Synthesis and antifungal activity of novel s-substituted 6-fluoro-4-alkyl(aryl)thioquinazoline derivatives

Article abstract of DOI:10.1016/j.bmc.2007.03.037

6-Fluoro-4-quinazolinol is prepared by the cyclization reaction of 2-amino-5-fluorobenzoic acid and formamide. The resulting thiol obtained by treatment of hydroxyl group with phosphorus (V) sulfide is converted under phase transfer condition to 4-substit

Full text of DOI:10.1016/j.bmc.2007.03.037

Bioorganic & Medicinal Chemistry 15 (2007) 3768–3774
Synthesis and antifungal activity of novel s-substituted
6-fluoro-4-alkyl(aryl)thioquinazoline derivatives
Guang-Fang Xu, Bao-An Song,* Pinaki S. Bhadury, Song Yang, Pei-Quan Zhang,
Lin-Hong Jin, Wei Xue, De-Yu Hu and Ping Lu
Center for Research and Development of Fine Chemicals, Key Laboratory of Green Pesticide and Bioengineering,
Ministry of Education, Guizhou University, Guiyang 550025, PR China
Received 14 January 2007; revised 10 March 2007; accepted 12 March 2007
Available online 16 March 2007
Abstract—6-Fluoro-4-quinazolinol is prepared by the cyclization reaction of 2-amino-5-fluorobenzoic acid and formamide. The
resulting thiol obtained by treatment of hydroxyl group with phosphorus (V) sulfide is converted under phase transfer condition
to 4-substituted 4-alkylthio-6-fluoroquinazoline derivatives by reaction with halide. The structures of the compounds are confirmed
by elemental analysis, IR, and 1H NMR. Title compounds 3a, 3g, and 3h are found to possess good antifungal activities. Using the
mycelial growth rate method in the laboratory, the mechanism of action of 3g against Fusarium oxysporum in vitro is studied. The
results indicate that 3a, 3g, and 3h have high inhibitory effect on the growth of most of the fungi with EC50 values ranging from 8.3
to 64.2 lg/mL. After treating F. oxysporum with compound 3g at 100 lg/mL, only 6.5% of its spore bourgeoned. The permeability of
the cell membrane increases along with the malformation of the hypha and condensation of its endosome. After treatment with com-
pound 3g at 100 lg/mL within 12 h, the mycelial reducing sugar, D-GlcNAc, content and chitinase activity decline, but the soluble
protein content shows no obvious change.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
Prompted by these results and in an attempt to evaluate
the modification of the fungicidal profile induced by the
change of the substituents at the quinazoline ring, we
designed and synthesized a series of 4-alkylthio-6-fluoro-
quinazolin derivatives with various substituents and
measured their fungicidal activities. The synthetic route
is shown in Scheme 1. The structures of 3 were firmly
established by well- defined IR, 1H NMR, and elemental
analysis. Preliminary bioassay tests showed that some
compounds possessed antifungal activity on three phy-
topathogenic fungi at 500 mg/L in vitro, but with a
degree of variation. It was found that title compounds
3a, 3g, and 3h, similar to a commercial product Hym-
exazol, displayed strong antifungal activities on hyphal
growth of G. zeae, Fusarium oxysporum, and C. mand-
shurica in vitro. Many crops are easily infected by
F. oxysporum, and the disease is hard to control. In
our earlier studies, we found Hymexazol having higher
antifungal activity compared to other commercial fungi-
cides against F. oxysporum. Therefore, the mechanism of
action of 3g against F. oxysporum in vitro was studied
with Hymexazol serving as the control. Some mechanis-
tic aspects of compound 3g on protein, metabolism, and
cell structure are studied and presented in this paper.
Fluorinated quinazoline derivatives represent one of the
most active classes of compounds possessing a wide
spectrum of biological activity. They are widely used
in pharmaceuticals and agrochemicals.1,2 A number of
researches mention the utility of fluorinated quinazo-
lines as important fungicide,3 herbicide,4 and antitumor
agent.5 Thus, their synthesis has been of great interest in
the elaboration of biologically active heterocyclic com-
pounds. Some high-bioactive compounds have been
commercialized, for example, fluquinconazole fungicide
for control of the agriculture disease.6 We have been
interested in the synthetic and agriculture chemistry of
quinazoline derivatives with diversity at 4-position for
many years. Recently, we reported the fungicidal activ-
ity of novel 3-alkylquinazolin-4-one derivatives, some
of which were found to possess good fungicidal
bioactivity.7
Keywords: Quinazoline; Fluorine moiety; Thioether; Antifungal
bioactivity; Mechanism of action.
