Synthesis, Characterization and Antimicrobial activity of Some Schiff Bases of 2-Amino-4-(4-Acetamido Phenyl)thiophene-3-carboxamide  

 

Monica Arora*, J. Saravanan, S. Mohan, Shivaji Bhattacharjee

Department of Pharmaceutical Chemistry, PES College of Pharmacy, Bangalore-50, Karnataka, India.

 

ABSTRACT:

2-Amino-4-(4-acetamido phenyl) Thiophene-3carboxamide was synthesized using versatile Gewald reaction .First step is preparation of cyanoacetamide which was carried out by condensation of ammonia (25%) and ethyl cyano acetate which was then reacted with p-acetanilido acetophenone, sulphur, diethyl amine to give 2-Amino-4-(4-acetamido phenyl) thiophene-3carboxamide.Later the compound was treated with twelve different substituted aryl aldehydes to yield twelve new Schiff bases(SM 1a-1l). The compounds were characterized IR, 1H NMR and mass spectral data and screened for antimicrobial activity.

 

 

 

INTRODUCTION:

Among the heterocyclic compound sulphur containing moieties have attracted maximum attention as they have several pharmacological activities as antimicrobial^1,2,3,4, CNS depressant activity⁵, analgesic⁶, antitumor⁷,ant-inflammatory⁸,antioxidant activity⁹ and so on. Similarly Schiff base derivatives also have been reported to possess biological activity as antimicrobial ^10,11. The therapeutic importance of these rings prompted us to synthesize novel benzo(b)thiophene and their Schiff base derivatives, characterize the compound by IR, NMR and Mass spectroscopic techniques and evaluate them for their antimicrobial activity.

 

MATERIAL AND METHODS

Chemicals:

Ammonia (25%), ethyl cyanoacetate, p-amino acetophenone, acetic anhydride, sulphur, diethyl amine, 4’-dimethyl amino benzaldehyde, 3’,4’5’-trimethoxy benzaldehyde, 3’,4’-dimethoxy benzaldehyde, 4’- methoxy benzaldehyde, 4’-hydroxy 3’-methoxy benzaldehyde, 4’-hydroxy 3’-methoxy benzaldehyde, 4’-hydroxy benzaldehyde, 2’-nitro benzaldehyde, 3’- nitro benzaldehyde, 4’-nitro benzaldehyde,  2’-chloro benzaldehyde, 2’- hydroxy benzaldehyde, 4’-chloro benzaldehyde were obtained from local dealer. All other chemical used were of laboratory grade.

 

Preparation of 3-(acetamidophenyl)-2-cyano but-2-enamide

Cyanoacetamide was prepared by cold condensation of ammonia and ethyl cyano acetate (1:1), ◦this is further reacted with p-acetanilido acetophenone which is prepared by acetylation of p-amino acetophenone which is done by acetic anhydride in presence of glacial acetic acid. Cyanoacetamide was refluxed with equimolar quantity of p-acetanilido acetophenone, ammonium acetate(1gm) and glacial acetic acid (2ml) in benzene (100 ml) for 12 hours in dean stark apparatus with continuous separation of water. After 12 hours the reaction mixture was cooled, diluted with 10 ml of benzene and washed with sodium carbonate solution (10%w/v in water ) and water successively and dried over anhydrous sodium sulphate. The solvent was removed under vacuum and the intermediate crude product obtained was immediately processed for the next step.

 

Preparation of 2-amino-4-(4-acetamidophenyl) thiophene-3-carboxamide.SM-1:

To a mixture of 3-(acetamido phenyl)-2-cyano butenamide in alcohol (40ml) and sulfur (1.28gm) at 50^oC , diethyl amine (7ml) was added drop wise with stirring. The reaction mixture was stirred for further 3 hours at same temperature. The reaction mixture was directly used for further derivatization.

 

Preparation of 2-[(substituted benzylidene)amino] 4-(4-acetamidophenyl) thiophene-3-carboxamide.SM-1a-l:

A mixture of equimolar amount (0.01) of 2-amino thiophenes, benzaldehyde derivatives (a-l) in ethanol (40ml) along with catalytic amount of glacial acetic acid was refluxed for 4 hours. The reaction mixture was concentrated cooled, the solid obtained was filtered and recrystallized from ethanol to give Schiff base (SM-1a-l). It was obtained 55-60% yield.

Antimicrobial studies

All the synthesized compounds were screened for their antibacterial and antifungal activity by agar diffusion method ¹² at a conc of 50µg/ml against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Klebsiella pneumonia, Aspergillus niger and Candida albicans. After 24 hours of drug addition, zone of inhibition was measured and recorded. Ampicillin, Norfloxacin and Mecanazole nitrate at 50µg/ml were used as standards in the experiment.

