Ma Ru
1989
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Journal
Chinese Journal of Pharmaceuticals
Abstract
Dexamethasone was synthesized from tigogenin in 14 steps. Theintroduction of 16a-methy-17a-hydroxy into steroid 2 could be achieved by 1,4-addition of Grignard reagent in the presence of CuCl and subsequent acetylationin one port to afford 3 which was subjected to epoxidation and hydrolysis togive 5in90% yield. Among them, two isomers of epoxide 4 were separated andidentified. The 1-and 4-double bonds were introduced by bromination anddehydrobromination followed by dehydrogenation with SeO_2, or by microbialtransformation. Compound 8 was incubated with a mixture of Mycobacteriumsmegmatis and Arthrobacter simplex to give 9. 11-Hydroxylation of 9 by Absidiatransformation gave about 40% of 10. Dexamethasone could further be synthesizedin 5 steps by the usual method.