Design, Synthesis, Antifungal Activities and SARs of (R)-2-Aryl-4,5-dihydrothiazole-4-carboxylic Acid Derivatives

Article abstract of DOI:10.1002/cjoc.201500619

Based on the structure of natural product 2-aryl-4,5-dihydrothiazole-4-carboxylic acid, a series of novel (R)-2-aryl-4,5-dihydrothiazole-4-carboxylic acid derivatives were designed and synthesized. Their structures were characterized by ¹H NMR, ¹³C NMR and HRMS. The single crystal structure of compound 9b was determined by X-ray diffraction analysis. The antifungal activities were evaluated for the first time. The bioassay results indicated that most compounds exhibited moderate to good antifungal activities. The antifungal activities of compound 13a (against Cercospora arachidicola Hori), 13d (against Alternaria solani), and 16e (against Cercospora arachidicola Hori) were 61.9%, 67.3% and 61.9%, respectively, which are higher than those of the commercial fungicides chlorothalonil and carbendazim. Moreover, compound 13d exhibited excellent antifungal activities against 7 kinds of the fungi tested (66.7%, 77.3%, 63.0%, 87.9%, 70.0%, 70.0% and 80.0% at 50 μg?mL). Therefore, 13d can be used as a new lead structure for the development of antifungal agents.

Full text of DOI:10.1002/cjoc.201500619

FULL PAPER
DOI: 10.1002/cjoc.201500619
Design, Synthesis, Antifungal Activities and SARs of
(R)-2-Aryl-4,5-dihydrothiazole-4-carboxylic Acid Derivatives
Jingbo Liu, Yuxin Li,* Youwei Chen, Xuewen Hua, Yingying Wan, Wei Wei,
Haibin Song, Shujing Yu, Xiao Zhang, and Zhengming Li*
State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science DQG
Engineering (Tianjin), Nankai University, Tianjin 300071, China
Based on the structure of natural product 2-aryl-4,5-dihydrothiazole-4-carboxylic acid, a series of novel
(R)-2-aryl-4,5-dihydrothiazole-4-carboxylic acid derivatives were designed and synthesized. Their structures were
1
characterized by H NMR, 13C NMR and HRMS. The single crystal structure of compound 9b was determined by
X-ray diffraction analysis. The antifungal activities were evaluated for the first time. The bioassay results indicated
that most compounds exhibited moderate to good antifungal activities. The antifungal activities of compound 13a
(against Cercospora arachidicola Hori), 13d (against Alternaria solani), and 16e (against Cercospora arachidicola
Hori) were 61.9%, 67.3% and 61.9%, respectively, which are higher than those of the commercial fungicides chlo-
rothalonil and carbendazim. Moreover, compound 13d exhibited excellent antifungal activities against 7 kinds of
the fungi tested (66.7%, 77.3%, 63.0%, 87.9%, 70.0%, 70.0% and 80.0% at 50 μg⁄mL). Therefore, 13d can be used
as a new lead structure for the development of antifungal agents.
Keywords (R)-2-aryl-4,5-dihydrothiazole-4-carboxylic acid, synthesis, antifungal activity, structure-activity rela-
tionship
Introduction
antifungal activities of 2-aryl-4,5-dihydrothiazole-4-
carboxylic acid and its analogues in agricultural chemis-
try. Natural product has good compatibility, biodegrad-
ability and low toxicity, so it can be used as ideal lead
structure to develop agrochemicals, such as pyrethroids,
strobilurins, triketone herbicides, and glufosinate.[20]
Thus, the synthesis of well biodegradable, low toxic and
highly bioactive thiazoline compounds has become an
active research in agricultural chemistry. Futher, het-
erocycles such as piperazine, piperidine, pyrimidine and
other heterocycles are important phamacophores for
fungicidal molecular design (compounds f, g, h, Scheme
1).[21-23]
In consideration of the above viewpoints, a series of
(R)-2-aryl-4,5-dihydrothiazole-4-carboxylic acid deriva-
tives 9a－9g, 13a－13g and 16a－16g were designed,
synthesized and tested against fungi in vitro systemati-
cally for the first time. The role of the substituents on A
ring and part B played in the biological activities was
studied.
In recent years, heterocyclic compounds containing
sulfur and nitrogen have received considerable attention
because of their medicinal and pesticidal importance.[1,2]
Thiazolines are often used in pharmacological, medici-
nal, and agricultural applications owing to good envi-
ronmental profiles and various excellent biological ac-
tivity,[3-10] especially fungicidal activity (compounds a,
b, c, Scheme 1).[8-10]
Thiazoline ring also existed in many natural products
with many kinds of biological activity, such as pyoche-
lin (compound d, Scheme 1) and (−)-(R)-dihydroaeru-
ginoic acid (compound e, Scheme 1). Pyochelin, pro-
duced from Pseudomonas aeruginosa and Burkholderia
cepacia, displayed a unique microbial siderophore ac-
tivity.[11] (−)-(R)-Dihydroaeruginoic acid has been found
to exhibit in vitro antiproliferative activity for L1210
cell lines.[12] They are two representative 2-aryl-4,5-di-
hydrothiazole-4-carboxylic acid derivatives. The re-
searches on 2-aryl-4,5-dihydrothiazole-4-carboxylic
acid or its analogues have been mainly focused on anti-
biotic activity,[13] anticancer reactivity,[14,15] antiprolif-
erative activity,[12,16] HIV-1 inhibition,[7] iron chelat-
ing[17,18] and metallo-β-lactamase inhibiting[19] in medi-
cal chemsitry. However, there are few reports about the
Experimental
General
Melting points were determined on an X-4 binocular
*
E-mail: nkzml@vip.163.com; liyx128@nankai.edu.cn; Tel.: 0086-022-23503732; Fax: 0086-022-23503732
Received August 28, 2015; accepted October 7, 2015; published online November 13, 2015.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201500619 or from the author.
