A novel synthesis of (E)-3-methylthio-3-substituted arylamino-2- cyanoacrylates under microwave irradiation

Article abstract of DOI:10.3390/10101351

A facile synthesis of 3-methylthio-3-arylamino-2-cyanoacrylates from 3,3-dimethylthioacrylate and aromatic amines or amino pyridines has been achieved in moderate to high yields (64.0% - 93.5%) in 30 minutes at 50°C under microwave irradiation. This metho

Full text of DOI:10.3390/10101351

Molecules 2005, 10, 1351-1357
molecules
ISSN 1420-3049
http://www.mdpi.org
A Novel Synthesis of (E)-3-Methylthio-3-Substituted Arylamino-
-Cyanoacrylates under Microwave Irradiation
2
Guiping Ouyang, Baoan Song*, Huiping Zhang, Song Yang, Linhong Jin, Qianzhu Li and Deyu
Hu
Research and Development Center for Fine Chemicals, Key Laboratory of Green Pesticide and
Agriculture Bioengineering, Ministry of Education, Guizhou University, Guiyang 550025, P. R. China.
Tel.: (+86) 851 362 0521, Fax: (+86) 851 362 2211.
*Author to whom correspondence should be addressed; e-mail: songbaoan22@yahoo.com
Received: 6 July 2005; in revised form: 15 August 2005 / Accepted: 17 August 2005 / Published:31
October 2005
Abstract: A facile synthesis of 3-methylthio-3-arylamino-2-cyanoacrylates from
3,3-dimethylthioacrylate and aromatic amines or amino pyridines has been achieved in
moderate to high yields (64.0% ~ 93.5%) in 30 minutes at 50°C under microwave
irradiation. This method is very simple and the reaction conditions are mild,
environmentally friendly and more importantly, quick. In the 3-(4,5-dimethylthiazol-
2-yl)-2,5-diphenyltetrazolium bromide (MTT) test, some of the title compounds were
found to possess good antiproliferation activity towards PC3 cells.
Keyword: 2-Cyanoacrylate; aromatic amine; aminopyridine; microwave irradiation.
.
Introduction
Cyanoacrylates are potent inhibitors of photosynthetic electron transport. A number of studies
concerning the inhibition of photosynthetic electron flow in photosystem II (PS II) with a series of
acrylate inhibitors have shown that the potency of acrylate in blocking photosynthetic electron flow is
extremely sensitive to minor structural variations [1]. Among these cyanoacrylates, (Z)-ethoxyethyl
2-cyano-3-(4-chlorophenyl)methylamino-3-isopropylacrylate (CPNPE) exhibits the highest Hill
inhibitory activity reported to date [2].

Molecules 2005, 10
1352
There are several methods for the synthesis of 2-cyanoacrylate inhibitors. The most used methods
over the last decade were: (a) synthesis of 3-methylthio-3′-aminocyanoacrylate from 2-cyano-3,3-
dimethylthioacrylate and benzylamine (anhydrous alcohol, room temperature, 6-11h) [3]; (b) synthesis
of ethyl 2-cyano-3-methylthio-3′-[(6-chloro)-3-pyridiylmethyl]acrylate from 3-aminomethyl or
2-chloro-5-aminopyridine reacted with 2-cyano-3,3-dimethylthio ethyl acrylate (anhydrous alcohol,
reflux, 2h) [4]; (c) synthesis of 3-methylthio-3′-arylaminocyanoacrylate from 2-cyano-3,3-dimethyl-
thioacrylate and 4-trifluoromethylaniline (dimethylformamide [DMF] – toluene, 10-20°C, 40 h) [5]; (d)
nucleophilic substitution with 2-amino-3-chloro-4-methylpyridine under ultrasonic irradiation [6].
These methods, however, suffer from various disadvantages. For methods (a), (b) and (c), the drawbacks
are time-consuming reactions, low yields and complex handling, while for method (d), long reaction
times are the main problem.
Microwave-assisted rapid organic reactions constitute an emerging technology that makes
experimentally and industrially important organic syntheses more effective and more eco-friendly than
conventional reaction methods [7]. Recently we have developed a new method to synthesize the title
products 3 under microwave irradiation in a DMF – tetrahydrofuran (THF) solvent mixture. The method
is very simple, the reaction conditions are mild, environmentally friendly and more importantly, quick.
In this article we describe the preparation of 2-cyanoacrylates containing aryl moieties and their
antitumor bioactivities. The reaction route is shown in Scheme 1. To the best of our knowledge, it is the
first report on the simultaneous reaction of arylamines and 2-cyano-3,3-dimethylthioacrylate under
microwave irradiation.
Scheme 1
NaOCH3
CH ) SO
CN
SCH3
SCH3
NC
SCH3
NHAr
ArNH (2)
2
CNCH CO Et + CS
2
2
2
DMF/THF, M.W.
(
3
2
4
EtOOC
EtOOC
1
3
Results and Discussion
Chemistry
In order to optimize the reaction conditions for preparing compounds 3, the synthesis of (E)-ethyl
-(4-trifluoromethylphenylamino)-2-cyano-3-methylthio acrylate (3c) was carried out under different
3
reaction conditions. First, the microwave irradiation method should be used for the reaction. Under the
normal reaction conditions without microwave irradiation, the reaction was much too slow and the yield
of the product 3c was decreased, for example, when the reaction time was extended to 10 h compound 3c
was obtained in 43.0 % yield (Table 1, entry 13), as compared to a yield of 64.0% in 30 min under
microwave irradiation (Table 1, entry 5). In addition, the effect of solvents was studied. The results
demonstrated that the use of DMF–THF accelerated the amination reaction and moreover, when other
solvents were used instead of DMF–THF, no remarkable improvement in the yields was observed (Table
1
, entries 1, 2, 3 and 4). Further, we also examined the effects of reaction temperature and reaction time
on the amination reactions (Table 1, entries 5-12). When the reaction time was prolonged from 10 min to
0 min, the yield of 3c increased from 47.3 % to 64.0% (Table 1, entries 6-7 and entry 5). When the
reaction time was prolonged further to 40 min under microwave irradiation, a tiny yield improvement
3

