An Optical Resolution of Racemic Organophosphorous Esters by Phosphotriesterase-Catalyzing Hydrolysis

Commercially available organophosphorous insecticides, such as malathion, vamidothion, profenofos (1), acephate (2), and so forth, often contain chiral carbon, phosphorous, or sulfur atoms. These chiral insecticides are used as racemic mixtures because of the absence of effective resolution procedures. However, the insecticidal activity of the optically pure compound is different from the racemic compound. For example, ethyl 4-nitrophenyl phenylphosphonothioate (EPN), which contains a chiral phosphorous atom, is more toxic as the R-form (Rp-EPN) than as the S-form (Sp-EPN) or as the racemic mixture against mice, hens, and insects (3). Therefore, further systematic analysis of biological activity of chiral insecticides is essential in order to design and develop novel insecticides with specificity. In addition, enantiospecific degradation of organophosphorous insecticides by soil bacterial enzymes should also be studied in detail for further understanding in selectively remaining enantiomers and their toxicity.