRMS analyses (see SI). A full crystal
structure was obtained for the target compound W2 (Figure
1S); the crystal data and the structure refinement parameters
are shown in Table 1S.
Structure−Activity Relationships. The enzymatic inhib-
ition exhibited by all newly synthesized compounds W1−W17
against porcine SDH was assayed, and the determined
inhibitory rate or IC50 values are listed in Table 1. For
comparison, the inhibitory activities of commercial fungicides,
pydiflumetofen and benzovindiflupyr, as well as the corre-
sponding nonsilyl-containing fungicide candidate flubeneter-
am, are also presented. Most of the compounds exhibited good
inhibitory activity against porcine SDH. Substitution at C-2 of
the distal phenyl ring with a trimethyl-silyl moiety in W4 (IC50
= 2.52 μM) led to a higher inhibitory activity than substitution
at either C-3 (W5, I = 37.49%) or C-4 (W3, I = 46.24%).
Moreover, even with additional alkyl substitution on the
phenyl ring, trimethyl-silyl substitution at C-2 is still found to
be optimal for inhibition. For example, W2 (with R1−R3 = Me
Liu et al. reported that fluorine substitution in pyrazole rings
enhanced compound activities.34,36−39 Considering the
enhancement in properties brought about by the incorporation
of fluorine into the pyrazole ring of SDHIs, compounds W15−
W17 were generated containing a fluorine atom in the pyrazole
ring at R5 (Figure S1). In general, except for W17, the fluorine-
substituted analogues W15 (IC50 = 0.25 μM) and W16 (IC50 =
0.44 μM) exhibited lower activities than their hydrogen-
containing counterparts W2 (IC50 = 0.23 μM) and W8 (IC50
=
at C-2 and R4 = Me at C-5) shows greater inhibition (IC50
=
0.083 μM), respectively. Overall, these results indicate that the
fungicidal activity is influenced by both the nature of the
aliphatic substituents on the silyl group and its position within
the phenyl group.
Evaluating our results, we can see that the optimal fungicidal
activity was obtained with W12 (IC50 = 0.034 μM), which is
more active than benzovindiflupyr (IC50 = 0.091 μM),
0.23 μM), compared to W1 (IC50 = 1.17 μM) with the same
substituents, but switched in position (Table 1). However,
when a triethyl-silyl moiety was substituted at C-2, the
opposite trend was observed and the inhibitory effect was
slightly reduced compared to substitution at C-5 (compare
W7, IC50 = 0.19 μM to W6, IC50 = 0.13 μM). From these
results, we concluded that the compound displayed preferred
activity with C-2 silyl-substituted analogues.
pydiflumetofen (IC50 = 0.13 μM), and flubeneteram (IC50
0.19 μM), by about 3, 4, and 6 times, respectively.
=
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Binding Free Energy Calculation. To further understand
the structure−activity relationships (SARs) at the atomic level,
we performed molecular docking and binding energy
calculations for target compounds with determined IC50
values. As summarized in Table 2, the calculated binding
greatly increasing the complementarity at the entrance of the
SDH binding site due to the formation of hydrophobic
interactions with D_Y91. A similar phenomenon was observed
in the other target compounds (Figure 3S, SI). Moreover, the
Anal module in Amber9 was used to calculate the VDW
energies between the inhibitor and some key residues in the
SDH binding site (Figure 4S, SI). The VDW energies between
W1−W17 and D_Y91, C_I43, and C_R46 residues ranged
from −5.62 to −7.78 kcal/mol, −4.98 to −8.01 kcal/mol, and
−5.04 to −7.96 kcal/mol, respectively, which were far larger
than those of flubeneteram (−2.45, −3.49, and −4.12 kcal/
mol, respectively). In addition, the ΔEvdw accounts for the
greatest contribution to ΔGcal (Table 2). Therefore, the nature
of the VDW interactions between the inhibitor and SDH plays
an important role in improving compound activity and, by
employing the C−Si switch strategy, strengthening these
interactions and therefore increasing the inhibition of silyl-
flubeneteram analogues.
Fungicidal Activities in a Greenhouse Environment.