*
Corresponding author. E-mail: songbaoan22@yahoo.com
0968-0896/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.03.037

G.-F. Xu et al. / Bioorg. Med. Chem. 15 (2007) 3768–3774
3769
SH
O
SR
COOH
HCONH2
F
F
F
F
P4S10
RX, NaOH
BTEAB
N
NH
N
Pyridine
NH2
N
N
1
N
2
3
Scheme 1. Synthesis of compound 3.
2. Chemistry
carried out at 20–65 ꢁC (Table 1, entries 9–11) than that
at 80–85 ꢁC.
The synthetic route designed for the thioether analogues
3 of quinzoline is summarized in Scheme 1. The 2-ami-
no-5-fluorobenzoic acid was converted to 6-fluoro-4-
quinazolinol 1 by a cyclization procedure. Treatment
of 1 with P2S5 in pyridine solution afforded compound
2, 6-fluoro-4-quinazoline-thiol. Then, compound 2 was
reacted with various halides under phase transfer catal-
ysis condition to afford the title compounds 3a–3h.
Using the optimal condition, the best result was thus
obtained when intermediate 2 was treated with 1 equiv
of halides and 60 equiv of NaOH (20%, 10 mL) under
PTC conditions (BTEAB, 0.06 equiv) with toluene as
solvent (10 mL) and heated at 80–85 ꢁC for 1 h. Under
these reaction conditions, the thioetherification reaction
proceeded smoothly, and products (3a–3h) were
obtained in 70.0–89.0% yield (refer Section 5).
In order to optimize the reaction conditions, the synthe-
sis of 3h was carried out under various conditions. The
effects of reaction time, reaction temperature, and phase
transfer catalyst (PTC) on the reaction were investigated
and the results are shown in Table 1. When no tribenz-
ylethylammonium bromide (BTEAB) was used as
catalyst, the reaction was relatively slow and the product
was obtained in 38.0% when heated at 80–85 ꢁC for 1 h
(Table 1, entry 1). The yield of 3h was increased to
89.0% under the same condition when the reaction was
catalyzed by 0.06 equiv BTEAB (Table 1, entry 2).
When the amount of BTEAB was varied as 2%, 4%,
8%, and 10%, 3h could be obtained in 58.8%, 64.0%,
84.2%, and 86.7%, respectively (Table 1, entries 3–6).
Using 6 mol% BTEAB as catalyst, the yield of 3h
increased from 79.9% to 89.0% when the reaction time
was prolonged from 0.5 to 1 h at 80–85 ꢁC (entries 2
and 7). When the reaction time was prolonged further
to 2 h, little improvement in the yield (89.9%, entry 8)
was observed, as compared to that of 1 h (89.0%, entry
2). As for the reaction temperature, it could be seen that
the yield was relatively low when the reaction was
The structures of title compounds 3 were established on
the basis of their spectroscopic data. They showed IR
absorption bands at 3035–3045 cmÀ1 (Ar–H) and
1465–1591 cmÀ1 (skeleton vibration of aromatic ring).
In the 1H NMR spectra, the 2-H signal appeared as sin-
glet in the range of 8.86–9.00 ppm. The chemical shift
peaks of 7-H for 6-fluoro-4-alkylthioquinazoline deriva-
tives were observed at 7.95–7.96 ppm as a quartet. The
5-H and 8-H signals were observed mostly as multiplets
in the range of 7.56–7.80 ppm.
