Pregnane and 21-norpregnane derivatives of ouabain that bind to the digitalis receptor

14β-Hydroxy-5β-pregnane and 14β-hydroxy-21-nor-5β-pregnane derivatives of ouabain were synthesised and their structures established by NMR measurements. Binding affinity in an [ 3 H]ouabain radioligand binding assay was determined. Pregnane derivatives of ouabain are more polar than pregnane rhamnoside derivatives of digitoxigenin. Whereas ouabain binds similarly to digitoxigenin rhamnoside, the pregnane derivatives of ouabain have significantly weaker binding affinity than their congeners from digitoxigenin.