Synthetic and structural studies on novel gibberellins

Abstract

The structure elucidation of a number of metabolites isolated during biosynthetic studies on gibberellin-like fern antheridiogens from the Anemia genus has been undertaken by synthesising a series of reference samples from gibberellin A7. Two of the metabolites were shown to be the 12β- and 12α-hydroxy derivatives of 9β,15-cyclogibberellin A9 (1) while the 11β-hydroxy isomer was identical with a new gibberellin (GA108) from developing apple seeds. In a cognate study, an efficient total synthesis of this type of gibberellin has been developed, the key step being the intramolecular cyclopropanation reactions of the aromatic ring in tetralin 2-diazomethyl ketones to give stable norcaradiene products. The [4+2] cycloaddition of selected dienophiles to some of these products allows the rapid stereo-controlled assembly of (1) and related gibberellins.