An efficient one-pot three-component synthesis and antimicrobial evaluation of tetra substituted thiophene derivatives

Article abstract of DOI:10.1016/j.cclet.2014.03.044

A convenient one-pot three-component method for the preparation of tetra-substituted thiophene derivatives has been developed. Reaction of acetyl acetone 1, phenyl isothiocynate 2 and 2-chloromethyl derivatives 3a-3c in the presence of potassium carbonate afforded the target compounds, namely ethyl 2-(4-acetyl-3-methyl-5-(phenylamino)thiophen-2-yl)-2-oxoacetate derivatives 4a-4e, ethyl 3-(4-acetyl-3-methyl-5-(phenylamino)thiophen-2-yl)-3-oxopropanoate derivatives 4f-4i, di((4-acetyl-3-methyl-5-phenylamino)thiophen-2-yl)ketone derivatives 4j-4n in reasonable overall yields. The synthesized compounds were screened for antimicrobial activity. The detailed synthesis, spectroscopic data and antimicrobial activities of synthesized compounds were reported.

Full text of DOI:10.1016/j.cclet.2014.03.044

Accepted Manuscript
Title: An efficient one-pot three-component synthesis and
antimicrobial evaluation of tetra substituted thiophene
derivatives
Author: Pravinkumar N. Sable Swastika Ganguly Pravin D.
Chaudhari
PII:
S1001-8417(14)00146-6
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.cclet.2014.03.044
CCLET 2930
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
11-9-2013
14-2-2014
4-3-2014
Please cite this article as: P.N. Sable, S. Ganguly, P.D. Chaudhari, An
efficient one-pot three-component synthesis and antimicrobial evaluation
of tetra substituted thiophene derivatives, Chinese Chemical Letters (2014),
http://dx.doi.org/10.1016/j.cclet.2014.03.044
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Graphical Abstract
An efficient one-pot three-component synthesis and antimicrobial evaluation of tetra
substituted thiophene derivatives
Pravinkumar N. Sable a, b, ∗, Swastika Ganguly a, Pravin D. Chaudharib
a Department of Pharmaceutical Sciences, Birla Institute of Technology, Mesra, Ranchi-835215, India
b Department of Pharmaceutical Chemistry, Progressive Education Society’s Modern College of Pharmacy Nigdi, Pune-411044, India
O
O
O
HN
S
Br
O
O
O
O
4a-4e
3a
R1
NCS
O
O
O
O
R1
O
Cl
O
O
O
O
O
O
2
S
HN
HN
SH
3b
K2CO3, DMF
1
4f-4i
R1
R1
Cl
Cl
R1
O
3c
O
HN
S
NH
S
O
O
4j-4n
R1
A simple and efficient method has been developed for preparation of tetra-substituted thiophene derivatives. The synthesized compounds were
characterized by infrared spectroscopy, 1H NMR, 13C NMR and MS. Antimicrobial activities of synthesized compounds were reported
———
∗ Corresponding author.
E-mail address: pravinpharmacist@gmail.com
Page 1 of 6

Original article
An efficient one-pot three-component synthesis and antimicrobial evaluation of tetra
substituted thiophene derivatives
Pravinkumar N. Sable a, b, ∗, Swastika Ganguly a, Pravin D. Chaudharib
a Department of Pharmaceutical Sciences, Birla Institute of Technology, Mesra, Ranchi-835215, India
b Department of Pharmaceutical Chemistry, Progressive Education Society’s Modern College of Pharmacy Nigdi, Pune-411044, India
ARTICLE INFO
ABSTRACT
Article history:
Received 11 September 2013
Received in revised form 24 February 2014
Accepted 4 March 2014
Available online
A convenient one-pot three-component method for the preparation of tetra-substituted
thiophene derivatives has been developed. Reaction of acetyl acetone 1, phenyl isothiocynate 2
and 2-chloromethyl derivatives 3a-3c in the presence of potassium carbonate afforded the
target compounds, namely ethyl 2-(4-acetyl-3-methyl-5-(phenylamino)thiophen-2-yl)-2-
oxoacetate derivatives 4a-4e, ethyl 3-(4-acetyl-3-methyl-5-(phenylamino)thiophen-2-yl)-3-
oxopropanoate derivatives 4f-4i, di((4-acetyl-3-methyl-5-phenylamino)thiophen-2-yl)ketone
derivatives 4j-4n in reasonable overall yields. The synthesized compounds were screened for
antimicrobial activity. The detailed synthesis, spectroscopic data and antimicrobial activities of
synthesized compounds were reported.
