| Popis: |
The Δ 4 -hydrogenases of male rat-liver supernatant fractions convert unsubstitued testosterone derivatives to the 4,5-dihydro-3-keto compounds which are then reduced further to 3-hydroxysteroids by saturated 3-keto reductases which are also present in these fractions. Introduction of a halogen substituent at the C-2α, C-4, C-6α or C-6β position not only increases the reduction rate but promotes an abnormal enzymic pathway, Δ 4 -3-ol formation. This reduction, which proceeds in the presence of TPNH or DPNH is believed to be mediated by the saturated 3-keto reductases and is rationalized on the basis of electronic destabilization of the α,β-unsaturated ketone moiety by electronegative substituents with stabilization of the proposed transition state for reduction. In contrast, methyl substitution retards reduction which is explained on electronic and in some cases steric grounds. |
