Oxycarboxin

Oxycarboxin is an organic chemical used in agriculture to protect crops from fungal diseases. It was first marketed by Uniroyal in 1969 using their brand name Plantvax. The compound is an anilide which combines a heterocyclic acid with aniline to give an inhibitor of succinate dehydrogenase (SDHI).

Synthesis
Oxyxarboxin was first made by the oxidation of carboxin, as disclosed in patents filed by Uniroyal.
 * Carboxin synthesis.svg

Ethyl 2-chloroacetoacetate is treated with 2-mercaptoethanol and base, followed by cyclisation and water removal under acidic conditions. The resultant ethyl ester of the 1,4-oxathiine heterocycle is then formed into an amide with aniline using standard conditions via the carboxylic acid and acid chloride. This gives carboxin in high overall yield. The synthesis is completed by treatment with 30% hydrogen peroxide in acetic acid.

Mechanism of action
Carboxin and oxycarboxin act by inhibition of succinate dehydrogenase (SDHI): they bind to the quinone reduction site of the enzyme complex, preventing ubiquinone from doing so. As a consequence, the tricarboxylic acid cycle and electron transport chain cannot function.

Uses
Oxycarboxin is used to control rust diseases (e.g. soybean rust) at an application rate of 200–400 g/ha.

History
Oxycarboxin has been commercially available since 1969, when it was introduced under the brand name Plantvax.