Modified cardenolides II. Synthesis, NMR spectra, and biological activity of C-19 halides and sulfonates

The synthesis of 19-halocardenolides by halide displacement of the corresponding 19-p-toluenesulfonate esters is described. The NMR spectra of the 19-substituted compounds indicate that the rotation of the 19-group is restricted and that one of the C-19 protons is shielded by the 5,6-double bond.