Synthesis Characterization and Antimicrobial Evaluation of Some New Schiff Bases

 

Deshpande M.M., Seema I. Habib, Deshpande V. G. and Praffullkumar A Kulkarni*

P.G. Department of Chemistry and Organic Research Laboratory, Yeshwant Mahavidyalaya, Nanded -431602

*Corresponding Author E-mail: sk_seema2007@yahoo.com

 

Eight different substituted Schiff bases are prepared by the reaction of 2-amino-4,7-dimethyl benzothiazole with eight different substituted aldehydes. All the synthesized Schiff bases were analysed by spectral analysis such as IR, 1H NMR, Mass and by elemental analysis. The Schiff bases were screened for antibacterial activity against four bacterial strains such as E. coli, S. typhi, S. aureus, B. subtilis and fungicidal activity against A. niger, A. flavus, P. chrysogenum and F. moneliforme.

 

 

INTRODUCTION:

Schiff bases are the compounds which contains –C=N- group. These compounds are also known as imines or anils or azomethines but most commonly they are known as Schiff bases to honor Hugo Schiff ¹, who synthesized these compounds first.

 

A lot of work has been done on this class of compounds due to its multi applicability. They are well known intermediate for the preparation of Zetidinone^2, thiazolidinone³, formazone^4, arylacetamide⁵, metal complexes^6-8 and many other derivatives^9,10.

 

The Schiff bases are also known to be useful as complexing agent¹¹, perfumery¹², analytical reagent¹³, as corrosion inhibitor¹⁴, as a catalyst and polymerization process ¹⁵. Further many workers reported a wide range of biological activity^16-18 of Schiff bases. Besides, several Schiff bases have been reported to possess remarkable antitumor¹⁹, antibacterial²⁰, diuretic²¹, insecticidal²², anti-HIV²³, antiparasitic²⁴, anticancer²⁵, anticancer²⁶, antimicrobial²⁷, antifungal²⁸, and anti-inflammatory²⁹ activities. In view of these observations and in continuation work on the synthesis of bioactive heterocyclic compounds it was thought to synthesize some new series of Schiff base derivatives.

 

EXPERIMENTAL:

All the reagents were chemically pure and are of AR grade.. All the melting points were determined in an open capillary tube and are uncorrected. Completion of the reaction was monitored by thin layer chromatography (TLC) on pre-coated sheets of silica gel-G.

 

General procedure for the synthesis of Schiff base derivatives (L₁-L₈):

Equimolar quantities of 2-amino-4,7-dimethyl benzothiazole and respective hydroxyl ketone/ substituted aldehyde were dissolved in minimum quantity of alcohol in RBF. The reaction mixture was then refluxed on water bath for 3-4 hours. The progress of the reaction was checked by TLC. After completion of the reaction, the reaction mixture was poured on ice/cold water. Solid separated was filtered off, dried and recrystallised from ethyl alcohol to give the corresponding product.

Scheme-1

 

(L₁-L₈)

Sr. no.	Compound	Substituent
		R1	R2
1	L1	CH3
2	L2	CH3
3	L3	H
4	L4	H
5	L5	H
6	L6	H
7	L7	H
8	L8	H

 

 

Spectral data of the synthesized compounds:

(L₁) IR (KBr) v in cm^-1:- 3443, 3216, 1620, 1554,1460, 1256, 848, 743

¹H NMR δ ppm:- 7.45, 6.40 (Ar-H), 8.7 (Ar-O-H), 9.3 (Ar-O-H), 2.01(Ar-CH₃), 2.3 (Ar-CH₃).

Mass (M/z) % rel. intensity:- 314 (M+2)

(L₂) IR (KBr) v in cm^-1:- 3400, 3216, 1620, 1554, 1460, 1256, 848, 743

Mass (M/z) % rel. intensity:- 312 (M+2)

(L₃) IR (KBr) v in cm^-1:-3400, 1608, 1548, 1281, 827 852, 740.

¹H NMR δ ppm:- 7.34, 6.25 (Ar-H), 8.1 (Ar-O-H), 2.20(Ar-CH₃), 5.3 (=C-H).

Mass (M/z) % rel. intensity:- 282 (M+)

(L₄) IR (KBr) v in cm^-1:- 3333, 1627, 1550, 450, 838,740

 ¹H NMR δ ppm:- 7.64, 6.43 (Ar-H), 5.8 (N-H), 2.10(Ar-CH₃), 4.7 (=C-H).

Mass (M/z) % rel. intensity:- 255 (M+2)

(L₅) IR (KBr) v in cm^-1:- 3306 1600, 1556, 1267, 749, 605.

 ¹H NMR δ ppm:- 7.45, 6.40 (Ar-H), 8.7 (Ar-O-H), 2.3 (Ar-CH₃), 2.1 (Ar-CH₃),4.9 (=C-H).

(L₆) IR (KBr) v in cm^-1:- 3448, 1608, 1558, 1442, 1267, 871, 744, 690

 ¹H NMR δ ppm:- 7.35, 6.40 (Ar-H), 8.3 (Ar-O-H), 2.09 (Ar-CH₃), 2.1 (Ar-CH₃) ,5.2 (=C-H).

Mass (M/z) % rel. intensity:- 439 (M+)

(L₇) IR (KBr) v in cm^-1:- 3417, 1620, 1558, 1454, 1411, 1284, 868, 738, 690.

