INTRODUCTION:

4-Thiazolidinones are very versatile group of heterocycles present in natural products and pharmaceuticals [1]. In the recent years lirature show that the thiazole derivatives exhibit better pharmacological properties such as antimicrobial [1], anti-inflammatory [2] , antitubercular [3], anticonvulsant [4], pesticides [5] and many others. Further more significant biological properties are associated with thiazolidinone derivatives like anticonvulsant [7], antihelmintics [8] , antidiabetic [9].

In present work we used various schiff bases on heterocyclization reaction with mercapto acetic acid give 4-thiazolidinones. Their structure has been characterized on the basis of their analytical and spectral data.

EXPERIMENTAL:

All the compounds were checked for their homogeneity by TLC on silica gel-G plates, IR spectra were recorded in KBr on a Perkin-Elmer BX series FT-IR spectrophotometer, ¹ H NMR spectra were recorded BRUKER Spectrometer on a 400 MHz in CDCl₃ using TMS as internal standard and satisfactory C, H, N and S analysis were obtained for all the compounds.

Melting Points were determined on Gallen-Kamp melting point apparatus .The mass spectra were recorded on (FAB mass), spectrometry used to confirm their structure. Antibacterial activity (anti-microbial activity) was carried out by cup-plate agar diffusion method. Experimental procedures for the synthesis of this series of compounds have been adopted according to reported methods [10-13]

Synthesis of 2-[1-N-phenyl-3-phenyl-pyrrazole]-3-N-arylthiazolidine-4-ones (2a-h)

The 1-N-phenyl-3-phenyl-4- formyl pyrazole and then after 2-[1-N-phenyl-3- phenylpyrrazole]-3-N-aryl-thiazolidine-4-ones was prepared by method reported in literature [14-17] . The procedure is as follows:

Synthesis of 1-(phenyl)-ethanone-(phenyl)-hydrazone

A mixture of phenyl hydrazine (I) (0.01 mole) and acetophenone (II) (0.01 mole) in absolute ethanol was refluxed in water bath for 2 hrs. in presence of 1 ml glacial acetic acid. The crude product was isolated and crystallized from absolute alcohol. Yield was about 94%.

Synthesis of 1-N-phenyl-3-phenyl-4-formyl pyrazole

1-(phenyl)-ethanone-(phenyl)-hydrazone (III) (0.01 mole) was added in mixture of Vilsmeir-Haack reagent (prepared by drop wise addition of 3 ml of POCl₃ in ice cooled 25 ml dimethylformamide [DMF] and refluxed for 5 hrs. The reaction mixture was poured into ice followed by neutralization using sodium bicarbonate. Crude product was isolated and crystallized from ethanol. Yield was about 82%.

Table 1: Physical constants of synthesis of 2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-arylthiazolidine- 4-ones: (2a-h)

S. No	Ar	Molecular Formula	Molecular Weight	M.P. °C	Yield (%)	% of C, H, N and S Cal / Found
S. No	Ar	Molecular Formula	Molecular Weight	M.P. °C	Yield (%)	C	H	N	S
2a	-C₆H₅	C₂₄H₁₉N₃OS	397	142	56	72.5 72.3	4.7 4.5	10.5 10.4	8.0 7.8
2b	4- OCH₃C₆H₄	C₂₅H₂₁N₃O₂S	427	157	60	70.2 70.5	4.9 4.6	9.8 9.4	7.4 7.3
2c	4- OHC₆H₄	C₂₄H₁₉N₃O₂S	413	165	59	69.7 69.3	4.6 4.5	10.1 9.9	7.7 7.6
2d	2- OHC₆H₄	C₂₄H₁₉N₃O₂S	413	168	72	69.7 69.5	4.6 4.5	10.1 9.9	7.7 7.4
2e	4- CH₃C₆H₄	C₂₅H₂₁N₃OS	411	172	59	72.9 72.7	5.1 5.0	10.2 10.0	7.7 7.4
2f	3,4- O₂CH₂C₆H₃	C₂₅H₁₉N₃O₃S	441	170	58	68.0 67.8	4.3 4.2	9.5 9.0	7.2 7.0
2g	4-OH-3-OCH₃C₆H₃	C₂₅H₂₁N₃O₃S	443	160	56	67.7 67.6	4.7 4.7	9.4 9.3	7.2 7.2
2h	3,4-(C₂H₅O)₂C₆H₃	C₂₈H₂₇N₃O₃S	485	171	56	69.2 68.8	5.5 5.3	8.6 8.5	6.5 6.4