3. Antifungal activity
The three fungi used in the fungicidal bioassay were
G. zeae, F. oxysporum, and C. mandshurica. The results
of preliminary bioassays were compared with that of a
commercial agricultural fungicide, Hymexazol. As indi-
cated in Table 2, most of the synthesized compounds
showed certain antifungal activities against the tested
fungi. The compounds 3a, 3g, 3h at 500 lg/mL inhibited
the growth of G. zeae at 100.0%, 100.0%, and 96.4%,
respectively; F. oxysporum at 92.3%, 98.5%, and
89.3%, respectively; C. mandshurica at 96.9%, 100.0%,
and 94.8%, respectively, which is a little higher than that
of Hymexozole (100.0% against G. zeae, 91.3% against
Table 1. Different reaction conditions for synthesis of 3h
Entrya Reaction The amount of Reaction
Yieldb
time (h)
BTEAB (mol%) temperature (ꢁC) (%)
1
2
1
—
6
80–85
80–85
80–85
80–85
80–85
80–85
80–85
80–85
20–25
40–45
60–65
38.8
89.0
58.8
64.0
84.2
86.7
79.9
89.9
10.1
29.3
68.0
Table 2. Inhibitiona effect of 4-substituted 6-fluoro-4-alkylthioquin-
azoline derivatives at 500 lg/mL on phytopathogenic fungi
1
3
1
2
4
1
4
Compound
Inhibition (%)
5
1
8
G. zeae
F. oxysporum
C. mandshurica
6
1
10
6
7
0.5
2
3a
3b
100.0 2.9
6.2 4.9
92.3 3.2
5.3 3.9
96.9 3.9
11.2 6.7
21.4 8.1
11.8 6.0
38.5 9.9
30.1 9.0
100.0 0.9
94.8 0.9
91.2 4.0
8
6
9
1
6
3c
3d
15.0 2.9
7.6 3.6
18.9 3.2
5.9 4.9
10
11
1
6
1
6
3e
16.3 8.1
13.3 4.6
100.0 1.1
96.4 0.9
100.0 3.2
21.9 7.9
20.3 7.2
98.5 0.8
89.3 1.2
91.3 3.9
3f
3g
a Reaction conditions, a mixture of 6-fluoroquinazolin-4-thiol (1 equiv)
(2), 1-bromopropane (1 equiv), BTEAB (0.02–0.1 equiv), and 20%
sodium hydroxide (60 equiv, 10 mL) in 10 mL of toluene was stirred
at 20–85 ꢁC for 0.5–2 h.
3h
Hymexazol
b Yields of isolated products.
a Average of three replicates.

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G.-F. Xu et al. / Bioorg. Med. Chem. 15 (2007) 3768–3774
Table 3. Toxicity of 3a, 3g, 3h, and Hymexazol on nine kinds of pathogenic fungi
Toxic regression equationa
EC50 (lg/mL)
r
a
Compound
Fungi
3a
G. zeae
y = 2.38x + 1.27
y = 1.40x + 2.90
y = 1.43x + 3.05
y = 2.29x + 1.18
y = 2.52x + 0.94
y = 1.78x + 1.96
y = 1.55x + 2.61
y = 2.30x + 1.25
y = 2.54x + 1.62
37.0 6.8
32.2 8.6
23.3 7.9
46.3 6.2
40.6 8.7
51.2 8.9
35.2 7.9
42.4 8.2
21.4 8.1
0.997
0.982
0.984
0.991
0.977
0.960
0.967
0.967
0.967
F. oxysporum
C. mandshurica
R. solani
T. cucumeris
P. infestans
S. sclerotiorum
B. cinerea
C. gloeosporioides
3g
G. zeae
y = 1.76x + 3.08
y = 1.51x + 3.10
y = 1.66x + 2.86
y = 2.03x + 2.16
y = 1.81x + 2.30
y = 3.04x + 0.67
y = 3.27x + 1.54
y = 1.42x + 3.70
y = 1.00x + 3.20
12.4 7.2
18.2 6.6
19.2 9.8
24.9 7.3
30.8 9.4
26.8 8.3
11.4 9.2
8.3 7.8
0.977
0.988
0.979
0.983
0.962
0.973
0.940
0.960
0.963
F. oxysporum
C. mandshurica
R. solani
T. cucumeris
P. infestans
S. sclerotiorum
B. cinerea
C. gloeosporioides
64.2 8.9
3h
G. zeae
y = 1.41x + 2.99
y = 0.95x + 3.66
y = 1.26x + 3.22
y = 1.43x + 2.91
y = 1.48x + 2.54
y = 2.18x + 1.89
y = 1.99x + 2.55
y = 1.10x + 3.78
y = 1.62x + 2.40
30.1 6.6
25.1 7.6
25.8 8.7
29.2 9.9
46.2 8.9
26.9 8.1
17.1 9.1
13.0 8.5
40.1 8.8
0.982
0.972
0.966
0.966
0.972
0.998
0.993
0.978
0.943
F. oxysporum
C. mandshurica
R. solani
T. cucumeris
P. infestans
S. sclerotiorum
B. cinerea
C. gloeosporioides
Hymexazol
G. zeae
y = 1.92x + 2.27
y = 1.05x + 3.46
y = 0.87x + 3.84
y = 2.73x + 1.33
y = 0.95x + 3.48
y = 1.60x + 2.76
y = 3.48x + 2.57
y = 3.55x + 2.63
y = 0.91x + 3.91
26.4 7.1
29.1 7.6
21.4 9.3
52.1 6.1
40.4 9.7
25.1 9.34
5.1 4.5
0.969
0.994
0.961
0.995
0.965
0.941
0.931
0.926
0.983
F. oxysporum
C. mandshurica
R. solani
T. cucumeris
P. infestans
S. sclerotiorum
B. cinerea
4.6 3.9
15.8 8.2
C. gloeosporioides
a Average of three replicates.
