[Unexpected anti-inflammatory activity of rigid structures derived from antihypertensive 6-arylpyridazinones. III. Synthesis and activity of 7-fluoro- and 5-keto-5H-indeno(1,2-c)pyridozines].

5H-Indeno[1,2-c]pyridazine (Ia) and its 3-oxo- and 4,4a-dihydro-3-oxo derivatives, already known to have antiinflammatory activity, were subjected to 7-fluoro substitution or to oxidation of the 5-methylene to a carbonyl group. The pharmacological evaluation of the resulting compounds indicated that the antiinflammatory activity disappeared in the fluoro derivatives, while it was still present in the 5-keto derivatives (I e), (II c). Moreover, the analgesic-antipyretic component of (I e) proved to be strongly enhanced compared with that of (I a).