The fungicidal activities of all of the target compounds were
evaluated against some important crop diseases, such as
soybean rust (SBR), wheat powdery mildew (WPM), rice blast
(RB), cucumber downy mildew (CDM), and soybean gray
mold (SGM), in a greenhouse environment. The recently
developed SDH commercial fungicides pydiflumetofen,
benzovindiflupyr, and isoflucypram were used as the positive
controls, and the results are presented in Tables 3, 2S, and 3S
(SI), respectively. It is noteworthy that W1−W17 exhibit
particularly strong fungicidal activity against P. pachyrhizi
Sydow, which causes SBR and is the most significant economic
threat to soybean growers all over the world, especially in
Brazil. When the crop was treated at a concentration of 100
mg/L, disease control effects against SBR were greater than
90% for most compounds, except W6−W7, W9, W11−W12,
and W14. Moreover, when the dosage was reduced from 100
to 6.25 mg/L, the control effect of most compounds was
directly dependent on their concentration. Even at a low
dosage of 6.25 mg/L, compounds W2−W4, W8, W13, and
W15−W17 still had a protective effect with control of over
90% against SBR. However, the fungicidal activities of these
compounds for other diseases, such as WPM, RB, CDM, and
SGM, were very low at dosages of 6.25 mg/L. Subsequently,
the compound candidates with the most promising fungicidal
activities (control effect > 80%) were selected for further
experiments at lower dosages ranging from 0.19 to 3.13 mg/L
Table 2. Binding Energies (kcal/mol) of Target Compounds
with SDH
a
no.
ΔEvdw
ΔEele
ΔGpol
ΔGnp
ΔGcal
ΔGexp
W1
W2
W4
W6
W7
W8
W10
W11
W12
W13
W15
W16
W17
−49.70
−48.85
−48.95
−52.29
−50.99
−51.34
−52.35
−50.33
−53.21
−51.21
−50.90
−48.58
−47.07
−27.89
−26.73
−22.02
−27.21
−24.97
−24.62
−26.08
−19.56
−25.41
−22.34
−21.25
−21.06
−23.64
50.32
45.27
44.92
48.78
45.43
44.57
47.27
41.35
47.32
44.74
42.43
41.92
43.13
−4.25
−4.41
−4.32
−4.55
−4.55
−4.44
−4.56
−4.52
−4.99
−4.50
−4.50
−4.46
−4.34
−31.52
−34.71
−30.38
−35.27
−35.08
−35.83
−35.72
−33.06
−36.28
−33.31
−34.21
−32.19
−31.93
−8.11
−9.08
−7.66
−9.42
−9.19
−9.68
−9.66
−8.86
−10.21
−8.98
−9.03
−8.69
−8.49
a
ΔGexp = −RTLnIC50.
energies (ΔGcal) ranged from −30.38 to −36.28 kcal/mol,
whereas the experimental binding energies (ΔGexp
=
−RTLnIC50) ranged from −7.66 to −10.21 kcal/mol. While
it is evident that the MM-PBSA calculations systematically
overestimated the absolute binding affinities of the ligand
toward SDH, the same trend in binding energies for the target
compounds (ΔGcal) was observed as in the experimental
energies (ΔGexp), with the correlation coefficient R2 0.93
between them (Figure 2S, SI), indicating the reliability of the
computational results.
The binding mode of compound W12 with SDH is shown in
Figure 2A. The compound showed a conserved binding mode
compared with commercial SDHI fungicides, forming hydro-
gen bonds (H-bonds) with B_W173 and D_Y91 and a cation-
π interaction with C_R46. The binding mode demonstrates
the importance of the silyl moiety for attaining an optimal fit
with the entrance to the SDH binding site via the formation of
hydrophobic interactions, and therefore for increasing
compound fungicidal activity. As shown in Figure 2B, the
distal phenyl ring substituted with tripropyl-Si in W12 reverses
the spatial configuration of the inhibitor by 180 degrees,
Figure 2. (A) Binding mode of W12 with SDH. (B) Binding mode overlay of W12 (cyan sticks) with flubeneteram (magenta sticks).
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than that of all of the positive controls (flubeneteram: 20%
control, isoflucypram: 20% control, benzovindiflupyr: 50%
control). The superiority of W2 over lead compound
flubeneteram can be observed by the fact that while at the
very low dosage of 0.19 mg/L, flubeneteram shows no control,
and W2 still maintains control of 30%. Furthermore, the logP
values for W2 (6.45) and flubeneteram (5.19), calculated using
tools from the Molinspiration website,40 are indicative of the
greater lipophilicity of W2 (imparted as a result of the C−Si
exchange strategy) and might be an important factor explaining
its enhanced fungicidal activity. These results suggest that the
incorporation of the trimethyl-silyl group into the flubeneteram
scaffold plays a key role in increasing fungicidal activities,
especially at very low treated concentrations.
