Design, synthesis, and biological evaluation of linear 1-(4-, 3- or 2-methylsulfonylphenyl)-2-phenylacetylenes: A novel class of cyclooxygenase-2 inhibitors

A group of regioisomeric 1-(methylsulfonylphenyl)-2-phenylacetylenes possessing a COX-2 SO2Me pharmacophore at the para-, meta- or ortho-position of the C-1 phenyl ring, in conjunction with a C-2 phenyl or substituted-phenyl ring substituent (3-F, 3-OMe, 3-OH, 3-OAc, 4-Me), were designed for evaluation as selective cyclooxygenase-2 (COX-2) inhibitors. These target linear 1,2-diarylacetylenes were synthesized via a palladium-catalyzed Sonogashira cross-coupling reaction followed by oxidation of the respective 1-(methylthiophenyl)-2-phenylacetylene intermediate. In vitro COX-1/COX-2 isozyme inhibition structure–activity studies identified 1-(3-methylsulfonylphenyl)-2-(4-methylphenyl)acetylene (12d) as a potent COX-2 inhibitor (IC50 = 0.32 μM) with a high COX-2 selectivity index (SI > 320) comparable to the reference compound rofecoxib (COX-2 IC50 = 0.50 μM; COX-2 SI > 200). A molecular modeling study where (12d) was docked in the binding site of COX-2 showed that the MeSO2 COX-2 pharmacophore was positioned in the vicinity of the secondary COX-2 binding site near Val523. The 1-(4-methylsulfonylphenyl)-2-(3-acetoxyphenyl)acetylene (11f, COX-1 IC50 = 1.00 μM; COX-2 IC50 = 0.06 μM; COX-2 SI = 16.7) and 1-(3-methylsulfonylphenyl)-2-(3-acetoxyphenyl)acetylene (12f, COX-1 IC50 = 6.5 μM; COX-2 IC50 = 0.05 μM; COX-2 SI = 130) regioisomers exhibited comparable COX-2 inhibition, and moderately lower selective COX-2 selectivity, relative to the reference drug celecoxib (COX-1 IC50 = 33.1 μM; COX-2 IC50 = 0.07 μM; COX-2 SI = 472). The most potent anti-inflammatory agent 1-(3-methylsulfonylphenyl)-2-(4-methylphenyl)acetylene (12d) exhibited moderate oral anti-inflammatory activity (ED50 = 129 mg/kg) at 3 h postdrug administration relative to the reference drug celecoxib (ED50 = 10.8 mg/kg) in a carrageenan-induced rat paw edema assay. The structure–activity data acquired indicate that the acetylene moiety constitutes a suitable scaffold (template) to design novel acyclic 1,2-diarylacetylenes with selective COX-2, or dual COX-1/COX-2, inhibitory activities.

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