Microwave-assisted solvent-free synthesis of biologically active novel heterocycles from 3-formylchromones

Article abstract of DOI:10.1007/s00044-010-9386-2

A series of novel chromone derivatives have been synthesized employing 3-formylchromones and 5-acetyl-1,3-dimethylbarbituric acid as starting materials both under conventional heating method and microwave irradiation technique in good yields. The synthesized compounds were screened in vitro antibacterial activity against the representative panel of two Gram-positive bacteria and two Gram-negative bacteria. The synthesized compounds were also tested for their inhibitory action against three strains of fungus. The various compounds show potent inhibitory action against test organisms. Springer Science+Business Media, LLC 2010.

Full text of DOI:10.1007/s00044-010-9386-2

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2011) 20:1473–1481
DOI 10.1007/s00044-010-9386-2
ORIGINAL RESEARCH
Microwave-assisted solvent-free synthesis of biologically active
novel heterocycles from 3-formylchromones
•
T. N. Mohammed Musthafa Zeba N. Siddiqui
•
•
Fohad M. Husain Iqbal Ahmad
Received: 23 February 2010 / Accepted: 5 July 2010 / Published online: 20 July 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A series of novel chromone derivatives have
been synthesized employing 3-formylchromones and
5-acetyl-1,3-dimethylbarbituric acid as starting materials
both under conventional heating method and microwave
irradiation technique in good yields. The synthesized
compounds were screened in vitro antibacterial activity
against the representative panel of two Gram-positive
bacteria and two Gram-negative bacteria. The synthesized
compounds were also tested for their inhibitory action
against three strains of fungus. The various compounds
show potent inhibitory action against test organisms.
vast array of oxygen containing compounds ubiquitous in
plants (Barton and Ollis, 1979). They form basic nucleus of
flavones and have been recognized as the essential com-
ponent of phamacophores of a large number of bioactive
molecules (Dewick, 1994; Hansch et al., 1990). Molecules
containing chromone structure possess a myriad of bio-
logical activities ranging from antifungal (Prakash et al.,
2008), antioxidant (Kuroda et al., 2009), neuroprotective
(Larget et al., 2000), HIV-inhibitory (Yu et al., 2004),
antibacterial (Deng et al., 2000) to anticancer (Valenti et al.,
2000) activities. Chromone derivatives are also active at
benzodiazepine receptors and on lipoxygenases and cyclo-
oxygenases (Horton et al., 2003). It was also sited in the
literature that Hormothamnione, a naturally occurring sty-
rylchromone isolated from the blue green algae, Hor-
mothamnione enteromophoides has potent cytotoxicity to
P-388 lymophocytic leukaemia and HL-60 human promy-
elocytic leukaemia cells (Alonso and Brossi, 1988; Grazul
and Budzisz, 2009). Chalcones, the flavanoid and isoflav-
anoid precursors, display a wide spectrum of biological
activities including antioxidant (Stevens et al., 2003; Vogel
et al., 2008), antibacterial (Sugamoto et al., 2008; Avila
et al., 2008), antimalarial, antileishmanial (Liu et al., 2003;
Quintin et al., 2009; Suryawanshi et al., 2008), anticancer
(Lawrence et al., 2006), antiangiogenic (Mojzis et al.,
2008), anti-infective, anti-inflammatory (Nowaskowska,
2007; Cheng et al., 2008), antifungal (Lahtchev et al.,
2008), nitric oxide inhibition (Rojas et al., 2002), tyrosinase
inhibition (Nerya et al., 2004), etc. It is also worth men-
tioning that the derivatives of chalcones particularly pyr-
azoline nucleus forms the core structure of many drugs and
have been reported to possess widespread biological
activities (Chimenti et al., 2005; Khode et al., 2009).
In view of variety of pharmacological properties
exhibited by chromones, chalcones and its derivatives, we
Keywords 3-Formylchromone ꢀ 5-Acetyl-1,
3-dimethylbarbituric acid ꢀ Microwave irradiation ꢀ
Antibacterial activity ꢀ Antifungal activity
Introduction
Development of new antibacterial agents with novel
structure and mode of action remains the primary goal of
scientists for the solution of increasing bacterial resistance
gained by microorganism to classical antibacterial agents
(Moneer et al., 2002). Chalcones and their derivatives are
an attractive molecular scaffold for the search of new
biologically active molecules. Also, chromones comprise a
T. N. Mohammed Musthafa (&) ꢀ Z. N. Siddiqui
Department of Chemistry, Aligarh Muslim University,
Aligarh 202002, India
e-mail: karamusth@yahoo.com
F. M. Husain ꢀ I. Ahmad
Department of Agricultural Microbiology, Aligarh
Muslim University, Aligarh 202002, India
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Med Chem Res (2011) 20:1473–1481
were prompted to undertake synthesis of chromonyl chal-
cones and conversion to other heterocycles like
pyrazolines, pyrazoles, dibromoderivatives and dihydro-
pyrimidines, which may show different or better physio-
logical activities.
Table 1 Synthesis of compounds 3a–7 under thermal heating and
Microwave irradiation
Entry Product Conventional heating
method
Microwave
irradiationa
Time
Yield (%)b Time
Yield (%)b
1
3a
3b
4a
4b
4c
4d
4e
5
7 h
78
79
74
74
63
65
75
76
6 min 88
6 min 88
3 min 94
3 min 92
7 min 86
6 min 86
9 min 89
7 min 92
2
7.5 h
1 h
Results and discussion
3
4
1 h
Chemistry
5
11 h
10.5 h
12 h
14 h
6
Microwave-assisted organic reaction enhancement (MORE)
is now a days a well-established technique for the synthesis
of various heterocycles particularly from the viewpoint of
green Chemistry. The e-Chemistry technique gives spec-
tacular results viz-shorter reaction time, experimental
simplicity, selectivity of products and easy work up, etc.
