Synthesis, crystal structure and fungicidal activity of novel 1,5-Diaryl-3-benzoyloxy-1H-pyrazoles

Article abstract of DOI:10.14233/ajchem.2014.16460

Seven novel 1,5-diaryl-3-benzoyloxy-1H-pyrazoles (2a-2g) were prepared by the DCC condensation of 1,5-diaryl-1H-pyrazol-3-ols (1a- 1g) with benzoic acid. Their structures were characterized by elemental analysis, IR, 1H NMR and mass spectral data. The structure of 5- (3,4-dimethoxyphenyl)-1-phenyl-3-benzoyloxy-1H-pyrazole (2d) was also determined by single crystal X-ray diffraction analysis. Bioassay results indicated that the compounds 5-(4-fluorophenyl)-1-phenyl-3-benzoyloxy-1H-pyrazole (2f) and 1,5-diphenyl-3-benzoyloxy-1Hpyrazole (2a) exhibited excellent-to-medium fungicidal activity against Sclerotinia sclerotiorum at a dosage of 10 ìg/mL. The structureactivity relationships (SAR) were also discussed.

Full text of DOI:10.14233/ajchem.2014.16460

Asian Journal of Chemistry; Vol. 26, No. 15 (2014), 4883-4886
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16460
Synthesis, Crystal Structure and FungicidalActivity of Novel 1,5-Diaryl-3-benzoyloxy-1H-pyrazoles
3
3
1
1
YUAN-YUAN LIU1,*,†, YI LI2,*,†, HONG-JUN ZHU , KAI CHEN , BIN HUANG and YA-PING YANG
1Department of Chemical and Pharmaceutical Engineering, Southeast University ChengXian College, Nanjing 210088, P.R. China
2College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210009, P.R. China
3Department of Applied Chemistry, College of Science, Nanjing University of Technology, Nanjing 210009, P.R. China
*Corresponding authors: E-mail: liuyuanyuan1985419@163.com; liynj2012@njut.edu.cn
†These authors contribute to this work equally
Received: 1 October 2013;
Accepted: 17 December 2013;
Published online: 16 July 2014;
AJC-15592
Seven novel 1,5-diaryl-3-benzoyloxy-1H-pyrazoles (2a-2g) were prepared by the DCC condensation of 1,5-diaryl-1H-pyrazol-3-ols (1a-
1g) with benzoic acid. Their structures were characterized by elemental analysis, IR, 1H NMR and mass spectral data. The structure of 5-
(3,4-dimethoxyphenyl)-1-phenyl-3-benzoyloxy-1H-pyrazole (2d) was also determined by single crystal X-ray diffraction analysis. Bioassay
results indicated that the compounds 5-(4-fluorophenyl)-1-phenyl-3-benzoyloxy-1H-pyrazole (2f) and 1,5-diphenyl-3-benzoyloxy-1H-
pyrazole (2a) exhibited excellent-to-medium fungicidal activity against Sclerotinia sclerotiorum at a dosage of 10 µg/mL. The structure-
activity relationships (SAR) were also discussed
Keywords: 1,5-Diaryl-3-benzoyloxy-1H-pyrazoles, Fungicidal activity, Crystal structure, Structure-activity relationships.
1H-pyrazol-3-ols (1a-1g) were prepared from methyl 3-aryl-
acrylates according to the reported procedure including addition-
cyclization and oxidation8.
INTRODUCTION
Since the discovery of pyrazole fungicide pyraclostrobin
by BASF scientists1-3, aryl substituted oxypyrazole derivatives
have gained enormous attention due to their diverse bioactivities
in fungicide4,5, insecticide6 and herbicide7. We have reported a
series of novel 1,5-diaryl-3-oxypyrazoles containing alkyloxy-
acetate8, oxy(2-thioxothiazolidin-3-yl)ethanone9, or glucopyra-
nosyl moieties10 with fungicidal activity. On the other hand,
several biological studies have also indicated the value of
benzoyloxy as bioactive group11,12. However, very few bioactive
benzoyl substituted 1,5-diaryl-3-oxypyrazole derivatives have
hitherto been described in the literature.
General procedure: Benzoic acid (0.24 g, 2 mmol) was
dissolved in a solution of DCC (0.43 g, 2.1 mmol) in CH2Cl2
(20 mL) and the mixture was stirred at 0 °C for 1 h. Then, 1a-1g
(2 mmol) and DMAP (0.02 g, 0.2 mmol) was added. The solu-
tion was stirred at 0 °C for 2 h and then kept at room tempe-
rature for 12 h. The white precipitate formed was filtered off
and the solvent was evaporated under reduced pressure. The
residue was purified by flash column chromatography over
silica gel (50 g) eluting with petroleum ether/ethyl acetate 4:1
to gain the pure product 2a-2g.
