Stereoselective degradation of tebuconazole in rat liver microsomes.

The aim of this study was to assess the stereoselectivity of two tebuconazole [(RS)-1-p-chlorophenyl-4,4-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl)pentan-3-ol] enantiomers in in vitro system (rat liver microsomes). The analytes were extracted with acetic ether and concentrations were determined by high performance liquid chromatography (HPLC) with a cellulose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phase. The degradation of rac-tebuconazole (15 μM) followed first-order kinetics, and the degradation of the S-tebuconazole (t(1/2) = 22.31 min) was faster than that of the R-tebuconazole (t(1/2) = 48.76 min), but no significant difference between the enantiomers was found in the respective incubation (7.5 μM for each). Kinetic assays showed that the K(m) was different between the two enantiomers (K(mR) = 14.83 ± 2.19, K(mS) = 12.23 ± 2.72). The interaction results revealed that there was competitive inhibition between S- and R-form, and there was a significant difference between the IC(50) of R- to S-tebuconazole and S- to R-tebuconazole (IC(50R/S)/IC(50S/R) = 4.98).