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Article

Synthesis and Antimicrobial Evaluation of Some Pyrazole Derivatives

by
Essam Mohamed Sharshira
1,* and
Nagwa Mohamed Mahrous Hamada
2,*
1
Department of Chemistry, Faculty of Science, Alexandria University, Alexandria 21321, Egypt
2
Department of Chemistry, Faculty of Education, Alexandria University, Alexandria 21526, Egypt
*
Authors to whom correspondence should be addressed.
Molecules 2012, 17(5), 4962-4971; https://doi.org/10.3390/molecules17054962
Submission received: 20 February 2012 / Revised: 23 March 2012 / Accepted: 18 April 2012 / Published: 30 April 2012
(This article belongs to the Special Issue Heterocycles)

Abstract

:
Reaction of a series of (E)-3-phenyl-4-(p-substituted phenyl)-3-buten-2-ones with p-sulfamylphenyl hydrazine in glacial acetic acid gave the corresponding hydrazones, subsequent treatment of which with 30% HCl afforded pyrazole-1-sulphonamides. On the other hand, refluxing of chalcones with either thiosemicarbazide or isonicotinic acid hydrazide in ethanol containing a few drops of acetic acid gave pyrazoline-1-thiocarboxamides and isonicotinoyl pyrazolines, respectively. The structures of the synthesized compounds were determined on the basis of their elemental analyses and spectroscopic data. The antimicrobial activity of the newly isolated heterocyclic compounds was evaluated against Gram-positive, Gram-negative bacteria and fungi. Most of the compounds showed a moderate degree of potent antimicrobial activity.

Graphical Abstract

1. Introduction

Pyrazoles and their variously substituted derivatives are important biological agents and a significant amount of research activity has been directed towards this class. In particular, they are used as antitumor [1], antibacterial and antifungal, antiviral, antiparasitic, anti-tubercular and insecticidal agents [2,3,4,5,6,7,8,9,10]. Some of these compounds have also anti-inflammatory, anti-diabetic, anesthetic and analgesic properties [11,12,13,14]. Moreover, chalcones have played a crucial part in the development of theory of heterocyclic compounds, and also they used extensively in organic synthesis [15,16,17,18,19]. A classical synthesis of these compounds involves the base-catalyzed aldol condensation reaction of ketones and aldehydes to give α,β-unsaturated ketones (chalcones), which undergo a subsequent cyclization reaction with hydrazines affording pyrazoles [11,20,21,22]. In recent years, a significant portion of research in heterocyclic chemistry has been devoted to pyrazoles containing different aryl groups, as evident from the literature [23,24,25,26,27,28,29,30].

