Synthesis and anti-bacterial activities of a bis-chalcone derived from thiophene and its bis-cyclized products

Article abstract of DOI:10.3390/molecules16010523

A chalcone was prepared by the reaction of terephthalaldehyde with 3-acetyl-2,5-dimethylthiophene. Treatment of this chalcone with thiosemicarbazide/phenyl hydrazine/guanidine hydrochloride/thiourea afforded the corresponding pyrazoline, pyrazole, and pyr

Full text of DOI:10.3390/molecules16010523

Molecules 2011, 16, 523-531; doi:10.3390/molecules16010523
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Communication
Synthesis and Anti-Bacterial Activities of a Bis-Chalcone
Derived from Thiophene and Its Bis-Cyclized Products
Abdullah M. Asiri 1,2 and Salman A. Khan 1,*
1
Chemistry Department, Faculty of Science, King Abdul Aziz University, P.O. Box 80203, Jeddah
21589, Saudi Arabia
2
The Center of Excellence for Advanced Materials, King Abdul Aziz University, P.O. Box 80203,
Jeddah 21589, Saudi Arabia
* Author to whom correspondence should be addressed; E-Mail: sahmad_phd@yahoo.co.in.
Received: 26 December 2010 / Accepted: 10 January 2011 / Published: 12 January 2011
Abstract: A chalcone was prepared by the reaction of terephthalaldehyde with 3-acetyl-
2,5-dimethylthiophene. Treatment of this chalcone with thiosemicarbazide/phenyl
hydrazine/guanidine hydrochloride/thiourea afforded the corresponding pyrazoline,
pyrazole, and pyrimidine in good yields. All the new compounds have been characterized
1
13
by IR, H-NMR, C-NMR, GC-MS and elemental analyses. The anti-bacterial activity of
these compounds were first tested in vitro by the disk diffusion assay against two Gram-
positive and two Gram-negative bacteria, and then the minimum inhibitory concentration
(MIC) was determined with the reference of standard drug chloramphenicol. The results
showed that the pyrazoline derivative is better at inhibiting growth of both types of bacteria
(Gram-positive and Gram-negative) compared to chloramphenicol.
Keywords: chalcone; pyrazoline; pyrimidine; anti-bacterial activity; chloramphenicol
1. Introduction
α,β-Unsaturated ketones are biogenetic precursors of flavonoids in higher plants. Also known
chemically as chalcones, they consist of open-chain flavonoids in which the two aromatic rings are
joined by a three carbon chain [1]. They display a wide range of pharmacological properties, including
cytotoxity towards cancer cell lines [2,3], antimitotic [4], antimutagenic [5] and antitumor-promoting
activities; antibacterial [6], antiviral [7], anti-inflammatory [8], antiulcerative [9] and hepatoprotective

Molecules 2011, 16
524
activities [10]. They are also useful in materials science fields such as non-linear optics (NLO) [11],
optical limiting [12], electrochemical sensing [13], Langmuir films and photoinitiated polymerization
[14]. Various chalcone derivatives are notable materials for their second harmonic generation (SHG)
[15]. They are well known intermediates for synthesizing various heterocyclic compounds. Cyclization
of chalcones, leading to thiazines, pyrimidines, pyrazline has been a developing field within the realm
of heterocyclic chemistry for the past several years because of their ready accessibility and the broad
spectrum of biological activity of the products as antibacterial, antifungal, antiprotozoal, anti-
inflammatory substances. A survey of literature in the recent past reveals that some pyrazoline
derivatives possess antibacterial [16], anti-inflammatory [17], and antifungal effects [18]. Thiazine
derivatives play a vital role in many biological processes and in the synthesis of drugs [19]. Pyrimidine
derivatives occur in natural products like nucleic acids and vitamin B1 and they have remarkable
pharmaceutical importance because of their biological activity as anti HIV, antitubercular, and
antidiabetic compounds [20,21]. These observations led us to synthesize a new bis-chalcone and its
corresponding bis-pyrazoline, bis-pyrazole and bis-pyrimidines and an examination of their
antibacterial properties.
