Synthesis of 4-Methyl-1,2,3-thiadiazole derivatives via ugi reaction and their biological activities

Article abstract of DOI:10.1021/jf902863z

The Ugi reaction is a green and rapid one-pot reaction for lead derivation. To develop novel candidate pesticides with diverse biological activities, two series of 4-methyl-1,2,3-thiadiazole derivatives containing active substructures of 3-chloro-4-methylphenyl or 3-fluoro-4-methylphenyl, respectively, were rationally designed and synthesized via Ugi reaction according to the principle of combinations of bioactive substructures. All of the structures of newly synthesized compounds were confirmed by proton nuclear magnetic resonance and high-resolution mass spectrometry. Biological activities of the target compounds including fungicide activity, antivirus activity in vitro and in vivo, and systemic acquired resistance were evaluated systematically. The results indicated that derivatives containing 3-(trifluoromethyl)phenyl and 2-methylphenyl possessed a potential wide spectrum of fungicidal activity. Derivatives containing 3-(trifluoromethyl)phenyl and 4-hydroxyphenyl possessed good potential direct antivirus activities against tobacco mosaic virus (TMV) in vitro, and the replacement of Cl atom by F atom improved their direct inhibition activities against TMV in vitro. Derivatives containing phenyl, 2-(trifluoromethyl)phenyl, 3-(trifluoromethyl)phenyl, 3-nitrophenyl, 4-nitrophenyl, 2-methylphenyl, and 4-hydroxyphenyl possessed good potential bioactivities in vivo including protection, inactivation, curative, and induction activities against TMV. These studies indicate that the newly synthesized 4-methyl-1,2,3-thiadiazole derivatives possessed good potential bioactivities, and a combination of bioactive substructures via Ugi reaction was an effective way to find bioactive compounds for novel pesticide development.

Full text of DOI:10.1021/jf902863z

J. Agric. Food Chem. 2010, 58, 2755–2762 2755
DOI:10.1021/jf902863z
Synthesis of 4-Methyl-1,2,3-thiadiazole Derivatives via Ugi
Reaction and Their Biological Activities†
X
IANG
Z
UO, N
A
MI
, ZHIJIN
F
AN,* QINGXIANG
AND HIKUN
Z
HENG, HAIKE
Z
HANG, HUAN
W
ANG
,
Z
Y
ANG
State Key Laboratory of Elemento-Organic Chemistry, Nankai University, No. 94, Weijin Road, Nankai
District, Tianjin 300071, People’s Republic of China. These authors contributed equally to this work.
The Ugi reaction is a green and rapid one-pot reaction for lead derivation. To develop novel
candidate pesticides with diverse biological activities, two series of 4-methyl-1,2,3-thiadiazole
derivatives containing active substructures of 3-chloro-4-methylphenyl or 3-fluoro-4-methylphenyl,
respectively, were rationally designed and synthesized via Ugi reaction according to the principle of
combinations of bioactive substructures. All of the structures of newly synthesized compounds were
confirmed by proton nuclear magnetic resonance and high-resolution mass spectrometry. Biological
activities of the target compounds including fungicide activity, antivirus activity in vitro and in vivo,
and systemic acquired resistance were evaluated systematically. The results indicated that
derivatives containing 3-(trifluoromethyl)phenyl and 2-methylphenyl possessed a potential wide
spectrum of fungicidal activity. Derivatives containing 3-(trifluoromethyl)phenyl and 4-hydroxyphenyl
possessed good potential direct antivirus activities against tobacco mosaic virus (TMV) in vitro, and
the replacement of Cl atom by F atom improved their direct inhibition activities against TMV in vitro.
Derivatives containing phenyl, 2-(trifluoromethyl)phenyl, 3-(trifluoromethyl)phenyl, 3-nitrophenyl,
4-nitrophenyl, 2-methylphenyl, and 4-hydroxyphenyl possessed good potential bioactivities in vivo
including protection, inactivation, curative, and induction activities against TMV. These studies
indicate that the newly synthesized 4-methyl-1,2,3-thiadiazole derivatives possessed good potential
bioactivities, and a combination of bioactive substructures via Ugi reaction was an effective way to
find bioactive compounds for novel pesticide development.
KEYWORDS: 4-Methyl-1,2,3-thiadiazole; systemic acquired resistance; Ugi reaction; fungicide
INTRODUCTION
4-methly-1,2,3-thiadiazole-5-carboxamide derivative containing a
3-chloro-4-methylphenyl moiety, has been recognized as a well-
known commercialized fungicide as well as a plant elicitor (14).
However, studies on the wide biological spectrum of 1,2,3-thiadi-
azoles are seldom reported. An elicitor is any compound with low
or no direct activity against a pathogen, but acts by stimulating
the immunosystem of the host plants to produce systemic acquired
resistance against the succeeding pathogen attack (15, 16). Un-
luckily, very limited documents report the development of novel
elicitors, too.
Combinatorial chemistry has attracted much attention as an
efficient tool for drug discovery. The use of combinatorial
chemistry or parallel synthesis for the optimization of highly
promising lead compounds arising from the drug-discovery
processes around privileged structures and their combinations
has been successful in many discovery and development
efforts (17). Our studies noted that the Ugi four-component
condensation reaction (U-4CR) could be an efficient and con-
venient green method to combine several active moieties into one
molecule, and it could be convenient to implement structural
modification via alternation of diverse starting materials. Gen-
erally, U-4CR refers to the reaction between an amine, a carbonyl
compound (aldehyde or ketone), an isocyanide, and a carboxylic
Since thiabendazole was discovered and developed as a fungi-
cide by Merck & Co. Inc. in the 1960s, many thiazoles including a
number of widely used fungicides (e.g., tricyclazole, probenazole,
and trifluzamide) and the best plant elicitor [i.e., acibenzolar-S-
methyl (BTH)] have been introduced into the pesticide mar-
ket (1, 2). As a class of compounds with various interesting
properties, 1,2,3-thiadiazoles are becoming a rapidly growing and
independent branch of the chemistry of thiazoles. Many 1,2,3-
thiadiazoles have shown biological activities such as antiviral (3,4),
systemic acquired resistance (5, 6), fungicidal (5, 7-10), and
insecticidal activities (11). Moreover, because of their various
biological activities, 1,2,3-thiadiazoles have attracted considerable
attention, and 1,2,3-thiadizoles have also been introduced into
other active compounds as an active moiety for lead discovery (12).
