Enantioselective analysis of thiobencarb sulfoxide produced by metabolism of thiobencarb by hydroxypropyl‐γ‐cyclodextrin modified micellar electrokinetic chromatography

Cyclodextrin-modified micellar electrokinetic chromatography was applied to the enantioseparation of thiobencarb sulfoxide, which is produced by S-oxygenation of thiobencarb, a herbicide, using γ-cyclodextrin together with sodium dodecyl sulfate. Factors affecting chiral resolution and migration time of thiobencarb sulfoxide were studied. The optimum running conditions were found to be 20 mM phosphate-5 mM borate buffer (pH 8.5) containing 60 mM hydroxypropyl-γ-cyclodextrin and 100 mM sodium dodecyl sulfate with an effective voltage of +20 kV at 20°C using direct detection at 220 nm. Under these conditions, the resolution (Rs) of racemic thiobencarb sulfoxide was approximately 1.7. Thiobencarb was treated with a rat liver microsomal fraction containing cofactors (known as S9mix). The ratio between (+)- and (-)-thiobencarb sulfoxide was found to be 15:85. It was also found that the ratio between (+)-and (-)-thiobencarb sulfoxide produced in soil spiked with thiobencarb was 3:7. These results indicated marked enantioselectivities for these metabolisms. The activities of thiobencarb, (+)- and (-)-thiobencarb sulfoxides on 5α-dihydrotestosterone-and 17β-estradiol-induced transcriptions were also investigated. Whereas thiobencarb and (+)-thiobencarb sulfoxide did not show any activities, (-)-thiobencarb sulfoxide showed significant anti-estrogenic and anti-androgenic activities, suggesting that thiobencarb sulfoxide can act as both an enantioselective anti-estrogen and an enantioselective anti-androgen.