Secondary mould metabolites. Part 16. Stemphyltoxins, new reduced perylenequinone metabolites from Stemphylium botryosum var. Lactucum

Abstract

The structure and stereochemistry of Stemphyltoxins I–IV (1)–(4), four epoxy derivatives of reduced perylenequinones isolated from the fungus Stemphylium botryosum var. Lactucum, have been elucidated, mainly on the basis of n.m.r. evidence. A further metabolite, stemphyperylenol (5), is a hexahydro-1,4,7,10-tetrahydroxyperylene-3,9-quinone, a structure which suggests an unusual head-to-tail biosynthetic coupling of two pentaketide units.