Synthesis and Biological Evaluation of Some Novel

Letters in Drug Design & Discovery, 2012, 9, ???-???

1

Synthesis and Biological Evaluation of Some Novel Thiazolylhydrazinomethylideneferrocenes as Antimicrobial Agents Navneet Chandaka, Pawan Kumara, Chetan Sharmab, Kamal R. Anejab and Pawan K. Sharma*,a a

Department of Chemistry, Kurukshetra University, Kurukshetra-136 119, India

b

Department of Microbiology, Kurukshetra University, Kurukshetra-136 119, India Received July 14, 2011: Revised September 28, 2011: Accepted September 28, 2011

Abstract: Some novel thiazolylhydrazinomethylideneferrocenes 4 and 5 bearing phenyl and coumarin analogues respectively at position-4 of 1,3-thiazole were synthesized using established procedures and were evaluated for their in vitro antibacterial activity against four pathogenic bacterial strains namely, S. aureus, B. subtilis (Gram-positive), E. coli, P. aeruginosa (Gram-negative), and in vitro antifungal activity against two pathogenic fungal strains namely, A. niger and A. flavus. Four tested compounds, 4a, 4d, 4e and 4f exhibited moderate antibacterial activity against Gram-positive bacteria and 4e exhibited moderate antifungal activity against the tested fungi. However, none of the compounds showed any activity against Gram-negative bacteria.

Keywords: Antibacterial activity, antifungal activity, thiazoles, coumarin, thiazolylhydrazinomethylideneferrocenes. 1. INTRODUCTION

2. EXPERIMENTAL

Metal containing macromolecules form an integral part of the human body system such as haemoglobin and transferrin (Fe), carbonic anhydrase (Zn), xanthine oxidase (Mb), hepatocuperin (Cu), etc. The introduction of metal ions in biologically active molecules is a continuing area of research for scientists and such organometallic medicinals [1] are widely used nowadays for curing various diseases, e.g. arsphenamine containing arsenic as antimalarial, silver sulfadizine as treatment of severe burns, meralein containing mercury as antiseptic, etc. Therefore, ‘metal-based drugs’ are assuming increasing importance in the area of medicinal chemistry. It has been reported that introduction of ferrocenyl moiety in a number of already used therapeutic drugs has considerably increased their bioactivities [2-9], e.g. ferrocene penicillins and cephalosporins (antibacterial), ferrocene fluconazole and triadimenol (antifungal), ferrocene aspirin (anti-inflammatory), ferroquine (antimalarial), ferrocifen (anti-cancer), etc. Because of its stability, non toxicity, membrane permeation, favorable electrochemical properties as well as its capability to exhibit various biomedicinal activities such as antimicrobial [4, 10, 11], anticancer [12], etc., chemists are trying for its further exploration and incorporation into various heterocyclic moieties. It is known in the literature that thiazole [13-16] and coumarin [17-21] heterocyclic moieties constituting various bioactive molecules, when present individually as well as together [22-24], exhibit diverse biological activities. It has been reported that ferrocene containing thiazole derivatives show significant antibacterial [25] as well as antifungal [26] activities. These considerations motivated us to synthesize some novel thiazolylhydrazinomethylideneferrocenes using various p-substituted phenacyl bromides and 6-substituted-3-bromoacetylcoumarins for their evaluation as antibacterial and antifungal agents.