2. Results and Discussion
2.1. Chemistry
In the present work, the cyclization of a bis-chalcone into the corresponding bis-pyrazoline, bis-
pyrazole and bis-pyrimidine derivatives was accomplished by the reaction of the chalcone with
thiosemicarbazide /phenyl hydrazine/guanidine hydrochloride/thiourea [22-24]. The synthetic route to
the compounds is outlined in Scheme 1. The chemical structures of the synthesized compounds were
established by spectroscopic data (FT-IR, 1H-NMR, 13C-NMR, GC-MS) and elemental analyses.
The IR spectrum of compound 1.1 showed the characteristic band at 1,648 cm-1 which indicates the
presence of a –C=O group. The IR spectrum of compound 1.2 showed the characteristic bands at 1,578
cm-1 and 1,361 cm-1 which indicate the presence of –C=N and C=S groups. The IR spectrum of
compound 1.3 also showed characteristic bands at 1,657 cm-1 and 1,594 cm-1 which indicate the
presence of –C=C and C=N groups. The IR spectrum of compound 1.4 showed characteristic bands at
3,323 cm-1 and 1,566 cm-1 indicative of the presence of NH2 and C=N groups. The IR spectrum of
compound 1.5 showed characteristic bands at 1,134 cm-1 and 678 cm-1 which indicate the presence of
C-N and C-S groups.
The structures of the chalcone and its cyclized products were further confirmed by the
corresponding 1H-NMR spectra. The 1H-NMR spectrum of compound 1.1 showed two doublets at 7.20
ppm (J = 15.3 Hz) and 8.04 ppm (J = 15.3 Hz), indicating that the ethylene moiety in the enone
linkage is in a trans-conformation in the chalcone. The 1H-NMR spectrum of compound 1.2 showed a
–CH2 multiplet at 3.02-5.85 ppm confirming the cyclisation of the chalcone to give pyrazoline 1.2. The
1H-NMR spectrum of compound 1.3 showed a singlet at 6.50 ppm due to CH=C protons and no peak
in the 3.05 5.85 ppm range, which indicates the oxidation of the pyrazoline in the reaction and its
conversion to a pyrazole.

Molecules 2011, 16
Scheme 1. The synthesis of the chalcone and its cyclized products.
525
O
CH3
CHO
CHO
+
H3C
CH3
S
NaOH
EtOH
O
O
H3
C
CH3
CH3
H3
C
S
S
Compound no. 1.1
NH
(i)
NH2-NH-Ph
[O]
NH2-C-NH2. HCl
(ii)
S
S
H3
C
CH3
CH3
H3C
CH3
N
N
S
N
N
N
H3
C
CH3
N
N
N
S
N
H2
NH2
H3
C
S
Compound no. 1.3
Compound no. 1.4
NH2-C-NH-NH2
H2NCSNH2
S
H2
N
S
S
H3
C
CH3
CH3
N
N
CH3
H3C
S
CH3
H3
C
S
N
N
S
N
N
H3
C
NH2
N
N
HS
SH
Compound no. 1.5
Compond no. 1.2
The 1H-NMR spectrum of compound 1.4 showed a sharp singlet at δ 8.12 due to the NH2 protons,
and it also showed a sharp singlet at δ 7.13 due to HC=C, which confirmed the cyclization of the
1
chalcone into a pyrimidine ring. The H-NMR spectrum of compound 1.5 shows a sharp singlet at δ
3.37 due to the S-H protons, and also a sharp singlet at δ 7.23 due to HC=C, confirming the cyclisation
of the chalcone to give a pyrimidine ring. Finally, the 13C-NMR spectra of the chalcone and the
cyclized producta were recorded in DMSO-d6 and the spectral signals were in good agreement with the
13
proposed structures. Details of the C-NMR spectra of all compounds are given in the Experimental
Section. Characteristic molecular ion peaks were observed in the mass spectra of the chalcone and the
cyclized products. For example, the spectrum of compound 1.5 shows a molecular ion peak (M+.) at
m/z 520.
