Synthesis and biological activity of novel 1-(2,3,4-trimethoxyphenyl)-2- {[5-(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazol-2-yl]thio}ethanone oxime ester derivatives

Article abstract of DOI:10.1002/jhet.5570430409

In a search for new fungicide and anticancer agent with improved biological properties and different bioactivity spectrum, we designed and synthesized a series of novel oxime esters containing 1,3,4-thiadiazole group in moderate yield starting from gallic acid. The title compounds were identified by IR, ¹H NMR, ¹³C NMR and elemental analysis. The bioassay tests showed that these title compounds exhibit weak to moderate anticancer activity in vitro by MTT method.

Full text of DOI:10.1002/jhet.5570430409

Jul-Aug 2006 Synthesis and Biological Activity of Novel 1-(2,3,4-Trimethoxyphenyl)-2-{[5-
(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazol-2-yl]thio}ethanone
Oxime Ester Derivatives
867
Wei Xue, Baoan Song*, Wei He, Hua Wang, Song Yang, Linhong Jin, Deyu Hu,
Gang Liu, and Ping Lu
Key Laboratory of Green Pesticide and Agricultural Bioengineering, Ministry of Education, Center for Research
and Development of Fine Chemicals, Guizhou University, Guiyang, P. R. China, 550025
songbaoan22@yahoo.com
Received August 8, 2005
H3CO
H3CO
OCH3
(1) (CH3)2SO4, NaOH
(2) MeOH, H2SO4
(3) NH2NH2 . H2O
HO
HO
C
O
CH2Br
H3CO
H3CO
OCH3
N
N
N
N
SH
HO
COOH
H2
Ar
S
C
O
C
(4) KOH, CS2
(5) concd. H2SO4
S
Ar
S
In(cat), NaOH, H2O, r.t
OCH3
OCH3
OCH3
H3CO
OCH3
C
N
N
(1) NH2OH•HCl, ethanol
(2) RCOCl, Py, THF
H2
Ar =
S
H3CO
C
Ar
S
NOCOR
In a search for new fungicide and anticancer agent with improved biological properties and different
bioactivity spectrum, we designed and synthesized a series of novel oxime esters containing 1,3,4-
thiadiazole group in moderate yield starting from gallic acid. The title compounds were identified by IR,
1H NMR, 13C NMR and elemental analysis. The bioassay tests showed that these title compounds exhibit
weak to moderate anticancer activity in vitro by MTT method.
J. Heterocyclic Chem., 43, 867 (2006).
Introduction.
found [15-16]. In our search for new classes of compounds
with high biological activity and low toxicity, a series of
facile oxime ester containing 1,3,4-thiadiazole were synthe-
sized from the starting material gallic acid 1, followed by
five reaction steps to obtain 5-(3,4,5-trimethoxyphenyl)-
1,3,4-thiadiazole-2-thiol (6). Thiadiazole compound 6 was
then coupled with 2-bromo-1-(2,3,4-trimethoxyphenyl)
ethanone (7) to give the key intermediate 1-(2,3,4-
trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-1,3,4-
thiadiazol-2-yl]thio}ethanone (8). Acetophenone 8 was
then condensed with hydroxylamine hydrochloride and the
resulted acetophenoxime 9 was treated with acyl chloride in
THF through which a number of new title compounds 10
were obtained. The synthetic route is shown in Scheme 1.
And the structures of the compounds were confirmed by 1H
NMR, IR, and elemental analysis. Preliminary bioassay
indicated that some of these compounds exhibit moderate
anticancer activity in vitro.
