Synthesis and Structure Determination of Gibberellin-Derived Antheridiogens From Fern Gametophytes of the Lygodium Genus

Abstract

Two successful and two unsuccessful synthetic routes are described for the conversion of commercially available fungal gibberellins to the antheridiogen GA₇₃ methyl ester (5), originally isolated from gametophytes of the fern Lygodium japonicum. The more efficient route began with the Birch reduction of either the GA₇ derivative (31) or methyl gibberellate 3,13-dimesylate (32) to give the ∆^1(10),16-diene acid (33), which was converted into the ∆^1,9-diene acid (40) by means of a four step procedure. This intermediate could be selectively hydrogenated to the ∆⁹-ene derivative which underwent iodolactonization and then elimination of HI to afford enone (29), Wittig methylenation of which furnished the target antheridiogen (5). In addition, (29) was functionalized at C12 by free radical bromination to give access to the 12β-hydroxy derivative of (5), i.e. (6), a new antheridiogen isolated from Lygodium circinnatum.