2.1. Materials and Methods All reactions were carried out under atmospheric pressure. Melting points were determined in open glass capillaries in an electrical melting point apparatus and are uncorrected. IR spectra were recorded on ABB MB 3000 DTGS IR instrument using the KBr pellet technique. 1 H NMR and 13C NMR spectra were recorded either in pure CDCl3 or DMSO-d6 or in CDCl3/DMSO-d6 mixture on Bruker NMR spectrometer at 300 MHz and 75.5 MHz respectively using tetramethylsilane (TMS) as internal standard. Chemical shifts are expressed in , ppm. Elemental analyses were performed on a varioMICRO V1.7.0 Elementar Analysensysteme GmbH instrument. The purity of the compounds was checked by 1H NMR and thin layer chromatography (TLC) on silica gel plates using a mixture of petroleum ether and ethyl acetate as eluent. Iodine or UV lamp was used as a visualizing agent. Abbreviations ‘s’ for singlet, ‘d’ for doublet, ‘m’ for multiplet, ‘ex’ for exchangeable proton are used for NMR assignments. ‘d’ stands for decomposition in melting point data. 2.1.1. Preparation of Thiazolylhydrazinomethylideneferrocenes (4a-f and 5a-c) To a solution of formylferrocene thiosemicarbazone (1, 2 mmol) in EtOH:THF (60 mL, 2:1 v/v) was added appropriate phenacyl bromide (2) or 3-bromoacetylcoumarin (3) ( 2.2 mmol) followed by anhydrous sodium acetate (2.2 mol) and refluxed the resulting reaction mixture for 6-7 h. After completion of the reaction, solution was reduced to 1/4th of its volume and cooled to room temperature. The solid separated out was filtered, washed with water (100 mL) followed by cold ethanol (10 mL) and crystallized from ethanol to afford the target thiazolylhydrazinomethylideneferrocenes 4 or 5 as reddish brown or black solid material.

*Address correspondence to this author at the Department of Chemistry, Kurukshetra University, Kurukshetra-136 119, India; Tel: +91 9416457355; Fax: +91 1744 238277; E-mail: [email protected] 1570-1808/12 $58.00+.00

© 2012 Bentham Science Publishers

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Letters in Drug Design & Discovery, 2012, Vol. 9, No. 1

Chandak et al.

R

S Fe

N

O R 4

Br 2 H2N Fe

N

N N H

CH3COONa, EtOH/THF, reflux, 6-7 h

S N H

CH3COONa, EtOH/THF, reflux, 6-7 h

1

R'

O S

R'

Br

Fe O

N

O

O

N N H

O

5

3 Compound 2 & 4

a

b

c

d

e

f

R

H

CH3

F

Cl

Br

NO2

Compound 3 & 5

a

b

c

R

H

Cl

Br

Scheme 1. Synthesis of novel thiazolylhydrazinomethylideneferrocenes 4 & 5.

2.1.1.1. Ferrocene-1-carbaldehyde N-(4-phenyl-1,3-thiazol2-yl)hydrazone (4a) Yield 90%; m.p. 138-140 °C (d); IR (KBr) cm-1: 3171 (N-H stretch), 3086 (C-H stretch), 1582 (C=N stretch), 1481, 1427; 1H NMR (CDCl3, 300 MHz): 10.65 (s, ex, 1H, NH), 7.90 (d, 2H, J = 7.2 Hz, Ar-H), 7.47-7.51 (m, 2H, Ar-H), 7.41 (d, 2H, J = 6.3 Hz, Ar-H), 7.15 (s, 1H, thiazole-H), 6.85 (s, 1H, CH=N), 4.32 (s, 2H, ferrocene-H), 4.28 (s, 2H, ferrocene-H), 4.11 (s, 5H, ferrocene-H); 13C NMR (CDCl3, 75.5 MHz): 169.9, 150.9, 142.7, 135.0, 128.8, 127.9, 126.3, 103.0, 79.0, 69.7, 69.1, 67.1. Anal. calc. for C20H17FeN3S (%): C, 62.03; H, 4.42; N, 10.85; found (%): C, 62.30; H, 4.53; N, 10.70. 2.1.1.2. Ferrocene-1-carbaldehyde N-[4-(4-methylphenyl)1,3-thiazol-2-yl]hydrazone (4b) Yield 88%; m.p. 150-152 °C (d); IR (KBr) cm-1: 3155 (N-H stretch), 3070 (C-H stretch), 1566 (C=N stretch), 1489, 1427; 1H NMR (CDCl3, 300 MHz): 10.62 (s, ex, 1H, NH), 7.80 (d, 2H, J = 7.8 Hz, Ar-H), 7.29 (d, 2H, J = 7.8 Hz, ArH), 7.09 (s, 1H, thiazole-H), 6.78 (s, 1H, CH=N), 4.27 (s, 4H, ferrocene-H), 4.08 (s, 5H, ferrocene-H), 2.43 (s, 3H, CH3); 13C NMR (DMSO-d6, 75.5 MHz): 168.6, 150.9, 142.4, 137.1, 132.6, 129.5, 125.9, 102.5, 80.1, 70.1, 69.3, 67.3, 21.2 (CH3). Anal. calc. for C21H19FeN3S (%): C, 62.85; H, 4.77; N, 10.47; found (%): C, 63.02; H, 4.89; N, 10.31. 2.1.1.3. Ferrocene-1-carbaldehyde N-[4-(4-fluorophenyl)1,3-thiazol-2-yl]hydrazone (4c) Yield 92%; m.p. 172-174 °C (d); IR (KBr) cm-1: 3263 (N-H stretch), 3086 (C-H stretch), 1551 (C=N stretch), 1481, 1412; 1H NMR (CDCl3, 300 MHz): 10.68 (s, ex, 1H, NH), 7.85 (dd, 2H, 4JHF = 5.4 Hz, 3JHH = 8.7 Hz, Ar-H), 7.23 (s,

