Insecticidal effect of phthalides and furanocoumarins from Angelica acutiloba against Drosophila melanogaster

Insecticidal activity of Angelica acutiloba extract and its constituents was investigated and compared with that of rotenone. Bioassay-guided isolation of the chloroform extract of A. acutiloba against larvae of Drosophila melanogaster afforded two phthalides, (Z)-butylidenephthalide (1) and (Z)-ligustilide (2), and two furanocoumarins, xanthotoxin (3) and isopimpinellin (4). The structures of these compounds were established by spectroscopic analysis. The isolated compounds 1, 2, 3, and 4 exhibited LC50 values of 0.94, 2.54, 3.35, and 0.82 mumol/mL of diet concentration against larvae of D. melanogaster, respectively. Against both sexes (males/females, 1:1) of adults (5-7 days old), compound 1 showed the most potent activity with a LD50 value of 0.84 mug/adult. Compound 1 is a more active insecticide than rotenone (LD50 = 3.68 mug/adult) and has potential as a novel insect control agent. However, compound 2 was inactive against adults. The structure-activity relationship of phthalides isolated indicated that the aromaticity appeared to play an important role in the activity of both larvae and adults. To determine the insecticide mode of action for acute adulticidal activity, acetylcholinesterase (AChE) inhibitory activity was also investigated in vitro, and the result indicated that the acute adulticidal activity of compounds 3 and 4 was due to the inhibition of AChE.