Synthesis and anti-juvenile hormone activity of alkyl 4-(2-phenoxyalkyloxy) benzoates and related compounds

A number of alkyl 4-(2-phenoxyhexyloxy)benzoates and related compounds were synthesized and evaluated their activity to induce precocious metamorphosis in larvae of the silkworm, which was clearly recognized as a juvenile hormone-deficiency symptom. In the alkyl 4-(2-phenoxyhexyloxy)benzoate series, only the methyl and ethyl esters showed precocious metamorphosis-inducing activity. Replacement of the ester group with an ethylcarbamoyl, butanoyl, nitro or a phenoxy group dramatically decreased or eliminated the activity. Both enantiomers of ethyl 4-(4-methyl-2-phenoxypentyloxy)benzoate (13) were prepared by starting with L- and D-leucine. There was no significant difference in precocious metamorphosis-inducing activity between 13R(+)- and 13S(-)-enantiomers. Conversion of the 4-ethoxycarbonyl group of 13 to the corresponding carboxylic acid eliminated the activity, indicating that the methyl or ethyl ester group is indispensable for the activity.