Molecules 2005, 10
1353
(65.1%, Table 1, entry 8) was obtained, compared to that obtained after 30 min (64.0%, entry 5). As for
the reaction temperature, it could be seen that the yield was relatively lower when the reaction was
carried out at room temperature (Table 1, entry 9) than at 50°C (Table 1, entry 5). No substantial
improvement was observed when the reaction system was heated to 60°C (Table 1, entry 12). Hence, we
conclude that it is better for the reaction to be carried out at 50°C than at either lower or higher
temperatures.
Table 1. Synthesis of 3c under different reaction conditions and microwave irradiation.
Compd.
Temperature
Entry
Substrate 2
Solvent
Time/min
Yield/%
No.
3c
3c
3c
3c
3c
3c
3c
3c
3c
3c
3c
3c
3c
/°C
50
50
50
50
50
50
50
50
25
35
45
60
50
a
1
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
4-trifluoromethylaniline
acetone
THF
30
30
30
30
30
10
20
40
30
30
30
30
600
33.7
31.2
43.4
57.8
64.0
47.3
51.3
65.1
45.5
55.0
53.0
63.0
43.0
a
2
a
3
DMF
a
4
DMF+PhCH
DMF+ THF
DMF+ THF
DMF+ THF
DMF+ THF
DMF+ THF
DMF+ THF
DMF+ THF
DMF+ THF
DMF+ THF
3
a
5
a
6
a
7
a
8
a
9
a
1
1
1
1
0
1
2
3
a
a
b
a
The reactions were carried out with stirring under 700W microwave irradiation.
Reaction carried out in DMF-THF under stirring without microwave irradiation.
b
Using the optimized conditions, the best result was obtained when 2-cyano-3,3-dimethylthio ethyl
acrylate (1) was reacted with 1 equivalent of aromatic amine or aminopyridine 2 [10] and 2 equivalents
of NaH under microwave irradiation with DMF-THF as co-solvent at 50°C for 30 minutes. Under these
conditions, the amination reaction proceeded smoothly, and the results were summarized in Table 2.
Table 2. Yields of the title compounds 3.
a
Compound
3a
CF
3b
3
3c
3d
3e
3f
3g
CF3
OMe
Me
NO2
Br
3
CH
N
N
Ar-
Cl
Cl
N
Cl
S
b
Yields /%
Yields /%
83.9
63.8
85.2
62.1
64.0
43.0
77.8
54.1
76.9
50.9
93.5
89.2
70.1
59.0
c
a
Isolated yields based on the amine.
b
c
All reactions were carried out in 6mL DMF/THF (1/1 v/v) at 50°C for 30 min under
microwave irradiation with 2 equiv. of NaH used as base.
All reactions were carried out in 6mL DMF/THF (1/1 v/v) at 50°C for 600 min with 2
equiv. of NaH used as base under stirring conditions without microwave irradiation.