Chin. J. Chem. 2015, 33, 1269—1275
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Liu et al.
FULL PAPER
Scheme 1 Some representative structures of thiazoline, piperazine, piperidine and pyrimidine and the strategy of title compounds’ de-
sign
S
N
N
H H
S
S
N
N
Me
COOH
a
OH
HOOC
N
d
R
∗
OH
S
S
N
Ar
2-aryl-4,5-dihydrothiazole-4-
carboxylic acid
S
COOH
b
N
OH
S
N
e
N
H
c
H3C
O
CH3
NH
Br
N
N
H
H
O
S
N
N
Cl
N
O
N
H
O
O
N
B
f
O
O
S
N
N
N
HN
N
N
N
N
N
N
B =
N
N
HC
A
CF3
N
R
g
O
N
N
HO
N
O
N
F
O
N
H
N
designed structrures
O
O
F
h
ences[24,25] with minor improvement. Benzonitrile 1a
(1.03 g, 10.0 mmol) and L-cysteine (1.33 g, 11.0 mmol)
were subsequently added to a solution of methanol and
phosphate buffer (pH＝6.7) (25 mL, 1∶1). The reaction
microscope melting point apparatus (Beijing Tech In-
struments Co., Beijing, China) and uncorrected. 1H
NMR and 13C NMR were recorded on a Bruker AV400
spectrometer (400 MHz) using CDCl3 or DMSO-d6 as
solvent. Chemical shift values (δ) were reported in ppm
with tetramethylsilane (TMS) as the internal standard.
Mass spectra were obtained by using a high-resolution
mass spectrometer (HRMS) (Varian 7.0T FTMS). All
solvents and liquid reagents were dried by standard
methods and distilled before use. Column chromatogra-
phy purification was carried out using silica gel (200－
300 mesh).
◦
mixture was stirred at 60 C and reaction progress was
monitored by thin layer chromatography (TLC). After
completion, the solvent was evaporated under reduced
pressure. The crude residue was basified to pH 11 with
sodium hydroxide solution (1.0 mol•L−1) and then
washed with ethyl acetate (3×10 mL). The water layer
was acidified to pH 1 with hydrogen chloride (1.0
mol•L−1) to precipitate a light-colored solid. The solid
was filtered, washed with a small amount of cool water,
dried under vacuum to give compound 3a as a white
solid (1.63 g, 78.9%); m.p. 124－126 ℃; 1H NMR (400
Synthesis of intermediates (R)-2-phenyl-4,5-dihydro-
thiazole-4-carboxylic acid (3a)
The procedure was similar to that described in refer-
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Antifungal Activities and SARs of (R)-2-Aryl-4,5-dihydrothiazole-4-carboxylic Acid Derivatives
ture was stirred for 2 h at 55－60 ℃, cooled to room
MHz, DMSO-d6) δ: 13.01 (s, 1H, COOH), 7.81 (d, J＝
8.9 Hz, 2H, Ph-H), 7.49－7.42 (m, 3H, Ph-H), 4.94 (t,
J＝9.0 Hz, 1H, NCH), 3.63－3.50 (m, 2H, SCH2).
Intermediates 3b－3g were synthesized according to
the method described for 3a, and their characterization
data are given in the Supporting Information.
temperature, and filtered. The filtrate was extracted with
ethyl acetate (3×10 mL), dried, filtered, and evaporated
in vacuum to give 4,6-dimethoxy-2-(piperazin-1-yl)-
pyrimidine (12) as a white solid (2.02 g, 90%); m.p. 95
◦
1
－97 C; H NMR (400 MHz, CDCl3) δ: 5.33 (s, 1H,
pyrimidine-H), 3.82 (s, 6H, OCH3), 3.77－3.73 (m, 4H,
NCH2), 2.90－2.86 (m, 4H, NCH2), 2.26 (s, 1H, NH).
Synthesis of 6-benzyltetrahydro-1H-pyrrolo[3,4-b]-
pyridine-5,7(6H,7aH)-dione (7)
Synthesis of 1-(4,6-dimethoxypyrimidin-2-yl)piperi-
din-4-ol (15)
Compound 5 was synthesized by heating 2,3-
pyridinedicarboxylic acid 4 to reflux in acetic anhydride.
