5.2
Impact Factor
Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Search in posts
Search in pages
Filter by Categories
Corrigendum
Current Issue
Editorial
Erratum
Full Length Article
Full lenth article
Letter to Editor
Original Article
Research article
Retraction
Retraction notice
Review
Review Article
SPECIAL ISSUE: ENVIRONMENTAL CHEMISTRY
5.3
Impact Factor
Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Search in posts
Search in pages
Filter by Categories
Corrigendum
Current Issue
Editorial
Erratum
Full Length Article
Full lenth article
Letter to Editor
Original Article
Research article
Retraction
Retraction notice
Review
Review Article
SPECIAL ISSUE: ENVIRONMENTAL CHEMISTRY
View/Download PDF

Translate this page into:

Original article
10 (
8
); 1098-1106
doi:
10.1016/j.arabjc.2015.05.002

Synthesis, characterization and biological evaluation of some novel nitrogen and sulphur containing organometallic heterocycles

, , , , ,
a Department of Chemistry, Faculty of Science, University of Tabuk, Tabuk, Saudi Arabia
b Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh 202002, India

⁎Corresponding author. Tel.: +966 551397507. h.nabi@ut.edu.sa (Humaira Parveen)

Received: , Accepted: ,
© The Author(s) 2015
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

A series of some novel sulphur and nitrogen containing ferrocenyl linked heterocyclic compounds were synthesized by multistep reactions and evaluated for in vitro antimicrobial activity against 15 ATCC strains out of which 8 were bacterial (Pseudomonas aeruginosa, Streptococcus bovis, Enterococcus faecalis, Klebsiella pneumoniae, Escherichia coli, Enterobacter cloacae, Methicillin-resistant Staphylococcus aureus and Streptococcus mutans) and 7 were fungal (Candida albicans, Candida dubliniensis, Candida glabrata, Candida parapsilosis, Candida tropicalis, Candida kefyr and Candida krusei) strains. The results clearly depict that the compounds (1–12) gave an average antimicrobial activity against the tested strains with an exception of compound 12 which stood out in terms of its activity against the tested organisms. All these compounds gave a range of MIC value between 32–64 μg/ml against S. bovis, E. coli and C. tropicalis except compound 12 which gave a MIC of 16 μg/ml against each of them. The MIC values of all these compounds against biofilm forming P. aeruginosa and S. mutans were 64–256 μg/ml and 64–128 μg/ml respectively which is apparently high, concluding that these compounds hold immense potential to be employed as a two in one formulation of antibacterial as well as antifungal agents.

Keywords

Organometallic heterocyclic compounds
Antibacterial activity
Antifungal activity
1

1 Introduction

In the past few decades, the incidence of microbial infection has increased on frightening level over the world as a result of antimicrobial resistance (Ghannoum and Rice, 1999; Fluit et al., 2001; Canuto and Rodero, 2002; Pfaller and Diekema, 2007; Mukherjee et al., 2005; Shapiro et al., 2011). Microbial infections are a growing problem in contemporary medicine and the use of antibiotics is common across the world. Consequently, there is an urgent need to widen antimicrobial agents, which have a broad spectrum of activity against the resistant microorganisms. The current literature is enriched with progressive findings about the synthesis and pharmacological action of fused heterocycles such as pyrazolines and related heterocyclic compounds (Yusuf and Jain, 2014; Kathiravan et al., 2012).

On the other hand, ferrocene and its derivatives, since their discovery have been attracting much attention due to their wide range of applications in catalysis, material sciences (Togni and Hayashi, 1995), biological studies and even in therapy (Jaouen et al., 2006; Lang and Heinze, 2013; Stepnicka, 2008; Scarcia et al., 1988; Hill et al., 1989; Neuse and Kanzawa 1990; Motohashi et al., 1990; Houlton et al., 1991; Top et al., 2001; Klimova et al., 2001; Ma et al., 2001; Delhaes et al., 2001; Weber et al., 2004; Jaouen et al., 2004; Bincoletto et al., 2005; Hillard et al., 2006). Ferroquine, the ferrocenyl derivative of antimalarial drug chloroquine, is currently at the phase II clinical trial stage as the best promise against the chloroquine-resistant strains of Plasmodium falciparum (Biot et al., 2005; Dive and Biot, 2008; Biot and Dive, 2010; Supan et al., 2012). Many ferrocenyl compounds also display interesting cytotoxic, anti-tumor, anticancer, antimalarial, antifungal and DNA-cleaving activity (Kealy and Pauson, 1951; Kelly et al., 2007; Fouda et al., 2007). Recently, some new ferrocenyl-substituted heterocyclic compounds have been reported as potential pharmaceuticals (Huang et al., 2014; Arancibia et al., 2014; Harry et al., 2014; Yu et al., 2007; Zora and Görmen, 2007; Zora and Velioğlu, 2008; Fabian et al., 2007; Mochida et al., 2007; Maity et al., 2008). Moreover, the stability and nontoxicity of the ferrocenyl moiety is of particular interest rendering such drugs compatible with other treatment (Biot et al., 2000). In this sense, the integration of one or more ferrocene units into a heterocyclic molecule has long been recognized as an attractive way to endow a novel molecule functionality (Sun et al., 2002; Haung and Wang, 2001). Recent publications also support that combination of pharmacologically active N-heterocycles among them pyrazolines and pyrazoles with ferrocene moiety results in favourable change of biological properties, often associated with decreased toxicity (Delhaes et al., 2001; Vázquez López et al., 2004; Fang et al., 2003). Moreover, thiazoles are found in many biologically active compounds, including natural products and pharmaceutical agents (Kashyap et al., 2012; Eicher and Hauptmann, 2003; Siddiqui et al., 2011) and it is well documented that the combination of two or more types of heterocycles into one molecule could afford a novel entity with increased bioactivities (Zhou and Wang, 2012; Wang and Zhou, 2011).

In view of these observations and as a part of our ongoing search devoted to the synthesis of biologically active heterocycles (Iqbal et al., 2009; Parveen et al., 2010, 2011) we report herein some novel 5-ferrocenyl-3-substituted aryl-4,5-dihydro-1H-pyrazol-1-carbothioamides (1–6) and their cyclized products 2-(5-ferrocenyl-3-aryl-4,5-dihydro-1H-pyrazol-1-yl)-4-(4-substituted-aryl) thiazoles (7–12), as useful leads towards the development of potent antimicrobial agents.

2

2 Results and discussion

2.1

2.1 Synthesis

The aforementioned compounds were prepared according to the synthetic sequences illustrated in Scheme 1. The ferrocenyl chalcones (a–f), were prepared by a classic Claisen–Schmidt condensation of substituted acetophenones/1-phenyl butane-1-one/2-acetyl ferrocene with ferrocene carboxaldehyde in the presence of KOH and absolute ethanol. The cyclization of ferrocenyl chalcones (a–f), with thiosemicarbazide and sodium hydroxide in the presence of absolute ethanol yielded their corresponding pyrazoline analogues 5-ferrocenyl-3-aryl-4,5-dihydro-1H-pyrazole-1-carbothioamides (1–6), which were further cyclized with 2-bromo-4′fluro acetophenone to yield their corresponding 2-(5-ferrocenyl-3-aryl-4,5-dihydro-1H-pyrazol-1-yl)-4-(4-substituted-phenyl)thiazoles (7–12). According to the mechanism, the formation of pyrazoline analogues is favoured via thiosemicarbazone formation, which undergoes cyclization under basic condition to form desired pyrazoline ring in all the compounds.

