Med Chem Res (2008) 17:318–325 DOI 10.1007/s00044-007-9067-y
MEDICINAL CHEMISTRY RESEARCH
ORIGINAL RESEARCH
Synthesis and biological activity of heterocycles from chalcone Zeba N. Siddiqui Æ Mohammad Asad Æ Shagufta Praveen
Received: 6 November 2007 / Accepted: 15 November 2007 / Published online: 2 February 2008 Ó Birkha¨user Boston 2008
Abstract The chalcone 3 was synthesized from 3-acetyl-4-hydroxy coumarin and 3-formylchromone by refluxing in ethanol in the presence of a catalytic amount of pyridine. 3 was converted to bipyrazoles 4a-b by treatment with hydrazine and phenylhydrazine. The compounds were screened for their antibacterial activity. Keywords 3 Acetyl-4-hydroxycoumarin (2E)-1-(4-hydroxy-1-benzopyran2-one-3-yl)-3-[1] (benzopyran-4-one-3-yl)-2-propen-1-one Antibacterial activity
Introduction Chalcones are important precursors of flavonoids and isoflavonoids (Harborne and Mabry, 1982). A large number of chalcones have been prepared by Claisen– Schmidt condensation of aldehydes with methyl ketones under basic conditions (Claisen et al., 1881). These compounds have shown in vitro antimalarial activity against chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falsciparum (Li et al., 1995). Recently authors have reported synthesis of chalcones under acidic conditions also using perchloric acid and acetic acid (Tuskaev et al., 2002). A variety of chalcones have been reported for activity as potent tyrosinase inhibitors, antioxidants and are, thus, used as new depigmentation agents (Nerya et al., 2004). Nitrogen heterocycles containing chalcone moiety have been reported as active compounds against herpes simplex virus-1(HSV-1) and human immunodeficiency virus 1(HIV-1) (El-Barbary et al., 1994; El-Subbagh et al., 2000). This class of compounds also exhibits cytotoxic activity towards leukemia cell lines (Dimmock et al., 1983; Dimmock et al., 1992). Various other chalcones are reported to exhibit insecticidal, antichinoviral, and antipicorniviral properties Z. N. Siddiqui (&) M. Asad S. Praveen Department of Chemistry, Aligarh Muslim University, Aligarh 202 002, India e-mail:
[email protected]
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319
(Nowakowska et al., 2001). In view of the variety of pharmacological properties exhibited by chalcones, we were prompted to undertake its synthesis and conversion to other heterocycles which may show different or better physiological activities. In continuation of our work on 3-formyl-4-hydroxycoumarin (Siddiqui and Asad, 2006) and 3-formylchromone (Siddiqui et al., 2006), we report herein the synthesis of chalcone and its conversion to bipyrazoles with nitrogen bases. It is pertinent to mention that bipyrazoles have been reported to show anti-inflammatory (ElKhawass and Bistawroos, 1990; Bruno et al., 1993), cytotoxic (Cuadro et al., 1985), insecticidal (Truboi et al., 1994), herbicidal (Hartfiel et al., 1993), and fungicidal (Das and Mittra, 1978; Nayak and Mittra, 1980) activities. Chemistry Due to the exceptional reactivity of the formyl group in 3-formylchromone as well as the versatile biological activities of chromone and coumarin derivatives, the chalcone 3 was synthesized by employing 3-formychromone (1) and 3-acetyl-4hydroxycoumarin (2) as starting materials under mild basic conditions. 1' 8'
O
O
O
7'
CHO O
HO
1
2
O
O 2'
O
Hb
8'' 7''
2'' 6''
6'
C CH3
1''
O
5'
2
3'
4'
1
3
O
Ha
O
3''
4''
5''
OH
3