Intermediate 6 was designed and prepared as previously
reported.[26] Compound 7 was prepared according to the
literature procedures.[26] 5.0 wt% Pd/C (0.366 g) was
added to a solution of 6-benzyl-5H-pyrrolo[3,4-b]pyri-
dine-5,7(6H)-dione 6 (4.76 g, 20.00 mmol) in methanol
(35mL) under nitrogen atmosphere in a 100 mL auto-
clave. The autoclave was stirred at 90 ℃ under hydro-
gen pressure of 4.0 MPa for 8 h. The resulting mixture
was filtered and washed with methanol (3×5 mL). The
solvent was evaporated to dryness in vacuum to give
crude 6-benzyltetrahydro-1H-pyrrolo[3,4-b]-pyridine-
5,7(6H,7aH)-dione (7). The crude 7 was used directly in
the next step without further purification.
Piperidin-4-ol 14 (1.01 g, 10 mmol) and triethyl-
amine (2.02 g, 20 mmol) were subsequently added to a
solution of 4,6-dimethoxy-2-(methylsulfonyl) pyrimi-
dine 10 (2.18 g, 10 mmol) in ethanol (20 mL). The mix-
ture was stirred and refluxed for 8 h, then cooled to
room temperature. The solvent was evaporated in vac-
uum. The residue was purified by silica gel column
eluted with petroleum ether-ethyl acetate (V∶V＝4∶1)
to obtain 1-(4,6-dimethoxypyrimidin-2-yl)piperidin-4-ol
15 as a white solid (2.30 g, 95%); m.p. 115－117 ℃;
1H NMR (400 MHz, CDCl3) δ: 5.32 (s, 1H), 4.43－4.32
(m, 2H), 3.91－3.86 (m, 1H), 3.82 (s, 6H,), 3.28－3.16
(m, 2H, NCH2), 1.92－1.89 (m, 2H, CH2), 1.65 (s, 1H,
OH), 1.53－1.44 (m, 2H, CH2).
Synthesis of 6-benzyltetrahydro-1H-pyrrolo[3,4-b]-
pyridine-5,7(6H,7aH)-dione (8)
General procedure for the synthesis of the target
compounds 9, 13, and 16
6-Benzyltetrahydro-1H-pyrrolo[3,4-b]pyridine-
5,7(6H,7aH)-dione 7 (4.88 g, 20.0 mmol) was dissolved
in 90% ethanol (30 mL), followed by the addition of
D(−)-tartaric acid (3.02 g, 20 mmol) in batches. The
reaction mixture was heated at 50 ℃ for 0.5 h, then
cooled slowly to 20 ℃ for up to 3 h and stirred over-
night at 20 ℃. The mixture was filtered, washed
throughly with cold anhydrous ethanol (3×20 mL), and
dried to afford a large amount of white solid. The white
solid was dissolved in distilled water (30 mL), basified
to pH 11 with sodium hydroxide solution (1 mol•L−1),
and then extracted with ethyl acetate (3×15 mL). The
organic extract was separated, dried, filtered, and con-
centrated in vacuum to give (4aR,7aS)-6-benzyltetra-
hydro-1H-pyrrolo[3,4-b] pyridine-5,7(6H,7aH)-dione (8)
N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide
hydrochloride (EDCI; 0.230 g, 1.2 mmol) and 1-
hydroxy-1H-benzotriazole (HOBT; 0.143 g, 1.06 mmol)
were subsequently added to a solution of (R)-2-aryl-4,5-
dihydrothiazole-4-carboxylic acid (3a) (0.207 g, 1.0
mmol) in anhydrous dichloromethane (10 mL). The re-
action mixture was stirred for 1 h at room temperature
under nitrogen atmosphere, followed by the addition of
compound 8 (0.244 g, 1.0 mmol) and triethylamine
(0.121 g, 1.2 mmol). The reaction was stirred overnight
at room temperature. The reaction mixture was washed
with water (2×10 mL), dilute hydrochloric acid (1.0
mol•L−1) (2×10 mL), saturated sodium bicarbonate
solution (2×10 mL) and brine (10 mL). The organic
layer was dried over anhydrous sodium sulfate, filtered
and concentrated in vacuum. The crude product was
purified by silica gel column eluted with petroleum
ether-ethyl acetate (V∶V＝3∶1) to give the desired
title compound 9a as a white solid (0.326 g, 75.2%).
1
as a white solid (2.35 g, 47.5%); m.p. 75－77 ℃; H
NMR (400 MHz, CDCl3) δ: 7.42－7.22 (m, 5H, Ar-H),
4.65 (s, 2H, PhCH2), 3.84 (d, J ＝7.0 Hz, 1H,
NHCHCO), 2.86 (q, J＝7.1 Hz, 1H, CHCO), 2.82－
2.75 (m, 1H, NHCH2), 2.66－2.56 (m, 1H, NHCH2),
2.21 (s, 1H, NH), 1.97 (dt, J＝13.0, 6.1 Hz, 1H,
CHCH2), 1.65 (td, J＝13.6, 6.9 Hz, 1H, CHCH2), 1.56
－1.46 (m, 2H, CH2CH2CH2).