(Kappe and Dallinger, 2009; Varma, 1999). It was found
that 3-formyl chromone has emerged as a valuable synthon
for incorporation of chromone moiety into a number of
molecular frameworks, which forms important component
of pharmacophores of a number of biologically active
molecules of synthetic as well as natural origin (Raj et al.,
2008). To the best of our knowledge, no reports have so far
made in the synthesis of chromonyl chalcones and its
derivatives under microwave irradiation. This inspired us
to go with these reactions. Due to exceptional reactivity of
formyl group in 3-formylchromone, as well as the versatile
biological activities of chromone and barbituric acid
derivatives (Aboul and Wainer, 1997), two chromonyl
chalcones 3a–b were synthesized by employing 3-form-
ylchromones 1a–b and 5-acetyl-1,3-dimethylbarbituric
acid 2 in the presence of mild base both under conventional
heating and microwave irradiation method. The chalcones
3a–b were synthesized in the presence of pyridine using
ethanol as a solvent in conventional method, which took
longer period for completion of reaction (7–7.5 h) with
yields (78–79%) (Table 1). The reactions when carried out
under microwave irradiation were completed within 6 min
with substantial increase in yield of products (88%).
Moreover, the reaction generated (E)-isomer only. The
infrared (IR) spectrum of 3a exhibited chromone and bar-
7
8
9
6a
6b
7
20 min (RT) 82
20 min (RT) 80
–
–
–
–
10
11
a
28 h (RT)
78
3 min 90
Microwave equipment multimode with full power was used
b
All yields refer to isolated products
Condensation of a,b unsaturated ketone with nitrogen
bases gives the corresponding pyrazolines (Wiley and
Jarboe, 1967). Thus, the compounds 3a–b when treated
with variously substituted hydrazines under conventional
heating procedure using glacial acetic acid and catalytic
amount of sodium acetate afforded the products 4a–e in
63–75% yield in a span of time period (1–12 h)
(Scheme 1). However, microwave irradiation technique
when applied increased yields of the products (86–94%)
within shorter period of time (3–9 min) even in the absence
of catalyst (Table 1). The IR spectrum of 4a displayed a
broad band at 3285 cm-1 due to the presence of NH group
of pyrazoline moiety. The absorption bands for barbituric
acid and chromone carbonyl groups were present in the
region 1698 and 1649 cm-1, respectively. The H NMR
1
spectrum of the compound showed the diagnostic singlet of
C-2 olefinic proton of the chromone moiety at d 8.20,
which clearly indicated that the pyrone moiety in the
compound didn’t suffer ring cleavage by the attack of
nitrogen base (Kostka, 1973). This fact was further sup-
ported by the presence of doublet of doublet of C-5 proton
appeared at d 8.14. The remaining three aromatic protons
of chromone nucleus appeared as multiplet at d 7.42–7.76.
The presence of pyrazoline unit was established by three
doublet of doublet at d 3.66 (Hd), 4.01 (He) and 4.87 (Hc).
A sharp singlet at d 3.36 integrating for six protons was
assigned to two N–CH3 groups. The Mass spectrum of the
compound showed M? at m/z 368.
bituric acid carbonyl groups at 1657 and 1719 cm-1
,
respectively. The 1H NMR spectrum showed trans olefinic
protons Ha and Hb as ortho-coupled doublets at d 9.26
(J = 15.7 Hz) and 7.84 (J = 15.7 Hz), respectively. The
N–CH3 protons of barbituric acid moiety were present as
two sharp singlets at d 3.37 and 3.39. The three aromatic
protons of chromone moiety were discernible in the form
of multiplet at d 7.49–7.76 whereas C-2 and C-5 protons
appeared as a singlet and doublet of doublet at d 8.39 and
8.32, respectively. Further, the structure was confirmed by
mass spectrum, which showed M? at m/z 354.
Due to the remarkable pharmacological activities exhib-
ited by dihydropyrimidine derivatives (Pani et al., 2009),
attempts were also made to synthesize dihydropyrimidine
derivative of chalcone by reacting 3a with urea in the
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Med Chem Res (2011) 20:1473–1481
1475
Scheme 1 Synthesis of
compounds 3a–5
O
O
O
O
Ha
Ethanol /Pyridine
Reflux
O
R
5
8
4
H
R
H3C
C
Q
6
3
or MW
Q
+
O
2
7
Hb
O
2
O
1a-b
1
3a-b
a=R=H
b=R=CH3
a=R=H
b=R=CH3
CH3
N
Q=
O
N
O
CH3
R1
N
N
O
O
R
Aceticacid / NaOAc
Reflux
Q
R1NHNH2
3a-b
+
H
cHe
Hd
or MW
4a-e
R
H
CH3
H
CH3
H
R1
H
H
C6H5
4a
4b
4c
4d
4e
C6H5 N
S
O
HN
N
O
O
O
R
Ethanol / NaOH
Reflux
Q
H2N
C
NH2
3a
+
Hc
He
or MW
Hd
4
5
R=H
presence of NaOH in ethanol under thermal heating
method and solvent free conditions (Scheme 1). The
reaction mixture as visualized afforded 5 in quantitative
yield (Table 1). The presence of dihydropyrimidine
nucleus in 5 was established on the basis of 1H NMR
spectrum which showed two doublet of doublet at d 3.20
(Hd), and 4.88 (Hc) whereas, the He proton at d 3.42 is
merged with two N–CH3 protons of barbituric acid moiety.
