Mycotoxins chemical structures

The different biosynthetic pathways through which mycotoxins are produced result in a broad diversity of chemical structures and, consequently, in a variety of toxic effects in humans and animals. An excellent review of the toxic effect of mycotoxins (3) is based on a system approach, where the toxic effects are discussed on the basis of the body systems affected by the mycotoxins. Hepatotoxic, gastrointestinal, hematopoietic, and nephrotoxic effects are treated, as well as... 

The range of chemical structures and biologic activity among the broad class of fungal metabolites is large and cannot be summarized briefly. Mycotoxins do not constitute a separate chemical category, and they lack common molecular features. 

Because of their diversity of chemical structures and differing physical properties, mycotoxins exhibit a wide array of biological effects on mammalian systems and individual mycotoxins can be genotoxic, mutagenic, carcinogenic, embryotoxic, teratogenic or oestrogenic (Smith and Henderson, 1991). Some... 

Humpf, H. U. and Voss, K. A. (2004). Effects of thermal food processing on the chemical structure and toxicity of fumonisin mycotoxins. Mol. Nutr. Food Res. 48(4), 255-269. 

FIGURE 26.1. Chemical structure of trichothecene mycotoxins from group A, T-2 toxin group B, deoxynivalenol (DON) and group D (satratoxin H). From Haschek et al. (2002). 

Mass spectrometry has proved highly suitable for the elucidation of chemical structures and sensitivity. It is thus an invaluable tool for resolving extremely complex natural mixtures. Thus, on-line coupled SFE-MS constitutes a rapid, reliable choice for the determination of mycotoxins in wheat, which possess a high toxicological interest. For example, an SF extractor coupled to an MS chemical ionization source provided limits of detection in the picogram range for diacetoxyscirpenol and toxin T-2 [122]. Used in tandem with chemical ionization-collision induced dissociation MS-MS, SFE has also enabled the rapid detection and identification of species without the need for complete extraction [131],... 

Ditryptophenaline (56), mp 204-205°C, was isolated from the mycelium of Asp. flavus during the investigation for food-borne mycotoxin by Biichi and coworkers (104). The chemical formula, C42H4QNg04, is assigned on the basis of the high-resolution mass spectrum (m/z 692.3095), and the NMR spectrum indicates a dimeric structure. It possesses a diketopiperazine ring derived from tryptophan and phenylalanine and has UV absorptions at 244 and 303 nm. The chemical structure was determined by single-crystal X-ray experiments. Later, Hino and co-... 

Fig. 2.16 Chemical structures of the most common mycotoxins. (Authors own work)...

There are more than 170 known trichothecenes which can be classified in four categories (A, B, C, and D) according to their chemical structure (Krska et al., 2001). All trichothecene mycotoxins have a basic tetracydic sesquiterpene structure with a six-membered oxygen containing ring, an epoxide group on the 12,13 position, and an olefinic bond on the 9,10... 

Major problems encountered in the analysis of mycotoxins arise because of their diversity of chemical structure and the wide range of foods and animal feeds in which some of them may occur. This often means the development of quite different analytical methods for each mycotoxin in each food... 

The use of a mass spectrometer as a detector for LC analysis brings a number of benefits to mycotoxin analysis. There is no need for chromophores or fluorophores in the analytes so derivatization can be avoided. The chemical structure of the analytes can be confirmed from molecular mass and fragmentation information and the use of tandem MS (MS/MS) allows greater selectivity. Multiple reaction monitoring and selected ion monitoring modes mean that chromatographic separation of all analytes is not necessary, as differentiation is carried out by the different ion transitions measured, and many multiresidue mycotoxin LC-MS methods now exist. These data acquisition modes can also increase the sensitivity of the method as the background noise is often reduced. 

There are more than 200 mycotoxins produced under certain conditions by about 120 fungi or molds. Table 9.3 presents data on mycotoxins of particular interest to food preservation and storage. The chemical structures of these toxins are presented in Fig. 9.1. 

Mycotoxins are an extremely diverse group of compounds. Their relative molecular weight usually does not exceed 1000 Da. Just as is the case for other secondary metabolites, mycotoxins cannot be simply classified into groups of compounds on the basis of their chemical structure, without consideration of their occurrence, producers or the nature and intensity of the induced toxic effects. Production of mycotoxins by toxinogenic fungi is subject to a number of factors. Under certain conditions, mycotoxins may... 

High levels of mycotoxins in the diet can cause acute and chronic adverse effects on human health and a variety of animal species affecting different organs, especially the liver, kidney or to other systems such as the nervous, endocrine and immune systems. The symptoms caused by mycotoxins are often as different from each other as are the chemical structures of such toxins (Pohland et al., 1990 Camean Repetto, 1997 Faustman Omenn, 2005 Martinez Larranaga Anadon, 2006). 

FIGURE 6.4 Chemical structure of most common grain mycotoxins. (a) Zeralenone. (b) Ochratoxin A or OTA. (c) Fumonisin. (d) Trichothecenes or T-2. (e) Deoxynivalenol or DON. (f) Ergotamine. 

FIGURE 6.4 Chemical structure of most common grain mycotoxins.168... 

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. 

A second stereoselective total synthesis of ( )-eremophilone (243) has been accomplished using 7-epinootkatone (242) as intermediate.109 The latter compound was synthesized from (—)-/3-pinene (241) by modification of the published procedure"0 and subsequently converted into eremophilone (243) by the series of functional-group transformations shown in Scheme 30. A mycotoxin isolated from Penicillium roqueforti has been assigned the highly oxygenated eremophilane structure (244) on the basis of chemical and spectroscopic evidence."1 The structure and... 

Natural products represent a diversity of chemical compounds with varied biological activities. Natural products are an important source of novel pharmaceuticals as well as agricultural pesticides (1,2). Natural products are derived from a number of pathways that create basic scaffolds that are further modified by various tailoring enzymes to create the wide diversity of structures that exist in nature. Polyketide synthases are responsible for the synthesis of an array of natural products including antibiotics such as erythromycin in bacteria (3) and mycotoxins such as aflatoxin in fungi (4). Furthermore, in plants they are part of the biosynthetic machinery of flavonoids, phytoalexins, and phenolic lipi (5,6). 

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