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.     

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.     

Chiral Separation and Enantioselective Degradation of Vinclozolin in Soils

Vinclozolin is a chiral fungicide with potential environmental problems. The chiral separation of the enantiomers and enantioselective degradation in soil were investigated in this work. The enantiomers were separated by high‐performance liquid chromatography (HPLC) on Chiralpak IA, IB, and AZ‐H chiral columns under normal phase and the influence of the mobile phase composition on the separation was also studied. Complete resolutions were obtained on all three chiral columns under optimized conditions with the same elution order of (+)/(?). The residual analysis of the enantiomers in soil was conducted using accelerate solvent extraction followed by HPLC determination. The recoveries of the enantiomers ranged from 85.7–105.7% with relative standard deviation (SD) of 0.12–3.83%, and the limit of detection (LOD) of the method was 0.013 µg/g. The results showed that the degradations of vinclozolin enantiomers in the soils followed first‐order kinetics. Preferential degradation of the (?)‐enantiomer was observed only in one soil with the largest |ES| value of 0.047, and no obvious enantioselective degradation was observed in other soils. It was found that the persistence of vinclozolin in soil was related to pH values based on the half‐lives. The two enantiomers disappeared about 8 times faster in basic soils than that in neutral or acidic soils. Chirality 26:155–159, 2014. © 2014 Wiley Periodicals, Inc.     

Stereoselective Interaction Between Tetrahydropalmatine Enantiomers and CYP Enzymes in Human Liver Microsomes

Tetrahydropalmatine (THP), with one chiral center, is an alkaloid that possesses analgesic and many other pharmacological actives. The aim of the present study is to investigate stereoselective metabolism of THP enantiomers in human liver microsomes (HLM) and elucidate which cytochrome P450 (CYP) isoforms contribute to the stereoselective metabolism in HLM. Additionally, the inhibitions of THP enantiomers on activity of CYP enzymes are also investigated. The results demonstrated that (+)‐THP was preferentially metabolized by HLM. Ketoconazole (inhibitor of CYP3A4/5) inhibited metabolism of (?)‐THP or (+)‐THP at same degree, whereas the inhibition of fluvoxamine (inhibitor of CYP1A2) on metabolism of (+)‐THP was greater than that of (?)‐THP; moreover, the metabolic rate of (+)‐THP was 5.3‐fold of (?)‐THP in recombinant human CYP1A2. Meanwhile, THP enantiomers did not show obvious inhibitory effect on the activity of various CYP isoforms (CYP1A2, 2A6, 2C8, 2C9, 2C19, 2E1, and 3A4/5), whereas (?)‐THP, but not (+)‐THP, significantly inhibited the activity of CYP2D6 with the Ki value of 6.42 ± 0.38 μM. The results suggested that THP enantiomers were predominantly metabolized by CYP3A4/5 and CYP1A2 in HLM, and (+)‐THP was preferentially metabolized by CYP1A2, whereas CYP3A4/5 contributed equally to metabolism of (?)‐THP or (+)‐THP. Besides, the inhibition of CYP2D6 by (?)‐THP may cause drug–drug interaction, which should be considered. Chirality 25:43–47, 2013. © 2012 Wiley Periodicals, Inc.     

Chiral HPLC determination and stereoselective pharmacokinetics of tetrahydroberberine enantiomers in rats

Tetrahydroberberine (THB), a racemic mixture of (+)‐ and (?)‐enantiomer, is a biologically active ingredient isolated from a traditional Chinese herb Rhizoma corydalis (yanhusuo). A chiral high performance liquid chromatography method has been developed for the determination of THB enantiomers in rat plasma. The enantioseparation was carried out on a Chiral®‐AD column using methanol:ethanol (80:20, v/v) as the mobile phase at the flow rate 0.4 ml/min. The ultraviolet detection was set at 230 nm. The calibration curves were linear over the range of 0.01–2.5 μg/ml for (+)‐THB and 0.01‐5.0 μg/ml for (?)‐THB, respectively. The lower limit of quantification was 0.01 μg/ml for both (+)‐THB and (?)‐THB. The stereoselective pharmacokinetics of THB enantiomers in rats was studied after oral and intravenous administration at a dose of 50 and 10 mg/kg racemic THB (rac‐THB). The mean plasma levels of (?)‐THB were higher at almost all time points than those of (+)‐THB. (?)‐THB also exhibited greater C_max, and AUC_0–∞, smaller CL and V_d, than its antipode. The (?)/(+)‐enantiomer ratio of AUC_0–∞ after oral and intravenous administration were 2.17 and 1.43, respectively. These results indicated substantial stereoselectivity in the pharmacokinetics of THB enantiomers in rats. Chirality, 2012. © 2012 Wiley Periodicals, Inc.     