1H, thiazole-H), 7.16 (t, 2H, J = 8.7 Hz, Ar-H), 6.79 (s, 1H, CH=N), 4.38 (s, 2H, ferrocene-H), 4.32 (s, 2H, ferrocene-H), 4.14 (s, 5H, ferrocene-H); 13C NMR (DMSO-d6, 75.5 MHz): 168.6, 162.0 (d, 1JCF = 244.6 Hz), 149.9, 142.6, 131.9, 127.9 (d, 3JCF = 7.5 Hz), 115.8 (d, 2JCF = 21.8 Hz), 103.1, 80.0, 70.1, 69.3, 67.3. Anal. calc. for C20H16FFeN3S (%): C, 59.27; H, 3.98; N, 10.37; found (%): C, 59.44; H, 4.11; N, 10.20. 2.1.1.4. Ferrocene-1-carbaldehyde N-[4-(4-chlorophenyl)1,3-thiazol-2-yl]hydrazone (4d) Yield 78%; m.p. 168-170 °C (d); IR (KBr) cm-1: 3263 (N-H stretch), 3101 (C-H stretch), 1551(C=N stretch), 1474, 1404; 1H NMR (CDCl3, 300 MHz): 10.67 (s, ex, 1H, NH), 7.79 (d, 2H, J = 8.4 Hz, Ar-H), 7.43 (d, 2H, J = 8.4 Hz, ArH), 7.37 (s, 1H, thiazole-H), 6.83 (s, 1H, CH=N), 4.44 (s, 2H, ferrocene-H), 4.35 (s, 2H, ferrocene-H), 4.16 (s, 5H, ferrocene-H); 13C NMR (CDCl3/DMSO-d6, 75.5 MHz): 168.9, 149.8, 142.2, 134.0, 132.4, 128.7, 127.3, 103.5, 80.0, 70.1, 69.2, 67.2. Anal. calc. for C20H16ClFeN3S (%): C, 56.96; H, 3.82; N, 9.96; found (%): C, 56.88; H, 3.75; N, 10.12. 2.1.1.5. Ferrocene-1-carbaldehyde N-[4-(4-bromophenyl)1,3-thiazol-2-yl]hydrazone (4e) Yield 85%; m.p. 174-176 °C (d); IR (KBr) cm-1: 3448 (N-H stretch), 3109 (C-H stretch), 1643 (C=N stretch), 1558 (C=N stretch), 1474, 1396; 1H NMR (DMSO-d6, 300 MHz): 11.85 (s, ex, 1H, NH), 7.86 (s, 1H, thiazole-H), 7.79 (d, 2H, J = 8.4 Hz, Ar-H), 7.58 (d, 2H, J = 8.4 Hz, Ar-H), 7.33 (s, 1H, CH=N), 4.59 (s, 2H, ferrocene-H), 4.38 (s, 2H, ferrocene-H), 4.18 (s, 5H, ferrocene-H); 13C NMR (CDCl3/DMSO-d6, 75.5 MHz): 168.9, 149.7, 142.3, 134.3,

Antimicrobial Ferrocene Derivatives


3

131.6, 127.6, 120.8, 103.6, 79.9, 69.9, 69.2, 67.2. Anal. calc. for C20H16BrFeN3S (%): C, 51.53; H, 3.46; N, 9.01; found (%): C, 51.70; H, 3.58; N, 8.91.

