Biogenesis of spirostan sapogenins: stereochemistry of reduction of the 24,25 double bond in the biosynthesis of sarsasapogenin

Abstract

It is well known that reduction of the 24,25 double bond of the Δ24-sterols such as lanosterol or cycloartenol (I) is a key step in the biosynthesis of many steroid components of plants. In this paper we show that during reduction of this 24,25 double bond in the biosynthesis of sarsasapogenin in Agave attenuata the incoming hydrogen at C-24 enters from the 24re,25re face, so that the whole reduction is a "trans" process (Scheme 1), unless stereochemical changes occur after reduction.