A series of 4-(methylsulfonyl)aniline derivatives were synthesized in order to obtain new compounds as a potential anti-inflammatory agents with expected selectivity against COX-2 enzyme. In vivo acute anti-inflammatory activity of the final compounds 11–14 was evaluated in rat using an egg-white induced edema model of inflammation in a dose equivalent to 3 mg/Kg of diclofenac sodium. All tested compounds produced significant reduction of paw edema with respect to the effect of propylene glycol 50% v/v (control group). Moreover, the activity of compounds 11 and 14 was significantly higher than that of diclofenac sodium (at 3 mg/Kg) in the 120–300 minute time interval, while compound 12 expressed a comparable effect to that of diclofenac sodium in the 60–240 minute time interval time, and compound 13 showed a comparable effect to that of diclofenac sodium at all experimental times. The result of this study indicates that the incorporation of the 4-(methylsulfonyl)aniline pharamacophore into naproxen, indomethacine, diclofenac and mefanamic acid maintained their anti-inflammatory activity and may increase selectivity towards the COX-2 enzyme which will be confirmed in the future by assessing COX-2: COX-1 inhibitory ratios using a whole blood assay.
