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0Arabian Journal of Chemistry (2013) xxx, xxx-xxx
King Saud University Arabian Journal of Chemistry
www.ksu.edu.sa www.sciencedirect.com
ORIGINAL ARTICLE
Synthesis and antimicrobial activity of pyrazole nucleus containing 2-thioxothiazolidin-4-one derivatives
H. B'Bhatt, S. Sharma *
Department of Chemistry, Hemchandracharya North Gujarat University, Patan 384 265, Gujarat, India Received 10 December 2012; accepted 30 May 2013
KEYWORDS
3-(4-Chlorophenyl)-2-thioxothiazolidin-4-one; Vilsmeier-Haack reaction; 1-Phenyl-3-(p-substituted phenyl)-1H-pyrazole-4-carbaldehyde; Antibacterial activity; Antifungal activity
Abstract A series of novel compounds of type 3-(4-chlorophenyl)-5-((1-phenyl-3-aryl-1H-pyrazol-4-yl)methylene)-2-thioxothiazolidin-4-one (3a-h) have been synthesized from the 3-(4-chlorophenyl)-2-thioxothiazolidin-4-one (1) and 1-phenyl-3-(p-substituted phenyl)-1H-pyra-zole-4-carbaldehyde (2a-h). The structures of all the synthesized compounds have been confirmed by elemental analyses, FT-IR, 1H NMR, 13C NMR and mass spectral data. These newly synthesized compounds were screened for in vitro antibacterial activity against Escherichia coli (MTCC 443), Pseudomonas aeruginosa (MTCC 1688), Staphylococcus aureus (MTCC 96), and Staphylococcus pyogenes (MTCC 442) using commercially available antibiotics ampicillin as a standard drug. Compound 3c was found as a potent compound against E. coli, compounds 3a, 3d and 3g were found as a potent against S. aureus, while 3d against S. pyogenes. For in vitro antifungal activity, these compounds were tested against Candida albicans (MTCC 227), Aspergillus niger (MTCC 282) and Aspergillus clavatus (MTCC 1323) using griseofulvin as a standard drug. Compounds 3b and 3d were found to have very good activity against C. albicans. Variable and modest activities were observed against the investigated strains of bacteria and fungi.
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1. Introduction
Microbial diseases have emerged as a main origin of morbidity and often as suppressor of immune power over the past two decades. Microbes are responsible for several poisonous syndromes and prevalent epidemics in human civilizations. Microbial diseases such as plague, diphtheria, typhoid, cholera,
pneumonia and tuberculosis have taken high toll of humanity in recent pasts (Todar, 2011). In present times, many of the accessible antimicrobial drugs are poisonous and create recurrence of diseases because they are bacteriostatic and not bactericides. These can also lead to the expansion of resistance due to the long periods of administration.
The growing potent literature of recent years demonstrated that the 2-thioxothiazolidin-4-one derivatives exhibit better pharmacological properties such as antimicrobial (Zhen-Hua et al., 2010; Habib et al., 1997; Tomasic et al., 2010; Dixit et al., 2010; Chen et al., 2010; Desai and Desai, 2006; Abdel-Halim et al., 1994; Pachhamia and Parikh, 1991), HIV-1 integrase inhibitors (Ramkumar et al., 2010) and anticonvulsant effect (Gursoy and Terzioglu, 2005). Additionally, rhodanine
* Corresponding author. Tel.: +91 2766 220932. E-mail address: smridhee2000@yahoo.co.in (S. Sharma). Peer review under responsibility of King Saud University.
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Table 1 Antibacterial and antifungal activities of compounds (3a-h).