Molecules 2005, 10
1354
As can be seen from the general structure (Scheme 1), compounds 3a-g may exist in two different
configurations. In practice, they have been shown to exist in the (E) configuration, as verified by single
crystal structure determination [5]. The structures of all the synthesized compounds were established on
the basis of their spectroscopic data. They showed IR absorption bands at 3149(s)-3367(s) (NH),
-
1
1
3
002-3008(C=C), 2200-2265 (CN) and 1620-1673 cm (COOR). In the H-NMR spectra all phenyl and
pyridyl protons appeared as multiplets at δ 6.85~8.21, while the peaks of the ester CH groups were
2
observed at about 4.18 and 4.32 ppm, respectively, appearing as two doublets. The NH protons of
compounds 3 were at 11.07~11.51 ppm as a singlet, probably due to the existence of hydrogen bonding
between the ester carbonyl and NH of phenylamino or aminopyridyl group which leads to its chemical
shift moving to lower field. The MS spectra revealed that the molecular ion and fragmentation peaks
were in accordance with the proposed structure of compounds 3.
Biological activity
The antitumor activity was assayed by the MTT method [9]. The results were listed in Table 3. It was
found that these compounds exhibit certain activity against the two kinds of cancer cells in vitro. The
compound 3f had relatively higher antitumor activity than the other compounds. The data given in Table
3
indicated that the nature of substituent affects the antitumor activity. For example, the antiproliferation
activities of compound 3f at the concentration of 10 µg/mL against PC3 and A431 cells were 90.1% and
8.0%, respectively.
8
Table 3. Inhibition rate ( x ±s) (%) (10µg/mL) of compounds 3a-3g in 72 hours (P<0.01).
Compd.
PC3 cells
81.3±12.0
22.8±7.8
A431 cells
72.1±11.0
32.1±8.8
48.9±10.0
38.8±4.9
31.6±7.8
88.0±19.0
72.1±14.2
3a
3
b
3c
51.5±11.0
47.3±9.0
3
d
3e
41.2±10.0
90.1±20.1
67.8±12.1
3
f
3g
*Inhibition rate (%) = (A
1 2
-A ) / A
1
1
×100%. A : the mean optical densities of untreated
cells, A : the mean optical densities of drug treated cells.
2
Conclusions
In summary, a mild and effective method for the preparation of (E)-3-methylthio-3-arylamine
2-cyanoacrylates was achieved by the amination reaction of arylamines and 3,3-dimethylthiolacrylate
under microwave irradiation. We believe that this procedure will offer a better and more practical
alternative to the existing methodologies.

Molecules 2005, 10
1355
Acknowledgements
This work was financially supported by the National Basic Research Program of China
2003CB114404), National Natural Science Foundation of China (Nos. 20362004, 20442003), Program
(
for New Century Excellent Talents in University in China (NCET-04-0912), and the Ph.D. Program
Foundation of Ministry of Education of China (20040657003)
Experimental
General
The reagents and solvents were all analytical reagents or chemically pure and were obtained from
Shanghai Reagent Company. All melting points were determined on a XT-4 binocular microscope
(
Beijing Tech Instrument Co., China) and were not corrected. Infrared spectra were recorded on a
1
13
Bruker VECTOR 22 spectrometer. The H-NMR and C-NMR spectra were recorded on a Varian
INOVA 400 (400MHz) Pulse Fourier-transform NMR spectrometer in CDCl using tetramethylsilane as
3
an internal standard. Splitting patterns were designated as s, singlet; d, doublet; t, triplet; q, quartet; m,
multiplet; br, broad. The mass spectra were taken on an HP5988A spectrometer using the EI method.
Elemental analyses were performed on a Vario III CHN analyzer. Microwave reaction was performed on
a Beijing XH-100A microwave (with a power of 700W). Analytical TLC and column chromatography
were performed on silica gel GF254. Column chromatographic purification was carried out using silica
gel. 2,6-Dichloro-4-trifluoromethylaniline and 3-amino-2-chloro-4-methylpyridine were prepared
according to a literature method [10]. 2-Cyano-3,3-dimethylthioacrylate (1) was also prepared according
to literature method [8].
General Method for the Preparation of (E)-3-Methylthio-3-Substituted Aryl Amino-2-Cyanoacrylates
3a-3g
2-Cyano-3,3-dimethylthioacrylate (1, 1.736 g, 8 mmol) [8], an aromatic amine (8.07 mmol), 60%
sodium hydride (0.76 g, 16 mmol), DMF (3 mL) and THF (3 mL) were placed in an oven-dried
three-necked 250 mL round-bottom flask fitted with a magnetic stirring bar. The resulting mixture was
then stirred at 50 °C for 30 min. under microwave irradiation. The completion of the reaction was
monitored by TLC. The mixture was poured into ice water (100 mL) and separated, then the aqueous
phase was acidified with 10% HCl to pH 6~7. The solid was then filtered and the crude product was
dried and recrystallized from ethanol to give the title compounds 3a-3g.
(
E)-Ethyl 3-(2,6-dichloro-4-trifluoromethylphenylamino)-2-cyano-3-methylthio acrylate (3a): colorless
1
crystals; m.p. 125-126°C; H-NMR: δ 1.38 (t, 3H, J=7.8Hz, CH
3
-C), 2.57 (s, 3H, SCH
3
), 4.32 (dd, 2H,
J=18.9Hz, 8.2Hz, OCH
625, 1610, 1571, 1533, 1492, 1471, 1452, 1419, 1244, 1060 cm ; MS: 398(M ); Anal. Calc. for
S: C 42.11; H 2.76; N 7.02. Found: C 42.00; H 2.52; N 7.00.
2
), 7.69 (s, 2H, Ar-H), 11.22 (s, 1H, NH); IR (KBr): 3319, 3300, 3002, 2208,
-
1
+
1
14 2 3 2 2
C H11Cl F N O

