The synthetic method of methyl 7-amino-1, 4 a-dimethyloctahydrophenanthrene-1-carboxylate (here after named methyl 13-amino-13-deisopropyldehydroabietate and abbreviated MADA) was highly improved as descrived below.12-Sulfodehydroabietic acid [2]prepared from dehydroabietic acid [1] by the treatment with 98% sulfuric acid was heated with a mixture of potassium bromide and bromine water to give 12-bromodehydroabietic acid, which was then converted to methyl 12-bromodehydroabietate [3] by the reaction with diazomethane. The treatment of [3] with 88% nitric acid gave methyl 12-bromo-13-nitro-13deisopropyldehydroabietate [4] in a moderate yield. MADA was obtained from 4 in a high yield on catalytic hydrogenation with Pd-C in the presence of triethylamine.
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