General synthesis of 5-ferrocenyl-3-substituted aryl-4,5-dihydro-1H-pyrazol-1-carbothioamides (1–6) and their cyclized derivatives (7–12).
Scheme 1 General synthesis of 5-ferrocenyl-3-substituted aryl-4,5-dihydro-1H-pyrazol-1-carbothioamides (1–6) and their cyclized derivatives (7–12).

All the synthesized compounds were characterized by spectroscopic methods such as IR, 1H NMR 13C NMR and Mass and the purity of compounds was confirmed by elemental analysis and melting points. All compounds showed sharp melting points and the elemental analysis was found in accordance with ±0.3%. The analytical data are presented in the experimental section.

In the IR spectra of ferrocenyl chalcones (a–f), the appearance of characteristic bands at 1642–1655 cm−1 and 1568–1580 cm−1 due to α, β unsaturated carbonyl group and C⚌C, respectively, suggested the condensation of substituted ketones/1-phenyl butane-1-one/2-acetyl ferrocene with ferrocene carboxaldehyde. The structures of all these compounds were further confirmed by 1H NMR spectra. The appearance of doublets in the region of δ 6.75–7.35 ppm for Hα and 6.82–7.71 ppm for Hβ with coupling constant (J) in the range of 15.2–16 Hz showed that they are transisomers. The rest of protons appeared in the expected region and their values are shown in the data given in experimental section. Additional support for the structures of the compounds (a–f), was obtained from 13C NMR. A characteristic signal for the ferrocenyl chalcones (C⚌O) appeared in the range of δ 189.81–192.00 ppm. The signals at δ 120.23–122.43 and 142.46–146.82 ppm confirmed the presence of α, β unsaturated keto function in all compounds (a–f).

Selected diagnostic bands of the IR spectra of pyrazoline analogues (1–6) of ferrocenyl chalcones (a–f) showed useful information about the structures of the compounds. All the compounds showed intense bands in the region 1032–1078 cm−1 due to ν (C⚌S) stretch of the thiocarboxamide group. The IR spectra of all the compounds showed ν (C⚌N) stretch at 1524–1587 cm−1 because of the ring closure. In addition, the absorption bands at 1125–1215 cm−1 were attributed to the ν (C—N) stretch vibrations, which also confirmed the formation of the desired pyrazoline ring in all the compounds. The structures of the pyrazoline analogues were further supported by their 1H NMR spectra which provided diagnostic tools for the positional elucidation of the protons. Assignments of the signals are based on the chemical shifts and intensity patterns. The pyrazoline protons Ha and Hb (Fig. 1) are geminal protons at C-4 carbon and appeared in the region of 3.35–3.36 and 3.50–3.83 ppm as doublet of doublets in all the compounds. The C—H proton (Hx) of the pyrazoline ring also appeared as doublet of doublets in the region of 6.30–5.91 ppm due to vicinal coupling with two nonequivalent germinal protons of C-4 carbon. The protons belonging to the aromatic ring and ferrocenyl group were observed within the expected chemical shift region along with the integral values and are shown in the data given in the experimental section. The structures of the pyrazoline derivatives (7–12) were also confirmed by spectral studies. The IR spectra of all these compounds showed ν (C⚌N) stretch at 1582–1598 cm−1 which suggest the formation of thiazole ring. The 1H NMR spectra of these compounds also support the proposed structures of these compounds. The H-5 proton of thiazole ring was observed as a singlet between 6.68–6.82 ppm, confirming the formation of thiazole ring in all the compounds. In addition, four protons in monosubstituted Cp of ferrocene moiety of the compounds (7–12) appeared as three singlet peaks in the region of 4.68–4.82, 4.64–4.69 and 4.59–4.61 ppm and five protons of unsubstituted Cp also appeared as a singlet in the region of 4.24–4.27 ppm. All the other aromatic and aliphatic protons were observed with expected chemical shift and integral values and are shown in the data given in the experimental section and the structures of all newly synthesized compounds (1–6) and (7–12) were further confirmed by mass spectrometry. All compounds showed a particular molecular ion peak which was in conformity with the respective molecular formula of compounds.

Novel nitrogen and sulphur containing organometallic heterocycles (1–12).
Figure 1 Novel nitrogen and sulphur containing organometallic heterocycles (1–12).

2.2

2.2 In vitro antimicrobial study

All the newly synthesized compounds (1–6) and (7–12) were screened for antimicrobial activity against 15 ATCC strains out of which 8 were bacterial (P. aeruginosa, S. bovis, E. faecalis, K. pneumonia, E. coli, E. cloacae, MRSA and S. mutans) and 7 were fungal (C. albicans, C. dubliniensis, C. glabrata, C. parapsilosis, C. tropicalis, C. kefyr and C. krusei) strains by broth microdilution method (Hasan et al., 2013, 2012). Four Gram-positive bacteria (Streptococcus bovis, Enterococcus, faecalis, Methicillin-resistant Staphylococcus aureus and Streptococcus mutans) and Four Gram-negative bacteria (Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, and Enterobacter cloacae) were used for antibacterial assay. The antibacterial effect was compared with the most widely used antibiotic Amoxicillin. This antibiotic is used for the treatment of a number of bacterial infections including both Gram-positive and Gram-negative bacteria. In our experiments it gave a minimum inhibitory concentration (MIC) of 8–64 μg/mL against the tested strains. The results clearly depict that the compounds (1–12) substituted at position 4 in the benzene ring, in pyrazoline moiety with ferrocenyl, phenyl ethyl, phenyl, hydroxy and bromo group, gave an average antimicrobial activity against the tested strains with an exception of compound 12 in the benzene ring, in pyrazoline moiety which fell into a close bracket of activity to Amoxicillin, that is, the activity of compound 12 was comparable to that of Amoxicillin. The MIC values of rest of the compounds against biofilm forming P. aeruginosa and S. mutans were 64–256 μg/ml and 64–128 μg/ml respectively which is apparently high.

All these compounds gave a range of MIC value between 32–64 μg/ml against S. bovis, E. coli and C. tropicalis except compound 12 which gave a MIC of 16 μg/ml against each of them. The results of antibacterial activity are summarized in Table 1.

