Synthesis and antifungal activities of 5-(3,4,5-trimethoxyphenyl)-2-sulfonyl-1,3,4-thiadiazole and 5-(3,4,5-trimethoxyphenyl)-2-sulfonyl-1,3,4-oxadiazole derivatives

Article abstract of DOI:10.1016/j.bmc.2007.04.014

Starting from the key intermediate 5-(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazole-2-thiol (4) or the oxadiazole analogue (5), the title compounds 9 and 10 are synthesized by a two-step process. Thioetherification reaction of 4 or 5 with an organic halide ca

Full text of DOI:10.1016/j.bmc.2007.04.014

Bioorganic & Medicinal Chemistry 15 (2007) 3981–3989
Synthesis and antifungal activities of
5-(3,4,5-trimethoxyphenyl)-2-sulfonyl-1,3,4-thiadiazole and 5-
(3,4,5-trimethoxyphenyl)-2-sulfonyl-1,3,4-oxadiazole derivatives
Cai-Jun Chen, Bao-An Song,* Song Yang, Guang-Fang Xu, Pinaki S. Bhadury,
Lin-Hong Jin, De-Yu Hu, Qian-Zhu Li, Fang Liu, Wei Xue, Ping Lu and Zhuo Chen
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 6 March 2007; revised 3 April 2007; accepted 4 April 2007
Available online 10 April 2007
Abstract—Starting from the key intermediate 5-(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazole-2-thiol (4) or the oxadiazole analogue
(5), the title compounds 9 and 10 are synthesized by a two-step process. Thioetherification reaction of 4 or 5 with an organic halide
catalyzed by indium or indium tribromide first affords appropriate sulfide 7 or 8, which is then converted into title compounds 9 or
10 by hydrogen peroxide oxidation catalyzed by ammonium molybdate in ionic liquid [bmim]PF6. The structures are unequivocally
confirmed by spectroscopic (IR, 1H and 13C NMR) data and elemental analyses. The structures of 8d and 10q are further established
by X-ray crystallographic diffraction analysis. The compounds have been shown to be fungicidally active. Title compounds 10i and
10j can inhibit mycelia growth by approximately 50% (EC50) at 2.9–93.3 lg/mL in vitro against 10 kinds of fungi.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
good antimicrobial bioactivities against Gram-positive
bacteria, B. mega and B. saphilis, Gram-negative bacteria
Escherichia coli and P. fluores, and fungus Aspergillus
niger.14 Kleefeld reported KMnO4 oxidation of 5-(4-
chlorophenyl)-2-methylthio-1,3,4-oxadiazole for the
preparation of 1,3,4-oxadiazole sulfones having
antifungal activity that could protect beans against artifi-
cial infection with Botrytis at the concentration of
100 mg/L.15 Hu reported a series of bisoxadiazole sul-
furether/sulfone derivatives and found part of the sulfone
compounds exhibiting medium inhibitory activity
against E coli.16 However, the most common substituents
that appear in the aryl(heterocycle) ring are nitro, halo,
hydroxyl or mono methoxy groups and to the best of
our knowledge, there is no report on antifungal activity
of sulfones having trimethoxyphenyl group attached to
the heterocyclic nucleus.
Sulfone derivatives containing heterocyclic moiety are
known for their interesting antifungal bioactivities and
have attracted considerable attention in pesticide and
medicinal formulation. A large number of reports on
their synthesis and biological activities have appeared
during the last three years.1–8 Among them, thiadiazole
and oxadiazole exhibit a wide range of biological espe-
cially antifungal activities.9–11 While p,p0-bis[[[(2-aryl-
sulfonamido)-1,3,4-oxadiazol-5-yl]methyl]amino] diphe-
nyl sulfones are known for their moderate antifungal
and antibacterial activities,11 p,p0-bis(5-aryl-1,3,4-
oxadiazole-2-yl-methylamino)diphenyl sulfones and
p,p0-bis (2-aryl-1,3,4-oxadiazol-5-yl)diphenyl sulfones
prepared by Meshkatalsadat et al.12,13 exhibit medium
inhibitory activity against Candida albicans and
Pseudomonas fluores. Vikani reported p,p0-bis(2-substi-
tuted-benzalamino/benzoylamino/sulfon-amido-1,3,4-
thiadiazol-5-yl-methyl amino)diphenyl sulfones displaying
The incorporation of trimethoxyphenyl moiety in organ-
ic compounds, not limited to sulfones, of late has at-
tracted considerable attention due to its naturally
derived characterization and wide prevalence in pesti-
cides and medicinal compounds.17,18 In our previous
work, many heterocyclic compounds containing trimeth-
oxyphenyl moiety were reported with good fungicidal,
Keywords: Sulfone; Antifungal activity; Synthesis; Catalyst; Ionic liq-
uid; Thiadiazole moiety; Oxadiazole moiety.