2. Results and Discussion

A convenient route for the synthesis of α,β-unsaturated ketones 1ae is achieved by base catalyzed condensation of benzyl methyl ketone with the appropriate p-substituted benzaldehyde in the presence of piperidine [31] (Scheme 1).
Scheme 1. Synthesis of compounds 1ae, 2ae, 3ae, 4ae, 5ae.
Scheme 1. Synthesis of compounds 1ae, 2ae, 3ae, 4ae, 5ae.
Molecules 17 04962 g001
The (E)-Configuration for 1ae comes from 1H-NMR measurements where the vinyl proton of the (E)-isomer appears at relatively higher field than the (Z)-one [32]. The hydrazone derivatives 2ae were obtained in good yields by heating 1ae with p-sulphamylphenyl hydrazine in ethanol containing few drops of glacial acetic acid. The IR of 2ae showed the characteristic bands for C=N at 1,626–1,633, and primary and secondary amine bands at 3,379–3,391 and 3,289–3,310 cm−1, respectively. The 1H-NMR spectra showed the presence of a singlet equivalent to one proton in the range δ = 8.21–8.73 ppm characteristic for a hydrazone NH proton, while the primary amine NH2 protons appeared at δ = 9.23–9.40 ppm, a multiplet at δ = 7.31–7.82 ppm characteristic for the aromatic protons, a singlet at δ = 6.89–6.97 ppm for N=C–C=CH and a singlet equivalent to three protons at δ = 2.19–2.37 ppm characteristic for N=C-CH3 protons. Treatment of 2ae with 30% HCl produced the pyrazole derivatives 3ae in good yields.
The IR of 3ae showed the characteristic bands for C=N at 1,632–1,656, C=C at 1,500–1,520 whereas NH2 band appeared at 3,378–3,393 cm−1. The 1H-NMR spectra for 3ae revealed the following signals: A singlet equivalent to two exchangeable protons at δ = 9.33–10.37 ppm characteristic for NH2 protons, a multiplet at δ = 7.13–8.29 ppm characteristic for the aromatic protons. The methyl protons at C3 of the pyrazole ring appeared as a singlet at δ 2.22–2.28 ppm. In the case of 3b, another singlet appeared at δ = 3.34 ppm characteristic for OCH3 group at the p-position to phenyl group. Finally, condensation of 1ae with either thiosemicarbazide or isonicotinic acid hydrazide in ethanol containing few drops of acetic acid gave pyrazolines 4ae or 5ae, respectively. The pyrazoline structures were fully confirmed by spectral and elemental analyses methods (Table 1 and Table 2). The IR spectra of 4ae lacked the carbonyl band but showed a thiocarbonyl band at 1,232–1,248 and primary and secondary amine absorption bands at 3,387–3,394 and 3,282–3,316 cm−1 respectively. On the other hand the IR of 5ae showed an amide carbonyl band at 1,628–1,634 cm−1 and a primary amine absorption band only. The 1H-NMR of either 4ae or 5ae revealed the presence of an exchangeable hydrogen of one proton intensity for a NH proton at δ = 8.26–8.48 ppm or 8.31–8.51 ppm, respectively. In the case of 4ae, another exchangeable hydrogens of two protons intensity was also appeared at δ = 10.71–10.93 ppm characteristic for thiocarboxamide protons (S=C–NH2). The pyrazole-C5-H for 4ae and 5ae appeared as a singlet at δ = 5.39–5.46 ppm and 5.37–5.47 ppm, respectively.
Table 1. Physical and analytical data of compounds 2ae, 3ae, 4ae, and 5ae.
Table 1. Physical and analytical data of compounds 2ae, 3ae, 4ae, and 5ae.
CompoundRYieldM.P.Molecular FormulaCalculated %Found %
(%)(°C)CHNCHN
2aH67147C22H21N3SO267.525.3710.7467.505.4010.70
2bOCH390160C23H23N3SO365.565.469.9865.605.449.95
2cCl87103C22H20N3SO2Cl61.974.699.8661.944.669.90
2dBr93110C22H20N3SO2Br56.174.268.9456.204.308.97
2eNO279135C22H20N4SO460.554.5912.8460.504.6312.80
3aH69187C22H19N3SO267.874.8810.8067.844.9210.84
3bOCH391193C23H21N3SO365.875.0110.0265.905.0510.06
3cCl76172C22H18N3SO2Cl62.264.259.9162.304.219.94
3dBr78177C22H18N3SO2Br56.413.858.9756.453.908.95
3eNO269197C22H18N4SO460.834.1512.9060.804.1512.94
4aH81149C17H17N3S69.155.7614.2469.105.7614.20
4bOCH383156C18H19N3SO66.465.8512.9266.505.8512.95
4cCl87172C17H16N3SCl61.824.8512.7361.864.8812.69
4dBr79146C17H16N3SBr54.554.2811.2354.504.2911.20
4eNO293166C17H16N4SO260.004.7116.4759.994.6616.43
5aH81159C22H19N3O77.425.5712.3277.455.5912.36
5bOCH369166C23H21N3O274.395.6611.3274.355.6911.30
5cCl89142C22H18N3OCl70.214.7911.1770.254.7411.24
5dBr86168C22H18N3OBr62.864.2910.0062.824.2510.05
5eNO297171C22H18N4O368.394.6614.5168.444.6014.55
Table 2. IR and 1H-NMR spectral data of compounds 2ae, 3ae, 4ae, and 5ae.
Table 2. IR and 1H-NMR spectral data of compounds 2ae, 3ae, 4ae, and 5ae.
CompoundIR cm−1 (KBr)1H-NMR (δ / ppm) a
VinylC=NC=OC=SNH and/orAr-H’S (m)N=C-C=CHpyrazoline-CH3 and/or Ar- OCH3 (s)NH and/or NH2
HC=CHNH2(s)C5-H (s)
2a16031632--3391, 32917.33–7.826.91-2.338.21 and 9.23
2b16091629--3389, 33097.31–7.816.93-2.22 and 3.268.46 and 9.29
2c16121626--3382, 32897.36–7.616.97-2.228.54 and 9.31
2d16041633--3383, 33027.41–7.716.89-2.198.61 and 9.39
2e16191627--3379,33107.26–7.766.95-2.378.73 and 9.40
3a15151632--33867.24–8.29--2.259.33
3b15101641--33847.35–7.94--2.28 and 3.349.76
3c15001644--33787.29–7.86--2.229.92
3d15151654--33917.13–7.64--2.259.71
3e15201656--33937.29–8.10--2.2810.37
4a1527--12463394, 32877.26–7.82-5.392.2510.73 and 8.26
4b1522--12453390, 32937.27–7.77-5.422.32 and 3.3910.77 and 8.37
4c1531--12483390, 32827.29–8.01-5.442.2710.79 and 8.42
4d1527--12473393, 33117.23–7.61-5.462.2910.93 and 8.43
4e1526--12323387, 33167.27–7.995.392.3210.71 and 8.48
5a1517-1630-32916.81–7.09 and 7.32–7.48-5.402.328.31
5b1530-1628-32936.79–7.12 and 7.29–7.49-5.372.25 and 3.318.36
5c1522-1631-32876.83–7.08 and 7.27–7.51-5.462.278.45
5d1519-1633-32896.82–7.11 and 7.27–7.52-5.472.228.47
5e1524-1634-33116.84–7.10 and 7.26–7.71-5.422.398.51
a Solution in DMSO-d6.