A broad singlet (D2O exchangeable) at d 14.12 was
assigned to OH proton. The other prominent peaks as
obtained are mentioned in the experimental part.
heterochalcones 3a–b with Br2 in chloroform at room
temperature afforded 2,3-dibromodihydrochalcones 6a–b
1
in quantitative yields. The H NMR spectrum of the 6a
showed two doublets attributable to Ha and Hb protons at d
5.56 and 7.76 with coupling constant of 11.3 Hz, which
was in accordance to the erythro configuration. The other
prominent peaks are given in the experimental part. Fur-
ther, 6a was converted to pyrazole derivative 7 in dry
pyridine at room temperature and in solvent-free condition.
The compound showed a sharp singlet at d 7.94 due to Hc
1
proton of pyrazole moiety in its H NMR spectrum. A
a,b-Dibromodihydrochalcones are interesting interme-
diates for the synthesis of various biologically active het-
erocycles such as pyrazoles, pyrazolines and pyrimidines.
(Joshi and Wadodkar, 1981; Abdel-Rahman et al., 2007).
On the basis of these findings, bromination of heterochal-
cones was also attempted (Scheme 2). Thus, the reaction of
broad singlet at d 10.31 was assigned to NH proton.
Biology
All the newly synthesized compounds were screened in
vitro antibacterial activity against an assortment of two
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Med Chem Res (2011) 20:1473–1481
Scheme 2 Synthesis of
compounds 6a–7
O
O
Br
O
O
Hb
R
R
Q
Q
Br2 / CHCl3
R.T
Ha
Br
O
O
6a-b
3a-b
a=R=H
b=R=CH3
a=R=H
b=R=CH3
N
HN
O
O
R
Q
PyrIdine / RT
or MW
+
NH2NH2
6a
Hc
7
R=H
Gram-positive bacteria, Staphylococcus aureus SA 22,
Bacillus subtilis MTCC 121, and two Gram-negative bac-
teria, Escherichia coli K12, Salmonella typhimurium
MTCC 98, in vitro antifungal activity was tested against
three fungal strains, Candida albicans IOA-109, Asper-
gillus niger (laboratory isolate) and Aspergillus fumigatus
(laboratory isolate). The minimum inhibitory concentra-
tions (MIC) of the tested compounds were 100 lg/ml. The
newly generated compounds 3a–7 exerted significant
inhibitory activity against the growth of the tested bacterial
and fungal strains. The data (Table 2) reveal that com-
pounds have significant influence on antibacterial profile of
Gram-positive bacteria. The compounds also showed
moderate to good inhibitory results against Gram-negative
bacteria viz S. typhimurium and E. coli. Among the tested
compounds, chalcones 3a and 3b showed more potent
inhibitory activity against both types of bacteria. However,
derivatives of chalcones exerted varying inhibitory action.
Further antifungal screening revealed that the compounds
3a–7 exhibited moderate to good inhibition to C. albicans
and lesser inhibition against A. niger and A. fumigatus.
Experimental
Melting points were taken in Riechert Thermover instru-
ment and are uncorrected. The IR spectra were recorded on
Perkin Elmer RXI spectrometer in KBr, 1H NMR on
Bruker DRX-300 and Bruker Avance II 400 spectrometer
using tetramethyl silane (TMS) as the internal standard and
DMSO-d6/CDCl3 as solvent. Mass spectra were obtained
on Jeol-SX-102 (FAB) spectrometer. The microanalyti-
cal data were collected on Elementar vario EL III
elemental analyzer. 3-Formylchromone, substituted-3-for-
mylchromone (Nohara et al., 1974), 5-acetyl-1,3-dimeth-
ylbarbituric acid (Jursic and Neumann, 2001) and
hydrazinobenzothiazole (Singh et al., 1990) were synthe-
sized by reported methods. All other chemicals used were
purchased from Merck (Mumbai, India) and Fluka Chem-
icals (Switzerland). The purity of the compounds was
checked by thin layer chromatography (TLC) on glass
plates coated with silica gel G254 (Merck, Mumbai, India)
using chloroform–methanol (3:1) mixture as mobile phase
and visualized by iodine vapours. All the experiments
under microwave irradiation were carried out in an
unmodified domestic microwave oven (National, Model
NN-S557WF, 1.3 KW, 2450 MHz).
Conclusion
In summary, we have described the synthesis of hitherto
unknown 3-substituted chromone derivatives from readily
synthesized starting materials, available reagents along
with short reaction time, simple workup and isolation, etc.,
under green reaction conditions, make the current method
feasible and attractive protocol for generation of novel
heterocycles. The antimicrobial activity of compounds
showed that various compounds are potent antimicrobial
agents.
Preparation of chalcones under thermal heating
conditions
To a well stirred solution of 5-acetyl-1,3-dimethylbarbitu-
ric acid (5.05 mmol) in ethanol (25 ml) containing pyridine
(0.5 ml) 3-formylchromone/substituted-3-formylchromone
was added (5.05 mmol). The reaction mixture was then
refluxed in a heating mantle for 7–7.5 h, cooled at room
temperature. The bright yellow solid thus obtained was
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Med Chem Res (2011) 20:1473–1481
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Table 2 In vitro antibacterial and antifungal activity of compounds 3a–7
Compounds
Gram positive
Gram negative
Fungal species
S. aureus
B. subtilis
E. coli
S. typhimurium
C. albicans
A. niger
A. fumigatus
Diameter of inhibition zone in mm at 100 lg/ml
3a
15
12
16
11
–
20
16
13
13
–
20
20
15
12
8
16
12
12
10
12
19
9
16
12
14
17
15
15
14
–
8
10
14
14
10
12
–
3b
12
8
4a
4b
–
4c
–
4d
–
–
–
–
4e
13
8
10
–
18
15
14
15
12
25
–
14
–
–
5
11
16
10
12
20
–
–
6a
8
–
15
17
–
–
–
6b
12
14
26
–
–
–
–
7
12
24
–
–
–
Chloramphenicol
Nystatin
–
–
–
20
–
18
–
18
–
DMSO
–
–
–
–
–, No activity detected
(2E)-1-(1,3-Dimethyl-2,4,6-pyrimidinetrione-5-yl)-3-(6-
methyl-4-oxo-4H-1-benzopyran-3-yl)-2-propene-1-one (3b)
filtered, washed with water, alcohol and dried to afford
3a–b.