2.2. Pharmacology
The in vitro antibacterial activity tests were performed using the disk diffusion method and the
Minimum Inhibitory Concentration (MIC) method. Chloramphenicol was used as positive control for
bacteria. The compounds 1.1-1.5 were tested for their antibacterial activities by disc-diffusion method

Molecules 2011, 16
526
[25] using nutrient broth medium [containing (g/L): beef extract 3 g; peptone 5 g; pH 7.0]. The Gram-
positive bacteria and Gram-negative bacteria utilized in this study were S. aureus, S. pyogenes, S.
typhimurium and E. coli. In the disc-diffusion method, sterile paper discs (0.5 mm) impregnated with
compound dissolved in dimethylsulfoxide (DMSO) at a concentration of 100 μg/mL were used. Then,
the paper discs impregnated with the solution of the compound tested were placed on the surface of the
media inoculated with the microorganism. The plates were incubated at 35 °C for 24 h. The growth
inhibition zones after incubation are shown in Table 1. The chalcone and its cyclized products were
further checked by the MIC method. The results are presented in Table 2. Among the five compounds
the pyrazoline derivative showed better anti-bacterial activity than the control drug chloramphenicol.
The distinct differences in the antibacterial properties of these compounds further justify the purpose
of this study. The importance of this work lies in the possibility that the new compound might be more
efficacious drugs against bacteria and a more thorough investigation regarding the structure–activity
relationships, toxicity and in their biological effects could be helpful in designing more potent
antibacterial agents for therapeutic use.
Table 1. Antibacterial activity of the chalcone and its cyclized products, positive control
chloramphenicol and negative control (DMSO) measured by the Halo Zone Test
(unit, mm).
Corresponding effect on microorganisms
Compounds
S. aureus
12.5 ± 0.3
18.8 ± 0.5
13.6 ± 0.5
15.5 ± 0.4
16.2 ± 0.2
17.0 ± 0.5
-
S. pyogenes S. typhimurium
E. coli
12.2 ± 0.5
21.8 ± 0.4
14.5 ± 0.5
16.2 ± 0.5
16.8 ± 0.4
20.0 ± 0.2
-
1.1
1.2
1.3
1.4
1.5
11.6 ± 0.4
19.5 ± 0.4
13.2 ± 0.2
15.8± 0.5
16.6 ± 0.5
18.2 ± 0.4
-
11.8 ± 0.2
19.4 ± 0.4
14.2 ± 0.2
15.2 ± 0.4
15.8 ± 0.4
17.2 ± 0.8
-
Chloramphenicol
DMSO
Table 2. Minimum inhibition concentration (MIC) of the chalcone and its cyclized
products, positive control: chloramphenicol.
MIC (μg mL-1) Compounds
Bacterial Strain
1.1
128
128
128
512
1.2
32
1.3
128
64
1.4
32
1.5
64
64
32
64
Positive control
Staphylococcus aureus
Streptococcus pyogenes
Salmonella typhimurium
Escherichia coli
32
32
32
32
32
16
32
64
63
128
128
64
3. Experimental
3.1. General
All the chemicals and solvents used for this work were obtained from Merck (Germany) and the
Aldrich Chemical Company (U.S.A.). Melting points of the synthesized compounds were determined
in open-glass capillaries on a Stuart-SMP10 melting point apparatus and are uncorrected. IR
absorption spectra were recorded in the 4,000–400 cm-1 range on a Shimadzu FTIR-8400s using KBr
1
pellets, H-NMR and 13C-NMR spectra were recorded on a Bruker-AVANCE-III 600 MHz

Molecules 2011, 16
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spectrophotometer. The 1H-NMR and 13C-NMR chemical shifts are reported as parts per million (ppm)
downfield from TMS (Me4Si) used as an internal standard. The splitting patterns are designated as
follows; s, singlet; d, doublet; m, multiplet. Mass spectra were recorded on an GC-MS spectrometer.