*
Corresponding author. E-mail: songbaoan22@yahoo.com
0968-0896/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.04.014

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C.-J. Chen et al. / Bioorg. Med. Chem. 15 (2007) 3981–3989
antiviral, and antitumor activities.19–22 In continuation
to extend our research on fungicidal compounds, we
designed a series of new sulfones with 3,4,5-trimethoxy-
phenyl functionality present in the heterocyclic ring.
Herein, we wish to report the synthesis and fungicidal
activities of some novel sulfone derivatives containing
trimethoxyphenyl substituted 1,3,4-thiadiazole and
1,3,4-oxadiazole moieties.
thioetherification reaction with halide (RX) catalyzed
by indium or indium tribromide. Treatment of sulfides
7 and 8 by H2O2 catalyzed by ammonium molybdate
in ionic liquid afforded the heterocyclic sulfones 9 and
10, with good yields.
In order to optimize the reaction conditions for the
preparation of 9 and 10, the synthesis of 10f was carried
out under several conditions. The effects of different cat-
alysts, solvents, reaction times, reaction temperatures,
and oxidant amounts on the reaction were investigated,
and the results are summarized in Table 1. First, effect of
two different catalysts was investigated in the presence
of ionic liquid [bmim]PF6. As it could be seen from
Table 1, the reaction catalyzed by 1% equiv of ammo-
nium molybdate yielded 94% 10f in 2 h, while for
MnSO4, the yield of 10f was only 37% for the same per-
iod (Table 1, entries 1 and 2). This proved superior cat-
alytic activity of (NH4)6Mo7O24. When the catalyst
amount was decreased to 0.5% and 0%, the reaction
yield of 10f declined to 90% and 71%, respectively (Ta-
ble 1, entries 3 and 4). Hence 1% equiv (NH4)6Mo7O24
catalyst was chosen as ideal catalyst concentration. Ef-
fect of different solvents such as acetone, CH3CN,
DMF, ethanol, and acetic acid was also compared with
2. Chemistry
The synthetic route designed for the sulfone analogues 9
and 10 is summarized in Scheme 1. Following the re-
ported method,23 5-(3,4,5-trimethoxyphenyl)-1,3,4-thi-
adiazole-2-thiol 4 was synthesized from gallic acid in
five steps: etherification, esterification, hydrazidation,
salt formation, and cyclization. 5-(3,4,5-Trimethoxy
phenyl)-1,3,4-oxadiazole-2-thiol 5 was easily prepared
by the reaction of 5-trimethoxy phenylhydride 3,
potassium hydroxide, and carbon disulfide in absolute
ethanol under reflux condition. Then, 5-(3,4,5-trimeth-
oxyphenyl)-1,3,4-thiadiazole-2-thiol 4 and the oxadia-
zole analogue 5 were converted to thioether derivatives
containing thiadiazole 7 or oxadiazole moiety 8 by a
HO
H3CO
c
H3CO
a
HO
HO
COOH
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
COOCH3
H3CO
H3CO
COOH
b
2
1
N
N
for 4:(1) e; (2) f
for 5:(1) g; (2) h
d
SH
H3CO
CONHNH2
X
4: X=S
5: X=O
3
H3CO
H3CO
H3CO
H3CO
H3CO
O
S
N
N
N
N
k
for 7: i
for 8: j
R
S
R
H3CO
H3CO
X
X
O
9a - 9i: X=S
10a - 10q: X=O
7a - 7i: X=S
8a - 8q: X=O
Scheme 1. Reagents and conditions: synthetic route to title compounds 9 and 10. (a) (CH3)2SO4, 10% NaOH; (b) 35% HCl; (c) CH3OH, 98% H2SO4,
reflux; (d) NH2NH2ÆH2O, CH3OH, reflux for 5 h; (e) KOH, CS2, C2H5OH , rt; (f) 98% H2SO4 , 0–5 ꢁC; (g) KOH, CS2, C2H5OH, reflux for 6 h ; (h) 5%
HCl, ice-bath; (i) In, 3% NaOH, H2O, RX(6), rt; (j) InBr3, 3% NaOH, H2O, RX(6), rt; (k) 30% H2O2, (NH4)6Mo7O24 (1 mol%), ionic liquid, 40 ꢁC, 2 h.
