Novel tetrahydro-2H-isoindoles have been prepared and evaluated as inhibitors of the COX-2 isoenzyme. A 1,3-diaryl substitution on the central polycyclic ring system and absence of a sulfonyl moiety are the two structural features of this chemical series. A short and easy synthetic pathway produced several derivatives which were shown to be potent and selective COX-2 vs COX-1 inhibitors (IC(50) = 0. 6-100 nM for COX-2, 100->1000 nM for COX-1). Structural modifications established that a bicyclic ring appended to the pyrrole nucleus and 4,4'-difluoro substitution on the phenyl rings were optimal for high inhibitory potency. Activity was confirmed in the human whole blood assay and subsequently in the murine air-pouch model in which in vivo PGE2 inhibitory activity was evaluated with respect to gastric tolerance (ED(50) for inhibition of exudate PGE2 of 3 mg/kg and gastric PGE2 of 20 mg/kg). Gastric tolerance was further assessed after administration to mice of high doses (up to 400 mg/kg) of the inhibitors by measurement of gastric damage. This panel of studies allowed selection of a number of tetrahydro-2H-isoindoles which were compared in the adjuvant-induced arthritis model. Compounds 32 and 37 showed the most potent activity with ED(50) values for edema inhibition in the noninjected paw of 0. 35 and 0.15 mg/kg/day, respectively, after oral administration. In addition, this interesting antiinflammatory profile was accompanied by a protective effect against arthritis-induced osteopenia, the decrease being 50% with a dose of 0.25 mg/kg/day.