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, Bombyx mori, for their activity to induce precocious metamorphosis. Of the compounds tested, 3-(2-methyl-1-phenyl-1-propenyl)pyridine (18) was the most active, indicating that both a phenyl substituent at the 1 position and a short alkyl chain at the 2 position in the ethenyl moiety were significant for activity. Precocious pupation induced by 18 was accompanied by the prolongation of the larval period and the increase of body weights. Both 20-hydroxyecdysone and methoprene, a juvenile hormone agonist, could fully counteract precocious metamorphosis induced by 18. When applied to newly molted 4th instar larvae, 18 suppressed the increase of hemolymph ecdysteroid titers leading to larval ecdysis to 5th instar. These results indicated that 18 acted as an anti-ecdysteroid agent and temporarily depressed the ecdysteroid titer in the hemolymph to induce precocious metamorphosis.