Synthetic utility of bifunctional thiophene derivatives and antimicrobial evaluation of the newly synthesized agents

Article abstract of DOI:10.1007/s00706-011-0456-z

The key intermediate ethyl 2-amino-5-benzoyl-4-methylthiophene-3- carboxylate was prepared by a Gewald reaction starting from benzoylacetone, sulfur, and ethyl cyanoacetate in the presence of diethylamine. This intermediate reacted with various reagents to afford different fused and polyfunctional substituted thiophenes. Antimicrobial screening of the synthesized compounds exhibited promising antimicrobial activities.

Full text of DOI:10.1007/s00706-011-0456-z

Monatsh Chem (2011) 142:539–545
DOI 10.1007/s00706-011-0456-z
ORIGINAL PAPER
Synthetic utility of bifunctional thiophene derivatives
and antimicrobial evaluation of the newly synthesized agents
•
Ameen A. Abu-Hashem Khadiga M. Abu-Zied
•
Mohamed F. El-Shehry
Received: 8 April 2010 / Accepted: 3 February 2011 / Published online: 11 March 2011
Ó Springer-Verlag 2011
Abstract The key intermediate ethyl 2-amino-5-benzoyl-
4-methylthiophene-3-carboxylate was prepared by a Gewald
reaction starting from benzoylacetone, sulfur, and ethyl
cyanoacetate in the presence of diethylamine. This inter-
mediate reacted with various reagents to afford different
fused and polyfunctional substituted thiophenes. Antimi-
crobial screening of the synthesized compounds exhibited
promising antimicrobial activities.
[3–5], antipyretic [6], antimicrobial [7, 8], anticonvulsant
[9], and antiplatelet activities [10, 11], and other central
nervous system (CNS) activities [12].
In addition, the pyrimidine nucleus can be found in a
broad variety of antibacterial, anticancer, and antitumor
agents as well as in agrochemicals and veterinary products
[13]. In continuation of our interest in the development of
new and simple methods for the synthesis of polyfunc-
tional substituted heterocycles and thienopyrimidines with
anticipated biological activity [14–17], the present work
describes the syntheses and antimicrobial activities of some
condensed heterocyclic thiophenes and thienopyrimidines.
Keywords Ethyl thiophene-3-carboxylate Á
Thienopyrimidines Á Thienopyridines Á
Tetrazole derivatives Á Pyrazole derivatives Á
Antimicrobial activity
Results and discussion
Introduction
Ethyl 2-amino-5-benzoyl-4-methylthiophene-3-carboxylate
(1) was prepared by the Gewald reaction [18] of benzoyl-
acetone, sulfur, and ethyl cyanoacetate in the presence of
diethylamine and used as a starting material. Its IR spec-
trum displayed absorption bands at 3,652 (NH2), 1,690, and
1,620 cm-1 (the last two signals attributed to two CO
groups), and absence of the CN group. The 1H NMR
spectrum showed two signals at d = 1.32 and 4.30 ppm for
the ester protons and an exchangeable broad signal at
d = 6.55 ppm for the two protons of the amino group.
The 13C NMR spectrum showed two CO signals at
d = 161.2 and 167.9 ppm for the ester and benzoyl car-
bonyl groups.
Ethyl 2-aminothiophene-3-carboxylate represents as a
versatile synthetic building block for the preparation of
many condensed heterocyclic systems, viz. tetrazole, aza-
pyrazole, pyridine, and pyrimidine ring systems [1],
especially when linked to a pyrimidine ring as thienopyr-
imidines show potent analgesic [2], anti-inflammatory
A. A. Abu-Hashem Á K. M. Abu-Zied
Photochemistry Department, National Research Center,
Dokki, Giza 12622, Egypt
Present Address:
A. A. Abu-Hashem
Treatment of 1 with triethyl orthoformate and sodium
azide afforded ethyl 5-benzoyl-4-methyl-2-(1H-tetrazol-
1-yl)thiophene-3-carboxylate (2) in good yield [19]. The
1H NMR spectrum of 2 showed a singlet signal at
d = 8.85 ppm characteristic of a tetrazole proton, and a
lack of the amino proton signal detected for the parent
Chemistry Department, Faculty of Science, Jazan University,
Jazan 2097, Saudi Arabia
M. F. El-Shehry (&)
Green Chemistry Department, National Research Center,
Dokki, Giza 12622, Egypt
e-mail: moh_elshehry2000@yahoo.com
123

540
A. A. Abu-Hashem et al.
1; moreover the mass spectrum of 2 showed the ion peak at
m/z = 342 (M?) in accordance with the molecular weight
(C16H14N4O3S).