In this article, the synthesis of a series of novel 1,5-diaryl-
3-benzoyloxy-1H-pyrazoles (2a-2g) and the crystal structure
of 5-(3,4-dimethoxyphenyl)-1-phenyl-3-benzoyloxy-1H-
pyrazole (2d) are reported. Meanwhile, their fungicidal activity
has been investigated with the aim of understanding the
structure-activity relationships (SAR) and developing novel
fungicides. A preliminary in vitro bioassay indicated that some
compounds displayed good fungicidal activity at the dosage
of 10 µg/mL.
Detection method: Melting points were measured on an
X-4 microscope electrothermal apparatus (Taike, China) and
were uncorrected. 1H NMR spectra were recorded on a Bruker
spectrometer at 300 or 500 MHz in CDCl3 or DMSO-d6, with
tetramethylsilane as an internal standard. IR spectra were
recorded in KBr disk using a Nicolet 380 FT-IR spectropho-
tometer. Mass spectra were recorded with an Agilent 1100
Series LC/MSD Trap SL. Elemental analyses were performed
on a Flash EA-1112 elemental analyzer.
X-ray crystallography: X-ray crystallographic analysis
of 2d were performed on a Nonius CAD-4 single-crystal
diffractometer by using MoKα radiation (λ = 0.71073 Å) with
an ω/2θ scan mode at 293 K. The structure was solved by
EXPERIMENTAL
All reagents were analytical grades and solvents were
dried by standard methods and distilled before use. 1,5-Diaryl-

4884 Liu et al.
Asian J. Chem.
direct methods and refined by full-matrix least-squares proce-
dures on F2 using SHELXL-97 program13. All non-hydrogen
atoms were refined anisotropically and the hydrogen atoms
were introduced at calculated positions. The isotropic temp.
factors were fixed to 1.2 times (1.5 times for CH3 groups) the
equivalent isotropic displacement parameters of the C-atom
the H-atom is attached to.
CCDC-906894 contains the supplementary crystallo-
graphic data for 2d. These data can be obtained free of charge
from the Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/data_request/cif (or from the CCDC, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 3360-
33; e-mail: deposit@ccdc.cam.ac.uk).
m/z (Irel, %) 371.6 [M + H]+ (100), 393.5 [M + Na]+ (72). Found,
%: C 74.82; H 4.92; N 7.53. C23H18N2O3. Calculated, %: C
74.58; H 4.90; N 7.56.
5-(3,4-Dimethoxyphenyl)-1-phenyl-3-benzoyloxy-1H-
pyrazole (2d): White crystal, m.p. 133-134 °C, yield 0.70 g
(87 %). 1H NMR spectrum (300 MHz, DMSO-d6) δ, ppm (J,
Hz): 8.16 (2H, d, J = 7.2, Ar-H), 7.79 (1H, t, J = 7.3, Ar-H),
7.65 (2H, t, J = 7.3, Ar-H), 7.48-7.31 (5H, m, Ar-H), 7.00-
6.80 (3H, m, Ar-H), 6.67 (1H, s, CH), 3.76 (3H, s, OCH3),
3.57 (3H, s, OCH3). IR spectrum (KBr, νmax, cm-1): 1745 (C=O),
1598, 1549, 1513, 1449 (C=C), 1257 (C-O). MS (ESI), m/z
(Irel, %) 401.5 [M + H]+ (100), 423.5 [M + Na]+ (27). Found,
%: C 71.75; H 5.01; N 7.03. C24H20N2O4. Calculated, %: C
71.99; H 5.03; N 7.00.
Fungicidal assays: The fungicidal activity against
Sclerotinia sclerotiorum, Gibberella zeae and Rhizoctonia cerealis
was investigated. The fungi were obtained from Jiangsu
Pesticide Research Institute Co., Ltd., China. The tested comp-
ounds 2a-2g were dissolved in acetone and added to a sterile
agarized Czapek-Dox medium at 45 ºC. In preliminary scree-
nings, the compounds were used in a concentration of 10 µg/mL.
The control sample contained only one equivalent of acetone.
The media were poured onto 8 cm Petri dishes (10 mL for
each dish) and after 2 days inoculated with 5 mm PDA discs
of overgrown mycelium. In the case of Sclerotinia sclerotiorum,
the medium was inoculated by a prick of laboratory needle
containing fungus spores. The Petri dishes were incubated at
room temperature in the dark. After 4 days, the diameters of
the inoculation of the cultures were measured. The percentage
inhibition of fungal growth was determined by comparison
between the development of fungi colonies on media conta-
ining compounds and on the control. Three replicates of each
test were carried out.