Synthesis of Arylidine-[1-N-phenyl-3-phenylpyrazole] (1a-h)

A mixture of equimolar amount of 1-Nphenyl-3-phenyl-4-formyl pyrazole (0.01 mole) (1) and various aromatic amines (0.01 mole) in 50 ml acetic acid was refluxed for about 10-12 hrs. on oil bath with TLC monitoring. The reaction mixture was cooled and it was poured into ice water and extracted with ethyl acetate and water and finally dried over anhydrous sodium sulfate. The solvent was evaporated to give the solid product. It was crystallized from ethyl acetatehexane using decolorizing charcoal to give various anils (i.e. Schiff bases) (1a-h).

Synthesis of 2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-arylthiazolidine- 4-ones (2a-h)

A mixture of schiff bases (1a-h) (0.01 mole) in THF (30ml) and mercapto acetic acid (thioglycolic acid) (0.01 mole) with a pinch of anhydrous ZnCl₂ was refluxed for 12 hours. The solvent was removed to get a residue, which was dissolved in benzene and passed through column of silica gel using benzene: chloroform (8:2; v/v) mixture as eluent. The eluent was concentrated and the product crystallized from alcohol to give 4-thiazolidinones (2a-h), which were obtained in 55-70% yield. The analytical and spectral data of compounds (2a-h) are described in Table (1).

2a: 2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-(phenyl)- thiazolidine-4-ones

IR (KBr, cm^-1): 3030, 1500, 1600 (-C-H, aromatic), 1680 (-C=O of thiazolidinone); PMR Spectra (CDCl₃): δ (ppm) 6.12-7.8 (1H, m, aromatic + H of pyrazole), 3.1 (2H of CH₂ for thiazolidinone), 5.35 (2H of C₂H for thiazolidinone); CMR Spectra (CDCl₃): δ (ppm) 113-130 (benzene), 136-145 (pyrazole), 169 (C=O), 36 (CH₂), 46 (CH).

2b:2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-(4- methoxyphenyl)-thiazolidine-4-ones

IR (KBr, cm^-1): 3030, 1600, 1500 (-C-H, aromatic), 1690 (pyridine ring, -C=O of thiazolidinone), 1200 (Ar-O-CH₃); PMR Spectra (CDCl₃): δ (ppm) 6.12-7.8 (1H, m, aromatic + H of pyrazole), 3.2 (2H of CH₂for thiazolidinone), 5.35 (H of C₂H for thiazolidinone), 3.35 (3H of CH₃ for thiazolidinone); CMR Spectra (CDCl₃): δ (ppm) 113-131 (benzene), 135-145 (pyrazole), 169 (C=O), 36 (CH₂), 46 (CH), 56 (CH₃).

2c:2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-(4- hydroxyphenyl)-thiazolidine-4-ones

IR (KBr, cm^-1): 3030, 1500, 1600 (-C-H, aromatic), 1670 (-C=O of thiazolidinone), 3200-2600 (-OH), 2880, 2920, 1400 (CH₂); PMR Spectra (CDCl₃): δ (ppm) 6.12-7.8 (1H, m, aromatic + H of pyrazole), 3.2 (2H for CH₂ of C₅ thiazolidinone), 5.35 (H for C₂H of thiazolidinones), 3.9 (H of OH); CMR Spectra (CDCl₃): δ (ppm) 113-132 (benzene), 135-146 (pyrazole), 169 (C=O), 36

(CH₂), 46 (CH).