Keywords:
Thiophene
Multicomponent reaction
One pot reaction
Antimicrobial agents
1. Introduction
Multicomponent reactions (MCRs) have emerged as a valuable tool in the preparation of structurally diverse chemical libraries of
heterocyclic compounds [1]. They are inherently atom economical processes in which relatively complex products can be obtained in a
one-pot reaction from simple starting materials, and thus they exemplify many of the desired features of an ideal synthesis. MCRs are
generally much more environmentally friendly and offer access to large compound libraries with diverse functionalities with the
avoidance of protection and deprotection steps for possible combinatorial surveying of structural variations. In view of the increasing
interest in the preparation of a large variety of heterocyclic compound libraries, the development of new synthetically valuable MCRs
with several diversity points remains a challenge for both academic and industrial institutions [2].
Thiophene and its derivatives are an important class of heterocyclic compounds possessing broad biological activities, such as anti-
inflammatory [3], analgesic [3], antioxidant [4], antitubercular [5], antidepressant [6], sedative [6], antiamoebic [7], oral analgesic [8],
anti-metabolite [9], and antineoplastic properties [10]. From the aforementioned reports, it seemed that the development of an efficient,
rapid, and clean synthetic route toward focused libraries of such compounds is of great importance to both medicinal and synthetic
chemists. Hence in this paper, we report a one-pot, three-component reaction for the synthesis of 4-acetyl tetra-substituted thiophene
derivatives and antimicrobial evaluation.
All the synthesized compounds were characterized using FT-IR, 1H NMR, 13C NMR, and mass spectrometry and were subjected to
minimum inhibitory concentration (MIC) antimicrobial screening against two Gram-positive bacteria (Staphylococcus aureus, Bacillus
subtilis), two Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa), and two fungi (Candida albicans, Aspergillus
niger) using the serial plate dilution method.
2. Experimental
All chemicals were purchased from Sigma Aldrich, SD Fine, Spectrochem, Merck, and Himedia. Yields refer to purified products
and are not optimized. Melting points were determined on a VEEGO-VMP I melting point apparatus and are uncorrected. IR spectra
1
were recorded on a JASCO-FTIR 4100 spectrophotometer. H NMR were recorded on a MERCURY VARIAN 300 MHz instrument
and chemical shifts (δ) were reported in parts per million (ppm) with CDCl3 (7.26 ppm) as the solvent. TMS was used as the internal
standard for NMR. MS analyses were done on an Applied Biosystem API 2000. Thin layer chromatography (TLC) was performed on
precoated aluminium plates with silica gel 60 F254
.
———
∗ Corresponding author.
E-mail address: pravinpharmacist@gmail.com
Page 2 of 6

General procedure for synthesis of compounds 4a-4n: Acetyl acetone 1 (1.0 mmol, 1 equiv.) and dried potassium carbonate (1.0
mmol, 1 equiv.) were added in dimethyl formamide (3 mL), and the mixture was stirred for 1 h at room temperature. Aryl
isothiocyanate 2a-2e (1.0 mmol, 1 equiv.) was then added drop wise, and the mixture was stirred for 1 h at room temperature. Then,
bromoethylpyruvate 3a (1.0 mmol, 1 equiv.) or chloroethylacetoacetate 3b (1.0 mmol, 1 equiv.) or dichloroacetone 3c (0.5 mmol, 0.5
equiv.) was added and the reaction mixture was heated for 1 h. The reaction was quenched with 10 mL water. The crude product 4a-4n
precipitated and was purified by filtration followed by crystallization in methanol.
