Microbial Transformation of Macrocyclic Trichothecenes

New tricks for old dogs: Two new macrocyclic trichothecene epimers and absolute configuration of 16-hydroxyverrucarin B

Two new compounds, 3'-epi-16-hydroxyverrucarin A and 3'-epiverrucarin X, have been isolated and identified, and the characterization data of a series of known trichothecenes have been refined. The interesting structure and potent biological activities of macrocyclic trichothecenes have been of interest to the scientific community for several decades. However, some of the characterization data for the older analogues of this class are not well documented, either because of a lack of absolute configuration or a lack of clarity in the NMR data, largely due to technological limitations at the time they were discovered. NMR techniques, application of Mosher's esters analysis, and electronic circular dichroism were used here both to refine the characterization of known trichothecenes, as well as to uncover new structures. These studies demonstrate strategies that can be used to interrogate the characterization data of well-known secondary metabolites, thereby gaining greater insight into methods that can be used to refine previous literature.

Macrocyclic Trichothecenes from Myrothecium roridum Strain M10 with Motility Inhibitory and Zoosporicidal Activities against Phytophthora nicotianae

The cytotoxicity of the extract obtained from Myrothecium roridum M10 and a characteristic (1)H signal at δH ∼8 led to the assumption that verrucarin/roridin-type compounds were present. Upscaling on rice medium led to the isolation of four new metabolites: verrucarins Y (1) and Z (6) (macrocyclic trichothecenes), bilain D (12) (a diketopiperazine derivative), and hamavellone C (14) (an unusual cyclopropyl diketone). In addition, nine known trichothecenes [verrucarin A (3), 16-hydroxyverrucarin A (5), verrucarin B (7), 16-hydroxyverrucarin B (8), verrucarin J (2), verrucarin X (4), roridin A (9), roridin L-2 (10), and trichoverritone (11)] and a bicyclic lactone [myrotheciumone A (15)] were identified. Their structures and configurations were determined by spectroscopic methods, published data, Mosher's method, and considering biosyntheses. Some trichothecenes showed motility inhibition followed by lysis of the zoospores against devastating Phytophthora nicotianae within 5 min. Compounds 2, 3, 7, and 9 also exhibited potent activities against Candida albicans and Mucor miehei.

Biological detoxification of fungal toxins and its use in plant breeding, feed and food production

Enzymatic inactivation of fungal toxins is an attractive strategy for the decontamination of agricultural commodities and for the protection of crops from phytotoxic effects of fungal metabolites. This review summarizes research on the biological detoxification of fungal toxins by microorganisms and plants and its practical applications. Some mycotoxins are detoxified during ensiling and other fermentation processes (aflatoxins, alternariol, mycophenolic acid, patulin, PR toxin) while others are transformed into toxic products or survive fermentation unchanged. Plants can detoxify fomannoxin, fusaric acid, HC-toxin, ochratoxin A and oxalate but the degradation of deoxynivalenol has yet to be proven. Microflora of the digestive tract of vertebrates and invertebrates exhibit detoxification activities towards aflatoxins, ochratoxin A, oxalate and trichothecenes. Some toxin-producing fungi are able to degrade or transform their own products under suitable conditions. Pure cultures of bacteria and fungi which detoxify mycotoxins have been isolated from complex microbial populations by screening and enrichment culture techniques. Genes responsible for some of the detoxification activities have been cloned and expressed in heterologous hosts. The detoxification of aflatoxins, cercosporin, fumonisins, fusaric acid, ochratoxin A, oxalic acid, patulin, trichothecenes and zearalenone by pure cultures is reviewed. Finally, current application of these results in food and feed production and plant breeding is summarized and expected future developments are outlined.

Mass spectral investigations on trichothecene mycotoxins. I. Application of negative ion chemical ionization techniques for the simultaneous and accurate analysis of simple trichothecenes in picogram levels

A fast and sensitive gas chromatographic/negative ion chemical ionization mass spectrometric method for the simultaneous detection and quantification of several simple trichothecene mycotoxins and related molecules with good precision has been developed. The method consists of the conversion of the polar trichothecenes into their volatile and stable heptafluorobutyryl esters, followed by gas chromatographic/mass spectrometric analysis of the derivatives. The derivatives were ionized under chemical ionization conditions and the negative ions were monitored. The samples were screened for the presence of trichothecenes by monitoring one characteristic ion by selected ion monitoring for each analyte. The detected compounds were confirmed by monitoring 5-6 characteristic ions by selected ion monitoring whenever the amount of analyte present was insufficient to obtain a full scan negative ion chemical ionization mass spectrum. Two semi-synthetic trichothecenes, 4-deoxyverrucarol and 16-hydroxyverrucarol, were investigated and found to be adequate internal standards both for detection and quantification of these toxic compounds. Femtogram and low picogram (1-5 pg) quantities of these compounds could be detected and confirmed, respectively, by this procedure. A short clean-up procedure using Sep-Pak (silica gel) cartridges was developed and found to be applicable for the analysis of some real samples. Several spiked and real samples were analysed by this method, with excellent sensitivity and precision.

Mass spectral investigations on trichothecene mycotoxins. III. Synthesis, characterization and applications of pentafluoropropionyl and trifluoroacetyl esters of simple trichothecenes

The pentafluoropropionyl, (PFP) and trifluoroacetyl (TFA) esters of several naturally occurring and synthetically modified simple trichothecenes were synthesized in nanogram amounts and characterized. Optimum conditions for the gas chromatographic (GC) separation of these derivatives and their analysis by negative ion chemical ionization (NICI) mass spectrometric technique were determined. These perfluoroacyl derivatives under the NICI conditions undergo limited but characteristic fragmentations similar to the fragmentations of heptafluorobutyryl esters of trichothecenes under the same conditions. Characteristic ions for the specific detection and accurate quantification of these PFP and TFA derivatives were chosen. Preliminary results indicated that the PFP derivatives are better suited for the analysis of simple trichothecenes by GC-NICI-MS technique. Ultra trace (0.5-2.0 pg) amounts of these PFP derivatives were detected by the developed procedure.