Table 1 MIC (μg/ml) value of synthesized compounds (1–12) on the tested ATCC strains using broth microdilution method.
Compounds Bacterial strains Fungal strains
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 256 64 32 128 64 128 256 128 128 256 128 128 64 128 128
2 128 32 32 128 32 128 128 64 128 256 64 64 32 64 128
3 128 64 32 64 32 128 128 128 128 256 64 128 64 128 128
4 128 32 32 64 32 64 64 128 128 256 64 64 32 256 128
5 128 64 32 64 64 64 64 128 128 128 64 128 64 128 128
6 128 64 64 128 32 64 128 128 128 128 64 64 32 128 128
7 128 64 32 128 32 128 64 128 128 128 64 128 32 128 128
8 128 32 32 128 32 128 128 256 256 256 64 64 32 128 128
9 256 64 64 128 32 64 128 256 128 256 64 128 32 128 128
10 128 32 32 64 64 64 64 128 256 256 64 64 64 64 128
11 128 32 32 64 32 128 128 128 128 256 64 128 32 128 128
12 64 16 16 64 16 32 32 64 64 64 32 32 16 64 64
Amoxycillin 64 8 8 16 8 16 16 16 – – – – – – –
Fluconazole – – – – – – – 64 64 64 64 64 64 64

2.3

2.3 In vitro antifungal activity

The antifungal activity of all compounds was screened against 7 fungal strains (Candida albicans, Candida dubliniensis, Candida glabrata, Candida parapsilosis, Candida tropicalis, Candida kefyr and Candida krusei). The effect was compared with the most widely used antifungal agent Fluconazole. It is a well-established first-line management option for the treatment of Candida infections. In our experiments it gave a minimum inhibitory concentration (MIC) of 64 μg/mL against all the tested strains. The results of antifungal activity indicated that out of all the tested compounds, compound 12, having nitro group at position 4 in the benzene ring, in pyrazoline moiety showed comparable or even better antifungal activity than Fluconazole against C. glabrata (32 μg/mL), C. parapsilosis (32 μg/mL), C. tropicalis (16 μg/mL). The results of antifungal activity are summarized in Table 1.

3

3 Conclusion

Some novel sulphur and nitrogen containing ferrocenyl linked heterocyclic compounds were synthesized and well characterized by spectroscopic methods such as IR, 1H NMR 13C NMR, Mass and elemental analyses. All the newly synthesized compounds (1–12) were screened for in vitro antimicrobial activity by broth microdilution method against 15 ATCC strains out of which 8 were bacterial (P. aeruginosa, S. bovis, E. faecalis, K. pneumonia, E. coli, E. cloacae, MRSA and S. mutans) and 7 were fungal (C. albicans, C. dubliniensis, C. glabrata, C. parapsilosis, C. tropicalis, C. kefyr and C. krusei) strains. The results of antimicrobial activity conclude that these compounds hold immense potential to be employed as a two in one formulation of antibacterial as well as antifungal agents. Also, being novel they can be a solution to the increasing resistance that has posed a major problem globally.

4

4 Experimental protocol

All the chemicals were purchased from Aldrich Chemical Company (USA). Precoated aluminium sheets (silica gel 60 F254, Merck Germany) were used for thin-layer chromatography (TLC) and spots were visualized under UV light. Melting points were determined on Stuart SMP10 melting point apparatus and are uncorrected. IR spectra were recorded on Perkin–Elmer model 1600 FT-IR RX1 spectrophotometer as KBr discs. 1H NMR and 13C NMR spectra were recorded on Bruker DPX-600 FT NMR spectrometer using CDCl3 as solvent with TMS as internal standard. Splitting patterns are designated as follows: s, singlet; d, doublet; dd, double doublet; m, multiplet. Chemical shift values are given in ppm. Elemental analyses were performed on a 2400 Perkin Elmer Series II analyser. ESI-MS was recorded on a MICROMASS QUATTRO II triple quadrupole mass spectrometer.

4.1

4.1 General procedure for the preparation of ferrocenyl chalcones (a–f)

The substituted aromatic ketone (3 mmol) and KOH (0.2 g) was dissolved in ethanol (5 mL) in a round bottomed flask and stirred at room temperature (25 °C) for 10 min. An ethanolic solution of the ferrocene carboxaldehyde (3 mmol, 5 mL) was added dropwise to the reaction mixture and stirred at room temperature. The progress of the reaction was monitored by TLC on silica gel sheets. The reaction was stopped by neutralizing the stirred solution with 2 M HCl. In most cases the product was obtained as a dark red precipitate after neutralization. It was then removed by filtration, and washed with water. In the absence of a precipitate on neutralization, the solution was extracted with ethyl acetate (20 mLx3). The organic layer was dried over anhydrous sodium sulphate and removed by evaporation under reduced pressure to give a liquid residue. The latter was passed through a column of silica gel (230–400 mesh) and eluted with THF–hexane (1:4) to yield pure compound.

4.1.1

4.1.1 1,3-Diferrocenyl-2-propen-1-one (a)

Yield 92%; m.p. 205 °C; deep red solid; Anal. calc. for C23H20Fe2O: C 65.11, H 4.75%. Found: C, 65.10, H 4.72% IR νmax (cm−1): 3054 (Ar—H), 2930 (C—H), 1652 (C⚌O), 1573 (C⚌C); 1H NMR (CDCl3) δ (ppm): 6.82 (d, 1H, J = 16 Hz, Hβ), 6.75 (d, 1H, J = 16 Hz, Hα), 4.61 (s, 2H, ferrocene), 4.46 (s, 2H, ferrocene), 4.58 (s, 2H, ferrocene), 4.55 (s, 2H, ferrocene), 4.19 (s, 5H, ferrocene), 4.16 (s, 5H, ferrocene); 13C NMR (CDCl3) δ (ppm): 192.00 (C⚌O), 142.46 (C-β), 79.46, 78.52 (2 ipso-C5H4), 71.95, 71.40, (2 meta-C5H4), 70.86, 70.48, (2 ortho-C5H4), 69.81,70.05 (2 C5H5), 120.23 (C-α); ESI-MS m/z: [M++1] 425.00.

4.1.2

4.1.2 5-Ferrocenyl-1-(phenyl)-pent-4-en-1-one (b)

Yield 75%; reddish gummy product; Anal. calc. for C21H20FeO: C 73.27, H 5.86%. Found: C 73.29; H 5.84%. IR νmax (cm−1): 3035 (Ar—H), 2936 (C—H), 1642 (C⚌O), 1578 (C⚌C); 1H NMR (CDCl3) δ (ppm): 7.88–7.63 (m, 2H, Ar—H), 7.69 (d, 1H, J = 15.2 Hz, Hβ), 7.56–7.21 (m, 3H, Ar—H), 7.33 (d, 1H, J = 15.2 Hz, Hα), 4.61 (s, 2H, ferrocene), 4.46 (s, 2H, ferrocene), 4.17(s, 5H, ferrocene), 2.98–2.86 (m, 2H, CH2), 2.85–2.64 (m, 2H, CH2); 13C NMR (CDCl3) δ (ppm): 189.81 (C⚌O), 146.45 (C-β), (138.67, 133.77, 128.59, 128.45, aromatic), 121.61 (C-α), 21.59 (CH3), 77.5 (ipso-C5H4), 69.8, 69.5 (meta-C5H4), 69.4, 69.0 (C5H5), 67.4, 66.3 (ortho-C5H4); ESI-MS m/z: [M++1] 345.22.

