Table 1: Spectral data of present thiazole derivatives

Molecular Formula

Elemental Analysis

Calculated (Found)

FTIR

ν_max

¹H NMR

-H

C₂₅H₂₀N₄O₃S

65.78

(65.40)

4.38

(4.10)

12.28

(12.01)

3400 (-NH-), 2900, 2850, 1690 (-COO-), 1670 (-C=O-), 1625 (-NH-), 1600 aromatic (-C=C-), 1590 (-N=N-), 1500, 1450, 1350(-C=S-), 1200, 1100, 980, 875 and 770 (st of thiazole nucleus

δ 1.30 (t, 3H, -CH₃), 4.25 (quart., 2H, -CH₂-), 7.47-7.63 (m, 6H, Ar-H at C- 3, C-4, C-5, C-3’, C-4’,C-5’), 7.90 (d, 2H, Ar-H at C-2” and C-6”), 8.00 (d, 2H, Ar-H at C-2’ and C-6’), 8.20 (d, 2H, Ar-H at C-2 and C-6), 8.30 (d, 2H, Ar-H at C-3’’ and C-5’’), 13.41 (s, 1H of -NH-)

-Cl

C₂₅H₁₉N₄O₃ClS

61.16

(60.95)

3.87

(3.59)

11.41

(11.32)

3375 (-NH-), 2950, 2900, 1700 (-COO-), 1650 (-C=O-), 1625 (-NH-), 1600 aromatic (-C=C-), 1590 (-N=N), 1500, 1450, 1350(-C=S-), 1200, 1100, 1000, 900, 875 and 770 (st of thiazole nucleus

δ 1.25 (t, 3H, -CH₃), 4.25 (quart., 2H, -CH₂-), 7.50-7.63 (m, 6H, Ar-H at C- 3, C-4, C-5, C-3’, C-4’,C-5’), 7.85 (d, 2H, Ar-H at C-2” and C-6”), 7.95 (d, 2H, Ar-H at C-2’ and C-6’), 8.20 (d, 2H, Ar-H at C-2 and C-6), 8.30 (d, 2H, Ar-H at C-3’’ and C-5’’), 13.50 (s, 1H of -NH-)

-NO₂

C₂₅H₁₉N₅O₅S

59.80

(59.55)

3.79

(3.65)

13.97

(13.65)

3400 (-NH-), 2950, 2900, 1700 (-COO-), 1650 (-C=O-), 1625 (-NH-), 1600 aromatic (-C=C-), 1590 (-N=N-), 1500, 1450, 1350(-C=S-), 1200, 1100, 1000, 900, 875 and 770 (st of thiazole nucleus)

δ 1.25 (t, 3H, -CH₃), 4.25 (quart., 2H, -CH₂-), 7.55-7.65 (m, 6H, Ar-H at C- 3, C-4, C-5, C-3’, C-4’,C-5’), 7.80 (d, 2H, Ar-H at C-2” and C-6”), 7.90 (d, 2H, Ar-H at C-2’ and C-6’), 8.20 (d, 2H, Ar-H at C-2 and C-6), 8.30 (d, 2H, Ar-H at C-3’’ and C-5’’), 13.45 (s, 1H of -NH-)

100 mL of water and extracted with ether to remove unreacted iodine and acetophenone. Excess of ether was distilled off. Residue was dissolved in boiling water and filtered off hot solution. Allowed to stand it for 30 minutes.

Make the reaction mixture alkaline (Up to pH 8-9) using ammonium hydroxide solution. The solid obtained was filtered and washed successively with water (2 X 150 mL). The separated solid was crystallized by aqueous ethanol (1:1). M. P.: 148^°C (Reported¹⁶M. P.: 147^°C). Yield: 80%.

Ethyl-4-aminobenzoate (II): Place 80 ml of absolute ethanol in 250 ml or round bottom flask and pass dry hydrogen chloride through the alcohol until it is saturated. Introduce 12gms of 4-aminobenzoic acid and heat the mixture under reflux for 2 hours. Pour this hot solution in 300 ml of water and add solid sodium carbonate until it is neutral. Filter off the precipitated ester and dry it. The separated solid was crystallized by aqueous ethanol. M. P.: 91°C (Reported¹⁹ M. P.: 91°C) Yield 65%.