Bacterial strains Fungal strains
E. Coli P. aeruginosa S. aureus S. pyogenes C. albicans A. niger A. clavatus
(MTCC443) (MTCC 1688) (MTCC 96) (MTCC 442) (MTCC 227) (MTCC 282) (MTCC 1323)
Comp. Code -R Minimum inhibition concentration (MIC) (ig/ml)
3a -H 500 125 100 125 500 1000 >1000
3b -CH3 250 500 250 125 250 200 200
3c -OH 62.5 125 250 250 500 500 500
3d -no2 200 200 100 100 200 >1000 >1000
3e -F 500 200 500 500 1000 >1000 >1000
3f -Br 100 250 200 200 1000 200 250
3g -Cl 500 125 100 125 500 1000 >1000
3h -OCH3 250 250 250 200 500 1000 >1000
Ampicillin 100 100 250 100
Griseofulvin 500 100 100
based molecules have gained much attention as small molecule inhibitors of various targets such as anti-diabetics (Murugan et al., 2009; Momose et al., 1991), aldose reductase (Bruno et al., 2002; Fujishima and Tsuboto, 2002), ß-lactamase (Grant et al., 2000), cathepsin D (Whitesitt et al., 1996), PMT inhibitors (Orchard et al., 2004), PDE4 inhibitors (Irvine et al., 2008), and histidine decarboxylase (Free et al., 1971).
Pyrazolo[3,4-d]pyrimidines are of considerable chemical and pharmacological importance as purine analogs (Ghorab et al., 2009; Bhat et al., 1981; Zacharie et al., 1996). Various compounds with related structures also possessed anti-tumor and antileukemia activities (Anderson et al., 1990; Avila et al., 1986). On the other hand, substituted pyridazines are often used in medicine because of their pronounced bactericidal and fungicidal effects (Contreras et al., 1999).
We report here, the synthesis of a series of novel rhodanine derivatives containing pyrazole moiety. The synthesized compounds have been structurally established with modern analytical tools like IR, NMR and mass spectroscopy with an aim to find new and more potent antibacterial and antifungal agents.
2. Experimental section
2.1. General
The melting points of the synthesized products were determined using Mettler Toledo FP 62 melting point apparatus (Metter Toledo-Switzerland) and were used without correc-
tion. The FT-IR spectra were recorded on a Perkin Elmer Spectrum GX FT-IR System (USA) in a KBr disk. 1H and 13C spectra (solvent DMSO-d6) were recorded on 200 MHz Bruker Avance DPX 200 NMR system. TMS was used as an
internal standard. The mass spectra were scanned on a Shima-dzu QP2010 spectrometer (equipped with a direct inlet probe) operating at 70 eV. Elemental analysis was performed on Per-kin Elmer CHNS (O) analyzer (PE-2400 Series II-USA). Analytical TLC was performed on silica gel GF 254.
2.2. Biological assay 2.2.1. Antibacterial activity
The newly synthesized compounds were screened for their antibacterial activity against gram positive bacteria Staphylococcus
aureus (MTCC-96) and Streptococcus pyogenes (MTCC-442) and gram negative bacteria Escherichia coli (MTCC-443) and Pseudomonas aeruginosa (MTCC-1688). Antibacterial activity was carried out by serial broth dilution method (Pier et al., 1997)|. The standard strains used for the antimicrobial activity were procured from the Institute of Microbial Technology, Chandigarh, India. Compounds (3a-h) were screened for their antibacterial activity in triplicate against E. coli, S. aureus, P. aeruginosa, and S. pyogenes at different concentrations of 1000, 500, 250, 100 (Table 1). The drugs which were found to be active in primary screening were diluted to obtain required concentrations to get more close result. The growths of bacterial cultures were monitored after 24 and 48 h. The lowest concentration, which showed no growth after spot subculture was considered as MIC for each drug. Also, the highest dilution showing at least 99% inhibition is taken as MIC. The test mixture selected for this assay contained 108 cells/ml. The standard drug used for this study was ampicillin and it showed MIC at 100, 100, 250, and 100 ig/ml against E. coli, P. aeru-ginosa, S. aureus, and S. pyogenes, respectively.