4.1.3

4.1.3 3-Ferrocenyl-1-phenyl-2-propen-1-one (c)

Yield 90%; m.p. 144 °C; deep red solid; Anal. calc. for C19H16FeO: C 72.17, H 5.10%. Found: C 72.12; H 5.06%. IR νmax (cm−1): 3031 (Ar—H), 2935 (C—H), 1655 (C⚌O), 1568 (C⚌C); 1H NMR (CDCl3) δ (ppm): 7.92–7.88 (m, 2H, Ar—H), 7.70 (d, 1H, J = 15.2 Hz, Hβ), 7.57–7.15 (m, 3H, Ar—H), 7.33 (d, 1H, J = 15.2 Hz, Hα), 4.60 (s, 2H, ferrocene), 4.48 (s, 2H, ferrocene), 4.18 (s, 5H, ferrocene); 13C NMR (CDCl3) δ (ppm): 189.88 (C⚌O), 146.82 (C-β), (138.63, 132.44, 128.59, 128.40, aromatic), 122.17 (C-α), 77.5 (ipso-C5H4), 69.9, 69.6 (meta-C5H4), 69.5, 69.2 (C5H5), 67.5, 66.4 (ortho-C5H4); ESI-MS m/z: [M++1] 317.17.

4.1.4

4.1.4 3-Ferrocenyl-1-(4-hydroxyphenyl)-2-propen-1-one (d)

Yield 95%; m.p: 225 °C reddish brown solid; Anal. calc. for C19H16FeO2: C 68.70, H 4.85. Found: C 67.05, H 5.74% IR ν max cm−1: 3041 (Ar—H), 2933 (C—H), 1645 (C⚌O), 1571 (C⚌C); 1H NMR (CDCl3) δ (ppm): 7.83–7.76 (m, 2H, Ar—H), 7.71 (d, 1H, J = 15.6 Hz, Hβ), 7.59–7.42 (m, 2H, Ar—H), 7.34 (d, 1H, J = 15.6 Hz, Hα), 4.92 (s, 2H, ferrocene), 4.58 (s, 2H, ferrocene), 4.24 (s, 5H, Ferrocene), 4.22 (s, 1H, OH); 13C NMR (CDCl3) δ (ppm): 191.16 (C⚌O), 144.64 (C-β), (138.61, 132.71, 130.04, 128.52, Aromatic), 122.24 (C-α), 77.2 (ipso-C5H4), 69.8, 69.5 (meta-C5H4), 69.2, 69.0 (C5H5), 67.8, 66.9 (ortho-C5H4); ESI-MS m/z: [M++1] 333.17.

4.1.5

4.1.5 3-Ferrocenyl-1-(4-bromophenyl)-2-propen-1-one (e)

Yield 95%; m.p: 168 °C red solid; Anal. calc. for C19H15BrFeO: C 57.76, H 3.83%. Found: C, 57.86, H 3.94% IR νmax (cm−1): 3051 (Ar—H), 2930 (C—H), 1650 (C⚌O), 1580 (C⚌C); 1H NMR (CDCl3) δ (ppm): 7.81–7.67 (m, 4H, Ar—H), 7.61 (d, 1H, J = 16 Hz, Hβ), 7.32 (d, 1H, J = 16 Hz, Hα), 4.96 (s, 2H, ferrocene), 4.61 (s, 2H, ferrocene), 4.26 (s, 5H, ferrocene); 13C NMR (CDCl3) δ (ppm): 191.43 (C⚌O), 143.41 (C-β), (136.07, 134.70, 130.02, 128.51, Aromatic), 121.42 (C-α), 77.2 (ipso-C5H4), 69.9, 69.7 (meta-C5H4), 69.5, 69.2 (C5H5), 67.6, 66.4 (ortho-C5H4); ESI-MS m/z: [M++1] 396.07.

4.1.6

4.1.6 3-Ferrocenyl-1-(4-nitrophenyl)-2-propen-1-one (f)

Yield 90%; m.p: 214 °C; deep red solid; Anal. calc. for C19H15FeNO3: C 63.18, H 4.19, N 3.85%. Found: C 63.15, H 4.14 N 3.82%. IR νmax (cm−1): 3067 (Ar—H), 2938 (C—H), 1647 (C⚌O), 1575 (C⚌C); 1H NMR (CDCl3) δ (ppm) 8.12–8.06 (m, 2H, Ar—H), 7.67 (d, 1H, J = 15.6 Hz, Hβ), 7.64–7.22 (m, 2H, Ar—H), 7.35 (d, 1H, J = 15.6 Hz, Hα), 4.61 (s, 2H, ferrocene), 4.48 (s, 2H, ferrocene), 4.19 (s, 5H, ferrocene); 13C NMR (CDCl3) δ (ppm): 189.88 (C⚌O), 146.47 (C-β), (138.60, 132.72, 128.53,127.54, aromatic), 122.43 (C-α). 77.7 (ipso-C5H4), 69.8, 69.7 (meta-C5H4), 69.5, 69.3 (C5H5), 67.4, 66.2 (ortho-C5H4); ESI-MS m/z: [M++1] 362.17.

4.2

4.2 General procedure for the synthesis of 5-ferrocenyl-3-substituted aryl-4,5-dihydro-1H-pyrazol-1-carbothioamides (1–6)

Thiosemicarbazide (12.6 mmol) was dissolved in absolute ethanol (50 mL) by refluxing under nitrogen. Then a solution of corresponding chalcone (a–f) (6.3 mmol), and NaOH (15.8 mmol) in absolute ethanol was added and the reaction mixture was refluxed for 6 h. The progress of the reaction was monitored by TLC on silica gel sheets. After completion of the reaction, reaction mixture was cooled to room temperature, then water (25 ml) was added to the reaction mixture and the solid obtained, was filtered, dried and recrystallized by appropriate solvent to yield corresponding pyrazolines (1–6).

4.2.1

4.2.1 3,5-Diferrocenyl-4,5-dihydropyrazole-1-carbothioamide (1)

Yield 70%; m.p: 214 °C; reddish brown solid. Anal. calc. for. C24H23Fe2N3S: C (57.97%) H (4.66%) Fe (22.46%) N (8.45%) S (6.45%) IR νmax (cm−1): 3370, 3166 (N—H), 1587 (C⚌N), 1258 (C—N), 1054 (C⚌S); 1H NMR (CDCl3) δ (ppm) 6.85 (s, 2H, -NH2), 6.32 (dd, 1H, Hx, Jax = 10.9, Jbx = 10.2 Hz, pyrazoline), 4.85 (s, 2H, ferrocene), 4.79 (s, 2H, ferrocene), 4.56 (s, 2H, ferrocene), 4.46 (s, 2H, ferrocene), 4.19 (s, 5H, ferrocene), 4.16 (s, 5H, ferrocene), 3.50 (dd, 1H, Hb, Jab = 17.4, Jbx = 10.2 Hz, pyrazoline), 3.47 (dd, 1H, Ha, Jab = 17.4, Jax = 3.2 Hz pyrazoline); 13C NMR (CDCl3) δ (ppm): 177.6 (C⚌S) pyrazoline), 159.5, (C⚌N), 58.7, (C-5, pyrazoline), 42.0 (C-4, pyrazoline) 72.5, 71.7 (2 × ipso-C5H4), 71.3, 71.1 (2 × meta-C5H4), 70.7, 70.1 (2 × C5H5), 67.8, 65.8 (2 × ortho C5H4); ESI-MS m/z: [M++1] 498.21.

