Synthesis and biological evaluation of benzofuroxan derivatives as fungicides against phytopathogenic fungi

Article abstract of DOI:10.1021/jf402388x

Forty-four benzofuroxan derivatives were designed and prepared as antifungal agents. Their structures were characterized by ¹H NMR, ¹³C NMR, and HRMS. Their antifungal activities were tested in vitro with four important phytopathogen

Full text of DOI:10.1021/jf402388x

Article
pubs.acs.org/JAFC
Synthesis and Biological Evaluation of Benzofuroxan Derivatives as
Fungicides against Phytopathogenic Fungi
†
,∥
§,∥
§
,†
,§
Lili Wang, Cong Li, Yingying Zhang, Chunhua Qiao,* and Yonghao, Ye*
†
College of Pharmaceutical Science, Soochow University, Suzhou 215123, Jiangsu, People’s Republic of China
§
College of Plant Protection, Jiangsu Key Laboratory of Pesticide Science, Nanjing Agricultural University, Nanjing 210095, People’s
Republic of China
*
S Supporting Information
ABSTRACT: Forty-four benzofuroxan derivatives were designed and prepared as antifungal agents. Their structures were
1
13
characterized by H NMR, C NMR, and HRMS. Their antifungal activities were tested in vitro with four important
phytopathogenic fungi, namely, Rhizoctonia solani, Sclerotinia sclerotiorum, Fusarium graminearum and Phytophthora capsici, using
the mycelium growth inhibition method. Compound A5 displayed the maximum antifungal activity against F. graminearum (IC50
=
1.1 μg/mL, which is about 2-fold higher than that of the well-known positive control carbendazim (IC50 = 0.5 μg/mL). A14
exhibited high antifungal effect against both S. sclerotiorum and F. graminearum Sehw., with IC values of 2.52 and 3.42 μg/mL,
50
2
3
respectively. Among 14 benzofuroxan derivatives with substitutions at the R and R positions of the phenyl ring (B series), 7
compounds displayed strong growth inhibition against R. solani (IC50 ≤ 3.0 μg/mL). Analysis of the structure−activity
2
relationship data of these compounds revealed that (1) introduction of an electron-donating amino group to the R position of
4
the phenyl ring favors antifungal activity against R. solani and (2) the presence of a nitro group at the R position and substituent
1
variation at the R position of the phenyl ring can result in good antifungal candidates against F. graminearum Sehw. Overall, the
benzofuroxan was discovered as a novel scaffold for the development of fungicides. Significantly, A14 was demonstrated to
successfully suppress disease development in S. sclerotiorum infected cole in vivo.
KEYWORDS: antifungal activity, phytopathogenic fungi, benzofuroxan derivative, Rhizoctonia solani, Sclerotinia sclerotiorum,
Fusarium graminearum
INTRODUCTION
chemists’ attention due to their broad and interesting
■
bioactivities, such as anticancer, antiparasite, antiaggregatory,
Plant pathogenic fungi remain a serious and global problem for
food security and human health. For example, fungus infection
can cause severe crop yield reduction and results in dramatic
economic losses in agriculture. In addition, the threat of
fungus-produced mycotoxins, such as aflatoxins, fumonisins,
and trichothecenes, can last for many years. Although fungus-
resistant crop varieties and other biological methods have been
employed to deal with the fungus problem, fungicidal chemicals
remain the principal control tool. However, like all other
microorganisms, plant pathogenic fungi exhibit a remarkable
ability to change and adapt. More virulent and fungicide-
resistant pathogenic strains continually arise and can no longer
be controlled by chemicals that were once effective. As a
result, it is necessary to develop novel and effective fungicidal
agents to effectively control those agricultural diseases.
6
−11
and vasodilating.
In the meantime, it was also demonstrated
that benzofuroxan derivatives had fungicidal activity even
though benzofuroxan derivatives as antifungal agents have not
1
12
been systematically investigated. In this study, 44 benzofur-
1
4
2
,3
oxan derivatives with modification on the R −R positions of
the phenyl ring were synthesized. Their fungicidal activities
were evaluated against four important plant pathogen strains
including Rhizoctonia solani, Sclerotinia sclerotiorum, Fusarium
graminearum, and Phytophthora capsici in vitro, and the in vivo
efficacies of A14 and A15 against S. sclerotiorum infected cole
leave were evaluated.
4
,5
MATERIALS AND METHODS
■
General. All reagents and solvents were of reagent grade or purified
according to standard methods. Analytical thin layer chromatography
(TLC) was performed with silica gel plates using silica gel 60 GF254
Recently, compounds containing furoxan (1,2,5-oxadiazole
N-oxide, Figure 1) have increasingly attracted medicinal
(Qingdao Haiyang Chemical Co., Ltd.). Column chromatography was
performed over silica gel (200−300 mesh, Qingdao Marine Chemical
1
13
Ltd.). The H NMR and C NMR spectra were recorded in
deuterochloroform at ambient temperature using a Varian Mercury
4
00. The ESIMS and ESI-HRMS were recorded with an Agilent
Received: May 31, 2013
Revised: August 7, 2013
Accepted: August 12, 2013
Published: August 12, 2013
Figure 1. Chemical structures of 1,2,5-oxadiazole N-oxide and
benzofuroxan.
©
2013 American Chemical Society
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a
Table 1. Antifungal Activity of Series A Benzofuraxan Derivatives against Four Phytopathogens
a
*Values are the mean ± standard deviation (SD) of three replicates.
1
260LC and an Agilent Technologies 6220 Accurate-Mass TOF LC/
used as positive controls. Compounds possessing good activities
(inhibitory rate >50% at 25 μg/mL) were further evaluated using the
above-mentioned method but with different concentrations. Each
measurement consisted of at least three replicates. The concentration-
dependent curve was the logarithmic values of inhibition rates for the
Y axis against the test sample concentrations (μg/mL) for the X axis.
The IC50 value was defined as the concentration required for 50%
inhibition of mycelial growth, shown in Tables 1−3.
MS, respectively. The melting points of the products were determined
on an XT5 apparatus (Beijing Keyielec-opti Instrument Factory,
Beijing, China). PE, petroleum ether (bp 60−90 °C); EA, ethyl
acetate; DMAP, N,N-dimethylaminopyridine; NBS, N-bromosuccini-
mide; BPO, benzoyl peroxide; DCM, dichloromethane.
Plant Pathogenic Fungi. All strains of fungi were provided by the
Laboratory of Plant Disease Control, Nanjing Agricultural University.
The strains were retrieved from the storage tube and incubated in
PDA at 25 °C for a week to get new mycelia for the antifungal assay.
