Partial synthesis of gibberellin A9 and [3α- and 3β-2H1]gibberellin A9; gibberellin A5 and [1β,3-2H2 and -3H2]gibberellin A5; and gibberellin A20 and [1β,3α-2H2 and -3H2]gibberellin A20

Abstract

The 3α-alcohols, obtained by reduction of 3-didehydrogibberellin A₃ methyl ester 13-acetate with lithium borohydride, borodeuteride, and borotritiide, have been converted into the 3β-chloro-derivatives and, hence, by reduction with tri-n-butylstannane followed by hydrolysis, into gibberellin A₂₀, [1β,3α-²H₂]gibberellin A₂₀, and [1 β,3α-³H₂]gibberellin A₂₀. [3ξ-²H₁]Gibberellin A₂₀ has been prepared from the product of the reduction of the 3-thiobenzoate of the 3α-alcohol with tri-n-butyl[²H]stannane. The 3β-alcohols, minor products of these reductions, have been dehydrated and hydrolysed to give gibberellin A₅ and [1β,3-²H₂ and -³H₂]gibberellin A₅. The 3α-alcohol, from the lithium borohydride reduction of 3-didehydrogibberellin A₇ has been transformed into the 3β-chloro-derivative and the 3-thiobenzoate which, with tri-n-butylstannane, or with tri-n-butyl[²H₁]stannane, followed by hydrolysis, yielded gibberellin A₉, [3β-²H₁]gibberellin A₉, or [3ξ-²H₁]gibberellin A₉. In an analogous way, the product of reduction of 3-didehydrogibberellin A₄ with lithium borodeuteride was converted into [3α-²H₁]gibberellin A₉. The mass spectral fragmentations of the methyl esters and methyl ester trimethylsilyl ethers of [²H]gibberellins are also discussed.