4.2.2

4.2.2 5-Ferrocenyl-3-(2-phenylethyl)-4,5-dihydropyrazole-1-carbothioamide (2)

Yield 68%; brown gummy product. Anal. calc. for. C22H23FeN3S: C (63.31%) H (5.55%) Fe (13.38%) N (10.07%) S (7.68%); IR νmax (cm−1): 3354, 3174 (N—H), 1582 (C⚌N), 1262 (C—N), 1078 (C⚌S); 1H NMR (CDCl3) δ (ppm) 7.32–7.45 (m, 5H, Ar—H), 6.81 (s, 2H, -NH2), 6.09 (dd, 1H, Hx, Jax = 10.5, Jbx = 11.2 Hz, pyrazoline), 4.51 (s, 1H, ferrocene), 4.47 (s, 1H, ferrocene), 4.38 (s, 2H, ferrocene), 4.27 (s, 5H, ferrocene), 3.83 (dd, 1H, Hb, Jab = 16.8, Jbx = 11.2 Hz, pyrazoline), 3.35 (dd, 1H, Ha, Jab = 16.8, Jax = 4.2 Hz, pyrazoline), 3.21–2.98 (m, 2H, CH2—Ar), 2.92–2.8 (m, 2H, CH2); 13C NMR (CDCl3) δ (ppm): 174.9 (C⚌S) pyrazoline), 160.3, (C⚌N), 60.9, (C-5, pyrazoline), 44.0 (C-4, pyrazoline), 145.1–125.1 (Ar—C), 71.5 (ipso-C5H4), 69.9, 69.7 (meta-C5H4), 68.8, 68.6 (C5H5), 67.9, 67.7 (ortho C5H4), 29.4, 27.5 (2 × CH2), ESI-MS m/z: [M++1] 418.34.

4.2.3

4.2.3 5-Ferrocenyl-3-phenyl-4,5-dihydropyrazole-1-carbothioamide (3)

Yield 62% m.p: 210 °C; orange solid. Anal. calc. for C20H19FeN3S: C (61.70%) H (4.92%) Fe (14.35%) N (10.79%) S (8.24%); IR νmax (cm−1): 3355, 3190 (N—H), 1550 (C⚌N), 1210 (C—N), 1034 (C⚌S); 1H NMR (CDCl3) δ (ppm) 7.34–7.46 (m, 5H, Ar—H), 6.30 (dd, 1H, Hx, Jax = 11.1, Jbx = 10.2 Hz, pyrazoline), 6.86 (s, 2H, -NH2), 4.61 (s,1H, ferrocene), 4.52 (s, 1H, ferrocene), 4.44 (s, 2H, ferrocene), 4.14 (s, 5H, ferrocene) 3.68 (dd, 1H, Hb Jab = 16.8, Jbx = 10.2, pyrazoline), 3.59 (dd, 1H, Ha, Jab = 16.8, Jax = 3.2 pyrazoline); 13C NMR (CDCl3) δ (ppm): 176.47 (C⚌S), 156.8 (C⚌N), 59.4, (C-5, pyrazoline) 41.9 (C-4, pyrazoline), 141.61–125.13 (Ar—C), 76.2 (ipso-C5H4), 69.9, 69.8 (meta-C5H4), 69.3, 69.0 (C5H5), 67.2, 66.6 (ortho-C5H4), ESI-MS m/z: [M++1] 390.29.

4.2.4

4.2.4 5-Ferrocenyl-3-(4-hydroxyphenyl)-4,5-dihydropyrazole-1-carbothioamide (4)

Yield 74%; m.p: 209 °C; orange solid. Anal. calc. for C20H19FeN3OS: C (59.27%) H (4.73%) Fe (13.78%) N (10.37%) O (3.95%) S (7.91%); IR νmax (cm−1): 3257, 3165 (N—H), 1562 (C⚌N), 1195 (C—N), 1044 (C⚌S); 1H NMR (CDCl3) δ (ppm) 7.75 (d, 2H, J = 7.8 Hz, Ar—H), 7.20 (d, 2H, J = 7.8 Hz, Ar—H), 6.88 (s, 2H, —NH2), 6.33 (dd, 1H, Hx, Jax = 10.9, Jbx = 10.2 Hz, pyrazoline), 4.72 (s, 1H, OH), 4.65 (s, 1H, ferrocene), 4.56 (s, 1H, ferrocene), 4.36–4.39 (br s, 2H, ferrocene), 4.08 (s, 5H, ferrocene), 3.76 (dd, 1H, Hb, Jab = 16.8, Jbx = 10.2 Hz, pyrazoline), 3.67 (dd, 1H, Ha, Jab = 16.8, Jax = 4.2 Hz, pyrazoline); 13C NMR (CDCl3) δ (ppm): 172.1 (C⚌S), 158.2 (C⚌N), 62.8, (C-5, pyrazoline), 44.9 (C-4, pyrazoline), 144.7–124.2 (Ar—C), 73.8 (ipso-C5H4), 69.8, 69.7 (meta-C5H4), 69.2 68.8, (C5H5), 66.5, 66.0 (ortho-C5H4), ESI-MS m/z: [M++1] 406.29.

4.2.5

4.2.5 5-Ferrocenyl-3-(4-bromophenyl)-4,5-dihydropyrazole-1-carbothioamide (5)

Yield 78%; m.p: 221 °C; deep orange solid. Anal. calc. for C20H18BrFeN3S: C (51.31%) H (3.88%) Br (17.07%) Fe (11.93%) N (8.97%) S (6.85%); IR νmax (cm−1): 3261, 3173 (N—H), 1578 (C⚌N), 1215 (C—N), 1062 (C⚌S); 1H NMR (CDCl3) δ (ppm) 7.70 (d, 2H, J = 8.4 Hz, Ar—H), 7.64 (d, 2H, J = 8.4 Hz, Ar—H), 6.81 (s, 2H, —NH2), 5.91 (dd, 1H, Hx, Jax = 10.1, Jbx = 10.2 Hz, pyrazoline), 4.63 (s, 1H, ferrocene), 4.46 (s, 1H, ferrocene), 4.38 (s, 2H, ferrocene), 4.23 (s, 5H, ferrocene), 3.78 (dd, 1H, Hb, Jab = 16.8, Jbx = 10.2 Hz, pyrazoline), 3.69, (dd, 1H, Ha, Jab = 16.8, Jax = 3.0 Hz, pyrazoline); 13C NMR (CDCl3) δ (ppm): 173.6 (C⚌S), 157.7, (C⚌N), 59.6, (C-5, pyrazoline), 42.3 (C-4, pyrazoline), 144.5–125.6 (Ar—C), 76.3 (ipso-C5H4), 69.9, 69.8 (meta-C5H4), 68.7, 68.3 (C5H5), 67.1, 65.3 (ortho C5H4), ESI-MS m/z: [M++1] 469.19.