1-Phenyl-5-(3,4,5-trimethoxyphenyl)-3-benzoyloxy-
1H-pyrazole (2e): Yellow crystal, m.p. 128-129 °C, yield 0.75
g (87 %). H NMR spectrum (500 MHz, DMSO-d6) δ, ppm
1
(J, Hz): 8.17 (2H, d, J = 7.2,Ar-H), 7.79 (1H, t, J = 7.3, Ar-H),
7.65 (2H, t, J = 7.3, Ar-H), 7.49-7.35 (5H, m, Ar-H), 6.76
(1H, s, CH), 6.54 (2H, s,Ar-H), 3.67 (3H, s, OCH3), 3.60 (6H,
s, OCH3). IR spectrum (KBr, νmax, cm-1): 1746 (C=O), 1586,
1545, 1506, 1445 (C=C), 1247 (C-O). MS (ESI), m/z (Irel, %)
431.5 [M + H]+ (86), 453.5 [M + Na]+ (100). Found, %: C
69.95; H 5.13; N 6.54. C25H22N2O5. Calculated, %: C 69.76; H
5.15; N 6.51.
5-(4-Fluorophenyl)-1-phenyl-3-benzoyloxy-1H-
pyrazole (2f): Yellow crystal, m.p. 120-121 °C, yield 0.59 g
(83 %). 1H NMR spectrum (500 MHz, DMSO-d6) δ, ppm (J,
Hz): 8.16 (2H, q, J = 1.3, 8.3, Ar-H), 7.79 (1H, t, J = 7.3, Ar-
H), 7.65 (2H, q, J = 7.3, 8.3, Ar-H), 7.45-7.22 (9H, m, Ar-H),
6.70 (1H, s, CH). IR spectrum (KBr, νmax, cm-1): 1745 (C=O),
1598, 1551, 1506, 1450 (C=C), 1260 (C-O). MS (ESI), m/z
(Irel, %) 359.5 [M + H]+ (100), 381.5 [M + Na]+ (33). Found,
%: C 73.52; H 4.23; N 7.85. C22H15N2O2F. Calculated, %: C
73.73; H 4.22; N 7.82.
1,5-Diphenyl-3-benzoyloxy-1H-pyrazole (2a): White
1
crystal, m.p. 110-111 °C, yield 0.68 g (86 %). H NMR
spectrum (500 MHz, DMSO-d6) δ, ppm (J, Hz): 8.17 (2H, q,
J = 1.3, 8.3, Ar-H), 7.80 (1H, t, J = 7.5, Ar-H), 7.65 (2H, q, J
= 7.5, 8.3, Ar-H), 7.45-7.28 (10H, m, Ar-H), 6.71 (1H, s, CH).
IR spectrum (KBr, νmax, cm-1): 1747 (C=O), 1597, 1545, 1504,
1452 (C=C), 1261 (C-O). MS (ESI), m/z (Irel, %) 341.5 [M +
H]+ (8), 363.6 [M + Na]+ (100). Found, %: C 77.37; H 4.72; N
8.26. C22H16N2O2. Calculated, %: C 77.63; H 4.74; N 8.23.
1-Phenyl-5-(p-tolyl)-3-benzoyloxy-1H-pyrazole (2b):
1-Phenyl-5-(4-(trifluoromethyl)phenyl)-3-benzoyloxy-
1H-pyrazole (2g): Yellow crystal, m.p. 93-94 °C, yield 0.69
1
g (84 %). H NMR spectrum (300 MHz, DMSO-d6) δ, ppm
(J, Hz): 8.16 (2H, d, J = 8.4, Ar-H), 7.82-7.75 (3H, m, Ar-H),
7.65 (2H, t, J = 7.9, Ar-H), 7.51 (2H, d, J = 8.2, Ar-H), 7.47-
7.32 (5H, m, Ar-H), 6.85 (1H, s, CH). IR spectrum (KBr, νmax
,
cm-1): 1747 (C=O), 1597, 1550, 1511, 1450 (C=C), 1259 (C-
O). MS (ESI), m/z (Irel, %): 409.6 [M + H]+ (100), 431.4 [M
+ Na]+ (45). Found, %: C 67.43; H 3.69; N 6.89. C23H15N2O2F3.
Calculated, %: C 67.65; H 3.70; N 6.86.
