1β-Hydroxygibberellin A5. Preparation and comparison with gibberellin A3

Abstract

The preparation of 1β-hydroxygibberellin A₅ from gibberellin A₃ is described. Unlike its naturally occurring allylic isomer gibberellin A₃,1β-hydroxygibberellin A₅ is stable to aqueous alkali and acid-catalysed aromatisation of ring A does not occur. Reasons for these differences, and for the hitherto unreported 3-epimerisation of gibberellin A₃ by base, are discussed in terms of O-alkyl fission of the lactone bridge.