Antifungal Bioassay. The fungicidal activities of the synthetic
compounds were tested in vitro against four plant pathogenic fungi (R.
solani, S. sclerotiorum, F. graminearum, and P. capsici) using a mycelia
growth inhibition method. The synthesized compounds were
dissolved in DMSO to prepare the 10 mg/mL stock solution before
mixing with molten agar below 60 °C. The medium containing
compounds at a concentration of 25 μg/mL for the initial screening
was then poured into sterilized Petri dishes. After appropriate days at
In Vivo Testing on Cole Leaves Infected by S. sclerotiorum.
Strain S. sclerotiorum and susceptible cole leaves collected from Pailou
Experimental Centre of Nanjing Agricultural University were used to
measure the efficacy of compounds in vivo. Healthy cole leaves were
sprayed with compounds (0.5 mg/mL) and subsequently cultivated at
20 °C for 24 h before artificial inoculation with strain S. sclerotiorum.
Results were observed as diameters of symptoms after cultivation at 20
°C for 36 h. Carbendazim (50% WP, Jiangsu Rotam Lanfeng
Biochemical Co., Ltd., China) was coassayed as the positive control.
The efficacy of disease control was calculated as (1 − c/d) × 100,
where c is the diameter of the treatment and d is the diameter of the
negative control. The disease control picture is shown in Figure 2.
General Synthetic Procedure for the Key Target Molecules.
Intermediates 1−5 were synthesized from commercially sourced
1
3
2
5 °C, the colony diameter of each strain was measured with the
original mycelial disk diameter (5 mm) subtracted from this
measurement. Percentage inhibition was calculated as (1 − a/b) ×
100, where a is the colony diameter in Petri dishes with compounds
1
4−16
and b is the mean colony diameter in Petri dishes without tested
compounds. DMSO served as negative control, whereas commercially
available agricultural fungicide carbendazim and chlorothalonil were
chemicals using the reported procedure.
New benzofuroxan
compounds were prepared using the synthetic routes shown in
Schemes 1−3.
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a
Table 2. Antifungal Activity of Series B Benzofuraxan Derivatives against Four Phytopathogens
a
*Values are the mean ± standard deviation (SD) of three replicates.
a
Table 3. Antifungal Activity of Series C Benzofuraxan Derivatives against Four Phytopathogens
a
*Values are the mean ± standard deviation (SD) of three replicates.
Synthesis of 7-Ethoxy-4-nitrobenzofuroxan (A1). To a solution of
concentrated in vacuo, the residue was subjected to silica gel column
chromatography (eluant: PE/EA 5:1 and then CH Cl ) for
4
-chloro-7-nitrobenzofuroxan (100 mg, 0.46 mmol) in ethanol (10
2
2
mL) was added at 0 °C with 0.5 M CH CH ONa (1.1 mL). The
purification to afford the desired product as a yellow solid (63 mg,
3
2
1
reaction mixture was stirred for 2 h. Then the reaction mixture was
yield 60%): R 0.2 (PE/EA 5:1); mp 94−96 °C; H NMR (400 MHz,
f
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Figure 2. Effects of compounds A14 and A15 against Sclerotinia sclerotiorum infected cole leaves.
Scheme 1. Synthetic Route of Benzofuroxan Derivatives A1−A8
Scheme 2. Synthetic Route of Benzofuroxan Derivatives B1−B8
CDCl ) δ 8.39 (d, J = 8.5 Hz, 1H, ArH), 6.42 (d, J = 8.5 Hz, 1H,
PE/EA 5:1 and then CH Cl ) to give the desired product as a red solid
2 2
3
1
ArH), 4.38 (q, J = 7.0 Hz, 2H, −CH −), 1.56 (t, J = 7.0 Hz, 3H, Me−
(15 mg, yield 29%): R 0.8 (CH Cl ); mp 180−182 °C; H NMR (400
2
f
2
2
H); 13C NMR (75 MHz, CDCl ) δ 153.7 (ArC), 146.0 (ArC), 135.3
MHz, CDCl ) δ 8.32 (d, J = 8.1 Hz, 1H, ArH), 6.76 (d, J = 8.1 Hz, 1H,
3
3
13
(
(
2
ArC), 129.3 (ArC), 109.2 (ArC), 101.6 (ArC), 67.5 (−CH −), 13.9
ArH), 2.66 (s, 3H, Me−H); C NMR (75 MHz, DMSO) δ 145.6
(ArC), 141.3 (ArC), 133.0 (ArC), 131.3 (ArC), 117.9 (ArC), 115.3
(ArC), 13.9 (Me−C); HRMS (ESI) m/z calcd for C H N NaO S [M
2
Me−C); HRMS (ESI) m/z calcd for C H N NaO [M + Na]
8
7
3
5
48.0283, found 248.0273.
7
5
3
4
Synthesis of 7-(Methylthio)-4-nitrobenzofuroxan (A2). To a
+ Na] 249.9899, found 249.9896.
solution of 4-chloro-7-nitrobenzofuroxan (50 mg, 0.23 mmol) in
ethanol/0.1 M sodium phosphate buffer (1:1 v/v, 5 mL) was added
Synthesis of 4-Nitro-7-(piperazin-1-yl)benzofuroxan (A3). To a
solution of 4-chloro-7-nitrobenzofuroxan (50 mg, 0.23 mmol) in
ethanol/0.1 M sodium phosphate buffer (1:1 v/v, 5 mL) was added
piperazine (199.8 mg, 2.32 mmol), and the reaction was stirred for 0.5
h. The solvent ethanol was removed in vacuo. The aqueous phase was
then extracted with EtOAc (50 mL × 2), dried over anhydrous
Na SO , and concentrated in vacuo. The residue was subjected to silica
15% sodium methanethiolate (130.1 mg, 0.28 mmol), and the reaction
mixture was stirred for 1.5 h. The solvent ethanol was removed in
vacuo. The aqueous phase was then extracted with EtOAc (25 mL ×
2
), dried over anhydrous Na SO , and concentrated in vacuo. The
2 4
residue was subjected to silica gel column chromatography (eluant:
2
4
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Scheme 3. Synthetic Route of Benzofuroxan Derivatives C1−C4
gel flash chromatography (DCM/MeOH = 10:1) to afford the title
7-(4-Benzoylpiperazin-1-yl)-4-nitrobenzofuroxan (A6): 44 mg;
1
compound as a red solid (34 mg, yield 55%): R 0.6 (DCM/MeOH =
yield 63%; R 0.7 (CH Cl /MeOH 10:1); mp 188−189 °C;
H
f
f
2
2
1
1
8
−
0:1); mp 149−150 °C; H NMR (300 MHz, CDCl ) δ 8.31 (d, J =
NMR (400 MHz, CDCl ) δ 8.32 (d, J = 8.4 Hz, 1H, ArH), 7.45 (s,
3
3
.6 Hz, 1H, ArH), 6.24 (d, J = 8.6 Hz, 1H, ArH), 3.47−3.32 (m, 4H,
5H, ArH), 6.29 (d, J = 8.5 Hz, 1H, ArH), 3.96 (t, J = 77.6 Hz, 4H,
1
3
13
NCH −), 3.13−3.05 (m, 4H, −NCH −); C NMR (75 MHz,
−NCH −), 3.39 (s, 4H, −NCH −); C NMR (75 MHz, DMSO) δ
2
2
2
2
DMSO) δ 147.6 (ArC), 146.9 (ArC), 136.0 (ArC), 124.0 (ArC), 111.7
169.3 (−CO), 147.5 (ArC), 146.5 (ArC), 136.1 (ArC), 135.5
(
ArC), 105.6 (ArC), 52.8(−NCH − × 2), 45.3 (−NCH − × 2);
(ArC), 129.8 (ArC × 2), 128.5 (ArC × 2), 127.1 (ArC), 125.5 (ArC),
2
2
+
HRMS (ESI) m/z calcd for C H N NaO [M + Na] 288.0709,
112.1 (ArC), 106.6 (ArC), 50.8 (−NCH −); HRMS (ESI) m/z calcd
10
11
5
4
2
+
found 288.0700.
