Abstract
In order to examine the physiological activity C-17 epimeric 5α, 13α-cardenolides have been synthesized from 3β-hydroxy-5α, 13α-pregnan-20-one acetates (I, VII). Condensation with lithium ethoxyacetylide gave rise to the ethoxyacetylenic carbinols (V, VIII), respectively. Being exposed to sulfuric acid these carbinols underwent easily rearrangement to form the α, β-unsaturated esters (IVa, IXa). Subsequent treatment with selenium dioxide effected oxidation followed by intramolecular condensation resulting in formation of the butenolide ring. Hydrolytic cleavage of the 3-acetates (VIb, Xb) with methanolic hydrochloric acid afforded the desired 3β-hydroxy-5α, 13α-card-20 (22)-enolides (VIa, Xa).
