Mechanism and stereochemistry of conjugate reduction of enones from gibberellins A3 and A7
Abstract
Conjugate reduction of the methyl esters of 3-didehydrogibberellin A3 13-acetate and of 3-didehydrogibberellin A7, in aprotic solvents by borohydride (or borodeuteride), is shown to introduce hydrogen (or deuterium) at the 1β- and 3β-positions in the products, 3-epi-gibberellin A1 13-acetate and 3-epi-gibberellin A4 methyl esters. The third hydrogen (or deuterium) comes from the proton (or deuteron) source used in the work-up. A mechanism for conjugate reduction of enones is proposed. The products from the borodeuteride reduction of 3-didehydrogibberellin A7 methyl ester with proton and deuteron work-up were chemically converted into [1β-2H1]-, [1β,22H2]-, and [1β3α-2H2]-gibberellin A4 and the stereochemistries of the deuterium atoms were determined from the deuterium content of the metabolites, formed from these labelled gibberellins in cultures of Gibberella fujikuroi, mutant B1-41a.