F. oxysporum, and 91.2% against C. mandshurica at
500 lg/mL) (Table 2). Further bioassays disclosed that
compounds 3a, 3g, 3h showed remarkable inhibitory
effect on nine kinds of plant pathogenic fungi with 3g
showing the best result. The EC50 of 3g on G. zeae,
F. oxysporum, C. mandshurica, R. solani, T. cucumeris,
P. infestans, S. sclerotiorum, B. cinerea, C. gloeosporioides,
were 12.4 lg/mL, 18.2 lg/mL, 19.2 lg/mL, 24.9 lg/mL,
30.8 lg/mL, 26.8 lg/mL, 11.4 lg/mL, 8.3 lg/mL,
and 64.2 lg/mL, respectively. Compound 3g had more
potent antifungal activities against most of the
tested fungi and showed a broad-spectrum bioactivity
(Table 3).
3.2. Effect of compound 3g on sporule germination of
F. oxysporum
It could be seen from Figure 2 that the sporule germina-
tion of F. oxysporum declined with the increase of the
concentration. When the concentration was 60 lg/mL,
the sporule germination was 68.7%, the inhibition
was only 32.9%. While the concentration was over
60 lg/mL, the sporule germination declined remarkably,
it was only 6.5% at 100 lg/mL.
3.3. Membrane permeability of F. oxysporum
After F. oxysporum was treated with compound 3g
(100 lg/mL), the relative permeability rate of the cell
membrane was higher than the control. After 5 min,
the relative permeability rate of the control was 6.0%,
and for the treated one was 12.0%. When treated with
Hymexazol, the observation was similar to that of the
control. With longer treatment time, the relative perme-
ability of the control rose gradually, but that of the one
treated with compound 3g and Hymexazol did not rise
3.1. The morphology changes of hypha
The hypha of the control was slippy, vimineous and
branched normally. The endosome of the cell distrib-
uted evenly. But when F. oxysporum was treated with
100 lg/mL of compound 3g, most of its hypha became
coarse and malformed. The cell of the hypha swelled
and its endosome condensed, and formed blanks (Fig. 1).

G.-F. Xu et al. / Bioorg. Med. Chem. 15 (2007) 3768–3774
3771
Figure 1. Microphotograph of the hyphal morphology of Fusarium oxysporum treated with compound 3g (800·).
Figure 4. Changes of mycelial reducing sugar content.
Figure 2. The effect of compound 3g on sporule germination of
Fusarium oxysporum.
the control, 3g- and Hymexazol-treated F. oxysparum
was 1.09 mg/mL, 0.67 mg/mL, and 0.85 mg/mL,
respectively.
3.5. Changes of mycelial chitosan content
From Figure 5, we can see that when F. oxysporum was
treated with compound 3g, the mycelial chitosan con-
tent, namely the content of D-GlcNAc in the mycelial
cell, started to fall at the beginning before showing a ris-
ing tendency. Initially, the observation was very similar
to that of the control. After 1 h, the content of the
D-GlcNAc was lower than that of the control. The con-
tent of D-GlcNAc was 0.0440 mg/mL when treated with
compound 3g at 6 h after inoculation, which was 6.1%
lower than the control (control was 0.0469 mg/mL).
