What is the synthesis of the nematicides Tioxazafen?
Synthesis of Tioxazafen
Tioxazafen, currently under development by Monsanto, is a compound which is claimed
to be useable in seed treatment for the control of nematodes in corn and soy. Tioxazafen belongs to a new class of nematicides, namely the 3,5-disubstituted-1,2,4-oxadiazoles.
The mode of action of the molecule remains unknown. The benzamide oxime is prepared in high
yields from the benzo nitrile (237). The product 238 is subsequently treated with the 2-
thiophenecarbonyl chloride (239) to produce tioxazafen (XXX) in high yields and purity.
Toxicity of Tioxazafen to Meloidogyne Incognita and Rotylenchulus Reniformis
Nematode toxicity and recovery experiments were conducted in water solutions of tioxazafen, while root infection assays were conducted on tomato. Nematode paralysis was observed after 24 hr of exposure at 27.0 µg/ml tioxazafen for both the nematode species. Based on an assay of nematode motility, 24-hr EC50 values of 57.69 µg/ml and 59.64 µg/ml tioxazafen were calculated for M. incognita and R. reniformis, respectively. Tioxazafen rates of 2.7 µg/ml and 27.0 µg/ml reduced the nematode hatch after 3 d of exposure for both the nematode species. There was no recovery in nematode motility after the 24-hr exposure of M. incognita and R. reniformis to their corresponding 48-hr EC50 values of 47.15 µg/ml and 47.25 µg/ml tioxazafen, respectively. Mortality of M. incognita continued to increase after 24 hr exposure, whereas R. reniformis mortality remain unchanged after nematodes were rinsed and removed for 48 hr from the tioxazafen solution. A 24-hr exposure to low concentrations of 0.38 to 47.15 µg/ml for M. incognita and 47.25 µg/ml for R. reniformis reduced the infectivity of each nematode species on tomato roots. The toxicity of tioxazafen was similar between nematode species; however, a greater rate of tioxazafen was needed to suppress R. reniformis infection of tomato than for M. incognita.
References:
[1] TRAVIS R FASKE Jesse K Katherine Brown. Toxicity of Tioxazafen to Meloidogyne Incognita and Rotylenchulus Reniformis.[J]. Journal of nematology, 2022: 20220007. DOI:10.2478/jofnem-2022-0007.
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