Bufadienolides. VIII. Epimerization of 14α-and 14β-Artebufogenin

Abstract

Epimerizations of 14α-artebufogenin (14α-H-15-oxo-bufadienolide, III) and 14β-artebufogenin (14β-H-15-oxo-bufadienolide, V) by acid were examined. From the results of nuclear magnetic resonance and optical rotatory dispersion measurements, the free energy difference between both compounds was calculated to be 0.4 kcal/mole. Therefore the 14β-isomer (C/D cis ring system) was more stable than the 14α-isomer (C/D trans ring system).