The biosynthesis of the gibberellins. Part III

Abstract

Seven ¹⁴C-labelled compounds, including gibberellins A₁₂(Ib), A₁₃(IIc), and A₁₄(IIIc), have been prepared and tested as precursors in the biosynthesis of gibberellic acid by Gibberella fujikuroi(see Table). It is suggested that gibberellic acid is biosynthesised from (–)-kaurene through 10β-formyl-1β,4aα-dimethyl-8-methylenegibbane-1 α-carboxylic acid (VIIIc) and gibberellin A₁₄ or the corresponding 10-aldehyde (XV). Gibberellin A₁₃ is not thought to be a precursor of gibberellic acid.

Although several kaurene derivatives, (VIIa), (XIVc), and (XIVe), having the 16-methylene group, undergo ring contraction to gibbanes, e.g., (VIIIa), with base, those having a 16-keto-group, (VIIb) and (XIVd), do not. This appears to be due to a long-range effect associated with the 16-keto-group.