2.2.2. Antifungal activity
Same compounds were tested for antifungal activity in triplicate against Candida albicans, Aspergillus niger, and Aspergil-lus clavatus at various concentrations of 1000, 500, 250, and 100 ig/ml as shown in (Table 1). The results were recorded in the form of primary and secondary screening. The synthesized compounds were diluted at 1000 ig/ml concentration, as a stock solution. The synthesized compounds which were found to be active in this primary screening were further tested in a second set of dilution against all microorganisms. The lowest concentration, which showed no growth after spot subculture and highest dilution showing at least 99% inhibition was considered as MIC for each drug. Antibiotic griseofulvin was used as a standard drug for antifungal activity study. It showed MIC at concentrations 500, 100 and 100 ig/ml for C. albicans, A. niger and A. clavatus, respectively.
2.3. General synthetic method
2.3.1. Synthesis of 3-(4-chlorophenyl)-2-thioxothiazolidin-4-one (1)
Synthesis of 3-(4-chlorophenyl)-2-thioxothiazolidin-4-one (1) was carried according to the procedure reported earlier
(Redemann, 1947). Characterization data were obtained using various analytical tools and were compared well with literature values. (It is reported as supplementary data).
2.3.2. Synthesis of 1-phenyl-3-(p-substituted phenyl)-1H-pyrazole-4-carbaldehydes (2a-h)
The compounds of 1-phenyl-3-(p-substituted phenyl)-1H-pyr-azole-4-carbaldehydes (2a-h) have been synthesized according to the method reported in the literature (Fieser et al., 1940; Prakash et al., 2011a,b). Characterization data have shown a good correlation with literature values and data of representative compound are attached herewith as supplementary data.
2.3.3. Synthesis of 3-(4-chlorophenyl)-5-((1-phenyl-3-aryl-1H-pyrazol-4-yl) methylene)-2-thioxothiazolidin-4-one (3a-h)
All the compounds (3a-h) were synthesized according to the Knoevenagel condensation reaction (Song et al., 2012).
To the solution of 3-(4-chlorophenyl)-2-thioxothiazolidin-4-one (10 mM) (1) in ethanol and anhydrous sodium acetate (10 mM), 1-phenyl-3-(p-substituted phenyl)-1H-pyrazole-4-carbaldehyde (2a-h) (10 mM) was added. The reaction mixture was heated and refluxed for 6 h. A bright yellow crystalline product was obtained and the excess solvent was removed under reduced pressure. Crude product was washed with water and isolated by filtration. It was recrystallized from ethanol to give compounds (3a-h).
2.4. Physical and spectral data
2.4.1. 3-(4-chlorophenyl)-5-((1,3-diphenyl-1H-pyrazol-4-yl)methylene-2-thioxothiazolidin-4-one) (3a)
Yield 59%; yellow crystalline solid; mp 196-198 0C; IR (KBr, cm-1) v: 3113, 3066 (Ar-H stretching, pyrazole -H stretching), 1725 (C=O stretching), 1579, 1499, 1443 (C=N, C=C, aromatic ring), 1332 (C=S stretching), 693 (C-S-C linkage); *H NMR (DMSO-d6) d (ppm): 8.91 (s, 1H, -C=CH group in the pyrazole ring), 8.11-7.06 (m, 15H, Ar-H, C-NH, -C=CH); 13C NMR (DMSO-d6) d: 193.6, 180.6, 166.3, 152.6, 138.8, 134.4, 134.3, 132.2, 130.9, 130.6, 129.8, 129.6, 129.6, 129.1, 128.0, 123.0, 122.8, 119.8, 115.8; MS: m/z: 473 (M + , % abundance = 2%), 469, 438, 276, 215, 122; analytical calculations for C25H16ClN3OS2 (473.0): C, 63.35; H, 3.40; N, 8.87; S, 13.53. found: C, 63.59; H, 3.61; N, 8.98; S, 13.71.