Meanwhile, the property of easy breakdown of the 1,2,3-thiadia-
zole ring into low molecular weight compounds favors the use of its
derivatives as pesticides with low toxicity (13). Tiadinil (TDL), a
†Part of the ECUST-Qian Pesticide Cluster.
*Author to whom correspondence should be addressed
(telephone þ86-22-23504367; fax þ86-22-23505948; e-mail fanzj@
nankai.edu.cn).
© 2009 American Chemical Society
Published on Web 12/14/2009
pubs.acs.org/JAFC

2756 J. Agric. Food Chem., Vol. 58, No. 5, 2010
Zuo et al.
Table 1. Yields and Physical Properties of the Target Compounds
compd
yield (%)
appearance, mp (°C)
compd
yield (%)
appearance, mp (°C)
ZX-3-1
ZX-3-2
ZX-3-3
ZX-3-4
ZX-3-5
ZX-3-6
ZX-3-7
ZX-3-8
ZX-3-9
ZX-3-10
ZX-3-11
ZX-3-12
ZX-3-13
ZX-3-14
ZX-3-15
ZX-3-16
ZX-3-17
ZX-3-18
50
52
76
78
55
72
89
8
white solid, 175-180
white needle crystal, 176-180
white solid, 198-203
white solid, 215-218
white solid, 132-135
white solid, 206-208
white solid, 213-217
yellow solid, 152-158
white solid, 205-207
white solid, 214-216
white solid, 171-173
white solid, 204-208
white solid, 113-115
white solid, 131-134
white solid, 172-173
white solid, 209-211
white solid, 167-172
white needle crystal, 135-139
ZX-4-1
ZX-4-2
ZX-4-3
ZX-4-4
ZX-4-5
ZX-4-6
ZX-4-7
ZX-4-8
ZX-4-9
ZX-4-10
ZX-4-11
ZX-4-12
ZX-4-13
ZX-4-14
ZX-4-15
ZX-4-16
ZX-4-17
52
22
81
78
62
75
78
52
46
74
68
90
71
62
84
79
22
white solid, 183-185
white needle crystal, 171-174
white needle crystal, 200-201
white needle crystal, 223-225
white solid, 139-141
white needle crystal, 223-225
white solid, 204-206
white solid, 167-169
white solid, 168-170
white needle crystal, 224-226
white solid, 187-189
white solid, 217-219
48
81
45
71
75
47
46
60
3
white solid, 231-233
white needle crystal, 170-172
white needle crystal, 209-211
white solid, 178-180
white needle crystal, 171-174
40
Scheme 1. Molecule Structures and Synthesis of the Target Compoundsa
a X = Cl (series ZX-3), R = phenyl (ZX-3-1); 2-chlorophenyl (ZX-3-2); 3-chlorophenyl (ZX-3-3); 4-chlorophenyl (ZX-3-4); 2-fluorophenyl (ZX-3-5); 3-fluorophenyl (ZX-3-6); 4-
fluorophenyl (ZX-3-7); 2-(trifluoromethyl)phenyl (ZX-3-8); 3-(trifluoromethyl)phenyl (ZX-3-9); 4-(trifluoromethyl)phenyl (ZX-3-10); 2-nitrophenyl (ZX-3-11); 3-nitrophenyl (ZX-3-
12); 4-nitrophenyl (ZX-3-13); 2-methylphenyl (ZX-3-14); 3-methylphenyl (ZX-3-15); 4-methylphenyl (ZX-3-16); 3-hydroxyphenyl (ZX-3-17); 4-hydroxyphenyl (ZX-3-18); X = F
(series ZX-4), R = phenyl (ZX-4-1); 2-chlorophenyl (ZX-4-2); 3-chlorophenyl (ZX-4-3); 4-chlorophenyl (ZX-4-5); 2-fluorophenyl (ZX-4-5); 3-fluorophenyl (ZX-4-6); 4-fluorophenyl
(ZX-4-7); 2-(trifluoromethyl)phenyl (ZX-4-8); 3-(trifluoromethyl)phenyl (ZX-4-9); 4-(trifluoromethyl)phenyl (ZX-4-10); 2-nitrophenyl (ZX-4-11); 3-nitrophenyl (ZX-4-12);
4-nitrophenyl (ZX-4-13); 2-methylphenyl (ZX-4-14); 3-methylphenyl (ZX-4-15); 4-methylphenyl (ZX-4-16); 4-hydroxyphenyl (ZX-4-17).
acid, which is a convenient rapid one-pot reaction with the
process itself and the disposal of its succedent being very
simple (18-20).
the products, and some of them also showed biological activities.
Our results indicated that 4-methyl-1,2,3-thiadiazole derivatives
had good potential bioactivities, and combination of bioactive
substructures via Ugi reaction was an effective measure for
structure-activity relationship studies and novel pesticide devel-
opment.
Our previous studies suggested that some 4-methyl-1,2,3-
thiadiazole-5-carboxamide derivatives designed and synthesized
showed good biological activities (5, 21-23), fluorinated 4-
methyl-1,2,3-thiadiazoles had good systemic acquired resistance,
and 4-methyl-1,2,3-thiadiazole was an important active substruc-
ture (5,21,23). These studies inspired our current hypothesis that
the introduction of phenyl moieties into the target compounds
may favor the biological activities of 1,2,3-thiadiazoles, and here
we designed and synthesized two series of 4-methyl-1,2,3-thi-
adiazole-5-carboxamide derivatives via U-4CR for the fungicidal,
antiviral, and systemic acquired resistance activity determination
because 1,2,3-thiadiazoles could be decomposed by releasing N2
and regarded as environmentally friendly molecules (24). One
series contained a 3-chloro-4-methylphenyl moiety and the other
one contained a 3-fluoro-4-methylphenyl moiety (Scheme 1). In
U-4CR, 4-methyl-1,2,3-thiadiazole-5-carboxylic acid was chosen
as the acid component and cyclohexyl isocyanide was chosen as
the isocyanide component; the amine components were 3-chloro-
4-methylbenzenamine and 3-fluoro-4-methylbenzenamine, res-
pectively, as described in the above two series. Because aromatic
rings play important roles in chemical and biological recogni-
tion (25), various substituted benzaldehyde derivatives were used
as the aldehyde component. The most important difference
between this study and our former study is in the substructures
coupled with 4-methyl-1,2,3-thiadiazole. Here, these were all
aromatic amines, and there was no H atom combined in the
carboxylic amine N nearest the 4-methyl-1,2,3-thiadiazole ring in
EXPERIMENTAL METHODS
Equipment for Structural Characterization. Melting points of all
compounds were determined on an X-4 binocular microscope (Gongyi
Technical Instrument Co., Henan, China), and the thermometer was not
corrected. Proton NMR spectra were obtained using a Bruker AVANCE-
400 MHz spectrometer, and chemical shift values (δ) were reported as
parts per million (δ) with deutero dimethyl sulfoxide (DMSO-d6) as the
solvent and tetramethylsilane (TMS) as the internal standard. High-
resolution mass spectrometry (HRMS) data were obtained on an
FTICR-MS Varian 7.0T FTICR-MS instrument. All solvents and liquid
reagents were of analytical reagent grade and were dried in advance and
distilled before use. Column chromatography purification was carried out
by using silica gel.
