Digoxin derivatives substituted by alkylidene at the butenolide part

A series of digoxin derivatives containing the γ-alkylidene butenolide moiety were synthesised by way of stereoselective vinylogous aldol reaction of the unactivated butenolide in simple conditions. The structures of compounds synthesised were characterised by infrared (IR), nuclear magnetic resonance (NMR) and HR-MS. Preliminary bioassay shows that some of them have cardiac functions, especially compound 2g that induced a marked increase in myocardial contractility at 10 ng ml−1 and 20 ng ml−1 concentrations without digitalis toxicity.