Enantioselective Degradation of Indoxacarb From Different Commercial Formulations Applied to Tea

The stereoselective degradation of indoxacarb enriched with (+)‐S‐indoxacarb (S/R:70/30) was investigated in three typical green teas. A convenient and precise chiral method was developed and validated for measuring indoxacarb enantiomers in green tea. The developed method was based on high‐performance liquid chromatography coupled with tandem mass spectrometry using a Chiralpak IC column. The stereoselective degradation of indoxacarb enantiomers showed that the (+)‐S‐enantiomer dissipated faster than the (?)‐R‐enantiomer in all three typical tea farms. However, no enantiomerization was observed after applying pure (+)‐S‐indoxacarb. Residues on tea plant of the active ingredient (+)‐S‐indoxacarb from suspension concentrate (SC) was more persistent than that from emulsifiable concentrate (EC). Chirality 27:262–267, 2015. © 2015 Wiley Periodicals, Inc.     

Stereoselective Degradation of alpha‐Cypermethrin and Its Enantiomers in Rat Liver Microsomes

Alpha‐cypermethrin (α‐CP), [(RS)‐a‐cyano‐3‐phenoxy benzyl (1RS)‐cis‐3‐(2, 2‐dichlorovinyl)‐2, 2‐dimethylcyclopropanecarboxylate], comprises a diastereoisomer pair of cypermethrin, which are (+)‐(1R‐cis‐αS)–CP (insecticidal) and (?)‐(1S‐cis‐αR)–CP (inactive). In this experiment, the stereoselective degradation of α‐CP was investigated in rat liver microsomes by high‐performance liquid chromatography (HPLC) with a cellulose‐tris‐ (3, 5‐dimethylphenylcarbamate)‐based chiral stationary phase. The results revealed that the degradation of (?)‐(1S‐cis‐αR)‐CP was much faster than (+)‐(1R‐cis‐αS)‐CP both in enantiomer monomers and rac‐α‐CP. As for the enzyme kinetic parameters, there were some variances between rac‐α‐CP and the enantiomer monomers. In rac‐α‐CP, the V_max and CL_int of (+)‐(1R‐cis‐αS)–CP (5105.22 ± 326.26 nM/min/mg protein and 189.64 mL/min/mg protein) were about one‐half of those of (?)‐(1S‐cis‐αR)–CP (9308.57 ± 772.24 nM/min/mg protein and 352.19 mL/min/mg protein), while the K_m of the two α‐CP enantiomers were similar. However, in the enantiomer monomers of α‐CP, the V_max and K_m of (+)‐(1R‐cis‐αS) ‐CP were 2‐fold and 5‐fold of (?)‐(1S‐cis‐αR)‐CP, respectively, which showed a significant difference with rac‐α‐CP. The CL_int of (+)‐(1R‐cis‐αS)–CP (140.97 mL/min/mg protein) was still about one‐half of (?)‐(1S‐cis‐αR)–CP (325.72 mL/min/mg protein) in enantiomer monomers. The interaction of enantiomers of α‐CP in rat liver microsomes was researched and the results showed that there were different interactions between the IC₅₀ of (?)‐ to (+)‐(1R‐cis‐αS)‐CP and (+)‐ to (?)‐(1S‐cis‐αR)‐CP(IC_50(?)/(+) / IC_50(+)/(?) = 0.61). Chirality 28:58–64, 2016. © 2015 Wiley Periodicals, Inc.     