The compound was identified on the basis of its spectroscopic data. The infrared (IR) spectrum showed chromone and coumarin carbonyl groups at 1650 and 1734 cm-1, respectively, in addition to a broad band for the OH group at 3318 cm1 . The 1H NMR spectrum showed trans olefinic protons Ha and Hb as ortho-coupled doublets at d 9.10 (J = 15.6 Hz) and 8.18 (J = 15.9 Hz), respectively. The C-20 and C-50 protons appeared as a singlet and a doublet at d 8.56 and 8.30 (J = 7.8 Hz), respectively. The remaining three aromatic protons of the chromone unit and the four protons of coumarin moiety appeared as a multiplet in the region d 7.45–7.93. The mass spectrum of 3 showed M+ at m/z 360 as its base peak. The other important peaks were obtained as shown in Scheme 1a–b. The condensation of hydrazines with a,b-unsaturated carbonyl compounds usually gives pyrazolines (Wiley and Jarboe, 1967). Thus, when compound 3 was treated with nitrogen bases such as hydrazine and phenylhydrazine pyrazolyl pyrazolines 4a and 4b were obtained, respectively. The IR spectrum of 4a showed broad bands at 3618, 3456, 3396, and 3269 cm-1 due to the presence of the two OH and NH groups. A sharp and strong absorption band at 1684 cm-1 indicated a carbonyl group in the compound. Since chromone carbonyl groups usually appear as sharp absorption bands in the region 1620– 1650 cm-1 (Ellis, 1977), the band at 1684 cm-1 was assigned to coumarin rather than the chromone carbonyl group. The 1H nuclear magnetic resonance (NMR)
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(a) O
O
O
O
O
OH
O
O
O
O
m/z 360
O
O
OH
O
O
O
O
O
OH
O
O
H +
O
O
O
H
O O
O
O
+ OH
O
m/z 360
+
O
O
CH2
O OH
O H
O
O
OH
O
C CH3
m/z 204
(b)
O
O
O
O
O
O
m/z 360 RDA Cleavage
O C=O
m/z 120
+
O
O H O
m/z 240
O - (CH=C=O)
-CO O C=O O
m/z 92
O
m/z 199 -CO
O
O
m/z 171 Scheme 1 Mass fragmentation of chalcone 3
+ O
m/z 157
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spectrum of 4a did not show the diagnostic singlet of the H-2 olefinic proton for the chromone moiety. Furthermore, the compound also showed a strong black color with ferric chloride on a thin-layer chromatography (TLC) plate. Since chromones usually undergo ring-opening reactions by nitrogen nucleophiles (Kostka, 1973), it was clear therefore that compound 3 had suffered ring cleavage at the C-2 position of the chromone unit by attack of the nitrogen bases (hydrazine, phenylhydrazine) followed by cyclization to form a pyrazole moiety. Furthermore, another molecule of the nitrogen nucleophile reacted with the a,b-unsaturated ketone unit to form a pyrazoline moiety (Scheme 2). The presence of the pyrazoline unit in 4a was clearly established by two double doublets at (d 3.66, 3.72(Ha); 4.04, 4.09 (Hb) and a multiplet at d 5.15 (Hc). The broad singlet (D2O exchangeable) at d 6.36 was assigned to the NH proton of pyrazoline unit. The aromatic region of the spectrum exhibited the eight protons of coumarin and the phenolic units in the form of a multiplet at d 6.91-7.58. A sharp singlet integrating for one proton at d 7.81 was assigned to the Hd proton of the pyrazole moiety. Two broad singlets (D2O exchangeable) at d 10.6 and 12.8 were due to the two OH groups. Further confirmation of the structure 4a was provided by mass spectrometry, which showed M+ at m/z 388. The other prominent peaks were at m/z 370 (M+–H2O), 295 [M+–Ph(OH)], 360 (M+–CO), and 267 (M+–C7H4O2). O
O Q O
Q
H2N - NHR
O
OH
NH-NH-R
O
O
NH-NH-R Q
O
Q
Q O
O HO
O
O H N
N
HO NH
N H
R
R N
Q
Q
-H2O N
HO
N
Q
N
R NH
Ha
R N
O H2NNHR (-H2O)
H Shift
Hc
R N
HO R
N
N
HO R
4a; R = H 4b; R = Ph O
O
Q= OH
Scheme 2 Formation of bipyrazoles 4a-b by the reaction of chalcone 3 and hydrazines
N
Hb Hd
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Biological activity All newly synthesized compounds were screened for antibacterial activity against Gram-positive (Bacillus subtilis, Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli, Salmonella typhimurium). Compound 4a exhibited strong activity against Gram-positive bacteria and moderate activity against Gramnegative bacteria as compared to the antibiotic drug chloramphenicol. However compounds 3 and 4b showed moderate activity against Gram-positive bacteria and did not show any activity against Gram-negative bacteria. The zone of growth inhibition ranged from 10 to 25 mm (Table 1).
