Identification of intermediates in the biosynthesis of PR toxin by Penicillium roqueforti.

The sesquiterpenoid 7-epi-neopetasone was synthesized via the Wieland-Miescher ketone. The compound was identical to a previously tentatively identified headspace constituent of Penicillium roqueforti. Feeding experiments with (13) C-labeled mevalonolactone isotopomers demonstrated that oxidation at C12 and an isomerization of the C11C12 to a C7C11 double bond must occur independently and not via a C7-C11-C12 allyl radical in one step. Feeding with (11,12,13-(13) C3 )-7-epi-neopetasone resulted in labelling of the PR toxin, thus establishing this compound as a newly identified pathway intermediate.