Also, when compound 1 reacted with phenyl isothiocya-
nate or phenyl isocyanate in the presence of a catalytic
amount of triethylamine, the corresponding thioureidothi-
ophene and ureidothiophene derivatives 7a and 7b were
afforded, respectively, which underwent cyclization in
ethanolic sodium ethoxide to yield the thieno[2,3-d]-
pyrimidine derivatives 8a and 8b, respectively. The 1H
NMR spectrum of 8b showed an exchangeable signal at
d = 9.32 ppm corresponding to the NH group (Scheme 2).
Compound 1 was diazotized with hydrochloric acid and
sodium nitrite. The desired diazonium chloride was then
coupled with some active methylene compounds, namely
malononitrile and acetylacetone to yield the corresponding
2,3-Diamino-6-benzoyl-5-methylthieno[2,3-d]pyrimidin-
4(3H)-one (3) was obtained by refluxing 2 with hydrazine
hydrate. The reaction sequence and mechanism are out-
1
lined in Scheme 1 [19–21]. The H NMR spectrum of 3
revealed two exchangeable broad singlet signals at
d = 6.41 and 11.49 ppm for two amino groups without the
ester proton signals detected for the parent 2. Moreover, the
mass spectrum of 3 showed the ion peak at m/z = 300
(M?) in accordance with the molecular weight (C14H12
N4O2S). It is noteworthy that when compound 1 was
hydrolyzed in an aqueous ethanolic solution of sodium
hydroxide, the corresponding acid 4 [22] was obtained in
fairly good yield, which on treatment with triethyl ortho-
formate and sodium azide yielded 5-benzoyl-4-methyl-2-
1
azo derivatives 9a and 9b, respectively [25, 26]. The H
NMR spectrum of 9b showed the absence of an amino
signal and the presence of signals at d = 2.34 and
2.35 ppm for two acetyl groups and d = 13.0 ppm for an
exchangeable NH proton. Hydrazones 9a and 9b reacted
with hydrazine hydrate in ethanol under reflux to afford the
1
(1H-tetrazol-1-yl)thiophene-3-carboxylic acid (5). The H
NMR spectrum of 5 showed a signal at d = 8.89 ppm
characteristic of a tetrazole proton and at d = 12.1 ppm for
the carboxylic proton (Scheme 1).
1
hydrazides 10a and 10b. The H NMR spectrum of 10b
exhibited signals at d = 6.90 (exchangeable NH2 protons)
and 9.10 and 11.50 ppm (exchangeable NH protons).
Moreover, its mass spectrum showed the ion peak at
m/z = 382 (M?) in accordance with the molecular weight
(C18H18N6O2S).
Compound 1 reacted with benzoyl isothiocyanate in
ethanolic sodium hydroxide to afford a cyclized product,
6-benzoyl-2,3-dihydro-5-methyl-2-thioxothieno[2,3-d]pyr-
imidin-4(1H)-one (6) [23, 24]. Its 1H NMR spectrum
showed signals at d = 9.52 and 11.21 ppm (exchangeable
NH protons), with the other protons in their expected
location and a lack of the signals attributed to the NH2
When 1 was thermally fused with ethyl cyanoacetate or
ethyl acetoacetate in the presence of a catalytic amount of
piperidine 11a and 11b, respectively, were formed. Fur-
thermore, compounds 11a and 11b underwent cyclization
in refluxing ethanolic sodium ethoxide to afford the cor-
responding thieno[3,2-b]pyridine-2-one derivatives 12a
and 12b, respectively. The NMR data supported the
assignment of structures of 11a, 11b, 12a, and 12b.
protons and ester protons detected in the parent 1. The 13
C
NMR spectrum showed the CS signal at d = 168.7 ppm
beside the two CO signals at d = 162.1 and 168.1 ppm.
The mass spectrum had an ion peak at m/z = 302 (M?) in
accordance with the molecular weight (C14H10N2O2S2).