◦
1
m.p. 126－128 C; H NMR (400 MHz, CDCl3) δ: 7.80
(d, J＝7.3 Hz, 2H, Ar-H), 7.46 (d, J＝7.3 Hz, 1H, Ar-H),
7.42－7.37 (m, 4H, Ar-H), 7.32 (dd, J＝14.3, 6.6 Hz,
3H, Ar-H), 5.81 (d, J＝8.4 Hz, 1H, NCHCO), 5.50 (t,
J＝8.6 Hz, 1H, NCH), 4.68 (d, J＝9.2 Hz, 3H, PhCH2,
SCH2), 4.23 (dd, J＝11.0, 8.1 Hz, 1H, SCH2), 3.50 (dd,
J＝10.9, 9.4 Hz, 1H, CHCO), 3.07 (dd, J＝13.7, 5.6 Hz,
2H, CONCH2), 2.20－2.12 (m, 1H, CHCH2), 1.80－
1.72 (m, 1H, CHCH2), 1.60 (m, 2H, CHCH2); 13C NMR
(100 MHz, CDCl3) δ: 176.93, 174.60, 170.08, 169.34,
135.51, 132.78, 131.61, 128.85, 128.78, 128.52, 128.45,
Synthesis of 4,6-dimethoxy-2-(piperazin-1-yl)pyrimi-
dine (12)
Compound 12 was prepared according to refer-
ence.[27] Potassium carbonate (4.14 g, 30.0 mmol) was
dissolved in distilled water (30 mL). Then piperazine 11
(1.72 g, 20.0 mmol) and 4,6-dimethoxy-2-(methylsul-
fonyl)pyrimidine 10 (2.18 g, 10.0 mmol) were added in
batches at 55－60 ℃ respectively. The reaction mix-
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FULL PAPER
128.14, 77.46, 51.69, 43.02, 42.56, 38.87, 33.78, 24.40,
21.31. HRMS calcd for C24H24N3O3S ([M ＋H] ＋ )
434.1538, found 434.1536.
Scheme 2 Synthetic route of compounds 3a－3g
COOH
Target compounds 9b－9g, 13a－13g and 16a－16g
were prepared by the similar above-mentioned method
using appropriate substrates, and their characterization
data are given in the Supporting Information.
N
S
NH2
CN
R1
a
R1
HS
+
COOH
R2
R2
3a - 3g
Fungicidal screening
1
2
Antifungal activities of the title compounds 9a－9g,
13a－13g and 16a－16g against Cercospora arachi-
dicola Hori, Physalospora piricola, Alternaria solani,
Fusarium graminearum, Phytophthora capsici, Sclero-
tinia sclerotiorum, Phytophthora infestans, Rhizoctonia
solani and Botrytis cinerea were tested with the myce-
lium growth inhibition in vitro[28] and their relative inhi-
bition ratio (%) was determined using the mycelium
growth rate method.[29] The relative inhibition rate was
calculated according to the formula: Relative inhibition
rate (%)＝(D1－D2)/D1×100%. In this formula, D1 is
the average diameter of circle mycelia during the blank
assay and D2 is the average diameter of circle mycelia
during test. Chlorothalonil and carbendazim were used
as the controls. The inhibition ratios of title compounds
at the dose of 50 μg⁄mL were summarized in Table 1.
The EC50 values of compound 13d and chlorothalonil
had been experimented and calculated by the Scatchard
method. And the results were summarized in Table 2.
3a: R1 = H, R2 = H;
3b: R1 = CH3, R2 = H
: R = Cl, R2 = H
1
2
1
3c
: R = F, R = H;
3d
3f
1
2
1
R2 = NO2
3e
: R = H, R = Br;
3g: R1 = H, R2 = CF3
: R = H,
Reagents and conditions: (a) phosphate buffer (pH＝6.7), MeOH, 60
℃, 12 h, 77.1%－86.8%
Scheme 3 Synthetic route of target compounds 9a－9g
O
OH
O
OH
a
b
O
N
O
N
O
5
4
O
O
H
c
d
N
N
N
Results and Discussion
N
O
H H
O
Chemistry
7
6
(R)-2-Aryl-4,5-dihydrothiazole-4-carboxylic acids
3a－3g were synthesized according to the reported
method with minor improvement in Scheme 2. The pure
products were obtained in 77.1%－86.8% yield after
filtration instead of extraction and distillation as de-
scribed in the references.[24,25]
O
N
O
H
H
H
e
H
O
N
S
N
N
O
N
H
Ph
O
R1
Compound 7 was prepared from pyridine-2,3-
dicarboxylic acid 4 by condensation, substitution and
reduction with a high overall yield. Temperature had a
great influence on resolution of enantiomers, during the
synthesis of compound 8 starting from compound 7,
programmed temperature control was utilized to opti-
mize the reaction conditions in our experiment. As
shown in Scheme 3, compound 7 was dissolved in 90%
ethanol, followed by the addition of D(−)-tartaric acid in
batches. The reaction mixture was held at 50 ℃ for 0.5
h, then cooled slowly to 20 ℃ for up to 3 h and stirred
overnight at 20 ℃. A large amount of white solid was
obtained after filtration. The white solid was basified to
pH 11, extracted and concentrated to give 8 in 47.5%
yield.