2.1. Antimicrobial Activity

All of our compounds, i.e., hydrazones 2ae, pyrazoles 3ae, pyrazolines 4ae and 5ae were tested for antimicrobial activity against four test organisms: Staphylococcus aureus ATCC6538P, Escherichia coli ATCC873, Pseudomonas aeruginosa ATCC9027 and Candida albicans ATCC2091 using rifampicin (5 μg/disc) and ampicillin (10 μg/disc) as standard drugs (Table 3).
Table 3. Antimicrobial activities of all the synthesized compounds.
Table 3. Antimicrobial activities of all the synthesized compounds.
CompoundZone of inhibition (mm)Minimum inhibition concentration (MIC) g/mL
S. aureusC. albicansS. aureusC. albicans
2a-20-250
2b-15--
2c172010050
2d1420120500
2e1215--
3a19226331
3b182512531
3c22265050
3d182063125
3e1717--
4a-15--
4b-15--
4c212010050
4d15186363
4e-15--
5a-15--
5b-15--
5c21245050
5d-15--
5e1717--
Rifampicin32---
Ampicillin30---
DMSO-14--
(-) Indicates no activity.
The agar well-diffusion method [33] was used for studying the potential activities of these compounds. All compounds only showed potent activity against Staphylococcus aureus and Candida albicans in the following ranking: 3ae > 5ae > 4ae2ae. Minimum inhibitory concentration (MIC) values for the individual compounds that showed inhibition zones > 10 were determined by means of the agar well-diffusion method in DMSO. The results of antimicrobial activities of our synthesized compounds against S. aureus and C. albicans are shown in Table 3 as zone of inhibition (in mm) and minimum inhibitory concentration, MIC (mg/mL). The trend of activity was observed as follows: X > H > OMe > NO2 where X = Cl, Br. Minimum bactericidal concentrations (MBC) were determined for all chloro derivatives such as 1c, 2c, 3c, 4c and 5c which exhibit good activities. These results are listed in Table 4.
Table 4. Determination of minimum bactericidal concentration (MBC) µg/mL of chloro-derivatives.
Table 4. Determination of minimum bactericidal concentration (MBC) µg/mL of chloro-derivatives.
Concentrations µg/mL1000500250125633110005002501256331
Microorganism GrowthS. aureusC. albicans
2c---+++----++
3c---+++---+++
4c---+++--++ ++
5c--++++----++

3. Experimental

3.1. General

Melting points were taken in open capillary tubes using an Electrothermal apparatus 9100 (Rochford, UK) and are uncorrected. Microanalyses were performed at Faculty of Science, Cairo University, Cairo, Egypt, using an Elementary Vario el III C, H, N, S analyzer (Hanau, Germany). IR spectra were recorded using potassium bromide disks on a Perkin Elmer Spectrum RXI/FT-IR System (Faculty of Pharmacy, Alexandria University, Alexandria, Egypt). 1H-NMR spectra were determined on a Varian EM-390 MHz spectrophotometer, using TMS as internal standard.

3.2. General Procedure for Preparation of 3-Phenyl-4-(p-substituted phenyl)-3-buten-1-ones 1ae

Compounds 1ad were obtained in a good yield according to a published method [31]. The physical properties and all the spectral data were as reported in the literature

3.3. General Procedure for Preparation of 3-Phenyl-4-(p-substituted phenyl)-3-buten-1-(p-sulphamyl-phenyl)hydrazones 2ae

A solution of the chalcone 1ae (10 mmol) in ethanol (30 mL) was refluxed with the appropriate amount of p-sulphamylphenylhydrazine (10 mmol) in glacial acetic acid (2 mL) for six hours, then the reaction mixture was poured into crushed ice and kept overnight at room temperature. The separated crude solid was filtered off, washed successively with water, dried and recrystallized from ethanol (95%) to give 2ae as needles. Physical and analytical data for the prepared compounds are shown in Table 1. IR and 1H-NMR data are listed in Table 2.