for C H N NaO [M + Na] 392.0971, found 392.0965.
17
15
5
5
Synthesis of 4-Nitro-7-(p-tolylamino)benzofuroxan (A4). To a
solution of 4-chloro-7-nitrobenzofuroxan (50 mg, 0.23 mmol) in
7-(4-(Cyclopropanecarbonyl)piperazin-1-yl)-4-nitrobenzofuroxan
(A7): 38 mg; yield 60%; R 0.8 (CH Cl /MeOH 10:1); mp 194−196
°C; H NMR (400 MHz, CDCl ) δ 8.33 (d, J = 8.4 Hz, 1H, ArH),
6.29 (d, J = 8.4 Hz, 1H, ArH), 3.92 (d, J = 23.8 Hz, 4H, −NCH −),
3.41 (d, J = 28.8 Hz, 4H, −NCH −), 1.83−1.67 (m, 1H, CH), 1.03 (s,
2H, −CH −), 0.84 (d, J = 5.0 Hz, 2H, −CH
DMSO) δ 171.4 (−CO), 147.5 (ArC), 146.5 (ArC), 136.0 (ArC),
125.2 (ArC), 112.0 (ArC), 106.4 (ArC), 55.0 (−NCH −), 51.4
(−NCH −), 50.5 (−NCH −), 44.3 (−NCH −), 10.4 (CH), 7.3
(−CH − × 2); HRMS (ESI) m/z calcd for C14 NaO
[M + Na]+
356.0971, found 356.0965.
7-(4-(Methylsulfonyl)piperazin-1-yl)-4-nitrobenzofuroxan (A8):
40 mg; yield 62%; R 0.6 (CH Cl /MeOH 10:1); mp 199−201 °C;
H NMR (400 MHz, CDCl ) δ 8.44 (d, J = 8.6 Hz, 1H, ArH), 6.65
(dd, J = 8.7, 4.2 Hz, 1H, ArH), 3.64−3.59 (m, 4H, −NCH −), 3.49−
−), 2.95 (s, 3H, Me−H); C NMR (75 MHz,
DMSO) δ 147.4 (ArC), 146.4 (ArC), 136.0 (ArC), 126.1 (ArC), 112.2
f
2
2
1
CH CN/0.1 M sodium phosphate buffer (1:1 v/v, 5 mL) was added
3
3
paratoluidine (248.6 mg, 2.32 mmol), and the reaction mixture was
stirred for 0.5 h. The methyl cyanide was removed in vacuo. The
resulting aqueous phase was then extracted with CH Cl (25 mL × 2),
2
2
1
3
−); C NMR (75 MHz,
2
2
2
2
and the organic layer was dried over anhydrous Na SO4 and
2
concentrated in vacuo. The residue was purified by silica gel column
chromatography (eluant: PE/EA = 10:1 and then DCM/PE = 2:1) to
2
2
2
2
H
give A4 as a red solid (46 mg, yield 69%): R 0.4 (PE/EA 10:1); mp
2
15
N
5
5
f
1
1
8
9
83−185 °C; H NMR (400 MHz, DMSO) δ 9.95 (br s, 1H, NH),
.34 (d, J = 9.0 Hz, 1H, ArH), 7.48−7.19 (m, 4H, ArH), 6.22 (d, J =
13
.0 Hz, 1H, ArH), 2.35 (s, 3H, Me−H); C NMR (75 MHz, DMSO)
f
2
2
1
δ 150.1 (ArC), 147.9 (ArC), 147.0 (ArC), 142.8 (ArC), 137.9 (ArC),
3
1
1
1
2
3
38.0 (ArC), 136.9 (ArC), 134.4 (ArC), 134.0 (ArC), 130.3 (ArC),
30.1 (ArC), 126.5 (ArC), 125.1 (ArC), 122.9 (ArC), 122.1 (ArC),
21.5 (ArC), 113.0 (ArC), 112.0 (ArC), 109.9 (ArC), 99.9 (ArC),
2
13
3.44 (m, 4H, −NCH
2
+
0.7 (Me−C); HRMS (ESI) m/z calcd for C H N NaO [M + Na]
(ArC), 107.2 (ArC), 50.4 (−NCH
2
− × 2), 44.9 (−NCH
2
− × 2), 34.4+
(Me−C); HRMS (ESI) m/z calcd for C11H N NaO S [M + Na]
13 5 6
13
10
4
4
09.0600, found 309.0608.
Synthesis of 7-(4-Acetylpiperazin-1-yl)-4-nitrobenzofuroxan (A5).
366.0484, found 366.0487.
