Hydrolysis of gibberellin 7-methyl esters: anchimeric assistance by a 15-alcohol

Abstract

The neighbouring group effects of 15α- and 15β-hydroxy groups on the rates of hydrolysis of gibberellin 7-methyl esters are described. The presence of a 15-alcohol increases the rate of ester hydrolysis and a 15α- has a greater influence than a 15β-alcohol. The 15α-alcohol may be effective either through hydrogen bonding between the hydroxy proton and the ester carbonyl thus stabilising the tetrahedral intermediate formed on hydrolysis of the ester, or via 7,15α-lactonisation followed by hydrolysis of the lactone. The 15β-hydroxy may act through hydrogen bonding of a water molecule between the proton of the 15β-alcohol and the 7-carbonyl function. The effect is enhanced by the presence of a 13-acetate.