Molecules 2005, 10
1356
(
E)-Ethyl 3-(2-chloro-4-methylpyridin-3-yl-amino)-2-cyano-3-methylthio acrylate (3b): colorless
1
crystals; m.p. 113-114°C; H-NMR: δ 1.38 (t, 3H, J=7.9Hz, CH
3 3
-C), 2.34 (s, 3H, Py-CH ), 2.55 (s, 3H,
SCH ), 4.31 (q, 2H, CH ), 7.22-8.26 (m, 2H, Py-H),11.17(s, 1H, NH); IR( KBr): 3284, 3003, 2200, 1637,
3
2
-
1
1
3
1
620, 1608, 1585, 1531, 1458, 1446, 1431, 1386, 1369, 1298, 1269, 1120, 1109, 1085, 779 cm ; MS:
+
11(M );Anal. Calc. for C13
3.48.
3 2
H14ClN O S: C, 50.08; H, 4.53; N, 13.48. Found: C, 50.00; H, 4.49; N,
(
E)-Ethyl 3-(4-trifluoromethylphenylamino)-2-cyano-3-methylthio acrylate (3c): colorless crystals; m.p.
1
1
7
1
1
93.5~194.5°C. H-NMR: δ 1.29~1.65 (m, 3H, CH
.26~7.74 (m, 4H, Ar-H), 11.07 (s, 1H, NH-Ar); C-NMR: 169.36, 161.83, 161.26, 138.40, 127.48,
27.44, 127.40, 125.18, 118.82, 60.32, 14.47; IR (KBr): 3204, 3002, 2976, 2200, 1635, 1620, 1608,
3
-C), 2.50(s, 3H, SCH
3
), 4.18~4.25 (q, 2H, -OCH
2
),
1
3
-
1
585, 1531, 1458, 1446, 1492, 1386, 1369, 1298, 1269, 1120, 1109, 1085, 779 cm ; Anal. Calc. for
: C, 52.18; H, 4.04; N, 14.04. Found: C, 52.13; H, 4.00; N, 13.98.
13 12 3 3 2
C H F N O
(
E)-Ethyl 3-(2-methoxypyridin-4-yl-amino)-2-cyano-3-methylthio acrylate (3d): white solid; m.p. 105-
1
1
06°C, H NMR (CDCl
3
): δ 1.26 (t, 3H, J=7.6Hz, CH
3 3
-C), 2.35 (s, 3H, SCH ), 3.91 (s, 3H, MeO), 4.26
(
dd, 2H, J=20.0Hz, 8.0Hz, OCH
002, 2265, 1673, 1599, 1586, 1530, 1464, 1264, 1234, 1134, 1081 cm ; MS: 280(M ); Anal. Calc. for
S: C 55.70; H 6.42; N 15.00. Found: C 55.69, H 6.39, N 14.89.
2
), 6.85-8.21 (m, 3H, Py-H), 11.21 (s, 1H, NH); IR (KBr): 3367, 3006,
-
1
+
3
13 18 3 2
C H N O
(
E)-Ethyl 3-(4-methylbenzothiazol-2-yl-amino)-2-cyano-3-methylthio acrylate (3e): white solid; m.p.
1
1
62- 163°C; H-NMR :δ 1.38 (t, 3H, J=7.9Hz, CH
3
-C), 2.64 (s, 3H, Hetero-CH
3 3
), 2.65 (s, 3H, SCH ),
4
.32 (dd, 2H, J=20.1.Hz, 7.2Hz, OCH
2
), 7.24-7.60 (m, 3H, Ar-H), 11.51 (s, 1H, Hetero-NH) ppm; IR
-
1
(KBr): 3287, 3007, 2214, 1658, 1593, 1568, 1498, 1471, 1288, 1257, 1234, 1259, 1024 cm ; MS:
+
3
19(M ); Anal. Calc. for C15
H
15
N
2
O
2
S
2
: C 56.42; H 4.70; N 8.77. Found: C 56.50; H 4.84; N 8.69.
(
E)-Ethyl 3-(4-nitrophenylamino)-2-cyano-3-methylthio acrylate (3f): colorless crystals; m.p.
1
1
18-120°C; H-NMR:δ 1.38 (t, 3H, J=6.4Hz, CH
3