Purified by recrystallisation from chloroform. Bright yel-
low crystals; m.p., [300°C. Anal. Calcd. for C19H16N2O6
(%): C 61.95, H 4.38, N 7.61. Found (%): C 61.86, H 4.27,
N 7.58. tmax/cm-1 (KBr): 1666 (C=O, chromone), 1716
(C=O, barbituric acid). 1H NMR (CDCl3, 400 MHz): d
2.48 (s, 3H, CH3), 3.38 (s, 3H, N–CH3), 3.40 (s, 3H,
N–CH3), 7.31-7.46 (m, 3H, Ar–H), 7.87 (d, 1H, J = 16.3 Hz,
Hb), 8.27 (s, 1H, C-2), 9.18 (d, 1H, J = 15.8 Hz, Ha). MS
(% rel int) m/z 368 (M?, 30), 367 (10).
Preparation of chalcones under microwave irradiation
conditions
3-Formylchromone/substituted-3-formylchromone (5.05
mmol), 5-acetyl-1,3-dimethylbarbituric acid (5.05 mmol)
and pyridine (0.3 ml) were mixed thoroughly in a mortar,
and air dried. The reaction mixture was then transferred to
an open Pyrex beaker and subjected to microwave irradi-
ation (multimode, full power). The progress of reaction
was monitored by TLC and on completion, the reaction
mixture was slurred in water (40 ml). The solid thus
obtained was filtered, washed with water, alcohol and dried
to afford 3a–b.
Preparation of pyrazolines under thermal heating
conditions
The mixture of 3a–b (2.52 mmol), hydrazine hydrate
(2.52 mmol)/phenylhydrazine (2.52 mmol)/hydrazinobenzo-
thiazole (2.52 mmol) and sodium acetate (0.7 mmol) was
refluxedin10 mlofaceticacidfor1–12 h.Aftercompletionof
the reaction (checked by TLC), the reaction mixture was
cooled and the solid precipitated out was filtered, washed with
water, acetone and dried to afford 4a–e.
(2E)-1-(1,3-Dimethyl-2,4,6-pyrimidinetrione-5-yl)-3-
(4-oxo-4H-1-benzopyran-3-yl)-2-propene-1-one (3a)
Purified by recrystallisation from chloroform. Bright yel-
low crystals; m.p., [300°C. Anal. Calcd. for C18H14N2O6
(%): C 61.02, H 3.98, N 7.91. Found (%): C 61.05, H 3.83,
N 7.84. tmax/cm-1 (KBr): 1657 (C=O, chromone), 1719
(C=O, barbituric acid). 1H NMR (CDCl3, 400 MHz): d
3.37 (s, 3H, N–CH3), 3.39 (s, 3H, N–CH3), 7.49-7.76
(m, 3H, Ar–H), 7.84 (d, 1H, J = 15.7 Hz, Hb), 8.32 (dd,
1H, C-5), 8.39 (s, 1H, C-2), 9.26 (d, 1H, J = 15.7 Hz, Ha).
MS (% rel int) m/z 354 (M?, 80), 353 (60), 336 (30).
Preparation of pyrazolines under microwave irradiation
conditions
The mixture of 3a–b (2.52 mmol) and hydrazine hydrate
(2.52 mmol)/phenylhydrazine (2.52 mmol)/hydrazinobenzo-
thiazole (2.52 mmol) were mixed thoroughly in a mortar
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Med Chem Res (2011) 20:1473–1481
1-Phenyl-3-(1,3-dimethyl-2,4,6-pyrimidinetrione-5-yl)-5-
(6-methyl-4-oxo-4H-1-benzopyran-3-yl)pyrazoline (4d)
and air dried. The reaction mixture was then transferred to
an open Pyrex beaker and subjected to microwave irradi-
ation (multimode, full power). The progress of reaction
was monitored by TLC and on completion, the reaction
mixture was slurred in water (25 ml). The solid obtained
was filtered, washed with water, alcohol and dried to get
4a–e.
Purified by recrystallisation from coloumn chromatography
using benzene-ethylacetate (3:1 v/v) as eluent. Pale yellow
crystals; m.p., 247°C (dec). Anal. Calcd. for C25H22N4O5
(%): C 65.49, H 4.84, N 12.22. Found (%): C 65.42, H
4.93, N 12.16. tmax/cm-1 (KBr): 1622 (C=O, chromone),
1712 (C=O, barbituric acid). 1H NMR (CDCl3, 400 MHz):
d 2.25 (s, 3H, CH3), 3.37 (s, 6H, 2N–CH3), 3.70 (dd, 1H,
J = 18.6 Hz, 7.9 Hz, Hd), 4.20 (dd, 1H, J = 18.4 Hz,
9.9 Hz, He), 4.45 (dd, 1H, J = 10.0 Hz, 7.9 Hz, Hc),
7.10–7.58 (m, 8H, Ar–H), 8.27 (s, 1H, C-2). MS (% rel int)
m/z 458 (M?, 75), 457 (50).
3-(1,3-Dimethyl-2,4,6-pyrimidinetrione-5-yl)-5-(4-oxo-4H-
1-benzopyran-3-yl)pyrazoline (4a)
Purified by recrystallisation from ethanol–DMF (3:2 v/v).
