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. 1979 Aug 15;182(2):445–453. doi: 10.1042/bj1820445

Isoepoxydon, a new metabolite of the patulin pathway in Penicillium urticae

Junichi Sekiguchi 1,*, G Maurice Gaucher 1
PMCID: PMC1161326  PMID: 508294

Abstract

A patulin-negative mutant (J1) of Penicillium urticae (N.R.R.L. 2159A) was known to accumulate about 100mg per litre quantities of the 5,6-epoxygentisyl quinone, (−)-phyllostine and another metabolite (UIII). Both were derived from acetate and hence were polyketides. Purified UIII (m.p. 53°C, [α]32D+206°, λmethanolmax. 240nm; ε 3806 litre·mol−1·cm−1) was characterized as a partially reduced derivative of (−)-phyllostine and was found to be a diastereoisomer of the known phytotoxin, (+)-epoxydon. Hence its designation as (+)-iso- or epi-epoxydon. From 1H n.m.r. and c.d. data the stereochemistry of the epoxide ring in (+)-isoepoxydon was determined to be identical with that in (+)-epoxydon (i.e. R,R) but the configuration of the secondary alcohol at C-4 was S rather than R as in (+)-epoxydon. Isoepoxydon (compound UIII) is therefore (4S,5R,6R)-5,6-epoxy-4-hydroxy-2-hydroxymethylcyclohex-2-en-1-one. The boat conformation in which the C-4 hydroxy group is axial is preferred. In the range of 1mm to 5mm, the antibiotic activity of (+)-isoepoxydon against Bacillus subtilis sp. was 56% of that obtained with patulin. Over a period of 1 to 3h, [14C]isoepoxydon was efficiently converted into patulin by a shake culture of the parent strain of P. urticae. The precursor relationship of isoepoxydon to patulin was confirmed by feeding unlabelled isoepoxydon (1mm) to a washed-cell suspension of a mutant (J2) in which, over a period of 3 to 5h, a better than 60% conversion into patulin was attained. The enzymic relationship between isoepoxydon and phyllostine and their positions in the late portion of the patulin biosynthetic pathway are discussed.

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Selected References

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