Five analogs of the insecticidal lignan of thePhrymawere synthesized by modifying its 3,4-methylenedioxyphenyl group with a phenyl, 4-methoxyphenyl, 3-methoxyphenyl, 3,4-dimethoxyphenyl, or 4-chlorophenyl group to evaluate the contribution of the methylenedioxy function to the activity. The assay results revealed that the 4-oxymethylene part of the 3,4-methylenedioxyphenyl group collaborated more for strengthening the insecticidal activity than the 3-oxymethylene part did. Unexpectedly, the 3,4-dimethoxyphenyl analog was totally inactive, even at a high dose level.