REVISION OF THE STEREOCHEMISTRY IN TRICHODIOL, TRICHOTRIOL AND RELATED COMPOUNDS, AND CONCERNING THEIR ROLE IN THE BIOSYNTHESIS OF TRICHOTHECENE MYCOTOXINS

Article abstract of DOI:10.1016/0031-9422(92)80114-T

Trichodiol and trichotriol are shown to have 9β-hydroxyls (trichothecene numbering), not 9α-hydroxyls as quoted in the literature.The C-9 configuration in other related trichodiene derivatives also need reassignment.Compounds with a 9β-hydroxyl are readily converted into a mixture of 9β- and 9α-hydroxy isomers on treatment with acid, typically in a ratio of about 4:1.An allylic carbocation intermediate is postulated, and the same carbocation can be generated from 11-hydroxy analogues such as isotrichodiol.Cyclization to trichothecenes occurs in the presence of a 2-hydroxyl.The natural occurence of both 9β- and 9α-isomers of trichodiol (in Trichothecium roseum) and of trichotriol (in Fusarium culmorum) suggests these result from acid-catalysed isomerization of isotrichodiol and isotrichotriol, respectively, via the appropriate carbocations.Accordingly, trichodiol and trichotriol are probably artefacts rather than biosynthetic intermediates on the pathway to trichothecenes.This is borne out by the result of competitive feeding experiments which indicate that the incorporation of isotrichodiol into trichothecene is not influenced by trichodiol, and only marginally by trichotriol.Isotrichotriol did repress incorporations, so the pathway to trichothecenes is now proposed to proceed via isotrichodiol and isotrichotriol, not via trichodiol and trichotriol.Pre-sambucoin, a further product from acid-catalysed cyclization of isotrichodiol, is an efficient precursor of sambucoin in Fusarium culmorum.Isotrichiol and the new metabolite 8α-hydroxyisotrichodiol were isolated from xanthotoxin-inhibited cultures of F. culmorum. Key Word Index - Fusarium culmorum; mycotoxin; trichothecene; biosynthesis; trichodiol; trichotriol.