-C), 2.55 (s, 3H, SCH
3
), 4.31 (q, 2H, CH
2
), 7.22∼8.26
1
3
(
m, 4H, Ar-H), 11.17 (s, 1H, NH); C-NMR: 172.62, 167.71, 150.06, 148.78, 148.18, 131.49, 124.77,
1
16.93, 61.32, 18.26, 17.89, 14.08; IR (KBr): 3284, 3008, 2200, 1637, 1620, 1608, 1585, 1531, 1458,
-
1
+
1446, 1431, 1386, 1369, 1298, 1269, 1120, 1109, 1085, 779 cm ; MS: 280(M ); Anal. Calc. for
S: C 50.00; H 4.11; N 13.55. Found: C 50.08; H 4.26; N 13.67.
13 18 3 2
C H N O
(
E)-Ethyl 3-(4-bromophenylamino)-2-cyano-3-methylthio acrylate (3g): colorless crystals; m.p. 130-
1
1
7
1
1
32°C; H-NMR: δ 1.26 (t, 3H, J=6.8Hz, CH
.63∼7.65 (m, 4H, Ar-H), 11.22 (s, 1H, NH-Ar). C-NMR: 206.142, 133.217, 127.708, 120.642,
3
-C), 2.85 (s, 3H, SCH
3
), 4.32 (d, 2H,J=8.8Hz, OCH
2
),
13
17.307, 61.635, 17.286, 14.531; IR (KBr): 3149, 3002, 2993, 2204, 1658, 1554, 1487, 1411, 1377,
-
1
+
18 3 2
253, 1165, 1028, 842, 779cm ; MS: 280(M ); Anal. Calc. for C13H N O S: C 45.80; H 3.48; N 8.00.
Found: C 45.76; H 3.48; N 8.21.

Molecules 2005, 10
1357
MTT Cell Proliferation Assay
Two types of cell line provided by ATCC were used in these studies: PC3 (prostate cancer) and
A431 (uterine cancer). These were cultivated in F-12 (for PC3) or RPMI 1640 (for A431) supplemented
with 10% fetal bovine serum and 2 mM of L-glutamine. Tissue culture reagents were obtained from
Gibco BRL. Tested compounds were dissolved in DMSO (1-100µM solution) and then diluted in the
3
culture medium before cell treatment. Tested cells were plated in 96-well plates at a density of 4×10
cells/well/100 µL culture medium and treated with the compounds at concentration of 10 µg/mL for 48h.
In parallel, the cells were treated with 0.1% of DMSO as control. A MTT [3-(4,5-dimethyl-
thiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay (Roche Molecular Biochemicals) was performed
30 h later following the instructions provided by Roche. This assay is based on the cellular cleavage of
the tetrazolium salt MTT to a formazan that is soluble in the cell culture medium and is measured at 550
nm directly in the 96-well assay plates. Absorbance is directly proportional to the number of living cells
in culture.
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Samples Availability: Available from the author.
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