White solid; m.p., [300°C. Anal. Calcd. for C18H16N4O5
(%): C 58.69, H 4.38, N 15.21. Found (%): C 58.54, H
4.43, N 15.12. tmax/cm-1 (KBr): 1649 (C=O, chromone),
1
1698 (C=O, barbituric acid), 3285 (N–H, pyrazolinyl). H
1-Benzothiazolyl-3-(1,3-dimethyl-2,4,6-pyrimidinetrione-
5-yl)-5-(4-oxo-4H-1-benzopyran-3-yl)pyrazoline (4e)
NMR (DMSO-d6, 400 MHz): d 3.36 (s, 6H, 2N–CH3), 3.66
(dd, 1H, J = 19.0 Hz, 6.0 Hz, Hd), 4.01 (dd, 1H,
J = 18.9 Hz, 9.8 Hz, He), 4.87 (dd, 1H, J = 9.7 Hz,
6.0 Hz, Hc), 7.42–7.76 (m, 3H, Ar–H), 8.14 (dd, 1H,
J = 8.0 Hz, 1.4 Hz, C-5), 8.20 (s, 1H, C-2). MS (% rel int)
m/z 368 (M?, 55), 367 (40).
Purified by recrystallisation from chlorofom-methanol (3:2
v/v). Brown crystals; m.p., 291°C (dec). Anal. Calcd. for
C25H19N5O5S (%): C 59.87, H 3.82, N 13.96. Found (%): C
59.81, H 3.88, N 13.84. tmax/cm-1 (KBr): 1647 (C=O,
chromone), 1709 (C=O, barbituric acid). 1H NMR (CDCl3,
400 MHz): d 3.37 (s, 6H, 2N–CH3), 4.02 (dd, 1H,
J = 19.3 Hz, 4.8 Hz, Hd) 4.24 (dd, 1H, J = 19.2 Hz
10.6 Hz, He), 5.57 (dd, 1H, J = 10.6 Hz, 4.7 Hz, Hc),
7.18–7.94 (m, 7H, Ar–H), 8.15 (dd,1H, J = 8.0 Hz,
1.6 Hz, C-5), 8.41 (s, 1H, C-2). MS (% rel int) m/z 502
(M?, 40), 501 (20), 354 (30).
3-(1,3-Dimethyl-2,4,6-pyrimidinetrione-5-yl)-5-(6-methyl-
4-oxo-4H-1-benzopyran-3-yl)pyrazoline (4b)
Purified by recrystallisation from ethanol–DMF (3:2 v/v).
White solid; m.p., [300°C. Anal. Calcd. for C19H18N4O5
(%): C 59.68, H 4.74, N 14.65. Found (%): C 59.53, H
4.83, N 14.49. tmax/cm-1 (KBr): 1646 (C=O, chromone),
1
1699 (C=O, barbituric acid), 3241 (N–H, pyrazolinyl). H
NMR (DMSO-d6, 400 MHz): d 2.46 (s, 3H, CH3), 3.34
(s, 6H, 2N–CH3), 3.70 (dd, 1H, J = 19.0 Hz, 6.0 Hz, Hd),
4.03 (dd, 1H, J = 19.0 Hz, 9.7 Hz, He), 4.89 (dd, 1H,
J = 9.1 Hz, 6.6 Hz, Hc), 7.31 (br s,1H, NH), 7.39–7.91
(m, 3H, Ar–H), 8.13 (s, 1H, C-2). MS (% rel int) m/z 382
(M?, 100), 381 (70).
Preparation of dihydropyrimidine under thermal
heating condition
A mixture of 3a (5 mmol), urea (7 mmol) and NaOH
(14 mmol) was refluxed in ethanol (20 ml) for 14 h. The
reaction mixture was then cooled, and poured into ice-cold
water (50 ml), acidified with conc.HCl. The crude product
thus obtained was filtered washed with acetone and dried to
afford 5.
1-Phenyl-3-(1,3-dimethyl-2,4,6-pyrimidinetrione-5-yl)-5-
(4-oxo-4H-1-benzopyran-3-yl)pyrazoline (4c)
Purified by recrystallisation from coloumn chromatography
using benzene-ethylacetate (3:1 v/v) as the eluent. Pale
yellow crystals; m.p., 236°C (dec). Anal. Calcd. for
C24H20N4O5 (%): C 64.86, H 4.54, N 12.61. Found (%): C
64.81, H 4.61, N 12.53. tmax/cm-1 (KBr): 1668 (C=O,
chromone), 1715 (C=O, barbituric acid). 1H NMR (CDCl3,
400 MHz): d 3.38 (s, 6H, 2N–CH3), 3.71 (dd, 1H,
J = 18.5 Hz, 7.9 Hz, Hd) 4.23 (dd, 1H, J = 18.6 Hz,
9.7 Hz, He), 4.49 (dd, 1H, J = 10.0 Hz, 7.9 Hz, Hc),
7.08–7.33 (m, 8H, Ar–H), 7.38 (dd, 1H, J = 7.4 Hz,
1.7 Hz, C-5), 8.27 (s, 1H, C-2). MS (% rel int) m/z 444
(M?, 90), 443 (40), 391 (40).
Preparation of Dihydropyrimidine Under Microwave
Irradiation Condition
The mixture of 3a (5 mmol), urea (7 mmol) and NaOH
(10 mmol) was grounded well using a mortar and pestle.
The reaction mixture was then transferred to an open Pyrex
beaker and exposed to microwave irradiation (multimode,
full power). The progress of reaction was monitored by
TLC and on completion the reaction mixture was slurred in
water (25 ml). The solid obtained was filtered, washed with
water, acetone and dried to afford 5.
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1479
4-(1,3-Dimethyl-2,4,6-pyrimidinetrione-5-yl)-6-(4-oxo-4H-
1-benzopyran-3-yl)-5H,6H-dihydropyrimidine-2-one (5)
Preparation of pyrazole under thermal heating condition
Hydrazine hydrate (2.5 mmol) was added with vigorous
stirring to a solution of 6a (2.5 mmol) in 10 ml of dry
pyridine at room temperature. The reaction mixture was
allowed to stand for 28 h. The pyrazole derivative 7 pre-
cipitated was filtered, washed with water, ethanol and
dried.