8
R2
9a
g
- 9
9a: R1 = H, R2 = H; 9b: R1 = CH3, R2 = H
9c: R1 = F, R2 = H; 9d: R1 = Cl, R2 = H
9e: R1 = H, R2 = Br; 9f: R1 = H, R2 = NO2
9g: R1 = H, R2 = CF3
Reagents and conditions: (a) Ac2O, reflux, 3.5 h, 95%; (b) (i) BnNH2,
toluene, 6 ℃, 2 h; (ii) Ac2O, reflux, 2 h, 89.1%; (c) 4 MPa H2, 5.0 wt%
Pd/C, CH3OH, 90 ℃, 8 h; (d) (i) D(−)-tartaric acid, 90% ethanol, 50 ℃,
0.5 h, 20 ℃, 12 h; (ii) NaHCO3, 47.5%; (e) 3a－3g, EDCI, HOBT, Et3N,
CH2Cl2, r.t., 6－7 h, 67.3%－75.2%
in 95% yield.
Compound 12 was prepared by treating compound
10 with piperazine 11 using potassium carbonate as al-
kali in distilled water in a good yield as described in the
literature.[27] Compound 15 was obtained from com-
pounds 10 and 14 in ethanol with triethylamine as base
In the initial step, we attempted to treat compound 8,
12 or 15 with (R)-2-aryl-4,5-dihydrothiazole-4-carbonyl
chloride (obtained from compound 3) in the presence of
triethylamine to prepare 9, 13 and 16. However, the title
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Antifungal Activities and SARs of (R)-2-Aryl-4,5-dihydrothiazole-4-carboxylic Acid Derivatives
Scheme 5 Synthetic route of target compounds 16a－16g
compounds 9, 13 and 16 were difficult to separate from
the by-products in the reaction mixture and the reaction
gave consistently poor yields. N-(3-Dimethylaminopro-
pyl)-N'-ethylcarbodiimide hydrochloride (EDCI) and
1-hydroxy-1H-benzotriazole (HOBT) are often used for
condensation reaction. As shown in Schemes 3 and 4, it
was observed that the title compounds 9 and 13 were
obtained by a simple and convenient one-step condensa-
tion reaction with EDCI and HOBT as condensation
agents in 67.3%－78.9% yields. However, the title
compounds 16 were not obtainable following the same
method. This result is probably due to the poor nucleo-
philicity of compound 15. In the presence of catalytic
amounts of dimethylaminopyridine (DMAP), the title
compounds 16 were synthesized with N-methylmorpho-
line (NMM) as acid-binding agent in 71.9%－78.2%
yields as shown in Scheme 5.
O
OH
O
N
N
N
N
a
SO2CH3
N
OH
+
N
H
O
O
10
14
15
O
N
O
S
b
N
N
R1
N
O
R2
O
16a -16g
16a: R1 = H, R2 = H; 16b: R1 = CH3, R2 = H
16c: R1 = F, R2 = H; 16d: R1 = Cl, R2 = H
16e: R1 = H, R2 = Br; 16f: R1 = H, R2 = NO2
16g: R1 = H, R2 = CF3
Scheme 4 Synthetic route of target compounds 13a－13g
Reagents and conditions: (a) Et3N, ethanol, reflux, 8 h, 90%; (b) 3a－
3g, EDCI, HOBT, DMAP (catalytic amount), NMM, CH2Cl2, r.t., 6－7 h,
71.9%－78.2%
O
O
H
N
N
N
N
N
a
N
NH
SO2CH3
+
N
H
O
O
12
10
11
O
O
N
N
N
N
b
N
S
O
R1
Figure 1 Molecular structure of compound 9b.
R2
13a - 13g
13a: R1 = H, R2 = H; 13b: R1 = CH3, R2 = H
of C14－N1－C8, C14－N1－C1 and C8－N1－C1
angles was 359.62°, indicating the sp2 hybridization
state of the N1 atom. Similarly, the N2 atom also
adopted an sp2 hybridization state. The torsion angles of
N3－C16－C17－S1, C13－N2－C12－C11 and C14
－N1－C8－C9 were 20.20 (11)°, 55.30 (13)° and
17.79(13)°, respectively, indicating that the dihydrothia-
zole ring, the piperidine ring and pyrrole ring were non-
planar.
13c: R1 = F, R2 = H; 13d: R1 = Cl, R2 = H
13e: R1 = H, R2 = Br; 13f: R1 = H, R2 = NO2
13g: R1 = H, R2 = CF3
Reagents and conditions: (a) K2CO3, H2O, 50－60 ℃, 2－3 h, 90%; (b)
3a－3g, EDCI, HOBT, Et3N, CH2Cl2, r.t., 6－7 h, 70.9%－78.9%
Crystal structure analysis
To identify the chiral characteristic of target com-
pounds, a colorless crystal 9b with dimensions of 0.20
mm×0.18 mm×0.12 mm suitable for X-ray sin-
gle-crystal diffraction study was cultivated in the test
tube from hexane and dichloromethane (V∶V＝5∶1).
