P. S. Steyn

Screening methods for the detection of thirteen common mycotoxins

A study of screening methods for thirteen mycotoxins showed that they can be separated as neutral and acidic metabolites. RF values were determined in several solvent systems. The reactions of the mycotoxins with well known spray reagents were investigated, and their detection limits were established. A general procedure for the extraction of mycotoxins from contaminated samples is described.

Biosynthesis of cyclopiazonic acids in Penicillium cyclopium: The isolation of dimethylallylpyrophosphate: Cyclo-acetoacetyltryptophanyl dimethylallyltransferase

Abstract During the production of β-cyclopiazonic acid (βCA) by Penicillium cyclopium , the following points are noted: (a) Dimethylallylpyrophosphate (DMAPP), which is incorporated into α-cyclopiazonic acid (αCA) in vivo , stimulates overall CA synthesis, whereas tryptophan, although incorporated into αCA, inhibits overall CA synthesis. (b) A previously suggested substrate, γ,γ-dimethylallyltryptophan, is not a precursor of αCA. (c) The accumulation of cyclo -acetoacetyl- l -tryptophanyl (cAATrp) is described in both the culture medium and mycelium with increasing growth. (d) A cell-free extract of mycelium will catalyze the conversion of exogenous cAATrp and exogenous DMAPP into βCA in 1:1 stoichiometry, the βCA being bound to a protein.

Trichothecene mycotoxins from Fusarium sulphureum

Abstract Four mycotoxins isolated from moulded maize cultures of Fusarium sulphureum have been characterized as 3α,4β,15-triacetoxy-12,13-epoxytrichothec-9-ene, 4β,15-diacetoxy-3α-hydroxy-12,13-epoxytrichothec-9-ene, 15-acetoxy-3α,4β-dihydroxy-12,13-epoxytrichothec-9-ene and 4β-acetoxy-3α,15-dihydroxy-12,13-epoxytrichothec-9-ene.

α-Acetyl-γ-(β-indolyl)methyltetramic acid. A biosynthetic intermediate of cyclopiazonic acid and of bis-secodehydrocyclopiazonic acid

It has been shown that tryptophan is not utilized in a cell-free system of Penicillium cyclopium; α-acetyl-γ-(β-indolyl)methyltetramic acid, a biosynthetic intermediate of the cyclopiazonic acids, has been identified, and the L-configuration at the asymmetric centre of the new indole established.

Quantum-chemical studies of aflatoxin B1, sterigmatocystin and versicolorin A, and a comparison with their mutagenic activity

The INDO atomic charges q and Wiberg bond indices p (in electrons) were calculated for aflatoxin B1, sterigmatocystin and versicolorin A. The C-2-C-3 bond in these compounds has the same bond order and is predicted to be the most reactive towards epoxidation. The electronic effects do not explain the observed differences in mutagenicity and toxicity.

Biosynthesis of PR toxin by Penicillium roqueforti, Part 2 evidence for an hydride shift from 2H N.M.R. spectroscopy

Abstract The biosynthesis of the eremophilane sesquiterpenoid PR toxin is shown to involve an 1,2-hydride migration from C(5) to C(4) of the molecule.

The biosynthesis of polyketide-derived mycotoxins

The biosynthesis of a few representative polyketide-derived mycotoxins is reviewed: patulin, citrinin, diplosporin, ochratoxin A, maltoryzine, xanthomegnin, cytochalasans, ergochromes, zearalenone, citreoviridin, and the aflatoxins. Particular attention is given to the biosynthetic sequence: acetate----averufin----versiconal acetate----versicolorin A----sterigmatocystin----aflatoxin B1.

The isolation and identification of some toxic constituents ofAspergillus wentii wehmer.

Extraction of a maize culture of a toxinogenic strain ofA. wentii led to the isolation and characterization of three anthraquinones, three bianthrones, a xanthone and a benzophenone. The structures were derived from spectroscopic data and were supported by chemical degradation. Of these, emodin, 1,6-di-0-methylemodin, 5-0-methylsulochrine and 1,3-di-0-methylemodin bianthrone were mildly toxic to ducklings.

Structure elucidation and absolute configuration of the tyledosides, bufadienolide glycosides from Tylecodon grandiflorus

The isolation and characterization of six related bufadienolide glycosides, tyledosides A, B, C, D, F, and G from Tylecodon grandiflorus(Burm. F) Toelken are reported. The structure elucidation of these metabolites is based on a detailed study of their highfield 1H and 13C n.m.r. spectra. Extensive use was made of two-dimensional homonuclear and heteronuclear correlation experiments in the assignment of the n.m.r. spectra. The results obtained upon chemical derivatization of tyledosides A, C, and D are in agreement with the assigned structures.

Some new mycotoxins

Abstract The advances on the structural chemistry of some recently discovered mycotoxins, e.g. the tremorgens, cytochalasins, austocystins, tetramic acids, azaphilones and cyclic peptides are briefly reviewed.