Table 1. Synthesis of 10f in ionic liquids under different reaction conditions
Entry
(NH4)6Mo7O24 (mol%)
H2O2 (equiv)
Solventa
Time/h
Temperature/ꢁC
10fb
1
2
1
5
5
5
5
5
5
5
5
5
5
5
5
5
3
[bmim]PF6
[bmim]PF6
[bmim]PF6
[bmim]PF6
Acetone
2
2
40
40
40
40
40
40
40
40
40
40
40
20
50
40
94
37
90
71
44
52
54
68
64
87
84
79
90
76
1c
0.5
0
3
2
4
2
5
1
2
6
1
CH3CN
DMF
Ethanol
2
7
1
2
8
1
2
9
1
Acetic acid
[bmim]PF4
[bmim]PF6
[bmim]PF6
[bmim]PF6
[bmim]PF6
2
10
11
12
13
14
1
2
1
1
1
2
1
2
10
1
a The amount of solvent was 12.8 equiv (with respect to the substrate 8f) for the ionic liquid or 10 mL for the other solvents.
b Isolated yields after work-up.
c MnSO4ÆH2O (1 mol%) was used as catalyst.

C.-J. Chen et al. / Bioorg. Med. Chem. 15 (2007) 3981–3989
3983
the ionic solvent [bmim]PF6 for the synthesis of 10f. It
was found that while oxidation could be easily achieved
in [bmim]PF6 in presence of catalyst (NH4)6Mo7O24
(Table 1, entry 1), the reaction afforded poor yield with
other solvents (Table 1, entries 5–9). The other ionic li-
quid [bmim][PF4] did not afford the same good result
and the yield of 10f decreased from 94% to 87% (Table
1, entries 1 and 10). Further, we also examined the effect
of reaction time on the oxidation reaction of sulfide to
sulfone. When the reaction time was prolonged from
1 h to 2 h, the yield of 10f increased from 84% to 94%
(Table 1, entries 1 and 11). As for the reaction tempera-
ture, it could be seen that the yield was relatively lower
when the reaction was carried out at room temperature
(Table 1, entry 12) than that at 40 ꢁC (Table 1, entry 1).
No substantial change was observed when the reaction
system was heated to 50 ꢁC (Table 1, entry 13). Hence,
the temperature 40 ꢁC was selected as the optimal one
for our reaction. When lower amount of oxidant (3
equiv) was employed, only 76% yield of sulfone 10f
was obtained even with extended reaction time up to
10 h (Table 1, entry 14). Using the optimized condition,
the best result was obtained when 8f was reacted with 5
equiv H2O2 and 0.01 equiv (NH4)6Mo7O24 in 12.8 equiv
of ionic solvent [bmim][PF6] at 40 ꢁC for 2 h.
the benzene is 82.76ꢁ. Also the trimethoxybenzene ring,
the oxadiazole ring [C(1), C(2), C(3), C(4), C(5), C(6),
C(10), C(11), N(1), N(2), O(4)], and the adjacent sulfur
atom S(1) linked to the later are all fairly planar. The
deviation from the least-squares plane through the ring
atoms is less than 0.0457 nm. The dihedral angle be-
tween the plane of oxadiazole group and the plane of
the trimethoxybenzene is 82.76ꢁ. As shown in the pack-
ing diagram of the title compound (Fig. 2), there exist no
hydrogen bonds.
As for compound 10q, the main structural characteristics
are similar as that of compound 8d. The bond lengths
˚
C(12)–S(1) and C(11)–S(1) are 1.798(5) A and
˚
1.786(3) A, respectively, which are similar to that of the
compound 8d. The S(1) atom and oxadiazole ring form
a configuration in which the S(1) atom is sp2 hybridized.
