Alternariol: evidence for biosynthesis via norlichexanthone

Alternaria molds produce numerous mycotoxins including many α-dibenzopyrones such as alternariol (AOH) and related polyketides. AOH, presumed to be the initial α-dibenzopyrone produced, has for 20 years been considered to be biosynthesized from a single polyketide chain in a single step reaction. The present study presents evidence that the reaction may proceed through an intermediate, norlichexanthone (NLX). Bond cleavage and rearrangement of NLX to form AOH may be similar to aflatoxin B1 formation from sterigmatocystin. The 2-D INADEQUATE experiment was used to assign the 13C spectrum of AOH and to distinguish between possible mechanisms by which AOH may be synthesized from 1-13C and 2-13C acetates via NLX.