| 摘要 |
<p>A method to stereospecifically prepare a steroidal sapogenin or a derivative thereof by reducing a 3-keto,5beta-H steroidal sapogenin with a hindered organoborane or an organo-aluminium hydride. A 3beta- hydroxy,5beta-H steroidal sapogenin or derivative thereof may be prepared by reducing the 3-keto,5beta-H steroidal sapogenin using as reducing agent a relatively highly hindered organoborane reagent or by SN 2 inversion of a 3alpha-hydroxy,5beta-H steroidal sapogenin or derivative thereof. The organo-aluminium hydride may be used to prepare a 3alpha,5beta-H steroidal sapogenin or derivative thereof. The invention provides a convenient route to useful steroidal sapogenins such as sarsasapogenin, episarsasapogenin, smilagenin, epismilagenin and esters thereof, from readily available or easily preparable starting materials (e.g. diosgenone, preparable from diosgenin).</p> |