The benzene ring [C(13), C(14), C(15), C(16), C(17),
C(18)] and the adjacent carbon atom C(12) are also fairly
planar. The trimethoxybenzene ring and the oxadiazole
ring [C(1), C(2), C(3), C(4), C(5), C(6), C(10), C(11),
N(1), N(2), O(4)] as well as the sulfur atom S(1) linked
to the later lie in a plane. As shown in the packing diagram
of 10q Figure 3(Fig. 4), there exist two intermolecular
hydrogen bonds. One is C(12)–H(12B). . .O(7), with the
˚
donor and acceptor distance 2.731 A, C(12)–H(12B) =
˚
0.97 A, and H(2). . .O(1) = 2.38 A, 2.731(5) C(12)–H
˚
Various substituted sulfones were obtained through
such optimized ammonium molybdate catalyzed oxida-
tion in ionic liquid. A wide range of aromatic, aliphatic.
and heterocyclic sulfides with 1,3,4-oxadiazole or 1,3,4-
thiadiazole moiety were employed in this procedure to
synthesize the corresponding sulfones in good yields.
2.1. Crystal structure analysis
In compound 8d, the bond lengths N(1)–C(11)
˚
(1.286(3) A) and N(2)–C(10) (1.371(3) A) are close to
˚
24
˚
the C@N double bond distance (1.34 A). The bond
length C(12)–S(1) [1.826(6) A] is close to that of similar
˚
compound reported.24 The bond length C(11)–S(1)
24
˚
[1.733(2)] is shorter than typical C–S (1.82 A). The
S(1) atom and oxadiazole ring form a configuration in
which the S(1) atom is sp2 hybridized. The benzene ring
[C(13), C(14), C(15), C(16), C(17), C(18)] and the adja-
cent carbon atom C(12) are fairly planar, and the devi-
ation from the least-squares plane through the ring
atoms is less than 0.0009(3) nm. The dihedral angle be-
tween the plane of oxadiazole group and the plane of
Figure 1. The molecular structure of compound 8d.
Figure 2. Packing diagram of the unit cell of compound 8d.

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C.-J. Chen et al. / Bioorg. Med. Chem. 15 (2007) 3981–3989
3. Antifungal activity
Inhibition effect of sulfone derivatives on phytopatho-
genic fungi was studied. The three fungi used in the fun-
gicidal bioassay, Gibberella zeae, Botrytis cinerea, and
Sclerotinia sclerotiorum, were collected and isolated from
corresponding crops. The results of preliminary bioas-
says were compared with that of a commercial agricul-
tural fungicide Hymexazol. As indicated in Table 2,
oxadiazole sulfone compounds 10a–10e, 10g, 10i, 10j,
and 10l showed potent antifungal activities against all
the tested fungi. However, significant lowering of activity
was noticed with homologues of thiadiazole moiety
(Table 2). It could be seen that there were two new title
compounds, 10i and 10j, exhibiting promising antifungal
activities even better than that of the commercial fungi-
cide Hymexazol. At the concentration of 50 lg/mL, title
compounds 10i and 10j inhibited growth of G. zeae at
55.8%, 100%, B. cinerea at 67.5%, 100%, and S. sclerotio-
rum at 100%, 100%, respectively, which are slightly better
than that of Hymexazol (52.9% against G. zeae, and
77.5% against S. sclerotiorum at 50 lg/mL). Among the
thiadiazole sulfone compounds, it could be seen that 9h
has higher antifungal activities against three phytopath-
ogenic fungi than the other compounds 9a–9g and 9i.
The inhibition effect of compounds 10i and 10j on myce-
lia growth in vitro at different concentrations (100, 50,
25, 12.5, and 6.25 lg/mL) is exhibited in Figure 5. Nearly
complete inhibition of G. zeae mycelia growth was ap-
proached by 10j at 100 lg/mL concentration, when com-
pared with the complete growth in the control (Fig. 5).
Figure 3. The molecular structure of compound 10q.
Figure 4. Packing diagram of the unit cell of compound 10q.
(12B). . .O(7) = 100.7ꢁ, the other being C(2)–H(2C)
˚
. . .O(6), with the donor–acceptor distance 3.462 A, and
˚
˚
C(2)–H(2C) = 0.96 A, H(2C). . .O(6) = 2.51 A, C(2)–
H(2C). . .O(6) = 172.7ꢁ.