Table 3. Fungicidal Activity of the Target Compounds in
Greenhouse
Soybean rust
C (mg/L)/control effect (%)
no.
100 (mg/L)
25 (mg/L)
6.25 (mg/L)
W1
W2
W3
W4
W5
W6
W7
W8
98
100
96
99
98
50
80
99
55
99
45
25
100
45
98
95
98
70
99
98
85
98
96
98
88
20
65
98
50
98
35
5
100
35
98
95
95
35
99
85
35
98
90
98
85
0
30
85
40
80
20
0
92
30
95
90
90
10
99
80
In addition, the EC50 value was elucidated for some of the
more potent target compounds, as well as the positive controls
for comparison. Compound W2 (EC50 = 0.21 mg/L) had the
greatest inhibitory effect, impressively even higher than that of
the positive controls (flubeneteram: EC50 = 0.76 mg/L,
W9
W10
W11
W12
W13
W14
W15
W16
W17
benzovindiflupyr: EC50 = 0.30 mg/L, isoflucypram: EC50
=
1.99 mg/L).
Field Trials. To further study the potential of compound
W2 against SBR, field experiments were performed during the
soybean-growing season. Two commercial fungicides with
different modes of action (MOA), benzovindiflupyr (targeting
SDH), and azoxystrobin (targeting the respiratory chain
cytochrome bc1 complex) were selected as positive controls.
As presented in Table 5 and Figure 5S (SI), compound W2
pydiflumetofen
benzovindiflupyr
isoflucypram
(Table 4). At a concentration of 0.78 mg/L, the control effect
against SBR varied widely among different fungicides,
including the positive controls, and often showed marked
decreases from higher concentrations of the compound; for
instance, the control in the commercial fungicide isoflucypram
decreased from 80% at 6.25 mg/L to 30% at 0.78 mg/L. In
contrast, compounds W2 and W8 had a greater protective
effect than isoflucypram at 0.78 mg/L with 80% control against
SBR, similar to that of the lead compound flubeneteram (78%
control) and slightly lower than that of benzovindiflupyr (90%
control). We should notice that benzovindiflupyr was the most
potent SDHI fungicide against SBR at present. Interestingly,
when the concentration was decreased to 0.38 mg/L, W2 still
had a protective effect with control of 80%, considerably higher
Table 5. Control Effect of W2 against Soybean Rust in Field
Trial
products
W2 50 (mg/L)
control effect (%)
68
W2 100 (mg/L)
72
W2 200 (mg/L)
80
benzovindiflupyr 100 (mg/L)
25% azoxystrobin SC 100 (mg/L)
CK
96
68
80% (disease index)
exhibited good inhibitory activity (72% control) against SBR at
100 mg/L, which was superior to that exhibited by
Table 4. Fungicidal Activity and EC50 Value of the Target Compounds in Greenhouse
Soybean rust
C (mg/L)/control effect (%)
no.
3.13
1.56
0.78
0.38
80
/
/
/
15
/
/
/
/
0.19
EC50(mg/L)
confidence limit 95% (mg/L)
W2
W3
W4
W5
98
30
80
40
88
80
65
92
70
88
100
96
40
95
25
65
40
85
68
10
85
65
70
98
95
35
80
20
45
0
80
60
10
75
50
65
78
90
30
30
/
/
/
10
/
/
/
/
/
0.21
/
/
/
0.54
/
/
/
/
/
0.05−0.33
/
/
/
0.31−0.90
/
/
/
a
W8
W10
W13
W15
W16
W17
/
/
/
flubeneteram
benzovindiflupyr
isoflucypram
20
50
20
0
40
5
0.76
0.30
1.99
0.69−0.85
0.17−0.43
1.57−2.72
a
Not tested.
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J. Agric. Food Chem. 2021, 69, 3965−3971

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Article
azoxystrobin (68% control) but lower than that of benzovindi-
flupyr (90% control). As we all know, SDH belongs to
membrane protein and the transmembrane ability of
compound W2 might be lower than that of benzovindiflupyr,
and this affected its fungicidal activity. Therefore, the results
indicate that W2 is the most promising candidate among our
synthesized analogues W1−W17 to be a lead compound for
the development of novel SDHIs.