2d:2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-(2- hydroxyphenyl)-thiazolidine-4-ones

IR (KBr, cm^-1): 3030, 1500, 1600 (-C-H, aromatic), 1690 (-C=O of thiazolidinone), 3200-2600 (-OH), 2880, 2920, 1400 (CH₂); PMR Spectra (CDCl₃): δ (ppm) 6.12-7.8 (1H, m, aromatic + H of pyrazole), 3.1 (2H for C₅H), 5.35 (H for C₂H), 3.9 (H of OH); CMR Spectra (CDCl₃): δ (ppm) 113-133 (benzene), 135-147 (pyrazole), 169 (C=O), 36 (CH₂), 46 (CH).

2e:2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-(4- methyphenyl)-thiazolidine-4-ones

IR (KBr, cm^-1): 3030, 1500, 1600 (-C-H, aromatic), 1690 (-C=O of thiazolidinone), 2950, 1370 (CH₃), 2880, 2920, 1400 (CH₂); PMR Spectra (CDCl₃): δ (ppm) 6.2-7.9 (1H, m, aromatic + H of pyrazole), 3.2 (2H for C₅H), 2.1 (3H for CH₃), 5.35 (H for C₂H); CMR Spectra (CDCl₃): δ (ppm) 113-134 (benzene), 135-148 (pyrazole), 169 (C=O), 36 (CH₂), 46 (CH), 25 (CH₃).

2f:2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-(3,4- methelenedioxyphenyl)-thiazolidine-4-ones

IR (KBr, cm^-1): 3030, 1500, 1600 (-C-H, aromatic, thiazole ring), 1690 (-C=O of thiazolidinone), 1200 (aryl-alkyl ether), 2880, 2920, 1400 (CH₂); PMR Spectra (CDCl₃): δ (ppm) 6.15-7.8 (1H, m, aromatic + H of pyrazole), 5.35 (H for C₂H), 5.35 (2H for CH₂of –O-CH₂-O-), 3.2 (2H of C₅H); CMR Spectra (CDCl₃): δ (ppm) 114-130 (benzene), 135-149 (pyrazole), 169 (C=O), 36 (CH₂), 46 (CH), 95 (O-CH₂-O).

2g: 2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-(4-hydroxy-3- methoxyphenyl)-thiazolidine-4-ones

IR (KBr, cm^-1): 3030, 1500, 1600 (-C-H, aromatic), 1680 (-C=O of thiazolidinone), 3200-2600 (-OH), 1200 (aryl-alkyl ether), 2880, 2920, 1400 (CH₂); PMR Spectra (CDCl₃): δ (ppm) 6.12-7.9 (1H, m, aromatic + H of pyrazole), 3.2 (2H for C₅H), 5.35 (H for C₂H), 3.9 (H of OH), 3.35 (3H for OCH₃); CMR Spectra (CDCl₃): δ (ppm) 113-135 (benzene), 135-150 (pyrazole), 169 (C=O), 36 (CH₂), 46 (CH), 56 (CH₃).

2h: 2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-(3,4- diethoxyphenyl)-thiazolidine-4-ones

IR (KBr, cm^-1): 3030, 1500, 1600 (-C-H, aromatic), 1670 (-C=O of thiazolidinone), 1200 (aryl-alkyl ether), 2880, 2920, 1400 (-CH₂-); PMR Spectra (CDCl₃): δ (ppm) 7.2-8.1 (1H, m, romatic + H of pyrazole), 3.25 (2H for C₅H), 3.35 (H for C₂H), 2.1-2.5 (6H for 2 CH₃), 2.89-3.18 (4H for 2 CH₂); CMR Spectra (CDCl₃): δ (ppm) 113-136 (benzene), 135-151 (pyrazole), 169 (C=O),

36 (CH₂), 14 (CH₃), 58 (OCH₂).

