Enantioselective degradation of hexaconazole in rat hepatic microsomes in vitro

Hexaconazole [(RS)-2-(2,4-dichlorophenyl)-1-(1H-1,2,4-triazol-1-yl) hexan-2-ol] is a potent triazole fungicide and consists of a pair of enantiomers. Enantioselective degradation of hexaconazole was investigated in rat hepatic microsomes in vitro. Concentrations of (-)- and (+)-hexaconazole and enantiomer fraction were determined by high performance liquid chromatography with a cellulose-tris-(3,5-dimethylphenylcarbamate)-based chiral stationary phase. The t(1/2) of (-)-hexaconazole and (+)-hexaconazole were 23.70 and 13.95 min for rac- hexaconazole and 44.18 and 23.54 for enantiomers examined separately. Furthermore, hexaconazole is configurationally stable in rat hepatic microsomes, demonstrating no chiral inversion from the (-)-hexaconazole to (+)-hexaconazole or vice versa. Intrinsic metabolic clearance of (+)-hexaconazole is 1.12 times than that of (-)-hexaconazole. Interaction study revealed that there was competitive inhibition between (-)-hexaconazole and (+)-hexaconazole. In addition, there was a significant difference between the inhibitory concentration (IC(50)) of (-)- to (+)-hexaconazole and (+)- to (-)-hexaconazole [IC(50)(-)/(+)/IC(50)(+)/(-) = 1.88]. These results may have potential implications for better environmental and ecological risk assessment for hexaconazole.     

Stereoselective kinetic study of hexaconazole enantiomers in the rabbit

Hexaconazole [(RS)-2-(2,4-dichlorophenyl)-1-(1H-1,2,4-triazol-1-yl)hexan-2-ol] is a potent triazole fungicide. The (-) isomer accounts for most of the fungicidal activity. The stereo- and/or enantioselective kinetics of hexaconazole were investigated in rabbits by intravenous injection. The concentrations of (-)- and (+)-hexaconazole in plasma, liver, and kidney tissue were determined by HPLC with a cellulose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phase and by gas chromatography-mass spectrometry. After intravenous administration of racemic hexaconazole (rac-hexaconazole) at 30 mg/kg, plasma, liver, and kidney levels of the (+)-enantiomer decreased more rapidly than those of the (-)-enantiomer. The (-)-/(+)-enantiomer ratio of the area under the concentration-time curve (AUC(0-infinity)) was 1.35. The total plasma clearance value (CL) of (+)-enantiomer was more than 1.3-fold higher than that of the (-)-hexaconazole. The enantiomeric ratio (ER) increased with time in plasma, liver, and kidney. Other pharmacokinetic parameters of the enantiomers were also different. These results indicate substantial stereoselectivity in the kinetics of hexaconazole enantiomers in rabbits.     

Gender‐Related In Vitro Metabolism of Hexaconazole and Its Enantiomers in Rats

In the present study we investigated the enantioselective disappearance of hexaconazole in rat liver microsomes system prepared from both genders. High‐performance liquid chromatography (HPLC) was used for identification and quantification. The degradation of the (+)‐hexaconazole was faster than that of the (?)‐hexaconazole in racemic hexaconazole and single enantiomer incubation in both sexes. The degradation half‐life of the (+)‐hexaconazole or (?)‐hexaconazole was also gender‐related. The metabolism of (+)‐hexaconazole and (?)‐hexaconazole were faster in male rat hepatic microsomes than that in female, suggesting that at least one of the cytochrome P450s (CYP) in the male rat liver microsomes system responsible for hexaconazole metabolism was male‐specific or considerably more active. Kinetic assays showed that the intrinsic clearance in male rat liver microsomes was higher than that in female. All these results strongly suggest that sexual dimorphic metabolism of hexaconazole exists in rats. The inhibition experiments with CYP inhibitors showed that the inhibitory effect of inhibitors was enantioselective and affected by sex. The results suggest that the enantioselective metabolism of hexaconazole was determined by the amount of hepatic cytochrome P450 and the expression of individual isoforms of CYPs. Chirality 25:852–857, 2013. © 2013 Wiley Periodicals, Inc.     

Enantioselective toxic effects of hexaconazole enantiomers against Scenedesmus obliquus

Enantioselectivity in ecotoxicity of chiral pesticides in the aquatic environment has been a subject of growing interest. In this study, the toxicological impacts of hexaconazole enantiomers were investigated with freshwater algae Scenedesmus obliquus. After 96 h of exposure, the EC₅₀ values for rac‐hexaconazole, (+)‐hexaconazole, and (?)‐hexaconazole were 0.178, 0.355, and 0.065 mg l^?1, respectively. Therefore, the acute toxicities of hexaconazole enantiomers were enantioselective. In addition, the different toxic effects were evaluated when S. obliquus were exposed to 0.2, 0.5, and 1.0 mg l^?1 of rac‐hexaconazole, (+)‐hexaconazole, and (?)‐hexaconazole during 96 h, respectively. The chlorophyll a and chlorophyll b contents of S. obliquus treated by (?)‐hexaconazole were lower than those exposed to (+)‐hexaconazole, whereas the malondialdehyde contents of S. obliquus treated by (?)‐form were higher than those exposed to (+)‐form at higher concentrations. In general, catalase activities were significantly upregulated by exposure to (?)‐enantiomer than (+)‐enantiomer at all three concentrations. However, superoxide dismutase activities exposed to (?)‐hexaconazole were lower than that exposed to (+)‐hexaconazole at 0.2 mg l^?1 and 0.5 mg l^?1. On the basis of these data, the acute toxicity and toxic effects of hexaconazole against S. obliquus were enantioselective, and such enantiomeric differences must be taken into consideration in pesticide risk assessment. Chirality 24:610–614, 2012. © 2012 Wiley Periodicals, Inc.     

Enantiomer separation of fungicidal triazolyl alcohols by normal phase HPLC on polysaccharide‐based chiral stationary phases

Three fungicidal triazolyl alcohols (triadimenol, hexaconazole, and cis/trans‐1‐4‐chlorophenyl‐2‐1H‐1,2,4‐triazol‐1‐yl‐cycloheptanol) were completely separated into enantiomers by chiral HPLC using polysaccharide‐based chiral stationary phases. A better separation was achieved on cellulose and amylose carbamate phases compared with a cellulose ester phase. Peak shapes were almost symmetrical except for two cases, where tailing of the first eluted enantiomer and unusual symmetric peak broadening were observed. The effect of eluents on enantioseparation was also investigated. Chirality 11:195–200, 1999. © 1999 Wiley‐Liss, 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.     

Azomethine based nano-chemicals: Development,in vitro and in vivo fungicidal evaluation against Sclerotium rolfsii,Rhizoctonia bataticola and Rhizoctonia solani

Fungal diseases posing a severe threat to the production of pulses, a major protein source, necessitates the need of new highly efficient antifungal agents. The present study was aimed to develop azomethine based nano-fungicides for protecting the crop from fungal pathogens and subsequent yield losses. The protocol for the formation of nano-azomethines was generated and standardized. Technically pure azomethines were transformed into their nano-forms exploiting polyethylene glycol as the surface stabilizer. Characterization was performed by optical (imaging) probe (Zetasizer) and electron probe (TEM) characterization techniques. The mean particle sizes of all nano-fungicides were below 100 nm. In vitro fungicidal potential of nano-chemicals was increased by 2 times in comparison to that of conventional sized azomethines against pathogenic fungi, namely, Rhizoctonia solani, Rhizoctonia bataticola and Sclerotium rolfsii. The performance of nano-chemicals in pot experiment study was also superior to conventional ones as antifungal agent.