INTRODUCTION:

Compounds with pyrazoline structures are known to possess antimicrobial^1,2,3, anti-inflammatory⁴, antidepressant^5,6, anti-tubercular⁷ activities. In the present study some new pyrazoline derivatives (1 to 6) have been synthesized by the reaction of chalcones of 2-acetyl thiophene and phenyl hydrazine hydrochloride. The structures of the various synthesized compounds are assigned on the basis of elemental analysis, IR and ¹H NMR spectral data. These compounds were also screened for their anti-inflammatory activity.

EXPERIMENTAL:

Melting points were determined on a capillary melting point apparatus and are uncorrected. ¹H NMR spectra was recorded in the indicated solvent on Bruker WM 400 MHz spectrometer with TMS as internal standard. Infrared spectra were recorded in KBr on Perkin-Elmer AC-1 spectrophotometer. Microanalyses were performed on Carlo Erba EA-1108 element analyzer and were within the ± 0.5% of the theoretical values. Column chromatography was performed on silica gel (Merck, 60-120 mesh).

General procedure for the preparation of 2-pyrazolines (1-6)

A chalcone of 2-acetyl thiophene (0.001 mol) dissolved in 20 mL of ethanol and phenyl hydrazine hydrochloride (500 mg) was added to it. To this mixture 0.3 mL of pyridine was added drop wise at room temperature. After that the mixture was refluxed for 5-6 hours and the solvent was evaporated completely.

The reaction mixture was poured into ice-cold water and the solid mass that separated out was filtered, dried and purified by column chromatography with ethyl acetate/ hexane and recrystalized from chloroform.

Scheme 1 : Synthesis of some new 2-pyrazoline derivatives

Table 1. Physical data of compounds (1-6)

Compound	M.F.	M.P (°C)	Yield (%)	Elemental analyses (%)
				C		H		N
				Cal.	Found	Cal.	Found	Cal.	Found
(1) (2) (3) (4) (5) (6)	C₂₀H₁₆ON₂S C₂₀H₁₆N₂S C₁₉H₁₃N₃SO₂ C₁₉H₁₃N₃SO₂ C₂₂H₂₀N₂SO₃ C₁₉H₁₃N₂SCl	211 172 205 231 237 239	68 68 71 72 71 74	72.28 75.94 65.70 65.70 67.34 67.65	72.12 75.81 65.58 65.42 66.81 67.64	4.81 5.06 3.74 3.74 5.10 3.8	4.72 5.04 3.04 3.73 5.04 3.74	8.43 8.86 12.10 12.10 6.12 8.30	8.06 8.74 12.04 11.74 5.74 8.28

Cal.= Calculated

Table 2. Spectral data of the compounds (1-6)

Compound

IR (KBr, cm^-¹)

¹H NMR (CDCl₃, ppm)

(1)

1642 (C=N), 1355 (C-N),

670 (C-S), 1160 (OCH₃).

3.13 (1H, dd, HA);, 3.77 (1H, dd, HB), 5.25 (1H, dd, HX),

3.85 (3H, S, -OCH₃), 6.70-7.62 (12H, Ar-H).

(2)

1648 (C=N), 1352 (C-N),

660 (C-S), 1160 (OCH₃).

2.35 (3H, S, Ar-CH₃), 3.15 (1H, dd, HA), 3.83 (1H, dd, HB)

5.28 (1H, dd, HX),6.80-7.50 (12H, Ar-H).

(3)

1648 (C=N), 1080 (C-N),

660 (C-S), 1510 (N=O).

3.15 (1H, dd, HA), 3.86 (1H, dd, HB),

5.35 (1H, dd, HX), 6.45-7.80 (12H, Ar-H).

(4)

1594 (C=N), 1104 (C-N),

693 (C-S), 1541 (N=O).

3.15 (1H, dd, HA), 3.85 (1H, dd, HB)

5.25 (1H, dd, HX), 6.50-7.60 (12H, Ar-H).

(5)

1640 (C=N), 1068 (C-N),

655 (C-S), 1180 (OCH₃).

3.5 (1H, dd, HA), 3.78 (1H, dd, HB),

5.20 (1H, dd, HX), 6.45-7.60 (10H, Ar-H).

(5)

1595 (C=N), 1097 (C-N),

689 (C-S), 822 (C-Cl).

