Optically active 1'-acetoxychavicol acetate and its positional isomers: Synthesis and repellent effect against adzuki bean weevil

1'-Acetoxychavicol acetate (1a), identified from the rhizomes of a Zingiberaceae plant as an anti-ulcer and insecticidal material, and its positional (meta and ortho) isomers were synthesized from hydroxybenz aldehydes. These racemic mixtures were resolved by HPLC equipped with a chiral column (Chiralpak AS or AD), and the absolute configuration of the separated enantiomers was studied with the correspond ing 1'-hydroxy derivatives. Examination of the 1 H NMR data of their esters with (S)- and (R)-α methoxy-a-(trifluoromethyl)phenylacetic acids by a modified Mosher's method indicated that the dextro rotatory enantiomers with a shorter Rt possess the R configuration, while the levorotatory enantiomers with a longer Rt possess the same S configuration as natural 1a. Both enantiomers of each compound showed almost the same insecticidal activity against the adzuki bean weevil (ABW). On the other hand, the (S)-enantiomers exhibited a stronger repellent effect against ABW females than the (R)-enantiomers. while a similar effect by the two stereoisomers was observed against the males. The number of eggs laid on adzuki beans was efficiently decreased when the beans were treated with the (S)-enantiomers, especially with (S)-1a.