After 6 h, while the content of control started to rise,
that of the treated one began to fall. It could be inferred
from Figure 5 that the content of D-GlcNAc of F. oxy-
sporum treated with compound 3g was lesser than that
of the one commercial fungicide Hymexazol.
Figure 3. The effect of compound 3g on membrane permeability of
Fusarium oxysporum.
at the same rate. The result showed that when F. oxyspo-
rum was incubated with compound 3g, the cell mem-
brane was destroyed in short time, and the relative
permeability of F. oxysporum treated with Hymexazol
was lower than that of the control. The result may be
attributed to the fact that Hymexazol site acting on
F. oxysporum was not the cell membrane (Fig. 3).
3.4. Changes of mycelial reducing sugar content
After treatment with compound 3g, mycelial reducing
sugar content of F. oxysporum was lower than that of
the control (Fig. 4). With prolonged treatment time,
the reducing sugar content showed decreasing tendency.
At 0.5 h, the mycelial reducing sugar content of the con-
trol was 1.27 mg/mL, but for the treated one, the value
was only 1.02 mg/mL which was 19.8% lower than that
of the control. After 6 h, the content of control started
to rise, but that of the treated assumed decreasing ten-
dency. At 12 h, the mycelial reducing sugar content of
Figure 5. Changes of mycelial D-GlcNAc content.

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G.-F. Xu et al. / Bioorg. Med. Chem. 15 (2007) 3768–3774
the control after being incubated with Hymexazol for
6 h. It should be noted that the reaction in the cell was
very complicated. It is not safe to conclude at this stage
that compound 3g has no effect on the synthesis of the
protein. The study requires further investigation.
4. Conclusion
In summary, the present method of formation of
4-substituted 6-fluoro-4-alkylthioquinazoline derivatives
under phase transfer catalyst condition offers several
advantages such as faster reaction rate, lesser by-prod-
ucts, and high yield. It was also found that title com-
pounds 3a, 3g, and 3h displayed good antifungal
activity, especially compound 3g, having a wide spec-
trum of bioactivity. The results showed that 3g had high
inhibitory effect on the growth of most of the fungi with
EC50 values ranging from 8.3 to 64.2 lg/mL. After
F. oxysporum was treated with compound 3g at
100 lg/mL, the permeability of the cell membrane rose
and the hypha became coarse, malformed, its endosome
condensed and formed blanks, and 6.5% of its spore
bourgeoned. After being treated with compound 3g at
100 lg/mL within 12 h, chitinase activity, the content
of mycelial reducing sugar and D-GlcNAc all declined.
We can conclude that the membrane of cell may be
destroyed by compound 3g, and the ability of sugar
absorption by the cell from the culture medium is
depressed. From the changes of chitosan content and
chitinase activity, we conclude that compound 3g can
inhibit the activity of chitinase in the cell of F. oxyspo-
rum and destroy the cell wall. But these were not
obvious when F. oxysporum was treated with
Hymexazol, perhaps due to the fact that cell structure
was not the main site that Hymexazole acts on. In
addition, the content of soluble protein was similar to
that of the control when F. oxysporum was treated with
compound 3g, and it reduced to 87.8% of the control
after being treated with Hymexazol for 24 h. These
results indicate that compound 3g had little effect on
the content of soluble protein and Hymexazol caused
a certain degree of disturbance on the synthesis of the
protein. The biochemical action in the cell is very
complicated. Although it is true that some work had
been done, the precise way in which compound 3g
efficiently inhibits the growth of the hypha still remains
to be ascertained. So, further investigation requires to be
done in the future research (Fig. 8).
Figure 6. Changes of mycelial chitinase activity.
3.6. Changes of mycelial chitinase activity
Mycelial chitinase activity of F. oxysporum began to fall,
then started to rise before showing a decreasing ten-
dency at the end again. And the changes were similar
to those of the D-GlcNAc content. With the increasing
of time, the mycelial chitinase activity of the control
rose gradually, and the treated one fell, 24 h after inoc-
ulation, the difference between control and that of the
treated one reaching its highest value. The content of
the D-GlcNAc that the chitinase had catalyzed in 1 h
was 0.0455 mg/mL without treatment. When treated
with compound 3g and Hymexazol, the content was
0.0364 and 0.0411 mg/mL. The changes between Hym-
exazol-treated one and control was a little (Fig. 6).