Anal. calc. for C23H16BrFeN3O2S (%): C, 51.71; H, 3.02; N, 7.87; found (%): C, 51.65; H, 2.95; N, 8.01.

2.1.1.6. Ferrocene-1-carbaldehyde N-[4-(4-nitrophenyl)1,3-thiazol-2-yl]hydrazone (4f)

2.2. Biological Assay

Yield 90%; m.p. 200-202 °C (d); IR (KBr) cm-1: 3310 (N-H stretch), 3109 (C-H stretch), 1574 (C=N stretch), 1504, 1420; 1H NMR (DMSO-d6, 300 MHz): 11.93 (s, ex, 1H, NH), 8.27 (d, 2H, J = 8.7 Hz, Ar-H), 8.09 (d, 2H, J = 8.7 Hz, Ar-H), 7.88 (s, 1H, thiazole-H), 7.66 (s, 1H, CH=N), 4.61 (s, 2H, ferrocene-H), 4.42 (s, 2H, ferrocene-H), 4.21 (s, 5H, ferrocene-H); 13C NMR (DMSO-d6, 75.5 MHz): 169.1, 148.9, 146.6, 143.2, 141.2, 126.7, 124.5, 108.3, 79.8, 70.2, 69.4, 67.4. Anal. calc. for C20H16FeN4O2S (%): C, 55.57; H, 3.73; N, 12.96; found (%): C, 55.68; H, 3.88; N, 12.77. 2.1.1.7. Ferrocene-1-carbaldehyde N-[4-(2-oxo-2H-chromen-3-yl)-1,3-thiazol-2-yl]hydrazone (5a) Yield 90%; m.p. 204-206 °C (d); IR (KBr) cm-1: 3232 (N-H stretch), 3132 (C-H stretch), 1705 (lactone C=O stretch), 1574 (C=N stretch), 1481, 1435, 1381; 1H NMR (DMSO-d6, 300 MHz): 11.82 (s, ex, 1H, NH), 8.52 (s, 1H, 4-H of coumarin), 7.84-7.89 (m, 2H, thiazole-H, coumarin), 7.72 (s, 1H, CH=N), 7.60-7.63 (m, 1H, coumarin), 7.39-7.46 (m, 2H, coumarin), 4.61 (s, 2H, ferrocene-H), 4.41 (s, 2H, ferrocene-H), 4.21 (s, 5H, ferrocene-H); 13C NMR (DMSOd6, 75.5 MHz): 168.1, 152.7, 143.2, 138.5, 132.1, 129.2, 126.7, 125.1, 119.6, 116.3, 110.5, 79.9, 70.2, 69.4, 67.4. Anal. calc. for C23H17FeN3O2S (%): C, 60.67; H, 3.76; N, 9.23; found (%): C, 60.82; H, 3.91; N, 9.08. 2.1.1.8. Ferrocene-1-carbaldehyde N-[4-(6-chloro-2-oxo2H-chromen-3-yl)-1,3-thiazol-2-yl]hydrazone (5b) Yield 74%; m.p. 194-196 °C (d); IR (KBr) cm-1: 3248 (N-H stretch), 3117 (C-H stretch), 1720 (lactone C=O stretch), 1574 (C=N stretch), 1481, 1427; 1H NMR (DMSOd6, 300 MHz): 11.88 (s, ex, 1H, NH), 8.45 (s, 1H, 4-H of coumarin), 7.99 (s, 1H, 5-H of coumarin), 7.89 (s, 1H, thiazole-H), 7.74 (s, 1H, CH=N), 7.63 (d, 1H, J = 8.7 Hz, H7 or H-8 of coumarin), 7.47 (d, 1H, J = 8.7 Hz, H-7 or H-8 of coumarin), 4.61 (s, 2H, ferrocene-H), 4.40 (s, 2H, ferrocene-H), 4.21 (s, 5H, ferrocene-H); 13C NMR (DMSOd6, 75.5 MHz): 168.1, 158.7, 151.2, 144.1, 143.2, 137.0, 131.4, 128.9, 128.1, 122.0, 121.1, 118.2, 111.3, 79.8, 70.6, 69.4, 67.4. Anal. calc. for C23H16ClFeN3O2S (%): C, 56.40; H, 3.29; N, 8.58; found (%): C, 56.59; H, 3.43; N, 8.41. 2.1.1.9. Ferrocene-1-carbaldehyde N-[4-(6-bromo-2-oxo2H-chromen-3-yl)-1,3-thiazol-2-yl]hydrazone (5c) Yield 76%; m.p. 198-200 °C (d); IR (KBr) cm-1: 3209 (N-H stretch), 3132 (C-H stretch), 3094 (C-H stretch), 1720 (lactone C=O stretch), 1574 (C=N stretch), 1474, 1435; 1H NMR (DMSO-d6, 300 MHz): 11.86 (s, ex, 1H, NH), 8.45 (s, 1H, 4-H of coumarin), 8.11 (s, 1H, 5-H of coumarin), 7.90 (s, 1H, thiazole-H), 7.75 (d, 2H, J = 8.7 Hz, CH=N, H-7 or H-8 of coumarin), 7.41 (d, 1H, J = 8.7 Hz, H-7 or H-8 of coumarin), 4.61 (s, 2H, ferrocene-H), 4.41 (s, 2H, ferroceneH), 4.21 (s, 5H, ferrocene-H); 13C NMR (DMSO-d6, 75.5 MHz): 168.1, 158.8, 151.7, 143.4, 137.0, 134.3, 131.0, 121.9, 121.6, 118.5, 116.8, 111.4, 79.8, 70.3, 69.4, 67.4.

