New 10‐membered lactones, named aspinolide A–C (3, 4, 5), and the aspinonene/aspyrone co‐metabolites, named trienediol (6), isoaspinonene (7), dihydroaspyrone (8), and dienetriol 9 were discovered by chemical screening methods in the cultures of Aspergillus ochraceus (DSM‐7428) under altered fermentation conditions. The structures were established by detailed spectroscopic analysis. The polyketide origin of the skeleton and the biogenesis of the oxygen atoms were verified by feeding sodium [1,2‐13C2]acetate and [18O2] gas, respectively, to growing cultures of the fungus. A comprehensive discussion of the supposed biosynthetic pathways draws the conclusion that two polyketide synthases (PKSα, PKSβ) exist, forming two different series of pentaketides in parallel. One pathway leads to branched‐chain metabolites by a Favorski‐like rearrangement of an epoxide intermediate, while the other involves detachment of the pentaketides from the PKSβ by lactonisation without any rearrangement of the carbon skeleton. The former pathway is affected by an inhibitor of cytochrome P450 dependent monooxygenases.
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Fuchser et al. (1997) studied this question.
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