4.2.6

4.2.6 5-Ferrocenyl-3-(4-nitrophenyl)-4,5-dihydropyrazole-1-carbothioamide (6)

Yield 69%; m.p: 204 °C; deep red solid. Anal. calc. for. C20H18FeN4O2S: C (55.31%) H (4.18%) Fe (12.86%) N (12.90%) O (7.37%) S (7.38%); IR νmax (cm−1): 3270, 3182 (N—H), 1581 (C⚌N), 1212 (C—N), 1070 (C⚌S); 1H NMR (CDCl3) δ (ppm) 7.65 (d, 2H, J = 7.8 Hz, Ar—H), 7.32 (d, 2H, J = 7.8 Hz, Ar—H), 6.96 (s, 2H, -NH2), 6.01 (dd, 1H, Hx, Jax = 10.5, Jbx = 11.2 Hz, pyrazoline), 4.67 (s, 1H, ferrocene), 4.53 (s, 1H, ferrocene), 4.36 (s, 2H, ferrocene), 4.04 (s, 5H, ferrocene), 3.80 (dd, 1H, Hb, Jab = 16.8, Jbx = 11.2 Hz, pyrazoline), 3.61, (dd, 1H, Ha, Jab = 16.8, Jax = 4.8 Hz, pyrazoline); 13C NMR (CDCl3) δ (ppm): 177.4 (C⚌S), 157.5, (C⚌N), 57.52, (C-5, pyrazoline), 44.5 (C-4, pyrazoline), 144.5–125.7 (Ar—C), 75.9 (ipso-C5H4), 69.8, 69.7 (meta-C5H4), 69.1, 69.0 (C5H5), 67.7, 66.4 (ortho C5H4), ESI-MS m/z: [M++1] 435.29.

4.3

4.3 General procedure for the synthesis of 2-(5-ferrocenyl-3-aryl-4,5-dihydro-1H-pyrazol-1-yl)-4-(4-substituted-phenyl)thiazoles (7–12)

A mixture of corresponding 5-ferrocenyl-3-substituted aryl-4,5-dihydro-1H-pyrazol-1-carbothioamide (1–6) (1.03 mmol), 2-bromo-4′-fluoroacetophenone (1.03 mmol) and dichloromethane (15 ml) was stirred and refluxed under nitrogen for 5 h. The progress of reaction was monitored by TLC, then the solvent was removed from the reaction mixture under reduced pressure. The residue was purified by column chromatography (3:1 Hexane–EtOAc) to afford the pure compound.

4.3.1

4.3.1 4-(4-Fluorophenyl)-2-(3,5-diferrocenyl)-4,5-dihydro-1H-pyrazol-1-yl)thiazole (7)

Yield 52%; m.p: 194 °C; brownish solid. Anal. calc. for. C32H26FFe2N3S: C (62.26%) H(4.57%) F (3.08%) Fe (18.09%) N (6.81%) S (5.19%); IR νmax cm−1: 3104, 3055, 3022, 2850, 1582, 1471, 1412, 1091, 1045, 885, 842, 825, 722, 690, 485; 1H NMR (CDCl3) δ (ppm) 7.96 (d, 2H, J = 8.4 Hz, Ar′—H) 7.53 (d, 2H, J = 8.4 Hz, Ar′—H), 6.80 (s, 1H, thiazole), 6.25 (dd, 1H, Hx, Jbx = 11.2, Jax = 6.2 Hz, pyrazoline), 4.68 (s, 2H, ferrocene) 4.67 (s, 2H, ferrocene), 4.65 (s, 2H, ferrocene), 4.61 (s, 2H, ferrocene), 4.26 (s, 5H, ferrocene), 4.22 (s, 5H, ferrocene), 3.62 (dd, 1H, Hb, Jab = 17.4, Jbx = 10.2 Hz, pyrazoline), 3.53 (dd, 1H, Ha, Jab = 17.4, Jax = 6.3 Hz, pyrazoline); 13C NMR (CDCl3) δ (ppm): 171.5 (C-2 thiazole), 165.2 (C-4 thiazole), 146.6–128.6 (2 × Ar—C), 122.3 (C-5 thiazole), 72.5, 71.5 (2 × ipso-C5H4). 72.4, 72.1 (2 × meta C5H4), 69.9, 69.8 (2 × C5H5), 64.5, 64.3 (2 × ortho C5H4); ESI-MS m/z: [M++1] 616.32.

4.3.2

4.3.2 4-(4-Fluorophenyl)-2-(5-ferrocenyl-3-phenylethyl)-4,5-dihydro-1H-pyrazol-1-yl) thiazole (8)

Yield 53%; m.p: 89 °C; yellowish brown solid. Anal. calc. for. C30H26FFeN3S: C (67.29%) H (4.89%) F (3.55%) Fe (10.43%) N (7.85%) S (5.99%); IR νmax cm−1: 3052, 3024, 2922, 1587, 1470, 1412, 1093, 1046, 885, 842, 826, 722, 691, 487; 1H NMR (CDCl3) δ (ppm) 7.96 (d, 2H, J = 8.4 Hz, Ar′—H), 7.50 (d, 3H, J = 8.4 Hz, Ar′—H), 7.32–7.40 (m, 5H, Ar—H), 6.74 (s, 1H, thiazole), 5.28 (dd, 1H, Hx, Jbx = 10.2, Jax = 6.3 Hz, pyrazoline), 4.69 (s, 1H, ferrocene), 4.65 (s, 1H, ferrocene), 4.62 (s, 2H, ferrocene), 4.25 (s, 5H, ferrocene), 3.90 (dd, 1H, Hb, Jab = 17.4, Jbx = 10.2 Hz, pyrazoline), 3.54 (dd, 1H, Ha, Jab = 17.4, Jax = 6.3 Hz, pyrazoline), 3.16–3.19 (m, 2H, CH2), 2.95–3.01 (m, 2H, CH2); 13C NMR (CDCl3) δ (ppm): 171.5 (C-2 thiazole), 165.2 (C-4 thiazole), 146.6–128.6 (2 × Ar—C), 122.3 (C-5 thiazole), 72.5 (ipso-C5H4). 71.3, 71.1 (meta C5H4), 68.7, 68.6 (C5H5), 65.4, 65.2 (ortho-C5H5); ESI-MS m/z: [M++1] 536.45.

4.3.3

4.3.3 4-(4-Fluorophenyl)-2-(5-ferrocenyl-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl) thiazole (9)

Yield: 59%; m.p: 196 °C; deep red solid. Anal. calc. for C28H22FFeN3S: C (66.28%) H (4.37%) F (3.74%) Fe (11.01%) N (8.28%) S (6.32%); IR νmax (cm−1): 3108, 3055, 2852, 1582, 1484, 1408, 1092, 1045, 884, 840, 820, 726, 693, 488; 1H NMR (CDCl3) δ (ppm) 7.97 (d, 2H, J = 7.2 Hz, Ar′—H), 7.31–7.42 (m, 5H, Ar—H), 7.50 (d, 2H, J = 7.2 Hz, Ar′—H) 6.82 (s, 1H, thiazole), 5.96 (dd, 1H, Hx, Jax = 10.1, Jbx = 10.2 Hz, pyrazoline),4.72 (s, 1H, ferrocene), 4.64 (s, 1H, ferrocene), 4.59 (s, 2H, ferrocene), 4.24 (s, 5H, ferrocene), 3.76 (dd, 1H, Hb, Jab = 16.8, Jbx = 10.2 Hz, pyrazoline), 3.62 (dd, 1H, Ha, Jab = 16.8, Jax = 6.3 Hz, pyrazoline); 13C NMR (CDCl3) δ (ppm): 164.9 (C-2 thiazole), 159.5 (C-4 thiazole), 145.5–129.2 (Ar—C), 126.04 (C-5 thiazole), 78.6 (ipso-C5H4), 73.5, 73.2 (meta-C5H4), 71.1 (C5H5), 68.4, 68.2 (ortho C5H4); ESI-MS m/z: [M++1] 508.40.

