Enantioselective synthesis of the sex pheromone of the grey pineapple mealybug, Dysmicoccus neobrevipes (Hemiptera: Pseudococcidae), for determination of the absolute configuration

The grey pineapple mealybug, Dysmicoccus neobrevipes Beardsley, originally found on Hawaii and on Australasian islands, was recently discovered on a southwestern island (Ishigaki Island) of Japan. Because D . neobrevipes is known to attack many fruits and other crops, it is essential to establish a strategy to prevent the spread of this potential pest. Detection and monitoring by use of pheromone traps would provide important information about its distribution. The sex pheromone of D . neobrevipes has been isolated and identified as ( E )-2-isopropyl-5-methylhexa-3,5-dien-1-yl acetate, although its absolute configuration was unknown. In this study, we achieved enantioselective synthesis of this compound by use of porcine pancreas lipase (PPL)-catalyzed acylation. Acetyl transfer from vinyl acetate to prochiral 2-isopropyl-1,3-propanediol in the presence of PPL in an organic solvent predominantly produced the ( R ) enantiomer of the monohydroxy acetate (86 % ee). In contrast, PPL-catalyzed hydrolysis of 2-isopropyl-1,3-diacetoxypropane in phosphate buffer yielded the ( S ) enantiomer of the monohydroxy acetate (75 % ee). Each enantiomer of the monohydroxy acetate was oxidized to a formyl acetate then coupled with a Wittig reagent, to produce the ( R )-(−) and ( S )-(+) pheromones. Analysis by gas chromatography with a chiral column and by polarimetry revealed the natural pheromone to be the ( S )-(+) enantiomer. In a field trap experiment, the attractiveness of the pheromone produced by this route was equivalent to that of the pure (+) enantiomer (>99 % ee).