2.4.2. 3-(4-chlorophenyl)-5-((1-phenyl-3-tolyl-1H-pyrazol-4-yl) methylene-2-thioxothiazolidin-4-one) (3b)
Yield 89%; yellow crystalline solid; mp 199-201 0C; IR (KBr, cm-1) v: 3100, 3030 (Ar-H stretching, pyrazole -H stretching), 1716 (C=O stretching), 1587, 1525, 1443 (C=N, C=C, aromatic ring), 1339 (C=S stretching), 685 (C-S-C linkage); *H NMR (DMSO-d6) d (ppm): 8.88 (s, 1H, -C=CH group in pyrazole ring), 8.11-7.38 (m, 14H, Ar-H, C-NH, -C=CH), 2.41 (s, 3H, Ar-H); 13C NMR (DMSO-d6) d: 193.8, 166.9, 154.5, 146.3, 139.3, 134.6, 131.2, 130.1, 130.0, 129.1, 128.0, 123.5, 122.2, 119.9, 116.0, 21.3; MS: m/z: 487(M + , % abundance = 30%), 290, 257, 187, 154; analytical calculations for C26H18ClN3OS2 (487.1): C, 63.99; H, 3.72; N, 8.61; S, 13.14. Found: C, 63.81; H, 3.64; N, 8.51; S, 13.23.
2.4.3. 3-(4-chlorophenyl)-5-((3-(4-hydroxyphenyl)-1-phenyl-1H-pyrazol-4-yl)methylene-2-thioxothiazolidin-4-one) (3c)
Yield 59%; yellow crystalline solid; mp 261-263 0C; IR (KBr, cm-1) v: 3110, 3030 (Ar-H stretching, pyrazole -H stretching), 1724 (C=O stretching), 1594, 1521, 1438 (C=N, C=C, aromatic ring), 1345 (C=S stretching), 685 (C-S-C linkage); *H NMR (DMSO-d6) d (ppm): 8.69 (s, 1H, =CH group in pyrazole ring), 8.28-7.33 (m, 15H, Ar-H, C-NH, -C=CH); 13H NMR (DMSO-d6) d: 190.6, 168.0, 150.6, 148.0, 138.6, 134.7, 133.0, 131.3, 130.6, 123.51, 123.1, 122.7, 121.6, 120.6, 119.5, 115.6; MS: m/z: 490 (M + , % abundance = 2%), 379, 292, 249, 156; analytical calculations for C25H16ClN3O2S2 (490.0): C, 61.28; H, 3.29; N, 8.58; S, 13.09. Found: C, 61.32; H, 3.41; N, 8.49; S, 13.22.
2.4.4. 3-(4-chlorophenyl)-5-((3-(4-nitrophenyl)-1-phenyl-1H-pyrazol-4-yl)methylene-2-thioxothiazolidin-4-one) (3d) Yield 64%; yellow crystalline solid; mp > 300 0C; IR (KBr, cm-1) v: 3121, 3085 (Ar-H stretching, pyrazole -H stretching), 1719 (C=O stretching), 1600, 1530, 1446 (C=N, C=C, aromatic ring), 1345 (C=S stretching), 684 (C-S-C linkage); *H NMR (DMSO-d6) d (ppm): 8.81 (s, 1H, =CH group in pyrazole ring), 8.47-7.41 (m, 14H, Ar-H, C-NH, -C=CH); 13C NMR (DMSO-d6) d: 193.7, 166.6, 150.6,
148.0, 138.6, 134.7, 133.0, 131.7, 131.31, 129.5, 128.4, 127.5, 126.7, 123.5, 123.1, 122.7, 121.6, 120.6, 119.6, 115.6; MS: m/z: 518 (M + , % abundance = 31%), 321, 275, 242, 169; analytical calculations for C25H15ClN4O3S2 (519.0): C, 57.86; H, 2.91; N, 10.80; S, 12.36. Found: C, 57.76; H, 2.70; N, 10.89; S, 12.42.
