Partialsynthesen von Cardenoliden und Cardenolid‐Analogen. VI. (20R)‐ und (20S)‐Cardanolide

Partial Syntheses of Cardenolides and Cardenolide Analogues. VI. (20R)- and (20S)-Cardanolides (20R)-Dihydrodigitoxigenin (2) and (20S)-dihydrodigitoxigenin (4) as well as their 3-acetates 3 and 5, respectively, were synthesized by catalytic hydrogenation of the appropriate cardenolides and separation by column chromatography on silica of the mixtures of stereoisomers. Hydroxymethylation of 3 and 5 followed by selective elimination yielded (20S)- and (20R)-14-hydroxy-22-methylene-5β,14β-cardanolide 3-acetate (10 and 16), respectively. The biological activities of the synthesized 20-stereoisomeric cardanolides are investigated and discussed. Cardanolides 10 and 16 have a strong inhibitory activity on the proliferation of Ehrlich ascites carcinoma cells in suspension culture.