Stereochemistry at C-11 and C-12 in the biosynthesis of olean-12-ene, urs-12-ene, and β-sitosterol from [5-13C,5-2H2]mevalonolactone in tissue cultures of Isodon japonicus Hara

Abstract

On the basis of the ¹³C-²H labelling patterns at C-11 and C-12 of 2α-hydroxyursolic acid, 3-epimaslinic acid, and β-sitosterol isolated from Isodon japonicus Hara tissue cultures fed with [5-¹³C,5-²H₂]mevalonolactone, all three types of metabolites were concluded to be synthesized from both squalene oxides (1) and (2); the different hydrogen elimination mechanisms to form the Δ¹² double bond were found to take place between the biosynthesis of olean-12-ene and urs-12-ene.