Studies on vitamin D and related compounds. XVI: Synthesis of model compounds for the study of the previtamin D ⇋ vitamin D interconversion

Abstract

AbstractThe syntheses are described of previtamin D ‐ and vitamin D analogues to be used for the study of the thermal precalciferol ⇋ calciferol isomerization reaction.A previtamin D analogue (4) prepared as indicated by Inhoffen could not be obtained in a pure state. Closer inspection revealed that the final step, the selective partial hydrogenation of the triple bond of 3, yielded a mixture of isomers. Two calciferol analogues (15A and 15B) were synthesized, following routes used by Harrison and Lythgoe for obtaining related compounds. These vitamin D analogues showed the same remarkable smooth isomerization as the vitamin itself. With the analogues, however, the equilibrium was found to be displaced towards the “previtamin” side. This enabled us to obtain the corresponding previtamin D analogues by heating the acetates of the calciferol analogues (15) at 90°, followed by saponification and chromatographic purification.