Preparation of Cyclohexyl Isocyanide (3). Ethyl formate (1.0 mol)
was added dropwise to cyclohexylamine (1.2 mol) in an ice-water bath
with stirring. After the exothermic reaction ceased, the solution was
refluxed for 5 h. Ethanol and excess cyclohexylamine were distilled off
under reduced pressure, and the residue N-cyclohexylformamide
was obtained as a white solid, with a yield of 85%. A solution including
1.0 mol of N-cyclohexylformamide, 500 mL of pyridine, and 250 mL of
petroleum ether (bp 60-90 °C) was mixed in a three-neck flask, round-
bottom flask. Phosphorus oxychloride (0.6 mol) was added dropwise to
the solution in an ice-water bath with stirring. After all phosphorus
oxychloride was added, the mixture was refluxed for 5 h, and a solid
appeared in the mixture. Ice water was added gradually with stirring until

Article
J. Agric. Food Chem., Vol. 58, No. 5, 2010 2757
HRMS (m/z)
Table 2. 1H NMR and HRMS Data of the Target Compounds
compd
1H NMR (solvent: CDCl3)
ZX-3-1
ZX-3-2
ZX-3-3
ZX-3-4
ZX-3-5
ZX-3-6
δ 7.29-6.94 (m, 8H), 6.17 (s, 1H), 5.39 (d, J = 7.6 Hz, 1H), 3.90-3.82 (m, 1H), 2.87 (s, 3H), 2.25
(s, 3H), 1.99-1.00 (m, 10H)
[M þ Naþ]: 505.1435
found: 505.1433
δ 7.39-6.89 (m, 7H), 6.57 (s, 1H), 5.50 (d, J = 7.8 Hz, 1H), 3.92-3.85 (m, 1H), 2.86 (s, 3H), 2.21
(s, 3H), 2.05-1.0 (m, 10H)
[M þ Naþ]: 539.1046
found: 539.1047
δ 7.28-7.01 (m, 7H), 6.08 (s, 1H), 5.45 (d, J = 7.6 Hz, 1H), 3.89-3.81 (m, 1H), 2.87 (s, 3H), 2.28 (s,
3H), 2.00-1.03 (m, 10H)
[M þ Naþ]: 539.1046
found: 539.1041
δ 7.24-6.97 (m, 7H), 6.11 (s, 1H), 5.40 (d, J = 8.0 Hz, 1H), 3.88-3.81 (m, 1H), 2.87 (s, 3H), 2.28 (s,
3H), 2.00-1.02 (m, 10H)
[M þ Naþ]: 539.1046
found: 539.1038
δ 7.29-6.93 (m, 7H), 6.44 (s, 1H), 5.43 (d, J = 7.8 Hz, 1H), 3.93-3.84 (m, 1H), 2.86 (s, 3H), 2.23 (s,
3H), 2.03-1.01 (m, 10H)
[M þ Naþ]: 523.1341
found: 523.1338
δ 7.25-6.91 (m, 7H), 6.10 (s, 1H), 5.44 (d,J = 7.8 Hz, 1H), 3.89-3.82 (m, 1H), 2.87 (s, 3H), 2.27 (s,
3H), 2.01-1.03 (m, 10H)
[M þ Naþ]: 523.1341
found: 523.1348
ZX-3-7
ZX-3-8
ZX-3-9
ZX-3-10
ZX-3-11
δ 7.16-6.92 (m, 7H), 6.14 (s, 1H), 5.40 (d, J = 7.8 Hz, 1H), 3.89-3.81 (m, 1H), 2.87 (s, 3H), 2.27 (s,
3H), 2.01-1.02 (m, 10H)
[M þ Naþ]: 523.1341
found: 523.1348
δ 7.72-7.05 (m, 7H), 6.58 (s, 1H), 5.29 (d, J = 7.8 Hz, 1H), 3.88-3.80 (m, 1H), 2.86 (s, 3H), 2.23 (s,
3H), 2.04-1.09 (m, 10H)
[M þ Naþ]: 573.1309
found: 573.1304
δ 7.54-6.95 (m, 7H), 6.20 (s, 1H), 5.49 (d, J = 8.0 Hz, 1H), 3.90-3.83 (m, 1H), 2.88 (s, 3H), 2.26 (s,
3H), 2.02-1.02 (m, 10H)
[M þ Naþ]: 573.1309
found: 573.1308
δ 7.54-6.98 (m, 7H), 6.16 (s, 1H), 5.44 (d, J = 8.0 Hz, 1H), 3.88-3.84 (m, 1H), 2.88 (s, 3H), 2.28 (s,
3H), 1.98-1.02 (m, 10H)
[M þ Naþ]: 573.1309
found: 573.1304
δ 7.93-6.91 (m, 7H), 6.63 (s, 1H), 5.66 (d, J = 7.0 Hz, 1H), 3.88-3.81 (m, 1H), 2.86 (s, 3H), 2.21 (s,
3H), 2.03-1.01 (m, 10H)
[M þ Naþ]: 550.1286
found: 550.1288
ZX-3-12
ZX-3-13
δ 8.16-7.00 (m, 7H), 6.21 (s, 1H), 5.59 (d, J = 7.5 Hz, 1H), 3.90-3.84 (m, 1H), 2.89 (s, 3H), 2.27 (s,
3H), 2.03-1.0 (m, 10H)
[M þ Naþ]: 550.1286
found: 550.1285
δ 8.12-7.00 (m, 7H), 6.18 (s, 1H), 5.55 (d, J = 7.8 Hz, 1H), 3.90-3.83 (m, 1H), 2.88 (s, 3H), 2.28 (s,
3H), 2.02-1.04 (m, 10H)
[M þ Naþ]: 550.1286
found: 550.1287
ZX-3-14
ZX-3-15
ZX-3-16
δ 7.20-6.81 (m, 7H), 6.51 (s, 1H), 5.29 (d, J = 7.8 Hz, 1H), 3.92-3.84 (m, 1H), 2.88 (s, 3H), 2.43 (s,
3H), 2.22 (s, 3H), 1.98-1.00 (m, 10H)
[M þ Naþ]: 519.1592
found: 519.1591
δ 7.14-6.89 (m, 7H), 6.13 (s, 1H), 5.38 (d, J = 8.3 Hz, 1H), 3.89-3.82 (m, 1H), 2.87 (s, 3H), 2.26 (s,
6H), 1.99-1.01 (m, 10H)
[M þ Naþ]: 519.1592
found: 519.1598