Bidirectional Chiral Inversion of Trantinterol Enantiomers After Separate Doses to Rats

The chiral inversion and pharmacokinetics of two enantiomers of trantinterol, a new β₂ agonist, were studied in rats dosed (+)‐ or (?)‐trantinterol separately. Plasma concentrations of (+)‐ and (?)‐trantinterol were measured by chiral stationary phase liquid chromatography tandem mass spectroscopy (LC‐MS/MS). The apparent inversion ratio was calculated as the ratio of AUC_0‐t of (?)‐trantinterol or (+)‐trantinterol inverted from their antipodes to the sum of the AUC_0‐t of (?)‐ and (+)‐trantinterol. Following single intravenous administration, both given enantiomers declined in similar plasma concentrations, suggesting that the two enantiomers have approximately the same disposition kinetics by the route of intravenous administration. However, after single oral administration, plasma concentrations of uninverted (?)‐trantinterol at many timepoints were significantly higher than those of uninverted (+)‐trantinterol, suggesting that the two enantiomers undergo apparently different absorption or metabolism after oral administration. Significant bidirectional chiral inversion occurred after intravenous and oral administration of (+)‐ or (?)‐trantinterol. After dosing with optically pure enantiomer, the concentration of the administered enantiomer predominated in vivo. The AUC_0‐36 of (+)‐trantinterol after intravenous and oral dosing of (?)‐trantinterol were 16.6 ± 5.2 and 33.3 ± 16%, respectively of those of total [(+) + (?)] trantinterol. The AUC_0‐36 of (?)‐trantinterol after intravenous and oral dosing of (+)‐trantinterol were 19.6 ± 8.8 and 37.9 ± 4.5%, respectively, of those of total [(?) + (+)] trantinterol. After intravenous administration of (+)‐ and (?)‐trantinterol the chiral inversion ratios of the two enantiomers were not significantly different and similar results were found for oral administration. The extent of chiral inversion after intravenous administration was apparently lower, indicating that the bidirectional chiral inversion was not only systemic but also presystemic. Chirality 25:934–938, 2013.© 2013 Wiley Periodicals, Inc.     

Studies of Enantiomeric Degradation of the Triazole Fungicide Hexaconazole in Tomato,Cucumber, and Field Soil by Chiral Liquid Chromatography–Tandem Mass Spectrometry

Chiral pesticide enantiomers often show different bioactivity and toxicity; however, this property is usually ignored when evaluating their environmental and public health risks. Hexaconazole is a chiral fungicide used on a variety of crops for the control of many fungal diseases. This use provides opportunities for the pollution of food and soil. In this study, a sensitive and convenient chiral liquid chromatography coupled with tandem mass spectrometry (LC‐MS/MS) method was developed and validated for measuring hexaconazole enantiomers in tomato, cucumber, and soil. Separation was by a reversed‐phase Chiralcel OD‐RH column, under isocratic conditions using a mixture of acetonitrile‐2 mM ammonium acetate in water (60/40, v/v) as the mobile phase at a flow rate of 0.4 mL/min. Parameters including the matrix effect, linearity, precision, accuracy and stability were undertaken. Then the proposed method was successfully applied to investigate the possible enantioselective degradation of rac‐hexaconazole in plants (tomato and cucumber) and soil under field conditions. The degradation of the two enantiomers of hexaconazole proved to be enantioselective and dependent on the media: The (+)‐enantiomer showed a faster degradation in plants, while the (?)‐enantiomer dissipated faster than the (+)‐form in field soil, resulting in relative enrichment of the opposite enantiomer. The results of this work demonstrate that both the environmental media and environmental conditions influenced the direction and rate of enantioselective degradation of hexaconazole. Chirality 25:160–169, 2013. © 2013 Wiley Periodicals, Inc.     

Stereoselective degradation of fungicide triadimenol in cucumber plants

The stereoselective degradation of triadimenol in different cucumber plant tissues (root, stem, leaf, and fruit) has been investigated. Rac‐triadimenol was applied to cucumber plants by root irrigation mode under field conditions. The degradation kinetics and the enantiomer fraction were determined by normal‐phase high‐performance liquid chromatography with diode array detector and on‐line optical rotatory dispersion detector on Chiralpak® AS‐H column. It has been shown that the degradation of triadimenol in cucumber plants was stereoselective under field conditions. The results indicated that RS enantiomer was degraded faster than SR enantiomer, and SS enantiomer was degraded faster than RR enantiomer, which resulted in plants enriched with SR and RR enantiomers. Furthermore, it was found that leaf was the dominating location for triadimenol enantiomer accumulation and stereoselective degradation, comparing with the root, stem, and fruit tissue. Chirality 2010. © 2009 Wiley‐Liss, Inc.     