Recently oxime ester derivatives have attracted
considerable attention in agrochemical and medicinal
research, since these compounds were found to possess
good bioactivities such as insecticidal, antiphytoviral,
herbicidal, antitumor and fungicidal activities. A large
number of researches on their synthesis and biological
activities have been reported during the last twenty years
[1-5]. However, little attention has been paid to the
synthesis of oxime esters containing 1,3,4-thiadiazole
moiety. Considered that 1,3,4-thiadiazole compounds tend
to contain multi-structure in a molecule, the biological
activity of these compounds may be improved by the
promotion of these combination with the cell’s
microstructure and the accumulation of various biological
activities resulting from the incorporation of different
heterocyclic and non-heterocyclic nucleated changes on
biological activity of the compounds [6-8]. In our previous
work in it, we reported that some 2-(1H-1, 2, 4-triazol)-1-
(2,3,4-trimethoxyphenyl)ethanoxime ester derivatives
showed fungicidal activities [9-14]. Based on the theory of
structure-activity relationship, we modified these structures
by replacement of 1,2,4-triazole with benzothiazole group
and found that some of them still kept high virucidal
activities. Then we designed and synthesized a series of 2-
(benzothiazol-2-thiol)-1-(2,3,4-trimethoxyphenyl)ethanoxime
ester from which new anticancer agent and viricide was
Results and Discussion.
Our synthetic route leading to the title compound 10 is
shown in Scheme 1. Methyl 3,4,5-trimethoxybezoate 3
was synthesized from the starting material gallic acid 1
through etherification and esterification reactions. In the
following three reaction steps, the hydrazide 4, potassium
hydrazidecarbdithioate 5 [17-19], and finally thiadiazole
thio compound 6 were obtained respectively.

868
W. Xue, B.-A. Song, W. He, H. Wang, S. Yang, L.-H. Jin, D.-Y. Hu, G. Liu, and P. Lu
Vol 43
Scheme 1
HO
HO
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
NH2NH2 . H2O
CH3OH
H2SO4
(CH3)2SO4
NaOH
KOH
CS2
HO
COOH
COOH
COOCH3
CONHNH2
H3CO
H3CO
4
3
1
2
OCH3
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
OCH3
(7)
H3CO
C
O
CH2Br
OCH3
N
N
N
N
H2SO4
H2
SH
CONHNHCSSK
C
O
C
S
OCH
3
S
S
In(cat), NaOH, H2O, r.t
OCH3
8
6
5
H3CO
H3CO
OCH3
C
H3CO
H3CO
OCH3
C
OCH3
OCH3
OCH3
OCH3
N
N
N N
NH2OH¡•HCl
ethanol, reffux
H2
H2
RCOCl, r.t
Py, THF
C
S
C
S
OCH3
OCH3
S
S
NOH
NOCOR
9
10
The synthetic route of oxime ester derivatives 10.
The key intermediate, 1-(2,3,4-trimethoxyphenyl)-2-
{[5-(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazol-2-yl]thio}
ethanone (8), was prepared by thioetherification reaction
through treating 2-bromo-1-(2,3,4-trimethoxyphenyl)
ethanone (7) with thio compound 6 in aqueous media
catalyzed by indium. The indium mediated aqueous
organic reaction had been so attractive due to its excellent
catalytic activity in water [20-24].
In order to optimize the reactions, the thioetherification
reactions of compound 6 with compound 7 mediated by
indium were studied, as shown in Table 1. When the
reaction was carried out at 20-25 °C for 3 h catalyzed by 7
mol% indium, compound 8 was obtained in the yield of
83.7% (Table 1, entry 3). Reducing the amount of indium
significantly lowered the product yield (Table 1, entries 1,
2). No obvious improvement could be found when indium
was increased to 10 mol% (Table 1, entry 4). When the
reaction was carried out at lower or higher temperature,
the yield decreased remarkably (Table 1, entry 6-8). No
reaction was observed when indium was not used (Table 1,
entry 9). When the reactions were carried out from 1 h to
2 h in aqueous media catalyzed by indium at 20-25 °C,
the yield of 8 was increased from 69.7% to 70.7% (Table
1, entries 5 and 10). Tiny improvement of the yield was
obtained when the reaction time was prolonged to 4 h
(Table 1, entry 11).