δ 7.06-6.94 (m, 7H), 6.13 (s, 1H), 5.36 (d, J = 8.0 Hz, 1H), 3.88-3.81 (m, 1H), 2.87 (s, 3H), 2.30 (s,
3H), 2.26 (s, 3H), 1.99-1.00 (m, 10H)
[M þ Naþ]: 519.1592
found: 519.1593
ZX-3-17
ZX-3-18
ZX-4-1
δ 6.99-6.69 (m, 7H), 6.17-6.07 (m, 2H), 5.49 (d, J = 8.3 Hz, 1H), 3.87-3.80 (m, 1H), 2.84 (s, 3H),
2.26 (s, 3H), 1.95-0.98 (m, 10H)
[M þ Naþ]: 521.1385
found: 519.1383
δ 6.97-6.69 (m, 8H), 6.05 (s, 1H), 5.57 (d, J = 8.0 Hz, 1H), 3.86-3.78 (m, 1H), 2.82 (s, 3H), 2.26 (s,
3H), 1.95-1.01 (m, 10H)
[M þ Naþ]: 521.1385
found: 519.1387
δ 7.28-6.87 (m, 8H), 6.19 (s, 1H), 5.38 (d, J = 8.0 Hz, 1H), 3.93-3.84 (m, 1H), 2.86 (s, 3H), 2.15 (d, J =
1.8 Hz, 1H), 1.99-1.00 (m, 10H)
[M þ Naþ]: 489.1731
found: 489.1740
ZX-4-2
ZX-4-3
ZX-4-4
ZX-4-5
δ 7.37-6.85 (m, 7H), 6.58 (s, 1H), 5.51 (d, J = 6.2 Hz, 1H), 3.93-3.84 (m, 1H), 2.86 (s, 3H), 2.11 (d, J =
1.8 Hz, 1H), 2.04-1.03 (m, 10H)
[M þ Naþ]: 523.1341
found: 523.1344
δ 7.21-6.93 (m, 7H), 6.11 (s, 1H), 5.43 (d, J = 8.0 Hz, 1H), 3.88-3.83 (m, 1H), 2.88 (s, 3H), 2.18 (d, J =
1.8 Hz, 1H), 2.00-1.03 (m, 10H)
[M þ Naþ]: 523.1341
found: 523.1347
δ 7.23-6.91 (m, 7H), 6.13 (s, 1H), 5.39 (d, J = 8.0 Hz, 1H), 3.88-3.81 (m, 1H), 2.87 (s, 3H), 2.18 (d, J =
1.8 Hz, 1H), 2.00-1.01 (m, 10H)
[M þ Naþ]: 523.1341
found: 523.1341
δ 7.28-6.89 (m, 7H), 6.45 (s, 1H), 5.54 (d, J = 8.0 Hz, 1H), 3.93-3.83 (m, 1H), 2.86 (s, 3H), 2.14 (d, J =
1.8 Hz, 1H), 2.03-1.04 (m, 10H)
[M þ Naþ]: 507.1637
found: 507.1642

2758 J. Agric. Food Chem., Vol. 58, No. 5, 2010
Zuo et al.
Table 2. Continued
compd
1H NMR (solvent: CDCl3)
HRMS (m/z)
ZX-4-6
δ 7.24-6.90 (m, 7H), 6.12 (s, 1H), 5.43 (d, J = 7.8 Hz, 1H), 3.89-3.82 (m, 1H), 2.88 (s, 3H), 2.18
(d, J = 2.0 Hz, 1H), 2.01-1.03 (m, 10H)
[M þ Naþ]: 507.1637
found: 507.1639
ZX-4-7
δ 7.16-6.91 (m, 7H), 6.16 (s, 1H), 5.40 (d, J = 8.0 Hz, 1H), 3.88-3.83 (m, 1H), 2.87 (s, 3H), 2.18
(d, J = 1.8 Hz, 1H), 2.00-1.01 (m, 10H)
[M þ Naþ]: 507.1637
found: 507.1640
ZX-4-8
δ 7.70-6.87 (m, 7H), 6.58 (s, 1H), 5.28 (d, J = 7.5 Hz, 1H), 3.87-3.80 (m, 1H), 2.85 (s, 3H), 2.13
(d, J = 1.5 Hz, 1H), 2.04-0.96 (m, 10H)
[M þ Naþ]: 557.1605
found: 557.1606
ZX-4-9
δ 7.54-6.93 (m, 7H), 6.22 (s, 1H), 5.47 (d, J = 8.0 Hz, 1H), 3.90-3.83 (m, 1H), 2.89 (s, 3H), 2.16 (d, J =
1.8 Hz, 1H), 2.01-1.02 (m, 10H)
[M þ Naþ]: 557.1605
found: 557.1612
ZX-4-10
ZX-4-11
ZX-4-12
ZX-4-13
ZX-4-14
ZX-4-15
ZX-4-16
ZX-4-17
δ 7.53-6.93 (m, 7H), 6.18 (s, 1H), 5.44 (d, J = 8 Hz, 1H), 3.89-3.82 (m, 1H), 2.88 (s, 3H), 2.18 (d, J =
1.8 Hz, 1H), 2.01-1.02 (m,10H)
[M þ Naþ]: 557.1605
found: 557.1597
δ 7.93-6.87 (m, 7H), 6.63 (s, 1H), 5.59 (d, J = 8.0 Hz, 1H), 3.89-3.83 (m, 1H), 2.88 (s, 3H), 2.12
(d, J = 1.8 Hz, 1H), 2.04-1.02 (m, 10H)
[M þ Naþ]: 534.1582
found: 534.1577
δ 8.15-6.96 (m, 7H), 6.23 (s, 1H), 5.60 (d, J = 8.0 Hz, 1H), 3.91-3.83 (m, 1H), 2.89 (s, 3H), 2.17
(d, J = 1.8 Hz, 1H), 2.04-1.05 (m, 10H)
[M þ Naþ] :534.1582
found: 534.1586
δ 8.12-6.97 (m, 7H), 6.21 (s, 1H), 5.54 (d, J = 7.5 Hz, 1H), 3.91-3.84 (m, 1H), 2.89 (s, 3H), 2.20
(d,J = 1.8 Hz, 1H), 2.04-1.05 (m, 10H)
[M þ Naþ]: 534.1582
found: 534.1586
δ 7.19-6.81 (m, 7H), 6.52 (s, 1H), 5.31 (d, J = 7.5 Hz, 1H), 3.92-3.84 (m, 1H), 2.88 (s, 3H), 2.43
(s, 3H), 2.12 (d, J = 1.3 Hz, 1H), 2.00-1.00 (m, 10H)
[M þ Naþ]: 503.1888
found: 503.1882
δ 7.13-6.89 (m, 7H), 6.15 (s, 1H), 5.38 (d, J = 7.8 Hz, 1H), 3.89-3.82 (m, 1H), 2.88 (s, 3H), 2.25
(s, 3H), 2.16 (d, J = 1.8 Hz, 1H), 1.98-1.00 (m, 10H)
[M þ Naþ]: 503.1888
found: 503.1881
δ 7.02-6.88 (m, 7H), 6.15 (s, 1H), 5.35 (d, J = 8.3 Hz, 1H), 3.88-3.81 (m, 1H), 2.87 (s, 3H), 2.30
(s, 3H), 2.16 (d, J = 1.8 Hz, 1H), 1.97-0.99 (m, 10H)