3.4. General Procedure for Preparation of 3-Methyl-4-phenyl-5-(p-substituted phenyl)-1-(p-sulphamyl-phenyl)pyrazoles 3ae

A mixture of the appropriate hydrazones 2ae (10 mmol) and 30% HCl (15 mL) was heated under reflux for three hours and left to cool. After the reaction mixture reached room temperature, it was poured into crushed ice and the oily product deposited was decanted from water and extracted with ether. The ether layer was washed two times by water, dried over anhydrous sodium sulphate and evaporated. The precipitate obtained was recrystallized from ethanol (95%) to afford the corresponding pyrazoles 3ae as needles. Physical and analytical data for 3ae are as shown in Table 1. IR and 1H-NMR data are shown in Table 2.

3.5. General Procedure for Preparation of 4,5-Dihydro-3-methyl-4-phenyl-5-(p-substituted phenyl)-pyrazole-1-thiocarboxamides 4ae

A mixture of the appropriate chalcone 1ae (10 mmol) in ethanol (30 mL) was refluxed with the appropriate amount of thiosemicarbazide (12 mmol) in glacial acetic acid (2 mL) for 17 hours, then the reaction mixture was poured into crushed ice and was kept overnight at room temperature. The separated crude solid was filtered off, washed successively with water, dried and recrystallized from ethanol/chloroform to give 4ae as needles. The results and characterization data are listed in Table 1 and Table 2.

3.6. General Procedure for Preparation of 4,5-Dihydro-3-methyl-4-phenyl-5-(p-substituted phenyl)-1-isonicotinoylpyrazoles 5ae

A mixture of the appropriate chalcone 1ae (10 mmol) in ethanol (30 mL) was refluxed with the appropriate amount of isonicotinic acid hydrazide (10 mmol) in glacial acetic acid (2 mL) for five hours. The reaction mixture was treated as mentioned for the preparation of 4ae to give the corresponding pyrazole 5ae. Physical and spectroscopic data of 5ae are listed in Table 1 and Table 2, respectively.

3.7. Determination of Antimicrobial Activity

All compounds were tested against four different microorganisms: Staphylococcus aurous, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. The agar well-diffusionmethod was applied for the determination of inhibition zone and minimum inhibitory concentration (MIC). Briefly, broth culture (0.75 mL) containing ca. 106 colon-forming units (CFU) per mL of the test strain was added to nutrient agar medium (75 mL) at 45 °C, mixed well, and then poured into a 15 cm sterile metallic Petri plate. The medium was allowed to solidify and 8 mm wells were dug with a sterile metallic borer, then a DMSO solution of the test sample (1 mL) at 1 mg/mL was added to the respective wells. DMSO served as negative control, and the standard antimicrobial drugs rifampicin (5 μg/disc) and ampicillin (10 μg/disc) were used as positive controls. Triplicate plates for each microorganism strain were prepared and were incubated aerobically at 37 °C for 24 h. The activity was determined by measuring the diameter of zone showing complete inhibition (mm), thereby, the zones were precisely measured with the aid of a Venier caliper (precision 0.1 mm). The growth inhibition was calculated with reference to the positive control. For the individual compounds that showed inhibition zones >10 mm, MIC values were determined by means of the agar well-diffusion method for concentrations of 1.0, 0.50, 0.25, 0.125, 0.063 and 0.031 mg/mL in DMSO. The tests were performed in triplicate, and the results were averaged. Minimum bactericidal concentrations (MBC) were determined for all chloro derivatives which exhibit good activities (1c, 2c, 4c and 5c) for concentrations of 1.0, 0.50, 0.25, 0.125, 0.063 and 0.031 mg/mL in DMSO. The results are listed in Table 3 and Table 4.

4. Conclusions

This work demonstrates a rapid, efficient method for synthesis of some pyrazole derivatives. Compounds having pharmacophores such as chloro- and bromo-substituents with lipophilic properties showed the greatest antimicrobial activity.

Acknowledgements

The authors wish to thank the management of microbiology lab, Faculty of Pharmacy, Alexandria University, for their support to carry out the antimicrobial activity.

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  • Sample Availability: Samples of all the compounds are available from the authors.

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Sharshira, E.M.; Hamada, N.M.M. Synthesis and Antimicrobial Evaluation of Some Pyrazole Derivatives. Molecules 2012, 17, 4962-4971. https://doi.org/10.3390/molecules17054962

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Sharshira EM, Hamada NMM. Synthesis and Antimicrobial Evaluation of Some Pyrazole Derivatives. Molecules. 2012; 17(5):4962-4971. https://doi.org/10.3390/molecules17054962

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Sharshira, Essam Mohamed, and Nagwa Mohamed Mahrous Hamada. 2012. "Synthesis and Antimicrobial Evaluation of Some Pyrazole Derivatives" Molecules 17, no. 5: 4962-4971. https://doi.org/10.3390/molecules17054962

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