Trichothecenes chemical types

Contamination occurs primarily in wheat, barley, rye, and maize. Type A trichothecenes include mainly T-2 toxin, HT-2, and diacetoxyscirpenol (DAS) mycotoxins of the group B include mainly 4-deoxynivalenol (DON), commonly known as vomitoxin, and nivalenol (NIV). Toxic effects include nausea, vomiting, visual disorder, vertigo, throat irritation, and feed refusal in farm animals. The most toxic is T-2, followed by DAS and NIV, with DON being the least toxic in acute toxicity studies but the most widespread in grains worldwide and therefore the most studied. Issues related to chemical and physical data, occurrence, toxicity, absorption, distribution, and metabolism of trichothecenes are reviewed in WHO (89) and IARC (34). Physicochemical data for some selected Fusarium toxins is given by Sydenham et al. (90). The molecular structures of the main trichothecenes are shown in Fig. 9. 

Epoxytrichothec-9-en-8-ones (Table 2) are often referred to as Type B trichothecenes [Group III on the chemical classification (2), based on ring A chemistry] the remaining simple trichothecenes, without a keto group at C-8, are Type A (Groups I and II of the chemical classification). 

The resistance of cereals is classified into different groups type I is resistance to primary infection, type II resistance to the spread of infection, type III is the resistance to infection of grains, type IV is tolerance against Fusarium head bhght (FHB) and trichothecenes, type V is the resistance to the accumulation of trichothecenes Class 1 is chemical modification (such as conjugation). Class 2 is inhibition of biosynthesis. 

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