Abstract
Abstract Reduction of 11-benzoyloxy-12-methoxyabieta-8,11,13-trien-7-one with sodium borohydride, followed by dehydration of the resulting alcohols with p-toluenesulfonic acid, afforded the corresponding 6,8,11,13-tetraene derivative. This was converted into 11-benzoyloxy-12-methoxyabieta-8,11,13-trien-6-one (8) via an epoxide. The 6-oxo compound (8) was reduced with lithium aluminium hydride. Subsequent oxidation of the resulting alcohol with m-chloroperbenzoic acid afforded 6β-hydroxy-12-methoxyabieta-8,12-diene-11,14-dione. This compound was further transformed into 11,14-diacetoxy-12-methoxyabieta-8,11,13-trien-6-one (13) by a series of reactions: Jones oxidation, reduction with a mixture of zinc powder and hydrochloric acid, and acetylation. The diacetate (13) was then oxidized with Jones reagent and the 6,7-dioxo product was immediately converted into 11-acetoxy-6,14-dihydroxy-12-methoxyabieta-5,8,11,13-tetraene (15) by repeated column chromatography on silica gel. The tetraene (15) was finally hydrolyzed with hydrobromic acid to give coleon U 12-methyl ether.
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