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.