Biosynthesis of (25S)- and (25R)-furostanol glycosides from [1,2-13C2] acetate in Dioscorea tokoro tissue cultures

Abstract

The biosynthesis of (25S)- and (25R)-furostanol glycosides, protoneotokorin (13) and prototokoronin (12) in cell cultures of Dioscorea tokoro fed [1,2-¹³C₂] acetate, was investigated by ¹³C n.m.r. spectroscopy. The ¹³C-labelling patterns of neotokorogenin (19) and tokorogenin (16), obtained from (13) and (12), indicate that the hydrogen atom at C-25 is introduced on the 25-si face of the Δ²⁴- intermediate, followed by oxidation of the pro-R(C-26) and the pro-S(C-27) methyl group at C-25 leading to (25S)- and (25R)-furostanol glycosides, respectively. The results were confirmed from the labelling patterns of yamogenin (21) and diosgenin (20), isolated by hydrolysis of crude furostanol glycosides. The oxidation at the pro-R methyl group was accelerated by increasing the concentration of sodium acetate without any effect on the ¹³C-labelling patterns.