A Synthesis of the Lichen Dibenzofuran Pannaric Acid 2-Methyl Ester and Its Isomer 3-O-Methylpannaric Acid

Abstract

A total synthesis of pannaric acid 2-methyl ester (2-methyl hydrogen 3,9-dihydroxy-1,7-dimethyldibenzofuran-2,6-dicarboxylae) (1) and 3-O-methylpannaric acid (9-hydroxy- 3-methoxy-1,7-dimethyldibemofuran-2,6-dicarboxylic acid) (2) has been achieved through a biomimetic-type approach by using palladium(n) acetate in the key cyclization step. The acid (1) was shown to be identical to a major metabolite of the lichen Roccella capensis and a minor or trace constituent of the lichens Leproloma diffusum and L. vouauxii.