2'-O-Methylphysodic acid and hydroxyphysodic acid: two new depsidones from the lichen Hypogymnia billardieri

Abstract

Two new depsidones, 2?-O-methylphysodic acid and hydroxyphysodic acid, have been identified as minor constituents of the lichen Hypogymnia billardieri (Mont.) R. Filson. The structure of 2?-O-methylphysodic acid was established by chemical interconversions. The overall substitution pattern of this depsidone was confirmed by methylation with excess diazomethane, whereupon methyl 4,2?,4?-tri-O- methylisophysodate was obtained. Further, a direct comparison showed that this metabolite was dissimilar from 4-O-methylphysodic acid which has been isolated previously.     The structure of hydroxyphysodic acid followed from the analytical data, spectroscopic properties and chemical interconversions. This compound is biogenetically unique, since it is the first depsidone isolated in which the basic orcinol nucleus has undergone further hydroxylation.