3.18 (1H, dd, HA), 3.85 (1H, dd, HB),

5.30 (1H, dd, HX), 6.40-7.90 (12H, Ar-H).

Table 3. Anti-inflammatory activity of the compounds (1-6)

Compound

% increase in paw thickness of various time intervals

0.5 hr

01 hr

2 Hr

3 hr

4 hr

6 hr

Standard

Control

20.26 ± 0.64

18.84 ± 1.52

16.74 ±1.32

19.87 ± 2.29^*

20.06 ±1.48

15.65 ± 1.42

10.32 ± 2.47^*

23.95 ± 0.66

27.85 ± 3.42^*

23.90 ± 3.72**

31.48 ± 3.68^**

31.69 ± 2.86^*

21.95 ± 2.30^*

16.34 ± 3.62^**

58.02 ± 1.54

42.85 ± 3.84^**

34.61 ± 2.37

57.85 ± 2.42^*

46.85 ± 3.76^**

38.12 ± 2.61

27.62 ± 4.37^**

67.93 ± 1.65

58.67 ± 2.02

51.98 ± 4.31^***

63.12 ± 1.45

59.84 ± 1.75^*

43.15 ± 3.40^*

36.94 ± 1.72

97.09 ± 1.95

79.7 ± 1.73

62.13 ± 1.52

86.98 ± 3.14^*

61.94 ± 2.74^**

66.26 ± 3.96^**

44.52 ± 1.24

98.98 ± 1.98

93.63 ± 1.65

72.4 ±4.22^**

95.4 ± 1.97

92.75 ±1.85

75.85 ±1.53

51.85 ±2.76^**

Control : 1% sodium CMC gel, Standard : aceclofenac Standard and sample solution is 100 mg/kg body weight. Values are expressed as mean ± (n = 6)^* = 2.28, ** = 3.75, *** = 4.35). P* < 0.05, P** < 0.01, P*** < 0.001 compared to control student t-test.

Anti-inflammatory activity:

Six compounds (1-6) were screened for anti-inflammatory activity. Male albino rats weighing between 200-250 g were used for the experiment. Carrageenan induced paw oedema method described by Singh and Ghosh⁸ was followed for the acute anti-inflammatory model (Table-3).

RESULTS AND DISCUSSION:

The screening results revealed that the compounds (1-6) exhibited moderate to considerable activity when compared with reference standard aceclofenac. It was found that compound 1 and 3 showed maximum activity while moderate activity observed in the case of 2 and 4. It is interesting to note that compound 6 is having an electron with drawing group chlorine substituent at paraposition. It is evident from the results we report the halogen substituent pyrazoline compounds showed considerable activity.

ACKNOWLEDGEMENTS:

We are thankful to the Head, Sophisticated Instrumentation Facility, Indian Institute of Sciences, Bangalore for ¹H NMR spectra and to Sipra Laboratories, Hyderabad for IR spectra.

REFERENCES:

1. M.L. Edwards, D.M. Stemerick and P.S. Sunkara, J. Med. Chem., 33, 1948 (1998).

2. Y.Rajendra Prasad, P.Ravi Kumar, Ch. Asha Deepti and M.Venkata Ramana, Asian J. Chem., 19(6), 4799 (2007).

3. Ankhiwala, M.D. and Hathi, M.V., Indian J Het. Chem., 5(3), 229 (1996).

4. J.F.Ballesteros, M.J.Sanz, A.Ubeda, M.A.Miranda, S.Iborra, M.Paya and M.J.Alcaraz, J. Med. Chem., 38, 2794 (1995).

5. Bilgin, A.A., Palaska, E., Sunal, Rumeysa and Gumesel, B. Pharmazie., 49(1), 67(1994).

6. Biligin, A.A., Palaska E. and Sunal, R. Arzneimittel – Forschung., 43(10), 1041 (1993).

7. Kumar M, P.Manoj, Kumar, R.Ajay and Ravi, T.K. Indian J. Pharm. Sci., 67(6), 755 (2005).

8. H.Singh and M.N. Ghosh, J.Pharm, Pharmcol, 20 (1958), 316.

Received on 28.01.2010 Modified on 05.02.2010

Research J. Pharm. and Tech. 3(2): April- June 2010; Page 625-626