IR, 1H-NMR, 13C-NMR and MS data were consistent with the assigned structures. Elemental analyses
(C, H, N) were done on a CHN Rapid analyzer. All the new compounds gave C, H and N analysis
within ±0.03% of the theoretical values. Purity of the compounds was checked by thin layer
chromatography (TLC) on Merck silica gel 60 F254 precoated sheets eluted with a
chloroform/methanol mixture and spots were developed using iodine vapours/ultraviolet light as
visualizing agent.
(2E,2'E)-3,3-(1,4-Phenylene)bis[1-(2,5-dimethyl-3-thienyl)prop-2-en-1-one] (1.1). A solution of
3-acetyl-2,5-dimethylthiophene (0.029 mol) and terephthalaldehyde (2 g, 0.014 mol) in an ethanolic
solution of NaOH (6 g in 10 mL of ethanol) was stirred for 20 h at room temperature. The solution was
poured into ice cold water of pH~2 (pH adjusted by HCl). The solid was separated and dissolved in
CH2Cl2, washed with saturated solution of NaHCO3 and evaporated to dryness. The residue was
purified by column chromatography using CH2Cl2 as eluent. Yield: 78%; m.p. 194-195 °C. Anal. calc.
for C24H22O2S2: C, 70.91, H, 5.41, S, 15.57, Found: C, 70. 86, H, 5.35, S, 15.52; GC-MS m/z (rel.
int.%): 407 (40) [M+1]+, 255 (70), 153 (45); IR (KBr) vmax cm-1: 3,050 (Ar-H), 2,914 (C-H), 1,648
1
(C=O), 1,585 (C=C); H-NMR (DMSO-d6) (δ/ppm): 7.71 (d, 2H, J = 15.6 Hz, C=CH), 7.30 (d, 2H,
J = 15.6 Hz, CO=CH), 7.64 (s, 4H, Ar-H), 7.09 (s, 2H, thiophene-H), 1.61 (s, CH3);13C-NMR (DMSO-
d6) (δ/ppm): 186.09, 147.77, 142.36, 136.77, 136.47, 135.46, 130.21, 125.76, 15.98, 15.07.
3.2. Synthesis of pyrazoline 1.2 from thiosemicarbazide
A mixture of bis-chalcone 1.1 (0.004 mol), thiosemicarbazide (0.009 mol) and NaOH (0.002 mol) in
dry ethanol (30 mL) was refluxed at 80 ºC for 12 h. The progress of reaction was monitored by TLC.
After the completion of reaction, the reaction mixture was poured into acidic ice water (~ pH 2,
adjusted by HCl). The solid was filtered off and the residue was purified by column chromatography
(20:80, diethyl ether-petroleum ether). The obtained solid was crystallized from ethanol. Yield: 72.6%;
m.p. 236 °C; Anal. calc. for C26H28N6S4: C, 56.49, H, 5.11, N, 15.20, Found: 56.45, H, 5.09, N. 15.18;
GC-MS m/z (rel. int.%): 554 (40) [M+1]+; IR (KBr) vmax cm-1: 3,436 (NH), 3,253 (Ar-H), 2,960 (C-H),
1
1,578 (HC=N), 1,361 (C=S), 1,092 (C-N); H-NMR (DMSO-d6) (δ/ppm): 7.98 (s, 4H, NH2), 7.51 (s,
4H, Ar-H), 7.07 (s, 2H, thiophene-H), 5.85 (dd, 2H, Hx, JXA = 3.0 Hz, JXB = 3.6 Hz), 3.90 (dd, 2H, HA,
JAB = 3.0 Hz, JAX = 3.6 Hz), 3.02 (dd, 2H, HB, JBA = 3.0 Hz, JBX = 3.6 Hz), 2.55 (s, CH3), 2.46 (s,
CH3);13C- NMR (DMSO-d6) (δ/ppm): 175.46 (C=S), 152.39 (C=N), 141.32, 135.17, 127.70, 126.38,
125.39 (Ar-C), 61.60 (CH), 44.39 (CH2), 15.42 15.41 (CH3).
