The Structures of Filixic Acids.

Abstract

Naturally occurring filixic acid, the characteristic phloroglucinol derivative from Dryopteris filix mas, has been shown to be a mixture of 6 homologues, which differ from each other in regard to the acyl side chains of the filicinic acid nuclei. For the main 3 compounds of these homologues the following names are proposed: filixic acid BBB (V), filixic acid PBB(VI) and filixic acid PBP (VII), in which the acyl side chains attached to filicinic acids are butyryl-butyryl, propionyl-butyryl or propionyl-propionyl, respectively. These 3 compounds, all of which have been isolated in a pure state, are shown to be the principal components of the natural filixic acid which after recrystallizations from ethyl acetate has a melting point of 183-185[degree]. The structures of the symmetrically composed filixic acids BBB and PBP have been proved by syntheses. When raw filixic acid isolated from male fern extracts is purified by treatments with methanol but without recrystallizations from ethyl acetate, a product is obtained which seems to contain 3 additional homologues with an analogous composition but with acetyl groups in the side chains. For these compounds the names filixic acids ABB, ABP and ABA are proposed.