Table 2. Fungicidal activities of sulfone derivatives 9 and 10a
Compound
R
Concentration (lg/mL)
Inhibitory rate (%)
Gibberella zeae
Botrytis cinerea
Sclerotinia sclerotiorum
9a
H2C@CH–CH2–
50
14.0 3.1
47.3* 9.0
40.5* 7.8
9b
9c
9d
9e
9f
50
50
50
50
50
50
50
50
ꢀ1.8
30.3* 7.1
25.9 4.2
27.5 7.1
33.5* 4.3
20.8 2.1
49.7* 10.0
53.4* 7.0
27.1* 3.1
20.0 3.8
21.3 7.2
22.9 3.9
38.1* 3.8
20.3 3.7
49.4* 6.2
74.5* 3.1
40.7* 7.2
O2N
CH2
Cl
CH2
ꢀ1.1
N
8.3 0.9
13.5 1.9
5.5 1.2
21.1 7.1
43.2* 6.6
11.6 0.9
CH2
CH3CH2CH2–
Cl
CH2
O
C
9g
9h
9i
H3CH2CO
MeO
CH2
CH2
H3C–

C.-J. Chen et al. / Bioorg. Med. Chem. 15 (2007) 3981–3989
3985
Table 2 (continued)
Compound
R
Concentration (lg/mL)
Inhibitory rate (%)
Gibberella zeae
Botrytis cinerea
Sclerotinia sclerotiorum
10a
10b
H2C@CH–CH2–
50
50
26.4 8.9
40.9* 2.2
40.9* 7.6
42.1* 10.1
38.9* 7.7
54.9* 6.0
76.8* 5.0
60.3* 8.0
67.3* 5.5
62.2* 4.4
67.9* 9.9
71.2* 4.3
O2N
Cl
CH2
CH2
10c
10d
50
50
N
CH2
10e
10f
CH3CH2CH2–
50
50
59.0* 12.1
23.3* 8.9
59.4* 8.8
64.0* 7.6
35.5* 8.9
30.8* 11.2
Cl
CH2
O
10g
10h
50
50
52.0* 4.9
5.7 1.9
81.9** 3.2
38.1* 7.1
79.9** 1.9
40.6* 10.1
H3CH2CO C CH2
MeO
CH2
10i
10j
H3C–
50
50
55.8* 3.0
67.5* 1.2
100** 3.1
100** 0.9
100** 2.0
100** 3.1
CH3CH2–
O2N
10k
10l
50
50
50
50
50
50
50
50
11.8 3.9
33.9* 3.8
9.3 0.3
40.7* 4.1
58.5* 5.5
35.8* 1.9
41.6* 2.2
52.3* 2.2
26.1* 2.2
42.3* 4.9
75.4** 4.1
38.3* 9.9
58.5* 4.2
38.3* 4.7
62.7** 1.9
33.4* 4.0
39.6* 1.2
37.2* 5.1
77.5** 2.8
CH2
MeO
F
CH2
10m
10n
10o
10p
10q
CH2
28.1* 3.7
18.2* 1.1
11.9 0.9
23.7* 3.0
52.9* 3.0
F
CH2
F
CH2
CH2
Cl
OMe
CH2
Hyme-xazol
n = 3 for all groups.
a Growth inhibition expressed as a percentage of the control.
* P < 0.05.
** P < 0.01.
Further bioassays disclosed that compounds 10i and 10j
had remarkable inhibitory effect on 10 kinds of plant path-
ogenic fungi under the laboratory condition (Table 3).
The EC50 of 10j on G. zeae, Fusarium oxysporum,
Cytospora mandshurica, Colletotrichum gloeosporioides,
B. cinerea, S. sclerotiorum, Pyricularia grisea, Phytophthora
infestans, Rhizoctonia solani, and Pyricularia oryzae
were 20.1 lg/mL, 18.0 lg/mL, 20.5 lg/mL, 26.3 lg/mL,
2.9 lg/mL, 4.3 lg/mL, 17.8 lg/mL, 51.4 lg/mL, 45.6 lg/
mL, and 39.8 lg/mL, respectively. Compound 10i was also

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C.-J. Chen et al. / Bioorg. Med. Chem. 15 (2007) 3981–3989
Figure 5. Effect of different concentrations of 10j (Left) and 10i (Right) on the mycelial growth of Gibberella zeae (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.