4.3.4

4.3.4 4-(4-Fluorophenyl)-2-(5-ferrocenyl-3-(4-hydroxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl) thiazole (10)

Yield 52%; m.p: 215 °C; brown solid. Anal. calc. for C28H22FFeN3OS: C (64.25%) H (4.24%) F (3.63%) Fe (10.67%) N (8.03%) O (3.06%) S (6.13%); IR νmax (cm−1): 3057, 2855, 1585, 1475, 1405, 1094, 1072, 885, 841, 820, 725, 691, 485; 1H NMR (CDCl3) δ (ppm) 7.96 (d, 2H, J = 8.4 Hz, Ar′—H) 7.70 (d, 2H, J = 8.4 Hz, Ar—H), 7.51 (d, 2H, J = 8.4 Hz, Ar′—H) 7.37 (d, 2H, J = 8.4 Hz, Ar—H), 6.80 (s, 1H, thiazole), 5.61 (dd, 1H, Hx, Jbx = 10.2, Jax = 6.2 Hz, pyrazoline), 4.82 (s, 1H, ferrocene), 4.68 (s, 1H, ferrocene), 4.63 (s, 2H, ferrocene), 4.61 (s, 1H, OH), 4.27 (s, 5H, ferrocene), 3.89 (dd, 1H, Hb, Jab = 17.2, Jbx = 11.7 Hz, pyrazoline), 3.74 (dd, 1H, Ha, Jab = 17.2, Jax = 6.2 Hz, pyrazoline); 13C NMR (CDCl3) δ (ppm): 171.0 (C-2 thiazole), 162.2 (C-4 thiazole), 145.2–129.5 (Ar—C), 128.2 (C-5 thiazole), 78.2 (ipso-C5H4). 71.7, 71.5 (meta C5H4), 69.8,69.6 (C5H5), 67.4, 67.2 (ortho-C5H5); ESI-MS m/z: [M++1] 524.40.

4.3.5

4.3.5 4-(4-Fluorophenyl)-2-(5-ferrocenyl-3-(4-bromophenyl)-4,5-dihydro-1H-pyrazol-1-yl) thiazole (11)

Yield 52%; m.p: 208 °C; yellow solid. Anal. calc. for C28H21BrFFeN3S: C (57.36%) H (3.61%) Br (13.63%) F (3.24%) Fe (9.53%) N (7.17%) S (5.47%); IR νmax (cm−1): 3052, 3025, 2921, 2855, 1584, 1475, 1405, 1085, 1045, 1005, 885, 841, 820, 725, 691, 485; 1H NMR (CDCl3) δ (ppm) 7.96 (d, 2H, J = 8.4 Hz, Ar′—H) 7.70 (d, 2H, J = 8.4 Hz, Ar—H), 7.62 (d, 2H, J = 8.4 Hz, Ar—H) 7.52 (d, 2H, J = 8.4 Hz, Ar′—H), 6.68 (s, 1H, thiazole), 5.96 (dd, 1H, Hx, Jbx = 10.2, Jax = 6.3 Hz, pyrazoline), 4.72 (s, 1H, ferrocene), 4.68 (s, 1H, ferrocene), 4.63 (s, 2H, ferrocene), 4.27 (s, 5H, ferrocene), 3.87 (dd, 1H, Hb, Jab = 17.4, Jbx = 10.2 Hz, pyrazoline), 3.74 (dd, 1H, Ha, Jab = 17.4, Jax = 6.3 Hz, pyrazoline); 13C NMR (CDCl3) δ (ppm): 171.2 (C-2 thiazole), 165.0 (C-4 thiazole), 143.2–129.5 (Ar—C), 131.1 (C-5 thiazole), 71.0 (ipso-C5H4). 70.7, 70.3 (meta C5H4), 68.7, 68.4 (C5H5), 67.5, 67.2 (ortho-C5H5); ESI-MS m/z: [M++1] 587.29.

4.3.6

4.3.6 4-(4-Fluorophenyl)-2-(5-ferrocenyl-3-(4-nitrophenyl)-4,5-dihydro-1H-pyrazol-1-yl) thiazole (12)

Yield 51%; mp: 179 °C; yellow solid. Anal. calc. for. C28H21FFeN4O2S: C (60.88%) H (3.83%) F (3.44%) Fe (10.11%) N (10.14%) O (5.79%) S (5.80%); IR νmax (cm−1): 3052, 2922, 2857, 1590, 1477, 1405, 1092, 1074, 886, 841, 822, 728, 692, 486; 1H NMR (CDCl3) δ (ppm) 7.97 (d, 2H, J = 8.4 Hz, Ar′—H) 7.71 (d, 2H, J = 8.4 Hz, Ar—H), 7.50 (d, 2H, J = 8.4 Hz, Ar′—H) 7.42 (d, 2H, J = 8.4 Hz, Ar—H), 6.79 (s, 1H, thiazole), 5.91 (dd, 1H, Hx, Jax = 16.8, Jbx = 11.7 Hz, pyrazoline), 4.72 (s, 1H, ferrocene), 4.69 (s, 1H, ferrocene), 4.65 (s, 2H, ferrocene), 4.23 (s, 5H, ferrocene), 3.88 (dd, 1H, Hb, Jab = 17.2, Jbx = 11.7 Hz, pyrazoline), 3.74 (dd, 1H, Ha, Jab = 17.2, Jax = 6.2 Hz, pyrazoline); 13C NMR (CDCl3) δ (ppm): 169.2 (C-2 thiazole), 162.5 (C-4 thiazole), 144.2–129.5 (Ar—C), 128.0 (C-5 thiazole), 76.2 (ipso-C5H4). 72.7, 72.4 (meta C5H4), 70.8, 70.2 (C5H5), 68.8, 68.5(ortho-C5H5); ESI-MS m/z: [M++1] 553.40.

4.4

4.4 In vitro antimicrobial assay

All the newly synthesized compounds (1–6) and (7–12) were screened for antimicrobial activity against (P. aeruginosa, S. bovis, E. faecalis, K. pneumonia, E. coli, E. cloacae, MRSA and S. mutans) and 7 were fungal (C. albicans, C. dubliniensis, C. glabrata, C. parapsilosis, C. tropicalis, C. kefyr and C. krusei) strains by broth microdilution method (Hasan et al., 2012). Inocula were prepared from an overnight Nutrient Broth culture plate of the bacterial test strains and Yeast Peptone Dextrose (YPD) culture plate for fungal test organisms (Himedia Labs, Mumbai, India). Inoculum for the minimum inhibitory concentration (MIC) test was prepared by taking two or three considerably isolated colonies from respective agar culture plate. These colonies were picked up by a sterile loop and were transferred into a tube containing 4 to 5 ml of respective sterile liquid medium. This broth was incubated at 37 °C until it attained a desired turbidity (Hasan et al., 2013).