Scheme 1
COOC2H5
COOH
O
O
S
NaOH
O
Ph
O
NH2
S
Et2NH
NH2
S
+
Ph
Ph
4
1
NC
COOC2H5
HC(OC2H5)3
NaN3
HC(OC2H5)3
NaN3
CONHNH2
COOC2H5
N
COOH
N
O
N
O
Ph
N2H4
N
N
O
S
A
N
N
S
N
N
Ph
N
S
N
N
Ph
2
5
-N2
O
CONHNH2
NH2
N
O
O
NH2
NHCN
S
N
S
Ph
B
Ph
3
123

Synthetic utility of bifunctional thiophene derivatives and antimicrobial evaluation
541
Scheme 2
O
Ph
COOC2H5
CONHNH2
N
C2H5ONa
H
H
O
O
O
X
N
R
N
N
N
S
S
S
Ph
H
Ph
Ph
N
Ph
X
N
7 a: X = S
8 a
b
: X = S
: X = O
10 a: R = NH2
NH
b: X = O
b: R = CH3
R
PhNCS
or
(C2H5)3N
N2H4
PhNCO
O
COOC2H5
COOC2H5
NH
S
NH
PhCONCS
NaOH
O
1) NaNO2 / HCl
O
O
S
N
NH2
S
S
H
R
N
R
H2C
R
Ph
Ph
Ph
2)
1
6
R
9 a
b
: R = CN
: R = COCH3
C2H5O
R
O
HO
R
COOC2H5
O
O
C2H5ONa
O
O
R
N
H
N
S
S
H
Ph
Ph
11 a: R = COCH3
b: R = CN
12 a: R = COCH3
b: R = CN
Antimicrobial screening
All compounds showed good to excellent activity against the
tested fungi. In particular, compounds 2, 3, 6, 8a, 8b, 10a,
and 10b exhibited even stronger activity than nystatin
against the tested fungi. The antimicrobial test results imply
that in general thienopyrimidine derivatives exhibit higher
activities than the corresponding thiophenes against human
pathogenic bacteria and phytopathogenic fungi.
Antibacterial activity
All the synthesized compounds were evaluated for their in
vitro antibacterial activity against Escherichia coli, a gram-
negative bacteria, and Staphylococcus aureus and Bacillus
cereus, which are gram-positive bacteria, using the cup
plate method [27, 28]. The activities were compared with
those of the known standard drug tavanic (used at 0.001
mol/cm3). The zone of inhibition (mm) of each compound
against the microorganisms is listed in Table 1. The inhi-
bition exhibited by compounds 2, 3, 6, 8a, 8b, 10a, and 10b
was more effective than that of the other novel compounds
for all bacterial strains. Moreover, these compounds
exhibited fairly good activity, comparable to that of the
standard tavanic. Other compounds were either fairly or
moderately active against the tested bacterial strains. The
enhanced antibacterial activity of the compounds is
attributed to the presence of tetrazole, pyrimidine, and
pyrazole moieties of the thiophene derivatives.
Conclusion
We have developed rapid and effective procedures for the
synthesis of the polycondensed heterocyclic ring systems.
The compounds 2, 3, 6, 8a, 8b, 10a, and 10b exhibited high
antimicrobial activity. The structure–activity relationship
suggested that heterocyclization reactions of bifunctional
thiophenes to tetrazole, pyrazole, and pyrimidine deriva-
tives can result in products with high antibacterial and
antifungal activity. Our prediction is that these compounds
may show even better antimicrobial activity.
Antifungal activity
Antifungal activity of the compounds was determined
against Aspergillus niger and Candida albicans usingthe cup
plate method, and the activities were compared with those of
the known standard drug nystatin (used at 0.001 mol/cm3).
Experimental
All melting points were measured on an Electrothermal IA
9100 series digital melting point apparatus. Microanalytical
123

542
A. A. Abu-Hashem et al.
absolute ethanol for 4 h. The reaction mixture was left
overnight in a refrigerator at 0 °C. The solid product was
collected by filtration, washed with ethanol, dried, and
recrystallized from ethanol to afford 1 (85%). M.p.:
Table 1 Antimicrobial activity of the new compounds
Sample
Inhibition of zone diameter (mm)
Antibacterial activity
Antifungal activity
ꢀ
215–217 °C; IR (KBr): m = 3,652 (NH2), 1,690, 1,620 (2
E. coli S. aureus B. cereus Candida Aspergillus
albicans niger
1
CO) cm-1; H NMR (500 MHz, DMSO-d6): d = 1.32 (t,
J = 6.9 Hz, 3H, CH3), 2.22 (s, 3H, CH3), 4.30 (q, 2H,
J = 7.2 Hz, CH2), 6.55 (br.s, 2H, NH2), 7.44–7.94 (m, 5H,
Ar–H) ppm; 13C NMR (125.7 MHz, DMSO-d6): d = 23.1,
24.3, 39.8, 40.1, 40.2, 115.3, 116.8, 119.5, 125.6, 129.1,
143.7, 161.2, 167.9 ppm; MS: m/z (%) = 289 (33) [M?].