[M þ Naþ]: 503.1888
found: 503.1887
δ 7.02-6.67 (m, 7H), 6.13 (s, 1H), 5.38 (d, J = 8.0 Hz, 1H), 5.04 (s, 1H), 3.88-3.81 (m, 1H), 2.87
(s, 3H), 2.17 (d, J = 1.8 Hz, 1H), 1.98-1.01 (m, 10H)
[M þ Naþ]: 505.1680
found: 505.1672
all solid dissolved, the organic phase was separated, the aqueous phase was
extracted with petroleum ether, and the extracts were combined with the
organic phase. The resulting organic phase was washed with water and
dried over magnesium sulfate. Pyridine and petroleum ether were distilled
off, and the residue was obtained under reduced pressure; cyclohexyl
isocyanide, a colorless foul-smelling liquid, was obtained with a yield of
73% (26).
Biological Screening. Biological activities of the target compounds
including fungicide and direct antivirus activities such as protection,
inactivation, and curative effects and systemic acquired resistance were
evaluated systematically according to the standard operation practice
(SOP) as described in ref 5 and the following procedures.
Fungicide Screening. Preliminary screening was conducted by fungus
growth inhibition method according to reference using potato dextrose
agar (PDA) as cultivation medium (5). Fungi used in this studies included
Alternaria solani (AS), Cercospora arachidicola (CA), Cercospora beticola
(CB), Colletotrichum lagenarium (CL), Fusarium oxysporum (FO), Gibber-
ella zeae (GZ), Phyricularia grisea (PG), Phytophthora infestans (Mont) de
Bary (PI), Physalospora piricola (PP), Pellicularia sasakii (PS), and
Rhizoctonia solani (RS).
Preparation of 4-Methyl-1,2,3-thiadiazolyl-5-carboxylic Acid.
4-Methyl-1,2,3-thiadiazole-5-carboxylic acid was prepared according to
the description in ref 5.
General Synthetic Procedure for 4-Methyl-1,2,3-thiadiazole-5-
carboxamide Derivatives via U-4CR. Benzaldehyde (0.30 g, 2.8 mmol)
was added to a solution of 3-chloro-4-methylbenzenamine (0.42 g,
3.0 mmol) in methanol in an ice-water bath, and then the reaction
mixture was stirred for 6 h at room temperature. A solution of 4-methyl-
1,2,3-thiadiazole-5-carboxylic acid (0.47 g, 3.6 mmol) in methanol was
added to the mixture. Five minutes later, cyclohexyl isocyanide (0.28 g,
2.6 mmol) was added to the mixture in an ice-water bath. The product
precipitated as a white solid within several minutes, and after stirring
overnight, the crude product was collected by filtration. All of the crude
products were obtained in this way but purified by different procedures.
Most of the title compounds were purified by washing and recrystalliza-
tion in methanol, whereas compounds ZX-3-8, ZX-3-14, ZX-3-17, ZX-3-
18, ZX-4-5, and ZX-4-9 were purifiedby column chromatography on silica
gel using ethyl acetate and petroleum ether (60-90 °C) with 1:2-1:4 (v/v)
as an eluent (21-23). The yields and physical properties of the target
compounds are listed in Table 1, and their proton nuclear magnetic
resonance (1H NMR) and HRMS data are listed in Table 2.
Systemic Acquired Resistance Screening. Systemic acquired resis-
tance of the target compounds was detected using tobacco against the
tobacco mosaic virus (TMV) system as described in ref 5. The induction
activity was evaluated using the antivirus inhibition ratio, which was
calculated by the average number of viral inflammations on the inoculated
leaves with the corresponding control accordingly. TDL and Ribavirin
were chosen as positive control and negative control, respectively, and all
compounds were tested at concentrations of 100 and 50 μg/mL, respec-
tively.
Protective Effects of the Target Compounds against TMV in Vivo.
