Abstract

In this study, a library of new N-(3-(5-(Substituted phenyl)-4,5-dihydro-1H-pyrazol-3-yl)-4-hydroxy phenyl) acetamide (4a-4j) were synthesized and evaluated for their in vivo analgesic activity. All the compounds were prepared in a multistep process involving the initial acetylation of acetaminophen with acetic anhydride to form o- acetyl- p- acetamido phenol (1a) which undergoes fries reaction in the presence of AlCl₃ to form 5- Acetamido -2- hydroxyacetophenone (2a). The reaction of corresponding acetophenones with substituted benzaldehydes gave Chalcones (α,β-unsaturated ketones) derivatives (3a-3j)  which on further reactions with hydrazine hydrate in presence of dioxane gave titled pyrazoline derivatives (4a-4j). The structures of the titled compounds were established on the basis of spectral (IR, ¹HNMR, Mass and Elemental) data. All the titled compounds showed significant (P<0.05) reduction in analgesic activity evidenced by increase in the reaction time by Eddy’s hot plate method. Some of these compounds exhibit promising activities against Diclofenac Sodium as standard drug. The research provides compounds with potent analgesic action and can be used for treatment arthritic and related problems.