Synthesis, Characterization and Study of In Vitro Antimicrobial Activity of Some Substituted N'-[Arylidene]-2-(5-Phenyl-1H- Tetrazol-1-yl) Acetohydrazide

Document Type: Research Paper

Authors

1 Department of Pharmaceutical Chemistry, MES College of Pharmacy, Sonai, Ahmednagar, Maharashtra, India

2 MP Patel College of Pharmacy, Kapadwanj, Gujrat, India

Abstract

      Reaction of 5-phenyl tetrazole with ethyl chloroacetate to form ethyl (5-phenyl-1H-tetrazol-1-yl) acetate (1). Compound 1 react with hydrazine hydrate in ethanol yield 2-(5-phenyl-1H-tetrazol-1-yl) acetohydrazide (2). The condensation of (2) with various aldehydes yield the corresponding substituted N'-[-arylidene]-2-(5-phenyl-1H-tetrazol-1-yl) acetohydrazide (3a- j). The compounds obtained were identified by spectral data and have been screened for antimicrobial activity. The most promising compounds having good antibacterial activity were 3b, 3c and 3i, and the best for antifungal activity were 3b, 3c and 3e.

Keywords


1. Introduction

 

     Tetrazole derivatives possess very interesting pharmacological and biological properties and are reported to exhibit variety of biological activities like antibacterial [1], antifungal [2, 3], analgesic [4], anti-inflammatory [5, 6], and antitubercular effects [7]. Similarly 1,5 substituted tetrazoles have long been known for their pharmacological activity as stimulants or depressants on the central nervous system and are reported to show oral antidiabetic, antithrombotic and antimicrobial properties. Compounds containing azomethine group (-CH=N-) are known as Schiff bases. Day by day, Schiff bases are more frequently applied for the betterment of human welfare. The importance of the Schiff base is due its versatile nature. Literature survey shows that many Schiff bases exhibit biological activities such as antibacterial and antifungal [8, 9], antitumor [10], anti-inflammatory [11, 12], and anticonvulsant effects [12]. Azole derivatives are well known for their antifungal and antibacterial effects. Various azole derivatives have also shown potent anticancer activity in vitro and in vivo in mice inoculated with human melanoma cells. Well known antifungal derivatives that are currently being clinically used are vorozole, letrozole, anastrazole, ketokonazole and liarozole.

 

       With the discovery of these application of tetrazoles as well as Schiff bases medicinal chemistry and in continuation of our interest in synthesis of tetrazole derivatives, different Schiff bases of 5-phenyl tetrazole in the same matrix have been synthesized to serve as new scaffold for the antimicrobial agents. The present work deals with the reaction of 2-(5-phenyl-1H-tetrazol-1-yl) acetohydrazide (2) with different aromatic aldehydes to form Schiff’s bases (3a-j). The reaction sequence for titled compounds is outlined in Scheme I. Finally, the structures of all the various synthesized compounds were assigned on the basis of IR and 1H NMR spectral data and these compounds were screened for their in vitro antimicrobial activity.

 

2. Material and methods

 

2.1. Materials

 

      All chemicals and solvents were purchased from Qualigens. All reactions are carried out at laboratory condition. Melting points were determined with open capillary and uncorrected. FT-IR spectra were recorded on a Shimadzu FT-IR model 8010 spectropho-tometer, 1H NMR spectra were recorded in DMSO on a Varian mercury FT-NMR model YH- 300 instrument using TMS as internal standard.

 


Table 1. Physicochemical characterization of  N'-[-arylidene]-2-(5-phenyl-1H-tetrazol-1-yl) acetohydrazide.

 

Sr. No

R

Molecular Formula

MW

M.P. (°C)

Yield (%)

1

H

C16H14N6

O

306

189° C

70%

2

2-Cl

C16H13ClN6O

340

220° C

34%

3

4-Cl

C16H13ClN6O

340

222° C

88%

4

4-Br

C16H13BrN6O

385

245° C

64%

5

4-CH3

C17H16N6O

320

256° C

69%

6

3-OCH3

C17H16N6

O2

336

258° C

78%

7

4-OCH3

C17H16N6

O2

336

260° C

74%

8

3-NO2

C16H13N7O3

351

198° C

64%

9

4-NO2

C16H13N7O3

351

199° C

83%

10

(CH3)2-N-

C18H92N7O

349

206° C

78%


2.2. General procedure for synthesis of ethyl (5-phenyl-1H-tetrazol-1-yl)acetate (1)

 

      An equimolar mixture of 5-phenyl tetrazole (0.03 mol, 5 g), ethyl chloroacetate (0.03 mol, 3.67 ml) and anhydrous potassium carbonate (0.03 mol, 3.76 g) in methanol (40 ml) was refluxed on a water bath for 4 h and cooled to the room temperature. The product obtained was filtered, dried and recrystalized from ethanol. The compound was separated as white amorphous powder.