The Chiral Separation and Enantioselective Degradation of the Chiral Herbicide Napropamide

The chiral pesticide enantiomers often have different toxic effects and environmental behaviors, which suggests that the risk assessments should be on an enantiomeric level. In this work, the chiral separation of the napropamide enantiomers and the stereoselective degradation in tomato, cucumber, rape, cabbage, and soil were investigated. Napropamide enantiomers could be separated absolutely by high‐performance liquid chromatography (HPLC) using a Chiralpak IC column with a resolution factor of 11.75 under the optimized condition. Solid phase extraction (SPE) was used for cleanup of the enantiomers in the vegetable samples. The residue analysis method was validated. Good linearities (R² = 0.9997) and recoveries (71.43% ‐97.64%) were obtained. The limits of detection (LOD) were 0.05 mg/kg in soil and 0.20 mg/kg in vegetables. The results of degradation showed that napropamide dissipated rapidly in vegetables with half‐lives of only 1.13–2.21 days, but much more slowly in soil, with a half‐life of 11.95 d. Slight stereoselective degradation of the two enantiomers was only observed in cabbage, with enantiomeric fraction (EF) = 0.46, and there was no enantioselectivity in the other vegetables. The degradation of napropamide in the five matrixes was fast, and there was no enantioselectivity. Chirality 28:108–113, 2014. © 2014 Wiley Periodicals, Inc.     

Separation and toxicity of salithion enantiomers

Enantioseletive toxicities of chiral pesticides have become an environmental concern recently. In this study, we evaluated the enantiomeric separation of salithion on a suite of commercial chiral columns and assessed the toxicity of enantiomers toward butyrylcholinesterase and Daphnia magna. Satisfactory separations of salithion enantiomers could be achieved on all tested columns, that is, Chiralcel OD, Chiralcel OJ, and Chiralpak AD column. However, the Chiralpak AD column offered the best separation and was chosen to prepare micro‐scale of pure salithion enantiomers for subsequent bioassays. The first and second enantiomers eluted on the Chiralpak AD column were further confirmed to be (?)‐S‐salithion and (+)‐R‐salithion, respectively. The half inhibition concentrations to butyrylcholinesterase of racemate, (+)‐R‐salithion, and (?)‐S‐salithion were 33.09, 2.92, and 15.60 mg/l, respectively, showing (+)‐R‐enantiomer being about 5.0 times more potent than its (?)‐S‐form. However, the median lethal concentrations (96 h) of racemate, (+)‐R‐salithion, and (?)‐S‐salithion toward D. magna were 3.54, 1.10, and 0.36 μg/l, respectively, suggesting that (?)‐S‐salithion was about 3.0 times more toxic than (+)‐R‐form. Racemic salithion was less toxic than either of the enantiomers in both bioassays, suggesting that antagonistic interactions might occur between the enantiomers during the toxication action. This work reveals that the toxicity of salithion toward butyrylcholinesterase and D. magna is enantioselective, and this factor should be taken into consideration in the environmental risk assessment of salithion. Chirality 2009. © 2009 Wiley‐Liss, Inc.     

Impact of microorganisms,humidity, and temperature on the enantioselective degradation of imazethapyr in two soils

Imazethapyr (IM) is a chiral herbicide composed of an (−)‐R‐enantiomer and an (+)‐S‐enantiomer with differential herbicidal activity. In this study, the effects of microbial organisms, humidity, and temperature on the selective degradation of the (−)‐R‐ and (+)‐S‐enantiomers of IM were determined in silty loam (SL) and clay loam (CL) soil with different pH values. The (−)‐R‐enantiomer of IM was preferentially degraded in two soils under different microorganism, humidity, and temperature conditions. The average half‐lives of R‐IM ranged from 43 to 66.1 days and were significantly shorter (P <  0.05) than those of S‐IM, which ranged from 51.4 to 79.8 days. The enantiomer fraction (EF = (+)‐S‐enantiomer/((−)‐R‐enantiomer + (+)‐S‐enantiomer)) values were used to describe the enantioselectivity of degradation of IM were >0.5 (P <  0.05) in two unsterilized soils under different humidity and temperature conditions. The highest EF values were observed at unsterilized CL soil samples under 50% maximum water‐holding capacity (MWHC) and 25 °C environmental conditions. The EF values of the IM enantiomers were significantly higher (P <  0.05) in CL soils (higher pH = 5.81) and were 0.581 (unsterilized) and 0.575 (50% MWHC; 25 °C) compared with those recorded in SL soil (lower pH = 4.85). In addition, this study revealed that microbial organisms preferentially utilized the more herbicidal active IM enantiomer.     

