Determination of the Microscopic Rate Constants for the Base-Catalyzed Conjugation of 5-Androstene-3,17-dione

Article abstract of DOI:10.1021/ja00198a066

The hydroxide ion catalyzed isomerization of 5-androstene-3,17-dione (1) to 4-androstene-3,17-dione (2) proceeds through the formation of an intermediate dienolate ion (1^-1).This dienolate ion has been observed in the ultraviolet spectrum (λ_max ca. 256 nm) during the isomerization reaction.Rate constants for the formation of the dienolate ion and both its reversion to reactant (1) and its conversion to product (2) in aqueous solution were measured.In addition, the rate of exchange of the C-6 protons of 2 in D2O/MeOD was determined.These results enable a complete description of the reaction profile to be made, including all rate constants and the pK_a values for 1 (12.7) and 2 (16.1).The possible relevance of these results to the mechanism of action of the enzyme 3-oxo-Δ⁵-steroid isomerase is briefly discussed.