Epimerization of C-22 in (25R)- and (25S)-sapogenins

• The formation of 22-epi-sapogenins from natural sapogenins and pseudosapogenins is described.
• The 22-epi-sarsasapogenin and 22-epi-yamogenin were obtained in good yield.
• An efficient route to obtain C-22 stereoisomers of 23-acetyldiosgenin is reported.
• The structures of 22-epi-sapogenins were established by NMR studies.

Most of the naturally occurring steroidal sapogenins (C-23 non-substituted frameworks), possess an R configuration at the spiro C-22 center. Their C-22 epimers have become important targets in biological research. This paper describes a procedure to obtain 22S-spirostans from 22R-sapogenins and pseudosapogenin skeletons, without affecting the chirality at either C-25 or C-20. An optimal way to synthesize the pair of C-22 stereoisomers of 23-acetyldiosgenin is also reported. The latter was obtained from a 22,26-epoxycholestane or from 23-acetylfurostene compounds.

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