The synthesis of 1-(2,3,4-trimethoxyphenyl)-2-{[5-
(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazol-2-yl]thio}etha-
none oxime (9) was investigated with different base
(including inorganic base such as NaOH, KOH, Na2CO3,
K2CO3, and organic base such as pyridine and
triethylamine) and different solvents (anhydrous methanol
and ethanol). The results are given in Table 2. Firstly, the
reaction temperature should be reflux condition. At room
temperature, no ketoxime 9 could be obtained. Secondly,
the results demonstrated that the presence of pyridine
could accelerate the oximation reaction. Moreover, when
other base instead of pyridine was used in the present
reaction, the yield could not be further improved. Further,
the effects of solvents, molar ration of the substrates on
the oximation reaction were also examined. The best
result was obtained when acetophenone 8 was treated
with 3 equiv of hydroxylamine and 18.2 equiv of pyridine
in anhydrous ethanol at reflux temperature for 8 h.
The esterification of ketoxime 9 with acyl chloride
produced 10 in moderate yield. In order to optimize the
reaction conditions, the esterification reactions were
carried out under several conditions. It was found that the
reaction temperature should be maintained between 0 °C
and 25 °C. Below 0 °C, the reaction was very slow.
Conversely, on increasing the reaction temperature over
25 °C, side reactions occurred and the yield of 10 was
significantly reduced. In addition, different bases such as
pyridine, triethylamine, sodium carbonate, and potassium
carbonate were studied. The results demonstrated that the
presence of pyridine could accelerate the esterification
reaction. Further, the effects of solvents on the
esterification reaction were also examined. The best result
was obtained when the ketoxime 9 was treated with 1.1
equiv. of acyl choride and 1.6 equiv. of pyridine in THF
at 0-25 °C for 8 h.
The antitumor activity was assayed by the MTT method
[25]. The results are listed in Table 3. It was found that
some of these compounds exhibit certain activities against
PC3 cancer cell line in vitro. The data listed in Table 3
indicate that the nature of substituent dramatically affects
the antitumor activity. As can be easily seen, the
antiproliferative bioactivity of three ketoxime benzoates,
that are benzoate 10b (41.5%), (3,4,5-trimethoxy)
benzoate 10c (66.1%) and 3,5-dinitrobenzoate 10g (70.2%)
at 10 μM are all higher than the other compounds. Hence
we may infer that the aryl group is very important to their
bioactivity and the substituted aryl group is even more
favorable. For example, the antiproliferation activity of
compound 10g at the concentration of 5 and 10 μM against
PC3 cells are 56.7% and 70.2%, respectively.

Jul-Aug 2006
Conclusion.
Synthesis and Biological Activity of Novel Oxime Ester Derivatives
869
IR: 3069, 3000, 2953, 1585, 1560, 1506, 1433, 1242, 1047, 833
1
cm-1; H NMR (400 MHz, CDCl3) ꢀ 3.772 (s, 3H, CH3O), 3.800
In summary, the present method for the formation of
key intermediate 8 in aqueous media catalyzed by indium
offers several advantages: faster reaction rates, fewer by-
products, high yields, and the use of water as reaction
medium. Some of the target compounds have moderate
antiproliferative bioactivity against cancer cell. For
example, compounds 10c and 10g can inhibit 66.1% and
70.2% of PC3 cell proliferation at 5 and 10 μM.
(s, 6H, 2ꢀCH3O), 6.977 (d, 2H, ArH, J = 8.8 Hz), 13.981 (s, 1H,
SH).
Anal. Calcd. For C11H12N2O3S2: C, 46.46; H, 4.25; N, 9.85.
Found: C, 46.53; H, 4.30; N, 9.81.
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-1,3,4-
thiadiazol-2-yl]thio}ethanone (8).
