Chemistry of Conjugate Anions and Enols. VII. Rates of Formation and Equilibria of Enolate Anions^1,2

Microbial hydroxylation of steroids. 9. Epoxidation of Δ6-3-ketosteroids by Rhizopusarrhizus ATCC 11145, and the mechanism of the 6β hydroxylase enzyme

“…[l]). This reaction has been shown to involve a product-like transition state with the C-6P bond approaching an axial position (25,26).…”

Studies on Δ5→4-3-oxo steroid isomerases. I. Extraction model for enzymic activity

“…With respect to the last consideration, Km and K¡ differences between various steroids and their 19-nor analogs could be explained on the following basis. Some of the factors influencing the rate of formation and stability of the enol form of 4-3steroids have been investigated by Subrahmanyam et al (1966). A fiveto sixfold enhanced rate of enol formation has been shown when comparing 19-norandrostenedione with androstenedione and was interpreted in terms of steric impediment by the Cis angular methyl group.…”

“…The fact, suggested by Wang et al (1963), that enolization of the steroid might occur in the formation of the isomeraseinhibitor complex, is relevant to these considerations. Therefore, some factors that control the formation and the stability of enolate anions of the 4-3steroids, already pointed out by Ringold (Subrahmanyam et al, 1966), will be considered in their relation with isomerase activity.…”

Thermodynamic and Kinetic Controlled Enolates: A Project for a Problem-Oriented Laboratory Course

“…This result is analogous to enolate anions of 2-methylcyclohexanone derivatives, where the solvent shell about the metal cation destabilizes an adjacent equatorial substituent (15,16). This leads to a relative stabilization of the 6-methyl substituent in an axial position and the consequent isolation of a substantial percentage of the trans isomer, following kinetically controlled protonation (15).…”