Stereoselective degradation of fungicide benalaxyl in soils and cucumber plants

The enantioselective degradation of benalaxyl has been investigated to elucidate its behavior in several agricultural soils and plants (cucumber). Racemic benalaxyl was fortified into five types of agricultural soils and sprayed leaves of cucumber plants, respectively. The degradation kinetics and the enantiomer fraction (EF) were determined by normal-phase high-performance liquid chromatography (HPLC) with diode array detection (DAD) on the chiral column filled cellulose-tri-(3,5-dimethylphenylcarbamate)-based chiral stationary phase (CDMPC-CSP). The process of the degradation of benalaxyl enantiomers followed pseudo-first-order kinetics in cucumber plant. However, the dissipation phases of benalaxyl enantiomers in soils were biphasic ("slow-fast-slow" process). It has been shown that the degradation of benalaxyl was stereoselective. The results indicated that the (+)-S-benalaxyl showed a faster degradation in plants, while the (-)-R-benalaxyl showed a faster degradation in Soils 3, 4, and 5. No stereoselective degradation was observed in other soils.     

Stereoselective degradation of benalaxyl in tomato, tobacco, sugar beet, capsicum, and soil

The stereoselective degradation of the racemic benalaxyl in vegetables such as tomato, tobacco, sugar beet, capsicum, and the soil has been investigated. The two enantiomers of benalaxyl in the matrix were extracted by organic solvent and determined by validated chiral high-performance liquid chromatography with a cellulose-tris-(3, 5-dimethylphenylcarbamate)-based chiral column. Rac-benalaxyl was fortified into the soil and foliar applied to vegetables. The assay method was linear over a range of concentrations (0.5-50 microg ml(-1)) and the mean recoveries in all the samples were more than 70% for the two enantiomers. The limit of detection for both enantiomers was 0.05 microg g(-1). The results in soil showed that R-(-)-enantiomer dissipated faster than S-(+)-enantiomer and the stereoselectivity might be caused by microorganisms. In tomato, tobacco, sugar, beet, and capsicum plants, there was significantly stereoselective metabolism. The preferential absorption and degradation of S-(+)-enantiomer resulted an enrichment of the R-(-)-enantiomer residue in all the vegetables.     

Stereoselective Behavior of the Fungicide Benalaxyl During Grape Growth and the Wine‐Making Process

Benalaxyl is widely applied as a fungicide during grape planting processing. In this experiment, the stereoselective behavior of benalaxyl was studied during the grape growth and wine‐making process. A simple method based on high‐performance liquid chromatography (HPLC) equipped with a chiral column and UV detector was established to separate and determine the enantiomers of benalaxyl. Stereoselective degradation of the two enantiomers of benalaxyl was found in grapes. The degradation of both enantiomers followed pseudofirst‐order kinetics, and the degradation rate of R‐(?)‐benalaxyl was faster than S‐(+)‐benalaxyl. The half‐life of R‐(?)‐benalaxyl was 27 h, while the half‐life of S‐(+)‐benalaxyl was 31 h. The enantiomer fraction value decreased from 0.50 to 0.34 and finally only S‐(+)‐benalaxyl could be detected. In the fermentation process, both enantiomers of benalaxyl were hardly degraded, and no configuration interconversion was observed. Meanwhile, both enantiomers of benalaxyl showed little influence on the growth of the yeast, consumption of carbon sources, or production of alcohol. The result of this study might provide more sufficient data for the evaluation of food safety and potential risk. Chirality 28:394–398, 2016. © 2016 Wiley Periodicals, Inc.     

Stereoselective determination of benalaxyl in plasma by chiral high-performance liquid chromatography with diode array detector and application to pharmacokinetic study in rabbits

A chiral high-performance liquid chromatography method with diode array detector was developed and validated for stereoselective determination of benalaxyl (BX) in rabbit plasma. Good separation was achieved at 20 degrees C using cellulose tris-(3,5-dimethylphenylcarbamate) as chiral stationary phase, a mixture of n-hexane and 2-propanol (97:3) as mobile phase at a flow rate of 1.0 ml/min. The assay method was linear over a range of concentrations (0.25-25 microg/ml) in plasma and the mean recovery was greater than 90% for both enantiomers. The limits of quantification and detection for both enantiomers in plasma were 0.25 and 0.1 microg/ml, respectively. Intra- and interday relative standard deviations (RSDs) did not exceed 10% for three-tested concentrations. The method was successfully applied to pharmacokinetic studies of BX enantiomers in rabbits. The result suggested that the pharmacokinetics of BX enantiomers was stereoselective in rabbits.     

Stereoselective metabolism of benalaxyl in liver microsomes from rat and rabbit

Benalaxyl (BX), methyl‐N‐phenylacetyl‐N‐2,6‐xylyl alaninate, is a potent acylanilide fungicide and consist of a pair of enantiomers. The stereoselective metabolism of BX was investigated in rat and rabbit microsomes in vitro. The degradation kinetics and the enantiomer fraction (EF) were determined using normal high‐performance liquid chromatography with diode array detection and a cellulose‐tris‐(3,5‐dimethylphenylcarbamate)‐based chiral stationary phase (CDMPC‐CSP). The t_1/2 of (?)‐R‐BX and (+)‐S‐BX in rat liver microsomes were 22.35 and 10.66 min of rac‐BX and 5.42 and 4.03 of BX enantiomers. However, the t_1/2 of (?)‐R‐BX and (+)‐S‐BX in rabbit liver microsomes were 11.75 and 15.26 min of rac‐BX and 5.66 and 9.63 of BX enantiomers. The consequence was consistent with the stereoselective toxicokinetics of BX in vitro. There was no chiral inversion from the (?)‐R‐BX to (+)‐S‐BX or inversion from (+)‐S‐BX to (?)‐R‐BX in both rabbit and rat microsomes. These results suggested metabolism of BX enantiomers was stereoselective in rat and rabbit liver microsomes. Chirality, 2011. © 2010 Wiley‐Liss, Inc.