1
6
5
9
8
12
27
30
14
23
28
22
20
26
25
21
18
23
24
16
19
15
17
–
2
22
24
9
23
26
8
24
27
11
17
26
19
17
23
22
18
15
20
21
13
16
12
14
28
–
23
26
10
19
24
18
16
22
23
17
14
19
20
12
15
11
13
–
3
4
5
18
23
17
15
21
20
16
13
18
19
11
14
10
12
20
24
17
14
22
21
15
12
18
20
10
13
9
6
Ethyl 5-benzoyl-4-methyl-2-(1H-tetrazol-1-yl)thiophene-
3-carboxylate (2, C16H14N4O3S)
7a
7b
8a
8b
9a
9b
10a
10b
11a
11b
12a
12b
A
mixture of 1 (10 mmol), triethyl orthoformate
(10 mmol), and sodium azide (10 mmol) in 40 cm3 glacial
acetic acid was stirred under reflux for 2 h. The reaction
mixture was cooled and suspended in 7 cm3 conc. HCl.
The solid was collected by suction filtration and washed
with water. The crude product was recrystallized from
ethanol to afford 2 (70%). M.p.: 243–245 °C; IR (KBr):
-1
;
1H NMR (500 MHz,
ꢀ
m = 1,695, 1,618 (2 CO) cm
DMSO-d6): d = 1.31 (t, 3H, J = 6.9 Hz, CH3), 2.23 (s,
3H, CH3), 4.29 (q, 2H, J = 7.3 Hz, CH2), 7.45–7.95 (m,
5H, Ar–H), 8.85 (s, 1H, tetrazole H-5) ppm; 13C NMR
(125.7 MHz, DMSO-d6): d = 20.2, 23.5, 60.2, 110.2,
128.7, 129.6, 132.5, 133.3, 138.3, 143.2, 144.4, 149.5,
162.1, 166.7 ppm; MS: m/z (%) = 342 (27) [M?].
11
26
–
Tavanic 30
Nystatin
DMF
-
27
?ve
26
?ve
?ve
?ve
?ve
2,3-Diamino-6-benzoyl-5-methylthieno[2,3-d]pyrimidin-
4(3H)-one (3, C14H12N4O2S)
Less active (2–5 mm); moderately active (6–14 mm); highly active
(15–30 mm); very highly active ([30 mm). ?ve indicates growth of
microbes. Control N,N-dimethylformamide (DMF) (0.01% solution in
distilled water). Standard for antibacterial: tavanic (0.001 mol/cm3).
Standard for antifungal: nystatin (0.001 mol/cm3). Inhibition was
recorded by measuring the diameter of the inhibition zone at the end
of 24 h for bacteria and for 48 h for fungi
Compound 2 (10 mmol) in 15 cm3 hydrazine hydrate
was heated under reflux for 7 h. The reaction mixture was
cooled and suspended in 50 cm3 water. The solid was
collected by suction filtration, washed with water, and
recrystallized from ethanol to afford 3 (75%). M.p.:
ꢀ
data were carried out in the microanalytical center, Faculty
of Science, Cairo University. The IR spectra (KBr disk)
were recorded using a Perkin-Elmer 1650 spectrometer.
270–272 °C; IR (KBr): m = 3,400, 3,385 (2 NH2), 1,650,
1
1,622 (2 CO), 1,585 (C=N) cm-1; H NMR (500 MHz,
DMSO-d6): d = 2.20 (s, 3H, CH3), 6.41 (br.s, 2H, CNH2),
7.43–7.94 (m, 5H, Ar–H), 11.49 (br.s, 2H, NNH2) ppm;
13C NMR (125.7 MHz, DMSO-d6): d = 19.2, 121.3,
128.6, 129.3, 131.5, 132.3, 135.3, 142.2, 146.4, 149.5,
158.1, 168.9 ppm; MS: m/z (%) = 300 (60) [M?].
