Abstract
As a candidate for bioherbicide, 4,8-dihydroxy-1-tetralone (4,8-DHT) was isolated from Caryospora callicarpa epicarp and its two enantiomers, S-(+)-isosclerone and R-(−)-regiolone, were separated by chiral high-performance liquid chromatography (HPLC) on a Chiralcel OD column with chiral stationary phase (CSP)-coated cellulose-tris(3,5-dimethylphenylcarbamate). Then, the phytotoxicity of 4,8-DHT and its enantiomers toward the seeds germination and seedling growth of the five tested plant species, including lettuce (Latuca sativa), radish (Raphanus sativus), cucumber (Cucumis sativus), onion (Allium cepa), and wheat (Triticum aestivum), were investigated and the results indicated a hormesis at low concentration of 4,8-DHT and its enantiomers, but a retardant effect at high concentration. Between the two enantiomers of 4,8-DHT, the S-(+)-isosclerone was more toxic to seeds germination and seedling growth of the five tested plant species than the R-(−)-regiolone, and also the phytotoxicity of S-(+)-isosclerone varied with different plants. For example, S-(+)-isosclerone was the most active to seedling growth of lettuce, indicating that S-(+)-isosclerone had specific effects on different organisms. Thus, all of the chirality and concentration of 4,8-DHT, as well as the affected plant species, need to be taken into consideration in the development and utilization of 4,8-DHT.
Highlights
Chirality of a pair of molecules with a non-superposable mirror image is almost caused by the presence of an asymmetric carbon atom
3,5-dimethylphenylcarbamate affords the most useful chiral stationary phase (CSP), which can separate a wide range of racemates [25], and in view of the structure of 4,8-DHT containing a C=O group, phenyl ring, and hydroxyl directly linking to the chiral center, the 3,5-dimethylphenylcarbamate was selected as the CSP
4,8-DHT and its enantiomers, we found that 4,8-DHT and its enantiomers could improve the quality of the five tested plants seedling at low concentration, while pure S-(+)-isosclerone was more effective than the others
Summary
Chirality of a pair of molecules with a non-superposable mirror image is almost caused by the presence of an asymmetric carbon atom. Chiral molecules are widely used as the mainstay of pesticides. As many as 25% of all pesticide active ingredients are chiral, existing as two mirror images called enantiomers [1]. Chiral pesticides are primarily used as a mixture of enantiomers or racemates [2]. The enantiomers of chiral pesticides have identical physical and chemical properties, they usually display different physiochemical and biochemical properties in metabolism, excretion, side effects, and toxicity, even acting as an antagonist [3,4,5]. One enantiomer of a chiral pesticide may have the desired effects on a target species, whereas the other enantiomer may not [2]. It was reported that the enantiomers of many chiral pesticides showed different activity. The toxicity to Daphnia revealed that the ( ́)-enantiomer of leptophos showed a lower toxicity than its (+)-form and racemic form [9]; (+)-fenamiphos proved be about 20 times more toxic to Daphnia than ( ́)-fenamiphos [10]; Molecules 2016, 21, 528; doi:10.3390/molecules21040528 www.mdpi.com/journal/molecules
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