Table 3. Toxicity of 10i and 10j on 10 kinds of pathogenic fungi
a
Compound
Fungus
Toxic regression equation
EC50 (lg/mL)
r
10j
G. zeae
P. grisea
Y = 0.671x + 4.054
Y = 1.690x + 2.887
Y = 1.306x + 3.142
Y = 1.710x + 4.218
Y = 0.867x + 4.452
Y = 0.762x + 3.736
Y = 0.953x + 3.465
Y = 1.640x + 2.193
Y = 1.107x + 2.364
Y = 0.997x + 2.466
20.1 2.9
17.8 5.1
26.3 3.8
2.9 2.0
0.992
0.986
0.973
0.951
0.985
0.987
0.959
0.986
0.970
0.989
C. gloeosporioides
B. cinerea
S. sclerotiorum
R. solani
4.3 3.1
45.6 11.9
39.8 9.7
51.4 13.7
20.5 1.1
18.0 3.1
P. oryzae
P. infestans
C. mandshurica
F. oxysporum
10i
G. zeae
P. grisea
Y = 0.809x + 3.816
Y = 2.530x + 1.233
Y = 2.505x + 1.644
Y = 0.974x + 3.958
Y = 1.041x + 3.858
Y = 0.667x + 3.686
Y = 2.278x + 0.540
Y = 1.301x + 2.496
Y = 1.199x + 2.715
Y = 1.395x + 1.661
28.8 10.1
30.8 15.0
21.8 5.9
11.7 7.9
12.5 8.9
93.3 4.4
90.7 3.1
83.2 6.5
80.5 10.8
24.5 2.3
0.991
0.932
0.839
0.946
0.980
0.966
0.988
0.991
0.978
0.998
C. gloeosporioides
B. cinerea
S. sclerotiorum
R. solani
P. oryzae
P. infestans
C. mandshurica
F. oxysporum
Hymexazolb
Hymexazolb
R. solani
F. oxysporum
Y = 2.729x + 1.330
Y = 1.049x + 3.464
52.1 8.5c
29.1 2.6
0.995
0.994
a EC50 concentrations needed to inhibit cell growth by 50% as determined from the dose–response curve. Determined in three separate experiments
and each was performed in triplicate.
b The standard compound used for comparison of activity.
c The value was determined by using our assay protocol.
Figure 6. Microphotograph of hyphal morphology of Gibberella zeae under the microscope (800·) (left: control; right: treated with 100 lg/mL of
10j).

C.-J. Chen et al. / Bioorg. Med. Chem. 15 (2007) 3981–3989
3987
highly effective against the ten kinds of fungi listed above
and its EC50 values were 28.8 lg/mL, 24.5 lg/mL, 80.5 lg/
mL, 21.8 lg/mL, 11.7 lg/mL, 12.5 lg/mL, 30.8 lg/mL,
83.2 lg/mL, 93.3 lg/mL, and 90.7 lg/mL, respectively.
Compound 10j is more active against F. oxysporum and
R. solani thanHymexazolanditsactivityonP. grisea is sim-
ilar to another commercial fungicide Myclobutanil.
out using silica gel. All reagents were of analytical
grade or chemically pure. All solvents were dried,
deoxygenated, and redistilled before use. 3,4,5-Tri-
methoxyphenylhydrides 3 and 5-(3,4,5-trimethoxyphe-
nyl)-1,3,4-thiadiazole-2-thiol 4 were prepared according
to literature method as described.23
5.2. Preparation of 5-(3,4,5-trimethoxyphenyl)-1,3,4-
oxadiazole-2-thiol (5)
The morphology changes of hypha were also studied.
After three days of inocualtion, the colony diameter of
G. zeae was 7.0 cm and its color was amaranth in the
middle and white on the periphery. When treated with
100 lg/mL of compound 10j, the hypha grew slowly
with ramification, the amaranth color of mycelium in
the middle became weaker.
A mixture of 0.56 g (10 mmol) of potassium hydroxide,
2.26 g (10 mmol) of compound 3, and 1.14 g (15 mmol)
of carbon disulfide in 50 mL of absolute ethanol was re-
fluxed for 8 h. After the solvent was evaporated in vac-
uum, the residue was dissolved in ice-cold water and
acidified with dilute hydrochloric acid. The precipitate
was filtered off, washed with water, dried, and recrystal-
lized from absolute ethanol to give compound 5. The
In the beginning, the hypha of the control was slippy,
vimineous and branched normally. The cytoplasm of
the cell was homogeneous and limpid. But after treating
with 100 lg/mL of compound 10j, the hypha of G. zeae
became coarse, malformed and branched at the tip. The
cell of the hypha swelled and shortened. Its cytoplasm
condensed and a few blanks were observed near the
tip of the hypha (Fig. 6).
1
structure was confirmed by H NMR, 13C NMR, IR,
and elemental analysis (see the Supporting information).
