[1-(4-nitrobenzyl)-2-butyl-4-chloro-1h-imidazol-5-yl]-4, 5-dihydro-1-phenyl-1h-pyrazole: Synthesis, Anti-inflammatory and Analgesic Activities

In the present investigation, series of Bis (heterocycle)s bearing pyrazoline in combination of the imidazole derivatives have been synthesized via 1,3-dipolar cycloaddition reactions of N-(nitrobenzyl)-imidazole nitrile imines with different dipolarophiles. All the newly synthesized compounds were characterized and screened for analgesic-anti-inflammatory activities and were compared with the standard drugs. The compounds exhibited excellent anti-inflammatory and analgesic activities. Out of the compounds studied 4b, 4d and 4g compounds shown statistically significant activity comparable to the standard drugs Ibuprofen and Aspirin at the same dose.


Introduction
By targeting the synthesis of nitrogen containing heterocylcles of biological interest, we synthesized new series of compounds.Heterocyclic compounds hold a special place in organic chemistry.Their role as lead candidates in drug design cannot be overstated and the appearance of heterocyclic motifs in natural products is astronomically frequent.Many heterocycles (e.g.thiazole, oxazole, isoxazoline, pyrazoline and imidazole etc.) have received enormous amount of attention from synthetic chemists from the standpoint of both their synthesis and their biological activity.Amongst five membered heterocycles, isoxazolines and pyrazoline are representing a class of compounds of great importance in biological chemistry.For instance, compounds including a pyrazole nucleus are known to possess analgesic, anti-inflammatory, antipyretic, antiarrhythmic, tranquillizing, muscle relaxant, psychoanaleptic, anticonvulsant, hypotensive, monoamine oxidase inhibitor, antidiabetic and antibacterial activities [1].In fact, Celecoxib, a pyrazole derivative and Valdecoxib, an isoxazole derivative are now widely used in the market as anti-inflammatory drugs [2].Isoxazoline possess broad spectrum of biological activities like antituberculosis, antifungal, anticancer, antiviral, insecticidal, antibiotic activities and act as precursors for different natural products [3].Imidazole derivatives are gaining synthetic interest in recent years due to their broad spectrum of biological activities like anti-inflammatory [4], analgesic [5], antibacterial [6], antifungal [7], antituberculosis [8], anticonvolusant [9] and potential anticytokine agents [10].Compounds possessing imidazole moiety acts as new potent and selective 20-HETE synthase inhibitors [11], 2-n-butyl-4-chloro-5-farmyl-imidazole is a key intermediate for the synthesis of Losartan a nonpeptide angiotensin antagonist, which is an orally active antihypertensive drug [12].
With this background, it is considered worthwhile to synthesize hitherto unknown series of Bis (heterocycle) bearing imidazole and pyrazoline ring systems by 1,3ipolar cycloaddition reaction of N-(nitrobenzyl)-midazole nitrile imines with different dipolarophiles and their antinflammatory and analgesic activities have been evaluated.

Pharmacological Results and Discussion
All the compounds were tested for anti-inflammatory activity in carrageenan-induced edema assay in rats at a dosage of 100 mg/kg po (Table 1).Three compounds Scheme 1. Synthesis of Bis (heterocycle)s bearing pyrazoline derivatives.

Table 1. Anti-inflammatory activities of 4(a-h).
Compound ±SD 1 Edema volume in ml (%) 2 Edema inhibition 4a 0.17 ± 0.07 (4b, 4d and 4g) have statistically significant activity.Amongst these compounds, the two halogenated derivatives, 4d and 4g have more than 60% activity.At all of the doses they were less active than Ibuprofen.All of these compounds were tested for analgesic activity at 100 mg/kg in acetic-acid induced assay in mice (Table 2).Six compounds had significant activity and the compound 4d exhibited the highest activity in the series.

Experimental Section
Melting points were determined on Thomas Hoover melting point apparatus and were uncorrected. 1H NMR spectra were recorded on a Bruker AM 300 MHz spectrometer using CDCl 3 as solvent and tetramethylsilane as internal standard. 13C NMR spectra were measured on Jeol 400 (100 MHz) instrument.The chemical shifts are expressed in  and following abbreviations were used.S = singlet, d = doublet, t = triplet and m = multiplet.Infrared (IR) spectra were recorded on Shimadzu 8300 IR spectrometer.Elemental analyses were obtained on a Vario-EL instrument.Thin layer chromatography was carried out with BDH silica gel G on glass slides.
After evaporation of the solvent the product was purified by the column chromatography using the chloroform/ acetone (8:2) as eluent, and yellow oil 4a was obtained (0.36 g, 64 %). 1

Pharmacology
Albino rats of either sex (150 -180 g) and albino mice of either sex (8 -25 g) were used.The compounds were administered po using a feeding tube as homogenized suspensions in 0.5% sodium carboxymethyl cellulose; 0.5% sodium carboxymethyl cellulose was administered as the vehicle control.

Carrageenan-Induced Edema
Groups of four rats were dosed at 100 mg/kg po with the test compounds, 1 h before 0.05 ml of a 1% suspension of Type IV Lambda (Sigma) carrageenan was injected into the subplantar region at the right hind paw; additional groups of four rats were similarly pretreated with 100 mg/kg ibuprofen (positive control) or 10 ml/kg 0.5% sodium carboxymethyl cellulose (vehicle controls) [22].Paw volumes were measured by water displacement in a plethysmograph immediately after carrageenan injection, and again 3 h later.Edema volumes for test-compoundtreated and positive-control rats were compared statistically with those for the vehicle-treated control rats; data are reported as percentage edema inhibition.

Analgesic Activity
This method is based on acetic-acid-induced writhings in mice [23].Groups of six mice each were dosed with the test compounds or with aspirin at a dose of 100 mg/kg po, 1 h before the ip injection of 0.6% acetic acid (10 ml/kg).Mice were observed for 1.5 min beginning 5 min after the acetic acid injection, and the total number of writhes recorded.The mean value of writhes for each group was calculated and compared statistically with that for the vehicle-treated control group (n = 6); data were reported as percent inhibition of the number of writhes.The test was repeated on additional groups of six mice, treated with compounds for which the reduction in writhes had been calculated to be >10%; these results are shown in Table 2.