Analysis of Oxcarbazepine and the 10‐Hydroxycarbazepine Enantiomers in Plasma by LC‐MS/MS: Application in a Pharmacokinetic Study

Oxcarbazepine is a second‐generation antiepileptic drug indicated as monotherapy or adjunctive therapy in the treatment of partial seizures or generalized tonic–clonic seizures in adults and children. It undergoes rapid presystemic reduction with formation of the active metabolite 10‐hydroxycarbazepine (MHD), which has a chiral center at position 10, with the enantiomers (S)‐(+)‐ and R‐(?)‐MHD showing similar antiepileptic effects. This study presents the development and validation of a method of sequential analysis of oxcarbazepine and MHD enantiomers in plasma using liquid chromatography with tandem mass spectrometry (LC‐MS/MS). Aliquots of 100 μL of plasma were extracted with a mixture of methyl tert‐butyl ether: dichloromethane (2:1). The separation of oxcarbazepine and the MHD enantiomers was obtained on a chiral phase Chiralcel OD‐H column, using a mixture of hexane:ethanol:isopropanol (80:15:5, v/v/v) as mobile phase at a flow rate of 1.3 mL/min with a split ratio of 1:5, and quantification was performed by LC‐MS/MS. The limit of quantification was 12.5 ng oxcarbazepine and 31.25 ng of each MHD enantiomer/mL of plasma. The method was applied in the study of kinetic disposition of oxcarbazepine and the MHD enantiomers in the steady state after oral administration of 300 mg/12 h oxcarbazepine in a healthy volunteer. The maximum plasma concentration of oxcarbazepine was 1.2 µg/mL at 0.75 h. The kinetic disposition of MHD is enantioselective, with a higher proportion of the S‐(+)‐MHD enantiomer compared to R‐(?)‐MHD and an AUC^0‐12 _{S‐(+)/R‐(?)} ratio of 5.44. Chirality 25:897–903, 2013. © 2013 Wiley Periodicals, Inc.     

Stereoselective uptake and degradation of (±)‐o,p‐DDD pesticide stereomers in water‐sediment system

The environmental stereoselective uptake and degradation of (±)‐o,p‐DDD pesticide stereomers in water‐sediment system are described. The results were analyzed by artificial neural network model. The optimized experimental parameters were concentration of o,p‐DDD streamers (7.0 μg L^?1), experimental time (60 min), pH (6), dose (5.0 g L^?1), and temperature (25°C). The maximum uptake and degradation were 87% and 85% and 33.0% and 30.5% for (?)‐ and (+)‐stereomers of o,p‐DDD in 15‐day time. Both uptake and degraded phenomenon showed first‐order rate reaction. Thermodynamic variables indicated exothermic nature of uptake and degradation processes. The uptake and degradation were slightly higher for (?)‐stereomer than (+)‐stereomer of o,p‐DDD. It was assumed that both uptake and degradation processes are accountable for the removal of the streomers of o,p‐DDD from earth's ecosystem, but the uptake is responsible for major contribution. The magnitudes of relative errors obtained by artificial neural network model were in the range of ±0.2 to 3.5, indicating good applicability of the experimental data. The results are very useful to control the environmental contamination due to the chiral o,p‐DDD pesticide as its two enantiomers have different ecological toxicities.     