1
The H and 13C NMR spectra were recorded on a Jeol
JMS-AX 500 (1H, 500 MHz; 13C, 125.76 MHz) with
Me4Si as internal standard. Mass spectra were recorded on
an EI MS-QP 1000 EX (Shimadzu, Japan) at 70 eV. The
pharmacological evaluations were carried out in the phar-
macological unit, Department of Chemistry of Natural and
Microbial Products, National Research Center, Egypt.
5-Benzoyl-4-methyl-2-(1H-tetrazol-1-yl)thiophene-3-
carboxylic acid (5, C14H10N4O3S)
Compound 5 was obtained from 4 in a manner similar to
1
Ethyl 2-amino-5-benzoyl-4-methylthiophene-3-carboxylate
(1, C15H15NO3S)
that described for 2 (yield 75%). M.p.: 292–294 °C; H
NMR (500 MHz, DMSO-d6): d = 2.24 (s, 3H, CH3),
7.45–7.93 (m, 5H, Ar–H), 8.89 (s, 1H, tetrazole H-5), 12.10
(br.s, 1H, COOH) ppm; 13C NMR (125.7 MHz, DMSO-
d6): d = 23.2, 108.2, 124.2, 126.7, 130.5, 131.3, 138.3,
A mixture of benzoylacetone (10 mmol), ethyl cyanoace-
tate (10 mmol), sulfur (10 mmol), and diethylamine
(10 mmol) was heated at 70 °C with stirring in 20 cm3
123

Synthetic utility of bifunctional thiophene derivatives and antimicrobial evaluation
543
134.6, 138.5, 144.4, 151.3, 164.6, 172.5 ppm; MS:
m/z (%) = 314 (31) [M?].
General procedure for preparation of compounds 8a, 8b
Compound 7a or 7b (10 mmol) in sodium ethoxide (0.23 g
of sodium metal in 40 cm3 ethanol) was stirred under reflux
for 8 h. After cooling, the mixture was neutralized with
10 cm3 10% HCl and the solid formed was filtered, washed
with water, dried, and recrystallized from ethanol to afford
8a, 8b.
6-Benzoyl-2,3-dihydro-5-methyl-2-thioxothieno-
[2,3-d]pyrimidin-4(1H)-one (6, C14H10N2O2S2)
A mixture of 1 (10 mmol) and benzoyl isothiocyanate
(10 mmol) in ethanolic NaOH (0.4 g in 40 cm3) was
refluxed for 6 h. The reaction mixture was cooled and
suspended in 6 cm3 conc. HCl. The solid was filtered,
washed with water, and recrystallized from ethanol to
6-Benzoyl-2,3-dihydro-5-methyl-3-phenyl-2-
thioxothieno[2,3-d]pyrimidin-4(1H)-one
ꢀ
afford 6 (70%). M.p.: 180–182 °C; IR (KBr): m = 3,360,
3,310 (2 NH), 1,665, 1,630 (2 CO), 1,575 (C=N) cm-1; 1H
NMR (500 MHz, DMSO-d6): d = 2.23 (s, 3H, CH3),
7.44–7.95 (m, 5H, Ar–H), 9.55 (br.s, 2H, NH), 11.21 (s,
1H, NH) ppm; 13C NMR (125.7 MHz, DMSO-d6):
d = 22.9, 25.7, 39.7, 40.2, 115.9, 118.1, 124.9, 126.8,
127.1, 129.4, 129.8, 138.6, 143.3, 162.1, 168.1, 168.7 ppm;
MS: m/z (%) = 302 (15) [M?].
(8a, C20H14N2O2S2)
Yield 70%; m.p.: 277–279 °C; 1H NMR (500 MHz,
DMSO-d6): d = 2.25 (s, 3H, CH3), 7.00–7.96 (m, 10H,
Ar–H), 9.20 (s, 1H, NH) ppm; 13C NMR (125.7 MHz,
DMSO-d6): d = 19.2, 109.4, 119.4, 125.9, 126.7, 127.4,
128.9, 130.5, 131.8, 132.5, 133.4, 135.6, 140.3, 155.7,
170.4, 182.3 ppm; MS: m/z (%) = 378 (71) [M?].
