SYNTHETIC AND STRUCTURAL STUDIES ON NOVEL GIBBERELLINS

The structure elucidation of a number of metabolites isolated during b iosynthetic studies on gibberellin-like fern antheridiogens from the A nemia genus has been undertaken by synthesising a series of reference samples from gibberellin A(7). Two of the metabolites were shown to be the 12 beta- and 12 alpha-hydroxy derivatives of 9 beta,15-cyclogibbe rellin A(9) (1) while the 11 beta-hydroxy isomer was identical with a new gibberellin (GA(108)) from developing apple seeds. In a cognate st udy, an efficient total synthesis of this type of gibberellin has been developed, the key step being the intramolecular cyclopropanation rea ctions of the aromatic ring in tetralin 2-diazomethyl ketones to give stable norcaradiene products. The [4+2] cycloaddition of selected dien ophiles to some of these products allows the rapid stereo-controlled a ssembly of (1) and related gibberellins.