4-(2-Amino-4-phenyl-thiazol-5-yl-azo)benzoic acid ethyl ester (III): An ice-cold solution of 0.02 mole of sodium nitrite in 25 mL water was added slowly to solution of 0.02 mole of ethyl-4-aminobenzoate in 15 mL of HCl at 0-5^°C. To well cool solution of 0.02 mole of 2-amino-4-phenylthiazole and 15 gms of sodium acetate in ethanol was gradually added the diazonium salt solution with stirring and cooling (0-5^°C). The reaction mixture was stirred at this temperature for 2 hours and then diluted with cold water. The separated solid was collected by filtration. The solid obtained was washed successively with water (2 X 150 mL). The separated solid was crystallized by aqueous ethanol (1:1). M. P.: 265^°C. Yield: 70%. Elemental Analysis: Calculated for C₁₈H₁₆N₄O₂S: C, 61.36; H, 4.54; N, 15.90 %. Found: C, 61.15; H, 4.19; N, 15.71 %. FTIR spectrum (KBr) ν_max/cm^-1: 3200 (-NH₂), 2900, 2850, 1700 (-COO-), 1625 (-N=N-), 1600 aromatic (-C=C-), 1500, 1450, 1375, 1250, 1190, 1075, 1025 and 790 (st. of thiazole nucleus). ¹H NMR spectrum (DMSO-d₆): δ 1.30 (t, 3H, -CH₃), 4.25 (quart., 2H, -CH₂-), 7.40-7.75 (m, 3H, Ar-H at C-3’, C-4’ and C-5’ ), 7.90 (d, 2H, Ar-H at C-2’’ and C-6’’), 8.00 (d, 2H, Ar-H at C-2’ and C-6’), 8.20(d, 2H, Ar-H at C-3’’ and C-5’’), 8.90 (br, 2H, -NH₂).

Table 2: Physical and antimicrobial activity data of present thiazole derivatives (IV)

Sr. No.	Ar	Yield (%)	Solvent for crystallization	M. P (°C)	Anti Bacterial		Anti Fungal
Sr. No.	Ar	Yield (%)	Solvent for crystallization	M. P (°C)	E. Coli	S. Aureus	A. Niger	A.O
1	Phenyl	65	Ethanol	200	13.00	12.50	12.25	12.25
2	2-Chlorophenyl	55	Ethanol	234	13.25	13.00	12.50	12.25
3	4-Chlorophenyl	60	Ethanol	222	13.50	13.25	13.25	13.50
4	2,4-Dichlorophenyl	63	Ethanol	253	13.75	12.75	12.50	13.25
5	2-Methylphenyl	70	Ethanol	216	12.25	12.50	12.25	12.75
6	3-Methylphenyl	72	Ethanol	223	12.25	12.50	12.25	12.25
7	4-Methylphenyl	78	Ethanol	244	12.50	12.75	12.25	12.50
8	3-Nitrophenyl	65	Ethanol	258	13.25	13.50	13.75	12.25
9	4-Nitrophenyl	67	Ethanol	276	13.75	13.75	13.75	13.75
10	3,5-Dinitrophenyl	65	Ethanol	285	13.75	13.50	13.50	13.75
11	4-Bromophenyl	70	Ethanol	248	12.25	12. 50	12.25	12.75
12	Phenylmethyl	68	Ethanol	192	12.50	12.50	12.25	12.25
13	2-Naphthoxy methylene	63	Ethanol	290	13.25	13.50	13.50	13.00
14	4-Phenylphenyl	65	Ethanol	165	12.25	12.50	12.50	12.25
15	Cinnamic acid	45	Ethanol	165	12.50	12.25	12.50	12.50
16	Nicotin	55	Ethanol	195	13.00	13.25	13.25	13.00
17	Isonicotin	55	Ethanol	245	13.00	13.00	13.00	13.00
18	4-Methoxyphenyl	60	Ethanol	128	13.00	13.00	12.75	12.75
19	2-Iodophenyl	45	Ethanol	245	12.50	12.75	12.50	12.75
20	2-Chlorophenyl methylene	55	Ethanol	188	13.25	13.50	13.75	13.25
21	2,4-Dichlorophenoxy methylene	65	Acetic acid	>300	13.50	13.25	13.75	13.25
22	4-Chloro-3-nitro phenyl	70	Ethanol	>300	13.50	13.50	13.50	13.50
23	Furacin (As a Standard)				17.50	17.50	-	-
24	Grieseofulvin				-	-	-	15.00

The solvent for crystallization and the physical data of all the prepared thiazole derivatives are given in table 2.

All compounds were screened for antibacterial activity against E-coli and S-aureus by cup plate method^17-18. For anti bacterial activity, we had taken 20 gms of luria broth (Hi media M-575) and 25 gms of agar-agar in 1000 mL distilled water and heated till dissolved. Then, the mixture was sterilized by autoclaving at 15 lbs pressure and 121°C for 15 minutes. Here, agar-agar was used to solidify the solution. After that, six petri dishes having flat bottom was taken and filled with about 18 mL of above solution. Overlay the plate with 4 mL soft agar-agar containing 0.1 mL test culture. Bored four well on each plate with 8 mm diameter cork bore aseptically. Now we had dissolved the compound in DMF having 1000 ppm concentration and added 0.1 mL of testing solution into each well. This solution was allowed to diffuse at 4°C. After 20 minutes diffusion, the plate was incubated at 37°C for over night. After incubation, we observed the zone of inhibition and measured the diameter of the zone. For anti fungal activity, we had taken 20 gms Sabouraud dextrose instead of lubria broth and followed the same procedure as above. All the synthesized compounds showed good antimicrobial activity (Table 2).