6-Benzoyl-5-methyl-3-phenylthieno[2,3-d]pyrimidine-
2,4(1H,3H)-dione (8b, C20H14N2O3S)
General procedure for preparation
of compounds 7a, 7b
Yield 75%; m.p.: 285–287 °C; 1H NMR (500 MHz,
DMSO-d6): d = 2.26 (s, 3H, CH3), 7.05–7.97 (m, 10H,
Ar–H), 9.32 (s, 1H, NH) ppm; 13C NMR (125.7 MHz,
DMSO-d6): d = 18.9, 109.8, 119.8, 124.8, 126.4, 128.2,
128.8, 130.7, 131.6, 132.3, 134.8, 135.2, 148.1, 152.0,
154.4, 166.9 ppm; MS: m/z (%) = 362 (41) [M?].
A mixture of compound 1 (10 mmol), phenyl isothiocya-
nate or phenyl isocyanate (10 mmol), and 1 cm3
triethylamine in 40 cm3 dioxane was reflux for 8 h. The
solution was evaporated to ꢀ 1=3 of its volume; the sep-
arated precipitate was filtered, washed with ethanol, dried,
and recrystallized from dioxane to afford 7a and 7b,
respectively.
General procedure for preparation of compounds 9a, 9b
Ethyl 5-benzoyl-4-methyl-2-(3-phenylthioureido)thiophene-
3-carboxylate (7a, C22H20N2O3S2)
A solution of compound 1 in conc. HCl (2 mmol in 5 cm3)
was kept in an ice bath at 0–5 °C for 10 min. An aqueous
solution of sodium nitrite (2.1 mmol in 5 cm3) was added
dropwise with stirring to the amine hydrochloride salt
solution over a period of 20–25 min at 0 °C. A yellow
precipitate of diazonium hydrochloride salt was formed. The
reaction mixture was stirred for additional 15 min while
maintaining the temperature at 0 °C. Malononitrile
(2 mmol) or acetylacetone (2.2 mmol) was added to a
solution of the amine hydrochloride salt and 5 g anhydrous
sodium acetate in 100 cm3 ethanol with stirring at 0–5 °C.
Stirring was continued for an additional 3 h. The mixture
was left overnight in the refrigerator. Water (250 cm3) was
added to the reaction mixture and the solid product was
collected by filtration and recrystallized from ethanol to
afford 9a, 9b.
ꢀ
Yield 60%; m.p.: 236–238 °C; IR (KBr): m = 3,370, 3,360
1
(2 NH), 1,710, 1,670 (2 CO) cm-1; H NMR (500 MHz,
DMSO-d6): d = 1.32 (t, 3H, J = 6.8 Hz, CH3), 2.25 (s,
3H, CH3), 4.28 (q, 2H, J = 7.2 Hz, CH2), 6.73–7.94 (m,
10H, Ar–H), 8.64 (s, 1H, NH), 9.10 (s, 1H, NH) ppm; 13C
NMR (125.7 MHz, DMSO-d6): d = 19.4, 23.5, 59.6,
104.9, 125.1, 126.8, 127.8, 128.4, 129.6, 130.8, 132.9,
137.7, 140.1, 157.1, 161.9, 174.3, 184.6 ppm; MS:
m/z (%) = 424 (65) [M?].
Ethyl 5-benzoyl-4-methyl-2-(3-phenylureido)-
thiophene-3-carboxylate (7b, C22H20N2O4S)
ꢀ
Yield 70%; m.p.: 250–252 °C; IR (KBr): m = 3,370, 3,365
(2 NH), 1,712, 1,685, 1,673 (3 CO) cm-1 1H NMR
;
(500 MHz, DMSO-d6): d = 1.31 (t, 3H, J = 6.8 Hz, CH3),
2.23 (s, 3H, CH3), 4.29 (q, 2H, J = 7.3 Hz, CH2),
7.01–7.95 (m, 10H, Ar–H), 8.59 (s, 1H, NH), 9.45 (s,
1H, NH) ppm; 13C NMR (125.7 MHz, DMSO-d6):
d = 19.5, 22.1, 58.3, 110.3, 119.4, 124.2, 126.2, 127.5,
128.7, 129.1, 131.6, 132.2, 133.0, 143.3, 150.5, 154.2,
163.6, 168.6 ppm; MS: m/z (%) = 408 (23) [M?].