In summary, to increase the fungicidal activity, the carbon−
silicon switch strategy was used in the design and synthesis of a
series of flubeneteram-silyl derivatives. The more potent
compounds from this class showed excellent fungicidal activity
not only in vitro but also in vivo. Among them, compound W2
(Figure 1) showed a fungicidal activity against SBR at a very
low concentration of 0.19 mg/L, comparable to that of
benzovindiflupyr but higher than that of flubeneteram in
greenhouse experiments. The results suggest W2 is a strong
candidate for the development of novel silylated fungicides of
the pyrazole-carboxamide class against SBR. SAR studies
indicate that silyl substitution at C-2 of the distal phenyl ring is
essential for increasing the compound’s fungicidal activity.
Computational results identified the important role of the
substituted silyl group for the formation of strong VDW
interactions with some key residues in the SDH binding site,
suggesting that the flubeneteram-silyl scaffold represents a
useful building block from which to develop novel SDHIs.
Intelligent Biosensor Technology and Health of Ministry of
Science and Technology, Central China Normal University,
Wuhan 430079, People’s Republic of China
Ming-Wei Huang − Key Laboratory of Pesticide and Chemical
Biology of Ministry of Education, International Joint Research
Center for Intelligent Biosensor Technology and Health of
Ministry of Science and Technology, Central China Normal
University, Wuhan 430079, People’s Republic of China
Wen-Jie Wang − Key Laboratory of Pesticide and Chemical
Biology of Ministry of Education, International Joint Research
Center for Intelligent Biosensor Technology and Health of
Ministry of Science and Technology, Central China Normal
University, Wuhan 430079, People’s Republic of China
Yuan Wu − Key Laboratory of Pesticide and Chemical Biology
of Ministry of Education, International Joint Research Center
for Intelligent Biosensor Technology and Health of Ministry of
Science and Technology, Central China Normal University,
Wuhan 430079, People’s Republic of China
Shu-Fen Mei − Key Laboratory of Pesticide and Chemical
Biology of Ministry of Education, International Joint Research
Center for Intelligent Biosensor Technology and Health of
Ministry of Science and Technology, Central China Normal
University, Wuhan 430079, People’s Republic of China
Li-Ming Zhou − Key Laboratory of Pesticide and Chemical
Biology of Ministry of Education, International Joint Research
Center for Intelligent Biosensor Technology and Health of
Ministry of Science and Technology, Central China Normal
University, Wuhan 430079, People’s Republic of China
Long-Can Mei − Key Laboratory of Pesticide and Chemical
Biology of Ministry of Education, International Joint Research
Center for Intelligent Biosensor Technology and Health of
Ministry of Science and Technology, Central China Normal
University, Wuhan 430079, People’s Republic of China
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jafc.0c07322.
Enzymatic and fungicidal assays; field trials; X-ray crystal
structure of compound W2; correlation between ΔGcal
and ΔGexp; binding modes overlay of W1−W17; VDW
energies; crystal data of compound W2; antifungal
activity of the target compounds in greenhouse; general
synthetic procedure; and 1H NMR, 13C NMR, and
HRMS spectral data (PDF)
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.jafc.0c07322
Author Contributions
§G.W. and M.-W.H. contributed equally to this work.
Funding
The research was supported in part by the National Key
Research and Development Program of China
(2018YFD0200100), the National Natural Science Foundation
of China (Nos. 21977035, 21837001, and 21772057), and the
Key Research and Development Program of Hubei Province
(2020BBA052).
AUTHOR INFORMATION
Corresponding Authors
■
Xiao-Lei Zhu − Key Laboratory of Pesticide and Chemical
Biology of Ministry of Education, International Joint Research
Center for Intelligent Biosensor Technology and Health of
Ministry of Science and Technology, Central China Normal
University, Wuhan 430079, People’s Republic of China;
orcid.org/0000-0002-5672-5209; Phone: 86-27-
67867800; Email: xlzhu@mail.ccnu.edu.cn; Fax: 86-27-
67867141
Guang-Fu Yang − Key Laboratory of Pesticide and Chemical
Biology of Ministry of Education, International Joint Research
Center for Intelligent Biosensor Technology and Health of
Ministry of Science and Technology, Central China Normal
University, Wuhan 430079, People’s Republic of China;
Collaborative Innovation Center of Chemical Science and
Engineering, Tianjin 300071, People’s Republic of China;
orcid.org/0000-0003-4384-2593; Email: gfyang@
mail.ccnu.edu.cn
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This paper is dedicated to Professor Youyou Tu, the 2015
Nobel Prize Laureate of Physiology or Medicine, on the
occasion of her 90th birthday and the 100th anniversary of
chemistry at Nankai University.
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