Purified by recrystallisation from ethanol. White powder,
m.p., 279–281°C. Anal. Calcd. for C19H16N4O6 (%): C
57.58, H 4.07, N 14.14. Found (%): C 57.42, H 3.91, N
14.12. tmax/cm-1 (KBr): 1651 (C=O, chromone), 1716
(C=O, barbituric acid), 3511 (OH). 1H NMR (CDCl3,
300 MHz): d 3.20 (dd, 1H, J = 16.5 Hz, 3.9 Hz, Hd), 3.37
(s, 6H, 2N–CH3), 3.42 (dd, 1H, He), 4.88 (dd, 1H,
J = 9.9 Hz 3.9 Hz, Hc), 7.44–7.76 (m, 3H, Ar–H), 8.02
(s, 1H, C-2), 8.24 (dd, 1H, J = 7.8 Hz, 0.9 Hz, C-5), 14.12
(br s, 1H, OH). MS (% rel int) m/z 396 (M?, 80), 395(50).
Preparation of pyrazole under microwave irradiation
A mixture of 6a (2.5 mmol) and hydrazine hydrate
(2.5 mmol) was mixed well and air dried. The reaction
mixture was subjected to microwave irradiation (multi-
mode, full power) in an open Pyrex beaker. On completion
(as checked by TLC), the reaction mixture was slurred in
water (20 ml). The crude product obtained was filtered,
washed with water, ethanol and dried.
General procedure for the preparation
of 2,3-dibromoderivatives of chalcones
Bromine (5 mmol) was added dropwise with vigorous
stirring to a solution of 3a–b (5 mmol) in 12 ml of chlo-
roform over a period of 20 min. After complete addition of
Br2 the reaction mixture was allowed to stand for 2 h. The
dibromoderivatives 6a–b were precipitated, filtered off,
and washed with 20 ml of ether to remove the excess of
bromine.
3-(1,3-Dimethyl-2,4,6-pyrimidinetrione-5-yl)-5-(4-oxo-4H-
1-benzopyran-3-yl)pyrazole (7)
Purified by recrystallisation from ethanol–DMF (3:2 v/v),
White powder; m.p., [300°C. Anal. Calcd. for
C18H14N4O5 (%): C 59.02, H 3.85, N 15.29. Found (%): C
59.14, H 3.79, N 15.22. tmax/cm-1 (KBr): 1654 (C=O,
chromone), 1710 (C=O, barbituric acid), 3247 (NH, pyra-
zole). 1H NMR (DMSO-d6, 300 MHz): d 3.20 (s, 6H,
2N–CH3), 6.97–7.39 (m, 3H, Ar–H), 7.77 (d, 1H, J =
7.5 Hz, C-5), 7.94 (s, 1H, pyrazole), 9.56 (s, 1H, C-2), 10.31
(br s, 1H, NH). MS (% rel int) m/z 366 (M?, 90), 365 (50).
1-(1,3-Dimethyl-2,4,6-pyrimidinetrione-5-yl)-2,3-dibromo-
3-(4-oxo-4H-1-benzopyran-3-yl) propan-1-one (6a)
Purified by recrystallisation from ethanol. Yellow solid;
m.p., 242°C (dec). Anal. Calcd. for C18H14N2O6Br2 (%): C
42.05, H 2.74, N 5.45. Found (%): C 42.14, H 2.75, N 5.42.
t
max/cm-1 (KBr): 1657 (C=O, chromone), 1729 (C=O,
barbituric acid). 1H NMR (CDCl3, 400 MHz): d 3.42
(s, 3H, N–CH3), 3.44 (s, 3H, N–CH3), 5.56 (d, 1H, J =
11.3 Hz, Ha), 7.44–7.72 (m, 3H, Ar–H), 7.76 (d, 1H, J =
11.3 Hz, Hb), 8.15 (s, 1H, C-2), 8.34 (dd, 1H, J = 7.9 Hz,
1.5 Hz, C-5). MS (% rel int) m/z 514 (M?, 55), 513 (30),
434 (30), 354 (30).
Biological activity
Antibacterial studies
All the synthesized compounds were dissolved to prepare a
stock solution of 1 mg/ml using DMSO. The antibacterial
activity of test compounds and standard chloramphenicol
was done by filter paper disc method (Bauer et al., 1966).
Media with DMSO was set up as control. All cultures were
routinely maintained on NA (nutrient agar) and incubated
at 37°C for overnight. The culture was centrifuged at
1000 rpm and pellets were resuspended and diluted in
sterile NSS to obtain viable count 105 cfu/ml. Approxi-
mately, 0.1 ml of diluted bacterial culture suspension was
spread with the help of spreader on NA plates uniformly.
Sterile 8-mm discs (Hi-media Pvt Ltd) were impregnated
with the test compounds. Antibiotic disc, chloramphenicol
(30 lg/disc Hi-Media) was used as control. The disc was
placed on the plate. Each plate had one control disc
impregnated with the solvent. The plates were then
1-(1,3-Dimethyl-2,4,6-pyrimidinrtrione-5-yl) -2,3-
dibromo- 3- (6-methyl-4-oxo-4H-1-benzopyran-3-yl)
propan-1-one (6b)
Purified by recrystallisation from ethanol. Yellow solid;
m.p., 202–204°C. Anal. Calcd. for C19H16N2O6Br2 (%); C
43.21, H 3.05, N 5.30. Found (%): C 43.13, H 3.13, N 5.22.
t
max/cm-1 (KBr): 1664 (C=O, chromone), 1730 (C=O,
barbituric acid). 1H NMR (CDCl3, 400 MHz): d 2.47 (s, 3H,
CH3), 3.42 (s, 3H, N–CH3), 3.43 (s, 3H, N–CH3), 5.57 (d,
1H, J = 11.2 Hz, Ha), 7.38–7.75 (m, 3H, Ar–H), 7.77(d,
1H, J = 11.3 Hz, Hb), 8.14 (s, 1H, C-2). MS (% rel int) m/z
528 (M?, 40) 527 (10), 526 (20), 448 (10) 368 (30).
