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Epimerization of C-22 in (25R)- and (25S)-sapogenins
Omar Viñas-Bravo1, Penélope Merino-Montiel2, Anabel Romero-López2
1Instituto de Química Aplicada, Universidad del Papaloapan, Circuito Central # 200, Colonia Parque Industrial, Tuxtepec, Oax. 68301, Mexico.
Abstract:
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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