2.2.1. In Vitro Antibacterial Assay The antibacterial activity of newly synthesized compounds was evaluated by agar well diffusion method [27]. All the microbial cultures were adjusted to 0.5 McFarland standard, which is visually comparable to a microbial suspension of approximately 1.5 x 108 cfu/mL [28]. 20 mL of Mueller Hinton agar medium was poured into each Petri plate and the agar plates were swabbed with 100 μL inocula of each test bacterium and kept for 15 min for adsorption. Using sterile cork borer of 8 mm diameter, wells were bored into seeded agar plates and these were loaded with a 100 μL volume with concentration of 4.0 mg/mL of each compound reconstituted in dimethylsulphoxide (DMSO). All the plates were incubated at 37 °C for 24 hrs. Antibacterial activity of 9 newly synthesized compounds was evaluated by measuring the zone of growth inhibition against the test bacteria with zone reader (Hiantibiotic zone scale). DMSO was used as a negative control whereas ciprofloxacin was used as a positive control. The experiments were performed in triplicates. The antibacterial activity of the compounds was compared with ciprofloxacin as standard. Minimum Inhibitory Concentration (MIC) of newly synthesized compounds against tested bacteria was determined using macrodilution tube method as recommended by NCCLS [28, 29]. MIC is the lowest concentration of an antimicrobial compound that will inhibit the visible growth of a microorganism after overnight incubation. In this method, various test concentrations of newly synthesized compounds were prepared from 128 to 0.25 μg/mL in sterile tubes No. 1 to 10. 100 μL sterile Mueller Hinton Broth (MHB) was poured in each sterile tube followed by addition of 200 μL test compound in tube 1. Two fold serial dilutions were carried out from tube 1 to tube 10 and excess broth (100 μL) was discarded from the last tube No. 10. To each tube, 100 μL of standard inoculum (1.5 x 108 cfu/mL) was added. Ciprofloxacin was used as control. Turbidity was observed after incubating the inoculated tubes at 37 °C for 24 hrs. 2.2.2. In Vitro Antifungal Assay The antifungal activity of newly synthesized compounds was evaluated by poisoned food method [30]. The molds were grown on Saburaud Dextrose Agar (SDA) at 25 °C for 7 days and used as inocula. 15 mL of molten SDA (45 °C) was poisoned by the addition of 100 μL volume of each compound having concentration of 4.0 mg/mL, reconstituted in DMSO, poured into a sterile petri plate and allowed to solidify at room temperature. The solidified poisoned agar plates were inoculated at the centre with fungal plugs (8 mm diameter), obtained from the actively growing colony and incubated at 25 °C for 7 days. DMSO was used as a negative control whereas fluconazole was used as a positive control. The experiments were performed in triplicates. Diameter of the fungal colonies was measured and expressed as percent mycelial inhibition determined by applying the following formula:

4


Chandak et al.