To a three-necked 100 mL round-bottom flask fitted with a
magnetic stirring bar was added compound 6 (4 mmol), 3.5%
NaOH aqueous solution (4 mmol) and 30 mL of water. The
mixture was stirred at room temperature for 10 min. Then 4
mmol 2-bromo-1-(2,3,4,-trimethoxyphenyl) ethanone (7) [14]
and indium (0.28 mmol) were added. The resulting mixture was
then stirred for 3 h at room temperature. The reaction was
followed and monitored by TLC (petroleum ether:acetone =
2:1), and the solid material collected by filtration. The solid was
washed with acetone, dried, and crystallized from acetone and
petroleum ether (V/V, 2/1) to give 8 as white solid, yield 83.7%,
m.p. 185-187 °C; IR: 2960, 2937, 2800, 1655, 1591, 1495, 1236,
1047, 837, 798 cm-1; 1H NMR (400 MHz, CDCl3) ꢀ 3.884 (s, 3H,
3-CH3O), 3.926(s, 6H, 3,5-di-CH3O), 3.906(s, 6H, 2ꢀ4-CH3O),
4.110 (s, 3H, 2-CH3O), 4.969 (s, 2H, SCH2), 6.744-7.693 (m,
4H, Ar-H); 13C NMR (CDCl3):191.810, 168.455, 164.111,
158.479, 154.519, 153.596, 141.987, 140.048, 126.492, 125.164,
123.066, 107.286, 104.836, 60.999, 56.321.
EXPERIMENTAL
Unless otherwise indicated, all common reagents and solvents
were used as obtained from commercial supplies without further
purifications. All melting points of the products were determined
on a XT-4 binocular microscope (Beijing Tech Instrument Co.,
China) and are not corrected. The infrared spectra were recorded
1
on a Bruker VECTOR22 spectrometer in KBr disks. H NMR
(solvent CDCl3) and 13C NMR spectra (solvent CDCl3) were
performed on a Varian-INOVA 400 MHz spectrometer at room
temperature using TMS as internal standard. The mass spectra
were taken on an HP5988A spectrometer. Elemental analysis
was performed by an Elementar Vario-III CHN analyzer.
3,4,5-Trimethoxybenzohydrazide (4).
A mixture of methyl 3,4,5-trimethoxybezoate (8.2 g, 3.6
mmol) and 20 mL hydride hydrazide in 10 mL methanol were
refluxed for 5 h. The product was collected by filtration. The
white solid was washed with water and recrystallized from water
to give colorless needles, yield 89.0%, m.p. 152-154 °C. (lit. ref.
[26], m.p. 158-159 °C).
Anal. Calcd. for C22H24N2O7S2: C, 53.60; H, 4.91; N, 5.69.
Found C, 53.50; H, 4.88; N, 5.46.
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-1,3,4-
thiadiazol-2-yl]thio}ethanone oxime (9).
To an oven-dried three-necked 250 mL round-bottom flask
fitted with a magnetic stirring bar was added compound 8 (2.51
g, 5 mmol), pyridine (7.20 g, 91 mmol) and 80 mL absolute
ethanol. The resulting mixture was stirred for 30 min. A solution
of NH2OH·HCl (1.05 g, 15.0 mmol) in anhydrous ethanol (20
mL) was added and the mixture was refluxed for 8 h. The
reaction was followed and monitored by TLC (petroleum
ether:acetone = 1:4). The mixture was then poured into ice water
(100 mL). The crude solid was collected by filtration, washed
with water, dried, and crystallized from acetone to give 9 as
white solid, yield 66.7%, m.p. 135-137 °C; IR: 2938, 2839,
Potassium 2-(3,4,5-trimethoxybenzoyl)hydrazidecarbdithioate
(5).
To
a three-necked 100 mL flask was added 3,4,5-
trimethoxybenzohydrazide (4) (6.8 g, 30 mmol), potassium
hydroxide (2 g) and methanol (80 mL). With stirring carbon
disulfide (2.28 g, 30 mmol) was added dropwise and the
reactants were refluxed for 2 h monitored by TLC (water ethanol
= 1:3). The reaction mixture was cooled to room temperature.
