Fungicides Carboxin

The fungicide Carboxin has received some study, but with varied results. A 0.43 mM solution gave protection at 5-10 days in white bean, a 0.36% spray gave no protection to pinto or tempo bean, and a 0.01% spray increased injury to azalea. Soil applications of Carboxin were generally more beneficial, but results were still varied. A Carboxin soil amendment was phytotoxic to tobacco and pinto bean, although protection was noted in pinto bean. Pinto and tempo bean were protected from oxidant for 36-40 days after a soil amendment with Carboxin... 

Farrow et al. [159] determined the systemic fungicide carboxin (2,3-dihy-dro-6-methyl-5-phenylcarbamoyl-l,4-oxathiin), which is used in barley and wheat seed treatment of cereals. 

The fungicides carboxin (5,6-dihydro-2-methyl-l,4-oxathi-ine-3-carboxani-lide) (V) and oxycarboxin (5,6-dihydro-2-methyl-l,4-oxathi-ine-3-carboxani-lide-4,4-dioxide) (VI) were photolysed in artificial solar light (A. >290nm) in pure water and in the presence of soil-extracted humic and fulvic acids (Scheyern, Germany) (1 mg IT1) [69]. 

Figure 3.2 A simple outline of the citric acid cyclus and the sites of inhibition by the insecticide/rodenticide fluoroacetic acid, and the fungicide carboxin.

Bean, cultivar Pinto Ozone Carboxin (2.3 ppm in soil) Fungicide 95 407... 

Bean, cultivars Tempo and Pinto Oxidant Carboxin (10% granular as soil amendment, 8 g/5-m row) Fungicide 100 305... 

Carboximide, trichloromethylthio-biocidal activity mechanism, 1, 400-401 fungicide, 1, 399 Carboximides as fungicides, 1, 194 Carboxin... 

The best listing of fungicides that we know of is published annually by the Meister Publishing Company of Willoughby, Ohio in their Farm Chemicals Handbook. They list the following compounds or types of compounds as officially "registered" for use on plants in the United States allyl alcohol, ammonium isobutyrate, antibiotics, benzimidazole types, carbofuran, cadmiums, captan types, coppers, carboxin, dehydroacetic acid, Dexon (sodium [4-(dime thy lamino) phenyl diazo sulfonate), diphenyl,... 

Carboxin was much more readily photodegraded than oxycarboxin in pure water. The oxidation of the sulphur atom yielded the sulphoxide Va and the subsequent loss of the heterocyclic ring produced the oxanilic acid Vb (see Scheme 6). Humic substances enhanced the phototransformation of both fungicides. For carboxin, this enhancement is possibly related to the presence of the sulphur atom that might be oxidized by singlet oxygen or other photo-oxidants. 

Carboxin was the first seed disinfection agent with systemic activity used in cereals to control loose smut in barley. Today, newer fungicides have displaced carboxin. 

The fungicidal properties of carboxin and related carboxanilides is due to their inhibition of glucose and acetate oxidative metabolism and RNA and DNA synthesis, although the later may be caused by lack of cellular energy due to the inhibition of respiration. 

Thiophosgene would poison the fungus by combination with vital thiol-, amino- or hydroxy-containing enzymes. Systemic fungicides, e.g. compounds (73)-(75) (Figure 10), can penetrate the host plant and may therefore be able to eradicate an established fungal infection. Carboxin (73) owes its activity to the inhibition of respiration in the fungus, and is synthesised from a-chloroacetoacetanilide (80) and 2-thioethanol (81) (Scheme 16). 

Fungicides of carboxamide type became known in 1966 with the discovery of carboxin (which has an oxathiin skeleton), which began a new chapter in the chemotherapy of plant diseases. This group actually has a much longer history —... 

Lipid-water distribution coefficients play an important role in the action of fungicides. Similar phenomena have also been seen in the case of carboxamides (Mathre, 1971a). The sulfoxide of carboxin, for example is an inactive compound, due to its low lipid solubility. However, a closer relationship between the fungicidal action and the distribution coefficient of carboxamides has not yet been established. 

The most widely used fungicide of the carboxamide group, carboxin (9), contains an oxathiin ring. Its composition is 5,6-dihydro-2-methyl-l,4-oxathiin-3-carboxanilide (Von Schmeling and Kulka, 1966). Its synthesis starts with acetoacetanilide (7), which with sulfuryl chloride gives 2-chloro-3-oxobutyranilide... 

Dihydro-2-methyl-l,4-oxathiin-3-carboxanilide (92), known as Carboxin (a fungicide), rearranges to the enamine (93) when refluxed in toluene with / -toluenesulfonic acid. The structural assignment of (93) are made on the basis of crystal x-ray diffraction analysis <84MI 609-02>. 

Carboxamides are a group of fungicides that control diseases caused by Basidiomycete type fungi (42). The best known member of this group is carboxin (Figure 6). Carboxamides specifically block membrane bound succinate-ubiquinone oxldoreductase activity in the mitochondrial electron transport chain (42, ). The carboxin receptor in the succinic dehydrogenase complex (SDC) is believed to be the iron-sulfur cluster Sj complexed with small coenzyme Q binding polypeptide(s) in a phospholipid environment (45.46 >. 

The first generation compound, carboxin, was developed about 40 years ago and has been used as an important seed treatment fungicide. Mepronil and flutolanil, developed in the eighties, are also used to control some diseases caused by basidiomycetes such as rhizoctonia. Then furametpyr and thifluzamide were developed in the late nineties, and they showed higher activity but their spectrum was not broadened. 

Carboxin is the one of the oldest members of the carboxanilide fungicide family and has been used as an important seed treatment fungicide for about 40 years. A new and more active fungicide, penthiopyrad, with the same mode of action as carboxin, has been discovered where its antifungal spectrum is much broader. 

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