THE POLYOXYPHENOLS OF WESTERN RED CEDAR (THUJA PLICATA DONN). II. DEGRADATION STUDIES ON PLICATIC ACID, A POSSIBLE LIGNAN ACID

Abstract

Plicatic acid, C₂₀H₂₂O₁₀, a polyoxyphenol from western red cedar heartwood, described in a previous paper, has been further characterized by preparation and analysis of additional crystalline derivatives. Crystalline trimethyl and triethyl ethers have been oxidized by alkaline permanganate. The trimethyl ether yielded 3,4,5-trimethoxybenzioc acid, 4,5-di-methoxyphthalic acid (m-hemipinic acid), a pentamethoxy anthraquinone, and a pentamethoxy o-benzoylbenzoic acid which decarboxylated to 3,4,5,3′,4′-pentamethoxy benzophenone. Correspondingly, the triethyl ether gave 3,4-diethoxy-5-methoxybenzoic and 4-ethoxy-5-methoxyphthalic acids, a mixture of pentaalkoxy anthraquinones and a pentaalkoxy o-benzoylbenzoic acid which decarboxylated to 3,3′,4-triethoxy-4′,5-dimethoxy benzophenone identified by cleavage to 3-ethoxy-4-methoxybenzoic and 3,4-diethoxy-5-methoxy-benzoic acids. These results fix the positions of the two methoxyl, three phenolic hydroxyls, and mode of linkage of the two benzene rings. Further evidence is provided indicating plicatic acid is probably a lignan of the 4-aryltetrahydronaphthalene series.