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A series of novel 1,5-diphenylpyrazole derivatives bearing hydrophilic substituents was prepared. The anti-inflammatory and analgesic activities of these compounds were evaluated by using the adjuvant arthritis and Randall-Selitto assays in rats, and the structure-activity relationships were studied. The optimal compound was 3-(difluoromethyl)-1-(4-methoxyphenyl)-5-[4-(methylsulfinyl)phenyl]pyraz ole (10) with oral ED50 values of 0.31 and 2.6 mg/kg on adjuvant-induced arthritis and carrageenin-induced foot edema, respectively. Compound 10 showed analgesic activities not only toward inflamed paw but also toward normal paw (ED30 = 0.55 and 1.8 mg/kg, respectively) in the Randall-Selitto assay, and moreover, 10 was effective in the tail-pinch assay (ED50 = 21 mg/kg) similarly to morphine. The asymmetric synthesis and pharmacological properties of the enantiomers of 10 are also reported.

A series of novel 1,5-diarylpyrazole derivatives was synthesized and tested for anti-inflammatory and analgesic activities to develop anti-inflammatory agents with fewer side effects than existing nonsteroidal anti-inflammatory drugs. The structure-activity relationships in this series were extensively studied. Electron-withdrawing substituents such as CN and CF3 were optimal at the 3-position of the pyrazole ring. Replacement of these substituents with bulky ones gave less active compounds. The 4-(methylsulfonyl)phenyl group seemed to be the optimal group at the 5-position of the pyrazole ring. The most potent compound was 1-(4-fluorophenyl)-5-[4-(methylsulfonyl)phenyl]-pyrazole-3-carbonitrile (19a), with oral ED50 value of 0.030 and 0.47 mg/kg on adjuvant-induced arthritis and collagen-induced arthritis, respectively, and an ED30 value of 7.4 mg/kg in the yeast-induced hyperalgesia (Randall-Selitto) assay. Compound 19a also showed potent inducible cyclooxygenase (COX-2)-inhibitory activity (IC50 = 0.24 microM) with no COX-1 inhibition even at 100 microM.

The anti-inflammatory effects of auranofin were studied and compared with those of indomethacin, gold sodium thiomalate (GST) and D-penicillamine. Auranofin was active as indomethacin in inhibiting carrageenan induced paw edema in rats, but was less potent than indomethacin in inhibiting UV-induced erythema in guinea pigs. Auranofin inhibited Arthus type paw edema and reverse PCA reaction in rats, on which indomethacin was ineffective. The inhibitory activity of auranofin on adjuvant arthritis was weaker than that of indomethacin. In in vitro experiments, auranofin did not show any suppression of cyclooxygenase activity, but was capable of suppression of lysosomal enzyme release and chemotaxis of neutrophils and macrophages. In addition to these anti-inflammatory activities, auranofin had almost equal anti-analgesic and anti-pyretic activity to that of indomethacin. The above results indicated that the anti-inflammatory profiles of auranofin and indomethacin differ, so we can expect new therapeutic activities of auranofin. GST had similar anti-inflammatory and anti-analgesic profiles to those of auranofin; however, the activities were less potent than auranofin and devoid of anti-pyretic activity. D-penicillamine did not show any anti-inflammatory, anti-analgesic or anti-pyretic activity.