Studies on biochemical transformation of plant steroids. Part I. Biochemical interconversion of the Δ 25(27) - and the saturated 25 D -or 25 L -sapogenins

Some Δ25(27)-sapogenins were isolated from Hosta kiyosumiensis F. Maek. together with the corresponding saturated sapogenins: i.e., Δ25(27)-tigogenin, Δ25(27)-gitogenin, Δ25(27)-manogenin, and Δ25(27)-9(11)-dehydromanogenin. [27-14C]-Δ25(27)-Gitogenin, [27-14C]-gitogenin ([27-14C]-neogitogenin), and [27-14C]-25-hydroxygitogenin were synthesised from Δ25(27)-gitogenin. Each labelled sapogenin thus obtained was incubated with the homogenate from the epigeous part of Hosta kiyosumiensis at 37° for 6–7 hr. The results from these experiments indicate the following interconversion between the unsaturated and the saturated sapogenins occurring by the action of the plant enzyme: Δ25(27)-gitogenin ⇄ gitogenin and/or neogitogenin. It was thus shown that the Δ25(27)-sapogenin is not an artifact but a naturally occurring product. We suggest three classifications of the naturally occurring spirostans: 25D- or R-sapogenin (iso); 25L- or S-sapogenin (neo); 25,27-unsaturated sapogenin.