Synthesis of novel Schiff base analogues of 4-amino-1,5-dimethyl-2-phenylpyrazol-3-one and their evaluation for antioxidant and anti-inflammatory activity.

4-Aminoantipyrine (4-amino-1,5-dimethyl-2-phenylpyrazole-3-one) and its analogues have been found to be compounds of interest for their anti-inflammatory, analgesic, antiviral, antipyretic, antirheumatic and antimicrobial activities. In the present study, Schiff base analogues of 4-aminoantipyrine were synthesized by the condensation reaction with substituted benzaldehydes and then evaluated for their antioxidant and anti-inflammatory activities. From among the synthesized compounds (3a-m, 4 and 5), 3 k and 3f exhibited the highest antioxidant activity followed by 3g, 3l, 3c, 3i, 5, 3m and 3h. The IC(50) values for compounds 3 k and 3f were found to be 0.44 and 0.93 μM, respectively, comparable to that of ascorbic acid (IC(50) 0.41 μM), a standard antioxidant agent. From the comparisons between the hydroxylated and methoxylated compounds, the rank order of antioxidant activity for the products resulting from benzylidene phenyl ring substitution was 2,4,6-OH>3,4-OH>3-OMe-4-OH>3,5-OMe-4-OH>2,4-OH>3-Me-4-OMe>3,4-OMe>4-OMe>4-OH. The structure-activity relationship study revealed that the position and nature of the substituted group on the benzylidene phenyl ring of the Schiff base analogues of 4-aminoantipyrine play an important role in their antioxidant activity. The anti-inflammatory activity of 3f, which also exhibited excellent antioxidant activity, was evaluated in terms of its inhibition of NO production, an inflammatory modulator, in LPS pretreated RAW 264.7 cells using the Griess method. We also examined whether or not this compound had effect on iNOS and COX-2 mRNA expression in RAW 264.7 cells. It was observed that compound 3f significantly reduced NO production and inhibited LPS-stimulated iNOS and COX-2 mRNA levels in a dose-dependent manner. Overall, 3f showed promising antioxidant and anti-inflammatory activities and may be used as the lead compound in a future study.