(25S)-5β-spirostan-3β-ol

Sarsasapogenin is a steroidal sapogenin, that is the aglycosidic portion of a plant saponin. It is named after sarsaparilla (Smilax sp.), a family of climbing plants found in subtropical regions. It was one of the first sapogenins to be identified, and the first spirostan steroid to be identified as such. The identification of the spirostan structure, with its ketone spiro acetal functionality, was fundamental in the development of the Marker degradation, which allowed the industrial production of progesterone and other sex hormones from plant steroids.
Sarsasapogenin is unusual in that it has a cis-linkage between rings A and B of the steroid nucleus, as opposed to the more usual trans-linkage found in other saturated steroids. This 5β configuration is biologically significant, as a specific enzyme – sarsasapogenin 3β-glucosyltransferase – is found in several plants for the glycosylation of sarsasapogenin. The (S)-configuration at C-25 is also in contrast to other spirostan sapogenins: the epimer with a (25R)-configuration is known as smilagenin.
Sarsasapogenin has been used as a starting material for the synthesis of other steroids. It has also attracted pharmaceutical interest in its own right, and is found in the rhizome of Anemarrhena asphodeloides, used in Chinese tradition medicine (知母, zhī mǔ), from which it is extracted commercially.