Several molecular characteristics were made apparent
upon crystal structure analysis of compound 9b (Figure
1, CCDC number: 1404863). The absolute configuration
of 9b was designated C9 (R), C13 (S) and C16 (R). The
average bond lengths and bond angles of the phenyl ring
were normal.[30,31] Due to the p-π conjugate effect, the
bond lengths of N1－C8, N1－C14 and N2－C15 were
1.3918 (16) Å, 1.3861 (15) Å and 1.3566 (15) Å, re-
spectively, which are much shorter than the normal C－
N (1.47 Å), but close to C＝N (1.33 Å).[32] The sum
Fungicidal activities and structure-activity relation-
ship (SAR)
As shown in Table 1, most compounds (9a－9d, 9f,
13a－13g, 16a－16c, 16e) selectively exhibited better
antifungal activities to certain fungi than either chloro-
thalonil or carbendazim; they showed higher activities
against Cercospora arachidicola Hori, Physalospora
piricola and Sclerotinia sclerotiorum than other fungi.
What is more, compound 13d against 7 kinds of the
tested fungi (Alternaria solani; Fusarium graminearum;
Phytophthora capsici; Sclerotinia sclerotiorum; Phyto-
phthora infestans; Rhizoctonia solani; Botrytis cinerea)
exhibited excellent antifungal activities (66.7%, 77.3%,
63.0%, 87.9%, 70.0%, 70.0% and 80.0% at 50 μg⁄mL).
Chin. J. Chem. 2015, 33, 1269—1275
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Liu et al.
FULL PAPER
Table 1 Antifungal activities (%) of target compounds 9, 13 and
16 against 9 kinds of fungus at 50 μg⁄mL
when the skeleton of part B is 4,6-dimethoxy-2-(pipera-
zin-1-yl)pyrimidine (12), 13d (ring A containing a chlo-
rine atom) against 7 kinds of the tested fungi (except
Cercospora arachidicola Hori and Physalospora piri-
cola) exhibited much better antifungal activities than the
others, while the inhibitory effects of 13a－13c and 13e
－13g against Cercospora arachidicola Hori and Phy-
salospora piricola were much better than that of 13d.
Compounds with electron-donating substitutes exhibited
more broad-spectrum antifungal activity than the others
when the skeleton of part B was 1-(4,6-dimethoxypyri-
midin-2-yl)piperidin-4-ol (15), such as 16b.
On the basis of the preliminary bioassays, compound
13d was selected for further bioassay at lower dose
(EC50). The subsequent results in Table 2 showed that
compound 13d had good antifungal activities against
Alternaria solani, Fusarium graminearum, Phyto-
phthora capsici, Sclerotinia sclerotiorum, Botrytis cine-
rea, with EC50 values of 32.20, 16.64, 17.11, 14.01 and
15.72 μg⁄mL, respectively, which implied that com-
pound 13d exhibited broad-spectrum antifungal activity
comparable to the commercial fungicide chlorothalonil.
Compd.
9a
C.H P.P A.S F.G P.C S.S P.I R.S B.C
55.2 2.4 30.0 17.1 14.3 78.3 16.0 65.2 19.5
6.9 17.1 45.0 53.7 40.0 32.6 44.0 53.0 43.9
3.4 0.0 40.0 34.1 11.4 73.9 24.0 65.2 61.0
58.6 29.3 30.0 24.4 17.1 21.7 16.0 15.2 19.5
34.5 17.1 40.0 48.8 31.4 32.6 24.0 40.0 48.8
41.4 24.4 20.0 12.2 14.3 54.3 12.0 45.5 12.2
34.5 12.2 15.0 17.1 17.1 17.4 20.0 22.7 12.2
61.9 70.2 26.7 27.3 9.3 45.5 20.0 42.5 10.0
57.1 74.5 33.3 50.0 11.1 69.7 10.0 10.0 22.5
33.3 76.6 13.3 27.3 7.4 45.5 10.0 27.5 12.5
33.3 34.0 66.7 77.3 63.0 87.9 70.0 70.0 80.0
47.6 83.0 20.0 45.5 11.1 30.3 15.0 15.0 12.5
47.6 80.9 13.3 36.4 14.8 12.1 12.5 12.5 10.0
57.1 66.0 20.0 36.4 11.1 45.5 20.0 22.5 15.0
19.0 31.9 26.7 40.9 3.7 57.6 15.0 35.0 12.5
47.6 55.3 40.0 13.6 14.8 69.7 10.0 67.5 42.5
57.1 55.3 20.0 22.7 3.7 21.2 20.0 42.5 10.0
47.6 70.2 13.3 36.4 7.4 45.5 15.0 10.0 20.0
61.9 34.0 10.0 13.6 11.1 36.4 10.0 11.3 12.5
47.6 8.5 10.0 22.7 3.7 21.2 12.5 10.0 10.0
19.0 53.2 20.0 13.6 14.8 15.2 10.0 10.0 12.5
9b
9c
9d
9e
9f
9g
13a
13b
13c
13d
13e
13f
13g
16a
16b
16c
16d
16e
16f
16g
Conclusion
In summary, a series of (R)-2-phenyl-4,5-dihydro-
thiazole-4-carboxylic acid derivatives were designed,
synthesized, and tested for their antifungal activities.