Aromatic acid chlorides (IV): A mixture of 0.01 mole of substituted aromatic acid was added to 15 mL of thionyl chloride. It was refluxed on water bath till the evolution of hydrogen chloride gas ceased. Excess of thionyl chloride was distilled off under reduced pressure and the acid chloride left behind as a residue was used in next reaction without further purification.

4-(2-Substituted phenylamino-4-phenyl-thiazol-5-yl-azo)-benzoic acid ethyl ester (V): 0.01 mole of 4-(2-Amino-4-phenyl-thiazol-5-yl-azo)benzoic acid ethyl ester (III) was dissolved in 10 mL dry pyridine and a cold solution of an appropriate 0.01 mole substituted aromatic acid chloride (IV) in dry pyridine was added slowly to it with constant stirring in an ice bath. The mixture was allowed to stand over night at room temperature and then heated on water bath for half an hour. It was acidified with cold 1:1 aqueous hydrochloric acid. The solid obtained was filtered and washed successively with water (2 X 50 mL), saturated solution of sodium bicarbonate (2 X 50 mL) and water (2 X 30 mL). The crude material obtained was chromatographed on silica gel (100-200 mesh) using mixture of ethyl acetate and hexane (20:80) as eluent. Removal of solvent from the

eluate afforded a solid material, which was crystallized repeatedly from appropriate solvent. The purity of all these compounds was checked by thin layer chromatography (Merck kieselgel 60F254 pre-coated plates).

RESULTS AND DISCUSSION:

Reaction of acetophenone, thiourea and iodine gives 2-amino-4-phenylthiazole (I). Iodine was used for cyclisation purpose because it is easy to handle. In second step, diazonium salt of ethyl-4-aminobenzoate (II) was coupled with 2-amino-4-phenylthiazole using sodium acetate and ethanol as solvent. 4-Aminobenzoic acid is very well known feed for microbial growth. So, we had introduced the ester of 4-aminobenzoic acid in structure moiety to get better antimicrobial activity. Sodium acetate acts as buffer, which can control the pH of solution. Coupling occurs at neutral pH. So finally we get a product 4-(2-Amino-4-phenyl-thiazol-5-yl-azo)-benzoic acid ethyl ester. Different substituted aromatic acid chlorides (IV) were prepared by the reaction of the corresponding aromatic acid with excess of thionyl chloride by heating on a water-bath till the evolution of hydrogen chloride gas ceased. Finally, the target thiazole derivatives with amide linkage were obtained when 4-(2-Amino-4-phenyl-thiazol-5-yl-azo)-benzoic acid ethyl ester (III) was condensed with different substituted acid chlorides (IV) by employing Schotten-Bauman synthesis protocol.

The elemental analyses of all the compounds were found to be satisfactory. The synthesized compounds were characterized by FTIR and ¹H NMR spectroscopy. The FTIR spectrums showed absorption bands in the region of ν_max/ cm^-1 3375 to 3400 for (-NH-) stretching and 1625 for (-NH-) bending, 2900-2950 for –CH₃ stretching, 1700 for (-COO-), 1600 (aromatic C=C), 1590 due to (-N=N-), and rest of the peaks appeared near 1350, 1200, 980, 1000, 790. In the ¹H NMR spectrum, -CH₃ and –CH₂protons appears as triplet at δ 1.25-1.30 and quart. at δ 4.25, respectively. All aromatic protons appeared in the region of δ 7.47–8.30, while amide proton appeared as a singlet in the region of δ 13.41–13.50. The spectral data of all the compounds were found to be consistent with their molecular structure. The data of elemental analysis, FTIR and ¹H NMR of few representative members with general structural formula are given in Table 1.

CONCLUSION:

All the synthesized thiazole derivatives were screened for the microbial activity. In the present study all compounds showed moderated to good microbial activity. The chloro and nitro substituted derivatives showed better anti-bacterial activity compared to other derivatives.

ACKNOWLEDGEMENT:

The authors are thankful to the Dean, Faculty of Technology and Engineering, and Head, Applied Chemistry Department, for providing the research facilities.

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Received on 23.09.2009 Modified on 19.11.2009

Asian J. Research Chem. 3(1): Jan.-Mar. 2010; Page 121-125

5. Sharma RN et al. Synthesis of 4-benzyl-1,3-thiazole derivatives as potential anti-inflammatory agents: an analogue-based drug design approach. Journal of enzyme inhibition and medicinal chemistry. 2009; 24: 890-897.

15. Craciunescu DG et al. Synthesis, Cytostatic, and Antitumor Properties of New Rh(I) Thiazole Complexes. Biological Trace Element Research. 1985; 8: 251-261.

5. SharmaRN et al. Synthesis of 4-benzyl-1,3-thiazole derivatives as potential anti-inflammatory agents: an analogue-based drug design approach. Journal of enzyme inhibition and medicinal chemistry. 2009; 24: 890-897.