2.4.5. 3-(4-chlorophenyl)-5-((3-(4-fluorophenyl)-1-phenyl-1H-pyrazol-4-yl)methylene-2-thioxothiazolidin-4-one) (3e)
Yield 81%; yellow crystalline solid; mp 224-226 0C; IR (KBr, cm-1) v: 3101, 3059 (Ar-H stretching, pyrazole -H stretching),
1718 (C=O stretching), 1596, 1526, 1442 (C=N, C=C, aromatic ring), 1345 (C=S stretching), 686 (C-S-C linkage); *H NMR (DMSO-d6) d (ppm): 8.92 (s, 1H, =CH group in the pyrazole ring), 8.10-7.49 (m, 14H, Ar-H, C-NH, -C=CH); 13C NMR (DMSO-d6) d: 193.3, 166.3, 163.6, 161.6, 152.9,
138.6. 134.1, 131.0, 130.7, 129.5, 129.3, 128.6, 127.6, 122.7,
122.1, 119.4, 116.1, 115.9; MS: m/z: 492 (M + , % abundance = 10%), 294, 233, 191, 147; analytical calculations for C25H15ClFN3OS2 (492.0): C, 61.03; H, 3.07; N, 8.54; S, 13.03;. Found: C, 61.22; H, 3.23; N, 8.69; S, 13.24.
2.4.6. 5-((3-(4-bromophenyl)-1-phenyl-1H-pyrazol-4-yl) methylene)-3-(4-chlorophenyl)-2-thioxothiazolidin-4-one (3f) Yield 61%; yellow crystalline solid; mp 237-239 0C; IR (KBr, cm-1) v: 3119, 3063 (Ar-H stretching, pyrazole -H stretching),
1719 (C=O stretching), 1590, 1524, 1439 (C=N, C=C, aromatic ring, 1341 (C=S stretching), 687 (C-S-C linkage); *H NMR (DMSO-d6) d (ppm): 8.90 (s, 1H, =CH group in the pyrazole ring), 8.11-7.45 (m, 14H, Ar-H, C-NH, -C=CH); 13C NMR (DMSO-d6) d: 193.8, 180.8, 166.8, 152.8, 139.0, 134.6, 134.5, 132.5, 131.17, 130.8, 130.1, 129.9, 129.3, 128.2, 123.0, 120.0, 116.1; MS: m/z: 552(M + , % abundance = 25%), 356, 275, 231, 169; analytical calculations for C25H15BrClN3OS2 (552.9): C, 54.31; H, 2.73; N, 7.60; S, 11.60. Found: C, 54.18; H, 2.67; N, 7.79; S, 11.76.
2.4.7. 3-(4-chlorophenyl)-5-((3-(4-chlorophenyl)-1-phenyl-1H-pyrazol-4-yl)methylene-2-thioxothiazolidin-4-one) (3g)
Yield 76%; yellow crystalline solid; mp 240-242 0C; IR (KBr, cm-1) v: 3095, 3060 (Ar-H stretching, pyrazole -H stretching), 1730 (C=O stretching), 1594, 1496, 1430 (C=N, C=C, aromatic ring), 1342 (C=S stretching), 683 (C-S-C linkage); 1H NMR (DMSO-d6) d (ppm): 8.91 (s, 1H, =CH group in the pyrazole ring), 8.11-7.45 (m, 14H, Ar-H, C-NH, -C=CH); 13C NMR (DMSO-d6) d: 193.8, 166.8, 153.1, 134.5, 131.2, 130.9, 130.4, 130.1, 129.90, 129.6, 129.3, 128.2, 123.1, 122.9, 120.0, 116.1; MS: m/z: 508 (M + , % abundance = 12%), 310, 275, 231, 169; analytical calculations for C25H15Cl2N3OS2 (508.4): C, 59.06; H, 2.97; N, 8.26; S, 12.61. Found: C, 59.11; H, 2.82; N, 8.19; S, 12.51.