5.3. Preparation of 2-substituted methylthio-5-(3,4,5-tri-
methoxyphenyl)-1,3,4-thiadiazole (7a–7i)
To
a 50 mL, three-necked, round-bottomed flask
equipped with a magnetic stirrer were added 1.5 mmol
of 4, 20 mL of distilled water, and 2 mL (3%, w/w) of
NaOH solution. The mixture was stirred at room tem-
perature for 10 min. Then 1.5 mmol of halide 6 and
17.2 mg (0.15 mmol) of indium were added. The result-
ing mixture was stirred at room temperature for 4 h, fil-
tered. The white solid resulted was washed with 5%
Na2CO3 solution and distilled water, dried under vac-
uum, and recrystallized from ethanol to give compound
723 (Characterization data are provided in the Support-
ing information).
4. Conclusion
A series of novel sulfone derivatives containing 1,3,4-
thiadiazole and 1,3,4-oxadiazole moieties were synthe-
sized by the treatment of intermediate sulfides 7 and
8 with H2O2 in the presence of catalytic amount of
ammonium molybdate in an ionic liquid. The method
is easy, rapid and produces the title compounds 9
and 10 in good yield. The structures were verified by
spectroscopic data. In the antifungal bioassay, the title
compounds 9h, 10a–10e, 10g, 10i, 10j, and 10l were
found to possess higher antifungal activities against
three kinds of fungi in vitro. In particular, 10i and
10j had high inhibitory effects on the growth of G.
zeae, P. grisea, C. mandshurica, C. gloeosporioides, B.
cinerea, S. sclerotiorum, P. oryzae, P. infestans, R.
solani, and F. oxysporum, with EC50 values ranging
from 2.9 lg/mL to 93.3 lg/mL.
5.4. Preparation of 2-substituted methylthio-5-(3,4,5-tri-
methoxyphenyl)-1,3,4-oxadiazole (8a–8q)
A 50 mL round-bottomed flask equipped with a mag-
netic stirrer was charged with 5 (1.5 mmol) and 2 mL
(3%, w/w) of sodium hydroxide solution. The mixture
was dissolved in 20 mL of distilled water. The flask
was stirred at room temperature for 10 min, and then
halide 6 (1.5 mmol) and indium tribromide (0.15 mmol)
were added to the reaction mixture and stirred at room
temperature for 4 h. The mixture was filtered and the
white solid obtained was washed with 5% Na2CO3 solu-
tion and distilled water, dried under vacuum, and recrys-
tallized from ethanol to give compound 8 (see the
Supporting information).
5. Experimental
5.1. Analysis and instruments
The title compounds were synthesized starting from
gallic acid following a six-reaction step sequence.
The melting points of the products were determined
on a XT-4 binocular microscope (Beijing Tech Instru-
ment Co., China) and were not corrected. The IR
spectra were recorded on a Bruker VECTOR 22 spec-
trometer in KBr disk. 1H and 13C NMR (solvent
CDCl3) spectra were recorded on a JEOL-ECX 500
NMR spectrometer at room temperature using TMS
as an internal standard. Elemental analysis was per-
formed on an Elementar Vario-III CHN analyzer.
Analytical TLC was performed on silica gel GF254.
Column chromatographic purification was carried
5.5. Preparation of 2-substituted sulfonyl-5-(3,4,5-tri-
methoxyphenyl)-1,3,4-thiadiazole (oxadiazole) (9a–9i,
10a–10q)
To a mixture of 1.1 mmol of compound 7 or 8, 4000 mg
(14 mmol) of [bmim]PF6, and 140 mg (0.011 mmol) of
(NH4)6Mo7O24 was added 560 mg (5.5 mmol) of 30%
H2O2. The mixture was stirred at 40 ꢁC for 2 h and then
extracted with toluene (5 · 5 mL). The combined tolu-
ene phase was concentrated in vacuum. The crude prod-

3988
C.-J. Chen et al. / Bioorg. Med. Chem. 15 (2007) 3981–3989
uct was recrystallized (from anhydrous ethanol) to af-
ford title compounds 9 and 10 (see the Supporting
information).
The molecular structures of the compounds 8d and 10q
are shown in Figures 1 and 3, respectively. The packing
diagrams of the unit cells of compounds 8d and 10q are
shown in Figures 2 and 4, respectively.