Retention model for the resolved enantiomers of felodipine on chiral-AGP using micellar mobile phases

A retention model for the chiral separation of an uncharged solute, felodipine, on CHIRAL-AGP, using a micellar mobile phase is proposed. The model assumes the presence of two stereoselective sites and each enantiomer was found to interact with different sites. Addition of a chiral aliphatic alcohol, (+)-(S)-2-octanol, preferentially interacted with the binding site for (?)-(S)-felodipine. The monomeric form of the micellar agent (Tween® 20) competed with the enantiomers for the adsorption sites, and the formation of a 1:1 complex between the enantiomers and the micelles was assumed. The retention of the solutes was effectively controlled by adding small quantities (<1.63 × 10^?3 M) of the nonionic detergent Tween 20 to the mobile phase. Baseline separation was achieved by addition of 1.0 mM n-octylamine to the mobile phase; 8.14 × 10^?4 M Tween 20 in phosphate buffer pH 7.0. The separation factor (α = 1.74) was unaffected by the detergent concentration in the presence of 1.0 mM n-octylamine. © 1995 Wiley-Liss, Inc.     

Bevantolol hydrochloride (nc-1400): Absolute configuration and direct separation of the enantiomers

Synthesis of (?)-bevantolol hydrochloride from 3,4-dimethoxyphenethylamine and (S)-(+)-m-tolyl glycidyl ether derived from (R)-(?)-epichlorohydrin established the absolute configuration of the (+) and (?) enantiomer as R and S, respectively. The purity of the enantiomers was determines using a chiral cellulose column (CHIRALCEL OD®) which allowed direct separation of the enantiomers. A separation factor (α) of 4.20 and a resolution factor (Rs) of 9.21 were obtained. © 1995 Wiley-Liss, Inc.     

Stereoselective metabolism and toxicity of the herbicide fluroxypyr methylheptyl ester in rat hepatocytes

We investigated the stereoselective degradation kinetics and toxicity of fluroxypyr methylheptyl ester (FPMH) in rat hepatocytes using a chiral high‐performance liquid chromatographic method. The T_1/2 of (−)‐FPMH was about two times longer than that of (+)‐FPMH after the rat hepatocytes were incubated with 10, 20, and 50 μM of rac‐FPMH. There was no chiral conversion or transformation during their incubation with the hepatocytes. Toxicity differences were observed among the two enantiomers of FPMH and fluroxypyr (FP) in their EC₅₀ values in rat hepatocytes. Of all the tested compounds, FP was most toxic to the rat hepatocytes. The (−)‐FPMH enantiomer showed higher toxicity than the (+)‐FPMH, whereas the racemic mixture displayed intermediate toxicity. The data presented here are important for a more thorough understanding of this pesticide and should be useful for its full environmental assessment. Chirality, 2011. © 2011 Wiley‐Liss, Inc.     

HPLC‐Fluorescence Method for the Enantioselective Analysis of Propranolol in Rat Serum Using Immobilized Polysaccharide‐Based Chiral Stationary Phase

A stereoselective high‐performance liquid chromatographic (HPLC) method was developed and validated to determine S‐(?)‐ and R‐(+)‐propranolol in rat serum. Enantiomeric resolution was achieved on cellulose tris(3,5‐dimethylphenylcarbamate) immobilized onto spherical porous silica chiral stationary phase (CSP) known as Chiralpak IB. A simple analytical method was validated using a mobile phase consisted of n‐hexane‐ethanol‐triethylamine (95:5:0.4%, v/v/v) at a flow rate of 0.6 mL min^‐1 and fluorescence detection set at excitation/emission wavelengths 290/375 nm. The calibration curves were linear over the range of 10–400 ng mL^‐1 (R = 0.999) for each enantiomer with a detection limit of 3 ng mL^‐1. The proposed method was validated in compliance with ICH guidelines in terms of linearity, accuracy, precision, limits of detection and quantitation, and other aspects of analytical validation. Actual quantification could be made for propranolol isomers in serum obtained from rats that had been intraperitoneally (i.p.) administered a single dose of the drug. The proposed method established in this study is simple and sensitive enough to be adopted in the fields of clinical and forensic toxicology. Molecular modeling studies including energy minimization and docking studies were first performed to illustrate the mechanism by which the active enantiomer binds to the β‐adrenergic receptor and second to find a suitable interpretation of how both enantiomers are interacting with cellulose tris(3,5‐dimethylphenylcarbamate) CSP during the process of resolution. The latter interaction was demonstrated by calculating the binding affinities and interaction distances between propranolol enantiomers and chiral selector. Chirality 26:194–199, 2014. © 2014 Wiley Periodicals, Inc.     

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

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. Chirality, 2010. © 2009 Wiley‐Liss, Inc.