3.3. Synthesis of pyrazole 1.3 from phenyl hydrazine
Bis-Chalcone 1.1 (0.004 mol) was refluxed with phenyl hydrazine (0.009 mol) in dry EtOH
(20 mL) and a catalytic amount of glacial acetic acid at 80 ºC for 8 h. The progress of the reaction was
monitored by TLC. After completion of the reaction, the solvent was removed under reduced pressure
and the residue was purified by column chromatography (20:80, diethyl ether-petroleum ether). The

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obtained solid was crystallized from ethanol. Yield: 88.5%; m.p. 134 °C; Anal. calc. for C36H30N4S2:
C, 74.19, H, 5.19, N, 9.61, Found: C, 74.15, H, 5.16, N, 10.97; GC-MS m/z (rel. int.%): 584 (72)
[M+1]+; IR (KBr) vmax cm-1: 3,258 (Ar-H), 2,956 (C-H), 1,657 (C=C), 1,594 (HC=N), 1,003 (C-N);
1H-NMR (DMSO-d6) (δ/ppm): 7. 29 (m, 10H, Ar-H), 7.22 (s, 2H, thiophene-H), 6.50 (s, 2H, C=CH),
7.28 (s, 4H, Ar-H), 2.50 (s, CH3), 2.24 (s, CH3);13C-NMR (DMSO-d6) (δ/ppm): 147, 146, 144, 143,
138, 136, 131, 129, 128, 126, 125, 121, 113, 112, 112, 15.38, 13.90.
3.4. Synthesis of pyrimidine 1.4 from guanidine hydrochloride
A mixture of chalcone 1.1 (0.004 mol), guanidine hydrochloride (0.009 mol) and sodium methoxide
(0.004 mol) in DMF (15 mL) was refluxed at 80 °C for 30 h. The progress of reaction was monitored
by TLC. After the completion of reaction, the reaction mixture was poured into ice water to give a
precipitated solid that was filtered off. The residue was purified by column chromatography (40:50,
diethyl ether-petroleum ether) and the obtained solid was crystallized from ethanol. Yield: 79.52%;
m.p. 123 °C; Anal. calc. for C26H24N6S2: C, 64.44, H, 4.99, N, 17.34, Found: C, 64.41, H, 4.96, N,
17.29; GC-MS m/z (rel. int.%): 486 (56) [M+1]+; IR (KBr) vmax cm-1: 3,323 (NH2), 2,919 (C-H), 1,566
1
(C=N); H-NMR (DMSO-d6) (δ/ppm): 8.12 (s, 4H, NH2), 7.26 (s, 4H, Ar-H), 7.13 (s, 2H, Ar-Pym),
7.04 (s, 2H, thiophene-H), 2.45 (s, CH3), 2.17 (s, CH3);13C-NMR (DMSO-d6) (δ/ppm): 139.49 (C=N),
139.49, 136.05, 135.20, 128.86, 127.18, 126.05, 125.32. 141.32, 135.17, 127.70, 126.38, 125.39 (Ar-
C), 15.25 15.01 (CH3).
