Analysis of steroids. Part XXXI. Mechanism of the tetrazolium reaction of corticosteroids

Abstract

The stoicheiometry and mechanism of the reaction between tetrazolium reagents and the α-ketol side-chain of corticosteroids was studied. On the basis of literature data plus some experimental results it is concluded that the side-chain is oxidised to the 20-keto-21-aldehyde, which then partly undergoes an intramolecular Cannizzaro reaction, leading to the 20-hydroxy-21-carboxylic acid. The doubled sensitivity of 16-hydroxycorticosteroids towards blue tetrazolium can be explained by a mechanism involving D-homo rearrangement of the D ring.

Equilibrium studies showed that under the usual experimental conditions the reduced blue tetrazolium reagent exists almost quantitatively in the monoformazan state.