The crude product was collected by filtration, washed with
methanol, and dried to give compound 5 as colorless crystal,
yield 66.5%, m.p. 213-214 °C; 1H NMR (400 MHz, CDCl3) ꢀ
3.805 (s, 3H, CH3O), 3.889 (s, 6H, 2CH3O), 6.798 (s, 2H, ArH),
9.980 (s, 1H, NH), 10.951(s, 1H, CONH).
1
1585, 1105, 972, 846 cm-1; H NMR (400 MHz, CDCl3): 3.777
(s, 3H, MeO), 3.800 (s, 3H, MeO), 3.805 (s, 3H, MeO), 3.825 (s,
3H, MeO), 3.903 (s, 6H, 2MeO), 4.604 (s, 2H, CH2S), 6.703 (d,
1H, ArH, J = 8.8 Hz), 6.966 (d, 1H, ArH, J = 8.8 Hz), 7.140 (s,
2H, ArH), 10.900 (s, 1H, NOH).
Anal. Calcd. for C22H25N3O7S2: C, 52.06; H, 4.96; N, 8.28.
Found: C, 52.00; H, 5.15; N, 8.09.
5-(3,4,5-Trimethoxyphenyl)-1,3,4-thiadiazole-2-thiol (6).
To an oven-dried three-necked 250 mL round-bottom flask
fitted with
a magnetic stirring bar was added 90 mL
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-
1,3,4- thiadiazol-2-yl]thio}ethanone oxime ester 10a-g.
concentrated sulfuric acid (purity 98%). The reactant was cooled
to -10 °C and then potassium salt 5 (41.0 g, 0.120 mol) was
slowly added. After reacted at -5-0 °C for 1.5 h, the resulting
solution was poured into ice-cold water and dissolved in dilute
aqueous sodium hydroxide. The insoluble solid was filtered and
the filtrate was acidified with dilute hydrochloric acid to pH 2.
The mixture was then kept at room temperature for 8 h. The
precipitate was then collected by filtration, washed twice with
water, dried, and recrystallized from DMF/Ethanol (V/V, 1/3) to
obtain compound 6, white solid, yield 43.8%, m.p. 257-258 °C ;
To a 50 mL three-necked-round-bottomed flask, ketoxime 9
(0.51 g, 1 mmol) was mixed with pyridine (0.13 g, 1.6 mmol),
and then dry THF (10 mL) was added. The resulting solution
was stirred for 30 min and cooled to 0 °C with an ice bath. A
solution of acyl chloride (1.1 mmol) in THF (6 mL) was added
dropwise during 20 min. After having been stirred at 0 °C for 1
h, the reaction was warmed to 20-25 °C for 8 h. Then the
solution was poured into 20 mL water, and the mixture was

870
W. Xue, B.-A. Song, W. He, H. Wang, S. Yang, L.-H. Jin, D.-Y. Hu, G. Liu, and P. Lu
Vol 43
neutralized by 5% potassium carbonate to pH 7.0. The crude
solid was collected by filtration, washed with water, dried, and
crystallized from acetone to give title compounds 10.
This compound was obtained as white solid, yield 80.2%,
m.p. 88-89 °C; IR: 2928 1773, 1586, 1252, 1076, 1009, 868
1
cm-1; H NMR (400 MHz, CDCl3): ꢀ 0.865 (t, 3H, CH3, J = 14
Hz), 1.239~1.329 (m, 10H, 5CH2), 1.678 (s, 2H, CH2), 2.404 (t,
2H, CH2, J = 15.2 Hz), 3.852 (s, 3H, CH3O), 3.86 (s, 3H, CH3O),
3.907 (s, 3H, CH3O), 3.929 (s, 6H, 2ꢀ CH3O), 3.971 (s, 3H,
CH3O), 4.689 (s, 2H, CH2S), 6.629 (d, 1H, ArH, J = 8.8Hz),
7.086 (s, 2H, ArH), 7.171 (d, 1H, ArH, J = 8.8 Hz); EIMS: m/z
647(M+, 14.1).
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-
1,3,4-thiadiazol-2-yl]thio}ethanone O-(3-phenylprop-2-enolyl)-
oxime (10a).