To a solution of 4-nitro-7-(piperazin-1-yl)benzofuroxan (20 mg, 0.08
mmol) in ethanol/pyridine (1:1 v/v, 1 mL) was added acetic
anhydride (23.1 mg, 0.23 mmol) at room temperature, the reaction
mixture was stirred for 30 min and then concentrated in vacuo, and the
residue was subjected to silica gel column chromatography (CH Cl /
Synthesis of 6-Chloro-5-methylbenzofuroxan (B1). The suspen-
sion of sodium hydroxide (70.7 mg, 1.77 mmol) in methanol (20 mL)
was stirred until the solid was completely dissolved and then 5-chloro-
4-methyl-2-nitroaniline (300 mg, 1.61 mmol) was added. The brown
solution was cooled to 0 °C, and then 5% aqueous NaClO solution
(4.6 mL, 3.22 mmol) was added dropwise until the red color
disappeared. The mixture was diluted with water (200 mL), and the
precipitate was filtered and purified by column chromatography on
2
2
MeOH 100:1) to give A5 as a red solid (21 mg, yield 91%): R 0.6
f
1
(
CH Cl /MeOH 10:1); mp 211−212 °C; H NMR (400 MHz,
CDCl ) δ 8.34 (d, J = 8.5 Hz, 1H, ArH), 6.29 (d, J = 8.5 Hz, 1H,
2
2
3
ArH), 3.81 (d, J = 52.0 Hz, 4H, −NCH −), 3.38 (d, J = 19.5 Hz, 4H,
silica gel (eluant: PE/EA 50:1) to give B1 as a yellow solid (210 mg,
2
13
1
−
NCH −), 2.17 (s, 3H, Me−H); C NMR (75 MHz, DMSO) δ
yield 71%): R
MHz, CDCl
f
0.7 (PE/EA 5:1); mp 118−120 °C; H NMR (400
2
1
68.7 (−CO), 147.5 (ArC), 146.6 (ArC), 136.1 (ArC), 125.3
3
) δ 7.51 (br s, 1H, ArH), 7.27 (br s, 1H, ArH), 2.42 (s,
3H, Me−H); C NMR (75 MHz, CDCl ) δ 140.0 (br m, ArC), 116.1
(br m, ArC), 112.4 (br m, ArC), 21.4 (Me−C;. MS (+ESI) m/z 186.0
13
(
4
ArC), 112.1 (ArC), 106.4 (ArC), 51.2 (−NCH −), 50.5 (−NCH −),
3
2
2
5.0 (−NCH −), 21.3 (Me−C); HRMS (ESI) m/z calcd for
2
+
+
C H N NaO [M + Na] 330.0814, found 330.0816.
[M + H] .
1
2
13
5
5
General Synthetic Procedure for the Preparation of
Synthesis of 5-(Bromomethyl)-6-chlorobenzofuroxan (B2). To a
solution of 6-chloro-5-methyl-benzofuroxan (200 mg, 1.08 mmol) in
CCl4 (15 mL) was added N-bromosuccinimide (192.9 mg, 1.08
mmol) and benzoyl peroxide (262.5 mg, 1.08 mmol). The reaction
mixture was stirred under nitrogen atmosphere at 78 °C for 24 h and
then concentrated in vacuo. The residue was purified by silica gel
Compounds A6−A8. To a solution of 4-nitro-7-(piperazin-1-
yl)benzofuroxan (50 mg, 0.19 mmol) in CH Cl (4 mL) was added
2
2
Et N (19.1 mg, 0.19 mmol) at 0 °C. Then three different acyl
3
chlorides including benzoyl chloride, cyclopropanecarbonyl chloride,
and methanesulfonyl chloride (0.19 mmol) were added dropwise. The
reaction mixture was stirred for another 15 min and concentrated in
vacuo, and the residue was subjected to silica gel column
chromatography (CH Cl /MeOH 100:1) to give A6−A8 as red solids.
column chromatography (eluant: PE/EA 200:1) to give B2 as a yellow
1
solid (150 mg, yield 52%): R 0.3 (PE/EA 40:1); mp 58−60 °C; H
f
NMR (400 MHz, CDCl ) δ 7.63 (br s, 2H, ArH), 4.56 (s, 2H,
2
2
3
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1
3
BrCH −); C NMR (101 MHz, CDCl ) δ 29.5 (BrCH −); MS (ESI)
filtered and subjected to silica gel column chromatography (CH Cl )
to give the desired product as a yellow solid.
2
3
2
2
2
−
m/z 262.6 [M − H] .
Synthesis of 6-Chloro-5-(pyrrolidin-1-ylmethyl)benzofuroxan
5-Chloro-6-(piperidin-1-yl)benzofuroxan (B4): 29 mg; yield 44%;
1
(
B3). To a solution of 5-(bromomethyl)-6-chlorobenzofuroxan (50
R 0.6 (PE/EA 15:1); mp 73−75 °C; H NMR (400 MHz, CDCl ) δ
f
3
mg, 0.19 mmol) in acetonitrile (1 mL) was added Et N (0.5 mL). The
7.52 (br s, 1H, ArH), 6.67 (br s, 1H, ArH), 3.02 (s, 4H, −NCH − ×
3
2
13
solution was cooled to 0 °C, and pyrrolidine (20.3 mg, 0.29 mmol)
was added dropwise. After 1 h, the reaction mixture was then diluted
with EtOAc (25 mL × 2) and washed with brine, and the organic layer
was dried over anhydrous Na SO and concentrated in vacuo. The
2), 1.75 (s, 4H, −CH − × 2), 1.62 (s, 2H, −CH −); C NMR (101
2
2
MHz, CDCl ) δ 53.2 (−NCH − × 2), 25.7 (−CH − × 2), 23.8
3
2
2
+
(−CH −); HRMS (ESI) m/z calcd for C H ClN NaO [M + Na]
2
11 12
3
2
276.0516, found 276.0515.
2
4
residue was purified by silica gel column chromatography (eluant:
CH Cl /MeOH 100:1) to give B3 as a yellow solid (35 mg, yield
5-Chloro-6-morpholinobenzofuroxan (B5): 52 mg; yield 81%; R
f
1
0.7 (CH
Cl
2
); mp 126−127 °C; H NMR (400 MHz, CDCl ) δ 7.59
3
2
2
2
1
7
3%): R 0.4 (PE/EA 5:1); mp 82−83 °C; H NMR (400 MHz,
(br s, 1H, ArH), 6.76 (br s, 1H, ArH), 3.90 (d, J = 3.9 Hz, 4H,
f
13
CDCl ) δ 7.59 (br d, J = 33.0 Hz, 2H, ArH), 3.73 (s, 2H, −NCH −),
2
−CH
CDCl
z 256.6 [M + H] .
5-Chloro-6-(piperazin-1-yl)benzofuroxan (B6): 25 mg; yield 40%;
2
O− × 2), 3.11 (s, 4H, −NCH
2
− × 2); C NMR (101 MHz,
3
2
13
.66 (s, 4H, −NCH − × 2), 1.85 (s, 4H, −CH − × 2); C NMR
3
) δ 66.4 (−CH O− × 2), 52.0 (−NCH
2
2
− × 2); MS (+ESI) m/
2
2
+
(
(
2
101 MHz, CDCl ) δ 57.5 (−NCH −), 54.4 (−NCH − × 2), 23.9
3
2
2
+
−CH − × 2); HRMS (ESI) m/z calcd for C H ClN O [M + H]
2
11 13
3
2
1
R 0.6 (CH Cl ); mp 125−127 °C; H NMR (400 MHz, CDCl ) δ
54.0696, found 254.0598.
f
2
2
3
7
2
(
.58 (br s, 1H, ArH), 6.76 (br s, 1H, ArH), 3.37 (s, 4H, −NCH − ×
Synthesis of 4-Chloro-2-nitro-5-(piperidin-1-yl)aniline (B4′). 4,5-
2
13
), 3.24 (s, 4H, −NCH − × 2); C NMR (101 MHz, CDCl ) δ 61.3
Dichloro-2-nitroaniline (100 mg, 0.48 mmol) was dissolved in
piperidine (0.5 mL). The solution was stirred at 100 °C for 2 h.
