Journal of the Chemical Society. Perkin transactions I p. 2177 - 2184 (1985)
Update date:2022-08-03
Topics:
MacMillan, Jake
Willis, Christine L.
The syntheses of 1α-methyl-, 1β-methyl-, and 1α,2α-methylene-gibberellins required for further investigations into structure-biological activity relationships are described.Thermolysis of the pyrazoline derived from GA7-3-ketone-7-methyl ester gave, as the major product, the corresponding 1-methyl enone with minor amounts of the 1α,2α-methyleneGA4-3-ketone-7-methyl ester.The latter compound was reduced and hydrolysed to 1α,2α-methyleneGA4.Reduction of the 1-methyl enone with sodium borohydride gave 1α-methylGA4 methyl ester, which was hydrolysed to 1α-methylGA4, and 1α-methyl-3-epi-GA4 methyl ester which was deoxygenated to give 1α-methylGA9.The palladium-catalysed reduction of the 1-methyl enone gave 1β-methylGA4-3-ketone and 1α-methylGA4-3-ketone which were converted into the corresponding 1β-methylGA4 and 1α-methylGA4.The analogous synthesis of the C-1 alkylated 13-hydroxylated gibberellins was improved by the use of a phenacyl ester to protect C-7, thus providing routes to 1β-methylGA1, 1α-methylGA1, and 1α,2α-methyleneGA1.Incubation of 1α-methylGA4 with the fungus Gibberella fujikuroi, mutant B1-41a, gave 1α-methyl-GA1 as the sole metabolite.Incubation of 1β-methylGA4 with the mutant B1-41a gave 1-methylGA3, 1-methylGA7, and 1β-methylGA1 confirming that it is the 1α-hydrogen which is lost in the 1,2-didehydrogenation process in the fungus.
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