Healthy fresh tobacco plants at six-leaf stage were selected
for the tests. The compound solution was smeared on the whole
leaves, and then the leaves were dried in the greenhouse. After 12 h,
TMV at a concentration of 5.88 ꢀ 10-2 μg/mL was inoculated on
the upper three leaves using the conventional juice robbing method,

Article
J. Agric. Food Chem., Vol. 58, No. 5, 2010 2759
Table 3. Fungicide Activity Determination of Target Compoundsa
compd
CB FO CA AS GZ PP PG PS CL RS PI
ZX-3-1
ZX-3-2
ZX-3-3
ZX-3-4
ZX-3-5
ZX-3-6
ZX-3-7
ZX-3-8
ZX-3-9
ZX-3-10
36
27
18
0
25
0
61
48
39
29
43
39
26
29
21
57
16
57
16
14
17
35
47
53
21
29
14
0
32 nd
26 nd
21 nd
38 35
38 46
21 nd
37 nd
38 12
32 nd
31 19
35 nd
38 12
35 nd
56 23
37 nd
42 nd
56 nd
50 nd
22
13
26
27
30
22
26
46
31
19
41
19
38
35
35
26
48
31
0
40
40
20
29
14
15
25
43
24
14
24
0
17
12
12
9
5
9
63 32
67 26
65 21
40 41
49 35
69 21
67 35
60 41
20 20
37 29
11
nd
nd
21
0
50 32
33 47
16
27
27
0
17
12
9
5
nd
31
nd
22
nd
22
nd
18
18
34
38
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
33 53
30 20
22 16
22 32
20 26
25 24
43 37
24 14
24 18
22 44
22
0
ZX-3-11 11
ZX-3-12
ZX-3-13 11
ZX-3-14
29
0
0
40 41
29 12
43 35
63 35
69 26
43 24
46 32
18
0
Figure 1. Parallel activity contrasts between series ZX-3 and series ZX-4
againstCB. The fungicidal activities were tested at 50 μg/mL. The numbers
on the x-axis represent the R group in Scheme 1: 1 = phenyl; 2 =
2-chlorophenyl; 3 = 3-chlorophenyl; 4 = 4-chlorophenyl; 5 = 2-fluorophenyl;
6 = 3-fluorophenyl; 7 = 4-fluorophenyl; 8 = 2-(trifluoromethyl)phenyl;
9 = 3-(trifluoromethyl)phenyl; 10 = 4-(trifluoromethyl)phenyl; 11 =
2-nitrophenyl; 12 = 3-nitrophenyl; 13 = 4-nitrophenyl; 14 = 2-methylphenyl;
15 = 3-methylphenyl; 16 = 4-methylphenyl; 17 = 3-hydroxyphenyl; 18 =
4-hydroxyphenyl.
0
ZX-3-15 27
ZX-3-16 27
ZX-3-17 44
ZX-3-18 33
10
50
29
41
14
14
29
43
43
0
37
0
8
ZX-4-1
ZX-4-2
ZX-4-3
ZX-4-4
ZX-4-5
ZX-4-6
ZX-4-7
ZX-4-8
ZX-4-9
33
0
0
45
14
28
5
19 23
25 27
38 12
31
8
22 26
28 16
22 37
33 42
37 47
34 29
43 24
49 41
13
0
23
31
0
0
29
21
43
29
38
0
0
38
8
inoculated leaves with the corresponding control according to eq 1
17
0
0
5
42
5
44
19
23
85
0
14
29
14
14
0
17 26
11 47
74 95
40 29
37 53
97 88
CK -A
CK
75
0
44 15
Y ¼
ꢀ 100
ð1Þ
71 100 62
ZX-4-10 50
ZX-4-11 67
ZX-4-12 33
ZX-4-13 17
ZX-4-14 67
ZX-4-15 33
ZX-4-16 17
ZX-4-17 17
57
21
57
14
79
21
14
36
0
0
0
0
24
41
28
34
6
0
5
5
35
37
0
5
where Y is the antivirus inhibition ratio (protection, inactivation, and
curative effects in vivo) (%), CK is the average number of viral inflamma-
tions on the control leaves in vivo, and A is the average number of viral
inflammations on the target compound treated leaves in vivo.
0
32
0
14
0
45 10
30 11
40 16
51 47
0
16 43
0
44 34
53
0
57
0
0
0
0
34
28
24
0
0
0
0
5
28
33
40
0
5
0
RESULTS AND DISCUSSION
0
29
14
0
14
Preparation of the Novel 4-Methyl-1,2,3-thiadiazole-5-carboxy-
amide Derivatives via U-4CR. Optimization of a lead structure
can be conducted via diverse methods. This study used U-4CR as
the synthesis method via parallel synthesis, and the target
compounds were proved to be easily synthesized and purified.
In U-4CR, the order of adding the reactants is very important;
usually, isocyanides in acidic medium are unstable, so it is
necessary to add isocyanides at the last step. Moreover, it is
well-known that the preformation of the imine favors the reac-
tion (21, 23). For these reasons, our experiments mixed an amine
component and an aldehyde component first to get an inter-
mediate imine, and then a carbonyl component was added in the
mixture for certain time intervals beforeanisocyanidecomponent
was added. Because the Ugi reaction is favored by high concen-
trations of the reactants, the amount of methanol added to the
reaction was as small as possible, just to make the agitation
effective. After all components were mixed, products usually
precipitated in solvent within 1 h. However, some products
containing strong polar group such as nitro or hydroxy were
not easily precipitated at room temperature; that process took
several days, or precipitation occurred only after removal of most
of the solvent. Our studies did not optimize the reaction condi-
tions, and the mother liquor was not recycled; therefore, some
yields of title compounds were low. All structures of the title
compounds synthesized were confirmed by 1H NMR and
HRMS.
a AS, Alternaria solani; CA, Cercospora arachidicola; CB, Cercospora beticola;
CL, Colletotrichum lagenarium; FO, Fusarium oxysporum; GZ, Gibberella zeae; PG,
Phyricularia grisea; PI, Phytophthora infestans (Mont) de Bary; PP, Physalospora
piricola; PS, Pellicularia sasakii (Shirai); PT, Puccinia triticina Eriks; RS, Rhizoctonia
solani Kuhn; nd, not detected.
and the solvent was smeared on the lower three leaves as a control.
The local lesion numbers were then recorded 2-3 days after ino-
culation. For each compound, three repetitions were conducted.
All compounds were tested at concentrations of 500 and 100 μg/mL,
respectively.
Inactivation Effect of the Target Compounds against TMV in
Vivo. Healthy fresh tobacco plants at six-leaf stage were selected for the
tests. The TMV virus at a concentration of 5.88 ꢀ 10-2 μg/mL was
inhibited by mixing with the target compound solution at the same volume
for 30 min. Then the mixture was inoculated on the upper three leaves
using the conventional juice robbing method, and the solvent was smeared
on the lower three leaves as a control. The local lesion numbers were then
recorded 2-3 days after inoculation. For each compound, three repeti-
tions were conducted. All compounds were tested at concentrations of 500
and 100 μg/mL, respectively.