2.4.8. 3-(4-chlorophenyl)-5-((3-(4-methoxyphenyl)-1-phenyl-1H-pyrazol-4-yl)methylene-2-thioxothiazolidin-4-one) (3h)
Yield 81%; yellow crystalline solid; mp 213-215 0C; IR (KBr, cm-1) v: 3103, 3036 (Ar-H stretching, pyrazole -H stretching), 1712 (C=O stretching), 1586, 1520, 1439 (C=N, C=C, aromatic ring), 1338 (C=S stretching), 684 (C-S-C linkage); *H NMR (DMSO-d6) d (ppm): 8.86 (s, 1H, =CH group in the pyrazole ring), 8.10-7.12 (m, 14H, Ar-H, C-NH, -C=CH), 3.84 (s, 3H, Ar-OCH3); 13C NMR (DMSO-d6) d: 193.3,
166.4, 160.0, 153.8, 138.6, 134.1, 130.7, 130.0, 129.5, 129.3,
128.5, 127.5, 123.2, 121.6, 119.4, 115.4, 114.4, 55.2; MS: m/z: 504 (M + , % abundance = 12%), 306, 263, 169, 111; analytical calculations for C26H18ClN3O2S2 (504.0): C, 61.96; H, 3.60; N, 8.34; S, 12.72. Found: C, 61.83; H, 3.42; N, 8.19; S, 12.91.
Liq. Ammonia
(i) 0" C DMF / POCI3
(ii) reflux 85° C, 6 hrs
2(a-h)
1 + 2(a-h)
Fused CH3COONa EtOH, Reflux, 6h
3 (a-h)
3a 3b 3c 3d 3e 3f 3g 3h
-H -CH3 -OH -NO2 -F -Br -CI -OCH3
Scheme 1 Schematic representation of synthesis of 3-(4-chlorophenyl)-5-((1-phenyl-3-aryl 1H-pyrazol-4-yl) methylene)-2-thioxothiaz-olidin-4-one (3a-h).
3. Results and discussion
3.1. Chemistry
The synthetic route followed for the preparation of the novel 3-(4-chlorophenyl)-5-((1-phenyl-3-aryl-1H-pyrazol-4-yl) meth-ylene)-2-thioxothiazolidin-4-one (3a-h) derivatives is illustrated in Scheme 1. The compound 3-(4-chlorophenyl)-2-thioxothiaz-olidin-4-one (1) was synthesized from the reaction of carbon disulfide, ammonia, and chloroacetic acid (1) (Redemann, 1947). The ketones on treatment with phenyl hydrazine formed required Schiffs bases. The Schiffs bases of ketones on treatment with dimethyl formamide and phosphorous oxychloride underwent cyclization reaction forming pyrazole derivatives and got formylated on to the pyrazole ring (2a-h) (Fieser et al., 1940). The final compounds 3-(4-chlorophenyl)-5-((1-phenyl-3-aryl-1H-pyrazol-4-yl)methylene)-2-thioxothiazolidin-4-one (3a-h) were synthesized with 3-(4-chlorophenyl)-2-thioxothiaz-olidin-4-one (1) and 1-phenyl-3-(p-substituted phenyl)-1H-pyr-azole-4-carbaldehyde (2a-h) (Scheme 1). All the synthesized compounds were characterized by FT-IR, 13C and *H NMR and GC-MS. The expected IR spectra were assigned to the synthesized compounds (3a-h). The band observed around 1350-1320 cm-1 was attributed to -C=S stretching vibration of the thiazole ring. Bands at about 1600-1560 cm-1 were attributed to -C=N stretching vibration of pyrazole moiety. Strong bands in the region 1740-1700 cm-1 was due to -C=O stretching of the amide group. *H and 13C NMR and mass spectral data of compounds (3a-h) are shown in Section 2. The 1H NMR spectra showed the most characteristics olefinic proton C=CH deshielded at d = 8.9-8.6 ppm in the pyrazole ring (Fig. 1). 13C NMR spectra show chemical shift around 193-190 due to the presence of-C=S in the rhodanine ring. Chemical shift at 168-166 represents the -C=O in the rhodanine ring and at 154-150 represents the -C=N in the pyrazole ring (Fig. 2). All these compounds were subjected to C, H, N and S analysis.