Most title compounds exhibited moderate to excellent
antifungal activity. The relevant SAR can be summa-
rized as follows: the title compounds containing the
skeleton of 4,6-dimethoxy-2-(piperazin-1-yl)pyrimidine
exhibited higher antifungal activities than the title com-
pounds containing the skeleton of (4aR,7aS)-6-benzyl-
tetrahydro-1H-pyrrolo[3,4-b]pyridine5,7(6H,7aH)-dione
or 1-(4,6-dimethoxypyrimidin-2-yl) piperidin-4-ol. The
antifungal activities of compound 13a (against Cercos-
pora arachidicola Hori), spora arachidicola Hori), 13d
(against Alternaria solani), and 16e (against Cercospora
arachidicola Hori) were 61.9%, 67.3% and 61.9%, re-
spectively, which are higher than those of the commer-
cial fungicides chlorothalonil and carbendazim. More-
over, compound 13d exhibited excellent antifungal ac-
tivity when tested against 7 kinds of fungi (66.7%,
77.3%, 63.0%, 87.9%, 70.0%, 70.0% and 80.0% at 50
μg⁄mL). Therefore, 13d can be used as a leading com-
pound for further structural optimization to develop a
potential antifungal agent.
Chlorothalonil 58.8 88.5 63.6 38.1 82.7 40.7 81.0 96.1 96.1
Carbendazim 8.3 45.9 43.5 100 26.1 99.2 100 100 15.7
C.H, Cercospora arachidicola Hori; P.P, Physalospora piricola;
A.S, Alternaria solani; F.G, Fusarium graminearum; P.C, Phy-
tophthora capsici; S.S, Sclerotinia sclerotiorum; P.I, Phy-
tophthora infestans; R.S, Rhizoctonia solani; B.C, Botrytis cine-
rea.
It is noteworthy that when the substituents on A ring
were same, the change of the part B had a great influ-
ence on antifungal activities. Overall, compounds 13
(Part B is 4,6-dimethoxy-2-(piperazin-1-yl)pyrimidine
12) exhibited higher activity than compounds 9 and 16
(Part B are (4aR,7aS)-6-benzyltetrahydro-1H-pyrrolo-
[3,4-b]pyridine5,7(6H,7aH)-dione (8) and 1-(4,6-dime-
thoxypyrimidin-2-yl)piperidin-4-ol (15), respectively).
Similarly, when part B was the same, the antifungal
activity was affected significantly with the change of the
substituents on the benzene ring (A ring). Interestingly,
Table 2 Antifungal activities as EC50 (μg⁄mL) of the target compound 3d and Chlorothalonil
3d
y＝a＋bx
EC50
R
Chlorothalonil
y＝a＋bx
EC50
17.92
7.65
3.00
1.15
5.79
R
A.S
F.G
P.C
S.S
B.C
y＝2.9004＋1.3924x
y＝2.9672＋1.6644x
y＝4.0728＋0.7517x
y＝2.8943＋1.8366x
y＝3.3757＋1.3573x
32.20
16.64
17.11
14.01
15.72
0.98
0.98
0.99
0.99
0.97
A.S
F.G
P.C
S.S
y＝3.9124＋0.8679x
y＝4.3815＋0.6998x
y＝4.5810＋0.8774x
y＝4.9397＋1.0344x
y＝3.7117＋1.6898x
0.98
0.99
0.99
0.99
0.98
B.C
A.S, Alternaria solani; F.G, Fusarium graminearum; P.C, Phytophthora capsici; S.S, Sclerotinia sclerotiorum; B.C, Botrytis cinerea.
1274 Chin. J. Chem. 2015, 33, 1269—1275
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© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Antifungal Activities and SARs of (R)-2-Aryl-4,5-dihydrothiazole-4-carboxylic Acid Derivatives
[15] Guo, R. S.; Kasbohm, E. A.; Arora, P.; Sample, C. J.; Baban, B.; Sud,
Acknowledgments
N.; Sivashanmugam, P.; Moniri, N. H.; Daaka, Y. Endocrinology
2006 147, 4883.
[16] Bergeron, R. J.; Wollenweber, M.; Weigand, J. J. Med. Chem. 1994,
37, 2889.
[17] Yoganathan, S.; Sit, C. S.; Vederas, J. C. Org. Biomol. Chem. 2011, 9,
2133.
We gratefully acknowledge the financial support of
this work by the “111” Project of Ministry of Education
of China (No. B06005) and the Natural Science Founda-
tion of China (No. 31370039).
[18] George, A. M.; Jones, P. M.; Middleton, P. G. FEMS Microbiol. Lett.
2009, 300, 153.
References
[19] Chen, P.; Horton, L. B.; Mikulski, R. L.; Deng, L.; Sundriyal, S.;
Palzkill, T.; Song, Y. Bioorg. Med. Chem. Lett. 2012, 22, 6229.
[20] Mann, R. S.; Kaufman, P. E. Mini-Rev. Org. Chem. 2012, 9, 185.
