Synthesis of 3-Substituted Pyrazolo[1, 5-a]pyridine Derivatives with Inhibitory Activity on Platelet Aggregation. I

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3-Nicotinoylpyrazolo[1, 5-a]pyridines were synthesized by the raation of 3-unsubstituted pyrazolo[1, 5-a]pyridines with nicotinoyl chloride hydrochloride. Tetrahydronicotinoyl derivatives were obtained by hydrogenation of the nicotinoyl derivatives. Furthermore, N-substituted derivatives were synthesized by the reaction of the tetrahydronicotinoyl derivatives with alkylating regents or isocyanates. These pyrazolo[1, 5-a]pyridines were tested for inhibitory activity on arachidonic acid induced platelet aggregation in vitro and ex vivo. Some of these compounds showed higher inhibitory activity than aspirin. Among them, 2-methyl-3-(1, 4, 5, 6-tetrahydronicotinoyl)pyrazolo[1, 5-a]pyridine was found to be the most active compound.