Stereospecificity of biosynthesis of triterpene alcohols in Calendula officinalis flowers

Flowers of Calendula officinalis were incubated with mevalonic acid doubly labelled with ¹⁴C in position 2 and ³H in positions 2R, 2S, 4R or 5R,S and the ³H/¹⁴C] ratios determined in squalene and pentacylic mono- and dihydroxy-triterpene alcohols and also in some derivatives prepared from the triterpene alcohols. ³H atoms were located in positions 3, 12, 16, 21, 29, 30 of the ursane skeleton, positions 3, 12, 29, 30 of the lupane skeleton and positions 3, 11, 12, 18 of the oleanane skeleton. Stabilization of α- and β-Amyrins, ω-taraxasterol and lupeol occurs with the elimination of a proton from positions 12, 21 and 29 (or 30) respectively. In addition, during hydroxylation of triterpene monols to the corresponding diols a proton is substituted by the hydroxyl group.