The Interconversion of the Lichen Depsides Para- and Meta-Scrobiculin, and the Biosynthetic Implications

Abstract

An equilibrium mixture of the isomeric depsides para- and meta- scrobiculin has been extracted from the lichen Lobaria scrobiculata. Acetylation of this mixture led to the isolation of two isomeric triacetates, the structures of which were confirmed by unambiguous synthesis. This equilibration provides compelling evidence that m-depsides arise biogenetically by C-hydroxylation of the B-ring of a p-depside followed by an intramolecular rearrangement.