3.5. Synthesis of pyrimidine 1.5 from thiourea
A mixture of chalcone (0.004 mol), and thiourea (0.009 mol) in DMF (15 mL) was refluxed at
80 °C for 12 h in the presence of few drops of HCl. The progress of the reaction was monitored by
TLC. After the completion of reaction, the reaction mixture was poured into ice water to give a
precipitate that was filtered off and purified by column chromatography (40:50, diethyl ether-
petroleum ether). The solid obtained was crystallized from ethanol. Yield: 77.6%; m.p. 166 °C; Anal.
calc. for C26H22N4S4: C, 60.20, H, 4.27, N, 10.80, Found: C, 60.17, H, 4.23, N, 10.76; GC-MS m/z (rel.
int.%): 520 (56) [M+1]+; IR (KBr) vmax cm-1: 2,960 (Ar-H), 1,651 (C=C), 1,590 (C=N), 1,134 (C-N),
1
678 (C-S); H-NMR (DMSO-d6) (δ/ppm): 7.75 (dd, 2H, Ar-H), 7.58 (dd, 2H, Ar-H), 7.51 (s, 2H,
thiophene-H), 7.23 (s, 2H, Ar-Pym) 3.37 (s, 2H, SH), 2.58 (s, CH3), 2.36 (s, CH3); 13C-NMR (DMSO-
d6) (δ/ppm): 184.93 (SH-C=N), 149.70, 145.61, 144.21, 142.80, 136.21, 134.74 (Ar-C), 14.57,
14.47 (CH3).
3.6. Organism culture and in vitro screening
Anti-bacterial activity was tested by the disk diffusion method with minor modifications. S. aureus,
S. pyogenes, S. typhimurium and E. coli were subcultured in BHI medium and incubated for 18 h at
37 °C, and then the bacterial cells were suspended, according to the McFarland protocol, in saline
solution to produce a suspension of about 10-5 CFU mL-1: 10 μL of this suspension was mixed with
10 mL of sterile antibiotic agar at 40 ºC and poured onto an agar plate in a laminar flow cabinet. Five
paper disks (6.0 mm diameter) were fixed onto the nutrient agar plate. One mg of each test compound
was dissolved in 100 μL DMSO to prepare stock solution from stock solution different concentration

Molecules 2011, 16
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10, 20, 25, 50, and 100 μg/μL of each test compound were prepared. These compounds of different
concentration were poured over disk plate on to it. Chloramphenicol (30 μg/disk) was used as standard
drug (positive control). A DMSO poured disk was used as negative control. The susceptibility of the
bacteria to the test compounds was determined by the formation of an inhibitory zone after 18 h of
incubation at 36 °C. Table 1 reports the inhibition zones (mm) of each compound and the controls.
The minimum inhibitory concentration (MIC) was evaluated by the macro dilution test using standard
inoculums of 10-5 CFL mL-1. Serial dilutions of the test compounds, previously dissolved in dimethyl
sulfoxide (DMSO) were prepared to final concentrations of 512, 256, 128, 64, 32, 16, 8, 4, 2 and
1 μg/mL. To each tube was added 100 μL of a 24 h old inoculum. The MIC, defined as the lowest
concentration of the test compound which inhibits the visible growth after 18 h, was determined
visually after incubation for 18 h, at 37 °C, and the results are presented in Table 2. Tests using
DMSO and chloramphenicol as negative and positive controls were also perfomed.
4. Conclusions
A chalcone was prepared by the reaction of terephthalaldehyde with 3-acetyl-2,5-dimethyl-
thiophene. Treatment of this chalcone with thiosemicarbazide/phenyl hydrazine/guanidine
hydrochloride/thiourea afforded the corresponding pyrazoline, pyrazole and pyrimidine in good yields.
The anti-bacterial activity of these compounds was examined using bacterial cultures and the results
showed that the pyrazoline and pyrimidine showed increased antibacterial activity. Among the five
compounds the pyrazoline derivative showed better anti-bacterial activity than the control
drug chloramphenicol.
Acknowledgements
The authors would like to thank the Deanship of Scientific Research at king Abdul Aziz University for
the financial support of this work via Grant No. (3-045/430).
.
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