3.2. Antimicrobial activity
Antimicrobial study of synthesized compounds was performed against two gram negative bacterial strains namely E. coli, and P. aeruginosa and two gram positive bacterial stains namely S. aureus, and S. pyogenes and against three different fungi e.g. C.
In1HNMR (ppm)
Figure 1 1H NMR chemical shift (d) representation for compound 3b.
154.557
193.837
21.369
In 13CNMR (ppm)
Figure 2 13C NMR chemical shift (d) representation for compound 3b.
§ 200
■— Compd.
Ampicillin
■ ■
3a 3b 3c 3d 3e 3f 3g 3h Compound Code
Figure 3 Graphical representation of ''MIC'' values comparison of synthesized compounds 3-(4-chlorophenyl)-5-((1-phenyl-3-aryl-1H-pyrazol-4-yl)methylene)-2-thioxothiazolidin-4-one (3a-h) for the Pseudomonas aeruginosa bacterial strain.
^ 700 J
500 § 400
300 200 100 0
3a 3b 3c 3d 3e 3f 3g 3h Compound Code
Figure 4 Graphical representation of ''MIC'' values comparison of synthesized compounds 3-(4-chlorophenyl)-5-((1-phenyl-3-aryl-1H-pyrazol-4-yl)methylene)-2-thioxothiazolidin-4-one (3a-h) for the Candida albicans fungal strain.
albicans, A. niger and A. clavatus. The standard antibiotics namely ampicillin and griseofulvin were used as positive control for bacteria and fungi, respectively. Solvent control was also checked to know the effect of the solvent on growth of microbes. The results were recorded for each tested compounds as the minimum inhibition concentration (MIC).
The results of antibacterial screening of newly synthesized compounds are presented in (Table 1) (Fig. 3 and Fig. 4). From the results, it has been revealed that all the tested compounds possess moderate to good antimicrobial activity against selected bacteria strains (E. coli, S. aureus, P. aerugin-osa, and S. pyogenes). On the basis of zone of inhibition test against test bacterium, E. coli, compound 3c (R' = 4-OH) was found to have very good activity and compound 3f (R' = 4-Br) possessed good activity, while compound 3d (R' = 4-NO2) showed moderate activity when compared with the standard drug ampicillin. In case of P. aeruginosa, compounds 3a (R' = 4-H), 3c (R' = 4-OH) and 3g (R' = 4-Cl) possessed moderate activity as compared to the standard drug ampicillin. For, S. aureus, compound 3d (R' = 4-NO2) was potent as it showed very good activity while other compounds like 3b (R' = 4-CH3), 3c (R' = 4-OH), 3f (R' = 4-Br) and 3h (R' = 4-OCH3) possessed only good activity when compared to the standard drug ampicillin. For, S. pyogenes, compound 3d (R' = 4-NO2) revealed good activity and compounds 3a (R' = 4-H), 3b C and 3g (R' = 4-Cl) showed moderate activity in comparison to the standard drug ampicillin. It is also concluded that compounds 3c (R' = 4-OH) and 3d (R' = 4-NO2) showed better antibacterial activity in comparison with their parent compound (Fig. 5 and Fig. 6). The reason for different sensitivities between gram-positive and gram-negative bacteria could be ascribed to the morphological difference between these micro-organisms. Gram-negative bacteria have an outer phospholipidic membrane carrying the structural lipo-polysaccharide components. This makes the cell wall impermeable to lipophilic solutes, while porins constitute a selective barrier to the hydrophilic solutes with an exclusion limit of about 600 Da (Nikaido and Vaara, 1985). The Gram-positive bacteria had been found to be more susceptible since they have only an outer peptidoglycan layer which is not an effective permeability barrier (Scherrer, 1971).
