1999 steroids

steroidsU 0300

24 - 200Acidic Isomerization of 9β-Hydroxy-11β-nitroxy-17α-ethynylestradiolin the Synthesis of 11α-Hydroxy-17α-ethynylestradiol. — The title9β-hydroxy-11β-nitroxyestradiol undergoes epimerization at position 9 underthe action of trichloroacetic acid to furnish an epimeric mixture (α:β = 7:3).The epimers can readily be separated by crystallization of their acetates. Achemical separation is achieved on NaBH4 reduction: while the 9α-epimerundergoes cleavage of the nitroxy group with conversion of the stereochemistryand reduction of the 9-hydroxy group, its 9β-epimer remains unaffected underthe reaction conditions. — (GOLUBOVSKAYA, L. E.; RZHEZNIKOV, V.M.; Zh. Org. Khim. 34 (1998) 12, 1874-1875; Inst. eksp. endokrinol. En-dokrinol. nauchn. tsentra Ross. Akad. med. nauk, Moskva 115478, Russia; RU)

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