Total Synthesis of Ouabagenin and Ouabain

The highly oxygenated steroid ouabagenin (1 b) and its glycoside ouabain (1 a) were prepared by a strategy based on a polyanionic cyclization. Starting building blocks A and B were combined to give the key intermediate C and transformed into 1 b in 27 steps. Finally, ouabagenin (1 b) was converted into ouabain (1 a) in six steps (see scheme).