3.7. Changes of mycelial soluble protein content
From Figure 7, we can see that when F. oxysporum was
treated with compound 3g for 0.5 h, the mycelial soluble
protein content was 33.1% higher than that of the con-
trol. Half an hour later, the soluble protein content of
F. oxysporum treated with compound 3g was similar to
that of the control. The value was lower than that of
Figure 7. Changes of mycelial soluble protein content.
Figure 8. Effect of different concentrations of 3a, 3g, and 3h on the mycelial growth of Fusarium oxysporum (6.25, 12.5, 25.0, 50.0 and 100 lg/mL).
Key (lg/mL): 1, 6.25; 2, 12.5; 3, 25; 4,50; 5,100; and C, control (the radial growth of the smallest).

G.-F. Xu et al. / Bioorg. Med. Chem. 15 (2007) 3768–3774
3773
5. Experimental
5.1. Analysis and instruments
5.2.2. Data for 2-(6-fluoroquinazolin-4-ylthio)-1-(2,3,4-
trimethoxyphenyl) ethanone (3b). White crystal; mp,
152–154 ꢁC; yield, 70.5%; IR (KBr) m (cmÀ1): 3039.5,
1662.6, 1591.3, 1568.1, 1492.9, 1336.7, 1290.4, 1103.3,
999.1, 839.0, 688.6; 1H NMR (400 MHz, CDCl3) d
(ppm): 3.92–4.12 (3s, 9H, 3CH3O), 4.88 (s,2H,CH2),
6.78 (d, J = 8.8Hz, 1H, PhH), 7.59–7.80 (m, 3H, Ph–H
and H-5, 8 of quinazoline), 7.95–7.99 (q, 1H, J = 5.2,
4.0 Hz, H-7 of quinazoline), 8.86 (s, 1H, 2-H of quinaz-
oline); Anal. Calcd for C19H17FN2O4S: C, 58.75; H,
4.41; N, 7.21. Found: C,58.52; H, 4.53; N,7.14.
The melting points of the products were determined on a
XT-4 binocular microscope (Beijing Tech Instrument
Co., China) and are not corrected. The IR spectra were
recorded on a Bruker VECTOR22 spectrometer in KBr
disks. 1H NMR spectra were recorded on a Varian-
INOVA 400 MHz spectrometer in CDCl3 at room tem-
perature using TMS as an internal reference. Elemental
analysis was performed on an Elementar Vario-III CHN
analyzer. The reagents were all of analytical grade or
chemically pure.
5.2.3. Data for 4-benzylthio-6-fluoroquinazoline (3c).
White crystal; mp, 83–84 ꢁC; yield, 73.8%; IR (KBr) m
(cmÀ1): 3035.3, 1566.2, 1492.9, 1485.2, 1334.7, 1184.3,
1
5.1.1. Preparation of 6-fluoro-4-quinazolinol (1). A mix-
ture of formamide (5.4 g, 120 mmol) and 2-amino-5-flu-
orobenzoic acid (2.4 g, 15 mmol) was stirred at 135 ꢁC
for 7 h. The mixture was then poured into ice water
(10 mL). The crude product was then filtered off and
recrystallized from ethanol. Yield 53%, mp 258–261 ꢁC.8
914.3, 837.1, 698.2, 686.7, 526.6. H NMR (400 MHz,
CDCl3): d 4.64 (s, 2H, CH2),7.26–7.47 (m, 5H, Ph–H)
7.56–7.66 (m, 2H, 5, 8-H of quinazoline), 7.95–7.98 (q,
1H, J = 5.2, 4.0 Hz, H-7 of quinazoline), 9.00 (s, 1H,
2-H of quinazoline); Anal. Calcd for C15H11FN2S: C,
66.65; H, 4.10; N, 10.36. Found: C, 66.46; H, 4.20; N,
10.25.
