Two new diphenyl ethers and a new depside from the lichen Micarea prasina Fr

Abstract

Two new diphenyl ethers, 4-(2-carboxy-3-heptyl-5-methoxyphenoxy)-2-heptyl-6-hydroxybenzoic acid (micareic acid) (13), 4-(2-carboxy-3-heptyl-5-methoxyphenoxy)-2-heptyl-6-hydroxy-3-methoxybenzoic acid (methoxymicareic acid) (27) and a new depside, 4-(2-heptyl-6-hydroxy-4-methoxybenzoyloxy)- 2-heptyl-6-hydroxybenzoic acid (prasinic acid) (34) have been detected in chemical races of the lichen Micarea prasina Fr. and isolated and characterized as the corresponding methyl esters. The structure of the latter compounds has been confirmed by total synthesis. The key steps in the synthesis of the diphenyl ethers (14), (26) involved Ullmann-like condensation between the 3-chloro 2-enone (17) and the phenols (11), (31), and subsequent aromatization of the enol ethers (23) and (32). A biomimetic-type synthesis of methyl micareate (48) has also been achieved by treatment of the depside (33) with sodium hydride in dimethylformamide.