Then the solution was cooled to room temperature and diluted with
2
3
−NCH −), 51.7 (−NCH −); HRMS (ESI) m/z calcd for
2
2
+
C H ClN O [M + H] 254.0571, found 255.0555.
10 11
4
2
5
-Chloro-6-methoxybenzofuroxan (B7): 40 mg; yield 80%; R 0.6
f
1
1
2
0 mL of water; the solution was then extracted with EtOAc (25 mL ×
) and washed with brine. The organic combination was dried over
(
PE/EA 5:1); mp 90−91 °C; H NMR (400 MHz, CDCl ) δ 7.55 (br
d, J = 82.4 Hz, 1H, ArH), 6.62 (br d, J = 85.2 Hz, 1H, ArH), 3.98 (s,
H, Me−H); C NMR (101 MHz, CDCl ) δ 57.1 (Me−C); MS
(+ESI) m/z 223.2 [M + Na] .
3
Na SO and concentrated in vacuo. The residue was subjected to silica
2
4
13
3
gel flash chromatography (eluant: PE/EA 10:1) to afford the
3
+
1
compound as B4′ (112 mg, yield 91%): R 0.3 (PE/EA 5:1); H
f
Synthesis of 4-Fluoro-2-nitro-5-(piperidin-1-yl)aniline (4a). To a
solution of 5-chloro-4-fluoro-2-nitroaniline (55 mg, 0.29 mmol) and
NMR (400 MHz, CDCl ) δ 8.09 (s, 1H, ArH), 6.21 (s, 1H, ArH), 6.16
3
(
4
s, 2H, NH ), 3.14−3.05 (m, 4H, −NCH − × 2), 1.72 (d, J = 4.3 Hz,
2
2
Et N (0.5 mL) was added piperidine (0.5 mL). The reaction mixture
3
H, −CH − × 2), 1.67−1.58 (m, 2H, −CH −).
2
2
was stirred at 100 °C for 24 h. Then the solution was cooled to room
temperature and diluted with 10 mL of water. The precipitate was
filtered and then subjected to purification by silica gel column
chromatography (PE/EA 10:1) to give the desired product as a yellow
Synthesis of 4-Chloro-5-morpholino-2-nitroaniline (B5′). A
solution of 4,5-dichloro-2-nitroaniline (100 mg, 0.48 mmol) in
morpholine (0.5 mL) was stirred at 100 °C for 3 h. Then it was
cooled to room temperature and diluted with 10 mL of water, and the
mixture was then extracted with EtOAc (25 mL × 2) and washed with
1
solid (66 mg, yield 96%): R 0.5 (CH Cl ); H NMR (400 MHz,
f
2
2
CDCl ) δ 7.73 (d, J = 14.1 Hz, 1H, ArH), 6.08 (s, 2H, NH ), 6.03 (d, J
3
2
brine. The combined organic layer was dried over Na SO4 and
2
=
4
7.7 Hz, 1H, ArH), 3.23−3.18 (m, 4H, −NCH − × 2), 1.70 (d, J =
2
concentrated under reduced pressure. The residue was then subjected
.7 Hz, 4H, −NCH − × 2), 1.63 (d, J = 4.8 Hz, 2H, −CH −).
2
2
to silica gel flash chromatography (eluant: CH Cl ) to afford B5′ as a
2
2
1
Synthesis of 5-Fluoro-6-(piperidin-1-yl)benzofuroxan (B8). 4-
yellow solid (117 mg, yield 94%): R 0.3 (CH Cl ); H NMR (400
f
2
2
Fluoro-2-nitro-5-(piperidin-1-yl)aniline (4a, 62 mg, 0.25 mmol) was
dissolved in alcohol (5 mL) with 25% (w/v) KOH. The solution was
cooled to 0 °C, and 5% aqueous NaClO solution was added dropwise
until the red color disappeared. The mixture was diluted with water
50 mL), and the precipitate was filtered and then subjected to
purification by column chromatography (PE/EA 100:1) to give B8 as
MHz, CDCl ) δ 8.12 (s, 1H, ArH), 6.24 (s, 1H, ArH), 6.13 (s, 2H,
3
NH ), 3.86 (s, 4H, −CH O− × 2), 3.14 (s, 4H, −NCH − × 2).
2
2
2
Synthesis of 4-Chloro-2-nitro-5-(piperazin-1-yl)aniline (B6′). To a
solution of 4,5-dichloro-2-nitroaniline (50 mg, 0.24 mmol) in Et N (3
3
(
mL) was added piperazine (208.04 mg, 2.42 mmol). The reaction
mixture was stirred at 100 °C for 48 h. Then the solution was cooled
to room temperature and diluted with 10 mL of water. The solution
was then extracted with EtOAc (25 mL × 2) and washed with brine.
The combined organic layer was dried over Na SO and concentrated
a yellow solid (49 mg, yield 80%): R 0.8 (PE/EA 5:1); mp 89−91 °C;
f
1
H NMR (400 MHz, CDCl ) δ 7.07 (br s, 1H, ArH), 6.42 (br s, 1H,
3
ArH), 3.15−3.04 (m, 4H, −NCH − × 2), 1.78−1.69 (m, 4H, −CH −
2
2
2
4
13
×
5
(
2
2), 1.67−1.60 (m, 2H, −CH −); C NMR (101 MHz, CDCl ) δ
2
3
under reduced pressure to give B6′ as a yellow solid (56 mg, 90%): R
f
1.8 (−NCH −), 51.8 (−NCH −), 25.6 (−CH − × 2), 23.8
1
2
2
2
0
.2 (CH Cl /MeOH 10:1); H NMR (400 MHz, CDCl ) δ 8.14 (s,
+
2
2
3
−CH −); HRMS (ESI) m/z calcd for C H FN NaO [M + Na]
2
11 12
3
2
1
H, ArH), 6.22 (s, 1H, ArH), 6.13 (s, 2H, NH ), 3.35 (s, 8H,
2
60.0811, found 260.0812.
−
NCH − × 4).