Physical, analytical and spectroscopic characterization data of compounds 4a-4n are given in Supporting information.
3. Results and discussion
3.1 Chemistry
We hypothesized that the N,S-ketene acetal obtained by condensation of acetyl acetone 1 with substituted phenyl isothiocynates 2a-e
would react in situ with 2-chloromethyl derivatives 3a-3c in the presence of potassium carbonate to give the target compounds 4a-4n
in one step. Our initial investigations were mainly aimed at finding a suitable base and solvent for the one-pot preparation of target
compounds 4a-4n.
After careful experimentation, we discovered that 1.0 equiv. of acetyl acetone 1, reacts with 1.0 equiv. of phenyl isothiocynates 2a-e
in the presence of 1.0 equiv. of potassium carbonate in DMF at room temperature to give N,S-ketene acetals. To this unisolated
intermediate, 1.0 equiv. of 3a-3b or 0.5 equiv. of 3c was added and the resultant reaction mixture when stirred at room temperature for
1.0 h gave 4a-4n in moderate to good yields (Scheme 1). The main attractions of this protocol are short reaction time and elimination
of the intermittent workup procedures necessary to isolate the intermediates, thus directly leading to the formation of the target
compounds. Encouraged by the successful results, we synthesized target compounds 4a-4n from the reactions of the acetyl acetone 1,
phenyl isothiocynates 2a-2e, and 2-chloromethyl derivatives 3a-3c by using the same strategy and the different substituents.
During the reaction, a proton from the active methylene of the acetylacetone 1 gets abstracted by the base added, i.e. K2CO3, to give
a nucleophile. This nucleophile then attacks the electron deficient carbon of the phenyl isothiocynates 2a-2e to give the intermediate
i.e. N,S-ketene acetals. After the addition of chloromethyl derivatives 3a-3b, the electronegative sulfur of the intermediate adduct
attacks the electron deficient carbon atom of chloromethyl derivatives 3a-3b. The keto-enol tautomerism takes place, and then
intramolecular cyclisation takes place to give 4-acetyl tetra-substituted thiophene derivatives 4a-4i with the removal of water as shown
in Scheme 2. In the case of dichloro acetone 3c the same mechanism takes place at both ends as shown in Scheme 3 to give target
compounds 4j-4n.
1
The title compounds 4a–4n were characterized by H NMR, FT-IR, and mass spectra. The IR spectra of title compounds 4a–4e
show a peak at 3441.35 cm-1 for an amino group, at 1634.38 cm-1 for a ketone group, at 2990.09 cm-1 for an aromatic group, and at
1726.94 cm-1 for an ester group. The 1H NMR spectrum of ethyl 2-(4-acetyl-3-methyl-5-(phenylamino)thiophen-2-yl)-2-oxoacetate 4a
shows a triplet at δ 1.40 for the 3 protons of a methyl group, singlet for the 3 protons of a methyl group at δ 2.62, a multiplet for the 2
protons of a methylene group at δ 4.42, a multiplet for an aromatic region proton at δ 7.3-7.5, a singlet for a –NH proton at δ 12.04. 13
C
NMR spectral data of the title compound 4a: The signals at around δ 9.70, 13.80 stand for methyl and δ 28.80 stands for methoxy,
while signals around δ 117.80–195.60 are attributed to all the aromatic carbons of compound 4a. Also, a distinctive signal at δ 60.80
stands for methylene carbon. The mass spectra of compound 4a show a molecular ion peak at 332.2 and calculated mass of compound
found to be 331.09. The IR spectrum of title compounds 4f–4i shows at 3427.85 cm-1 a peak for an amino group, at 1636.3 cm-1 a peak
for a ketone group, at 2922.59 cm-1 for an aromatic group, and at 1744.3 cm-1 for an ester group. The 1H NMR spectrum for ethyl 3-(4-
acetyl-3-methyl-5-(phenylamino)thiophen-2-yl)-3-oxopropanoate 4f shows at δ 1.29 a triplet for the 3 protons of a methyl group, at δ
