Synthesis and anti-juvenile hormone activity of ethyl 4-(2-benzylalkyloxy)benzoates and their enantiomers

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A number of ethyl 4-(2-benzylalkyloxy)benzoates were prepared and their activity to induce precocious metamorphosis was evaluated in larvae of the silkworm, Bombyx mori, which was clearly recognized as a juvenile hormone (JH)-deficiency symptom. Ethyl 4-(2-benzylhexyloxy)benzoate (6) and its 2-benzylheptyloxy analog (7) were found to induce precocious metamorphosis at relatively low doses. Both enantiomers of 6 and 7 were prepared using a chiral auxiliary oxazolidinone. (S)-Enatiomers were more active than (R)-isomers at low doses of 0.1 and 1 μg, but at higher doses their activity was reversed. The activity of compound 6 could be fully counteracted by methoprene, a JH agonist, but not by the dietary administration of 20-hydroxyecdysone. The ester group was important in the ability to induce precocious metamorphosis. The (S)-enatiomer of 6 prolonged the duration of the instar and delayed the onset of cocoon spinning when applied to 5th instar larvae, suggesting that this compound might have JH-like activity as well as anti-JH activity.