1
Buff crystal, m.p. 89-90 °C, yield 0.71 g (85 %). H NMR
spectrum (500 MHz, CDCl3) δ, ppm (J, Hz): 8.16 (2H, q, J =
1.3, 8.3, Ar-H), 7.79 (1H, t, J = 7.6, Ar-H), 7.64 (2H, q, J =
7.6, 8.3, Ar-H), 7.45-7.16 (9H, m, Ar-H), 6.64 (1H, s, CH),
2.31 (3H, s, CH3). IR spectrum (KBr, νmax, cm-1): 1745 (C=O),
1598, 1550, 1508, 1450 (C=C), 1260 (C-O). MS (ESI), m/z
(Irel, %) 355.5 [M + H]+ (100), 377.5 [M + Na]+ (59). Found,
%: C 77.72; H 5.10; N 7.93. C23H18N2O2. Calculated, %: C
77.95; H 5.12; N 7.90.
5-(4-Methoxyphenyl)-1-phenyl-3-benzoyloxy-1H-
pyrazole (2c): Yellow crystal, m.p. 115-116 °C, yield 0.74 g
(85 %). 1H NMR spectrum (500 MHz, DMSO-d6) δ, ppm (J,
Hz): 8.16 (2H, d, J = 8.4, Ar-H), 7.79 (1H, t, J = 7.6, Ar-H),
7.64 (2H, q, J = 7.6, 8.4, Ar-H), 7.45-7.29 (5H, m,Ar-H), 7.21
(2H, d, J = 8.5, Ar-H), 6.94 (2H, d, J = 8.6, Ar-H), 6.61 (1H, s,
CH), 3.76 (3H, s, OCH3). IR spectrum (KBr, νmax, cm-1): 1744
(C=O), 1599, 1551, 1508, 1450 (C=C), 1250 (C-O). MS (ESI),
RESULTS AND DISCUSSION
Two common methods are known for the formation of ester
bonds. One involves the following two steps: acyl chlorides
were first prepared by the acylation reaction of acids with
thionyl chloride, which further proceeded dehydrochlorination
with alcohols14,15. The other involves the condensation of acids
with alcohols, using DCC as dehydrating agent and DMAP as
catalyst16,17. In contrast to thionyl chloride, DCC is a convenient
and environment-friendly reagent for the synthesis of hetero-
cyclic ester compounds. So in our procedure, the seven novel
1,5-diaryl-3-benzoyloxy-1H-pyrazoles (2a-2g) were prepared
by the DCC condensation of 1,5-diaryl-1H-pyrazol-3-ols

Vol. 26, No. 15 (2014)
Synthesis, Crystal Structure and Fungicidal Activity of Novel 1,5-Diaryl-3-benzoyloxy-1H-pyrazoles 4885
(1a-1g) with benzoic acid in CH2Cl2 as solvent. The most
satisfactory results were obtained when the reactions were first
stirred at 0 °C for 3 h and then at room temperature for 12 h.
The crude solids were purified via flash chromatography to
furnish good yield of 2a-2g (Scheme-I).
hydrogen bond C-H···O links the molecules to form a three
dimensional network, in which it may be effective in the
stabilization of the structure (Fig. 2).
C14
C15
C16
O
a: X = H;
X
b: X = 4-CH
C13
N2
X
OH
O
O
;
3
c: X = 4 -OCH
;
3
N1
HO
C17
d: X = 3,4-(OCH ) ;
2
3
C12
N
N
N
DCC
DMAP (cat.)
N
e: X = 3,4,5-(OCH ) ;
3
3
03
C23
C20
C11
C6
f: X = 4-F;
C5
g: X = 4-CF
C24
C19
3
C7
C8
1a-1g
2a-2g
C18
C9
C10
Scheme-I: Synthesis of 1,5-diaryl-3-benzoyloxy-1H-pyrazoles 2a-2g
C1
C22
04
C4
C21
In the 1H NMR spectra of 2a-2g, as a result of deshielding
C3
01
02
effect of benzoyloxy group, the CH of the pyrazole ring appears
as a singlet at the low field of 6.85-6.61 ppm. The aromatic
protons resonated in the range of 8.17-7.64 ppm pointed out
2a-2g have the benzoyloxy group. All products showed a
multiplet of phenyl protons in the region of 7.49-6.54 ppm.
The IR spectra of 2a-2g exhibited signals at about 1745 cm-1
which was attributed to the characteristic absorption of C=O.
Four bands at about 1600, 1550, 1510 and 1450 cm-1 showed
the absorption feature ofAr-H. The strong bands at about 1260
cm-1 were the characteristic absorption of C-O.