123

1480
Med Chem Res (2011) 20:1473–1481
Chimenti F, Bizzari B, Manna F, Bolasco A, Secci D, Chimenti P,
Granese A, Rivanera D, Lilli D, Scaltrito MM, Brenciaglia MI
(2005) Synthesis and in vitro anti-helicobacter pylori activity of
pyrazoline derivatives. Bioorg Med Chem Lett 15:603–607
Deng Y, Lee JP, Ramamonjy MT, Snyder JK, Etages SA, Kanada D,
Snyder MP, Turner CJ (2000) New antimicrobial flavanones
from Physena madagascariensis. J Nat Prod 63:1082–1089
Dewick DM (1994) Isoflavanoids. In: Harborne JB (ed) The
flavanoids. advances in research since 1986. Chapman and Hall,
London, pp 117–238
Grazul M, Budzisz E (2009) Biological activity of metal ions
complexes of chromones, coumarins and flavones. Coord Chem
Rev 253:2588–2598
Hansch C, Sammes PG, Taylor JB (1990) Comprehensive medicinal
chemistry, vol 1–6. Pergamon, New York
Horton DA, Bourne GT, Smythe ML (2003) The combinatorial
synthesis of bicyclic privileged structures or privileged sub-
structures. Chem Rev 103:893–930
Joshi MG, Wadodkar KN (1981) Action of phenylhydrazine hydro-
chloride on chalconedibromides in dimethylformamide. Indian
J Chem 20B:1090–1092
Jursic BS, Neumann DM (2001) Preparation of 5-formyl- and 5-acetyl
barbituric acids, including the corresponding Schiff bases and
phenyl hydrazones. Tetrahedron Lett 42:8435–8439
Kappe CO, Dallinger D (2009) Controlled microwave heating in
modern organic syntheses: highlights from the 2004–2008
literature. Mol Divers 13:71–193
Khode S, Maddi V, Aragade P, Palkar M, Ronad PK, Mamledesai S,
Thippeswamy AHM, Satyanarayana D (2009) Synthesis and
pharmacological evaluation of a novel series of 5-(substi-
tuted)aryl-3-(3-coumarinyl)-1-phenyl-2-pyrazolines as novel
anti-inflammatory and analgesic agents. Eur J Med Chem
44:1682–1688
incubated for 24 h at 37°C, and the resulting zones of
inhibition (in mm) were measured.
Antifungal studies
The synthesized compounds were dissolved in DMSO.
Media with DMSO was set up as control. All cultures were
routinely maintained on SDA and incubated at 28°C. Spore
formation of filamentous fungi was prepared from 7 day
old culture in sterile normal solution (8% NaCl) and
approximately diluted to obtain 105 cfu/ml. The inoculums
of non-sporing fungi, C. albicians was performed by
growing the culture in SD broth at 37°C for overnight. The
culture was centrifuged at 1,000 rpm and pellets were
resuspended and diluted in sterile NSS to obtain viable
count 105 cfu/ml. Approximately, 0.1 ml of diluted fungal
culture suspension was spread with the help of spreader on
SDA plates uniformly. Sterile 8 mm discs (Hi-media Pvt
Ltd) were impregnated with the test compounds. Antibiotic
disc, nystatin (30 lg/disc Hi-Media) was used as control.
The disc was placed onto the plate. Each plate had one
control disc impregnated with the solvent. The plates were
incubated at 28°C for filamentous fungi for 72 h or more,
while for C. albicans plates were incubated at 37°C for
18–48 h. Antifungal activity was determined by measuring
the diameters of the inhibition zone.
Kostka K (1973) Chromone derivatives. VI. Reaction of phenylhydr-
azine with chromone and x-formyl-o-hydroxyacetophenone.
Rocz Chem 47:305–313
Kuroda M, Uchida S, Watanabe K, Mimaki Y (2009) Chromones
from the tubers of Eranthis cilicica and their antioxidant activity.
Phytochemistry 70:288–293
Acknowledgements Financial assistance in the form of major
research project [F.No. 37-15/2009 (SR)] from UGC, New Delhi, is
gratefully acknowledged. The authors would also like to thank SAIF,
CDRI, Lucknow and SAIF, Panjab University, Chandigarh for spec-
tral data.