 

Scheme

Table -1 Physical data of 2-amino-4-(4-acetamidophenyl) thiophene-3-carboxamide SM-1

Comp Code	Molecular Formula	M.W(g)	Recrystalization Solvent	M.P(oC)	%Yield	TLC Solvent	Rf Value
SM-1	C13H29N3O2S5	339	2-propanol	170	40	Methanol: Chloroform(9:1)	0.66

 

Table-2 Physical data of 2-[(substituted benzylidene)amino] 4-(4-acetamidophenyl) thiophene-3-carboxamide SM-1a-l

Comp Code	X	Molecular Formula	M.W (g)	M.P (oC)	% Yield	T.L.C Solvent	Rf Value
SM-1a	4’- dimethyl    amino benzaldehyde	C22H22N4O2S	406.2	200	52	Methanol: Chloroform (9:1)	0.49
SM-1b	3’4’5’–trimethoxy benzaldehyde	C29H47N3O5S	453.3	209	72	Methanol: Chloroform (9:1)	0.72
SM-1c	3’4’–dimethoxy benzaldehyde	C22H21N3O4S	423.7	185	58	Methanol: Chloroform (9:1)	0.62
SM-1d	4’-methoxy benzaldehyde	C21H19N3O3S	393.2	192	67	Methanol: Chloroform (9:1)	0.57
SM-1e	4’ –hydroxy  3 methoxy benzaldehyde	C21H19N3O4S	409.7	185	51	Methanol: Chloroform (9:1)	0.70
SM-1f	4’-hydroxy benzaldehyde	C20H17N3O3S	379.1	225	55	Methanol: Chloroform (9:1)	0.49
SM-1g	2’-nitro benzaldehyde	C20H16N4O4S	408.2	208	50	Methanol: Chloroform (9:1)	0.50
SM-1h	3’-nitro benzaldehyde	C20H16N4O4S	408.2	212	57	Methanol: Chloroform (9:1)	0.47
SM-1i	4’ –nitro benzaldehyde	C20H16N4O4S	408.2	215	57	Methanol: Chloroform (9:1)	0.33
SM-1j	2’- chloro benzaldehyde	C20H16ClN3O2S	397.5	175	71	Methanol: Chloroform (9:1)	0.70
SM-1k	2’ – hydroxy benzaldehyde	C20H17N3O3S	379.1	190	55	Methanol: Chloroform (9:1)	0.65
SM-1l	4’ –chloro benzaldehyde	C20H16ClN3O2S	397.5	180	69	Methanol: Chloroform (9:1)	0.69

 

Table-3 Spectral data of 2-amino-4-(4-acetamidophenyl) thiophene-3-carboxamide SM-1

Comp Code	λmax. (nm)	IR	1 H NMR
SM-1	155	3397 cm-1 (NH);1697 cm-1 (C=O); 3144 cm-1 (Ar-CH); 1530 cm-1 (ArC=C); 770.72 cm-1 (C-S)	8.1(s,1H of CONH- )7.6(s,2H of NH2 of amide)7.3-7.5(m,2H of aromatic H)7.2-7.4(m,2H of aromatic )6.4(s,1H of  thiophene)5.5(s,2H of NH2)2.2(s,3Hof CH3)

 

Table-4 Spectral data of 2-[(substituted benzylidene) amino] 4-(4-acetamidophenyl) thiophene-3-carboxamide SM-1a-l