This compound was obtained as white solid, yield 70.3%,
m.p. 144-146 °C; IR: 2932 1746, 1630, 1585, 1238, 1103, 989,
1
864 cm-1; H NMR (400 MHz, CDCl3 ) ꢀ 3.776 (s, 3H, CH3O),
Anal. Calcd. for C31H41N3O8S2 (647): C, 57.58; H, 6.40; N,
6.55. Found: C, 57.48; H, 6.38; N, 6.49.
3.843 (s, 6H, 2ꢀCH3O), 3.845 (s, 3H, CH3O), 3.871 (s, 3H,
MeO), 4.002 (s, 3H, CH3O), 4.772 (s, 2H, CH2S), 6.514 (d, 1H,
ArH, J = 8.8 Hz), 6.822 (d, 1H, ArH, J = 8.8 Hz), 7.129 (s, 2H,
Ar), 7.342 (t, 2H, ArH, J = 11.2 Hz), 7.405 (t, 1H, ArH, J = 14.4
Hz), 7.169 (d, 1H, =CH, J = 8.4 Hz), 7.635 (d, 2H, =CH, J = 7.6
Hz), 7.765 (d, 1H, ArH, J = 16 Hz); EIMS: m/z 637 (M+, 10.2).
Anal. Calcd. for C31H31N3O8S2 (637): C, 58.38; H, 4.90; N,
6.59. Found: C, 58.33; H, 4.92; N, 6.58.
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-
1,3,4-thiadiazol-2-yl]thio}ethanone O-(2-methylheptanoyl)-
oxime (10f).
This compound was obtained as white solid, yield 65.5%,
m.p. 95-96°C; IR: 2959, 1757, 1585, 1260, 1074, 1001, 924, 841
1
cm-1; H NMR (400 MHz, CDCl3): ꢀ 0.865 (t, 3H, CH3, J = 14
Hz), 1.239~1.329 (m, 8H, 4CH2), 1.678 (s, 3H, CH3), 2.406 (t,
1H, CH, J = 15.2 Hz), 3.852 (s, 3H, CH3O), 3.860 (s, 3H,
CH3O), 3.907 (s, 3H, CH3O), 3.929 (s, 6H, 2ꢀ CH3O), 3.971 (s,
3H, CH3O), 4.689 (s, 2H, CH2S), 6.629 (d, 1H, ArH, J = 8.8Hz),
7.086 (s, 2H, ArH), 7.171 (d, 1H, ArH, J = 8.8 Hz); EIMS: m/z
633 (M+, 12.0).
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-
1,3,4-thiadiazol-2-yl]thio}ethanone O-benzoyloxime (10b).
This compound was obtained as white solid, yield 53.7%,
m.p. 144-145 °C; IR: 2932, 1742, 1586, 1238, 1109, 965, 861
cm-1; 1H NMR (400 MHz, CDCl3): ꢀ 3.869 (s, 3H, CH3O), 3.883
(s, 3H, CH3O), 3.906 (s, 6H, 2ꢀCH3O), 3.936 (s, 3H, CH3O),
4.001 (s, 3H, CH3O), 4.834 (s, 2H, CH2S), 6.662 (d, ArH, 1H, J
= 8.8 Hz), 7.029 (s, 2H, ArH), 7.561 (d, 1H, ArH, J = 8.8 Hz),
7.256 (t, 1H, ArH, J = 13.6 Hz), 7.447 (t, 2H, ArH, J = 14.8 Hz),
8.089 (d, 2H, ArH, J = 7.6 Hz); EIMS: m/z 611(M+, 18.0).
Anal. Calcd. for C29H29N3O8S2 (611): C, 56.94; H, 4.58 N,
6.87. Found: C, 56.97; H, 4.74; N, 6.98.
Anal. Calcd. for C30H39N3O8S2 (633): C, 56.80; H, 6.11; N,
6.59. Found: C, 56.85; H, 6.20; N, 6.63.
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-
1,3,4-thiadiazol-2-yl]thio}ethanone O-(3,5-dinitrobenzoyl)-
oxime (10g).