2.6 a singlet for the 3 protons of a methyl group, at δ 2.82 a singlet for the 3 protons of a methyl group, at δ 3.8 a singlet for the 2
protons of a methylene group, at δ 4.25 a multiplet for the 2 protons of a methylene group, at δ 7.3-7.5 a multiplet for aromatic region
proton, and at δ 11.96 shows singlet for –NH proton. 13C NMR spectral data of the title compound 4f: The signals at around δ 9.78,
14.10 stand for methyl and δ 28.85 stands for methoxy, while signals around δ 117.80–195.60 are attributed to all the aromatic carbon
of compound 4f. Also, the distinctive signals δ 49.71 & 60.80 stand for methylene carbon. Mass spectra of compound 4f shows
molecular ion peak at 346.3 and calculated mass of compound found to be 345.10. The IR spectra of title compounds 4j–4n show peak
1
at 3436.53 cm-1 for the an amino group, at 1632.45 cm-1 for ketone group, and at 2927.41cm-1 for aromatic group. The H NMR
spectrum of di((4-acetyl-3-methyl-5-phenylamino)thiophen-2-yl)ketone 4j shows at δ 2.58 a singlet for the 6 protons of two methyl
groups, at δ 2.6 a singlet for the 6 protons of two methyl groups, at δ 7.2-7.4 a multiplet for an aromatic region proton, and at δ 12.11 a
singlet for two –NH protons. 13C NMR spectral data of the title compound 4j: The signal at around δ 9.72 stands for methyl and δ
28.82 stands for methoxy, while signals around δ 117.89–195.60 are attributed to all the aromatic carbons of compound 4j. Mass
spectra of compound 4j show a molecular ion peak at 489.3, and the calculated mass of the compound found to be 488.12.
3.2 Antimicrobial studies
All the synthesized compounds were analyzed for antimicrobial activity. The in vitro antibacterial and antifungal activity of the title
compounds was determined by the serial dilution method [11-14]. The minimum inhibitory concentration (MIC) is given in μg/mL.
Page 3 of 6

Samples of different concentrations (0-50 μg/mL) were prepared using dilutions of a 100 μg/mL stock solution, prepared by dissolving
the compounds in dimethyl sulfoxide and adjusting the volume to 100 mL. Under identical conditions, Azithromycin and Fluconazole
were tested as the reference standard drugs for bacteria and fungi respectively. Synthesized compounds were tested for activity against
two Gram-positive bacteria (Bacillus substilis, Staphylococcus aureus), two Gram-negative bacteria (Pseudomonas aeruginosa,
Escherchia coli), and two fungal strains (Candida albicans, Aspergillus niger). Specifications of the microorganisms are given in Table
1. The synthesized series showed excellent to good activity against Gram-negative bacteria (P. aeruginosa and E. coli) and the least
activity against Gram-positive bacteria (S. aureus and B. subtilis). All compounds of the series exhibited excellent to moderate
antifungal activity against Aspergillus niger and Candida albicans. Examination of the antimicrobial data (Table 2) revealed that
against Gram-positive bacteria Staphylococcus aureus, compounds 4a, 4c, and 4j were found to be equipotent to azithromycin.
Compounds 4d-4h and 4k have shown MIC values (1 μg/mL), indicating good antibacterial activity. Against the species Bacillus
subtilis, compound 4f shows more potency than standard azithromycin. The compounds 4d and 4e are equipotent to azithromycin.
Compounds 4a-c and 4g-k show moderate to good activity. Towards E. coli, compounds 4a-4n shows more potency than the standard.
Against Pseudomonas aeruginosa, compounds 4a-4d and 4f-4m shows more activity than standard azithromycin. All compounds show
moderate to minimal activity against fungi Candida Albicans and Aspergillus niger.
