Through site-directed mutagenesis targeted at identification of the catalytic base in the rice (Oryza sativa) syn-copalyl diphosphate synthase OsCPS4, changes to a single residue (H501) were found to induce rearrangement rather than immediate deprotonation of the initially formed bicycle, leading to production of the novel compound syn-halimadienyl diphosphate. These mutational results are combined with quantum chemical calculations to provide insight into the underlying reaction mechanism.

Substitution of a histidine, comprising part of the catalytic base group in the ent-copalyl diphosphate synthases found in all seed plants for gibberellin phytohormone metabolism, by a larger aromatic residue leads to rearrangements. Through a series of 1,2-hydride and methyl shifts of the initially formed bicycle predominant formation of (-)-kolavenyl diphosphate is observed. Further mutational analysis and quantum chemical calculations provide mechanistic insight into the basis for this profound effect on product outcome.