 

2.3. General procedure for synthesis of 2-(5-phenyl-1H-tetrazol-1-yl) acetohydrazide (2)

      To a mixture of compound 1, (0.03 mol, 9 g) in methanol (40 ml), 99% hydrazine hydrate (0.03 mole, 1.95 ml) was added with continuous stirring to get clear solution. Reflux the reaction mixture on water bath for about 5 h. The solution was concentrated and allowed to cool overnight. The resulting solid obtained was filtered, washed with cold ethanol, dried and recrystalized from ethanol. The compound was separated as white powder.

 

2.4. General procedure for the synthesis of N'-[-arylidene]-2- (5-phenyl-1H-tetrazol-1-yl) acetohydrazide (3a- j)

 

      Equimolar quantity of the hydrazide compound (2, 0.009 mol) and various aromatic aldehydes ( 0.009 mol) in ethanol and dioxane (50 ml) were heated on a water bath for 8 h. The resulting Schiff’s bases (3a-j) were cooled and poured into crushed ice. The precipitate thus obtained was filtered washed with cold water and purified by recrystallized from ethanol (Compound 3a,MS:(m/z):306(M+).

 Table 2. Spectral characterization of N’-[-arylidene]-2-(5-phenyl-1H-tetrazol-1-yl) acetohydrazide.

Sl No.

R

IR (KBr) cm-1

1H NMR (DMSO D6,) δ ppm

 

3a

H

3430(-NH), 3054(Ar-CH),

9.27 (s, 1H, NH), , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

2376,2247(-NCH2),

10H, Ar), 5.56 (s, 2H, -CH2)

 

 

 

1650 (-CO),

 

 

 

 

1625(-N=CH-),

 

 

3b

2-Cl

3442(-NH), 3054(Ar-CH),

9.20 (s, 1H, NH), , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

2378,2242(-NCH2),

9H, Ar), 5.56 (s, 2H, -CH2).

 

 

 

1652 (-CO),

 

 

 

 

1623(-N=CH-),785(C-Cl)

 

 

3c

4-Cl

3445(-NH), 3054(Ar-CH),

9.20 (s, 1H, NH) , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

2378,2243(-NCH2),

9H, Ar), 5.56 (s, 2H, -CH2).

 

 

 

1652 (-CO),

 

 

 

 

1623(-N=CH-),785(C-Cl)

 

 

3d

4-Br

3435(-NH), 3054(Ar-CH),

9.27 (s, 1H, NH), , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

2380,2247(-NCH2),

9H, Ar), 5.56 (s, 2H, -CH2).

 

 

 

1656 (-CO),

 

 

 

 

1620(-N=CH-),697(C-Br).

 

 

3e

4-CH3

3428 (-NH), 3054(Ar-CH),

9.24 (s, 1H, NH), , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

2370,2240(-NCH2),

9H, Ar), 5.56 (s, 2H, -CH2),2.88(s,3H,CH3).

 

 

 

1655 (-CO),

 

 

3f

 

1625(-N=CH-).

 

 

3-OCH3

3450(-NH), 3054(Ar-CH),

9.25 (s, 1H, NH), , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

2372,2240(-NCH2),

9H, Ar), 5.50 (s, 2H, -CH2),4.02(s,3H,-OCH3)

 

 

 

1656 (-CO),

 

 

3g

4-OCH3

1627(-N=CH-),1165(-OCH3).

 

 

3442(-NH), 3054(Ar-CH),

9.23 (s, 1H, NH), , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

2371,2238(-NCH2),

9H, Ar), 5.50 (s, 2H, -CH2),4.02(s,3H,-OCH3

 

 

 

1656 (-CO),

 

 

 

 

1627(-N=CH-),

 

 

3h

 

1165(-OCH3).

 

 

3-NO2

3430(-NH), 3054(Ar-CH),

9.22 (s, 1H, NH), , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

2376,2249(-NCH2),

9H, Ar), 5.56 (s, 2H, -CH2).

 

 

 

1653 (-CO),

 

 

3i

4-NO2

1628(-N=CH-),1564 (-NO2).

 

 

3438(-NH), 3054(Ar-CH),

9.30 (s, 1H, NH), , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

2376,2248(-NCH2),

9H, Ar), 5.56 (s, 2H, -CH2).