Antibacterial activity

The study has been conducted according to the method adopted by Cruickshank et. al.[18]. Nutrient agar broth was melted in a water bath and cooked to 45⁰C with gentle shaking to bring about uniform cooling. It was inoculated with 0.5-0.6 ml of 24 hour old culture especially and mixed well by gentle shaking before pouring on the sterilized Petri dish (25 ml each). The poured material was allowed to set (1.5 hour) and there after the “cups” were made by punching into the agar surface with a sterile cork borer. Into this “cups” 0.1 ml of test solution (prepared by dissolving 10gm of sample in 10ml DMF) was added by sterile micropipette. The plates were noted. Ampicillin, Tetracycline, Gentamycin, and Chloramphenicol were used as standard drugs and a solvent control was also run to know the activity.

Activity of standards and inhibition due to DMF (solvent) are given in Table-2.

Table 2: Antibacterial activity of standards and solvent (DMF)

Compounds	Zone of Inhibition (in mm)
	Gram positive		Gram negative
	*B. subtillis*	*S. aureus*	*E. coli*	*P. aeruginosa*
DMF	6	5	5	5
Ampicillin	18	15	20	20
Tetracyclin	21	22	15	19
Gentamycin	20	18	18	22
Chloramphenicol	20	23	18	23

The compounds tested for antimicrobial activity are listed in Table-3 show size of zone of inhibition of bacterial growth procedure by test compounds for broad range of antimicrobial activity inhibiting growth of gram-positive bacterial strains B. subtillis and S. aureus, and gram-negative bacterial strains E. coli and P. aeruginosa. Comparison of antimicrobial activity of produced compounds with that of standard antimicrobial drugs reveals that the produce compounds (Schiff Bases, 2-Azetidinones, 4- Thiazolidinones, 2H-Pyrrole-2-ones and 2-Pyrrolidiones) shows moderate to good activity against all four bacterial strains. Among 2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-arylthiazolidine- 4-ones (2a-h).

Table 3: Antibacterial activity of 2-[1-N-phenyl-3-phenyl-pyrazole]-3-N-aryl-thiazolidine-4-ones (2a-h)

Compounds	Zone of Inhibition (in mm)
	Gram positive		Gram negative
	*B. subtillis*	*S. aureus*	*E. coli*	*P. aeruginosa*
2a	9	9	16	9
2b	10	10	14	10
2c	11	13	11	16
2d	15	17	18	14
2e	7	9	10	8
2f	12	12	15	13
2g	8	9	10	12
2h	16	15	12	13

Compound, 2b, 2c, 2d, 2f and 2h show good antimicrobial activity.

RESULTS AND DISCUSSION:

As we know that the azomethines are the crucial material for the preparation of heterocyclic compounds like 2- azetidinones, 4-thiazolidinones, etc. These azomethines (1a-h) on cyclocondensation reaction with thioglycolic acid in the presence of anhydrous ZnCl₂ affords the biologically active of 4-thiazolidinones derivatives (2a-h). Their structures were confirmed by analytical and spectral data. The C, H, N and S contents of the prepared compounds were consistent with their predicted structures as shown in Scheme-3. The infrared spectra show the band in the region 1680-1700cm-1 for carbonyl (>C=O) group of 4-thiazolidinone ring.

The proton magnetic resonance spectra of the prepared compounds (2a-h) shows signal at 5.35 δ for CH₂ proton at position-5 in the 4-thiazolidinone ring and a signal at 3.2 δ for -CH protons at position-2 in the ring. All other signals are at their respective positions in the PMR spectrum.

The CMR spectra of the compounds also show the signal at 163 for C=O and 36 δ ppm for CH₂ of 4- thiazolidinone. All other signals appeared at their respective positions.

CONCLUSION

Newly synthesized compounds of azomethines (2a to 2h) have been tested for their anti bacterial activity against gram positive bacteria B. subtillis and S. aureus gram negative bacteria E. coli and P. aeruginosa by the help of borer in agar medium and filled with 0.04ml (40μg) solution of sample in DMF. Ampicillin, Tetracyclin, Gentamycin, Chloramphenicol were used as a reference compound. The compound 2b, 2c, 2d, 2f and 2h were shown significant activities and compound 2a, 2e and 2g have shown moderate activity against gram positive and gram negative bacteria.

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Received on 20.07.2012 Modified on 10.08.2012

Asian J. Research Chem. 5(9): September, 2012; Page 1155-1158