This compound was obtained as white solid, yield 55.5%,
m.p. 155-156 °C; IR: 2943 1759, 1587, 1262, 1072, 1009, 861
cm-1; 1H NMR (400 MHz, CDCl3): ꢀ 3.884 (s, 3H, CH3O), 3.905
(s, 3H, CH3O), 3.915 (s, 6H, 2ꢀ CH3O), 3.930 (s, 3H, CH3O),
4.053 (s, 3H, CH3O), 4.852 (s, 2H, CH2S), 6.709 (d, 1H, ArH, J
= 8.8 Hz), 6.910 (s, 2H, ArH), 7.290 (d, 1H, ArH, J = 8.8 Hz),
9.066 (s, 1H, ArH), 9.190 (s, 2H, ArH); EIMS: m/z 701 (M+,
14.1).
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-
1,3,4-thiadiazol-2-yl]thio}ethanone O-(3,4,5-trimethoxybenz-
oyl) oxime (10c).
This compound was obtained as white solid, yield 42.1%,
m.p. 160-162 °C; IR: 2939, 1732, 1589, 1234, 1105, 993, 840
cm-1; 1H NMR (400 MHz, CDCl3): ꢀ 3.867 (s, 3H, CH3O), 3.882
(d, 6H, 2ꢀ CH3O, J = 8.2 Hz), 3.926 (s, 6H, 2ꢀ CH3O), 3.929 (s,
9H, 3ꢀ CH3O), 4.011 (s, 3H, CH3O), 4.79 (s, 2H, CH2S), 6.664
(d, 1H, ArH, J = 8.8 Hz), 7.021 (s, 2H, ArH), 7.221-7.334 (m,
2H, ArH), 8.210 (q, 1H, ArH, J = 9.6 Hz), 8.466 (q, 1H, ArH, J
= 6.0 Hz); EIMS: m/z 701 ( M+, 13.1).
Anal. Calcd. for C29H27N5O12S2 (701): C, 49.94; H, 3.99; N,
9.58. Found: C, 50.05; H, 4.02; N, 9.64.
MTT Assay Against Cell Proliferation.
All compounds tested were dissolved in DMSO (1-100 μM
solutions) and subsequently diluted in the culture medium before
treatment of the cultured cells. Tested cells were plated in 96-
well plates at a density of 3ꢀ103 cells/well/100 μL of the proper
culture medium and treated with the compounds at concentration
of 1-100 μM for 48 h. In parallel, the cells were treated with
0.1% of DMSO as control. A MTT [3-(4,5-dimethylthiazol-2yl)-
2, 5-diphenyltetrazolium bromide] assay (Roche Molecular
Biochemicals) was performed according to the instructions
provided by Roche. This assay is based on the cellular cleavage
of the tetrazolium salt, MTT, into a formazan that is insoluble in
the cell culture medium and is measured at 550 nm directly in
96-well assay plates. Absorbance is directly proportional to the
number of living cells in culture. PC3 (prostate cancer) cell lines
(provided by Cell Bank of Committee on Type Culture
Collection of Chinese Academy of Science) were cultivated in
F-12 medium supplemented with 10% fetal bovine serum
(provided by TBD & HY Bio. Co.) and 2 mM of L-glutamine.
Tissue culture reagents were obtained from Gibco Co.
Anal. Calcd. for C32H35N3O11S2 (701): C, 54.77; H, 5.03; N,
5.99. Found: C, 54.96; H, 5.04; N, 5.93.
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-
1,3,4-thiadiazol-2-yl]thio}ethanone O-[(2-chloropyridin-3-yl)-
carbonyl]oxime (10d).
