Sporidesmins. Part XI. The reaction of triphenylphosphine with epipolythiodioxopiperazines

Dehydrogliotoxin and sporidesmin react with triphenylphosphine to give an epithiodioxopiperazine and triphenylphosphine sulphide. The reaction involves epimerization of the asymmetric centres of the dioxopiperazine ring. The epithiodioxopiperazines from sulphoxides when treated with peracids and these compounds are racemic. Evidence is presented, which suggests, that the reaction of sporidesmin E with triphenylphosphine occurs primarily at the sulphur-bound sulphur atom and that one conformation of this trisulphide reacts preferentially to the other.