5.5.1. 2-Methylsulfonyl-5-(3,4,5-trimethoxyphenyl)-1,3,4-
oxadiazole (10i). White needle, yield, 89%; mp
5.7. Antifungal activity bioassay
1
120 ꢁ 122 ꢁC; H NMR (500 MHz, CDCl3): d 3.50 (s,
3 H, CH3), 3.95 (s, 3H, MeO), 3.96 (s, 6H, 2 · MeO),
7.34 (d, 2H, ArH, J = 2.8 Hz); 13C NMR (125 MHz,
CDCl3): d 42.9, 56.4, 61.0, 104.8, 116.7, 142.3, 153.7,
161.8, 166.6; IR (KBr): 860, 1128, 1144, 1184, 1238,
1344, 1493, 1545, 1593, 2962, 3065 cmꢀ1; Anal. calcd
for C12H14N2O6S (314.3): C, 45.86; H, 4.49; N, 8.91.
Found: C, 45.79; H, 4.30; N, 8.88.
Fungicidal activities of all the title compounds were bio-
assayed against three kinds of pathogenic fungi namely
G. zeae, B. cinerea, S. sclerotiorum, using the mycelia
growth rate test.27 The compounds 10i and 10j were
subjected to further evaluation against ten pathogenic
fungi, namely, G. zeae, P. grisea, C. mandshurica,
C. gloeosporioides, B. cinerea, S. sclerotiorum, P. oryzae,
P. infestans, R. solani, and F. oxysporum. Experimental
details28 are provided in the Supporting information.
5.5.2. 2-(Ethylsulfonyl)-5-(3,4,5-trimethoxyphenyl)-1,3,4-
oxadiazole (10j). White needle, yield, 97%; mp 109–
111 ꢁC; 1H NMR (500 MHz, CDCl3): d 1.56 (t, 3H,
–CCH3,J = 7.6 Hz), 3.64 (q, 2H, –CH2C, J = 7.6 Hz),
3.95 (s, 3H, MeO), 3.96 (s, 6H, 2 · MeO), 7.35 (s, 2H,
ArH). 13C NMR (125 MHz, CDCl3): d 16.8, 50.0,
56.5, 61.1, 104.9, 116.9, 142.3, 153.8, 161.0, 166.6; IR
(KBr): 841, 1130, 1145, 1173, 1240, 1350, 1495, 1551,
Acknowledgments
We thank the National Key Project for Basic Research
(2003CB114404), Key Technologies R&D Program
(Grant No. 2006BAE01A01-15), Program for New Cen-
tury Excellent Talents in University in China (NCET-
04-0912), and the National Natural Science Foundation
of China (20442003) for the financial support.
1595, 2922, 2972, 3080 cmꢀ1
;
Anal. calcd for
C13H16N2O6S (328.3): C, 47.55; H, 4.91; N, 8.53.
Found: C, 47.75; H, 4.92; N, 8.52.
5.6. Crystal structure determination
A sample of size 0.30 · 0.24 · 0.20 mm3 was selected for
the crystallographic study. All diffraction measure-
ments were performed at room temperature (293 K)
using graphite monochromated MoKa radiation
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.bmc.2007.04.014.
˚
(k = 0.71073 A) and an Enraf–Nonius CAD-4 four-cir-
cle diffractometer. Accurate cell parameters and orienta-
tion matrix were obtained by least-squares refinement of
the setting angles of 3049 reflections at the h range of
2.09ꢁ < h < 25.01ꢁ (for compound 8d), and 3598 reflec-
tions at the h range of 1.41ꢁ < h < 26.00ꢁ (for compound
10q). The systematic absences and intensity symmetries
indicated the triclinic P ꢀ 1 space group (for compound
8d) and the monoclinic P21/c (for compound 10q). A to-
tal of 4440 intensities with hmax = 25ꢁ were collected in
the x/2h scan mode, as suggested by peak-shape analy-
sis. The crystal and equipment stabilities were checked
by the intensities of three standard reflections monitored
every 2 h. No significant intensity decay was observed
(2.0% variation). The intensities were corrected for Lor-
entz and polarization factors, but not for absorption ef-
fect (l = 0.211 mmꢀ1). The structure was solved by
direct methods using SHELXS-97.25 The refinement
(on F2) was carried out by full-matrix least-squares
method on the positional and anisotropic temperature
parameters of the non-hydrogen atoms. The structure
was refined to R = 0.0592 for the observed reflections
and wR2 = 0.1268 for all data (for compound 8d). For
compound 10q, the structure was refined to R = 0.1785
for the observed reflections and wR2 = 0.2011 for all
data. The scattering factors were taken from SHEL-
XL-97.26 The CIF file has been deposited at the Cam-
bridge Crystallographic Data Center as CCDC Nos.
282029 (for compound 8d) and 619360 (for compound
10q).
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