SYNTHESIS, STABILITY AND BIOLOGICAL-ACTIVITY OF 19-DEOXY-GIBBERELLINSA1 AND A3

The synthetic conversion of gibberellin A3 (GA3) to the 19-desoxy-deri vatives of GA1 and GA3 is described. The key steps involve regiospecif ic reduction of the known GA3 hydrogenolysis product at the C-19 carbo xyl group via treatment of the acyl chloride with zinc borohydride, fo llowed by an iodocyclization of the resultant alcohol. 19-Desoxy-GA1 a nd GA3 are stable in alkali, unlike their parent lactones GA1 and GA3. Both derivatives are biologically active in inducing alpha-amylase pr oduction in protoplasts of Avena fatua aleurone. They have biological activities of one order of magnitude less than that of the natural ana logues. These data reveal the significant contribution of the lactone carbonyl to the observed response (receptor affinity) of GA1 and GA3.