The structure–activity relationship study (SAR) indicates that a change in the substituent might also affect the antibacterial activity
of title compounds 4a–4n. Compounds having R=H/Cl appeared to have more potential against Gram-positive bacteria Staphylococcus
aureus, Gram-negative bacteria E. coli and Pseudomonas aeruginosa; and moderate potential against fungal pathogens Candida
albicans and Aspergillus niger. Compounds having R=CH3/OCH3 were found to be more active against Gram-positive Bacillus
subtilis, Gram-negative bacteria Escherichia coli, and Pseudomonas aeruginosa .
4. Conclusion
We have reported a one-pot synthesis of ethyl 2-(4-acetyl-3-methyl-5-(phenylamino)thiophen-2-yl)-2-oxoacetate derivatives 4a-4e,
ethyl 3-(4-acetyl-3-methyl-5-(phenylamino)thiophen-2-yl)-3-oxopropanoate derivatives 4f-4i, and di((4-acetyl-3-methyl-5-
phenylamino)thiophen-2-yl)ketone derivatives 4j-4n from readily available acetyl acetone 1, phenyl isothiocynates 2a-2e, and 2-
chloromethyl derivatives 3a-3c under mild conditions. The reaction is applicable to a wide range of starting materials. All the
synthesized compounds were evaluated for their antibacterial activities against S. aureus, B. subtilis, E. coli, P. aeruginosa, Candida
albicans, and Aspergillus niger microorganisms by the serial dilution method. The synthesized series showed excellent to good activity
against Gram-negative micro-organisms (P. aeruginosa and E. coli) and the least activity against Gram-positive bacteria (S. aureus
and B. subtilis). All compounds of the series exhibited moderate to less antifungal activity against Aspergillus niger and Candida
albicans.
Acknowledgments
The authors are thankful to the Dr. S. B. Jadhav Head, Dept of Pharmaceutical Chemistry, Modern College of Pharmacy Nigdi Pune-
44 & Mr. Dnyaneshwar D. Daware for providing necessary help during this work.
References
[1] A. Dömling, W. Wang, K. Wang, Chemistry and biology of multicomponent reactions, Chem. Rev. 112 (2012) 3083-3135.
[2] A. Dömling, Recent developments in isocyanide based multicomponent reactions in applied chemistry, Chem. Rev. 106 (2006) 17-89.
[3] F.M. Moghaddam, H.Z. Boinee, An efficient and facile one-step synthesis of highly substituted thiophenes, Tetrahedron 60 (2004) 6085-6089.
[4] K.I. Molvi, M. Mansuri, V. Sudarsanam, et al., Synthesis, anti-inflammatory, analgesic and antioxidant activities of some tetrasubstituted thiophenes,
J. Enzyme. Inhib. Med. Chem. 23 (2008) 829-838.
[5] M.K. Parai, G. Panda, V. Chaturvedi, Y.K. Manju, S. Sinha, Thiophene containing triarylmethanes as antitubercular agents, Bioorg. Med. Chem. Let.
18 (2008) 289-292.
[6] W. Wardakhan, O. Abdel-Salam, G. Elmegeed, Screening for antidepressant, sedative and analgesic activities of novel fused thiophene derivatives,
Acta. Pharm. 58 (2008) 1-14.
[7] S. Sharma, F. Athar, M.R. Maurya, A. Azam, Copper(II) complexes with substituted thiosemicarbazones of thiophene-2-carboxaldehyde: synthesis,
characterization and antiamoebic activity against E. histolytica, Eur. J. Med. Chem. 40 (2005) 1414-1419.
[8] O.F. William, Principles of Medicinal Chemistry, 3rd. ed., Lippincott Williams & Wilkins Publication, Philadelphia, 1989.
[9] A.A. Sagardoy, M.J. Gil, R. Villar, et al., Benzo[b]thiophene-6-carboxamide 1,1-dioxides: Inhibitors of human cancer cell growth at nanomolar
concentrations, Bioorg. Med. Chem. 18 (2010) 5701-5707.