Lahtchev KL, Batovska DI, Parushev SP, Ubiyvovk VM, Sibirny AA
(2008) Antifungal activity of chalcones: a mechanistic study
using various yeast strains. Eur J Med Chem 43:2220–2228
Larget R, Lockhart B, Renard P, Largeron M (2000) A convenient
extension of the Wessely-Moser rearrangement for the synthesis
of substituted alkyl amino flavones as neuroprotective agents in
vitro. Bioorg Med Chem Lett 10(8):835–838
Lawrence NJ, Patterson RP, Ooi LL, Cook D, Ducki S (2006) Effects
of a-substitutions on structure and biological activity of
anticancer chalcones. Bioorg Med Chem Lett 16:5844–5848
Liu M, Wilairat P, Croft SL, Tan ALC, Go ML (2003) Structure-
activity relationships of antileishmanial and antimalarial chal-
cones. Bioorg Med Chem 11:2729–2738
Mojzis J, Varinska L, Mojzisova G, Kostova I, Mirossay L (2008)
Antiangiogenic effects of flavonoids and chalcones. Pharmacol
Res 57:259–265
Moneer AA, Abouzid KAM, Said MM (2002) Synthesis of certain
thiopyrimidine derivatives as antimicrobial agents. Az J Pharm
Sci 30:150–160
References
Abdel-Rahman AAH, Abdel-Megied AES, Hawata MAM, Kasem
ER, Shabaan MT (2007) Synthesis and antimicrobial evaluation
of some chalcones and their derived pyrazoles, pyrazolines,
isoxazolines and 5,6-dihydropyrimidine-2-(1H)-thiones. Mon-
atshefte fur Chemie 138:889–897
Aboul EHY, Wainer IW, (1997) Chiral barbiturates: synthesis
chromatographic resolutions and biological activity. In: Aboul-
Enein HY, Wainer IW (eds) The impact of stereochemistry on
drug development and use. Wiley, New York, pp 201–235
Alonso R, Brossi A (1988) Synthesis of hormothamnione. Tetrahe-
dron Lett 29:735–738
Avila HP, Smania EFA, Monache FD, Junior AS (2008) Structure-
activity relationship of antibacterial chalcones. Bioorg Med
Chem 16:9790–9794
Barton D, Ollis WD (1979) Comprehensive organic chemistry, vol
1–6. Pergamon Press, Oxford
Bauer AW, Kirby WMM, Sherris JC, Turch M (1966) Antibiotic
susceptibility testing by a standardized single disk method. Am
J Clin Pathol 45:493–496
Cheng JH, Hung CF, Yang SC, Wang JP, Won SJ, Lin CN (2008)
Synthesis and cytotoxic, anti-inflammatory and anti-oxidant
activities of 20,50-dialkoxychalcones as cancer chemopreventive
agents. Bioorg Med Chem 16:7270–7276
Nerya O, Musa R, Khatib S, Tamir S, Vaya J (2004) Chalcones as
potent tyrosinase inhibitors: the effect of hydroxyl positions and
numbers. Phytochemistry 65:1389–1395
Nohara A, Umetani T, Sanno Y (1974) A facile synthesis of 4-oxo-
4H-1-benzopyran-3-carboxaldehydes by vilsmeier reagents.
Tetrahedron 30:3353–3561
Nowaskowska Z (2007) A review of anti-infective and anti-inflam-
matory chalcones. Eur J Med Chem 42:125–137
123

Med Chem Res (2011) 20:1473–1481
1481
Pani MS, Arjun M, Sridhar D, Srinivas K, Raviprasad T (2009)
N-substituted benzoxazolyl ureas and thioureas in biginelli
reaction promoted by trifluoromethane sulfonic acid. An efficient
and convenient synthesis of substituted benzoxazolyl 3,4-dihy-
dropyrimidine 1H(thio)-ones. Chin Chem Lett 20:909–912
Prakash O, Kumar R, Prakash V (2008) Synthesis and antifungal
activity of some new 3-hydroxy-2-(1-phenyl-3-aryl-4-pyrazolyl)
chromones. Eur J Med Chem 43:435–440
Quintin J, Desrivot J, Thoret S, Menez PL, Cresteil T, Lewin G
(2009) Synthesis and biological evaluation of a series of
tangeretin-derived chalcones. Bioorg Med Chem Lett 19:
167–169
the a,b-unsaturated keto functionality of 20-hydroxychalcones as
a novel antioxidant pharmacophore. Chem Res Toxicol
16:1277–1286
Sugamoto K, Kurogi C, Matsushita YI, Matsui T (2008) Synthesis of
4-hydroxyderricin and related derivatives. Tetrahedron Lett
49:6639–6641
Suryawanshi SN, Chandra N, Kumar P, Porwal J, Gupta S (2008)
Chemotherapy of leishmaniasis part-VIII: synthesis and bioeval-
uation of novel chalcones. Eur J Med Chem 43:2473–2478
Valenti P, Bisi A, Rampa A, Belluti F, Gobbi S, Zampiron A, Carrara M
(2000) Synthesis and biological activity of some rigid analogues of
flavone-8-acetic acid. Bioorg Med Chem 8:239–246
Raj T, Ishar MPS, Gupta V, Pannu APS, Kanwal P, Singh G (2008)
Unusual conversion of substituted 3-formyl chromones to 3-(5-
phenyl-3H-[1, 2, 4] dithiazol-3-yl)chromen-4-ones:a facile and
efficient route to novel 1,2,4-dithiazoles. Tetrahedron Lett
49:243–246
Rojas J, Paya M, Dominguez JN, Ferrandiz ML (2002) The synthesis
and effect of fluorinated chalcone derivatives on nitric oxide
production. Bioorg Med Chem Lett 12:1951–1954
Varma RS (1999) Solvent-free organic synthesis using supported
reagents and microwave irradiation. Green Chem 1:43–55
Vogel S, Ohmayer S, Brunner G, Heilmann J (2008) Natural and non-
natural prenylated chalcones: synthesis, cytotoxicity and anti-
oxidative activity. Bioorg Med Chem 16:4286–4293
Wiley RH, Jarboe CH (1967) The chemistry of heterocyclic
compounds, vol 22. Interscience, New York, p 183
Yu D, Chen CH, Brossi A, Lee KH (2004) Anti-AIDS agents 60.
Substituted 30R, 40R-Di-O-(-)-camphanoyl-20,20-dimethyldihy-
dropyrano[2,3-f]chromone (DCP) analogues as potent anti-HIV
agents. J Med Chem 47:4072–4082
Singh SP, Sehgal S, Tarar LS, Dhawan SN (1990) Synthesis of 2-[3-
methyl or trifluromethyl-5-(2-thienyl)-pyrazol-1-yl]thiazol and
benzothiazoles. Indian J Chem 29B:310–314
Stevens JF, Miranda CL, Frei B, Buhler DR (2003) Inhibition of
Peroxynitrite-mediated LDL oxidation by prenylated flavanoids:
123