Curative Effect of Target Compounds on TMV in Vivo. Healthy
fresh tobacco plants at six-leaf stage were selected for the tests. TMV
at a concentration of 5.88 ꢀ 10-2 μg/mL was inoculated on the whole
leaves using the conventional juice robbing method. After the leaves were
dried in the greenhouse, the compound solution was smeared on the upper
three leaves, and the solvent was smeared on the lower three leaves as
control. The local lesion numbers were then recorded 2-3 days after
inoculation. For each compound, three repetitions were conducted.
All compounds were tested at concentrations of 500 and 100 μg/mL,
respectively.
Biological Activity. Fungicidal Activity. Eleven fungi repre-
senting typical fungi often occurring in the Chinese agro-ecosys-
tem, including AS, CA, CB, CL, FO, GZ, PG, PI, PP, PS, and RS,
were chosen for fungicide screening, and the results are shown in
Table 3. All compounds showed a certain degree of fungicidal
The activities of protection, inactivation, and curative effects against
TMV were calculated by the average number of viral inflammations on the

2760 J. Agric. Food Chem., Vol. 58, No. 5, 2010
Zuo et al.
Table 4. Inhibition Activities against TMV in Vitro
concentration
concentration
compd
500 μg/mL
100 μg/mL
compd
500 μg/mL
100 μg/mL
ZX-3-1
ZX-3-2
ZX-3-3
ZX-3-4
ZX-3-5
ZX-3-6
ZX-3-7
ZX-3-8
ZX-3-9
ZX-3-10
ZX-3-11
ZX-3-12
ZX-3-13
ZX-3-14
ZX-3-15
ZX-3-16
ZX-3-17
ZX-3-18
Tiadinil
24 ( 4
20 ( 2
29 ( 2
29 ( 4
24 ( 3
18 ( 7
16 ( 1
38 ( 2
19 ( 4
34 ( 1
47 ( 2
9
19
ZX-4-1
ZX-4-2
ZX-4-3
ZX-4-4
ZX-4-5
ZX-4-6
ZX-4-7
ZX-4-8
ZX-4-9
ZX-4-10
ZX-4-11
ZX-4-12
ZX-4-13
ZX-4-14
ZX-4-15
ZX-4-16
ZX-4-17
19 ( 1
23 ( 2
39 ( 7
30 ( 1
23 ( 4
29 ( 3
36 ( 5
48 ( 5
67 ( 5
25 ( 3
29 ( 9
58 ( 1
39
19 ( 5
21 ( 4
15 ( 2
28 ( 1
22 ( 1
9 ( 1
19 ( 3
21 ( 2
38 ( 8
18
9 ( 3
15 ( 3
18 ( 5
22 ( 5
11 ( 1
15 ( 7
11 ( 2
26 ( 2
38 ( 11
11 ( 3
25 ( 13
24 ( 3
14 ( 2
37 ( 5
40 ( 15
33
29 ( 9
10 ( 3
17 ( 3
44 ( 2
26 ( 2
23 ( 5
18
Figure 2. Parallel activity contrasts between series ZX-3 and series ZX-4
againstAS. The fungicidal activities weretested at 50 μg/mL. The numbers
on the x-axis represent the R group in Scheme 1: 1 = phenyl; 2 = 2-
chlorophenyl; 3 = 3-chlorophenyl; 4 = 4-chlorophenyl; 5 = 2-fluorophenyl;
6 = 3-fluorophenyl; 7 = 4-fluorophenyl; 8 = 2-(trifluoromethyl)phenyl; 9 =
3-(trifluoromethyl)phenyl; 10 = 4-(trifluoromethyl)phenyl; 11 = 2-nitrophe-
nyl; 12 = 3-nitrophenyl; 13 = 4-nitrophenyl; 14 = 2-methylphenyl; 15 = 3-
methylphenyl; 16 = 4-methylphenyl; 17 = 3-hydroxyphenyl; 18 = 4-
hydroxyphenyl.
32
42 ( 5
19
52 ( 2
29 ( 2
36 ( 5
70 ( 4
40 ( 5
35 ( 4
17 ( 1
51 ( 4
52 ( 8
20 ( 4
Ribavirin
38 ( 5
28 ( 2
studies that strongly electroattractive groups favored the fungi-
cide activity of 1,2,3-thiadiazole-containing molecules (15)
Anti-TMV Activity and Systemic Acquired Resistance
Activity. TDL and Ribavirin were used as two positive controls.
The results of activity screening by half leaf juicy method against
TMV indicated that (Table 4) most compounds showed a certain
degree of direct inhibition activities against TMV. The activity of
any ofthe compounds including ZX-4-8, ZX-4-9, ZX-4-12, ZX-4-
14, and ZX-4-17 was equal to or higher than that of TDL at
500 μg/mL. Compounds ZX-3-4, ZX-3-14, ZX-4-7, ZX-4-8, ZX-
4-12, and ZX-4-16 had good activities of 38, 38, 40, 33, 44, and
52%, respectively, equal to or higher than that of TDL (37%) at
100 μg/mL. Moreover, compounds ZX-3-8, ZX-3-11, ZX-3-14,
ZX-3-16, ZX-4-3, ZX-4-8, ZX-4-9, ZX-4-12, ZX-4-13, ZX-4-14,
and ZX-4-17 had inhibition activities of 38, 47, 42, 40, 48, 67, 58,
38, 52, and 70%, respectively, which was equal to or higher than
that of Ribavirin (38%) at 500 μg/mL, and compounds ZX-3-4,
ZX-3-14, ZX-4-4, ZX-4-7, ZX-4-8, ZX-4-9, ZX-4-12, ZX-4-13,
and ZX-4-16 had activities of 38, 38, 28, 40, 33, 29, 26, 44, and
52%, respectively, which was equal to or higher than that of
Ribavirin (28%) at 100 μg/mL. All of these results indicated that
more compounds belonging to series ZX-4 had better activities
than members of series ZX-3; the replacement of Cl by F might
improve their direct inhibition activities against TMV in vitro.