4.5

4.5 Determination of minimum inhibitory concentration

The minimum inhibitory concentration (MIC) was determined by using a broth microdilution method (Hasan et al., 2012). Stock standard solutions at 2 mg/mL were prepared in DMSO for all the compounds to be tested. Working solutions were prepared by dilution in microtiter plates at concentrations between 500 μg/mL and 0.244 μg/mL using nutrient medium as the diluent. DMSO (50 μl) was used as control and did not show any inhibitory activity. The bacterial suspension for each strain was added in the wells of the microtiter plate at the concentration of 105–106 cfu/mL (colony forming units/mL). Each inoculum was prepared in its respective medium and was diluted to 1:100 for the broth microdilution procedure. The plates were incubated at 37 °C with bacterial strains and at 30 °C for fungal stains and the minimum inhibitory concentration (MIC) was recorded after 24 h. Bacterial and fungal growth was shown by the presence of turbidity in the wells. The MIC was determined as the lowest concentration of the compound that completely inhibited the visible bacterial/fungal growth (turbidity) of the organism after 24 h of incubation. All these determinations represent the mean of three independent experiments. The results of antimicrobial activity are summarized in Table 1 and Table 2.

Table 2 Strains used to study antibacterial/antifungal activity of synthesized compounds.
Code Names of organisms (ATCC)
1 Pseudomonas aeruginosa
2 Streptococcus bovis
3 Enterococcus faecalis
4 Klebsiella pneumoniae
5 Escherichia coli
6 Enterobacter cloacae
7 Methicillin-resistant Staphylococcus aureus [MRSA]
8 Streptococcus mutans
9 Candida albicans
10 Candida dubliniensis
11 Candida glabrata
12 Candida parapsilosis
13 Candida tropicalis
14 Candida kefyr
15 Candida krusei

Acknowledgements

The authors are thankful to the Department of Chemistry, University of Tabuk, Saudi Arabia, for providing necessary facilities and Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India, for the antimicrobial activity of novel compounds.

References

  1. , , , , , , , , , . J. Organomet. Chem.. 2014;755:1-6.
  2. , , , , , , , , , . Bioorg. Med. Chem.. 2005;13:3047-3055.
  3. , , . Top. Organomet. Chem.. 2010;32:155-193.
  4. , , , , , , , . Eur. J. Med. Chem.. 2000;35:707-714.
  5. , , , , , , , , , , . Mol. Pharm.. 2005;2:185-193.
  6. , , . Lancet Infect. Dis.. 2002;2:550-563.
  7. , , , , , , , , , . Parasitol. Res.. 2001;87:239-244.
  8. , , . Chem. Med. Chem.. 2008;3:383-391.
  9. , , . The Chemistry of Heterocycles (second ed.). Weinheim, Germany: Wiley VCH; . pp. 316–336
  10. , , , , , . J. Organomet. Chem.. 2007;692:5621-5632.
  11. , , , , . J. Organomet. Chem.. 2003;674:1-9.
  12. , , , . Clin. Microbiol. Rev.. 2001;14:836-871.
  13. , , , , . Appl. Organomet. Chem.. 2007;21:613-625.
  14. , , . Clin. Microbiol. Rev.. 1999;12:501-517.
  15. , , , , , , , , . J. Organomet. Chem.. 2014;757:28-35.
  16. , , , . PloS ONE. 2012;7(7):e40319. (IF: 4.4)
  17. , , , . Future Microbiol.. 2013;8:939-944.
  18. , , . J. Organomet. Chem.. 2001;637–639:94-98.
  19. , , , , , , . Inorg. Chem.. 1989;28:3529.
  20. , , , , , . Angew. Chem. Int. Ed.. 2006;45:285-290.
  21. , , , . J. Organomet. Chem.. 1991;418:107-112.
  22. , , , , , , , , , . J. Organomet. Chem.. 2014;749:157-162.
  23. , , , , , . Eur. J. Med. Chem.. 2009;44:4747-4751.
  24. , , , , , . Curr. Med. Chem.. 2004;11:2505-2517.
  25. , , , . Organometallics targeted to specific biological sites: the development of new therapies. In: , ed. Bioorganometallics: Biomolecules, Labeling, Medicine. Weinheim, FRG: Wiley-VCH Verlag GmbH & Co. KGaA; .
    [Google Scholar]
  26. , , , , , , . Med. Chem. Res.. 2012;21:2123-2132.
  27. , , , , , , , . Bioorg. Med. Chem.. 2012;20:5678-5698.
  28. , , . Nature. 1951;168:1039-1040.
  29. , , , , , , , , , . J. Organomet. Chem.. 2007;692:1327-1331.
  30. , , , , , , , . J. Organomet. Chem.. 2001;628:107-113.
  31. , , . Organometallics. 2013;32:5623-5625.
  32. , , , , , . J. Organomet. Chem.. 2001;637:742-744.
  33. , , , . J. Organomet. Chem.. 2008;693:1395-1399.
  34. , , , , , , . J. Organomet. Chem.. 2007;692:1834-1844.
  35. , , , , . J. Organomet. Chem.. 1990;398:205-217.
  36. , , , , . Clin. Microbiol. Rev.. 2005;18:163-194.
  37. , , . Appl. Organomet. Chem.. 1990;4:19-26.
  38. , , , , . Eur. J. Med. Chem.. 2010;45:3497-3503.
  39. , , , , , , , . Eur. J. Med. Chem.. 2011;46:4669-4675.
  40. , , . Clin. Microbiol. Rev.. 2007;20:133-163.
  41. , , , , , . Inorg. Chim. Acta. 1988;153:67-70.
  42. , , , . Microbiol. Mol. Biol. Rev.. 2011;75:213-267.
  43. , , , , . Int. J. Drug. Dev. Res.. 2011;3:156-164.
  44. , . Ferrocenes. U.K.: John Viley & Sons Ltd.; .
  45. , , , , . J. Organomet. Chem.. 2002;655:182-185.
  46. , , , , , , , , , , , , . Antimicrob. Agents Chemother.. 2012;56:3165-3173.
  47. , , eds. Ferrocenes (Homogenous Catalysis, Organic Synthesis, Material Sciences). Weinheim: VCH Verlagsgesellschaft; .
  48. , , , , , , , . J. Organomet. Chem.. 2001;637:500-506.
  49. , , , , , , , . Synthesis. 2004;15:2471-2478.
  50. , , . Sci. Sin. Chim.. 2011;41:1429-1456.
  51. , , , , , , . Anticancer Res.. 2004;24(2B):763-770.
  52. , , , . J. Organomet. Chem.. 2007;692:991-996.
  53. , , . Arabian J. Chem.. 2014;7:553-596.
  54. , , . Curr. Med. Chem.. 2012;19:239-280.
  55. , , . J. Organomet. Chem.. 2007;692:5026-5032.
  56. , , . J. Organomet. Chem.. 2008;693:2159-2162.

Fulltext Views
1,109

PDF downloads
642
View/Download PDF
Download Citations
BibTeX
RIS
Show Sections

Suggested read for related articles: