Simple trichothecenes

The oxygenation pattern of the trichothecene nucleus in the fungal macrolides is similar to that of the simple trichothecenes, but roritoxin C is a 9yS,10/3-epoxide and four of the five known products of an unidentified Cylindrocarpon sp. have a 7/3,8/3-epoxide. A 7/ ,8/ -epoxide is also found in the simple trichothecene crotocin. 

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Figure 1. Structure of Some Simple Trichothecene Mycotoxins...

The simple trichothecenes are products of Acremonium, Fusarium, Myrothecium, Stachybotrys and Trichoderma spp., and one species each of Cephalosporium, Cylindrocladium, Dendrostilbella, Gliocladium, Memnoniella, Microdocium, Spicellum and Trichothecium. Trichothecium roseum is, nevertheless, responsible for 12 metabolic products with... 

Of the 98 known simple trichothecenes, 82 have been obtained from Fusarium spp. This is, in part, a reflection of the interest shown in toxins produced by the grain pathogens F. sporotrichioides (45 trichothecenes) and F. graminearum (33 trichothecenes). 

Hydroxyscirpene (Table 1 C15H22O3) (fromE sporotrichioides) is the only known example of 8/3-hydroxylation in the simple trichothecenes. 

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). 

Trichodiene (49), the last hydrocarbon intermediate in the pathway, has been isolated from T. roseum, from Fusarium spp., and also from S. atra (Table 8). Specific labelling experiments have shown it to be a precursor of trichodiol (55) and 12,13-epoxy trichothecene (73), in addition to trichothecolone (101), in T. roseum (277) it is also a precursor of isotrichodiol (53) (219) and 3-acetylvomitoxin (104) in F. culmorum (278). However, relatively little work has been done on this stage of the pathway to simple trichothecenes in Myrothecium, Stachybotrys and Trichoderma spp. 

The genes controlling the initial stages of the biosynthetic pathway to the verrucarol moiety of the macrocychc trichothecenes have been studied in Myrothecium roridum (311). In so far as the pathways overlap, the pathway outlined above for simple trichothecenes is followed, and clustered genes MRTri4-6, similar to Tri4-6 and with the same function. 

To date, over 80 naturally occurring trichothecenes have been identified and can be classified into three distinct structural groups Simple trichothecenes, macrocyclic trichothecenes and the recently discovered tri-choverroids. The simple trichothecenes, with 38 members, contain the basic mono- or polyhydroxylated sesquiterpene skeleton, with none, one, or more of the hydroxy groups esterified by acetic, crotonic, isovaleric, lactic or P-hydroxyisovaleric acid. This grouping can be further subdivided based on the oxidation level of C-8. Table I contains those simple sesquiterpenes in which C-8 is fully reduced. Table II is comprised of those members which possess an 8a-hydroxy group, while Table III lists all the compounds in... 

In the second structural group, the macrocyclic trichothecenes, the hydroxy groups at C-4 and C-15 of the simple trichothecene skeleton are bridged by a di- or trilactide ribbon. The verrucarins (triesters. Table IV), the roridins (diesters. Table V) and the baccharins (diesters. Table VI) are the major structural subunits of this group. Vertisporin and the satratoxins complete this class, and can be found at the bottom of Table V. Verrucarol (82) is most often the sesquiterpene onto which the macrocycle is attached. Verrucarin K (43) is a notable exception and was the first trichothecene known which lacks the 12,13-epoxide unit. A number of macrocyclic... 

More recently, acetylene is reported to give under irradiation a photoadduct 48 with enone 47 by a-attack [46], After deacetoxylation and ionic rearrangement, a simple approach to the synthesis of optically active trichothecene seems possible [46 a] using the rearranged cyclopenteno bicyclic compound 48 (Scheme 22). 

Stachybotrys chartarum (previously also called S. atrd), the fungal cause of stachybotryotoxicosis and sick building syndrome, is a black mold. There are two toxic chemo-types of S. chartarum, one elaborating highly toxic macrocyclic trichothecenes and the other less toxic atra-nones and simple, but not macrocychc, trichothecenes (Andersen et al, 2002). Exposure may be by ingestion, e.g. exposure to contaminated straw, or inhalation as when mold grows in water-damaged homes or air ducts. 

Screening tests for the trichothecene mycotoxins are generally simple and rapid but, with the exception of the immunochemical methods, are nonspecific. A number of bioassay systems have been used for the identification of trichothecene mycotoxins.73 Although most of these systems are very simple, they are not specific, their sensitivity is generally relatively low compared to other methods, and they require that the laboratory maintain vertebrates, invertebrates, plants, or cell cultures. Thin-layer chromatography (TLC) is one of the simplest and earliest analytical methods developed for myco-toxin analysis. Detection limits for trichothecene mycotoxins by TLC is 0.2 to 5 ppm (0.2 to 5 pg/ mL). Therefore, extracts from biomedical samples would have to be concentrated 10- to 1,000-fold to screen for trichothecene mycotoxins. 

To overcome the difficulties encountered with the bioassays and TLC methods, immunoassays using specific polyclonal and monoclonal antibodies have been developed for most of the major trichothecene mycotoxins and their metabolites.73 These antibodies have been used to produce simple, sensitive, and specific radioimmunoassays (RIAs) and enzyme-linked immunosorbent assays (ELISAs) for the mycotoxins. In the presence of the sample matrix, the lower detection limits for identification of trichothecene mycotoxins by RIA is about 2 to 5 ppb73 and by ELISA, 1 ppb.74 We conclude that immunoassays are useful tools for screening biomedical samples for evidence of a biological warfare attack with trichothecene mycotoxins. 

Limited data are available on the respiratory effects of inhaled trichothecene mycotoxins, although acute pulmonary edema is one of the serious, often lethal consequences of a yellow rain attack.16,27 One of the major symptoms following the yellow rain attacks was an upper respiratory irritation (sore throat, hoarseness, nonproductive cough),716,27 which can be relieved by steam inhalation, codeine, or another substance to suppress the cough, and other simple measures.85 A casualty who develops severe respiratory symptoms should be under the care of a physician skilled in respiratory care. 

The analytical procedure that is used by this laboratory for the analysis of simple Fusarium mycotoxins will be reported separately. However, the analytical scheme is outlined in Figure 2. The method is very arduous due to several sample clean-up steps which necessitates transfer of the sample between containers. The trichothecenes and their derivatives have a tendency to adhere to glass and can be quantitatively transferred only with numerous methanol washes. While the analytical method is both sufficiently sensitive and definitive for the program requirements, the sheer amount of human manipulation required for the completion of this analysis makes it somewhat unreliable if implemented without a responsible quality assurance and quality control program. 

McCormick SP, Stanley AM, Stover AN, Alexander NJ (2011) Trichothecenes From Simple to Complex Mycotoxins. Toxins 3 802... 

For both. A- and B- trichothecenes there is still a lack of simple and reliable screening methods enabling the rapid detection of these mycotoxins at low cost. Besides the increasing demand for rapid screening methods for both A- and B-trichothecens, the use of liquid chromatography with tandem mass spectrometry (LC-MS/MS) enabling both quantification and identification of several trichothecenes simultaneously can be considered a major future trend in the analysis of these Fusarium mycotoxins in cereals (Krska et al., 2001). 

Sagawa N, Takino T, KurogochL S (2006) A simple method with liquid chromatography/ tandem mass spectrometry for the detmminatimi of the six trichothecene mycotoxins in rice medium. Biosci Biotechnol Biochem. 70 230... 

Approaches to the simple sesquiterpenoid trichothecenes can be categorized by the type of reaction used to form the ring system. Primarily, four bond associations have been used to construct the trichothecene skeleton as depicted in Scheme 1. Groups 1 and 2 (X = O, Y or Z = OH)... 

In analogy to Roush s earlier studies (see Scheme 14) the A-ring was incorporated by a Robinson annulation (176 177) which provided the desired stereochemistry at C-5 and C-6. Reduction then unraveled the bicyclic system to yield the expected precursor for cydization (178). Although attempts to cyclize this tetraol were unsuccessful, simple conversion of the 15-hydroxy group to the acetate (179) allowed for smooth cydization and provided the 13-nortrichothecene (180). After standard elaboration to the hydroxy diene (181) it was found that, in sharp contrast to other oxygenated trichothecenes, peracid oxidation selectively epox-idized the 12,13-double bond. This result allowed for rapid completion of the synthesis yielding the natural antipode of anguidine (9). 

The isolation of trichodermadiene (72) marked the discovery of the newest class of trichothecene metabolites, the trichoverroids. As noted previously, these are derivatives of the simple sesquiterpenes which possess complex ester side chains, structurally related to those found in the macrocyclic trichothecenes, at C-4 or both C-4 and C-15 (see Table VIII). Evidence for their role as biosynthetic intermediates to the macrocyclic trichothecenes 42, 78) has spurred interest in their synthesis. 

The most recent model study, undertaken by Trost and McDougal, has explored an unusual approach to verrucarin-type trilactides 148). Their supposition was that thermal isomerization of the cw-cyclobutene (242), which could produce two possible. Z-isomers by competing conrotatory processes, would exhibit selectivity due to the conformational constraint imposed by the macrocycle. The synthesis of the target molecule is outlined in Scheme 29. Importantly, the key macrolactonization (241->-242) proceeded without isomerization of the cw-cyclobutene moiety. Upon thermolysis a mixture of. Z-isomers (243) and (244) was obtained. Comparison with an authentic sample revealed that the natural isomer (243) was indeed the major compound present (2 1). The applicability of such an approach to the verrucarins must yet be explored. Interestingly, these relatively simple models inhibit protein synthesis in a fashion reminiscent of the natural trichothecenes. 

Trichothecenes can be divided into two broad groups simple... 

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