Terreic acid

The knowledge of biosynthesis gene clusters, production improving methods, and bioactivity mechanisms is very important for the development of filamentous fungi metabolites. Metabolic engineering and heterologous expression methods can be applied to improve desired metabolite production, when their biosynthesis pathways have been revealed. And, stable supplement is a necessary basis of bioactivity mechanism discovery and following clinical trial. Aspergillus terreus is an outstanding producer of many bioactive agents, and a large part of them are polyketides. In this review, we took polyketides from A. terreus as examples, focusing on 13 polyketide synthase (PKS) genes in A. terreus NIH 2624 genome. The biosynthesis pathways of nine PKS genes have been reported, and their downstream metabolites are lovastatin, terreic acid, terrein, geodin, terretonin, citreoviridin, and asperfuranone, respectively. Among them, lovastatin is a well-known hypolipidemic agent. Terreic acid, terrein, citreoviridin, and asperfuranone show good bioactivities, especially anticancer activities. On the other hand, geodin and terretonin are mycotoxins. So, biosynthesis gene cluster information is important for the production or elimination of them.

We present the results from stable isotope labeled precursor feeding studies combined with ultrahigh performance liquid chromatography-high resolution mass spectrometry for the identification of labeled polyketide (PK) end-products. Feeding experiments were performed with (13)C8-6-methylsalicylic acid (6-MSA) and (13)C14-YWA1, both produced in-house, as well as commercial (13)C7-benzoic acid and (2)H7-cinnamic acid, in species of Fusarium, Byssochlamys, Aspergillus, and Penicillium. Incorporation of 6-MSA into terreic acid or patulin was not observed in any of six evaluated species covering three genera, because the 6-MSA was shunted into (2Z,4E)-2-methyl-2,4-hexadienedioic acid. This indicates that patulin and terreic acid may be produced in a closed compartment of the cell and that (2Z,4E)-2-methyl-2,4-hexadienedioic acid is a detoxification product toward terreic acid and patulin. In Fusarium spp., YWA1 was shown to be incorporated into aurofusarin, rubrofusarin, and antibiotic Y. In A. niger, benzoic acid was shown to be incorporated into asperrubrol. Incorporation levels of 0.7-20% into the end-products were detected in wild-type strains. Thus, stable isotope labeling is a promising technique for investigation of polyketide biosynthesis and possible compartmentalization of toxic metabolites.

The absolute configuration of the ring system of the antibiotic G7063-2 has been established as being the same as that reported for terreic acid, based on circular dichroism data. During structure elucidation experiments, reaction with ethereal diazomethane gave an adduct whose structure is proposed.