On the basis of the results of screening in vitro, some com-
pounds with good direct anti-TMV activity in vitro were chosen
for further evaluation of protection, inactivation, and curative
effect and induction activities against TMV in vivo (Table 5). To
study the structure-activity relationship conveniently, seven
compounds with various phenyl moieties from one series includ-
ing ZX-4-1, ZX-4-8, ZX-4-9, ZX-4-12, ZX-4-13, ZX-4-14, and
ZX-4-17 were chosen for comparative studies against TMV in
vivo. As shown in Table 5, all seven compounds had a certain
degree of activity against TMV in vivo. It was noteworthy that
compounds containing phenyl, trifluoromethylphenyl, and hy-
droxyphenyl such as ZX-4-1, ZX-4-8, and ZX-4-17 had equal
protection effects with corresponding control at 100 and 500 μg/
mL. Moreover, compounds ZX-4-1, ZX-4-9, ZX-4-12, ZX-4-13,
ZX-4-14, and ZX-4-17 had curative effects equal to or higher than
controls at 500 and 100 μg/mL, respectively; that is to say,
trifluoromethyl-, nitro-, and hydroxyl-substituted phenyls were
beneficial to the curative effect. Among these compounds,
activity at 50 μg/mL; the results indicate that compounds ZX-4-8,
ZX-4-10, ZX-4-11, and ZX-4-14 exhibited 75, 50, 67, and 67%
fungicidal activity against CB, respectively; compounds ZX-3-1,
ZX-3-10, ZX-3-12, ZX-3-18, ZX-4-9, ZX-4-10, ZX-4-12, and
ZX-4-14 showed 61, 57, 57, 52.63, 71, 57, 57, and 79% fungicidal
activities against CA, respectively; compounds ZX-3-18, ZX-3-
14, ZX-3-17, and ZX-4-9 showed 50, 56, 56, and 100% fungicidal
activities against AS, respectively; compound ZX-4-9 showed
62% fungicidal activity against GZ; compounds ZX-4-9 and ZX-
4-14 showed 85 and 53% fungicidal activities against PP, respec-
tively; compounds ZX-3-16 and ZX-4-14 showed 50 and 57%
fungicidal activities against PG, respectively; compounds ZX-3-4
and ZX-4-9 showed 50 and 74% fungicidal activities against PS,
respectively; compounds ZX-3-8 and ZX-4-9 showed 63 and 95%
fungicidal activities against CL, respectively; compounds ZX-3-1,
ZX-3-2, ZX-3-3, ZX-3-6, ZX-3-7, ZX-3-8, ZX-3-15, ZX-3-16,
ZX-4-9, and ZX-4-14 exhibited 63, 67, 65, 69, 67, 60, 63, 69, 97,
and 51% fungicidal activities against RS, respectively; and
compounds ZX-4-8 and ZX-4-9 showed 53 and 88% fungicidal
activities against PI, respectively. As the results described above,
most of the target compounds showed a very narrow spectrum
against the fungi tested; however, two of them showed broad-
spectrum activities against several fungi. For example, compound
ZX-4-9 had good activities against AS (100%), CA (71%), CL
(95%), GZ (62%), PI (88%), PP (85%), PS (74%), and RS
(97%), and ZX-4-14 also had good fungicide activities against
CA (79%), CB (67%), PG (57%), PP (53%), and RS (51%).
As mentioned above, the differences between two series of
target compounds were that they contained different moieties of
3-chloro-4-methylphenyl and 3-fluoro-4-methylphenyl, respec-
tively. According to the results, the structure-activity relation-
ship via parallel activity contrasting between the two series of
compounds against fungi at the same concentration (50 μg/mL)
can be evaluated. Most of the contrasting results between the
chlorine and fluorine in the two series had almost equal fungicidal
activities as a whole. However, series ZX-4 showed better activity
against CB but worse activity against AS than series ZX-3 as a
whole (Figures 1 and 2). Moreover, when the R group was 2-
substituted with strong electron-withdrawing groups in the ben-
zene ring such as trifluoro and nitro groups, the fungicidal
activities were usually raised. This coincided with our former

Article
J. Agric. Food Chem., Vol. 58, No. 5, 2010 2761
Table 5. Antivirus in Vivo and Systemic Acquired Resistance Activity of the Title Compounds
protective effect (%)
curative effect (%)
inactivation effect (%)
induction effect (%)
compd
500 μg/mL
100 μg/mL
500 μg/mL
100 μg/mL
500 μg/mL
100 μg/mL
100 μg/mL
50 μg/mL
ZX-4-1
ZX-4-8
ZX-4-9
49
51
54
55
38
35
55
48
44
41
49
19
27
18
23
40
35
40
81
30
42
56
59
47
43
44
46
47
13
28
39
36
18
34
12
14
29
39
31
62
57
60
68
70
71
11
26
21
48
48
27
65
70
57
54
45
38
68
68
58
65
49
10
69
57
68
50
36
63
44
47
40
ZX-4-12
ZX-4-13
ZX-4-14
ZX-4-17
Tiadinil
Ribavirin
compound ZX-4-1 stood out, with curative effects of 81 and 47%
at 100 and 500 μg/mL, respectively. As for activity evaluation of
the inactivation effect, only compound ZX-4-17 had an equal
effect with control at 500 and 100 μg/mL, respectively. The
evaluation of systemic acquired resistance can be described by
the induction activity. All seven compounds had induction
activities equal to or higher than control agent TDL at 500 and
100 μg/mL, respectively.
Our studies on the synthesis of 4-methyl-1,2,3-thiadiazole
derivatives and biological evaluation indicated that the combina-
tion of bioactive substructures via Ugi reaction was an effective
way to find potential bioactive compounds.
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ABBREVIATIONS USED
AS, Alternaria solani; BTH, acibenzolar-S-methyl; CA,
Cercospora arachidicola; CB, Cercospora beticola; CL, Colle-
totrichum lagenarium; DMSO-d6, deutero-, dimethyl sulfo-
xide; FO, Fusarium oxysporum; GZ, Gibberella zeae; 1H
NMR, hydrogen nuclear magnetic resonance; HRMS, high-
resolution mass spectrometry; nd, not detected; PDA, potato
dextrose agar; PG, Phyricularia grisea; PI, Phytophthora
infestans (Mont) de Bary; PP, Physalospora piricola; PS,
Pellicularia sasakii; RS, Rhizoctonia solani; SOP, standard
operation practice; TDL, Tiadinil; TMS, tetramethylsilane;
TMV, tobacco mosaic virus; U-4CR, Ugi four-component
condensation reaction.
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Received for review August 15, 2009. Revised manuscript received
October 11, 2009. Accepted November 19, 2009. This study was
funded in part by grants from the National Natural Science
Foundation of China (No. 20872071 and 20672062), the National Key
Project for Basic Research (No. 2003CB114402 and 2010CB126105),
the Tianjin Natural Science Foundation (No. 07JCYBJC01200), and
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Science Foundation of China (No. 20911120069).
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