X	λ max (nm)	IR	1 H NMR	Mass
4’- dimethyl    amino benzaldehyde		3387.98cm-1 (NH); 3455.06 cm-1  (Ar-CH,Str)2924.88cm-1(Ali-CH)  1616.78cm-1 (C-N, imine, Str); 1466.83 cm-1 (C=C,Ar, Str); 1311.66 cm-1 (C=N); 1713.75 cm-1 (C=O). 750.50 cm-1  (C-S).
3’4’5’–trimethoxy benzaldehyde	290	3402.98cm-1 (NH); 3417.98 cm-1  (Ar-CH, Str)2923.10cm-1(Ali-CH)  1616.52 cm-1 (C-N, imine  Str); 1454.38 cm-1 (C=C,Ar  Str);  1126 cm-1.47(C-O-C Str); 1387.77 cm-1 (C=N); 1713.75 cm-1 (C=O).  713.75 cm-1 (C-S).	8.2(s,2H 1H of CONH- ,1H of N=CH)7.6-7.8((m,2H aromatic H) 7.5-7.6(m,4H aromatic H) 7.1(s,2H NH2 of amide) 6.9 (s,1H of thiophene) 3.9(s,9H of –OCH3) 2.1(s,3H of CH3)	453
3’4’–dimethoxy benzaldehyde	249	3476.12 cm-1  (NH); 3327.98 cm-1  (Ar-CH,Str) 2808.19cm-1(Ali-CH)  1670.12 cm-1 (C-N, imine Str); 1504.08 cm-1 (C=C,Ar  Str);  1092.76 cm-1 (C-O-C Str); 1267.59 cm-1 (C=N); 1612.32 cm-1  (C=O) ;776.42 cm-1 (C-S).	8.4(s,2H 1H of CONH- ,1H of N=CH)7.3-7.5((m,2H aromatic H) 7.5-7.6(m,4H aromatic H) 7.4(s,2H NH2 of amide) 6.7 (s,1H of thiophene) 3.5(s,6H of –OCH3) 2.0(s,3H of CH3)	423
4’-methoxy benzaldehyde	269	3072.33 cm-1  (NH); 3217.09 cm-1  (Ar-CH Str) 2808.19cm-1(Ali-CH)  1676.65 cm-1  (C-N, imine Str); 1498.08 cm-1  (C=C,Ar, Str);  1126.47 cm-1  (C-O-C Str); 1387.77 cm-1  (C=N); 1713.75 cm-1   (C=O). 713.75 cm-1   (C-S)
4’ –hydroxy  3 methoxy benzaldehyde	271	3301 cm-1  (OH); 3242.33 cm-1   (NH); 3111.00 cm-1   (Ar-CH,Str) 2908.10cm-1(Ali-CH)  1599.65 cm-1  (C-N, imine, Str); 1432.61 cm-1  (C=C,Ar, Str);  1016.74 cm-1  (C-O-C Str); 1299.01 cm-1  (C=N); 1671.50 cm-1  (C=O). 701.83 cm-1   (C-S)	8.6(s,2H 1H of CONH- ,1H of N=CH)7.5-7.7((m,2H aromatic H) 7.8-7.9(m,4H aromatic H) 7.4(s,2H NH2 of amide) 6.9 (s,1H of thiophene)6.2(s,1Hof OH) 3.8(s,3H of –OCH3) 2.3(s,3H of CH3)
4’-hydroxy benzaldehyde	247	3348.54 cm-1  (OH); 3276.31 cm-1  (NH); 3101.00 cm-1   (Ar-CH,Str); 2899.67cm-1(Ali-CH)  1599.65 cm-1  (C-N, imine, Str); 1432.61 cm-1  (C=C,Ar, Str);1299.01 cm-1  (C=N); 1671.50 cm-1   (C=O). 701.83 cm-1   (C-S)	8.4(s,2H 1H of CONH- ,1H of N=CH)7.5-7.7((m,2H aromatic H) 7.8-7.9(m,4H aromatic H) 7.4(s,2H NH2 of amide) 6.6 (s,1H of thiophene)6.2(s,1Hof OH)  2.3(s,3H of CH3)	433
2’-nitro benzaldehyde	253	3222.01 cm-1 (NH); 3001.04 cm-1   (Ar-CH,Str); 2911.07cm-1(Ali-CH)  1609.55 cm-1  (C-N, imine, Str); 1502.91 cm-1 1348 cm-1 (NO2);(C=C,Ar, Str);1309.66 cm-1  (C=N); 1654.43 cm-1   (C=O). 754.73 cm-1 (C-S)
3’-nitro benzaldehyde	219	3526.01 cm-1 (NH); 3001.00 cm-1   (Ar-CH,Str); 2998.06cm-1(Ali-CH)  1609.55 cm-1  (C-N, imine, Str); 1502.91 cm-1 1350 cm-1 (NO2);(C=C,Ar, Str);1377.66 cm-1  (C=N); 1603.99cm-1   (C=O). 699.03 cm-1 (C-S)
4’ nitro benzaldehyde	209	3526.01 cm-1 (NH); 3001.00 cm-1   (Ar-CH,Str); 2998.06cm-1(Ali-CH)  1609.55 cm-1  (C-N, imine, Str); 1502.91 cm-1 1350 cm-1 (NO2);(C=C,Ar, Str);1377.66 cm-1  (C=N); 1603.99cm-1   (C=O). 699.03 cm-1 (C-S)
2’ –chloro benzaldehyde	289	3322.01 cm-1 (NH); 3001.00 cm-1   (Ar-CH,Str); 2998.06cm-1(Ali-CH)  1609.55 cm-1  (C-N, imine, Str); 1502.91 cm-1 1350 cm-1 (NO2);(C=C,Ar, Str);1377.66 cm-1  (C=N); 1603.99cm-1   (C=O);702cm-1 (C-Cl)778.53 cm-1 (C-S)
2’ –hydroxy benzaldehyde	249	3408.54 cm-1  (OH);3246.01 cm-1 (NH); 3043.00 cm-1   (Ar-CH,Str); 2876.06cm-1(Ali-CH)  1622.21 cm-1  (C-N, imine, Str); 1521.91 cm-1 1321.00cm-1 (NO2);(C=C,Ar, Str);1321.21 cm-1  (C=N); 1609.06cm-1   (C=O). 776.03 cm-1 (C-S)
4’ –chloro benzaldehyde	220	3246.01 cm-1 (NH); 3043.00 cm-1   (Ar-CH,Str); 2876.06cm-1(Ali-CH)  1622.21 cm-1  (C-N, imine, Str);(C=C,Ar, Str);1321.21 cm-1  (C=N); 1609.06cm-1   (C=O);741cm-1 (C-Cl);776.03 cm-1 (C-S)	8.4(s,2H 1H of CONH- ,1H of N=CH)7.8-7.9((m,2H aromatic H) 7.7-7.6(m,4H aromatic H) 7.3(s,2H NH2 of amide) 7.0(s,1H of thiophene)  1.5(s,3H of CH3)