This compound was obtained as white solid, yield 52.1%,
m.p. 152-154 °C; IR: 2930, 1767, 1584, 1267, 1111, 1028, 922
cm-1; 1H NMR (400 MHz, CDCl3): ꢀ 3.867 (s, 3H, CH3O), 3.882
(s, 6H, 2ꢀ CH3O), 3.910 (s, 3H, CH3O), 3.926 (s, 3H, CH3O),
4.011 (s, 3H, CH3O), 4.790 (s, 2H, CH2S), 6.653 (d, ArH, 1H, J
= 8.8Hz), 7.021 (s, 2H, ArH), 7.232 (d, 1H, ArH, J = 8.8 Hz),
7.331 (t, 1H, PyH, J = 12.4 Hz), 8.222 (d, 1H, PyH, J = 9.6 Hz),
8.474 (d, 1H, PyH, J = 6.8 Hz); EIMS: m/z 647 (M+, 10.9).
Anal. Calcd. for C28H27ClN4O8S2 (647): C, 51.87; H, 4.10; N,
8.60. Found: C, 51.97; H,4.21; N, 8.66.
1-(2,3,4-Trimethoxyphenyl)-2-{[5-(3,4,5-trimethoxyphenyl)-
1,3,4-thiadiazol-2-yl]thio}ethanone O-nonanoyloxime (10e).

Jul-Aug 2006
Synthesis and Biological Activity of Novel Oxime Ester Derivatives
871
Table 1
Indium-catalyzed synthesis of key intermediate 8 [a].
Tech Research and Development Program of China (Grant
Nos. 2003AA2Z3542 and 2002AA217131), the National Nature
Science Foundation of China (Grant No. 20362004), the
Foundation for New Century Talent in University of China
(Grant No. NCET-06-0913), the Excellent Youth Scientist
Foundation of Guizhou Province of China (Grant No.
20050515), and the Nature Science Foundation of Guizhou
Province in China (Grant No. 20043019).
Entry
Indium
Temp / °C
Time / h
Yield / %
1
2
3
4
5
6
7
8
9
1 mol%
5 mol%
7 mol%
10 mol%
7 mol%
7 mol%
7 mol%
7 mol%
0 mol%
7 mol%
7 mol%
20~25
20~25
20~25
20~25
20~25
10~15
30~35
40~45
20~25
20~25
20~25
3
3
3
3
1
3
3
3
3
2
4
53.0
67.8
83.7
84.1
69.7
69.2
71.1
69.9
---
REFERENCES AND NOTES
*To whom correspondence should be addressed. Tel: +86-851-3620521,
Fax: +86-851- 3622211, E-mail: songbaoan22@yahoo.com
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10
11
70.7
83.9
[a] Reaction conditions: 4 mmol of 5-(3,4,5-trimethoxyphenyl)-1,3,4-
thiadiazole-2-thiol (6), 4 mmol of 2-bromo-1-(2,3,4-trimethoxyphenyl)
ethanone (7), 30 mL of water, 3.5 % NaOH (4 mmol), appropriate
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Table 2
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Entry
Molar
ratio [b]
Base
Solvent
Temp /
°C
Yield
%
1
2
3
4
5
6
7
8
9
1 : 1
1 : 2
1 : 3
1 : 3
1 : 3
1 : 3
1 : 4
1 : 3
1 : 3
pyridine
pyridine
KOH
pyridine
Et3N
ethanol
ethanol
ethanol
ethanol
ethanol
ethanol
ethanol
methanol
ethanol
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
20-25
13.2
34.5
32.5
66.7
35.6
35.6
66.9
51.2
0
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pyridine
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[a] Reaction condition: stirred for 8 h in anhydrous solvent; [b] Molar
ratio of compound 8 to NH2OHꢀHCl.
Table 3
Inhibition rate (%) of the title compounds 10a-10g
against PC3 cell at 5 and 10 μM.
Comp.
5 μM
10 μM
10a
10b
10c
10d
10e
10f
8.9
3.9
62.5
10.1
3.3
5.2
41.5
66.1
33.2
28.7
33.1
70.2
6.7
56.7
10g
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Acknowledgement.
This work was financially supported by the National Basic
Research Program of China (Grant No. 2003CB114404), High-