2
Synthesis of 6,7-Dichloro-4-nitrobenzofuroxan (C1). A solution of
,6-dichlorobenzofuroxan (0.450 mg, 2.20 mmol.) in concentrated
sulfuric acid (6 mL) was treated with fuming nitric acid (152.2 mg,
.41 mmol) at 0 °C for 20 min. The solution was then treated with
Synthesis of 4-Chloro-5-methoxy-2-nitroaniline (B7′). A solution
5
of 4,5-dichloro-2-nitroaniline (100 mg, 0.48 mmol) in methanol (5
mL) with 25% (w/v) sodium methoxide was heated under reflux for 3
h. Then the solution was cooled to room temperature, diluted with 20
mL of water, and extracted with CH Cl ; the organic layer was dried
2
ice−water to form the precipitation as the crude nitro product. This
crude product was dissolved in acetic acid (6 mL). The temperature
was raised to 110 °C, and the solution was stirred for 3 h. The reaction
mixture was extracted with EtOAc (50 mL × 3), and the combined
organic layer was dried over anhydrous Na SO and concentrated in
2
2
over Na SO and concentrated to give B7′ as a yellow solid (90 mg,
2
4
1
yield 92%): R 0.2 (PE/EA 5:1); H NMR (300 MHz, CDCl ) δ 8.18
f
3
(
s, 1H, ArH), 6.21 (d, J = 14.4 Hz, 3H, ArH, NH ), 3.92 (s, 3H, Me−
2
2
4
H).
General Synthetic Procedure for Compounds B4−B7. The
suspension of sodium hydroxide (11.10 mg, 0.28 mmol) in methanol
5 mL) was stirred until the solid was completely dissolved. Then four
different anilines including 4-chloro-2-nitro-5-(piperidin-1-yl) aniline,
-chloro-5-morpholino-2-nitroaniline, 4-chloro-2-nitro-5-(piperazin-1-
vacuo. The residue was then subjected to flash chromatography (PE/
EA = 30:1) to afford the title compound as a yellow solid (360 mg,
1
6
5%): R 0.7 (PE/EA 5:1); mp 143−145 °C; H NMR (400 MHz,
f
(
13
CDCl ) δ 8.40 (s, 1H, ArH); C NMR (101 MHz, acetone) δ 145.7
3
(
ArC), 136.4 (ArC), 134.4 (ArC), 131.1 (ArC), 126.3 (ArC), 115.3
+
4
(ArC); MS (+ESI) m/z 250.8 [M + H] .
yl)aniline, and 4-chloro-5-methoxy-2-nitroaniline (0.25 mmol) were
added. The solution was cooled to 0 °C, and 5% aqueous NaClO
solution was added dropwise until the red color disappeared. The
mixture was diluted with water (50 mL), and the precipitate was
Synthesis of 6-Chloro-4-nitro-7-(pyrrolidin-1-yl)benzofuroxan
(C2). To a solution of 6,7-dichloro-4-nitrobenzofuroxan (125 mg,
0.50 mmol) in acetonitrile (3 mL) was added pyrrolidine (106.68 mg,
1.50 mmol). The reaction was stirred for 15 min and then diluted with
8
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Journal of Agricultural and Food Chemistry
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1
00 mL of water, and the precipitation was filtered to give C2 as a red
Scheme 4. Two Resonance Structures for Compounds A3−
A8
1
solid (75 mg, yield 53%): R 0.5 (PE/EA 5:1); mp 119−121 °C; H
f
NMR (400 MHz, CDCl ) δ 8.03 (s, 1H, ArH), 4.22 (s, 4H, −NCH −
3
2
13
×
2), 2.06 (s, 4H, −CH − × 2); C NMR (101 MHz, CDCl ) δ
49.7 (ArC), 141.4 (ArC), 136.3 (ArC), 135.5 (ArC), 120.3 (ArC),
2
3
1
1
2
07.1 (ArC), 106.7 (ArC), 55.5 (t, J = 17.3 Hz, −NCH −), 26.6 −
2
5.1 (m, −CH −); HRMS (ESI) m/z calcd for C H ClN NaO [M +
2
10
9
4
4
+
Na] 307.0210, found 307.0207.
Synthesis of 6-Chloro-4-nitro-7-(piperazin-1-yl)benzofuroxan. A
solution of 6,7-dichloro-4-nitrobenzofuroxan (100 mg, 0.40 mmol) in
methyl cyanide (5 mL) was treated with pyrrolidine (172.3 mg, 2.0
mmol). The reaction mixture was stirred for 15 min. The solution was
concentrated in vacuo, and the residue was subjected to silica gel
column chromatography (CH Cl /MeOH 100:1 to 20:1) to give the
reaction of 3 with corresponding amine or sodium methoxide
gave B4′−B7′ in >90% yields, in which only a C5-substituted
1
2
2
product was observed on the basis of the H NMR assignment.
desired product as a red solid (72 mg, yield 60%): R 0.2 (CH Cl /
f
2
2
Again, the formation of the benzofuroxan was accomplished by
1
MeOH 10:1); H NMR (400 MHz, CDCl ) δ 8.32 (s, 1H, ArH), 3.51
3
treatment of B4′−B7′ with sodium hypochlorite, affording
(
d, J = 4.6 Hz, 4H, −NCH − × 2), 3.10 (s, 4H, −NCH − × 2).
1
2
2
B4−B7. Common features of the H NMR spectra of
Synthesis of 7-(4-Acetylpiperazin-1-yl)-6-chloro-4-nitrobenzofur-
compounds B1−B8 were that both hydrogen signals of the
oxan (C3). A solution of 6-chloro-4-nitro-7-(piperazin-1-yl)-
benzofuroxan (20 mg, 0.07 mmol) in ethanol/pyridine (1:1 v/v, 1
mL) was treated with acetic anhydride (10.22 mg, 0.10 mmol) at room
temperature for 15 min. The solution was concentrated in vacuo. and
the residue was subjected to silica gel column chromatography (PE/
1
3
phenyl ring were broad peaks. Furthermore, the C NMR
signals of their aromatic carbon could barely be observed. This
phenomenon was reported in other benzofuroxan derivatives as
1
7,18
well.