 

Table-5 Antimicrobial activity of 2-amino-4-(4-acetamidophenyl) thiophene-3-carboxamide SM-1

Comp Code	S.aureus	B.subtilus	E.coli	K.pneumonia	A.niger	C.albicans
SM-1	15	14	12	12	16	--
Ampicillin	22	17	24	18	--	--
Norfloxacin	23	28	26	28	--	--
Miconazole	--	--	--	--	30	27

 

Table -6 Antimicrobial activity of  2-[(substituted benzylidene)amino] 4-(4-acetamidophenyl) thiophene-3-carboxamide SM-1a-l

Comp Code	S.aureus	B.subtilus	E.coli	K.pneumonia	A.niger	C.albicans
4’- dimethyl    amino benzaldehyde	12	14	12	--	15	--
3’4’5’–trimethoxy benzaldehyde	20	17	--	14	13	--
3’4’–dimethoxy benzaldehyde	15	14	--	14	14	--
4’-methoxy benzaldehyde	14	14	15	17	17	08
4’ –hydroxy  3 methoxy benzaldehyde	20	16	19	15	18	09
4’-hydroxy benzaldehyde	21	18	16	18	17	10
2’-nitro benzaldehyde	13	12	11	10	12	--
3’ –nitro benzaldehyde	12	11	10	10	11	--
4’ –nitro benzaldehyde	14	12	13	--	14	--
2’ –chloro  benzaldehyde	21	18	18	19	18	09
2’ –hydroxy benzaldehyde	22	16	19	16	17	09
4’ –chloro benzaldehyde	23	19	20	17	19	11
Ampicillin	22	17	24	18	--	--
Norfloxacin	33	28	26	28	--	--
Miconazole	--	--	--	--	30	27

 

 

 

RESULTS:

From the antibacterial activity results it was observed that both electron donating and electron withdrawing groups on the aldehydic phenyl ring of the compounds influenced the activity. Among the drugs tested for antimicrobial activities Table 5, Table 6 showed that compounds SM-1e, SM-1f, SM-1j, SM-1k, SM-1l exhibited potent activity by showing zone of inhibition ranging from 14mm-22mm.All these drugs showed potent activity against Staphylococcus aureus  with high zone of inhibition. All other drug showed drugs showed moderate inhibititory properties against the test organism. Against Candida albicans none of the test drugs showed significant activity. Standard drugs, Ampicillin, Norfloxacin and Mecanazole nitrate exhibited potent inhibitory properties against all the test organism.

 

DISCUSSION:

From the IR, 1H, NMR and mass spectrum obtained, characterization of data has been done and given in table 1, 2, 3 and 4. The IR spectrum of 2-amino-4-(4-acetamidophenyl) thiophene-3-carboxamide (SM-1) shows NH₂ peak at3397 cm^-1.The NMR spectrum shows a broad peak at δ =5.5 of NH₂.

 

The IR spectra of all the Schiff bases shows the disappearance of NH₂ peak and the appearance of –N=CH (Imine) peak at the range of 1640-1690 cm^-1 which clearly suggest the formation of expected compounds. The NMR spectra of the compounds SM-1b,SM-1c, SM-1e,SM-1f and SM-1l shows sharp singlet peak at the range of δ =8.2-8.8 of –N=CH (Imine)  which also further confirms the formation of the compounds of the series. The compounds SM-1b.SM-1c and SM-1f were also confirmed by Mass spectrum.                                                                                         

 

ACKNOWLEDGEMENTS:  

The authors are thankful to Management, PES college of Pharmacy for providing necessary facilities.

 

REFRENCES: 

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Received on 30.10.2012        Modified on 07.11.2012

Accepted on 14.11.2012        © AJRC All right reserved