New pyridazine derivatives as selective COX-2 inhibitors and potential anti-inflammatory agents; design, synthesis and biological evaluation.

New pyridazinone and pyridazinthione derivatives were designed, synthesized and identified through performing 1H NMR, 13C NMR, IR and MS spectroscopic techniques. All the newly synthesized derivatives were evaluated for cyclooxygenase inhibitory activity and COX-2 selectivity using celecoxib and indomethacin, as reference drugs. All compounds showed highly potent COX-2 inhibitory activity with IC50 values in nano-molar range. Moreover, they demonstrated higher selectivity towards COX-2 inhibition compared to indomethacin. Compounds 3d, 3g and 6a exhibited significantly increased potency towards COX-2 enzyme compared to celecoxib with IC50 values of 67.23, 43.84 and 53.01 nM, respectively. They were 1.1-1.7 folds more potent than celecoxib (IC50 = 73.53 nM) and extremely much more potent than indomethacin (IC50 = 739.2 nM). Of particular interest, Compound 3g showed SI of 11.51 which was as high as that of celecoxib (SI 11.78). This compound was further challenged by in vivo anti-inflammatory activity assay and gastric ulcerogenic effect. It showed comparable anti-inflammatory activity to indomethacin as positive control. Moreover, the anti-inflammatory activity of compound 3g was found to be equipotent to celecoxib. Furthermore, the selective COX-2 inhibitor 3g exhibited a superior gastrointestinal safety profile compared to the reference drugs celecoxib and indomethacin with less number of ulcers and milder ulcer score. The molecular docking study of this compound with COX-2 protein revealed more favorable binding mode compared to celecoxib, explaining its remarkable COX-2 inhibitory potency.