Summary A novel chalcone analogue 3 was synthesized under mild basic conditions and in quantitative yield. Compound 3 was easily converted to the bipyrazoles 4a and 4b by treatment with hydrazine and phenylhydrazine. All the compounds showed moderate to strong antibacterial activity against Gram-positive and Gram-negative bacteria.
Experimental section Melting points were taken in open capillaries and are uncorrected. The IR spectra were recorded on a Fourier-transform (FT)-IR spectrometer 2020,1H NMR spectra on a Bruker DRX-300 spectrometer using tetra methyl silane (TMS) as an internal standard and the mass spectra on a Jeol SX-120 (FAB). Compound 1 and 2 were synthesized by reported procedures (Eisenhauer and Link, 1953; Nohara et al., 1974). The purity of all compounds was checked by TLC plates using silica gel (E. Merck G254). The plates were run in a chloroform:methanol (3:1) mixture and visualized by iodine vapors. The elemental analysis data (C, H, and N) were the same with a variation of ±0.4% from calculated values.
Table 1 Antibacterial activity of compounds synthesized S. no.
Test microorganisms
Zone of inhibition, size in mm
Antibiotic control chloramp henicol
Compounds 3 G+ G-
4a
4b
1.
Bacillus subtilis
12
25
10
33
2.
Staphylococcus aureus
–
20
–
33
3.
Escherichia coli
–
12
–
30
4.
Salmonella typhimurium
–
–
–
30
– No activity detected The compounds were tested at 1000 lg/disc
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Biological data Culture media and inoculum Nutrient (N) (Hi-Media Pvt. Ltd., Mumbai, India) was used to culture the test bacteria. The microbial culture was grown at 37°C for 18 h and then appropriately diluted with sterile 0.8% saline solution to obtain a cell suspension of 105 colony forming unit (CFU)/ml (Aqil and Ahmad, 2003).
Antimicrobial assays Antibacterial activity of the compounds was assayed by the disc diffusion method (Bauer et al., 2003) with little modification. Briefly 0.1 ml of diluted inoculum (105 CFU/ml) of the test organism was spread on nutrient agar plates. Sterile paper disc was impregnated with 1000 lg of the compounds and a disc without compound was used as a negative control. The inoculated plates were incubated for the appropriate temperature and time as described above. The antibacterial activity was evaluated by measuring the zone of growth inhibition of the test organism around the disc. Antibiotic chloramphenicol was used as positive control.
