Integration of metabolomics and in vitro metabolism assays for investigating the stereoselective transformation of triadimefon in rainbow trout

Abstract

Triadimefon is a systemic agricultural fungicide of the triazole class whose major metabolite, triadimenol, also a commercial fungicide, provides the majority of the actual fungicidal activity, i.e., inhibition of steroid demethylation. Both chemicals are chiral: triadimefon has one chiral center with two enantiomers while its enzymatic reduction to triadimenol produces a second chiral center and two diastereomers with two enantiomers each. All six stereoisomers of the two fungicides were separated from each other using a chiral BGB-172 column on a GC-MS system so as to follow stereospecificity in metabolism by rainbow trout hepatic microsomes. In these microsomes the S-(+) enantiomer of triadimefon was transformed to triadimenol 27% faster than the R-(-) enantiomer, forming the four triadimenol stereoisomers at rates different from each other. The most fungi-toxic stereoisomer (1S,2R) was produced at the slowest rate; it was detectable after 8 h, but below the level of method quantitation. The triadimenol stereoisomer ratio pattern produced by the trout microsomes was very different from that of the commercial triadimenol standard, in which the most rat-toxic pair of enantiomers (known as "Diastereomer A") is about 85% of the total stereoisomer composition. The trout microsomes produced only about 4% of "Diastereomer A". Complementary metabolomic studies with NMR showed that exposure of the separate triadimefon enantiomers and the racemate to rainbow trout for 48 h resulted in different metabolic profiles in the trout liver extracts, i.e., different endogenous metabolite patterns that indicated differences in effects of the two enantiomers.

Stereoselective metabolism, distribution, and bioaccumulation brof triadimefon and triadimenol in lizards

“…The EF measured for each of the four triadimenol stereoisomers are calculated according to Eq. (2) (Kenneke et al, 2010).…”

“…The stereoselective formation of TF and TN is an important issue in ecological risk assessment when considering the difference in fungicidal activity and toxicity among the enantiomers (Li et al, 2014). Stereoselective metabolism of TF to TN has been observed in soil microorganisms and rainbow trout (Garrison et al, 2011;Kenneke et al, 2010;Li et al, 2011). Unfortunately, the stereoselectivity of TF and TN in reptiles have never been studied.…”

Stereoselective separation and determination of triadimefon and triadimenol in wheat, straw, and soil by liquid chromatography–tandem mass spectrometry

“…Wu et al [9,10] developed a method for simultaneous separation of TF and TN by sulfated b-cyclodextrin-mediated CE, and applied this method to study biotransformation of TF to TN by soil microorganisms. Kenneke et al [5] reported on the integration of metabolomics and in vitro metabolism assays for investigating the stereoselective transformation of TF in rainbow trout by GC-MS. Dong et al [24] analyzed stereoselective degradation of TN in cucumber plants by HPLC. Compared with CE and HPLC, the extraction and purification procedures of this LC-MS/MS method were fast and the sensitivity was better.…”

“…TF was a systemic fungicide that acts by inhibiting steroid demethylation, and used to control powdery mildews and fungi on fruits, vegetables, wheat, and other agricultural crops. It has a single chiral center and correspondingly present two enantiomers, and can be enzymatically reduced to TN with four stereoisomers in plants, soil, and fungi [5]. The (1S, 2R)-isomer has the highest fungicidal activity (up to 1000-fold more active than the other three) in four stereoisomers of TN [3].…”

“…However, most of these methods used ultraviolet detector to separate and detect pesticide stereoisomers with high concentrations [5,[7][8][9][10][11][12][13][14]. There are relatively few publications focusing on trace analyses of chiral pesticides in environmental samples.…”