3.3. Antifungal activity
Antifungal screening of newly synthesized compounds is summarized in Table 1. All the compounds were also tested for their in vitro antifungal activity against three different fungal strains namely C. albicans, A. niger and A. clavatus. Griseo-fulvin was used as a reference drug for comparison of the activity of the tested compounds and the results were recorded as the percentage of the mycelial growth inhibitions. From the results, it has been revealed that most of the compounds possessed remarkable antifungal activity against selected fungal strains. For, C. albicans, compounds 3b (R' = 4-CH3) and 3d (R' = 4-NO2) showed very good activity and compounds 3a (R' = 4-H), 3c (R' = 4-OH), 3g (R' = 4-Cl) and 3h (R' = 4-OCH3) showed good activity as compared to the standard drug griseofulvin. For, A. niger strains, compounds 3b (R' = 4-CH3) and 3f (R' = 4-Br) possessed moderate activity as compared to the standard drug. In case of A. clavatus, compounds 3b (R' = 4-CH3) and 3f
^^ Compd.(1) KM Compd.(2c) E^ Compd.(3c)
E.C P.A S.A S.P C.A A.N A.C Microbial strains
Figure 5 Graphical representation of ''MIC'' values comparison of synthesized 3-(4 chlorophenyl)-5-((3-(4-hydroxyphenyl)-1-phe-nyl-1H-pyrazol-4-yl)methylene-2-thioxothiazolidin-4-one) (3c) with 3-(4-chlorophenyl)-2-thioxothiazolidin-4-one (1) and (3-(4-chlorophenyl)-5-((3-(4-hydroxyphenyl)-1-phenyl-1H-pyrazol-4-yl) methylene)-2-thioxothiazolidin-4-one (2c) for said bacterial and fungal strain.
(R' = 4-Br) represented as moderately potential molecule as compared to the standard drug griseofulvin.
4. Conclusions
A series of compounds 3-(4-chlorophenyl)-5-((1-phenyl-3-aryl-1H-pyrazol-4-yl) methylene)-2-thioxothiazolidin-4-one
Hi Compd.(1) Hi Compd.(2d) Compd.(3d)
E.C P.A
S.A S.P C.A Microbial strains
A.N A.C
Figure 6 Graphical representation of ''MIC'' values comparison of synthesized 3-(4-chlorophenyl)-5-((3-(4-nitrophenyl)-1-phenyl-1H-pyrazol-4-yl)methylene-2-thioxothiazolidin-4-one) (3d) with 3-(4-chlorophenyl)-2-thioxothiazolidin-4-one (1) and3-(4-chloro-phenyl)-5-((3-(4-nitrophenyl)-1-phenyl-1H-pyrazol-4-yl)methy-lene)-2-thioxothiazolidin-4-one (2d) for said bacterial and fungal strain.
(3a-h) have been synthesized from 3-(4-chlorophenyl)-2-thi-oxothiazolidin-4-one (1) and 1-phenyl-3-(p-substituted phe-nyl)-1H-pyrazole-4-carbaldehydes (2a-h). Analytical and spectral data (FT-IR, 1H-NMR, 13C-NMR, GC-MS) of all the synthesized compounds are in full agreement with the proposed structure. Comparison of the antimicrobial results of synthesized compounds (3a-h) has revealed that the addition of pyrazole derivatives in 3-(4-chlorophenyl)-2-thioxo-thiazolidin-4-one (1) has improved their antimicrobial activities. The series of compounds synthesized as 3-(4-chlo-rophenyl)-5-((1-phenyl-3-aryl-1 H-pyrazol-4-yl) methylene)-2-thioxothiazolidin-4-one (3a-h) exhibited moderate to very good antimicrobial activities. The reason for different sensitivities between gram-positive and gram-negative bacteria could be ascribed to the morphological difference between these micro-organisms.
Acknowledgments
Authors are thankful to Micro Care laboratory and TRC, Surat, India for carrying out microbial studies.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.arabjc. 2013.05.029.
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