5.1.2. Preparation of 6-fluoro-4-quinazoline-thiol (2).
P2S5 (10.8 g, 48 mmol) was added to a solution of 6-flu-
oro-4-quinazolinol (4.0 g, 24 mmol) in anhydrous pyri-
dine (100 mL), and the mixture was heated at 90 ꢁC
for 2 h. The reaction mixture was then poured into ice
water, and the resultant precipitate was dissolved in
aqueous KOH (10%). Acidification of the solution with
acetic acid afforded the product, which was filtered off
and dried. Yield 95%, mp >300 ꢁC. 1H NMR
(400 MHz, CDCl3): d 7.50–7.59 (m, 1H, 8-H of quinazo-
line), 7.66 (dd, 1H, J = 8.5, 2.2 Hz, H-5 of quinazoline),
7.93 (q, 1H, J = 5.5, 4.0 Hz, H-7 of quinazoline), 8.90 (s,
1H, H-2 of quinazoline), 10.52 (s, 1H, SH); Anal. Calcd
for C8H5FN2S: C, 53.32; H, 2.80; N, 15.55. Found: C,
53.10; H, 2.70; N, 15.43.
5.2.4. Data for 4-(4-chlorobenzylthio)-6-fluoroquinazoline
(3d). White crystal; mp, 115–117 ꢁC; yield, 74.0%; IR
(KBr) m (cmÀ1): 3045.5, 1559.2, 1492.5, 1398.7, 1325.4,
1243.2, 1190.4, 1080.3, 920.5, 880.3, 674.5. 1H NMR
(400 MHz, CDCl3): d 4.60 (s, 2H, CH2),7.30 (d,
J = 8.4 Hz, 2H, Ph–H), 7.42 (d, J = 8.4 Hz, 2H, Ph–
H), 7.59–7.66 (m, 2H, 5, 8-H of quinazoline), 7.96–
8.00 (q, 1H, J = 5.2, 3.6 Hz, H-7 of quinazoline), 8.99
(s, 1H, 2-H of quinazoline). Anal. Calcd for
C15H10ClFN2S: C, 59.11; H, 3.31; N, 9.19. Found: C,
59.58; H, 3.69; N, 9.36.
5.2.5. Data for 4-(2-chloro-5-pyridylmethylthio)-6-fluoro-
quinazoline (3e). White crystal; mp, 113.5–115.5 ꢁC;
yield, 88.0%; IR (KBr) m (cmÀ1): 3045.3, 1566.2, 1492.9,
1
5.2. General procedure for the preparation of the title
compounds (3a–3h)
1465.9, 1382.5, 1332.8, 1184.3, 1113.5, 950.2, 835.2; H
NMR (400 MHz, CDCl3): d 4.59 (s, 2H, CH2), 7.29 (d,
J = 8.4 Hz, 1H, pyridine–H),7.61–7.65 (m, 2H, 5, 8-H
of quinazoline), 7.79 (d, J = 8.4 Hz, 1H, pyridine–H),
7.98–8.02 (q, 1H, J = 5.2, 4.8 Hz, H-7 of quinazoline),
8.54 (s, 1H, pyridine–H), 8.99 (s, 1H, 2-H of quinazoline);
Anal. Calcd for C14H9ClFN3S: C, 54.99; H, 2.97; N,
13.74. Found: C, 55.09; H, 3.06; N, 13.65.
A mixture of 6-fluoro-4-quinazoline-thiol (225 mg,
1.25 mmol), halides (1.25 mmol), and tribenzyl ethylam-
monium bromide (0.075 mmol) was dissolved in toluene
(10 mL) and 20% aqueous potassium hydroxide
(60.5 mmol, 10 mL). The solution was stirred for 1 h
and then the organic layer was separated, washed with
water, and dried over magnesium sulfate. After
evaporation of solvent, the oily crude product was puri-
fied by preparative TLC with petroleum ether/ethyl ace-
tate (1:1, v/v) as developing solvent to give title
compounds 3.