 

 

 

1656 (-CO),

 

 

 

 

1628(-N=CH-),1564 (-NO2).

 

 

3j

(CH3)2-N

3425(-NH),3054(Ar-CH),

9.20 (s, 1H, NH), , 7.95 (s, 1H, N=CH).7.91- 6.80 (m,

 

 

 

3155(-N(CH3)2).

9H, Ar), 5.56 (s, 2H, -CH2),2.44 (s,6H,-N(CH3)2)

 

 

 

2380,2250(-NCH2),

 

 

 

 

1651 (-CO),1626(-N=CH-).

 

 


2.5. Antimicrobial activity

 

     All of the newly synthesized compounds (3a-j) were screened for antimicrobial activity against both gram positive S. aureus and gram negative E .coli bacteria and antifungal activity against C. albicans and A. niger according to cup plate method at concentrations of 50 and 100 mg/ml. Ciprofloxacin and griseofulvin were used as standard for comparison of antibacterial and antifungal activity. Solvent dimethyl sulphoxide (DMSO) was used as control.

 

3. Results and discussion

 

     In the course of our search for therapeuti-cally useful antimicrobial agent, we have prepared new series of Schiff bases of 5-phenyl tetrazole by reaction of 2-(5-phenyl-1H-tetrazol-1-yl) acetohydrazide with aromatic aldehyde in ethanol: dioxane.  5-Phenyl tetrazole reacted with ethyl chloroacetate to form ethyl (5-phenyl-1H-tetrazol-1-yl) acetate which on further reaction with hydrazine hydrate in ethanol yield 2-(5-phenyl-1H-tetrazol-1-yl) acetohydrazide. The series contain ten analogues. All of the compounds were prepared in good yields. The results of physicochemical properties are depicted in Table 1. The structure confirmation of synthesized compounds was done by IR, NMR spectroscopy and results of analysis were in good agreement with the structure of synthesized compounds. Results of spectral data are summarized in Table 2. From the results of antibacterial screening in Table 3, it is evident that most of the compounds are very weakly active and few are moderately active against Staphylococcus aureus and Escherichia coli but compounds 3b, 3c, 3e and 3i possess very good activity against Staphylococcus aureus and Escherichia coli at concentration of 100 mg/ml. Similarly from the results of antifungal screening, it is evident that the compounds 3b, 3c and 3e possess very good activity against fungi Candida albicans and Aspergillus niger, and compound 3d showed moderate activity all bacteria and fungi tested.

 

Scheme I. Synthesis of some substituted N'-[-arylidene]-2-(5-phenyl-1H-tetrazol-1-yl) acetohydrazide: Where R: H, , 2-Cl ,4-Cl, 4-Br, 4-CH3, 3-OCH3,4-OCH3,3-NO2, 4-NO2, 4-N (CH3)2, Reagents and conditions: i. methanol, K2CO3 reflux 2 h; ii. NH2NH2, methanol, reflux 5 h; iii. aryl Aldehydes, abs. EtOH:Dioxane, reflux 8h.

Table 3. Antibacterial and antifungal activity data of the syntesyzed Schiff bases.

 

 

 

 

 

Zone of inhibition in mm

 

 

 

Comp.

S. aureus

E. coli

C. albicans

A. niger

 

50 mg/ml

100mg/ml

50 mg/ml

100mg/ml

50 mg/ml

100mg/ml

50 mg/ml

100mg/ml

3a

13

15

10

12

12

15

10

12

3b

15

16

15

17

18

20

15

17

3c

15

16

14

15

18

20

13

15

3d

11

14

10

12

16

18

11

13

3e

12

17

08

10

19

22

20

22

3f

12

15

08

11

12

15

08

11

3g

13

15

10

11

13

15

10

12

3h

12

13

10

12

15

17

09

11

3i

13

17

09

13

12

14

11

12

3j

13

14

12

15

11

13

11

14

Ciprofloxacin

20

24

20

24

-

-

-

-

Griseofulvin

-

-

-

-

20

24

20

24

4. Conclusion

 

       We prepared a series of tetrazole Schiff bases and demonstrated that these compounds possessed good antibacterial and antifungal activities tested by cup plate method. The most promising compounds having good antibacterial and antifungal activity were 3b, 3c and 3i and 3b, 3c and 3e, respectively.

 

Acknowledgments

 

     We are highly thankful to Professor V.K. Deshmukh, Principal of M.E.S. College of Pharmacy, Sonai and Prashant Patil Gadakh, Secreatary, Mula Education Society for providing excellent research facilities.

 

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