This was due to the fast tautomeric equilibrium
EA = 1:1 to 1:2) to give C3 as a red solid (14 mg, yield 61%): R 0.7
f
between the two benzofuroxan tautomers of benzofuroxan via
o-dinitroso intermediates (Scheme 5), which caused the
1
(
CH Cl /MeOH 10:1); mp 163−165 °C; H NMR (400 MHz,
2
2
CDCl ) δ 8.29 (s, 1H, ArH), 3.83 (s, 2H, −NCH −), 3.73−3.69 (m,
3
2
2
H, −NCH −), 3.52−3.47 (m, 4H, −NCH − × 2), 2.16 (s, 3H, Me−
2
2
13
Scheme 5. Rearrangement Occurring in Benzofuroxan
H); C NMR (75 MHz, DMSO) δ 168.5 (−CO), 146.3 (ArC),
1
5
(
41.7 (ArC), 137.6 (ArC), 127.4 (ArC), 114.9 (ArC), 114.2 (ArC),
1.9 (−NCH −), 51.5 (−NCH −), 46.3 (−NCH −), 41.4
−NCH −), 21.3 (Me−C); HRMS (ESI) m/z calcd for
2
2
2
2
+
C H ClN NaO [M + Na] 364.0425, found 364.0424.
12
12
5
5
Synthesis of 6-Chloro-7-(4-(ethoxycarbonyl)piperazin-1-yl)-4-ni-
trobenzofuroxan (C4). A solution of 6-chloro-4-nitro-7-(piperazin-1-
yl)benzofuroxan (20 mg, 0.07 mmol) in CH Cl (2 mL) was treated
2
2
with ethyl carbonochloridate (10.9 mg, 0.10 mmol) at room
temperature for 15 min. The solution was concentrated in vacuo,
and the residue was subjected to silica gel column chromatography
coalescence of the individual signals into a very broad multiplet.
High-concentration (200 mg/mL in CDCl3) 1 C NMR was
attempted for B1, and again, the aromatic carbons originated
some broad multiplets (B1: δ 140.0, 116.1, 112.4) because of
the very fast tautomeric equilibrium.
Compound C1 was prepared by reaction of 5 with fuming
nitric acid in concentrated sulfuric acid, which gave 6-dichloro-
3
(
0
PE/EA = 1:1 to 1:2) to give C4 as a red solid (16 mg, yield 65%): Rf
1
.8 (CH Cl /MeOH 10:1); mp 167−169 °C; H NMR (400 MHz,
2
2
CDCl ) δ 8.31 (s, 1H, ArH), 4.21−4.16 (m, 2H, −CH O−), 3.71 (d, J
=
7
3
2
5.0 Hz, 4H, −NCH − × 2), 3.48 (s, 4H, −NCH − × 2), 1.29 (t, J =
2
2
13
.1 Hz, 3H, Me−H); C NMR (101 MHz, CDCl ) δ 155.3 (−C
3
4
-nitrobenzofuroxan first. Refluxing of this nitro product in
O), 145.7 (ArC), 141.2 (ArC), 137.2 (ArC), 133.0 (ArC), 128.8
(
5
ArC), 116.4 (ArC), 113.4 (ArC), 61.9 (−NCH −), 52.1 (−NCH −),
acetic acid for 3 h caused rearrangement to give the more stable
C1. Nucleophilic substitution reaction of C1 with pyrrolidine
or piperazine afforded C2 and 6. Intermediate 6 is unstable and
could quickly decompose upon exposure to air. Therefore, 6
was immediately treated with acetic anhydride or ethyl
carbonochloridate to gave target molecules C3 and C4,
respectively, which were stable. The remaining compounds
2
2
1.2 (−NCH −), 44.1 (−NCH −), 14.7 (Me−C); HRMS (ESI) m/z
2
2
+
calcd for C H ClN NaO [M + Na] 394.0530, found 394.0541.
13
14
5
6
RESULTS AND DISCUSSION
Chemistry. The synthetic routes for target molecules A1−
■
A8, B1−B8, and C1−C4 are shown in Schemes 1−3.
Compounds 1−5 were the key intermediates, which were
listed in Tables 1−3 were prepared according to the literature
14−16
19−27
prepared according to reported procedures.
Nucleophilic
reported methods.
Before submission for biological
substitution reaction of compound 1 with nucleophiles such as
sodium ethoxide, sodium methanethiolate, piperazine, and
paratoluidine afforded the target molecules A1−A4. On the
other hand, treatment of A3 with anhydride or acyl chloride
under basic condition gave compounds A5−A8 in moderate to
evaluation, all compounds were analyzed by high-pressure
liquid chromatography to ensure >95% purity.
Antifungal Activity. The antifungal activities of the
synthetic molecules, which are expressed as IC50 (median
inhibitory concentration) values, were determined using
mycelia growth inhibitory rate method. The results are shown
in Tables 1−3.
1
good yields. It is worth mentioning that the H NMR spectra of
compounds A3−A8 showed the coexistence of two sets of
signals, which comes from the resonance forms for these
benzofuroxan derivatives (Scheme 4).
The synthesis of target molecules B1−B8 is outlined in
Scheme 2. Reaction of 2 with sodium hypochlorite in methanol
gave B1 in 70% yield, which was then treated with NBS to
introduce a bromine atom at the benzylic position, affording B2
in 52% yield. Subsequent substitution reaction between B2 and
pyrrolidine provided B3 in 73% yield. Nucleophilic substitution
For series A benzofuroxan derivatives, all compounds with
amino substitution at the nitro para-position exhibited
antifungal effect with IC < 25 μg/mL. Specifically, compound
50
A9 displayed very good fungicidal activity against R. solani and
F. graminearum Sehw. with IC values of 3.02 and 2.28 μg/mL,
50
respectively. A5 gave IC of 1.1 μg/mL against F. graminearum
50
Sehw., which was half-fold less active than the positive control
carbendazim (IC = 0.5 μg/mL), but had no antifungal effects
50
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Journal of Agricultural and Food Chemistry
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on other fungal pathogens (IC > 25 μg/mL). With the
In Vivo Testing on Cole Leaves Infected by S.
sclerotiorum. Among the compounds tested for antifungal
activity in vitro, A14 and A15 were found to be potent against
S. sclerotiorum. Therefore, they were further evaluated in the
greenhouse for the control of S. sclerotiorum infected cole. The
efficacy of the treatment is shown in Figure 2. The untreated
negative control (pathogen only) resulted in 100% disease
incidence (0% healthy plant standard) 24 h after trans-
plantation. Treatment with 0.5 mg/mL benzofuroxan derivative
A14 resulted in 46.1% healthy plant standard after 36 h of
treatment. Accordingly, A15 resulted in 11.9% disease
incidence (Table 4). In contrast, leaves treated with
5
0
1
pyrrolidine substitution at the R position, A14 was found to
show high antifungal activity against S. sclerotiorum and F.
graminearum Sehw. with IC50 = 2.52 and 3.42 μg/mL,
respectively. Although these three compounds are the most
potent derivatives among the A series, their IC50 values were
similar to that of the positive control carbendazim and lower
than that of another positive control, chlorothalonil. All other
compounds in this series of benzofuraxan derivatives show
moderate to weak antifungal activities, as illustrated by their
high IC50 values. In addition, the following five compounds
show >25 μg/mL IC50 values against all four tested fungi
phytopathogens: A1, A12, A13, A16, and A18, with methoxyl,
phenylsulfonyl, benzylmethiolate, ethoxyl, and phenyl amino
Table 4. In Vivo Efficacy of 500 μg/mL Compounds on Cole
1
a
groups at the R position, respectively. These findings indicated
Leaves Infected by Sclerotinia sclerotiorum
1
that the presence of an amino group at the R position and
diameter of lesions (mm)
protection efficacy (%)
formation of resonance-stabilized structures may be essential
for the antifungal activity of type A benzofuraxan derivatives.
