1α,2α-Epoxygibberellin A3: Partial synthesis, NMR spectra, biological activity, and crystal structure of its methyl ester

1α,2α-Epoxygibberellin A3 has been obtained for the first time in almost quantitative yield by the dehydroiodination of the known 1β-iodogibberellin A56, and the structure of its molecule has been established by the XSA method. An interpretation of all the signals in its1H and13C spectra has been made from the results of two-dimensional NMR. In the amylase biotest, 1α,2α-epoxgibberellin A3 exhibited an activity amounting to one third of the activity of gibberellin A3 at concentrations of 10−7 to 10−9 M.