C2
Fig. 1. Molecular structure of 2d
To further validate the structures, the X-ray crystallo-
graphic analysis of 5-(3,4- dimethoxyphenyl)-1-phenyl-3-
benzoyloxy-1H-pyrazole (2d) was also investigated. The
detailed crystal and structure refinement data for 2d are collec-
ted in Table-1. An ORTEP view of the 2d molecule is shown
in Fig. 1. The C-linked benzene ring A (C3-C8), N-linked
benzene ring B (C12-C17) and benzoyloxy ring C (C19-C24)
are twisted 50.95º, 40.62º and 64.18º, respectively, from the
plane of the bridge pyrazole ring (N1/N2/C9-C11). Rings A,
B and C are planar and the dihedral angles between them are
61.33º, 32.20º and 47.99º, respectively. The intermolecular
TABLE-1
CRYSTAL DATA AND STRUCTURE REFINEMENT FOR 2d
Empirical formula
CCDC No.
Formula weight
Temperature
C24H20N2O4
906894
400.42
293(2)
Fig. 2. A partial packing diagram of 2d (hydrogen bonds shown by dashed
lines)
Compounds 2a-2g were screened for bioactivity against
three fungi, namely Sclerotinia sclerotiorum, Gibberella zeae
and Rhizoctonia cerealis, at a dosage of 10 mg/mL. As a result,
in Table-2, most compounds have weak fungicidal activity
except 2f (X = 4-F) and 2a (X = H) exhibiting excellent-to-
medium inhibitory activity against Sclerotinia sclerotiorum.
This might imply that the introduction of the mono-fluoro
group was important for improving its fungicidal activity. In
terms of substituents X, compounds with electron-withdrawing
groups showed higher fungicidal activity against Sclerotinia
sclerotiorum than that with electron-donating groups, as seen
in the comparison of 2f (X = 4-F) vs 2b (X = 4-CH3), 2c (X =
4-OCH3), 2d (X = 3,4-(OCH3)2) and 2e (X = 3,4,5-(OCH3)3).
However, 2g (X = 4-CF3) with no inhibitory activity against
Sclerotinia sclerotiorum was one exception, which indicated
switching X from F to the strong electron-withdrawing CF3
group had negative impact on the inhibition rates and taking
the electronic effect into full consideration was significant.
Wavelength
Crystal system, space group
Unit cell dimensions
0.71073 Å
Triclinic, P-1 (No. 2)
a = 9.3040(19) Å α = 68.70(3)º
b = 10.507(2) Å β = 81.40(3)º
c = 12.075(2) Å γ = 67.99(3)º
1019.5(4) Å3
Volume
Z, Calculated density
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Limiting indices
2, 1.304 Mg/m3
0.090 mm-1
420
0.10 × 0.20 × 0.30 mm
1.81 to 25.36 deg.
0 < = h < = 11, -11 < = k < = 12,
-14 < = l < = 14
4002 / 3750 [Rint = 0.045]
0.9911 and 0.9736
Full-matrix least-squares on F2
3750 / 0 / 271
Reflections collected / unique
Max. and min. transmission
Refinement method
Data / restraints / parameters
Final R indices [I>2σ(I)]
Largest diff. peak and hole
R1 = 0.0688, wR2 = 0.1508
0.149 and -0.169 e·Å-3

4886 Liu et al.
Asian J. Chem.
Moreover, 2a (X = H), 2b (X = 4-CH3) and 2c (X = 4-OCH3)
with weak fungicidal activity against Gibberella zeae pointed
out the introduction of the mono-substituted electron-donating
groups had effective influence on their fungicidal activity.
However, these compounds showed no fungicidal activity
against Rhizoctonia cerealis. The present work indicated that
2f and 2a could be used as potential lead compounds for further
study of novel fungicides.
ACKNOWLEDGEMENTS
This work was jointly supported by the Natural Science
Foundation for Young Scholars of Jiangsu Province
(BK20130749) and the Youth Foundation of Southeast
University ChengXian College (7303600001).
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TABLE-2
ANTIFUNGAL ACTIVITY OF NEWLY SYNTHESIZED
COMPOUNDS (% INHIBITION)
10 µg/mL
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Seven novel benzoyl substituted 1,5-diaryl-3-oxypyra-
zoles (2a-2g) were synthesized by the DCC condensation. The
spectroscopic and crystal data provide the useful structural
information. Excellent-to-medium fungicidal activity against
Sclerotinia sclerotiorum shown by compounds 2f and 2a
implies that the introduction of electron-withdrawing groups
to the phenyl ring by taking the electronic effect into full
consideration seems to have somewhat positive effect on
fungicidal activity. The most promising compounds in this
study, 2f and 2a, can be used as potential lead compounds for
further study of novel fungicides.