[21] Wang, B. L.; Shi, Y. X.; Ma, Y.; Liu, X. H.; Li, Y. H.; Song, H. B.; Li,
B. J.; Li, Z. M. J. Agric. Food. Chem. 2010, 58, 5515.
[22] Li, F. Y.; Zhu, Y. J.; Fan, Z. J.; Xu, J. H.; Guo, X. F.; Zong, G. N.;
Song, H. B.; Chen, L.; Song, Y. Q.; Qian, X. L.; Ma, L. Y.; Wang, J.
R. Chin. J. Struct. Chem. 2015, 34, 659.
[23] Li, Y.; Zhang, Z. G.; Zhu, M. N.; Li, Z. N.; Liu, C. L.; Li, Z. M. Ag-
rochemicals 2010, 49, 246 (in Chinese).
[24] Lu, Y.; Li, C. M.; Wang, Z.; Chen, J. J.; Mohler, M. L.; Li, W.; Dal-
ton, J. T.; Miller, D. D. J. Med. Chem. 2011, 54, 4678.
[25] Maltsev, O. V.; Walter, V.; Brandl, M. J.; Hintermann, L. Synthesis
2013, 45, 2763.
[1] Zhang, H.; Liu, K. C.; Liu, R. Q.; Li, Q. B.; Li, Y. Q.; Wang, Q. M.;
Liu, S. Z. Chin. J. Chem. 2015, 33, 749.
[2] Zhou, H.; Duan, Z. G.; Zhao, S.; Bao, M. Y.; Li, Z. W.; Pei, Y. Z.
Chem. J. Chin. Univ. 2015, 36, 1694 (in Chinese).
[3] Ino, A.; Hasegawa, Y.; Murabayashi, A. Tetrahedron Lett. 1998, 39,
3509.
[4] Bergeron, R. J.; Wiegand, J.; McManis, J. S.; McCosar, B. H.; Wei-
mar, W. R.; Brittenham, G. M.; Smith, R. E. J. Med. Chem. 1999, 42,
2432.
[5] Li, W.; Lu, Y.; Wang, Z.; Dalton, J. T.; Miller, D. D. Bioorg. Med.
Chem. Lett. 2007, 17, 4113.
[6] Li, W.; Wang, Z.; Gududuru, V.; Zbytek, B.; Slominski, A. T.; Dalton,
J. T.; Miller, D. D. Anticancer Res. 2007, 27, 883.
[7] Pattenden, G.; Thom, S. T. J. Chem. Soc., Perkin Trans 1 1993, 1629.
[8] Mao, J.; Chen, J. Y.; Li, R. X.; Wang, H. Y.; Li, J.; Han, J. X. Chin. J.
Appl. Chem. 2004, 21, 1265 (in Chinese).
[26] Ramakrishnan, A.; Bhawsar, S.; Narayana, V. WO 2009125425 A2,
2009 [Chem. Abstr. 2009, 152, 215256].
[27] Mao, M. Z.; Li, Y. X.; Zhou, Y. Y.; Yang, X.; Zhang, X. L.; Zhang,
X.; Li, Z. M. Chem. Res. Chin. Univ. 2013, 29, 900.
[28] Zhu, H. W.; Wang, B. L.; Zhang, X. L.; Xiong, L. X.; Yu, S. J.; Li, Z.
M. Chem. Res. Chin. Univ. 2014, 30, 409.
[9] Zheng, Z. B.; Sun, Y. J.; Liu, L.; Yu, Y. B.; Yuan, H. J.; Fu, B. Mod-
ern Agrochemicals 2009, 8, 8 (in Chinese) .
[10] Liu, L.; Zheng, Z. B.; Qin, Z. H.; Fu, B.; Yuan, H. Z. Chin. J. Org.
Chem. 2008, 28, 1841 (in Chinese).
[11] Rinehart, K. L.; Staley, A. L.; Wilson, S. R.; Ankenbauer, R. G.; Cox,
C. D. J. Org. Chem. 1995, 60, 2786.
[29] Chen, N. C. Bioassay of Pesticides, Beijing Agricultural University
Press, Beijing, 1991 (in Chinese).
[12] Elliot, G. T.; Kelly, K. F.; Bonna, R. L.; Wardlaw, T. R.; Burns, E. R.
Cancer Chemoth. Pharma. 1988, 21, 233.
[30] Liu, X. H.; Pan, L.; Tan, C. X.; Weng, J. Q.; Wang, B. L.; Li, Z. M.
Pestic. Biochem. Physiol. 2011, 101, 143.
[13] Zamri, A.; Schalk, I. J.; Pattus, F.; Abdallah, M. A. Bioorg. Med.
Chem. Lett. 2003, 13, 1147.
[14] Gududuru, V.; Hurh, E.; Dalton, J. T.; Miller, D. D. J. Med. Chem.
2005, 48, 2584.
[31] Liu, X. H.; Sun, Z. H.; Yang, M. Y.; Tan, C. X.; Weng, J. Q.; Zhang,
Y. G.; Ma, Y. Chem. Biol. Drug Des. 2014, 84, 342.
[32] Ye, Z. J.; Shi, L. N.; Shao, X. S.; Xu, X. Y.; Xu, Z. P.; Li, Z. J. Agric.
Food Chem. 2013, 61, 312.
(Lu, Y.)
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