Inhibition of mycelial growth % = (dc-dt) / dc x 100 Where dc = average diameter of fungal colony in negative control plates dt = average diameter of fungal colony in experimental plates 3. RESULTS AND DISCUSSION

3.2. Biological Evaluation

3.1. Chemistry The synthetic route used to synthesize the target thiazolylhydrazinomethylideneferrocenes 4a-f and 5a-c is outlined in Scheme 1. Using Hantzsch thiazole synthesis strategy [31], the present synthesis of thiazolylhydrazinomethylideneferrocenes 4 and 5 consist of the condensation of appropriate p-substituted phenacyl bromide 2 or 6-substituted-3-bromoacetylcoumarin 3 with formylferrocene thiosemicarbazone 1 in refluxing EtOH : THF in the presence of sodium acetate. Starting materials, formylferrocene thiosemicarbazone 1 [32, 33] from ferrocene carbaldehyde, p-substituted phenacyl bromides 2 [34, 35] from p-substituted acetophenones and 6substituted-3-bromoacetylcoumarins 3 [36, 37] from 6substituted-3-acetylcoumarins were synthesized following established literature procedures. 3-Acetylcoumarins, in turn, were synthesized by Knoevenagel condensation [38] of salicylaldehydes with ethylacetoacetate in presence of piperidine [39]. Analytical and spectral data (1H NMR, 13C NMR, IR) of the newly synthesized compounds were in full agreement with the proposed structures. In general, 1H NMR spectra of 4 or 5 displayed an exchangeable singlet in the range of 10.62-10.68 in CDCl3 and 11.82-11.93 in DMSOd6 corresponding to NH. A singlet in the range of 7.09-7.37 in CDCl3 and 7.84-7.90 in DMSO-d6 was attributed to C5proton of thiazole ring and another one in the range of 6.78-6.85 in CDCl3 and 7.33-7.75 in DMSO-d6 was attributed to CH=N connected to ferrocene. Values suggest that all these three protons show solvent dependant shift in 1 H NMR. Higher value for thiazole proton as compared to Table 1.

that of CH=N was assigned considering slight shielding of the later due to cyclopentadienyl anion ring of ferrocene but might be interchangeable. All ferrocene protons were clearly assigned in the range of 4-5 as two or three singlets in the relative ratio of either 4 : 5 or 2 : 2 : 5. All coumarin thiazoles (5a-c) were showing characteristic C=O stretch of lactone nature at 1705-1720 cm-1 in FT-IR.

3.2.1. In Vitro Antibacterial Activity All the newly synthesized thiazolylhydrazinomethylideneferrocenes (4a-e & 5a-c) were evaluated for their in vitro antibacterial activity against Staphylococcus aureus (MTCC 96) and Bacillus subtilis (MTCC 121) representing Grampositive bacteria, and Escherichia coli (MTCC 1652) and Pseudomonas aeruginosa (MTCC 741) representing Gramnegative bacteria (Table 1) by agar well diffusion method [27] using ciprofloxacin as the reference drug. The results were recorded for each tested compound as the average diameter of inhibition zones of bacterial growth surrounding the well in mm. The minimum inhibitory concentration (MIC) measurements were performed using a macrodilution tube method [28, 29] (Table 1). Results revealed that in general, all the tested compounds possessed moderate antibacterial activity against Grampositive bacteria (S. aureus, B. subtilis). However, none of them was found to be effective against any of the Gramnegative bacteria (E. coli, P. aeruginosa). On the basis of zone of inhibition against the test bacterium, compound 4e was found to be the most effective against S. aureus showing the maximum zone of inhibition of 18.3 mm and compound 4a against B. subtilis producing 19.6 mm zone of inhibition (Table 1) as compared with the standard drug ciprofloxacin which showed the zone of inhibition 27.6 mm against S. aureus and 26.3 mm against B. subtilis. Besides 4e, no compound was found possessing significant antibacterial activity against S. aureus with zone of inhibition >18.0 mm while compounds 4d, 4e and 4f showed significant