Ethyl 5-benzoyl-2-[2-(dicyanomethylene)-
hydrazinyl]-4-methylthiophene-3-carboxylate
(9a, C18H14N4O3S)
Yield 60%; m.p.: 190–192 °C; 1H NMR (500 MHz,
DMSO-d6): d = 1.35 (t, 3H, J = 6.9 Hz, CH3), 2.22 (s,
3H, CH3), 4.30 (q, 2H, J = 7.4 Hz, CH2), 7.44–7.94 (m,
123

544
A. A. Abu-Hashem et al.
5H, Ar–H), 12.60 (s, 1H, NH) ppm; 13C NMR (125.7 MHz,
DMSO-d6): d = 17.2, 20.3, 54.3, 94.9, 103.4, 111.7, 119.3,
128.7, 130.3, 131.5, 133.1, 137.2, 144.3, 162.4, 171.5 ppm;
MS: m/z (%) = 366 (28) [M?].
filtration, washed with ether, and recrystallized from eth-
anol to afford 11a and 11b, respectively.
Ethyl 5-benzoyl-4-methyl-2-(3-oxobutyrylamino)thiophene-
3-carboxylate (11a, C19H19NO5S)
1
Ethyl 2-[2-(1-acetyl-2-oxopropylidene)hydrazinyl]-
5-benzoyl-4-methylthiophene-3-carboxylate
Yield 65%; m.p.: [300 °C; H NMR (500 MHz, DMSO-
d6): d = 1.30 (t, 3H, J = 6.9 Hz, CH3), 2.23 (s, 3H, CH3),
2.30 (s, 3H, COCH3), 3.35 (s, 2H, CH2) 4.31 (q, 2H,
J = 7.2 Hz, CH2), 7.44–7.94 (m, 5H, Ar–H), 9.75 (br.s,
1H, NH) ppm; 13C NMR (125.7 MHz, DMSO-d6):
d = 22.2, 38.9, 39.2, 39.4, 39.7, 77.2, 112.4, 115.4,
126.3, 128.8, 129.2, 129.3, 130.5, 142.6, 160.9, 167.3,
171.1, 173.2 ppm; MS: m/z (%) = 373 (44) [M?].
(9b, C20H20N2O5S)
Yield 70%; m.p.: 175–177 °C; 1H NMR (500 MHz,
DMSO-d6): d = 1.30 (t, 3H, J = 6.8 Hz, CH3), 2.29 (s,
3H, CH3), 2.34 (s, 3H, COCH3), 2.35 (s, 3H, COCH3), 4.31
(q, 2H, J = 7.3 Hz, CH2), 7.45–7.95 (m, 5H, Ar–H), 13.00
(s, 1H, NH) ppm; 13C NMR (125.7 MHz, DMSO-d6):
d = 22.2, 23.7, 25.1, 31.9, 39.2, 77.2, 112.4, 115.4, 126.3,
128.8, 129.2, 129.3, 130.5, 134.8, 142.6, 160.9, 167.3,
171.1, 173.2 ppm; MS: m/z (%) = 400 (20) [M?].
Ethyl 5-benzoyl-2-(2-cyanoacetylamino)-4-
methylthiophene-3-carboxylate (11b, C18H16N2O4S)
Yield 55%; m.p.: 295–297 °C; 1H NMR (500 MHz,
DMSO-d6): d = 1.32 (t, 3H, J = 7.0 Hz, CH3), 2.24 (s,
3H, CH3), 3.36 (s, 2H, CH2), 4.32 (q, 2H, J = 7.4 Hz,
CH2), 7.45–7.95 (m, 5H, Ar–H), 9.80 (br.s, 1H, NH) ppm;
13C NMR (125.7 MHz, DMSO-d6): d = 14.6, 18.7, 27.2,
60.1, 110.8, 124.3, 127.4, 129.9, 130.5, 131.5, 135.1,
137.0, 140.6, 152.4, 163.7, 169.6 ppm; MS: m/z (%) = 356
(62) [M?].
General procedure for preparation
of compounds 10a, 10b
A mixture of 9a or 9b (10 mmol) and hydrazine hydrate
(15 mmol) in 30 cm3 ethanol was heated under reflux for
6 h. The solid precipitated after concentration was filtered,
dried, and recrystallized from ethanol to afford 10a, 10b.
2-(3,5-Diamino-1H-pyrazol-4-ylazo)-5-benzoyl-4-methyl-
thiophene-3-carboxylic acid
General procedure for preparation of compounds
12a, 12b
hydrazide (10a, C16H16N8O2S)
Yield 55%; m.p.: 257–259 °C; 1H NMR (500 MHz,
CDCl3): d = 2.22 (s, 3H, CH3), 2.65, 2.80, 4.43 (3br.s,
6H, 3NH2), 7.43–7.93 (m, 5H, Ar–H), 9.15 (br.s, 1H, NH),
11.55 (br.s, 1H, NH) ppm; 13C NMR (125.7 MHz, DMSO-
d6): d = 19.7, 120.6, 125.4, 128.7, 129.4, 130.6, 131.4,
133.7, 134.9, 139.1, 140.2, 146.0, 163.3, 168.7 ppm; MS:
m/z (%) = 384 (30) [M?].