 ¹H NMR δ ppm:- 7.55, 6.25 (Ar-H), 8.6 (Ar-O-H), 2.15 (Ar-CH₃), 2.2 (Ar-CH₃) ,3.9 (Ar-O-CH₃), 4.9 (=C-H).

Mass (M/z) % rel. intensity:- 437 (M+)

(L₈) IR (KBr) v in cm^-1:- 3209, 1620, 1558, 1411, 972, 868, 783.

 ¹H NMR δ ppm:- 7.35, 6.40 (Ar-H), 2.09 (Ar-CH₃), 1.8 (Ar-CH₃) , 5.2 (=C-H).

¹³C-NMR δ ppm:- 17.3, 52.5, 124, 126, 128, 129 135, 149.9 163.8 ppm.

Mass (M/z) % rel. intensity:-  267 (M+).

 

Table-1: Physical and Analytical data of synthesized Schiff bases

 

Table-2- Antimicrobial activity of synthesized compounds (L₁-L₈)

Sr.no.	Compound	Bacterial Strain			Fungal Strain
		Ec	St	Sa	Bs	An	Pc	Fm	Af
1	L1	RG	-ve	-ve	16	RG	-ve	-ve	RG
2	L2	RG	-ve	-ve	18	RG	-ve	-ve	RG
3	L3	-ve	-ve	-ve	17	-ve	-ve	-ve	RG
4	L4	-ve	-ve	17	24	-ve	-ve	-ve	-ve
5	L5	-ve	-ve	-ve	12	RG	-ve	-ve	RG
6	L6	-ve	-ve	13	18	-ve	-ve	-ve	-ve
7	L7	-ve	-ve	-ve	14	-ve	-ve	-ve	-ve
8	L8	-ve	-ve	-ve	18	-ve	-ve	-ve	-ve
	Penicillin	13	18	36	18	NA	NA	NA	NA
	Grysofulvin	NA	NA	NA	NA	-ve	-ve	-ve	-ve

Ec-E.coli, St-S.typhi, Sa- S.aureus, Bs-B.subtilis; An-A.niger, Pc-P.chrysogenum, Fm-F.moneliformae, Ca-C.albicans:-ve: No growth of fungi,+ve; Growth of fungi, RG-Reduced growth, NA-Not Applicable, Zone of inhibition was measured in mm.

 

 

 

Antimicrobial activity

The antibacterial activity of the compounds was determined by agar diffusion method against various bacteria like E. coli, S. typhi, S. aureus, B. subtilis at various concentrations such as 20, 50 and 100 μg /ml. The zone of inhibition was measured in mm and DMSO was used as solvent. Sterile nutrient agar was seeded with test organism and layered in sterile petri plate. After solidification, agar cups were borered with cork borer 0.1 ml of the compound solution was added to the cup with the help of micropipettes, one cup in the plates was filled with solvent. Standard penicillin (10v/ml) was used as reference drug. The plates were kept at low temperature (4 °C) for 20 minute to allow diffusion of the compound. Then the plates were incubated at 37 °C for 24 hr. After proper incubation the plates were observed for zone of no growth (zone of inhibition of growth) around the cup. Similarly the same compounds were screened for the antifungal activity against different organisms like P. chrysogenum, A. niger, F. moniliformae, and A. flavus by using poison plate method. The compound was mixed with sterile potato dextrose agar medium so as to get final concentration 2%. It was then poured in sterile petri plate and allowed to solidify. Spots of test organisms were placed on the agar surface. A plate without compound was prepared for control. The plates were incubated at room temperature for 48 hr. After proper incubation plates were observed for growth of the test organisms. The growth indicates that the compound is not antifungal while inhibition of growth of test organism indicates antifungal activity. The antifungal activities of the compounds were compared with standard grysofulvin.

 

RESULT AND DISCUSSION:

In this present paper, a series of various substituted Schiff bases were synthesized by the condensation of 2-amino-4, 7-dimethyl benzothiazole with eight different substituted aldehydes (Scheme-1 and Table-1).

 

The products were confirmed by their spectral analysis. Appearance of IR bands at 3209-3417 (-OH) and 1554- 1620 cm^-1 (>C=N) supported the structure. ¹H NMR spectra, the multiplet around the δ 7.64-6.43 ppm assigned to the aromatic protons. The aromatic -OH proton appeared as singlet at δ12.20-13.50 ppm, while other aliphatic protons are appeared at excepted regions. The mass spectra of the compounds were showed corresponding molecular ion peak which was correlated with their molecular weight of that respected compounds. The results of antimicrobial data are given in Table-2. The data revealed that all the compounds were found to be active against almost all the tested fungi and bacteria.

 

CONCLUSION

In summary, we have synthesized some novel Schiff bases. All the synthesized compounds gave satisfactory spectral and analytical data. The screening of antimicrobial data revealed that the compounds L₄, L₆, L₇ and L₈ showed good antifungal activity.

 

ACKNOWLEDGEMENT:

The authors are thankful to Principal, Yeshwant Mahavidyalaya, Nanded for providing laboratory facilities and also to the Director, IICT, Hyderabad for providing the instrumentation facilities.

 

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Received on 15.01.2013         Modified on 24.01.2013

Accepted on 31.01.2013         © AJRC All right reserved