[10] A.A. Fadda, E. Abdel-Latif, R.E. El-Mekawy, Synthesis and molluscicidal activity of some new thiophene, thiadiazole and pyrazole derivatives, Eur.
J. Med. Chem. 44 (2009) 1250-1256.
[11] Indian Pharmacopoeia, Microbiological assay of Antibiotics, vol. I, 2007, pp. 45-52.
[12] C.R. Kokare, Pharmaceutical Microbiology and Biotechnology, 3rd. ed., Nirali Prakashan, Pune, 2006, pp. 21.1-21.12.
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[14] Y.J. Huang, A. Dömling, The Gewald multicomponent reaction, Mol. Divers. 15 (2011) 3-33.
Page 4 of 6

O
Compd.
R1
Compd.
R1
O
Cl
4a
4c
O
Br
O
HN
H3C
S
4b
4e
H3CO
4d
O
O
3a
O
CH3
4a-4e
R1
NCS
O
O
O
O
O
R1
Cl
Cl
O
O
4f
O
O
4h
4i
O
O
S
HN
2
3b
H3CO
HN
SH
H3C
4g
K2CO3, DMF
1
4f-4i
R1
R1
R1
Cl
Cl
Cl
4j
4l
O
O
S
3c
H3C
H3CO
4k
4m
HN
S
NH
CH3
4n
O
O
4j-4n
R1
Scheme 1. The synthesis route for compounds 4a-4n.
Scheme 2. Possible reaction mechanism involved in formation of compounds 4a-4i.
Page 5 of 6

O
O
O
S
O
O
O
O
S
O
H
O
O
-S
NH
NH
DMF, K2CO3
NH
N
C
O
S
1
Cl
Cl
R1
R1
R1
2
R1
3c
O
O
O
O
S
O
O
O
O
O
O
S
-S
NH
HN
S
NH
HN
S
Cl
HN
Cl
O
O
O
R1
R1
R1
R1
R1
R1
O
O
H
O
O
O
S
O
H
N
OH
N
R1
H
S
S
- H2O
H
N
S
NH
S
Heat
H
HN
S
NH
R1
R1
O
O
O
HO
O
O
4j-4n
R1
R1
Scheme 3. Possible reaction mechanism involved in formation of compounds 4j-4n.
Table 1
Specification of microorganisms.
Sr. no.
1
Microorganism
Staphylococcus aureus
Nature
Gram-positive
NCIM no.
2079
ATCC no.
6538P
2
3
4
5
6
Bacillus subtilis
Escherichia coli
Pseudomonas aeruginosa
Candida Albicans
Aspergillus niger
Gram-positive
Gram-negative
Gram-negative
Fungus
2063
2065
2200
3471
545
6633
8739
9027
10231
9029
Fungus
Table 2
Minimum inhibitory concentration.
Compd.
Minimum inhibitory concentration (MIC) ( μg/mL )
Gram-positive bacteria
Gram-negative bacteria
Fungi
Staphylococcus
Bacillus
Escherichia coli
Pseudomonas
Candida
Aspergillus
aureus
0.1
9.5
0.5
1
1
1
1
subtilis
4.5
5
4
1
1
0.2
3
aeruginosa
4
4
3.5
0.6
7.5
0.6
2
albicans
1
2.5
*
*
*
2.5
*
niger
*
*
*
4.5
*
1
8.5
0.8
0.5
1
7.5
0.3
1
4a
4b
4c
4d
4e
4f
4g
*
1
9
7.5
3
4
10
*
*
*
1
-----
0.3
4
8
1
9.5
1
7.5
12.5
-----
0.3
2.5
4.5
0.3
0.3
0.2
7.5
6.25
-----
2.5
1
*
*
8
1
1
-----
0.25
7.5
*
*
1
9.5
9
*
-----
0.5
4h
4i
4j
4k
4l
4m
4n
0.1
1
4.5
4.5
*
Azithromycin
Fluconazole
0.1
-----
* Indicates microorganisms are resistant to the compounds up to 50 μg/mL
Page 6 of 6