A solution of 11a or 11b (10 mmol) in sodium ethoxide
(0.23 g of sodium metal in 40 cm3 ethanol) was stirred
under reflux for 9 h. After cooling the reaction mixture was
neutralized with cooled 10% HCl and the solid formed
was collected by filtration, washed with water, dried,
and recrystallized from ethanol to afford 12a and 12b,
respectively.
5-Benzoyl-2-(3,5-dimethyl-1H-pyrazol-4-ylazo)-
4-methylthiophene-3-carboxylic acid hydrazide
5-Acetyl-2-benzoyl-4-hydroxy-3-methylthieno[2,3-b]-
pyridin-6(7H)-one (12a, C17H13NO4S)
1
(10b, C18H18N6O2S)
Yield 60%; m.p.: [300 °C; H NMR (500 MHz, DMSO-
Yield 70%; m.p.: 238–240 °C; 1H NMR (500 MHz,
CDCl3): d = 2.24 (s, 3H, CH3), 2.38 (s, 3H, CH3), 2.82 (s,
3H, CH3), 6.90 (br.s, 2H, NH2), 7.44–7.94 (m, 5H, Ar–H),
9.10 (br.s, 1H, NH), 11.50 (br.s, 1H, NH) ppm; 13C NMR
(125.7 MHz, DMSO-d6): d = 12.3, 119.1, 124.2, 126.5,
128.4, 130.1, 131.5, 133.3, 135.2, 138.9, 141.7, 144.5,
148.3, 162.8, 166.8 ppm; MS: m/z (%) = 382 (70) [M?].
d6): d = 2.23 (s, 3H, CH3), 2.32 (s, 3H, COCH3),
7.44–7.95 (m, 5H, Ar–H), 10.65 (br.s, 1H, NH), 12.25
(br.s, 1H, OH) ppm; 13C NMR (125.7 MHz, DMSO-d6):
d = 22.2, 38.9, 39.2, 39.7, 77.28, 112.4, 115.4, 126.3,
128.8, 129.2, 129.3, 130.5, 142.6, 160.9, 167.3, 171.0,
173.1 ppm; MS: m/z (%) = 327 (25) [M?].
2-Benzoyl-6,7-dihydro-4-hydroxy-3-methyl-
6-oxothieno[2,3-b]pyridine-5-carbonitrile
(12b, C16H10N2O3S)
General procedure for preparation
of compounds 11a, 11b
ꢀ
Yield 70%; m.p.: [300 °C; IR (KBr): m = 3,522 (OH),
1
3,377 (NH), 2,225 (CN), 1,680, 1,637 (2 CO) cm-1; H
A mixture of 1 (10 mmol), ethyl acetoacetate or ethyl
cyanoacetate (10 mmol), and few drops of piperidine were
thermally fused for 5 h. The reaction mixture was cooled to
room temperature and the solid formed was collected by
NMR (500 MHz, DMSO-d6): d = 2.22 (s, 3H, CH3),
7.43–7.96 (m, 5H, Ar–H), 10.60 (br.s, 1H, NH), 12.20
(br.s, 1H, OH) ppm; MS: m/z (%) = 310 (54) [M?].
123

Synthetic utility of bifunctional thiophene derivatives and antimicrobial evaluation
545
Acknowledgments The authors are extremely grateful to Dr. Tamer
A. Mahmoud (Department of Chemistry of Natural and Microbial
Products, National Research Center) for helping us to screen the
newly synthesized compounds for antimicrobial activity.
14. Hussein AA, Alalla AA, Hafiz TSA, Elnagdi MH (1997) J Het-
eroat Chem 4:93
15. Bhuiyan MMH, Rahman KMM, Hossain MK, Hossain MI (2005)
Croat Chem Acta 78:633
16. Bhuiyan MMH, Rahman KMM, Hossain MI, Naser MA, Summi
W (2005) J Appl Sci Res 1:218
17. Bhuiyan MMH, Rahman KMM, Hossain MK, Rahim MA,
Hossain MI, Naser MA (2006) Acta Pharm 56:441
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