In Vitro Antibacterial Activity and MIC of Compounds 4 and 5

Compounda

Diameter of growth of inhibition zone (mm)b

Minimum inhibitory concentration (MIC) (μg/ml)

S. aureus

B. subtilis

E. coli

P. aeruginosa

S. aureus

B. subtilis

4a

17.3

19.6

-

-

128

64

4b

14.6

15.3

-

-

256

128

4c

14.3

15.0

-

-

256

128

4d

16.6

18.3

-

-

128

64

4e

18.3

18.6

-

-

64

64

4f

16.6

19.3

-

-

128

64

5a

15.3

16.3

-

-

128

128

5b

15.0

16.6

-

-

128

128

5c

13.6

14.3

-

-

256

256

Ciprofloxacin

27.6

26.3

25.0

25.3

5

5

– No activity. a Concentration 4.0 mg/mL. b Values, including diameter of the well (8 mm), are means of three replicates.

Antimicrobial Ferrocene Derivatives


antibacterial activity against B. subtilis with zone of inhibition >18.0 mm. However, in terms of MIC, none of the compounds was found to possess appreciable antibacterial activity. Amongst all the compounds, the MIC ranged between 64 (4a, 4d, 4e, 4f) and 256 g/mL against Grampositive bacteria (Table 1). A comparison between the two series of compounds (4 and 5) indicates that in general, there is an appreciable decrease in activity against both Grampositive bacteria when phenyl analogues (4a, 4d, 4e) replaced by coumarin analogues (5a, 5b, 5c). Within the individual series, no correlation between the antibacterial activity with respect to the substituent on phenyl or coumarin ring is observed. 3.2.2. In Vitro Antifungal Activity Compounds 4 and 5 were also evaluated for their in vitro antifungal activity against two fungal strains, Aspergillus niger (MTCC 282) and Aspergillus flavus (MTCC 871) by poisoned food method [30]. Fluconazole was used as the reference drug and the results were recorded as the percentage inhibition of mycelial growth. When compared with reference drug (75.3% & 74.6% inhibition against A. niger and A. flavus respectively), it was noted that the only compound, 4e showed moderate antifungal activity with >55% inhibition of mycelial growth against both the fungal strains (Table 2). Others were found to possess no appreciable antifungal activity. The same trend was observed here also that there is slight to appreciable decrease in activity against both fungi when phenyl analogues (4a, 4d, 4e) replaced by coumarin analogues (5a, 5b, 5c). Table 2.

a

analogues were replaced by coumarin analogues. Out of the tested compounds, 4a, 4d, 4e and 4f exhibited moderate antibacterial activity against Gram-positive bacteria and 4e exhibited moderate antifungal activity against the tested fungi. However, none of the newly synthesized compounds was found to be superior over the reference drugs. ACKNOWLEDGEMENTS Defence Research and Development Organization (DRDO), New Delhi is thankfully acknowledged for financial support in the form of a research project. Authors (NC and PK) are grateful to the Council of Scientific and Industrial Research (CSIR), New Delhi for the award of senior and junior research fellowship respectively. REFERENCES [1]

[2] [3] [4] [5] [6]

In Vitro Antifungal Activity Of Compounds 4 and 5 Through Poisoned Food Method

Compounda

Mycelial growth inhibition (%) A. niger

A. flavus

4a

50.0

51.1

4b

48.8

50.0

4c

51.1

52.2

4d

52.2

51.1

4e

58.8

55.5

4f

53.3

52.2

5a

44.4

50.0

5b

48.4

51.1

5c

53.3

52.2

Fluconazole

75.3

74.6

Concentration 4.0 mg/mL.

[7]

[8]

[9]

[10]

[11] [12]

4. CONCLUSION In the present study, some novel thiazolylhydrazinomethylideneferrocenes 4 and 5 bearing phenyl and coumarin analogues respectively at position-4 of 1,3-thiazole were synthesized and were screened for their in vitro antibacterial activity and antifungal activity. No appreciable results were obtained by combining the biochemistry of ferrocene with thiazole and coumarins. A general decrease in antibacterial as well as antifungal activity was found when phenyl

5

[13]

[14]

[15]

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