Meanwhile, in general, this series of compounds have
demonstrated better fungicidal activity against R. solani and F.
graminearum Sehw. as compared to the other two fungi
phytopathogens, S. sclerotiorum and P. capsici.
A14
9.0 ± 0.8
14.8 ± 1.3
4.9 ± 0.5
16.8 ± 1.7
46.1
11.9
71.1
A15
carbendazim
negative control
a
Statistical analysis of the data was performed by analysis of variance
(
one-way ANOVA). A probability value of p ≤ 0.05 was considered to
In the case of series B benzofuraxan derivatives, the
2
3
denote a statistically significance difference.
substituent varies at the R and R positions, whereas both
1
4
R and R positions are hydrogen atoms. B6 and B10, with
2
carbendazim at the same concentration resulted in 71.1%
healthy plant standard. Thus, significant differences existed
among the treated and untreated groups for disease control
experiments in the greenhouse cole leaves.
piperazyl group at the R position, displayed >25 μg/mL IC50
values against all four fungi phytopathogens. The other
compounds exhibited high potency only against R. solani.
Especially, B4 (IC50 = 1.81 μg/mL) and B8 (IC50 = 1.76 μg/
mL) showed inhibitory potency similar to that of carbendazim
In conclusion, we have synthesized a series of benzofuroxan
derivatives and evaluated their inhibitory ability against four
phytopathogenic fungi. Most compounds displayed significant
antifungal activity against certain strains of phytopathogenic
fungi. Significantly, the antifungal activity of A5 was half-fold
that of the well-known commercial fungicide carbendazim and
was identified as the most potent compound against F.
graminearum Sehw. B8 displayed strong antifungal activity
against R. solani with an IC50 value of 1.76 μg/mL, which is
comparable with that of carbendazim (1.42 μg/mL). A14 was
found to have the lowest IC50 (2.52 μg/mL) against S.
sclerotiorum. However, among the benzofuroxan derivatives
reported herein, none was found to possess strong antifungal
activity against P. capsici.
(
IC50 = 1.42 μg/mL). Significantly, all compound IC50 values
are <8.0 μg/mL. These results suggest that benzofuroxan
2
3
derivatives with variation at the phenyl R and R positions may
serve as new leads for the development of potentially useful
antifungal agents against R. solani. In contrast, the series B
derivatives did not generally exhibit good antifungal activity
against the other three plant phytopathogens. However, B2
showed a low IC value against all fungus strains. The presence
50
of a benzyl bromide in B2 may be the reason for it to act as a
universal nucleophilic attack acceptor to exert its cytotoxicity
against plant fungi.
Most series C benzofuroxan derivatives showed weak
antifungal activity, as illustrated with their higher than 25 μg/
mL IC50 values. Replacement of a hydrogen atom at the R2
position with a chlorine atom leads to the IC50 value increase
from 2.52 μg/mL (for A14) to >25 μg/mL (for C2) against S.
sclerotiorum and F. graminearum Sehw. This suggested that the
introduction of an electron-withdrawing group at the R2
position is unfavorable for the compound antifungal activity
toward the tested phytopathgenic fungi; the same trend was
confirmed with C3 (IC > 25 μg/mL) versus A5 (IC = 1.10
2
Overall, the series B compounds, with substituents at the R
3
and R positions of the phenyl ring, exhibited strong fungicidal
potency against R. solani. Several series A benzofuroxan
derivatives were revealed to display strong antifungal effect
against F. graminearum Sehw. Additionally, A9 was the only
compound that displayed high potency and selectivity to both
R. solani and F. graminearum Sehw. The benzofuroxan
structural scaffold with variations at different phenyl positions
could be further explored for the discovery of more potent
antifungal agents against different pyhtopathogenic fungi.
5
0
50
μg/mL) or C4 (IC > 25 μg/mL) versus A19 (IC = 9.15 μg/
5
0
50
4
mL) against F. graminearum Sehw. Substitution of the R nitro
group with methanesulfonyl or benzenesulfonyl caused
significant loss of fungicidal activity, C5, C6, and C7 all having
>
25 μg/mL IC50 values, which indicates that the strongly4
electron-withdrawing and bulky sulfonyl group at the R
position appeared to be less favorable for the antifungal
activity. The remaining four compounds, C1, C8, C9, and C10,
displayed >25 μg/mL IC50 values. Overall, the low activity of
series C benzofuroxan derivatives suggested that the presence
of more than two electron-withdrawing groups on the phenyl
ring would cause antifungal activity decrease.
ASSOCIATED CONTENT
■
*
S
Supporting Information
H NMR, 13C NMR, and HRMS spectra of new synthetic
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
8
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Journal of Agricultural and Food Chemistry
Article
(
15) Dixon, B. R. Preparation of flavin derivatives to be used as
AUTHOR INFORMATION
■
*
riboswitch ligands or anti-infective agents. PCT Int. Appl. WO
Corresponding Authors
2
010019208 A1 20100218, 2010.
(C.Q.) Phone: +86-512-65882092. E-mail: qiaochunhua@
suda.edu.cn.
(Y.Y.) Phone: +86-512-65882092. E-mail: yeyh@njau.edu.cn.
(16) Sheremetev, A. B.; Aleksandrova, N. S.; Ignat’ev, N. V.; Schulte,
M. Straightforward one-pot synthesis of benzofuroxans from o-
*
halonitrobenzenes in ionic liquids. Mendeleev Commun. 2012, 22, 95−
9
7.
Author Contributions
L.W. and C.L. contributed equally to this paper.
(17) de Carvalho, P. S.; Marostica, M.; Gambero, A.; Pedrazzoli, J.
∥
Synthesis and pharmacological characterization of a novel nitric oxide-
releasing diclofenac derivative containing a benzofuroxan moiety. Eur.
J. Med. Chem. 2010, 45, 2489−2493.
Funding
This work was financially supported by grants from the Priority
Academic Program Development of Jiangsu Higher Education
Institutions, Jiangsu Province “333” Project, and The Scientific
Research Foundation for the Returned Overseas Chinese
Scholars, State Education Ministry (to C.Q.), and cosupported
by National Basic Research Program of China
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