5.2.6. Data for 4-(2-ethoxycarboxylmethylenethio)-6-flu-
oroquinazoline (3f). White crystal; mp, 119.5–122 ꢁC;
yield, 90.0%; IR (KBr) m (cmÀ1): 3042.5, 2980.5,
2810.2, 1743.7, 1489.1, 1365.6, 1334.7, 1305.8, 1186.2,
1165.0, 1003.0, 841.0, 688.6; 1H NMR (400 MHz,
CDCl3): d 1.31 (t, J = 7.2 Hz, 3H, CH3), 4.17 (s, 2H,
SCH2), 4.26 (q, J = 6.8, 7.2 Hz, 2H, OCH2), 7.61–7.71
(m, 2H, 5, 8-H of quinazoline), 7.98–8.02 (q, 1H,
J = 5.2, 4.0 Hz, 7-H of quinazoline), 8.95 (s, 1H, 2-H of
quinazoline); Anal. Calcd for C12H11FN2O2S: C, 54.12;
H, 4.16; N, 10.52. Found: C, 54.22; H, 4.27; N, 10.52
5.2.1. Data for 4-allylthio-6-fluoroquinazoline (3a). White
crystal; mp, 62–64 ꢁC; yield, 72.1%; IR (KBr) m (cmÀ1):
3040.2, 1558.3, 1543.1, 1490.1, 1336.7, 1290.5, 1180.4,
1
999.1, 912.3, 848.9, 837.1, 525.3; H NMR (400 MHz,
CDCl3): d 4.07 (d, 2H, SCH2), 5.19–6.07 (m, 3H,
CH@CH2), 7.58–7.69 (m, 2H, 5, 8-H of quinazoline),
7.95–7.99 (q, 1H, J = 5.2, 4.0 Hz, 7-H of quinazoline),
8.97 (s, 1H, 2-H of quinazoline); Anal. Calcd for
C11H9FN2S: C, 59.98; H, 4.12; N, 12.72. Found: C,
59.71; H, 4.22; N, 12.63.
5.2.7. Data for 4-ethylthio-6-fluoroquinazoline (3g).
White crystal; mp, 39–41 ꢁC; yield, 80.7%; IR (KBr) m
(cmÀ1): 3040.2, 2966.5, 1566.2, 1541.1, 1492.9, 1336.7,
1290.5, 1180.4, 966; 1H NMR (400 MHz, CDCl3): d

3774
G.-F. Xu et al. / Bioorg. Med. Chem. 15 (2007) 3768–3774
1.46 (t, J = 7.5 Hz, 3H, CH3), 3.39 (q, J = 7.5 Hz, 2H,
CH2), 7.58–7.65 (m, 1H, 8-H of quinazoline), 7.68 (dd,
J = 8.6, 2.3 Hz, H-5 of quinazoline), 7.95 (q, 1H,
J = 5.2, 4.0 Hz, H-7 of quinazoline), 8.95 (s, 1H, H-2
of quinazoline); Anal. Calcd for C10H9FN2S: C, 57.60;
H, 4.32; N, 13.44. Found: C, 57.70; H, 4.20; N, 13.43.
References and notes
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Farmaco 2000, 55, 249.
5.2.8. Data for 4-n-propylthio-6-fluoroquinazoline (3h).
White crystal; mp, 62–64 ꢁC; yield, 89.0%; IR (KBr) m
(cmÀ1): 3040.2, 2966.5, 1564.3, 1545.0, 1492.9, 1336.0,
4. (a) Khan, I. A.; Hassan, G.; Ihsanullah; Khan, M. A.
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1
1291.0, 1182.0. H NMR (400 MHz, CDCl3): d 1.09 (t,
J = 7.5 Hz, 3H, CH3), 1.80–1.84 (m, 2H, CH2), 3.35 (t,
J = 7.5 Hz, 2H, SCH2), 7.57–7.96 (m, 3H, 5, 7, 8-H of
quinazoline), 8.94 (s, 1H, H-2 of quinazoline); Anal.
Calcd for C11H11FN2S: C, 59.38; H, 4.94; N, 12.60.
Found: C, 59.21; H, 4.82; N, 12.53.
Acknowledgments
We thank the National Key Project for Basic Research
(2003CB114404), Program for New Century Excellent
Talents in University in China (NCET-04-0912), Ph.D.
Program Foundation of Ministry of Education of China
(20040657003), and the National Natural Science Foun-
dation of China (20562003, 20442003) for their financial
support.
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S. J. Agric. Food. Chem. 2005, 53, 3888.
13. Yuji, H.; Yukari, O.; Koki, H. J. Agric. Food. Chem. 2006,
54, 9895.
Supplementary data
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Pestic. Sci. 2004, 6, 28.
15. Heux, L.; Brugnerotto, J.; Desbrieres, J.; Versali, M. F.;
Rinaudo, M. Biomacromolecules 2000, 1, 746.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.bmc.
2007.03.037.