SYNTHESIS, ABSOLUTE-CONFIGURATION, AND ANALYSIS OF MALATHION, MALAOXON, AND ISOMALATHION ENANTIOMERS

Syntheses of the enantiomers of malathion, malaoxon, and isomalathion are reported herein. Malathion enantiomers were prepared from (R)- or (S)-malic acid in three steps. Enantiomers of malathion were converted to the corresponding enantiomers of malaoxon in 52% yield by oxidatio n with monoperoxyphthalic acid, magnesium salt. The four isomalathion stereoisomers were prepared via two independent pathways using strychn ine to resolve the asymmetric phosphorus moiety. The absolute configur ations of the four stereoisomers of isomalathion were determined by X- ray crystallographic analysis of an alkaloid salt precursor. A high-pe rformance liquid chromatography technique was developed to resolve the four stereoisomers of isomalathion, and to determine their stereoisom eric ratios.