Partial synthesis of gibberellins

Irradiation of the a -unsaturated ketone derived by manganese dioxide oxidation of methyl gibberellate, affords, in the solid state, a dimer in which addition of the unsaturated ketone across the terminal methylene group has occurred. Photolysis in solution leads to addition of the solvent to the unsaturated ketone. Some interest has centred on the partial synthesis of gibberellin Ajg (105), whose total synthesis was reported earlier. Details of the conversion of gibberellin A g into some 5-lactones related to gibberellin A15, and on the partial synthesis of gibberellin Ajg nor-ketone from 7-hydroxykaurenolide, reported... 

Figure 2.8 Partial synthesis of gibberellin C. Modified by permission of Shokabo Publishing Co., Ltd...

A partial synthesis of gibberellin Ajj nor-ketone from 7-hydroxykaurenolide has been described. The key stage in this synthesis is the activation of the C-20 methyl group by photolysis of a C-19 amide (173). 

Cross, B. E., and I. L. Gatfield New Metabolites of Gibberella fujikuroi. Part XVII. The Partial Synthesis of Gibberellin Ais Norketone from 7-Hydroxykaurenolide. J. Chem. Soc. (C) 1971,1539. 

A useful method has been developed for converting the readily accessible 3-hydroxy-gibberellins into 2-hydroxy-gibberellins and it has been applied to the partial synthesis of two new gibberellins, A46 (74), isolated from Echinocystis macrocarpa (Cucurbitaceae), and A47 (75), isolated from the fungus Gibberella... 

Interest in the structure-activity relationships of the gibberellins has led to the partial synthesis of the four stereoisomers about positions 5 and 6 of the hexa-hydrofluorene (57). The unsaturated acid anhydride (56) was prepared by the benzilic acid ring-contraction of the 6,7-diketones obtained from oxidation of desisopropyl dehydroabietic acid, and converted into the saturated acids by reduction and base-catalysed epimerisation. 

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