Synthesis and precocious metamorphosis-inducing activity of 3-(1-alkenyl)pyridines

A series of 3-pyridine derivatives with an I-alkenyl group was synthesized and evaluated against 4th instar (penultimate) larvae of the silkworm, Bomb yx mori, for their activity to induce precocious metamorphosis. Of the comp ounds tested, 3-(2-methyl-1-phenyl-1-propenyl)pyridine (18) was the most ac tive, indicating that both a phenyl substituent at the 1 position and a sho rt alkyl chain at the 2 position in the ethenyl moiety were significant for activity. Precocious pupation induced by 18 was accompanied by the prolong ation of the larval period and the increase of body weights. Both 20-hydrox yecdysone and methoprene, a juvenile hormone agonist, could fully counterac t precocious metamorphosis induced by 18. When applied to newly molted 4th instar larvae, 18 suppressed the increase of hemolymph ecdysteroid titers l eading to larval ecdysis to 5th instar. These results indicated that 18 act ed as an anti-ecdysteroid agent and temporarily depressed the ecdysteroid t iter in the hemolymph to induce precocious metamorphosis.