Synthesis of (2E)-1-(4-hydroxy-1-benzopyran-2-one-3-yl)-3-[1] (benzopyran-4-one-3-yl)-2-propen-1-one (3) To a well-stirred solution of 3-acetyl-4-hydroxycoumarin (4.9 mmol) in ethanol (30 mL) containing pyridine (0.5 mL) was added 3-formylchromone (4.9 mmol). The reaction mixture was refluxed in a water bath for 12 h, cooled at room temperature, and poured into ice-cold water (200 mL). The light yellow solid 3 was obtained, filtered, washed with water, alcohol, dried, and recrystallized from chloroform as shining needles (65%); mp 260–262°C; IR (KBr) mmax 3310, 1734, 1650 cm-1; 1H NMR (CDCl3) d 7.45-7.93 (m, 7H, Ar-H), 8.18 (d, 1H, J = 15.9 Hz, 0 0 Hb), 8.30 (d, 1H, J = 7.8 Hz, H-5 ), 8.56 (s, 1H, H-2 ), 9.10 (d, 1H, J = 15.6 Hz, + Ha); MS (% rel Int) m/z 360 (M , 100), 342 (30), 240 (5), 204 (90), 199(35), 171(20), 156 (20), 120 (40), 107 (15), 92 (10). Synthesis of 3-[4-hydroxy-[1]benzopyran-2-one-3-yl]-5-[5-(20 hydroxyphenylpyrazol-4-yl]- pyrazolin (4a) Compound 3 (2.7 mmol) was dissolved in alcohol (25mL) and hydrazine hydrate (5.4 mmol) added to it. The reaction mixture was refluxed in a water bath for 30 min. On cooling at room temperature, a light-green solid 4a was obtained. It was filtered, washed with ethanol–water, dried, and recrystallized from N,N-dimethyl formamide (DMF), (79%); mp 162°C; IR (KBr) mmax 3618, 3456, 3396, 3269, 1684, 1608, 1578 cm-1; 1H NMR (DMSO – d6) d 3.72 (dd, 1H, J = 17.7 Hz, 8.1 Hz,
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Hb), 4.09 (dd, 1H, J = 17.1 Hz, 8.7 Hz, Ha), 5.15 (m, 1H, Hc), 6.37 (br s, 1H, exchangeable, NH), 7.81 (s, 1H, Hd), 6.91 – 8.04 (m, 8H, Ar – H), 10.60 (br s, 1H, exchangeable, OH), 12.80 (br s, 1H, exchangeable, OH); MS (% rel int) m/z 388 (M+, 100), 387 (40), 386 (70), 370((15), 342 (5), 295 (7), 268 (8), 240 (40), 229 (50), 227 (10),161 (20), 159 (5), 134 (25), 136 (25), 118 (20), 107 (10). Synthesis of 1-phenyl-3-[4-hydroxy-[1]benzopyran-2-one-3-yl]-5-[5-(20 hydroxyphenyl)- 1-phenylpyrazol-4-yl] pyrazolin (4b) Compound 3 (2.7 mmol) and phenylhydrazine (5.4 mmol) were taken in methanol (25 mL) and five drops of acetic acid were added. The reaction mixture was refluxed in a water bath for 45 min. It was cooled at room temperature and poured into ice-cold water (200 mL), filtered, washed with ethanol–water mixture, and dried. The yellow solid 4b as obtained was recrystallized from chloroform–benzene (53%); mp 185–190°C; IR (KBr) mmax 3614, 3452, 1710, 1610, 1553 cm-1; 1H NMR (DMSO-d6) d 3.74 (m, 1H, Ha), 4.17 (m, 1H, Hb), 5.21 (m, 1H, Hc), 6.757.62 (m, 17H, Ar-H), 7.45 (s, 1H, Hd), 8.04 (d, 1H, J = 7.2 Hz, H-500 ); MS (% rel int) m/z 540 (M+, 90), 539 (50), 522 (5), 496 (5), 463 (6), 447 (10), 420 (5), 379 (5). Acknowledgement Financial assistance from UGC, New Delhi, is gratefully acknowledged. The authors would also like to thank SAIF, CDRI, Lucknow for spectral data, Dr. Iqbal Ahmad, Department of agricultural microbiology, Aligarh Muslim University, Aligarh for biological screening and Prof. N. U. Khan, Department of Chemistry, A.M.U. Aligarh for sincere advice.
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